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Home My WebLink About12/03/1991, 1 - ADOPTION OF SEISMIC STRENGTHENING STANDARDS FOR UNREINFORCED MASONRY BUILDINGS BY CREATING A NEW APPENDIX CHAPTER IN THE BUILDING CODE. I��`I1��IIIIIIIIII IIU3 f ME ING AT jl�� c� o san suis og�spo �-�- � / MaZa COUNCIL AGENDA REPORT ITEM NUMBER: FROM: Arnold Jonas, Community Development Director_ PREPARED BY: Tom Baasch, Chief Building Official .. SUBJECT: Adoption of seismic strengthening standards for unreinforced masonry buildings by creating a new appendix chapter in the Building Code. CAO RECOMMENDATION: Introduce ordinance to print establishing (1) seismic strengthening standards for buildings of unreinforced masonry (URM) construction, and (2) administrative regulations requiring that all URM buildings be structurally analyzed within 18 months and that any URM building subject to major remodel or occupancy change be strengthened to the established standards. DISCUSSION: Background i The California State Legislature enacted Senate Bill No. 547 in 1986 to address the hazards presented by unreinforced masonry (URM) buildings located throughout the State. The URM law requires that all local jurisdictions in Seismic Zone 4 identify all "potentially hazardous" (URM) buildings by January 1, 1990, and then develop a mitigation program to reduce the hazard. The inventory of URM buildings located in the City of San Luis Obispo was completed in 1989, and a list of 148 "potentially hazardous" buildings was submitted to the State of California Seismic Safety Commission by the January 1, 1990 deadline. As a result of voluntary strengthening completed or submission of documentation establishing reinforcement, the current inventory totals 137. Of this number, 38 buildings are designated as Historic Resources, and 100 are located in the downtown area. A voluntary strengthening project is currently under construction for one downtown building on the list. All owners of the identified URM buildings in the City were notified of the determination in December of 1989 , which is considered by the Seismic Safety Commission to be the minimum element of a mitigation plan. To assist the City in the development of mitigation measures, staff requested proposals from consulting firms with demonstrated experience and ability in the preparation of URM strengthening programs. After a thorough selection process, a contract was awarded to Howard Stup and Associates and development work began in April of 1990. Why pursue development of a strengthening program? The data resulting from the URM building survey indicates that approximately 15,600 building occupants (based on the maximum occupant load calculated per the Building Code) could be subjected to the hazards of unreinforced masonry building failure a��N►►►�uiINIIIIlUp1°°'��III MY of San L-ais OBISPO iMIGn COUNCIL AGENDA REPORT during an earthquake. In addition, an unknown number of occupants in adjacent buildings and pedestrians passing by may be at risk due to falling debris from URM failures resulting from an earthquake. Although the proposed strengthening standards may not prevent irreparable building damage, lives will be saved and injury will be reduced. Recent earthquakes (i.e. , Loma Prieta) have again substantiated the significant hazards associated with URM buildings; the damage in Santa Cruz could be repeated in San Luis Obispo. Staff recommends that the life safety issue be considered paramount and that the City exercise its responsibility to protect the health, safety, and welfare of its citizens and visitors. What has been the process for developing the proposed ordinance? In moving forward with ordinance development, the first task was the establishment of the relative seismic risk for the City of San Luis Obispo. Although the City is located in Seismic Zone 4 , staff determined that it would be prudent to conduct a site specific analysis to establish the level of ground shaking expected to occur. The creation of subzones of lower classification within a given seismic zone is not endorsed by the Seismic Safety Commission, but the generation of strengthening factors based on expected ground acceleration is at the City' s discretion when designing a mitigation program. A computer- aided seismic hazard analysis was performed by Staal, Gardner & Dunne, a geotechnical engineering firm. The results recommended that the seismic forces likely to be encountered in the City i would be in the moderate range. Consequently, the consultant proceeded to develop a strengthening ordinance utilizing the criteria characteristic to Zone 3 . The proposed strengthening standards represent a modified version of the most current model ordinance promoted by the Seismic Safety Commission, which has received support from the International Conference of Building Officials (ICBG) by inclusion in the Uniform Code for Building Conservation. ICBO endorsement establishes nationwide acceptance of the technical approaches to URM strengthening contained in the model document. In short, the proposed ordinance is the model ordinance modified to Seismic Zone 3 criteria, and includes administrative provisions applicable to San Luis Obispo. The proposed ordinance was reviewed by the Technical Committee and the Administrative Committee of the Seismic Task Force sponsored by the San Luis Obispo Chamber of Commerce. The Technical Committee, composed of architects and engineers from the community, studied the structural engineering components of the proposed ordinance. The Administrative Committee consisted of URM building owners and tenants, bankers, contractors, architects, and realtors, and focused on the implementation procedures and a compliance timetable in the proposed ordinance. After five meetings held by each committee, as well as a special meeting by the Administrative Committee to reconsider deadlines, the Seismic Task Force indicated unanimous endorsement of the 1-- ��► ►►�Illllllllp°�°►9�UI11 MY Of San LUIS OBISPO COUNCIL AGENDA REPORT proposed ordinance. However, two events occurred which altered staff efforts to develop a mitigation program: (1) In July of 1991, the Governor signed legislation known as AB 204, which may ultimately have a significant impact on the City's URM mitigation program. This legislation requires that the Building Standards Commission adopt Appendix I of the Uniform Code for Building Conservation (UCBC) as the statewide URM strengthening standard by January 1, 1993 , with an effective implementation date of July 1, 1993 . The UCBC does not include administrative provisions, but discussion with staff at the Building Standards Commission found that they intend to propose such provisions in the adoption process. Such provisions would most likely supersede any local program. (2) In early August of 1991, modifying their earlier endorsement, the Chamber of Commerce expressed concern regarding the implementation provisions of the ordinance proposed at that time. Members of the Seismic Task Force then suggested that the strengthening of all URM buildings by the year 2000 was not a mandate imposed by the State. Although it is not mandated by law, the California Earthquake Hazards Reduction Act of 1986 (Government Code Sections 8870, 8872 (b) ) has set a goal of "significantly reducing" hazards by the year 2000. A more detailed discussion of this issue is outlined in an attached memo prepared by the City Attorney. Staff met with the Administrative Committee several times beginning on August 20, 1991. Alternative administrative sections of the ordinance were prepared and discussed. On November 23, agreement was reached on an interim ordinance that would establish a mitigation program until State deliberation on AB 204 is completed, which is presented as the proposed ordinance attached to this report. Staff has been working with the Chamber Committees for almost 10 months to reach consensus on a strengthening program to reduce the URM hazard. There is agreement on the technical standards but not on a comprehensive mandatory implementation schedule. Staff feels that a mandatory strengthening ordinance that is certain to include all URM buildings before the year 2000 is the best recommendation because: (1) it is responsive to the City's obligation to protect the health, safety, and welfare of the people; (2) it is consistent with guidelines established by the Seismic Safety Commission; (3) it is consistent with strengthening programs /+� ��n��Hi�IIiIIIIIIPn IIBIII City Of San LaIS OBISPO COUNCIL AGENDA REPORT implemented in comparable jurisdictions throughout the State; and (4) it satisfies the intent of the Earthquake Hazards Reduction Act of 1986 (Government Code § 8875 et sea) . However, the CAO recommendation recognizes the uncertainty of State regulations at this time, resistance from the business community to a specific implementation schedule, the current economic climate, and the meed to establish some basic mandatory features. As such, the proposed ordinance offers a "middle ground" interim approach which staff believes represents a consensus of the numerous people involved. Environmental Review The proposed ordinance in itself will have no effect on the environment. Most strengthening projects will be ministerial in nature, requiring only a building permit for interior work such as fastening the roof structure to the walls. Any project involving change of occupancy, exterior modifications to a building, or other changes which would conceivably result in environmental impact will be subject to approvals in addition to the building permit, and will undergo project specific environmental review at that time. Ordinance Summary The proposed ordinance amends the Uniform Building Code as adopted by the City by adding Appendix Chapter 23 , Seismic Strengthening Provisions for Unreinforced Masonry Buildings. Sections A2301 and A2302 state the purpose and application. Sections A2303 thru A2307 outline definitions, symbols used, material requirements, and special inspection required. Sections A2308 thru A2310 establish design values and the procedures to be used in the structural design for strengthening a URM building. Section A2309 references the State Historical Building Code, which offers consideration of alternative structural regulations for the 38 qualified historic structures in the City. Section A2311 requires that the owner of a URM building have the building structurally analyzed within 18 months, requires that URM buildings be strengthened when alterations exceed 50% of the replacement cost of the building or when the occupancy classification changes, requires the recording of a potentially hazardous building document with the County Recorder, establishes the duties of the Building Official in obtaining compliance, and requires the submission of an annual report to the City Council outlining progress of the program. Costs The consultant has determined that the average cost to strengthen URM buildings in the City will be $10.55 per square foot, ranging from $4. 50 to $15. 00 per square foot. This average cost /�i� ��n��u►�ulllllllll1°s9�Ulll city Or San Lays OBISPO Ofto COUNCIL AGENDA REPORT translates to a total of $6.5 million to strengthen all such buildings. Funding for strengthening projects is not readily available. An assessment district concept similar to the program implemented in the City of Long Beach appears to be a viable funding resource, and may be structured to include the cost of seismic strengthening and the downtown fire sprinkler retrofit. A mandatory strengthening plan must be in place first; without such a catalyst, there is no cause for the creation of an assessment district as "a public purpose in furtherance of general public health and safety. " The City Council will be given an opportunity to review details of the potential assessment district in the near future. Also discussed is the City' s consideration of a credit towards the cost of a future building permit to strengthen a building equal to the cost of the structural analysis. CONCURRENCES: The proposed ordinance is supported by the Chamber of Commerce, the BIA, and the San Luis Obispo Property Owner' s Association. FISCAL IMPACT: There are no immediate fiscal impacts for the City. Notice and Order procedures and the processing of building permits for strengthening projects can be accomplished by existing staff. The Council would later specify the degree of City involvement in a seismic/fire sprinkler assessment district program. ALTERNATIVES: (1) Do not adopt a URM Strengthening Ordinance The Council could choose not to adopt a strengthening ordinance to mitigate the potential hazards associated with unreinforced masonry buildings. However, strengthening or demolition are the only programs that effectively reduce the hazards. Section 8877 of the Government Code suggests that strengthening should be a part of an overall mitigation program. Because City responsibility under the law is not satisfied and the public safety aspects of this issue warrant, in staff' s opinion, the need for a mandatory strengthening ordinance, this alternative is not recommended. (2) Adopt modified strengthening provisions The Council could adopt a strengthening ordinance that differs from the proposed ordinance from an engineering standpoint. However, the proposal is based on standards that are supported by the Seismic Safety Commission, /SVM5 ��niiilil�llllllll�° IIIIIII MY Of San .—AIS OBS SPO ONGin COUNCIL AGENDA REPORT Structural Engineers Association of California, International Conference of Building Officials, and numerous large-city jurisdictions throughout the state. Because of the lack of any other recognized standards available, the consultant and staff do not recommend this alternative. (3) Adopt a strengthening ordinance with Seismic Zone 4 criteria The Council could direct staff to return, with a revised ordinance using Seismic Zone 4 criteria. The consultant estimates that the cost of strengthening will increase an average of 10%, but could be considerably more for some buildings. This alternate may be consistent with indications that forthcoming State legislation will mandate use of Appendix Chapter 1 of the Uniform Code for Building Conservation (same as model ordinance) with Zone 4 factors only. However, buildings strengthened under the proposed criteria using Zone 3 would be eliminated from the hazardous building inventory and would not be affected by future legislation. Designers will always have the option of a Zone 4 upgrade; minimums can always be exceeded. Because the proposed ordinance is based on the best documented information available at this time (see attached letter from consultant summarizing seismic hazard analysis) , staff recommends against pursuing the Zone 4 alternative. SUMMARY: I The staff recommended strengthening ordinance represents the "state of the art" for designing structural improvements to unreinforced masonry buildings to achieve the most cost effective reduction in potential seismic hazard. The primary purpose of the ordinance is to improve life safety. The minimum strengthening methodology will limit damage to a URM building and adjacent buildings, but may not prevent irreparable damage. However, the technical standards in the proposed ordinance are a � reasonable compromise that will provide a safer environment for occupants of a URM building and pedestrians passing by. Because the proposed ordinance does not insure a significant reduction in the URM earthquake hazard, it is to be considered an interim measure leading to in a more comprehensive mitigation program satisfying State mandate. ATTACHMENTS: 1. Proposed Ordinance 2 . Memo From City Attorney 3 . Letter from Chamber of Commerce 4 . Letter from San Luis Property Owners Association 5. Letter from Howard Stup & Associates ORDINANCE NO. (1991 Series) AN ORDINANCE OF THE CITY OF SAN LUIS OBISPO AMENDING TITLE 15, CHAPTER 15. 04 OF THE MUNICIPAL CODE TO ADD DIVISION III OF APPENDIX CHAPTER 23 TO THE UNIFORM BUILDING CODE AS ADOPTED AND TO ESTABLISH FINDINGS OF FACT TO SUPPORT THE IMPOSITION OF REQUIREMENTS GREATER THAN REQUIREMENTS ESTABLISHED BY THE STATE BUILDING STANDARDS CODE WHEREAS, it is the desire and intent of the City Council of the City of San Luis Obispo to provide citizens with the greatest degree of life and structural safety in unreinforced masonry buildings in the most cost effective manner by amending the 1988 editions of the Uniform Building Code and Uniform Building Code Standards as adopted to add requirements for strengthening buildings of unreinforced masonry construction; and WHEREAS, the California Health and Safety Code, Chapter 4 , Part 1.5, Division XIII, Section 17958, Section 17958 . 5 and Section 17958.7 requires the City Council, before making any modifications or changes to the State Building Standards Code pursuant to Health and Safety Code Section 17958. 5, to make an express finding that each such modification or change is needed; and, WHEREAS, the California Health and Safety Code Section 17958 .5 requires that such changes must be determined to be reasonably necessary because of local climatic, geological, or topographical conditions; and, WHEREAS, such findings must be made available as a public record and a copy thereof with each such modification or change shall be filed with the State of California Department of Housing and Community Development; and WHEREAS, the City Council of the City of San Luis Obispo hereby determines that the addition of Division III of Appendix Chapter 23 to the 1988 Uniform Building Code and Standards No. 24-40, 24- 41, and 24-42 to the 1988 Uniform Building Code Standards due to the findings contained herein are greater requirements than those set forth in the California State Building Standards Code; and WHEREAS, the City Council of the City of San Luis Obispo finds that each of the changes or modifications to measures referred to herein are reasonably necessary because of local climatic, geological, or topographical conditions in the area encompassed by the boundaries of the City of San Luis Obispo, and that the following findings support the local necessity for the changes or modifications: FINDING 1 That the City of San Luis Obispo contains approximately 138 buildings considered to be of unreinforced masonry construction Ordinance No. (1991 Series) Page 2 and defined as "potentially hazardous" during a seismic event. An unreinforced masonry building has proven to be particularly susceptible to damage during an earthquake. The protection of occupants in potentially hazardous buildings and the general public and preservation of property in the event of such occurrence support the imposition of structural requirements greater than those set forth in the California State Building Standards Code and in particular support the addition of Appendix Chapter 23 - Division III to the 1988 Uniform Building Code. FINDING 2 That the City of San Luis Obispo is situated near three major faults each capable of generating earthquakes with a magnitude of 7. 5. These are the San Andreas to the east of the City, the Nacimiento-Rinconada that crosses Hwy 101 north of the City then parallels the City to the east, and the Hosgri to the West. other faults of importance are the Huasna and West Huasna to the Southeast of the City, the San Simeon to the Northwest, and the Edna and Edna Extended faults which enter the southern areas of the City. In as much as these faults are included as major California earthquake faults, which are subject to becoming active at any time, the City of San Luis Obispo is particularly vulnerable to devastation should such an earthquake occur. The protection of human life and the preservation of property in the event of such an occurrence support the imposition structural requirements not set forth in the California State Building Standards Code and in particular support the addition of Appendix Chapter 23 - Division III to the 1988 Uniform Building Code. FINDING 3 That the City of San Luis Obispo is located in Seismic Zone 4 and is subject to the provisions of Chapter 12 . 2, Division 1 of Title 2 of the Government Code. Government Code Section 8875 et seq. requires that the City establish a mitigation program to reduce the hazards associated with unreinforced masonry buildings. The mandate by the State of California to mitigate the hazards of such buildings supports the imposition of structural requirements greater than those set forth in the California State Building Standards Code, and in particular, supports the addition of Appendix Chapter 23 - Division III to the 1988 Uniform Building Code. FINDING 4 That adoption of the Ordinance in and of itself will not have the potential for environmental effects. Most seismic strengthening projects will not be visible on the exterior of the involved structure, requiring ministerial approval of building permits for attachment of the roof structure to walls and similar operations. Those projects involving change of occupancy, architectural review, or more extensive permit activity will require specific environmental review prior to their approval . /—V Ordinance No. (1991 Series) Page 3 NOW THEREFORE BE IT ORDAINED by the City Council of the City Of San Luis Obispo that the provisions of the State Building Standards Code are hereby modified, changed and amended, as provided for herein, based upon the foregoing findings and the public interest in protecting life and preserving public safety and property, as follows: SECTION 1. Chapter 15. 04 of Title 15 of the San Luis Obispo Municipal Code is hereby amended by adding subsection Q to Section 15. 04. 040 as follows. SECTION 15. 04 . 040 AMENDMENTS ; UNIFORM BUILDING CODE Q. Amend the Appendix to Chapter 23 by adding Division III to read as follows: Chapter 23 Division III SEISMIC STRENGTHENING PROVISIONS FOR UNREINFORCED MASONRY BUILDINGS Purpose Section A2301. The purpose of this Chapter is to promote public safety and welfare by reducing the risk of death or injury that may result from the effects of earthquakes on existing buildings of unreinforced masonry wall construction. The provisions of this Chapter are intended as minimum standards for structural seismic resistance established primarily to reduce the risk of life loss or injury. Compliance with these standards will not necessarily prevent loss of life or injury or prevent earthquake damage to rehabilitated buildings. Scope Section A2302 . The provisions of this Chapter shall apply to all existing buildings having at least one unreinforced masonry wall. Except as provided herein, all other provisions of the Building Code shall apply. EXCEPTION: This Chapter shall not apply to detached one or two family dwellings and detached apartment houses containing less than 5 dwelling units and used solely for residential purposes. Definitions Section A2303. For the purposes of this Chapter, the applicable definitions in the Building Code shall also apply. COLLAR JOINT is the vertical space between adjacent wythes and Ordinance No. (1991 Series) Page 4 may contain mortar. CROSSWALL is a wall that meets the requirements of Section A2309 (d) 3. A crosswall is not a shear wall. CROSSWALL SHEAR CAPACITY is the length of the crosswall times the allowable shear value, VCLC . DIAPHRAGM EDGE is the intersection of the horizontal diaphragm and a shear wall or other line of shear collection. DIAPHRAGM SHEAR CAPACITY is the depth of the diaphragm times the allowable shear value, vUD. FLEXIBLE DIAPHRAGM is a diaphragm of wood construction or other construction of similar flexibility. NORMAL WALL is a wall perpendicular to the direction of seismic forces. OPEN FRONT is an exterior building wall plane on one side only without vertical elements of the lateral force resisting system in one or more stories. POINTING is the partial reconstruction of the bed joints of a URM wall as defined in U.B.C. Standard No. 24-42 . UNREINFORCED MASONRY (URM) WALL is a masonry wall in which the area of reinforcing steel is less than 25 percent of the minimum required by the Building Code for reinforced masonry. UNREINFORCED MASONRY BEARING WALL. A URM wall which provides the vertical support for a floor or roof for which the total superimposed load exceeds 100 pounds per linear foot of wall. YIELD STORY DRIFT is the lateral displacement of one level relative to the level above or below at which yield stress is first developed in a frame member. Symbols and Notations Section A2304 . For the purposes of this Chapter, the applicable symbols and notations in the Building Code shall also apply. A = Area of unreinforced masonry pier, square inches. Ab = Area of the bed joints above and below the test specimen for each in-place shear test. CP = Numerical coefficient specified in Table A23-A of this Chapter. D = In-plane width dimension of pier, inches, or depth of Mo Ordinance No. (1991 Series) Page 5 diaphragm, feet. DCR = Demand-capacity ratio specified in Section A2309 (d) . FP = Wall anchor tension force, pounds. FW = Force applied to a wall at level x, pounds. H = Least clear height of opening on either side of pier, inches. h/t = Height/thickness ratio of URM wall. Height h is measured between wall anchorage levels and/or slab-on- grade. L = Span of diaphragm between shear walls, or span between shear wall and open front, feet.. LC = Length of crosswall, feet. Li Effective span for an open front building specified in Section A2309 (d) 7, feet. Pp = Superimposed dead load at the top of the pier under consideration, pounds. Pd = Axial dead load pressure, pounds per square inch. Pu = Weight of wall, pounds. Ve = The allowable shear in any URM pier, pounds. Vcb = Total shear capacity of crosswalls in- the direction of analysis immediately below the diaphragm level being investigated, EvCLC , pounds. VCa = Total shear capacity of crosswalls in the direction of analysis immediately above the diaphragm level being investigated, EvcLc , pounds. Vr = 0.5Pp (D/H) , the rocking shear of any URM wall or wall pier, pounds. VW = Total shear force resisted by a shear wall at the level under consideration, pounds. VP = Shear force assigned to a pier on the basis of its relative shear rigidity, pounds. Vs = Shear force assigned to a spandrel on the basis of the shear forces in the adjacent wall piers and tributary dead plus live loads. Vtest = Load in pounds at incipient slipping for each in-place Ordinance No. (1991 Series) Page 6 shear test per Section A2306 (c) 3A. va = Allowable shear stress for unreinforced masonry, pounds per square inch. ve = Allowable shear value for a crosswall sheathed with any of the materials given in Tables A23-C or A23-D, pounds per foot. vt = Mortar shear strength as specified in Section A2306 (c) 3D. vto = Mortar shear test values as specified in Section A2306 (c) 3D. vu = Allowable shear value for a diaphragm sheathed with any of the materials .given in Tables A23-C or A23-D, pounds per foot. EVUD = Sum of diaphragm shear capacities of both ends of the diaphragm. EEVUD= For diaphragms coupled with crosswalls EEVUD includes the sum of shear capacities of both ends of diaphragms coupled at and above the level under consideration. Wd = Total dead load tributary to a diaphragm, pounds. EWd = Total deal load tributary to all of the diaphragms at and above the level under consideration, pounds. WP = Wall dead load tributary to an anchor, pounds. Ww = Total dead load of an unreinforced masonry wall above the level under consideration or above an open front of a building, pounds. Wwx = Dead load of a URM wall assigned to Level x halfway above and below the level under consideration. Z = The Seismic Zone Factor for Seismic Zone 3 specified in Table 23-I of the Building Code. General Requirements Section A2305. (a) General. All buildings shall have a seismic resisting system conforming with Section 2303 (b) of the Building Code, except as modified by this Chapter. (b) Alterations and Repairs. Alterations and repairs required to meet the provisions of this Chapter shall comply with all other applicable requirements of the Building Code unless specifically provided for in this Chapter. Ordinance No. (1991 Series) Page 7 (c) Requirements for Plans. The following construction information shall be included in the plans required by this Chapter: 1. Accurately dimensioned floor and roof plans showing existing walls and the size and spacing of floor and roof framing members and sheathing materials. The plans shall indicate all existing and new crosswalls and their materials of construction. The location of the crosswalls and their openings shall be fully dimensioned or drawn to scale on the plans. 2. Accurately dimensioned wall elevations showing openings, piers, thicknesses, and heights, wall shear test locations, cracks or damaged portions requiring repairs. The general condition of the mortar joints and if and where the joints require pointing. where the exterior face is veneer, the type of veneer, its thickness and its bonding and/or ties to the structural wall masonry shall also be reported. 3 . The type of interior wall and ceiling surfaces. 4 . The extent and type of existing wall anchorage to floors and roof when utilized in the design. 5. The extent and type of parapet corrections which were previously performed, if any. 6. Repair details, if any, of cracked or damaged unreinforced masonry walls required to resist forces specified in the Chapter. 7. All other plans, sections, and details necessary to delineate required retrofit construction including those items in Section A2310. Material Requirements Section A2306. (a) General. All materials permitted by this Chapter, including their appropriate allowable design values and those existing configurations of materials specified herein, may be utilized to meet the requirements of this Chapter. (b) Existing Materials. All existing materials utilized as part of the required force resisting system shall be in sound condition or shall be repaired or removed and replaced with new material. (c) Existing Unreinforced Masonry. 1. General. All unreinforced' masonry walls utilized to carry vertical loads or seismic forces parallel and 1-13 Ordinance No. (1991 Series) Page 8 perpendicular to the wall plane shall be tested as specified in this subsection. All masonry that does not meet or exceed the minimum standards established by this Chapter shall be removed and replaced by new materials or alternatively shall have its structural functions replaced by new materials and shall be anchored to supporting elements. 2. Lay-Up of Walls. The facing and backing shall be bonded so that not less than 10 percent of the exposed face area is composed of solid headers extending not less than 4 inches into the backing. The clear distance between adjacent full-length headers shall not exceed 24 inches vertically or horizontally. Where the backing consists of two or more wythes, the headers shall extend not less than 4 inches into the most distant wythe or the backing wythes shall be bonded together with separate headers whose area and spacing conform to the foregoing. Wythes of walls not bonded as described above shall be considered as veneer. Veneer wythes shall not be included in the effective thickness used in calculating the height to thickness and the shear capacity of the wall. EXCEPTION: Veneer wythes, anchored as specified by the Building Code and made composite with backup masonry, can be used for calculation of the effective thickness. 3. Mortar. A. Tests. The quality of mortar in all masonry walls shall be determined by performing in-place shear texts in accordance with U.B.C. Standard No. 24-40. Alternative methods of testing may be- approved by the Building Official for masonry walls other than brick. B. Location of Tests. The shear tests shall be taken at locations representative of the mortar conditions throughout the entire building, taking into account variations in workmanship at different building height levels, variations in weathering of the exterior surfaces, and variations in the condition of the interior water and/or by the deleterious effects of other substances contained within the building. The exact test location shall be determined at the building site by the engineer in responsible charge of the structural design work. An accurate record of all such tests and their location in the building shall be recorded and these results shall be submitted to the Building Department for approval as part of the structural analysis. C. Number of Tests. The minimum number of tests shall be as follows: Ordinance No. (1991 Series) Page 9 (1) At each of both the first and top stories, not less than two per wall or line of wall elements providing a common line of resistance to lateral forces. (2) At each of all other stories, not less than one per wall or line of wall elements providing a common line of resistance to lateral forces. (3) When grouted or chemically set tension anchors are utilized above the roof line additional in-plane shear tests shall be performed above the intersection of the roof sheathing with the wall. The test locations shall be distributed around the perimeter of the building such that a minimum of one test is performed in each predominant wall direction. The minimum quality mortar in each of the shear tests shall not be less than 50 psi. (4) In any case, not less than one per 1500 square feet of wall surface nor less than a total of eight. D. Minimum Quality Mortar. (1) Mortar shear test values, vto , in psi shall be obtained for each in-place shear test in accordance with the following equation: vto = (Vtest /Ab) -Pd . . . . . . . . . . . . . . . . . . (A23-1) (2) The mortar shear strength, vt , is the value in psi that is exceeded by 800 of all of the mortar shear test values, vto • (3) Unreinforced masonry with mortar shear strength, vt , less than 30 psi shall be removed or pointed and retested. E. Collar Joints. The collar joints shall be inspected at the test locations during each in-place shear test, and estimates of the percentage of the surfaces of adjacent wythes which are covered with mortar shall be reported along with the results of the in-place shear tests. F. Pointing. All deteriorated mortar joints in unreinforced masonry walls shall be pointed according to U.B.C. Standard No. 24-42 . Nothing shall prevent pointing with mortar of all the masonry wall joints before the tests are made, except as required by Section A2307 (a) . Alternative methods of pointing may be used with prior approval of the Building Official . HS Ordinance No. (1991 Series) Page 10 (d) Existing Wall Anchors. Existing wall floor anchors, if found to be acceptable by testing, may be utilized in the design. Anchors utilized as all or part of the required tension anchors shall be tested in pullout according to U.B.C. Standard No. 24- 41. The minimum number of anchors tested shall be four per floor, with two tests at walls with joists framing into the wall and two tests at walls with joists parallel to the wall, but not less than ten percent of the total number of existing tension anchors at each level. Quality Control Section A2307. (a) Pointing. All preparation and mortar pointing shall be performed with special inspection. EXCEPTION: At the discretion of the Building Official, incidental pointing may be performed without special inspection. (b) New Bolts. One-fourth of all new shear bolts and combined tension and shear bolts in unreinforced masonry walls shall be tested according to U.B.C. Standard 24-41. EXCEPTION: Special inspection may be provided during installation in lieu of testing. (c) New Anchors. All installation of grouted or chemically set tension anchors shall be performed with special inspection. Allowable Design values Section A2308. (a) Allowable Values. 1. Allowable values for existing materials are given in Table A23-C and for new materials in Table A23-D. 2 . Allowable values not specified in this Chapter shall be as specified elsewhere in the Building Code. (b) Masonry Shear. The allowable unreinforced masonry shear stress, vat shall be determined from the following equation: vB = 0. 1vt + 0. 15Pp/A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (A23-2) The mortar shear test value, vt , shall be determined in accordance with Section A2306 (c) 3, and shall not exceed 100 psi for the determination of vB . The one-third increase in allowable values of the Building Code is not allowed for ve . (c) Masonry Compression. Where any increase in dead plus live /4 Ordinance No. (1991 Series) Page 11 compression stress occurs the allowable compression stress in unreinforced masonry shall not exceed 100 psi. The one-third increase in allowable stress of the Building Code is allowed. (d) Masonry Tension. Unreinforced masonry shall be assumed as having no tensile capacity. (e) Existing Tension Anchors. The allowable resistance values of the existing anchors shall be 40 percent of the average of the tension tests of existing anchors having the same wall thickness and joist orientation. The one-third increase in allowable stress of the Building Code is not allowed for existing tension anchors. (f) Foundations. For existing foundations new total loads may be increased over existing loads by 25 percent. New total dead load plus live load plus seismic forces may be increased over existing dead load plus live load by 50 percent. Higher values may be justified only in conjunction with a geotechnical investigation. Analysis and Design Section A2309. (a) General. Except as modified herein, the analysis and design relating to the structural alteration of existing buildings shall be in accordance with the Building Code. (b) Selection of Procedure. Buildings shall be analyzed by the General Procedure of Section A2309 (c) which is based on Chapter 23 of the Building Code, or when applicable, buildings may be analyzed by the Special Procedure of A2309 (d) . Unreinforced masonry bearing wall buildings constructed of hollow concrete or clay tile shall be analyzed by the general procedures unless it can be shown by testing that all masonry units were manufactured and installed in compliance with U.B.C. Standards No. 24-4 or 24- 8 as applicable for bearing type units and that the capacity of the wall in bearing and shear, based on the net area in contact through the bed joints, is not less than that allowed for solid bricks, in which case the special procedure may be used. Buildings with a substantially complete steel or concrete frame capable of supporting gravity dead and live loads and that utilize unreinforced masonry walls as non-bearing infill between frame members shall be analyzed by a procedure approved by the building official. Qualified historic structures may be analyzed per Title 24, California Administrative Code, Part 8, State Historical Building Code. (c) General Procedure. 1. Minimum Design Lateral Forces. Buildings shall be analyzed to resist minimum lateral forces assumed to act noncurrently in the direction of each of the main axes of the structure in accordance with the following: /-/7 Ordinance No. (1991 Series) Page 12 V = 0. 33ZW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (A23-3) 2. Lateral Forces on Elements of Structures. Parts or portions of structures shall be analyzed as required in Chapter 23 of the Building Code. EXCEPTIONS: 1. Unreinforced masonry walls for which height-to-thickness ratios do not exceed ratios set forth in Table A23-B need not be analyzed for out-of- plane loading. Unreinforced masonry walls which exceed the allowable h/t ratios of Table A23-B shall be braced according to Section A2310 (e) . 2 . Parapets complying with Section A2310 (f) need not be analyzed for out-of-plane loading. 3 . Shear Walls (In-Plane Loading) . Shear walls shall comply with subsection A2309 (e) . (d) Special Procedure. 1. Limits for the Application of Subsection A2309 (d) . The Special Procedure of this subsection may only be applied to buildings with the following characteristics: A. Flexible diaphragms at all levels above the base of the structure. B. A maximum of 6 stories above the base of the building. C. The vertical elements of the lateral force resisting system shall consist predominantly of masonry or concrete shear walls. D. New vertical elements of the lateral force resisting system consisting of steel braced frames or special moment resisting frames shall have a maximum overall height-to-length ratio of 1-1/2 to 1. E. A minimum of two lines of vertical elements of the lateral force resisting system shall be parallel to each axes of the building except for single-story buildings with an open front on one side only. (See Section A2309 (d) 8 for open front buildings. ) 2. Lateral Forces on Elements of Structures. With the exception of the diaphragm provisions in subsection 12309 (d) , elements of structures shall comply with subsection A2309 (c) 2 . 3 . Crosswalls. Crosswalls shall meet the requirements of this subsection. Ordinance No. (1991 Series) Page 13 A. Crosswall Definition. A crosswall is a wood- framed wall sheathed with any of the materials described in Tables A23-C or A23-D. Spacing of crosswalls shall not exceed 40 feet on center measured perpendicular to the direction of consideration, and shall be placed in each story of the building. Crosswalls shall extend the full story height between diaphragms. EXCEPTIONS: 1. Crosswalls need not be provided at all levels in accordance with subsection A2309 (d) 4B(iv) . 2 . Existing crosswalls need not be continuous below a wood diaphragm at/or within four feet of grade provided: (i) Shear connection requirements Section A2309 (d) 5 are satisfied at all edges of the diaphragm. (ii) Crosswalls with total shear capacity of 0.20ZEWd interconnect the diaphragm to the foundation. (iii) The demand/capacity ratio of the diaphragm between the crosswalls that are continuous to their foundations shall be calculated as: DCR = [0.75ZWd + VCe ]/2vuD. . . . . . (A23-4) and DCR shall not exceed 2 . 5. B. Crosswall Shear Capacity. Within any 40 feet measured along the span of the diaphragm, the sum of the crosswall shear capacities shall be at least 30 percent of the diaphragm shear capacity of the strongest diaphragm at or above the level under consideration. C. Existing Crosswalls. Existing crosswalls shall have a length-to-height ratio between openings of not less than 1. 5. Existing crosswall connections to diaphragms need not be investigated as long as the crosswall extends to the framing of the diaphragm above and below. D. New Crosswalls. New crosswall connections to the diaphragm shall develop the crosswall shear capacity. New crosswalls shall have the capacity to resist an overturning moment equal to the crosswall shear capacity times the story height. Crosswall overturning moments need not be cumulative over more than two H9 Ordinance No. (1991 Series) Page 14 stories. E. Other Crosswall Systems. Other systems such as special moment resisting frames may be used as crosswalls provided that the yield story drift does not exceed 1 inch in any story. 4 . Wood Diaphragms. A. Acceptable Diaphragm span. A diaphragm is acceptable if the point (L,DCR) on Figure A23-1 falls within Regions 1, 2 or 3 . B. Demand-Capacity Ratios. Demand-Capacity Ratios shall be calculated for the diaphragm according to the following formulas: (i) For a diaphragm without qualifying crosswalls at levels immediately above or below: DCR = 0.75ZWd/EvuD. . . . . . . . . . . . . . . . . . (A23-5) (ii) For a diaphragm in a single-story building with qualifying crosswalls: DCR = 0.75ZWd/ (EvuD + Vcb ) . . . . . . . . . . (A23-6) (iii) For diaphragms in a multi-story building with qualifying crosswalls in all levels: DCR = 0.75ZEWd/ (EEvuD + Vcb ) . . . . . . . . . (A23-7) DCR shall be calculated at each level for the set of diaphragms at and above the level under consideration. In addition, roof diaphragm shall also meet the requirements of Formula A23-6. (iv) For a roof diaphragm and the diaphragms directly below if coupled by crosswalls: DCR = 0.75ZEWd/EEv,D. . . . . . . . . . . . . . . . . (A23-8) C. Chords. An analysis for diaphragm flexure need not be made and chords need not be provided. D. Collectors. An analysis of diaphragm collector forces shall be made for the transfer of diaphragm edge shears into vertical elements of the lateral force resisting system. Collector forces may be resisted by new or existing elements. E. Diaphragm Openings. (i) Diaphragm forces at corners of openings shall �-,Zo Ordinance No. (1991 Series) Page 15 be investigated and shall be developed into the diaphragm by new or existing materials. (ii) In addition to calculating demand-capacity ratios per Section A2309 (d) 4B, the demand-capacity ratio of the portion of the diaphragm adjacent to an opening shall be calculated using the opening dimension as the span. (iii) where an opening occurs in the end quarter of the diaphragm span, vUD for the demand-capacity ratio calculation shall be based on the net depth of the diaphragm. 5. Diaphragm Shear Transfer. Diaphragms shall be connected to shear walls with connections capable of developing a minimum force given by the lesser of the following formulas: V = 0.50ZCPWd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (A23-9) using CP values of Table No. 23-A, or V = vu D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (A23-10) 6. Shear Walls (In-Place Loading) - Special Procedure. A. Wall Story Force. The wall story force distributed to a shear wall at any diaphragm level shall be the lesser value calculated as: (i) For buildings without crosswalls: Fwx = 0. 33Z (WWx +Wd/2) . . . . . . . . . . . . . (A23-11) but need not exceed FWx = 0.33ZWWx + VUD. . . . . . . . . . . . . . . . (A23-12) (ii) For buildings with crosswalls in all levels: Fwx = 0.25Z (Wwx +Wd/2) . . . . . . . . . . . . . . . (A23-13) but need not exceed Fwx = 0.25Z (WWx +EWd (vu D/EEvuD+Vcb ) ) . . (A23-14) and need not exceed Fwx = 0.25ZWwx + VUD. . . . . . . . . . . . . . . . (A23-15) B. Wall Story Shear. The wall story shear shall be the sum of the wall story forces at and above the level of consideration. Ordinance No. (1991 Series) Page 16 Vwx = EFwx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (A23-16) C. Shear wall Analysis. Shear walls shall comply with subsection A2309 (e) . D. Moment Frames. Moment frames used in place of shear walls shall be designed as required in Chapter 23 of the Building Code except that the forces shall be as specified in Section A2309 (d) 6A and the interstory drift ratio shall be limited to 0. 005 except as for further limited in Section A2309 (e) 3B. 7. Buildings with Open Fronts. A building with an open front on one side shall have crosswalls parallel to the open front and shall be designed by the following procedure: A. Effective Diaphragm Span, L, , for use in Figure A23-1 shall be determined in accordance with the following formula: Li = 2 [ (Ww/Wd) x L + L] . . . . . . . . . . . . . . . . . . (A23-17) B. Diaphragm demand-capacity ratio shall be calculated as: DCR = 0.75Z9Wd + Ww)/ [ (vuD) + Vc ] . . . . . . . . (A23-18) (e) Analysis of vertical Elements of the Lateral Force-Resisting System. Applicable to both General Procedure and Special Procedure Buildings. 1. Existing URM walls. A. Flexural Rigidity. Flexural components of deflections may be neglected in determining the rigidity of a URM wall. B. Shear walls with Openings. Wall piers shall be analyzed according to the following procedure: (i) For any pier, (1) The pier shear capacity shall be calculated as: Va = VaA. . . . . . . . . . . . . . . . . . . . . . . (A23-19) (2) The pier rocking shear capacity shall be calculated as: Vr = 0. 5PDD/H. . . . . . . . . . . . . . . . . . (A23-20) (ii) The wall piers at any level are acceptable if they comply with one of the following modes of Ordinance No. (1991 Series) Page 17 behavior: (1) Rocking Controlled Mode. When the pier rocking shear capacity is less than the pier shear capacity, i.e. Vr < V. for each pier in a level, forces in the wall at that level, Vwx , shall be distributed to each pier, Vp , in proportion to PD/H. For the wall at that level: Vwx : EVA . . . . . . . . . . . . . . . . . . . . . . (A23-21) (2) Shear Controlled Mode. Where the pier shear capacity is less than the pier rocking capacity, i.e. Ve < Vr in at least one pier in a level, forces in the wall at that level, Vwx , shall be distributed to each pier, VP , in proportion to D/H. For at least one pier at that level: VP < VB . . . . . . . . . . . . . . . . . :. . . . . . (A23-22) and VP < Vr . . . . . . . . . . . . . . . . . . . . . . . (A23-23) If VP < Va for each pier and VP > V� for one or more piers, omit such piers from the analysis and repeat the procedure for the remaining piers, or strengthen and reanalyze the wall. (iii) Masonry Pier Tension Stress. Unreinforced masonry wall piers need not be analyzed for tension stress. C. Shear Walls Without openings. Shear walls without openings shall be analyzed as for walls with openings except that Vr shall be calculated as follows: V _ (0.50Pp + 0. 25PW) D/H. . . . . . . . . . . . . . . . (A23-24) 2. Plywood Sheathed Shear Walls. Plywood sheathed shear walls may be used to resist lateral forces for buildings with flexible diaphragms analyzed according to provisions of Section A2.309 (c) . Plywood sheathed shear walls may not be used to share lateral loads with other materials along the same line of resistance. 3 . Combination of Vertical Elements A. Lateral Force Distribution. Lateral forces shall be distributed among the vertical resisting elements in proportion to their relative rigidities, except that �-z3 Ordinance No. (1991 Series) Page 18 moment frames shall comply with Section A2309 (e) 3B. B. Moment Resisting Frames. A moment frame shall not be used with a URM wall in a single line of resistance unless the wall (s) have piers that are capable of sustaining rocking in accordance with Section A2309 (e) 1B and the frames are designed to carry 100 percent of the lateral forces, and the interstory drift ratio shall be limited to . 0025. Detailed System Design Requirements Section A2310. (a) Wall Anchorage. 1. Anchorage Locations. All unreinforced masonry walls shall be anchored at the roof and floor levels as required in Section A2309 (c) 2. Ceilings with substantial rigidity and abutting masonry walls shall be connected to walls with tension bolts at a maximum anchor spacing of 6 feet. Ceiling systems with substantial mass shall be braced at the perimeter to diaphragms. 2. Anchor Requirements. Anchors shall be tension bolts through the wall as specified in Table No. A23-D, or by an approved equivalent at a maximum anchor spacing of 6 feet. All existing wall anchors shall be secured to the joists to develop the required forces. 3 . Minimum Wall Anchorage. Anchorage of masonry walls to each floor or roof shall resist a minimum force determined by: FP = ZCPWP . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . (A23-25) or 200 pounds per linear foot, whichever is greater, acting normal to the wall at the level of the floor or roof. Existing floor wall anchors must meet or must be upgraded to meet the requirements of this Chapter if utilized in the design. Existing embedded roof anchors shall not be utilized in the design. 4. Anchors at Corners. At the roof and all floor levels, both shear and tension anchors shall be provided within 2 feet horizontally from the inside of the corners of the walls. 5. Anchors with Limited Access. When access to the exterior face of the masonry wall is prevented by proximity of an existing building, wall anchors conforming to Item 5b in Table A23-D may be used. (b) Diaphragm Shear Transfer. Shear bolt spacing shall not exceed 6 feet. Ordinance No. (1991 Series) Page 19 (c) Collectors. Collector elements shall be provided which are capable of transferring the seismic forces originating in other portions of the building to the element providing the resistance to those forces. (d) Ties and Continuity. Ties and continuity shall conform to Section 2312 (h) 2E of the Building Code. (e) Wall Bracing. 1. General. Where a wall height-to-thickness ratio exceeds the specified limits, the wall may be laterally supported by vertical bracing members per Section A2310 (e) 2 or by reducing the wall height by bracing per Section A2310 (e) 3 . 2 . Vertical Bracing Members. Vertical bracing members shall be attached to floor and roof construction for their design loads independently of required wall anchors. Horizontal spacing of vertical bracing members shall not exceed one-half the unsupported height of the wall nor 10 feet. Deflection of such bracing members at design loads shall not exceed one-tenth of the wall thickness. 3 . Wall Height Bracing. The wall height may be reduced by bracing elements connected to the floor or roof. Horizontal spacing of the bracing elements and wall anchors shall be as required by design but shall not exceed 6 feet on center. Bracing elements shall be detailed to minimize the horizontal displacement of the wall by the vertical displacement of the floor or roof. (f) Parapets. Parapets and exterior wall appendages not conforming to this Chapter shall be removed, or stabilized or braced to ensure that the parapets and appendages remain in their original position. The maximum height of an unbraced unreinforced masonry parapet above the lower of either the level of tension anchors or roof sheathing, shall not exceed one and one-half (1-1/2) times the thickness of the parapet wall. If the required parapet height exceeds this maximum height, a bracing system designed for the force factors specified in Table 23-P of the Building Code for walls shall support the top of the parapet. Parapet corrective work must be performed in conjunction with the installation of tension roof anchors. The minimum height of a parapet above the wall anchor shall be 12 inches. EXCEPTION: If a reinforced concrete beam is provided at the top of the wall, the minimum height above the wall anchor may be 6 inches. Ordinance No. (1991 Series) Page 20 (g) veneer. 1. Unreinforced masonry walls which carry no design loads other than their own weight may be considered as veneer if they are adequately anchored to new supporting elements. 2 . Veneer shall be anchored with approved anchor ties, conforming to the required design capacity specified in the Building Code and placed at a maximum spacing of 24 inches with a -maximum supported area of 2 square feet. EXCEPTION: Existing veneer anchor ties may be acceptable provided the ties are in good condition and conform to the following minimum size, maximum spacing and material requirements. Existing veneer anchor ties shall be corrugated galvanized iron strips not less than 1 inch in width, 8 inches in length and 1/16 of an inch in thickness (1" X 8" X 1/16") or equal and shall be located and laid in every alternate course in the vertical height of the wall at a spacing not to exceed 17 inches on centers horizontally. .. As an alternate, such ties may be laid in every fourth course vertically at a spacing not to exceed 9 inches on centers horizontally. 3 . The location and condition of existing veneer anchor ties shall be verified as follows: A. An approved testing laboratory shall verify the location and spacing of the ties and shall submit a report to the Building official for approval as a part of the structural analysis. B. The veneer in a selected area shall be removed to expose a representative sample of ties (not less than four) for inspection by the Building Official. (h) Truss and Beam Supports. Where trusses and beams other than rafters or joists are supported on masonry, independent secondary columns shall be installed to support vertical loads of roof or floor members. The loads shall be transmitted to adequate support. Administrative Provisions Section A2311. (a) Definitions. For the purposes of this Chapter, the applicable definitions in the Building Code shall apply. (b) Compliance Requirements. 1. The owner of each building within the scope of this 1-� Ordinance No. (1991 Series) Page 21 Chapter shall, upon service of an order cause a structural analysis to be made of the building by an engineer or architect licensed by the state to practice as such. Said analysis shall include the preparation of a report detailing the investigation, evaluation, test data, conclusions, and recommendations to establish compliance with this Chapter. If the building does not comply with seismic standards established in this Chapter, the report shall specify the work and cost necessary to structurally alter the building to conform to such standards. The Building Official shall establish a basic outline for the format of the report. 2 . The owner of a building within the scope of this Chapter shall comply with the requirements set forth above by submitting the analysis report to the Building Official for review and acceptance within 18 months of the service of an order. 3 . The owner of a building within the scope of this Chapter shall structurally alter the building to conform to the seismic standards of this Chapter or cause the building to be demolished when either of the following occurs: A. The value of additions, alterations, and/or repairs, cumulative from the effective date of this Chapter, exceeds 50 percent of the replacement value of the building established by the Building Official per Section 304 (b) of the Uniform Administrative Code. B. The use of the building changes to a different division of the same group of occupancy or to a different occupancy group. EXCEPTION: Buildings containing more than one occupancy classification need not comply with this Chapter if changes in use, cumulative from the effective date of this Chapter, do not exceed 50 percent of the floor area of the building. 4 . This Chapter does not require alteration of existing electrical, plumbing, mechanical, or fire safety systems. (c) Administration. 1. Order - Service. The Building Official shall, within 30 days of the effective date of this Chapter, issue an order as provided in this section to the owner of each buildings within the scope of this Chapter. 2 . order - Contents. The order shall be in writing and shall be served either personally or by certified or registered mail upon the owner as shown on the last equalized assessment roll, and upon the person, if any, in apparent charge or control of the building. The order shall AV Ordinance No. (1991 Series) Page 22 specify that the building has been determined by the Building Official to be within the scope of this Chapter and, therefore, is subject to the minimum seismic standards of this Chapter. The order shall specify the rating classification of the building and shall be accompanied by a copy of Section A2311 (b) , which sets forth the owner' s responsibilities. 3 . Appeal. The owner of the building may appeal the Building Official 's initial determination that the building is within the scope of this Chapter to the Board of Appeals established by Section 204 of the Uniform Administrative Code. Such appeal shall be filed with the Board within 60 days from the service date of the order described in Section A2311 (c) 2 . Appeals or requests for modifications from any other determinations, orders or actions by the Building Official pursuant to the Chapter shall be made in accordance with the procedures established in Sections 107, 108 and 204 of the Uniform Administrative Code. Any appeal shall be decided by the Board no later than 90 days after filing and the grounds thereof shall be stated clearly and concisely. 4 . Recordation. At the time that the Building Official serves the aforementioned order, the Building Official shall also file and record with the office of the county recorder a certificate stating that the subject building is within the scope of this Chapter and is a potentially earthquake hazardous building. The certificate shall also state that the owner thereof has been ordered to structurally analyze the building to determine compliance with this Chapter. If the building is either demolished, found not to be within the scope of this Chapter, or is structurally capable of resisting minimum seismic forces required by this Chapter as a result of structural alterations or an analysis, the Building Official shall file and record with the office of the county recorder a form terminating the status of the subject building as being classified within the scope of this Chapter. 5. Enforcement. If the owner in charge or control of the subject building fails to comply with any order issued by the Building Official pursuant to this Chapter within the time limit set forth in Section A2311 (b) , the Building Official shall verify that the record owner of this building has been properly served. If the order has been served on the record owner, then the Building Official shall order that the entire building be vacated and that the building remain vacated until such order has been complied with. If compliance with such order has not been accomplished within 90 days after the date the building has been ordered vacated or such additional time as may have been granted by the Board of Appeals, the Building Official may order its demolition in accordance with the provisions of section 203 Ordinance No. (1991 Series) Page 23 of the Uniform Administrative Code. 6. Annual Report. During January of each year, the Building Official shall submit a report to the City Council outlining the progress to date concerning reduction of the hazards presented by the unreinforced masonry building inventory for the City. The report shall include: A. The number of unreinforced masonry buildings strengthened, demolished, or otherwise eliminated from the inventory; B. The number of unreinforced masonry buildings remaining on the inventory, including the status of orders issued pursuant to this Chapter that are not resolved. TABLE NO. A23-A HORIZONTAL FORCE FACTOR CP CONFIGURATION OF MATERIALS CP Roofs with straight or diagonal sheathing and 0. 6 roofing applied directly to the sheathing or floors with straight tongue-and-groove sheathing Diaphragm with double or multiple layers of 0. 83 boards with edges offset and blocked plywood systems Wall anchors 0. 8 TABLE NO. A23-B MAXIMUM HEIGHT-TO-THICKNESS RATIO OF UNREINFORCED MASONRY WALLS Wall Types H/T Ratio Walls of 20 one-story buildings First-story 20 wall of multi- story buildings Walls in top 14 story of multi- story buildings All other walls 22 1-�9 Ordinance No. (1991 Series) Page 24 TABLE NO. A23-C ALLOWABLE VALUES FOR EXISTING MATERIALS EXISTING MATERIALS OR CON- FIGURATIONS OF MATERIALS ALLOWABLE VALUES 1. HORIZONTAL DIAPHRAGMS a. Roofs with straight sheathing and 100 lbs. per foot roofing applied directly to the for seismic shear sheathing. b. Roofs with diagonal sheathing and 250 lbs. per foot roofing applied directly to the for seismic shear sheathing. C. Floors with straight tongue-and-groove 100 lbs. per foot sheathing. for seismic shear d. Floors with straight sheathing and 500 lbs. per foot finished wood flooring with board for seismic shear edges offset of perpendicular. e. Floors with diagonal sheathing and 600 lbs. per foot wood flooring. for seismic shear 2 . CROSSWALLS2,4 a. Plaster on wood or metal lath 200 lbs. per foot per side for - seismic shear b. Plaster on gypsum lath 175 lbs. per foot for seismic shear C. Gypsum wall board, 75 lbs. per foot unblocked edges for seismic shear d. Gypsum wall board, 125 lbs. per foot blocked edges for seismic shear 3 . EXISTING FOOTINGS, WOOD FRAMING, STRUCTURAL STEEL, AND REINFORCED STEEL a. Plain concrete footings f'c = 1500 psi unless otherwise shown by tests b. Douglas fir wood Allowable stress same as No. 1 D.F.3 l�3� Ordinance No. (1991 Series) Page 25 TABLE NO. A23-C ALLOWABLE VALUES FOR EXISTING MATERIALS (continued) EXISTING MATERIALS OR CON- FIGURATIONS OF MATERIALS ALLOWABLE VALUES C. Reinforcing steel ft = 18, 000 lbs. per square inch maximum.3 d. Structural steel ft = 20, 000 lbs. per square inch maximum.3 Material must be sound and in good condition. 2 Shear values of these materials may be combined, except the total combined value shall not exceed 300 lbs. per foot. 3 Stresses given may be increased for combinations of loads as specified in the Building Code. 4 A one-third increase in allowable stress is not allowed. !-3l Ordinance No. (1991 Series) Page 26 540 - - - -I- - -� - - r - - � - - � ; - ; - - �- - -,- - -r - - � - - I 480 - - -1- - - t' - - r - j - - y - - --,- - -L - - r - - L - - � - - J I 1 t 420 I 1 1 1 , 1 1 1 , 1 I 1• 360 Diaphragm Span, 300 —;—1- - � - - - - -t- - -'-- -r - - � - - � - - y - - -t- - -1 L (Feet) 240 180 - -'- - 1 120 1 , , t , 1 , , I , 1 - - -� - - r - - ,- - - r - - - 1' -+- - -, - -r - - r - - r - - 7 - - n - - r - - • - - � - -�- - -IJr - - - 1 - - � - - -t- - -1. 1 60 Y 1 Q ' ' t J - , • 1 ' , 1 � 1 , 1 , , 1 0 0 1 2 3 4 5 6 FIGURE NO. A23-1. ACCEPTABLE DIAPHRAGM SPAN /-3,Z, Ordinance No. (1991 Series) Page 27 TABLE NO. A23-D ALLOWABLE VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION NEW MATERIALS OR CONFIGURATIONS ALLOWABLE VALUES OF MATERIALS 1. HORIZONTAL DIAPHRAGMS Plywood sheathing applied directly over 225 lbs. per foot straight sheathing with ends of plywood sheets bearing on joists or rafters and edges of plywood located on center of individual sheathing boards. 2. CROSSWALLS4 a. Plywood sheathing applied directly The value over wood studs. 'No value shall be specified in given to plywood applied over Table No. 25- existing plaster or wood sheathing. K-1 of the Building Code for shear walls. b. Drywall or plaster applied directly 100 percent of over wood studs, values in Table No. 47-I of the Building Code. C. Drywall or plaster applied to 50 percent of the sheathing over existing wood studs. - values specified in Table No. 47- I of the Building Code. 3. TENSION BOLTS' Bolts extending entirely through 1800 lbs. per masonry walls secured with bearing bolt, 900 lbs. plates on far side of a 3 wythe for 2 wythe minimum wall with at least 30 square inches of area.2.3 4. SHEAR BOLTS Bolts embedded a minimum of 8 inches 133 percent of into unreinforced masonry walls. the values for Bolts shall be centered in 2-1/2 specified in inch-diameter hole with the dry-pack Table No. 24-E or non-shrink grout around circumference of the Building �-33 Ordinance No. (1991 Series) Page 28 TABLE NO. A23-D ALLOWABLE VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION (continued) NEW MATERIALS OR CONFIGURATIONS ALLOWABLE VALUES OF MATERIALS of bolt.',3,5 Code. No values larger than those given for 3/4 inch bolts shall be used. S. COMBINED TENSION AND SHEAR BOLTS a. Through Bolts - Combined Shear and Tension: Same as Tension Bolts meeting the above for tension bolts requirements for tension bolts and Shear: Same as shear bolts. 1,2,3,5 for shear bolts b. Embedded Bolts - Combined Shear and Tension: 1200 Tension Bolts extending to the lbs. per bolt exterior face of the wall with a 2-1/2 inch round plate under the head and drilled at an angle of 22-1/2 degrees to the horizontal, installed as specified for shear bolts.I.2,3,5 6. INFILLED WALLS Reinforced masonry infilled openings Same as values in existing unreinforced masonry specified for walls. Provide keys or dowels to unreinforced match reinforcing. masonry walls. 7 . REINFORCED MASONRY Masonry piers and walls reinforced Same as values per Chapter 24 of the Building Code.6 specified in Section 2409 of the Building Code. 8. REINFORCED CONCRETE Concrete footings, walls and piers Same as values reinforced as specified in Chapter specified in 26 of the Building Code and designed Chapter 26 of for tributary loads.6 the Building Code. Ordinance No. (1991 Series) Page 29 TABLE NO. A23-D ALLOWABLE VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION (continued) 1 Bolts to be tested as specified in section A2307. z Bolts to be 1/2-inch minimum in diameter. 3 Drilling for bolts and dowels shall be done with an electric rotary drill. Impact tools shall not be used for drilling holes or tightening anchors and shear bolt nuts. 4 A one-third increase in allowable stress is not allowed except as noted. 5 Similar chemical set anchors may be used with prior approval of the Building Official. 6 Stresses given may be increased for combinations of loads as specified in the Building Code. 7 In addition to sheathing value. SECTION 2. Chapter 15. 04 of Title 15 of the San Luis Obispo Municipal Code is hereby amended by adding Section 15. 04 . 041 as follows. SECTION 15. 04 . 041 AMENDMENTS; UNIFORM BUILDING CODE STANDARDS A. Amend the Uniform Building Code Standards by adding Standards No. 24-40, 24-41, and 24-42 to read as follows: UNIFORM BUILDING CODE STANDARD NO. 24-40 IN-PLACE MASONRY SHEAR TESTS Scope Section 24.4001. This standard covers procedures for conducting in-place masonry shear tests. Procedure Section 24.4002. The bed joists of the outer wythe of the masonry shall be tested in shear by laterally displacing a single brick relative to the adjacent bricks in the same wythe. The Ordinance No. (1991 Series) Page 30 head joint opposite the loaded end of the test brick shall be carefully excavated and cleared. The brick adjacent to the loaded end of the test brick shall be carefully removed by sawing or drilling and excavating to provide space for a hydraulic ram and steel loading blocks. Steel blocks, the size of the end of the brick, shall be used on each end of the ram to distribute the load to the brick. The blocks shall not contact the mortar joints. The load shall be applied horizontally, in the plane of the wythe, until either a crack can be seen or slip occurs. The strength of the mortar shall be calculated by dividing the load at the first crack or movement of the test brick by the nominal gross area of the sum of the two bed joists. UNIFORM BUILDING CODE STANDARD NO. 24-41 TESTS OF ANCHORS IN UNREINFORCED MASONRY WALLS Scope Section 24.4101. This standard covers procedures for conducting tests of anchors installed in unreinforced masonry walls. Existing Anchors Section 24.4102 . The test apparatus shall be supported on the masonry wall at a minimum distance of the wall thickness from the anchor tested. Existing wall anchors shall be given a preload of 300 pounds prior to establishing a datum for recording elongation. The tension test load reported shall be recorded at 1/8-inch relative movement of the anchor and the adjacent masonry surface. Results of all tests shall be reported. The report shall include the test results as related to the wall thickness and joist orientation. Combined Shear and Tension Bolts Section 24.4103. Combined shear and tension bolts embedded in unreinforced masonry walls shall be tested using a torque calibrated wrench to the following minimum torques: 1/2-inch-diameter bolts -- 40 foot lbs. 5/8-inch-diameter bolts -- 50 foot lbs. 3\4-inch-diameter bolts -- 60 foot lbs. All nuts shall be installed over malleable iron or plate washers when bearing on wood and heavy cut washers when bearing on steel . Ordinance No. (1991 Series) Page 31 UNIFORM BUILDING CODE STANDARD NO. 24-42 POINTING OF UNREINFORCED MASONRY WALLS Scope Section 24.4201. This standard covers procedures for pointing of unreinforced masonry walls. Pointing Section 24.4202. The old or deteriorated mortar should be cut out, by means of a toothing chisel or nonimpact power tool, to a uniform depth of 3/4 inch or until sound mortar is reached. Care must be taken not to damage the brick edges. After cutting is completed, remove all loose materials with a brush, air or water stream. Mortar mix shall be Type N or S proportions as called for in the construction specifications, preferably as close to the original mortar proportion as possible. Prehydrate pointing mortar to reduce excessive shrinkage. To prehydration mortar, thoroughly mix all ingredients dry, then mix again adding only enough water to produce a damp unworkable mix which will retain its shape when pressed into a ball. After keeping mortar in this dampened condition for 1 to 1-1/2 hours, add sufficient water to the prehydrated mortar to bring it to a proper consistency that is somewhat drier than conventional masonry mortar. To ensure good bond, wet the mortar joints thoroughly before applying pointing mortar. The joints should not be visibly wet with free-standing water which must be absorbed into the wall . Pack mortar tightly in thin layers (1/4-inch maximum) until the joint is filled, then tool to a smooth surface to match the original profile. SECTION 3 . If any provision of this Ordinance is for any reason held to be invalid by a court of competent jurisdiction, the City of San Luis Obispo hereby declares that it would have passed each and every remaining provision irrespective of such holding in order to accomplish the intent of this ordinance. SECTION 4 . A summary of this ordinance, approved by the City Attorney, together with the ayes and noes shall be published at least (5) days prior to its final passage in the Telegram Tribune, a newspaper published and circulated in said City, and the same shall go into effect at the expiration of thirty (30) days. after its said final passage. A copy of the full text of this ordinance shall be on file in the Office of the City Clerk on and after the date following introduction and passage to print and shall be available to any interested member of the public. I SECTION 5. The City Clerk is hereby authorized and directed to transmit a certified copy of this ordinance modifying the /-37 Ordinance No. (1991 Series) Page 32 Uniform Building Code and Uniform Building Code Standards to the State of California Department of Housing and Community Development. INTRODUCED AND PASSED TO PRINT by the Council of the City of San Luis Obispo at a meeting held on the day of 1991, on motion of , seconded by and on the following roll call vote: AYES: NOES: ABSENT: MAYOR RON DUNIN ATTEST: CITY CLERK PAM VOGES APPROVED: City Ad 'nistrative Officer for e Director ofmmunity Development Chief Building fficial 1-� ��io�� i��►►►II IIIIIh��►�►►��i IIIcity of sAn tuis oaspo 990 Palm Street/Post Office Box 8100 • San Luis Obispo, CA 93403-8100 September 23, 1991 TO: Lynn Block, BIA Administrator FROM: Jeff Jorgensen, City Attorne RE: Seismic Retrofit Ordinance Thank you for your September 16, 1991 memorandum requesting an opinion ". . . on the mandatory requirements, time frame, and guidelines for the [seismic retrofit] ordinance." while this is a rather open-ended question, I can comment generally on the requirements of Government Code § 8875 et sea. concerning building earthquake safety (commonly referred to as the URM Law) . The primary provisions affecting. the City of San Luis Obispo are found in Government Code § 8875.2, which provides as follows: 11§8875.2 Local building departments; participation in mitigation programs; reports "Local building departments shall do all of the following: " (a) Identify all potentially hazardous buildings within their respective jurisdictions on or before January 1, 1990. This identification shall include current building use and daily occupancy load. In regard to identifying and inventorying the buildings, the local building departments may establish a schedule of fees to recover the cost of identifying potentially hazardous buildings and carrying out this chapter. " (b) Establish a mitigation program for potentially hazardous buildings to include notification to the legal owner that the building is considered to be one of a general type of structure that historically has exhibited little resistance to earthquake motion. The mitigation program may include the adoption by ordinance of a hazardous buildings program, measures to strengthen buildings, measures to change the use to acceptable occupancy levels or to demolish the RECEl V E ® SEP 2 3 1991 !-U3� CITY OF SAN LUIS OBISPO BUILDING DIVISION - Lynn Block September 23, 1991 Page Two building, tax incentives available for seismic rehabilitation, low-cost seismic rehabilitation loans available under Division 32 (commencing with Section 55000) of the Health and Safety Code, application of structural standards necessary to provide for life safety above current code requirements, and other incentives to repair the buildings which are available from federal, state, and local programs. Compliance with an adopted hazardous buildings ordinance or mitigation program shall be the responsibility of building owners. "Nothing in this chapter makes any state building subject to a local building mitigation program or makes the state or any local government responsible for paying the cost of strengthening a privately owned structure, reducing the occupancy, demolishing a structure, preparing engineering or architectural analysis, investigation, or design, or other costs associated with compliance of locally adopted mitigation programs. " (c) By January 1, 1990, all information regarding potentially hazardous buildings and all hazardous building mitigation programs shall be reported to the appropriate legislative body of a city or county, and filed with the Seismic Safety Commission. " (Emphasis added. ) 1. Analysis. Section 8875.2 (a) imposes a mandatory duty on the City to identify all potentially hazardous buildings, including current building use and occupancy load, by January 1, 1990. This requirement has been fulfilled. Section 8875. 2 (b) imposes a mandatory duty on the City to establish a "mitigation program" for potentially hazardous buildings. The only mandatory element of the mitigation program is notification to affected property owners. Other discretionary elements which may be considered by the City include adoption by ordinance of: /- 11A Lynn Block September 23 , 1991 Page Three • a hazardous building program • measures to strengthen buildings • measures to change the use to acceptable occupancy levels or to demolish buildings • tax incentives for seismic rehabilitation • low-cost seismic rehabilitation loans • application of structural standards which exceed current code requirements • other incentives to repair buildings While not explicitly stated, the City may also establish other standards or programs which the City determines necessary to protect the public health, safety and welfare or meet local conditions. Finally, compliance with any mitigation program adopted by the City is the responsibility of the property owner. There are no mandatory time frames established to implement the mitigation of potentially hazardous buildings. However, the California Earthquake Hazards Reduction Act of 1986 (Government Code Sections 8870, 8872 (b) ) and the Seismic Safety Commission have established a goal of "significantly reducing" seismic hazards by the year 2000. Other than the identification and notice requirements discussed above, there are no specific mandatory provisions which must be included in a mitigation program. However, the Seismic Safety Commission has developed Guidelines and a model ordinance to assist local governments with this difficult task. In developing the draft ordinance currently under consideration, the City has relied on the model ordinance, and mitigation programs developed by other cities throughout the State. 2. Conclusion. The City has broad discretion in developing a mitigation program to protect its citizens from seismic hazards. What the elements of such a program should be are a policy matter to be determined by the City Council, based upon their assessment of the state's requirements and their responsibility to protect public health and safety. An argument has been made that because the mitigation program required by Government Code § 8875.2 is largely discretionary, the City should simply do nothing, or take the minimum required step of notification to property owners. There are several reasons why this may not be an acceptable alternative. First, it would not accomplish the goal of significantly reducing seismic hazards. The Seismic Safety Commission has the responsibility to report annually to the State Legislature on the progress made toward seismic hazard f ��I Lynn Block September 23, 1991 Page- Four reduction. If a significant number of cities fail to act, or adopt ineffective programs that do little to reduce hazards, the Legislature may be persuaded to mandate further requirements which would take away local flexibility and discretion to deal with unique local problems. Second, while . the City has various immunities, in the event of an earthquake disaster, it is a very high probability that the City will be subjected to numerous claims for damages. While this is: an unsettled and evolving area of law, and City liability is by no means certain, it would be foolish to assume that the City would not be subject to . any liability if it failed to act meaningfully in the face of a known significant hazard. Finally and most importantly, failure to .develop an effective mitigation program would leave a large number of people in the City exposed to a very .high level of .seismic hazard. Therefore, as you can conclude, the City has a most significant responsibility under the law and it is ultimately up to the City Council to chose the most appropriate way for the City to exercise this responsibility. JGJ/sw cc: City Council John Dunn Arnold Jonas Tom Baasch /�� DEC-03-1991 12:42 FROM '9IL BOXES WEST TO 18057817109 P.02 11EnNQ AGM DATE �2=_REM#__ 148 East Alexander Ave lvlerced, CA 95340 Dec 3. 1991 San Luis Obispo City Council Mayor Ron Dunin Public Hearing. Unreinforced Ordinance BAASCH / 707 Speaking for my Mother, Lillian P. Smith, owner of property on the 1100 block of Garden Street, ( Ehistian Science Reading Room to and including the Trans-America ) we sincerely hope that you will follow the leadership of the Merced City Council as reported in the Merced Sun-Star, Dec 3. 1991 and attached. Let this proposed ordinance die now and remove this c' pud from down town San Luis Obiapo as has been done in Idierced S i=pjc�� rvine T. Smith. 209-722-0175 Lillian P. Smiths son COPUS 136 Adim F" e nut. C � ❑❑ HREQ Y O max � FOLJMCH ❑ max ►L FII E RECEIVED DE1991 SAN.L C ISPO.CA I0•� qc o °> 4'j (~j� g ztj 1 .9 lid V 3WAI 0 c i0 d+ � � o � X � J9 lid as m Ain— • x J 2 g1 is N� o > on bo ■ang � � Not „ L -091 s o .� � �"�•� Nal E ' c� J.0 4 wimIg I0'd 60TLI84SOBT 01 1S3M S3XOS 'IIyW WO?-W ZI:ET I66i-£0-03Q MEET DATE IN?' '��ITGEM #= LYI C E rAIZ DOWNTOWN SAN LUIS OBISPO �o 11M.MR_ C�' Cno ❑ Fug aiW BUSINESS IMPROVEMENT ASSOCIATION � ro��T ❑ FW DR Lff am Iuom. ❑ POUCECri ❑ MCMT•TFAM ❑ RSCDIX TO: Mayor Ron Dunin ❑ CRFADHU ❑ UILDIR. Council Member Peg Pinard 12er•F_-L�7" Council Member Penny Rappa `/ c Council Member Jerry Reiss /:ooPH .- Council Member Bill Roalman j 4,01 FROM: BIA Board of Directors 4N `i -4 DATE: December 3 , 1991 RE: Seismic Retrofit Ordinance The Business Improvement Association has been actively involved with the Seismic Task Force committee in evaluating the URM Ordinance. In addition, the BIA appointed a sub-committee to analyze the issues concerning seismic retrofit and it's impact on downtown. '-)th the BIA sub committee and the Seismic Task Force agreed that the :iginal mandatory retrofit time frame was financially not feasible given the present business situation. Several members of the BIA reported that the property owners of their buildings would choose to demolish or walk away from the property if a mandatory deadline was enforced. The concern for a mandatory time frame also lies in the economic impact of retrofitting 95 buildings in the downtown core. The neighboring businesses would realize a financial hardship that would make daily operation questionable. The BIA supports the conclusion obtained by the City staff and Seismic Retrofit Task Force to enact the retrofit requirements with the remodel of the structure or change of occupancy to a larger, more hazardous level. while the financial implications are still of grave concern to the BIA, the staff efforts to include the financial proposal as part of the ordinance- are greatly appreciated. The development fee credits toward the initial analysis costs should not be overlooked. Every effort should be made to protect public safety should an earthquake occur, however, it is important to note the conclusions drawn by Mr. William Dexter in his article "Risk Assessment in Seismic "ilicy Making". The BIA Board appreciates the opportunity to work with the City staff on addressing this issue which we feel to be tantamount in importance. P.O. Box 1402, Son Luis Obispo, CA 93406 (805) 541 -0286 Risk Assessment in Seistonic Po/icy Making An Overview William F. Dexter RECEIVED !_LCC 1991 CITY CLERK SAN 11mm a Oi 1 J Risk Assessment in Seismic Po/icy Making An GLervicpw William F. Dexter In light of the massive destruction inflicted by earthquakes in California,The State legislature in Sacramento has mandated that local governments enact a mitigation program aimed at reducing the risk of mortality associated with un-reinforced masonry buildings(URM'S). Since the State law allows for mitigation programs to be left at the discretion of the local agencies,our San Luis Obispo City Council is now considering the measures which would responsibly address the intent of this law. The policy makers, understandably,walk the fine line that separates over-reaction and rational recognition of the actual risks posed by this hazard. The public's concern for protection from this unpredictable,catastrophic event will weigh considerably toward the preparation of this ordinance. Quite often,the public demand for protection against dreaded risks disregards the quantitative danger to human life as a result of the disastrous nature of the event. Earthquakes, in which millions of dollars of property damage occur in the span of several seconds, are perfect examples of this vein of thought. Severity of risk is not always the primary criteria that society uses to decide which hazards it will abate or mitigate. Public opinion,public perception,and existing legislative mandates arejust some of the elements that are factored into the decision making process. Perceptions are a strong and compelling factor in determining what risks society will address. Popular opinion shows that the public considers earthquake damage to pose far greater risks than some very high risk activities that we willingly participate in everyday(e.g.,smoking,drinking,driving). In addition, legislation from the State requires that local governments take action to mitigate seismic hazards resulting from URM buildings,simply because they represent one of the sources of loss of life during an earthquake, giving little or no weight to identifying the actual risks posed by these structures. In addition to making quantitative assessments of the risk to human life,establishing priorities to take actions on those risks that pose the more serious threat is a crucial aspect of risk assessment Our society and community is limited by funds,people and time to act on reducing every risk that comes to our attention. Given the fact that our community does not have unlimited resources to address every hazard that has been identified,it is imperative that we,as a community,through the judgement of our city council,develop a consistent,scientific methodology to identify and evaluate risk. We must promote an inquiry that will assist us in pursuing a rational plan to address the worse risks first Page 1 Risk Comparisons and Perceptions In the process of mitigating or abating any risk it is always helpful if not considerably instructive to conduct some comparisons and contrasts. We live our lives taking risks and avoiding others. As we awake every morning,the process of turning on the light is a life threatening event. We are probably not aware that every year 200 Americans die from electrocution in their homes. This represents a risk of death of about 10-6 per year or in "Lotto" terms,one in a million Americans will die from faulty wiring in their own home. To reduce this risk we can replace the wiring, but we will not eliminate the risk entirely. As we walk downstairs for our first cup of coffee,we rarely consider that every year 7000 people die in falls in their homes. Virtually every thing we do during the course of a normal day has a risk of mortality associated with it. These first examples represent extremely small risks. But as soon as we start up our car,to make the daily journey to work,we engage in the highest risk activity in the world; over 50,000 American men,women and children die in automobile accidents every year. As members of a technically advanced society,we are outraged, however, by the catastrophic risks posed by air pollution, nuclear energy and,closer to home, un-reinforced masonry buildings. We demand from our government representatives, legislation to protect us, that we should not have to suffer exposure to these catastrophic, uncontrollable, inequitable life threatening hazards; yet we rarely mention concern for the ongoing threats to our daily lives that pose far greater dangers. Below is a brief comparison of some of the risks that we face every day, nationally,as compiled by Wilson and Crouch of Harvard University(8); earthquake data is taken from the Waverly J. Person report(9). ANNUAL RISK OF FATALITY PER MILLION POPULATION Cigarette Smoking All Cancers Mountaineering Auto Accidents Air Pollution Represents 1/4th fatality per million Home Accidents All Earthquakes 1i i7 i i 0 500 1000 1500 2000 25DO 3000 3500 Page 2 One thing that is very clear about the public's perception of comparative risks, is that we do not always worry about the risk averaged over time quite as dramatically as we do the risks that are sharply peaked in time. Wildaysky(7)commented as follows on this state of affairs: How extraordinary! The richest, longest lived, best protected, most resourceful civilization,with the highest degree of insight into its own technology,is on its way to becoming the most frightened Is it our environment or ourselves that have changed?Would people like us have had this sort of concern in the past? ...Today there are risks from numerous small dams far exceeding those from nuclear reactors. Why is the one feared and not the other? Is it just that we are used to the old or are some of us looking differently at essentially the same sorts of experiences? Extensive research has been done in an attempt to answer such questions by examining the opinions people express when they are asked to evaluate hazardous activities and events. This research has attempted to develop techniques for assessing the complex and subtle opinions that people have about risk. Researchers have sought to discover what is meant when the public says that something is "too risky" (or "not risky")and what factors are intrinsic in those perceptions. The basic assumption underlying this research is that regulators of public health and safety need to understand the ways in which people think about and respond to risk.(5) The overwhelming conclusions reached by the analysts show that the greater the sense of"dread" or the more uncontrollable,catastrophic, involuntary aspects characterizing the event,the higher was the demand for legislation to eliminate the risks. This end of the spectrum included such events as nuclear weapons'fall-out, radioactive waste, pesticides,asbestos insulation, railroad collisions and the sort. The other end of the spectrum of hazardous events which did not receive an outcry from the public represented the "known" risks or those that were old, individual, controllable,not catastrophic. These risks included deaths from fireworks, bicycles, electric appliances,home swimming pools,trampolines,chainsaws and skateboards. The selection of what was deemed "important" risks and the disregard of "unimportant" risks had no bearing,whatsoever,on the actual threat to human life. The more "terrible"the event,the more regulation was requested. This is extremely evident in our present search for legislative language in the preparation of the seismic retrofitting ordinance before our city council. In spite of the documented hazards associated with the actions listed in the above chart,the "dread" associated with them cannot compare with the horror of recalling the tragedy of the Whittier Narrows Earthquake of 1987 in the Los Angeles area More recently, we recall the 6.9 magnitude Loma Prieta earthquake that shook eight Bay Area counties as we were settling in to watch the 1989 World Series. We collectively perceive seismic events as fearful,uncontrollable catastrophes that snuff out lives, inequitably and without notice. These elements which describe our Page 3 perception of earthquakes represent a high order of"dread". The surprising data regarding loss of life associated with earthquakes,however, is far from what we expect (9) Specifically,the October 1, 1987 Whittier shock,which registered 5.9 on the Richter scale and resulted in damage to more than 10,400 buildings, unexpectedly claimed only 8 lives. Three days later,an after shock of 5.6 magnitude claimed additional structural damage and accounted for one more life;a victim of a heart attack. (9) In the continental United States and Alaska,earthquakes in 1987 claimed 11 American lives. In the entire world 1,098 lives were lost to earthquakes as reported in the U.S. Geological Survey publication "Significant Earthquakes of the World, 1987",by Waverly J. Person. By comparison,this represents a global risk to life of about 1 in 4 million(2S x 10-7). In our country alone, compared to our first example of risk,we. are twenty times more likely to suffer the loss of our life by electrocution from turning on an appliance or light than we are from being in an earthquake. If we were to extrapolate some risk figures for the city of San Luis Obispo,we would conclude that there is a risk of the loss of one human life in our town from home electrocution every 22 years. And similarly, based on global statistics,there is the risk in SLO from earthquakes of one life lost every 89 years. Additionally, if we were to factor in only the risk of fatality from damage to an un-reinforced masonry building,we would expect to see one life lost in SLO every 1,777 years. Nonetheless, the images of devastation and property damage,far out-shadow our actual perception of risk to human safety and life. Obviously,the need for incorporation of this statistical data in the drafting of the "Seismic Ordinance" is the grave responsibility of our policy makers. Cost of Reducing o Risk Another interesting and instructive way of evaluating risks is by comparing the amount people have paid in the past to reduce them. Researchers have shown that the amounts spent vary by a factor of more than a million. It would be possible for an American to save lives in Indonesia by aiding an immunization program at$100 per life saved. Our society is willing to spend more on environmental protection to prevent cancer(over$1 million per life)than on cures(about$50,000 per life). What this data suggests, is that the government could save more lives by directing its vast expenditures into the hospitals and funding the life saving medical procedures facing every"terminal" patient than by expending public funds to reduce certain elements in the atmosphere. This ratio is very much in accord with the maxim "an ounce of protection is better than a pound of cure". (1) (8) Economists and others argue that efficiency depends on adjusting society until the amounts spent to save lives in different situations are equalized. It seems,though_that socidy does not work that way. Quite evidently, we attach greater meaning to the dramatic loss of life than we do the mundane. Invariably,we will vote to spend Page 4 millions to protect against the dramatic mortalities,while funds allocated to protecting against the death from a fall in our homes,for example, is virtually ignored by comparison. Even, though people are aware of the order of magnitude of these differences,they support the cost of protection from "dread" versus "known". Nonetheless,providing this information to policy-makers is essential for an informed decision. Standing before our City Council, is the decision as to the nature of the structural analysis that will be required for city building officials to adequately assess the relative weakness of each URM in San Luis Obispo. There is a considerably wide range of engineering reports that could be required by the proposed ordinance. The scope could run from an extremely detailed quantitative analysis which tested the materials and recommended restructuring or at the other end of the scale, it could be an analysis which qualitatively assessed the structural liabilities of each building in question and made probability recommendations regarding its retrofitting. Naturally the cost impact of these two methods of analysis is dramatically divergent If we were to calculate the cost,for example,of conducting a quantitative engineering analysis of every URM identified by the City of SLO,we could arrive at a cost per life at risk in SLD. Let us consider the following conservative assumptions. 1. There are 100 buildings subject to a detailed engineering report 2. The average cost of a structural analysis is$5,000 per building 3. The probability of mortality from earthquakes is 1 per million(1 x 10.6) 4. The population of San Luis Obispo is 45,000 5. The entire population of the city is at equal risk To calculate,we multiply the number of buildings times the cost of each report divided by the fractional probability of mortality to arrive at the cost per life at risk. The formula looks like this. 100 buildings x$5,000_45,000 x(1 x 106) _$11, 111, 111 cost per life at risk This engineering requirement,if enacted in the form of a city ordinance,will represent a cost per life 11 times greater than that assumed by the automobile industry and eventually the consumer to protect life with air bags in cars(estimated at$1,000,000 per life saved)(11). We are proposing through this ordinance to spend a lot of money to protect against a risk of high consequence but very low probability. Most important,these expenditures will not make any building safer. The other scenario which addresses the need to evaluate the areas of critical threat to life from our URM's is to propose that each building owner conduct a qualitative engineering analysis similar to the work done on the Carrillo Hotel in Santa Barbara (2). Using the same assumptions as before,except that the average cost of the engineering is$600 per report Page 5 100 buildings x$600:45,000 x(1 x 106) _$1,333,333 cost per life at risk In spite of the relatively low cost of each report,when it is combined with the extremely low probability of harm,the cost per life at risk is still considerably high but dramatically less than our first scenario. Throughout this analysis,it is critical to acknowledge that the money spent in both scenarios,above,does not reduce the risk to human life from earthquakes. It is merely money spent to learn more about the buildings which are believed to be the source of mortality during severe seismic activity. The information gained, however,may be important to decision makers if it is used to priortize risks. Regardless, it is a cost which is affordable by the individual building owners to,first of all,comply with the State legislation aimed at mitigating the threat to loss of life,and secondly, it adequately provides sufficient information for the city building officials to evaluate and prioritize the structures most needing attention. A further aspect of protection of the public welfare might include some closer analysis of the buildings deemed to pose the greatest threat after review of the engineers' qualitative appraisal. Whe are We Protecting ? Obviously,the conclusions drawn from this study address the concern for protection to human life. It is the purpose of the State mandate to enact local ordinances to "mitigate the loss of human life"from the collapse of URM's, not to structurally reinforce them. Damage to businesses,buildings,freeways and homes are,obviously, going to be the consequence of any major seismic activity in our area, regardless of what structural changes we apply to our older buildings. Reviewing the data from the Loma Prieta earthquake in 1959, however,we can see that from all the damage incurred by thousands of buildings in San Francisco,the lives lost from URM's represented a very small fraction of the total casualties. Ten deaths were attributed to URM's when bricks fell off the buildings, no URM's collapsed(12). More than 20 times that number were killed in the collapse of freeways. In light of the limited damage to URM's in San Francisco, it might be concluded that we were spending millions of dollars to reduce the damage to the structures but not to significantly protect from the loss of life. The responsibility for protection of the public welfare rests with the policy makers at the local level. The city council and its supporting divisions and staff members must use a scientific basis for risk assessment,in order to set priorities, tailor regulations and make decisions at particular sites. The tendency to include the emotional perception of harm,as perceived by the public,to protect against this hazard is always present to some degree. We know that the public often lacks certain information about hazards. However,their basic conceptualization of risk is much richer than that of the experts and reflects legitimate concerns that are typically omitted from expert risk assessments. The risk analysis should not attempt to overstate or understate threats, but rather to give a best ectimate�ran=of uncertainty. Our policy makers(City Council)can choose the proper amount of conservatism in setting the r Page 6 standard. Each side,policy maker and public,has something valid to contribute. Each side must respect the insights and intelligence of the other. The city can do much to improve public understanding of the meaning of risk assessment and risk management. In so doing,they can find solutions to the problems of mitigating the risks consistent with the parameters of finite, private funds and with full regard to our experience of the historical threat to life posed by this one event. REFERENCES AND NOTES 1. B.L. Cohen,Health Phys,38,33(1980) 2. Englekirk,Hart&Sabol,Seismic Study for Carrillo Hotel,(1991) 3. Lester B. Lave,Science,236,294(1987) 4. Don Ritter,Risk Analysis,Vol.8,No.2, 169(1988) 5. Paul Slovic,Science,236,281-2(1987) 6. C.Starr,Science, 165, 1232(1969) 7. A.Wildayskv,Am Sci 67,32(1979) 8. Richard Wilson and E.A.C. Crouch,Science,236,270(1987) 9. California Department of Insurance,California Fmthquake Zoning and Probable Maxbnum Loss Evaluation Program, 11-16(1988) 10. Randall M.Ward,Department of Conservation,Seismic Hazard Information Needs of the Insurance Industry,Local Government,and Property Owners in California,An Analysis(1990) 11. Department of Health, Data Sumumary of the Health Data&Statistics Branch of the Health and Welfare Agency, State of California(1988) 12. Eric Brazil,San Francisco F.xmniner and Chronicle, 10-13-91,A-13 William Dexter is a local Construction Systems Consultant who has served in the leadership of community business associations, the PTA and Scouting. He has been a resident of San Luis Obispo for 20 years. Page 7 r . • i 1 I I Seismic Study and Recommendat/ons for Carrillo Hotel Santa Barbara, California Prepared for Urban Group Santa Barbara, California August 1991 REC1� C 3 19�� CITY CLERK SAN L BIS of CA EHS nglekirk, Hart & Sabol Consulting Engineers, Inc. THE CARRILLO HOTEL Santa Barbara, California 1.0 GENERAL This report presents the seismic study performed on the Carillo Hotel, a reinforced concrete structure with unreinforced masonry infill located at Chapala and Carrillo Streets in.Santa Barbara, California. The building has been classified as a high risk, potentially hazardous building pursuant to Santa Barbara Municipal Code Section 22.18. This ordinance is intended to mitigate the potential hazard of the existing unreinforced masonry buildings which are typically buildings with bearing walls or lateral force resisting systems consisting of unreinforced masonry. In structures where unreinforced masonry is used only as infill panels bordered by the columns and beams, the unreinforced masonry may not play the primary role in resisting vertical or horizontal forces. However, these infill panels can be fractured by inclined cracks due to forces in their plane. Since the cracking pattern is not controlled, it may adversely affect the behavior of the concrete frame. Also, the lateral forces ENGLEKIRK,HART AND SABOL,INC. Page-1- perpendicular to their plane can produce an out-of-plane failure of the panels. Consequently, the presence of these infill panels walls may pose a threat to life safety. For this reason, the Santa Barbara Ordinance extends its application beyond strictly bearing wall URM structures to include "an infill wall that will experience lateral forces as a result of the inability of other lateral load resisting framing elements to resist the lateral forces. The purpose of this report is to present our opinion concerning the expected performance of unreinforced masonry infill when the structure is subjected to severe earthquake ground motion of the type anticipated in Santa Barbara County. A review of the dynamic response of the concrete frame structure of the Carrillo Hotel is essential to understand the performance of the unreinforced masonry infill. From this perspective, the expected response and performance of the building to the anticipated ground motion also are investigated. The Ordinance does not specify lateral loads to be used in the analysis of the frame building inasmuch as it was drafted to address shear wall structures. Section 3.0 addresses our approach to develop a loading criterion that is consistent with the life-safety intent of the Ordinance but can more realistically reflect the actual earthquake forces that the building will experience. This report is organized as follows: 1. Section 2.0: Existing structural systems in the building; 2. Section 3.0: Seismic analysis and design criteria utilized; 3. Section 4.0: Review and recommendations regarding the masonry infill; 4. Section 5.0: Anticipated seismic performance of the frame structure; and ENGLEKIRK,HART AND SABOL,INC. Page -2- 2.0 EXISTING STRUCTURAL SYSTEMS 2.1 Physical Description The Carrillo Hotel is a 5-story plus basement reinforced concrete frame building with unreinforced masonry infill. The original structure was constructed from drawings prepared by Marston & Van Pelt, Architects and Paul E. Jeffers, structural Engineers, dated 1923. Strengthening work at the perimeter of the building was designed in 1952 by D.F.Shugart, Structural Engineer following the 1952 Santa Barbara Earthquake. Information related to the relevant dates is listed in the Building Summary, Table 2.1. The structure of the Carrillo Hotel consists of five stories with a Basement. The Ibuilding has an U-shape in plan with a North-South dimension of 115 feet and an East- West dimension of 119 feet. The legs of the U are 43 and respectively 48 feet wide and are North-South oriented. IThe floor-to-floor height between the Basement and First Floor is 12 feet The Ifloor-to-floor height of the First Level is 18 feet and 6 inches. The Second, Third and Fourth Floors are 10 feet high while the Fifth Floor is 9 feet high. The total height of the building is approximately 70 feet measured from the Basement. I IENGLEKIRK,HART AND SABOL,INC. I Page -3- 1 TABLE 2.1 BUILDING SUMMARY ARCHITECT ' Marston & Van Pelt ENGINEER: Paul E. Jeffers (Original Building) D. F. Shugart (Strengthening) DATE DRAWINGS: February 1923 (Original,Building) December 9, 1952 (Strengthening) GEOTECHNICAL REPORT: None available NUMBER OF STORIES: Basement and five stories STORY HEIGHTS: Basement 12'-0" First Floor 18'-6" Second to Fourth Floor 10'-0" Fifth Floor 9'-0" 2.2 Foundations Reinforced concrete bell-caissons support column loads. Continuous footings of reinforced concrete support reinforced concrete basement walls. Reinforced concrete basement retaining walls span vertically. The retaining walls themselves have continuous footings along their length. No results from a geotechnical investigation of the site were available. Based on the foundation dimensions and the column loads specified in the Column Schedule of the original design, the allowable bearing capacity is assumed to be approximately 8,000 pounds per square foot. Allowable bearing pressures for use in building design contain ENGLEKIRK,HART AND SABOL,INC. Page-4- animplicit settlement criterion that is inappropriate for establishing the ultimate bearing strength of the soil. Allowances for increased ultimate bearing strengths have been used in the analysis. 2.3 Vertical Load Carrying System All gravity loads from the structure (dead loads) and the occupant and furnishings (live loads) are carried by a system of reinforced concrete slabs joists, beams and girders supported by reinforced concrete columns. The floor slab thickness varies between 24 and 4 in. The typical joist is 4x104 in. and is located at two feet on center. Beam size vary with the location in the building. The typical girder is 12x214 in. The column dimensions vary with respect to their location in the building from 12x12 in. to 23x23 in. The longitudinal reinforcement in the columns varies with height. Confinement in most columns consists of a 4 in. diameter spiral with a pitch that varies from 2 to 3 in.ches. Confinement in the remaining columns consists of 3/16 in diameter ties located at 9 inches on center. 2.4 Seismic Resisting System The structure employs the same lateral force resisting system in both directions. The lateral resistance against earthquake forces is provided by the stiffness of the reinforced concrete non-ductile frames. These frames are not detailed to sustain cyclic horizontal loads. The transverse reinforcement near the girders' ends, consisting typically ENGLEKIRK,HART AND SABOL,INC. Page-6- of in. diameter stirrups located at 6 in. on center does not provide the same level of confinement that one would expect to see in flexural elements that must develop plastic hinges. Similarly, the-bottom reinforcement in the girders is discontinued at column lines. This detailing is not intended for transferring moments created by load reversals found in earthquake ground motion. Consequently, the connections are capable of developing only a nominal amount of rotational restraint. The confinement in the columns is also less than one would expect to see in modern designs, although the spiral ties will provide better levels of confinement than rectangular hoops common in buildings of this age. The concrete slab functions as a horizontal load distributing diaphragm. The lateral loads from the roof and floor diaphragms to the frames is accomplished by dowel action and shear friction. The strengthening of the structure after the 1952 Santa Barbara earthquake consists of additional reinforced concrete columns, enlarging of the existing columns, additional deep arched beams, and two short shear walls. All this work was limited to the First Story, along the perimeter of the building. The typical new column is 12x36 in. The vertical reinforcement consists of six #5 bars. The horizontal reinforcement consists of two #3 open stirrups (U shaped) completed with two #5 bars, all located at 18 in. on center. The shear walls are 12 in. thick and are reinforced with a double curtain of #5 bars located at 18 in. on center each way. The additional beams are approximatively 40 in. deep. Their reinforcement consisting of the typical wall reinforcement plus two #5 bars along the line of the arch. ENGLEKIRK,HART AND SABOL,INC. Page -6- i 3.0 SEISMIC ANALYSIS AND DESIGN CRITERIA 3.1 General General building codes are intended for use in the design of new buildings rather than in the analysis of existing buildings. The distinction between design and analysis is particularly acute in the area of evaluating seismic resistance. Significant advances have been made over the past 30 years in understanding the structural behavior of buildings subjected to earthquake loads. This knowledge and the knowledge gained in observing building performance during earthquakes has been incorporated into the building code. Higher yield level forces are now required in current building codes and, more significantly, levels of component ductility are now required. Detailed prescriptive requirements are used to insure adequate levels of ductility in the structure. These prescriptive requirements have been shown to permit structural materials to perform satisfactorily during earthquakes. Buildings constructed prior to the adoption of current building codes will be deficient with respect to many of the provisions contained therein. In most cases, older buildings were designed to resist a yield criterion less than that specified in current design standards and, perhaps more importantly,they will not possess the construction detailing ENGLEKIRK,HART AND SABOWNC. Page-7- required by the prescriptive provisions of the code. Therefore, evaluated according to the requirements of the current building code, older buildings will be judged to be seismically deficient. The analysis criteria employed in this seismic evaluation uses earthquake loads that are specific to this site and that do not incorporate the modifiers used in building codes to account for assumed building behavior. Therefore, instead of relying on the building code provisions, these existing buildings must be reviewed with respect to the actual characteristics of the structural system. Section 4.0 of this Report outlines the anticipated performance identified with respect to the structural system used in these structures. I The Santa Barbara Ordinance, while only intended for the evaluation and rehabilitation of existing unreinforced masonry buildings, also makes implicit assumptions regarding the assumed behavior of the structural system response to eartquake ground motion. It permits the building to be analyzed for a load level that is approximately 30% less than that used in new shear wall building design. This lowered force level implicitly accepts the proposition that greater building damage is acceptable in the URM buildings compared with new buildings because of the tremendous economic penalty attached to using values equal to those in current buidling codes. The Ordinance also assumes that the buildings being analyzed are shear wall structures instead of the frame structure actually being evaluated in this study. This distinction is significant because the Ordinance would require the use of earthquake loads significantly higher than typically used in the analysis of framed structures. This assumption might be justified on the Page-8- ENGLEKIRK,HART AND SABOL,INC. grounds that these older, non-ductile concrete frames do not possess the detailing assumed when the lower load levels are used in current design practice. Nevertheless, a careful review-of the earthquake loads is required to ensure that reasonable loads are utilized in the analysis that are not punitive compared to the lower loads used in rehabilitating the URM buildings. We have accomplished this by using realistic earthquake loads while accepting the potential for relatively greater building damage. The earthquake loading levels were developed in a manner consistent with the intent of the Ordinance, which is the mitigation of life safety risks due to unreliable building materials subjected to earthquake ground motion. The accepted earthquake criterion for life safety applied to buildings constructed today requires that the building not collapse if subjected to accelerations and displacements that might reasonably be anticipated during the fife of the structure. This loading is associated with a 90 percent chance of not being exceeded during the 50-year design fife of the building. The assumed design life of 50 years is consistent with that used in new construction. Since this criterion addresses the life safety concern, we have used in our analysis the earthquake loads and deformations consistent with the 90% level of non-exceedance in 50 years. It should be understood that a building designed or rehabilitated to this life safety criteria may sustain major and possibly irreparable structural damage. ENGLEKIRK,HART AND SABOWNC. Page -9- 3.2 Earthquake Loading We have used response spectra from our files for the general Santa Barbara area to obtain the earthquake loading. The earthquake ground motions at the site were estimated using a probabilistic seismic hazard evaluation procedure. The elements of the probabilistic analysis are the following: 1. Defining the location and geometry of earthquake sources relative to the site. 2. Estimating the recurrence of earthquakes of various magnitudes, up to the maximum magnitude, on each source. 3. Selecting an attenuation relationship relating the variation of the earthquake ground motion parameter with distance and magnitude. A probabilistic seismic hazard evaluation at the site due to a particular source involves the appropriate combination of the following three probability functions: 1. The recurrence rate is used to calculate the probability that an earthquake of a particular magnitude will occur on the source during a specified time interval. This probability function is usually expressed in terms of the mean number of earthquakes, per year, with a given magnitude on this source. 2. The probability that the rupture surface is at a specified distance from the site assessed by considering both fault geometry and the rupture length (or area) magnitude relation. 3. The probability that the ground motions from an earthquake of a certain magnitude occurring at a certain distance will exceed a specified level at the site is based on the selected attenuation relationship. ENGLEKIRK,HART AND SABOWNC. Page-10- By combining the three probability functions for each source, the annual probability of exceeding a specified level of ground motion at the site is computed. If there are N sources, then the.above process is repeated for each source, and the contributions are added to obtain the total seismic hazard at the site. A relationship between ground motion level and probability of exceedance is obtained by repeating the computations for several levels of ground motion. The ground motion level corresponding to a specified probability of exceedance over a specified time period is then obtained from the relationship. Figure 3.1 presents the response spectra used in the analysis. Analysis of the existing structure is based on the spectral loads corresponding to the natural periods of vibration. Damping values of 5% for elastic response and 10%for inelastic response are assumed in our analysis. 3.3 Approach used In the analysis The intent of this study is to identify the critical structural systems or components which may affect the structural performance in the event of severe seismic activity. Life safety considerations will, in general, result in the acceptance of a number of excursions beyond the elastic limit for some elements in the structure. A measure of the amount of plastic deformation that a structure will have to sustain during a certain strong motion is the ratio between the maximum deformation and the deformation corresponding to the first yield in the structure. This ratio is called "ductility demand". The use of higher ductility Page-11- ENGLEKIRK,HART AND SABOL,INC. Acceleration (g) 1.2 I 1 I 0.8 - 0.6 - 0.4 .80.60.4 0.2 0 0 1 2 3 4 5 6 7 8 Period (seconds) I HOTEL CARRILLO I ENGLEKIRK, HART. SANTA BARBARA _ & SABOL I rEnomere k" DESIGN RESPONSE SPECTRUM WITH 10% PROBABILITY OF _ �xr =�nntirc IKI cn WCADC FIGURE 3.1 demands assumes that there will be some, and perhaps significant, damage to the buildings themselves but that they will not collapse. If we .replace the maximum deformation reached during the motion by the maximum deformatin that the structure may undergo without collapse, we obtain the available system ductility. The system ductility is a measure of building toughness and expresses the ability of a building to sustain significant structural deformations without collapse. We used our earthquake loading to estimate the ductility demand on the structure and our knowledge of building systems to estimate the available system ductility. ■ µ` ENGLEKIRK,HART AND SABOWNC. Page -12- 4.0 MASONRY INFILL 4.1 Anticipated Seismic Performance A review of the unreinforced masonry infill at the exterior frames has been performed in order to identify the potential for instability during the anticipated earthquake. During a strong earthquake, the unreinforced masonry infill is subjected to in-plane and out-of-plane forces. We discuss in Section 5.0 the effect of in-plane forces for the masonry infill as well as the impact of the infill behavior on the concrete frame performance. This section discusses the problems associated with the out-of-plane loading of the masonry infill and how the Ordinance (UCBC) criteria affects the building. The Uniform Code for Building Conservation contains a set of requirements for h/t ratios. The allowable h/t ratios are prescribed as a function of the location in the building (first story, intermediate story, or top story). The prescribed values are intended for buildings where the unreinforced masonry walls support the vertical loads and resisting the lateral forces. For this reason, the stability of walls located at lower levels in the structure are helped by the larger overburden. The UCBC limitations are presented in Table 4.1 together with the resulting allowable infill thickness for each story of the Carrillo Hotel. ENGLEKIRK,HART AND SABOL,INC. Page-13. Table 4.1 Minimum Thickness of Uneinforced Masonry Infill Uniform Code for Building Conservation Height Allowable Allowable He Story (ft) height to thickness thickness ratio (in) 5 9 9. 12 4 10 13 9 3 10 13 9 i 2 10 13 9 1 18.5 13 17 Figure 4.1 presents the thickness of the infill at different locations in the building and indicates the walls that do not meet the UCBC requirements. According to the results in the last column of Table 4.1, only the 10 in. thick infill at the Second Floor and the 12 in. thick infill at the Third and Fourth Floor are acceptable. There are several factors that make comparisons difficult between the h/t ratios in the UCBC for bearing walls with what might be acceptable for infill panels: 1. The infill panels do not benefit from overburden. 2. The degree of fixity of the upper edge of the infill panel depends on the how tightly the masonry and mortar were wedged in when constructed. 3. The frame structure is more flexible than the structure consisting of masonry bearing walls and this is reflected in the type of motion to which the infill panels are subjected. Page -14 ENGLEKIRK,HART AND SABOL,INC. 1 I" Olt, 7��Z:7 J- FIRST FLOOR FOURTH FLOOR I,--1 i U.J.LJ I � ........ IM I SECOND FLOOR FIFTH FLOOR 07, rr-El _ _ LEGEND 8" INFILL � II I . w w m . 9" INFILL LJ 10" INFILL o•��•�•��• 12" INFILL I NOTE: DASHED LINES INDICATE THAT THE THICKNESS OF INFILL PANELS IS BELOW THE ALLOWABLE THIRD FLOOR THICKNESS ACCORDING TO UCBC HOTEL CARRILLO Engleklrk, Hart SANTA BARBARA & Sabot &v l°ee`srs°Inc EnUNREINFORCED MASONRY pinse INFILL THICKNESS AT FIGURE 4.1 DIFFFRFNT FI nnR.q If Item 3 tends to favor the stability of the infill panels with respect to URM bearing walls, it is expected that Items 2 and 3 will have a negative effect. For cost-benefit reasons, the UCBC earthquake loads are conventionally set at lower levels compared to the real motions. i 4.2 Recommended Rehabilitation of the Masonry Infill According to recommendations in Section 4.1, unri3inforced masonry panels at selected locations have to be secured against out-of-plane instability. To accomplish this, the flexural (out-of-plane) strength of the URM infill must be substantially improved. One reason for poor out-of plane flexural capacity of the infill is a lack of tensile capacity. An efficient method of providing this tensile capacity is by using ferrocement, a reinforced Portland cement material consisting of high strength mortar (5000 to 8000 psi compressive strength) and a wire mesh [2]. The wire mesh provides the tensile capacity while the mortar matrix transfers the stress from masonry to the wire mesh, through anchors in the masonry. This, in effect, creates a composite element. The ferrocement coating can also improve the shear strength of the panel which can be used to improve the performance of the frame structure. The ferrocement coating will be applied to the inside face of the masonry. This approach will permit selective applications of the coating (i.e. room-by-room applications) that should limit disruption of building operations. Another advantage of the ferrocement is that it is relatively thin (approximately 1 in. or so) and can be applied without significant alterations to the existing window casings, outlets, etc. ' . ENGLEKIRK,HART AND SABOL,INC. Page -15- Figure 4.2 illustrates a typical application of the ferrocement to the inside face with the.dowels to tie the outer wythes ofmasonry into the ferrocement. . Another option is to.apply the ferrocement to the exterior of the structure, and, since it has a finished consistency similar to the existing plaster finish, impacts to the exterior elevations should be limited. An advantage .of this approach is that the competent material (the ferrocement) is on the exterior of the. building where it is more effective in preventing falling hazards on pedestrians and cars below. Another advantage is that the work can be done on the exterior, thereby limiting disruption to building operation. Disadvantages of this approach are that the entire exterior must be treated, scaffolding would be required for installation, and it cannot be used on the side abutting the adjacent building. ■ ENGLEKIRK,HART AND SABOL,INC. Page-is- a WIN�oM/ D � r•. • 4--t�`h!i}IOR 61M1{.�P- TO DaLow OH IT FE "JaMF44T F<RRo c,smaN T wlNoow I I shy UeTe ' \\� I6o GA. FEAT 44%- win , WIRE MESH IINQ2611.1, ANCHoR rATP,II, 0 O j I . FF • k:' �WF.LDEG To . L; '/4- o 0j,. II • �z.9 G7EGT10H 7HRU INFILL, e�.sE �•NGHor2 N p"" D L Lo a HOTEL CARRILLO ENGLEKIRK, HART SANTA BARBARA & SABOL �a�sen a� STRENGTHENING OF FIGURE 4.2 THE MASONRY INFILL i l 5.0 ANTICIPATED STRUCTURAL PERFORMANCE The seismic force resisting systems of the Carrillo Hotel possess several characteristics that suggest undesirable and possibly life-threatening structural behavior I during a significant earthquake. This poor seismic behavior is expected because: 1. The lack of sufficient flexural strength in the elements (girders and columns) of the reinforced concrete frames; 2. The poor detailing of the reinforced concrete elements and connections. 3. The presence of the unreinforced masonry infill at the exterior frames. The lateral forces are resisted in this structure by the shear strength of the concrete frames. In frames, as opposed to walls, the reduced size of the element sections means that the flexural moments developed in the beams and columns govern the ultimate behavior. If there is enough flexural capacity in the beams and columns, the istructure can resist the imposed deflections. In older structures, the flexural capacity of the elements is exceeded by the demand. However, most seismic load resisting systems are designed to resist the additional load by the deformation of the structure in a relatively controlled manner. The structural degradation accompanying this deformation absorbs l the additional energy from the overload. The greater the level of additional deformation that can be withstood by the structure without collapse or sudden failure gives an I ENGLEKIRK,HART AND SABOL,INC. Page-17- I I indication of the "toughness" or "ductility" possessed by the building. Greater ductility, hence greater toughness, is a desirable characteristic in earthquake load resisting systems.. Our review of the seismic resisting systems of the Carrillo Hotel leads us to the i conclusion that the flexural capacity of the beams and columns is exceeded by the ■ demand. Further, the poor detailing of the concrete elements and joints limits the amount of available ductility. In this building, the connections between columns and beams are detailed with the intention of transferring moments due to vertical forces only and are only marginally effective in resisting lateral loads. Because the bottom reinforcement of beams lacks continuity and sufficient development length, the bending moment produced by the lateral forces can not be resisted by the beams and the beams will fail at the column connection. On the positive side, the threat of structural collapse is mitigated by the ability of spirally reinforced columns to resist the vertical loads under significant lateral displacements. The spirals efficiently provide needed confinement that permits the columns to continue to support vertical loads although the flexural capacity of the column has been exceeded by the demand. The relatively small size of the spiral (;") will limit the amount of confinement that can be provided, but the positive impact of the spiral reinforcing is not insignificant. The presence of the unreinforced masonry infill at the exterior frames can exacerbate the problems of the frame as it undergoes the cyclic behavior generated by ENGLEKIRK,HART AND SABOL,INC. Page-18- 1 the earthquake. The infill panels have large window openings reducing the in-plane thickness of the masonry (e.g. the in-plane width of masonry is greater above and below the window). As a resusit, the masonry will fail first at the window head and sill. Their failure will change the behavior of the frame: instead of accommodating the interstory displacement through the bending of beams and columns, the columns are constrained to accommodate the interstory displacement within the height of the opening because the "spandrels° serve to reduce the effective length of the column. In these "short columns," the imposed interstory displacement will develop much higher shear forces or bending moments that can be resisted by the columns [1]. The strengthening work performed after the Santa Barbara earthquake in 1952 mitigates one flaw of the initial structure: the "soft first story" generated by the height of the first floor, which is almost double that of the stories above. However, other than adding initial stiffness and some strength, this work does little to confer additional ductility to the structure. For example the column reinforcement in the added columns provides little confinement because of the wide spacing of the ties and the lack of cross ties and 135 degree hooks. In some respects, the added columns have less available ductility than the original columns. For reasons discussed in the previous paragraphs, it is our opinion that the lateral resisting systems of the Carrillo Hotel do not possess the strength and ductility required by the ground motion corresponding to the life safety criterion and, as a consequence, require seismic rehabilitation that should be pursued at a later date. The assumed performance of the building does not alter our opinion regarding the recommended strengthening of the unreinforced masonry for out-of plane loads. ENGLEKIRK,HART AND SABOL,INC. Page-19- 1 i REFERENCES ■ 1. Krause, G.L, Wight, J.K, - 'Strengthening of Reinforced Concrete Frame Structures", Proceedings of Fourth U.S. National Conference on Earthquake Engineering, Palm Springs, Ca, 1990. 1 ENGLEKIRK,HART AND SABOL,INC. Page-20- 1 1, ANG AGENDA DATE1�tTEY#0 San Luis Obispo Chamber of Commerce 1039 Chorro Street • San Luis Obispo, California 93401 (805) 543-1323 • FAX (805) 543-1255 David E. Garth, Executive Manager November 25, 1991 CoiEMTO. De oto Action ❑ FYI L" O El N.DIIt Honorable Mayor and Councilmembers cnr DR Q�r WNEY �D� City of San Luis Obispo �' � ' CLOWORIG ❑ PoUaCFL ❑ MGMT.TEAM ❑ RFC DIR P.O. Box 8100 NOV 2 6 1991 ❑ CxEADFU ❑ L-rn.Lg ut. San Luis Obispo, CA 93403-8100 12,r la' CITY CLERK Dear Mayor and Councilmembers: SAN LUIS OBISPO,CA As you may be aware, the Chamber of Commerce has been actively involved in the development of a seismic retrofit ordinance for unreinforced masonry buildings. Our involvement has been driven by our concern that a hastily drafted ordinance could have devastating effects on our downtown business district and cause the permanent loss of our community's character and heritage. We formed two seismic task forces. The first task force, Seismic Technical, was made of engineers and architects. Their task was to review the draft ordinance technical standards. The second task force, Seismic General, was made of building owners, tenants and leasing professionals. They had the task of making sure the ordinance was financially and economically feasible. After almost 30 meetings with and without City staff, we are pleased to report that your staff and our task force members have found mutually acceptable solutions to almost all of the difficult dilemmas posed by the URM problems. These positions were worked out because of a genuine feeling of flexibility and compromise on the part of both City staff and our task force members and board of directors. (Please see attached board of director's recommendations.) Our most important joint conclusion was that it was not in the City's best interest to pursue an aggressive mandated retrofit timetable without any idea as to how these retrofit will be paid for. Many building owners, unable to pay for the retrofit, would be likely to let their buildings revert to the lenders, abandon them, or let the city demolish their building. All of these scenarios would spell disaster for the community. On two points however, we could not reach agreement with staff. First, we believe strongly that change of occupancy of a building should trigger a retrofit only when that building changes to a more dangerous (intense) occupancy. Second, we feel that part of the cost of the structural analysis should be shared ACCREDITED C[MEM OF Comer C r.a VUr.Gf COVV[PCI 01 :+[ Pilf[151 F1[S . j City Council, Seismic Page 2 by.the City. If cash contributions are not available, a possible credit towards eventual building permits might be workable. Like you, we are very concerned about the threat to public safety in the event of a major earthquake. The solution to this threat, however, must reflect economic and social realities and not be a cure which is worse than the disease. For that reason, the delay and deliberation necessary to reach this point have been prudent. We very much appreciate the opportunity to participate in the process and hope that our input has been valuable. Sincerely, Dennis D. Law Chamber of Commerce President SAN LUIS OBISPO CHAMBER OF COMMERCE Board of Directors Position on Seismic Retrofitting of URM Buildings September 19, 1991 The following are recommended for near term action by the City Council- 1. Adopt technical standards (as outlined in technical portion of draft ordinance) immediately. Add language to make it clear that if a building owner voluntarily upgrades his or her building to these standards, the building will be deemed to be in compliance with any future seismic upgrade ordinance. 2. Require all buildings currently on the URM list to be structurally analyzed within 18 months of the adoption of ordinance. Such analysis should determine the extent of the seismic upgrade necessary and the cost of such upgrade. 3. Allocate City funds to participate in the funding of these structural analyses. The city through either grants, credits or other incentives should contribute approximately 50% of the cost of the analysis. 4. Require any remodeling of any URM building which exceeds 50% of the replacement cost of the building to include seismic upgrade to the new standards. The Task Force further recommends- 1. That the adoption of any mandatory upgrade ordinance be postponed 18 months wallow a fresh look to be taken at the possible options. Specifically, this 18 months would allow time to gather more information on the following subjects: • actual costs of upgrade (based on the structural analysis) • the recent creative seismic upgrade solutions of other California communities • possible incentives and financing packages available • availability of necessary seismic upgrade resources such as materials and labor. • possible economic harm to the community from upgrade construction • possible harm to the historic character of the community caused by seismic upgrading or demolition of historic buildings. 2. That it is essential that any future ordinance includes City sponsored financing, credits and incentives as part of the package.