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Home My WebLink About03/03/1992, C-13 - SEISMIC SAFETY CORRECTIONS TO CITY BUILDINGS MffT1NG DATE: I1�II city O f san LUIS OBISPO MN ch 3. 19 992 I E COUNCIL AGENDA RPORT FROM: David F. Romero, Public Works Director L4d' -t)rk_ w PREPARED BY: David Elliott, Administrative Analyst SUBJECT: Seismic Safety Corrections to City Ings CAO RECOMMENDATIONS: By motion: 1) Receive and file the summary reports submitted by Howard F. Stup & Associates on structural corrections 2) Approve deferring structural corrections to the attic and roof at City Hall 3) Approve transferring $200, 0.00 allocated for structural corrections at City Hall from the capital outlay fund control account to the general fund unappropriated balance 4) Appropriate $30, 500 in the buildings program operating budget to complete non-structural corrections DISCUSSION: Background A survey conducted by H.J. Degenkolb Associates in fall 1990 found that structural elements in several City buildings might not withstand a major earthquake because of possible deficien- cies. The survey also found many non-structural deficiencies like unanchored file cabinets and water heaters. Earthquake damage to buildings and equipment could threaten lives and prevent dispatch of emergency workers and equipment. Structural Corrections The Degenkolb survey identified potential structural weaknesses and recommended further engineering work to determine the extent of these weaknesses and the need for corrective measures. Following on this recommendation, the City Council approved the Seismic- Safety Corrections project in the 1991/93 Financial Plan (pages E-10 -and E-23) for structural corrections to City Hall and Fire Stations #2 and #3 . In October 1991 the Council awarded a structural engineering contract to Howard F. Stup & Associates. The agreement called for the engineer to perform five specific tasks: 1) Structural analysis to calculate the effect of assumed earthquake forces and the suitability of various streng- thening methods 2) Field investigation to verify structural conditions and identify building materials for independent testing C- 13 - � i�iH11bNIIVIIIIIIIIII�N ��lll MY Of San LJ1S OsispO Warms COUNCIL AGENDA REPORT Seismic Safety Corrections to City Buildings page 2 3) Construction documents preparation 4) Bid assistance to prepare any addenda needed to clarify construction contract documents 5) Construction administration to answer requests for informa- tion and assist in preparing contract change orders if necessary Summary of City Hall Findings. In letters dated December 2 , 1991 and January 30, 1992 (copies attached) , Project Engineer John Nelson presented his findings about City Hall. His structural analysis and field work confirmed four deficiencies tentatively identified in the Degenkolb survey: 1) eight basement-level columns are not strong enough 2) the interior masonry partitions on the main floor are not braced at the top where they extend. into the attic 3) the roof trusses are not strong enough and 4) the cementitious panels which form the roof sheathing are not positively attached to the roof framing; they are held in place by gravity only. Mr. Nelson prepared construction documents for strengthening the basement columns, and the construction contract went out for bids on February 8, 1992. The remaining work is complicated by high asbestos content in the cementitious panels. Trying to mechanically fasten these panels to the roof framing would be extremely difficult and expensive because of precautions to prevent release of asbestos fibers. Instead, Mr. Nelson has recommended removing the existing roof tiles, removing the cemen- titious panels (removal alone would not create an asbestos hazard) , replacing the panels with metal decking, installing plywood furring over the decking, and reinstalling the roof tiles. This procedure has four important advantages: 1) it would eliminate the last vestiges of asbestos in City Hall 2) it would eliminate the potential hazard of panels separating from the roof framing and falling through the ceiling 3) it would strengthen the roof system enough that the trusses would not need additional bracing and 4) it would simplify bracing the interior masonry partitions. The major disadvantage would be severe disruption of City Hall activities. Because of this disruption, staff recom- mends that this work be postponed until construction of the City Hall expansion project, when much of the roof would have to be removed anyway. Summary of Fire Station #2 Findings. In letters dated November 12, 1992 and January 30, 1992 (copies attached) , Mr. Nelson presented his findings on Fire Stations #2 and #3. Structural analysis confirmed the primary deficiency for Station #2 iden- tified in the Degenkolb report: lack of adequate bracing across the front of the building. A severe earthquake could collapse the apparatus room doors and prevent dispatch of firefighting C- 13•�l ��►b►i►►�IIIIIIIIIP° ��III city of San L"is OBISpo COUNCIL AGENOA REPORT Seismic Safety Corrections to City Buildings page 3 equipment. Field investigation confirmed another problem: the roof system is poorly anchored to the masonry walls. Mr. Nelson is now preparing construction documents to reinforce the concrete block wall at the front of the building, brace the openings in the apparatus room with a steel frame, and adequately secure the roof system to the walls. Securing the roof system will require removing the roof sheathing. Summary of Fire Station #3 Findings. At Station #3 the Degenkolb report also pointed out apparently inadequate bracing across the front and rear doors of the apparatus room which might lead to partial collapse in a major earthquake. (Unlike Station #2, Station #3 has a drive-through apparatus room. ) The Degenkolb report further suggested that shear-resisting steel frames across both openings would correct .the perceived problem. Contrary to this survey determination, Mr. Nelson's structural analysis and field investigation demonstrated that the building could theore- tically withstand a major earthquake. Nonetheless, because 1950s-vintage buildings have generally performed poorly in major earthquakes, Mr. Nelson suggested installing a simpler energy- absorbing steel frame for an extra margin of safety. Fire Chief Bob Neumann concurred and recommended this improvement. Mr. Nelson is now preparing construction documents for this work. Non-Structural Corrections The Degenkolb report listed many non-structural conditions which could lead to injuries and expensive equipment damage in a major earthquake. These conditions include: • unanchored file cabinets and shelves • unbraced mechanical equipment, ceiling grids, light fixtures and demountable partitions • unrestrained desktopequipment like computers, typewriters and cash registers At first, staff thought that the City's regular building main- tenance- workers could perform this work within the existing budget. But a heavy existing workload and a limited budget have allowed completion of only about one fifth of the work over 14 months. To finish this work up quickly, staff recommends extend- ing the contract of the building maintenance technician until June 30, 1992 and adding money to the buildings program budget for hardware to brace furniture and equipment and for special velcro material to restrain desktop equipment. ��►��►bN►IVIIIIIIIII I° 91�III MY Of San L"I S OBI SPO COUNCIL AGENDA REPORT Seismic Safety Corrections to City Buildings page 4 FISCAL IMPACT: Structural Corrections. The following amounts were budgeted in the 1991/93 Financial Plan for structural seismic safety correc- tions: $ 24, 000 City Hall basement $200, 000 City Hall roof and attic $ 60, 000 Fire Station #2 $ 55, 000 Fire Station #3 Mr. Nelson's cost estimate for the City Hall basement is $20, 000. Although he hasn't completed final estimates for the fire sta- tions, he thinks that higher costs for more work at Station #2 will be balanced by lower costs for less work at Station #3 . There should be about $200, 000 made available by postponing the City Hall roof and attic work. Non-Structural Corrections. Extending the building maintenance technician's contract would cost $19, 500. Purchasing required materials would cost $11, 000. These costs could be covered by deferring the structural corrections to the attic and roof at City Hall. The $200, 000 deferred could be returned to the general fund unappropriated balance from the capital outlay fund control account. The $30, 500 needed for non-structural correc- tions could then be appropriated to the building program operat- ing budget accounts. The net effect would be a $169,500 increase in the general fund unappropriated balance. attach: letters from Howard F. Stup & Associates dated 11/12/91, 12/2/911 1/30/92 , 1/30/92 and 1/31/92 HOWARD F. STUP & ASSOCIATES CONSULTING STRUCTURAL ENGINEERS November 12, 1991 City of San Luis Obispo Department of Public works 970 Palm Street ' P.O. Box 8100 San Luis Obispo Ca 93401 Attn: David Elliott Administrative Analyst Re: Summary Report for the Structural Analysis Phase Mitigation of Structural Seismic Hazards to Fire Stations #2 and #3 San Luis Obispo CA HFS&A #910041 Gentlemen The H. J. Degenkolb report identified structural deficiencies of the seismic lateral resistive systems of both facilities by qualitative evaluation. Briefly, those deficiencies were identified as: 1 . Fire Station #2 : The front of the building lacks a competent lateral force resisting system. Block walls are not anchored to the roof . 2 . Fire Station #3 : The front and rear of the apparatus bay lacks a competent lateral force resisting system. Block walls are not anchored to the wood-framed floor at above grade conditions . The Degenkolb report describes seismic upgrading work necessary i to mitigate these deti cies!Our &tx_wtur_al- analysis verified e n en ♦ comrlete the work, but also determine �-----' appropriate methodology. As part of our analysis work original contract drawings were reviewed: 1. Fire Station #2 drawings, sheets 1 through 6, Kenneth H. Hess, Architect, April 11, 1953. 2. Fire Station #3 drawings, sheets 1 through 8, Kenneth H. Hess, Architect, October 26; 1959. 601 DAILY DRIVE . SUITE 205 • CAMARILLO. CA 93010 • 805.987-7887 • FAX 805.388-2041 C 5 David Elliott / City of San Luis Obispo 910041 - November 11, 1991 Page 2 of 3 Title 24 of the California Administrative Code (CAC) was utilized as the basis of our analysis and retrofit design. Structural analysis work was completed cognizant of the facilities being within seismic zone 4 of the CAC. . An importance factor of 1. 5 was used in conjunction with a type 1 soil coefficient. Fire Station #2 To provide lateral resistance at the front of the building, we recommend that the interior of the westerly masonry office wall be strengthened with a 3-1/2-inch-thick shell of pneumatically placed reinforced concrete. Seismic loads from the high roof over the apparatus bay will be collected by a steed frame, which will be stabilized by the reinforced office wall . Enclosed drawings SK-1 and SK-2 show conceptual plans and details for completion of the effort . The Degenkolb report recommends installing a single moment resisting steel frame at the front of the apparatus bay with a grade beam below. Additionally, they recommended that the large • open bay window at the office be in-filled with new masonry units . The methodology that we propose will maintain the current architectural appearance of the facility by retaining the open bay window. The proposed steel frame will not require a grade beam; hence, use of the apparatus bay will not be severely interrupted during construction. Anchorage of the masonry walls to the roof framing will be designed and detailed in conjunction with the preparation of the contract drawings . We anticipate that installation of the anchors will require that the roof membrane be removed and replaced as part of the rehabilitation effort. Fire Station #3 To provide lateral resistance across the drive-through apparatus bay, the two existing steel roof girders over the bay will be incorporated into a moment frame by the addition of steel columns and a grade beam. Enclosed drawing SK-3 shows conceptual plans for the completion of the effort. Recommendations within the Degenkolb report are similar; however, they suggest the installation of a completely new moment frame and grade beam near the front and rear doors of the apparatus bay. The methodology that we propose will eliminate the need to C- 13-` HOINARD F. STUF $ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIVE • SUITE 205 • CAMARILLO, CA 93010 • 805-987.7887 -- FAX 805-388-2041 David Elliott / City of San Luis Obispo 910041 November 11, 1991 Page 3 of 3 remove the doors during construction; however, during construction, use of the apparatus bay will be interrupted for installation of the concrete grade beam. The need for anchorage of the masonry walls to the floor framing will be determined during the field investigation phase. If anchors are not present, they will be designed and detailed in conjunction with the preparation of the contract drawings. Agency Review Structural calculations are being provided for preliminary Agency review. Likewise, drawings SK-1 through SK-3 should also be reviewed. We will proceed with our field investigation work after receipt of your review comments . Sincerely HOWARD-Y. STUP 6 ASSOCIATES ,\ l JIo `El Nelson Enclosure: (1) Fire Station #2 Calculations , Revision 0, 11/11/91 (1) Fire Station #3 Calculations, Revision 0 , 11/11/91 (3) Drawings SK-1 through SK-3, 11/11/91 C - �3- 7 HOWARD F. STUP &ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY.DRIVE • SUITE 205 • CAMARILLO, CA 93010 • 805-987.7887 • FAX 805.388-2041 HOWARD F. STUP & ASSOCIATES CONSULTING STRUCTURAL ENGINEERS December 2 , 1991 City of San Luis Obispo Department of Public Works 970 Palm Street P.O. Box 8100 San Luis Obispo CA 93401 Attn: David Elliott . Administrative Analyst Re: Summary Report for the Structural Analysis Phase Mitigation of Structural Seismic Hazards to San Luis Obispo City Hall San Luis Obispo CA HFSSA $910041 Gentlemen • The H. J . Degenkolb report identified structural deficiencies of the lateral seismic resistive system by qualitative evaluation. Briefly, they were identified as: 1. Eight basement-level reinforced concrete columns create a soft story below first floor interior masonry shear walls . 2 . First floor interior masonry walls are not. braced for out- of-plane loading. 3 . The cementious roof panels and horizontal roof truss bracing appear inadequate to resist severe ground shaking. Our structural analysis has determined seismic loading to the eight basement-level columns . Future analysis work will address remaining issues associated with the first floor masonry walls, cementious roof panels, and horizontal roof trusses . As part of our analysis work, original contract drawings . were reviewed: 1. City Hall drawings, Sheets 1 through 20 and S1 through S6, William Decker Holdredge Architect , July 1950 . 601 DAILY DRIVE • SUITE 205 • CAMARILLO, CA 93010 • 805-987-7887 • FAX 805-388.2041 Mitigation of Structural Seismic Hazards Summary Report 910041 San Luis Obispo City Hall David Elliott, Administrative Analyst December 2, 1991 Page 2 To complete the structural analysis, horizontal roof trusses were modeled as flexible elastic elements. Truss reactions .were determined, cognizant of nodal tributary loadings. The first floor concrete diaphragm was modeled as a rigid element capable of rotation and translation. Because the diaphragm is coupled with the first floor masonry shear walls that are rigid, they were modeled as firm base oscilators driving the flexible horizontal roof trusses . Discrete dynamic analysis was performed for the interior shear walls supported by the eight basement columns . The seismic base shear coefficient was determined, cognizant of the facility being located in Uniform Building Code seismic zone 4. An importance factor, I equal to 1 .0 was used in conjunction with a global performance factor, Rw , equal to 6 .0. For the static analysis, the spectral amplification coefficient C was limited to a maximum value of 2 . 12 , as recommended by ATC-14. Dynamic analysis was completed utilizing the Uniform Building Code response spectra for soil type S1. Spectra results were scaled by a coefficient equal to: Z = 0 . 4 = 0 .067 RN 6 Our analysis indicates that the existing concrete columns have adequate capacity to resist the analyzed seismic loads; however, traverse confinement of the vertical column reinforcement is inadequate to insure column ductility. Our analysis also indicates that the existing concrete beams below discontinuous shear walls have inadequate flexural capacity to resist superimposed seismic loads from the masonry shear wall above Strengthening to increase the positive moment capacity will be required. We anticipate that strengthening can be accomplished with pneumatically placed reinforced concrete. Drilling of existing concrete and placement of epoxy-set dowel bars along with the welding of column confinement steel will also be required. HOWARD F. STUP &ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIVE • SUITE 205 . CAMARILLO, CA 93010 • 805.987.7887 • FAX 805.388-2041 Mitigation of Structural Seismic Hazards Summary Report 910041 San Luis Obispo City Hall David Elliott , Administrative Analyst December 2 , 1991 Page 3 Structural calculations are being provided for preliminary Agency review. We are proceeding with preparation of Phase I contract drawings for strengthening of the columns and beam. Phase II contract drawings will address strengthening issues regarding first floor wall bracing and horizontal truss strengthening. Sincerely HOWARD F. STUP 5 ASSOCIATES joh Nelson, S.E. E osure: City Hall Structural Calculations Revision¢, 12/04/91 CO-0 13- 10 HOWARD F. STUP&ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIvE • SUITE 205 • CAMARILLO• CA 93010 • 805-987-7887 . FAX 805.388-2041 HOWARD F. STUP & ASSOCIATES January 30, 1992 CONSULTING STRUCTURAL ENGINEERS City of San Luis Obispo Department of Public Works 990 Palm Street P.O. Box 8100 San Luis Obispo CA 93401 Attn: David Elliott Administrative Analyst Re: Summary Report for the Field Investigation Phase Mitigation of Seismic Hazards to Fire Station #2 and #3 San Luis Obispo CA HFS&A #910042 Gentlemen On January 7 and 8, 1992 a field investigation of the two (2) subject facilities was completed to confirm that existing construction is in general compliance with the original contract drawings. These drawings were utilized to complete our structural analysis, the results of which were reported to you in our correspondence dated November 12, 1991. Information obtained during our field investigation was also used to investigate issues identified by the structural analysis and Degenkolb's report, and to verify the constructability of upgrading design proposals. FIRE STATION #2 Our field investigation work confirmed that the seismic upgrading methodology identified by our structural analysis is both necessary and feasible. During the investigation we determined that: 1. The location of vertical and horizontal wall reinforcement correlates well to the original drawings; however, horizontal bond beam locations do not correspond to the locations shown on the drawings. Pacometer investigation of the bond beams indicates that only 50% of the required reinforcement is present. 2. No tension anchorage between the masonry walls and roof diaphragm is present. Existing shear bolt spacing is inconsistent with the original drawings. 3. The existing shear wall at the front of the office is partially grouted and has only minimal reinforcement. 601 DAILY DRIVE • SUITE 205 • CANARILL0, CA 93010 • 805.987-7887 City of San Luis Obispo 910042 Summary Report/Field Investigation Phase Fire Station #2 and #3 January 30, 1992 Page 2 Final drawings for the seismic upgrading effort will address that work which was shown-on our preliminary drawings, SK-1 and SK-2, dated November 11, 1991. As a result of our constructability review, we will modify that design to eliminate the overhead steel beam and northerly steel column proposed within the apparatus room; both of which infringe upon clearances and would affect vehicle ingress and egress from the apparatus bay. FIRE STATION #3 Our structural analysis identified the need to add structural frames across the apparatus bay. These frames would be designed to supplement the existing easterly and westerly masonry shear walls, should they fail. These masonry shear walls are perforated by several openings and, by qualitative analysis, represent a "weak-link" in the seismic load path. At the request of the'City, these walls were structurally analyzed to determine their capacity. Utilizing information found on the original drawings, we determined that the wall capacity exceeded the seismic demand; however, the wall reinforcement placement patterns would be subject to • a field verification. As part of the field investigation we addressed this issue and others. Specifically, we determined that: 1. The location of vertical and horizontal reinforcement correlates well with the original drawings. 2. Degenkolb's report discusses missing anchor bolts at the intersection of the ground level floor framing to the peripheral masonry wall. The original drawings required that two (2), 5/8-inch-diameter anchor bolts at four (4) feet on centers -- one anchoring the sill plate and the other anchoring the blocking — be installed where framing is perpendicular to the masonry wall. We determined that the existing condition is appropriate anchor spacing; however, no nuts have been installed on the sill anchors, the tops of which have been set flush to the top of the wood plate. No anchors were identified where the floor framing runs parallel to the masonry wall. 3. Plywood shear walls atop the north and south masonry walls are used to transfer roof loads into the masonry walls. At the southeast corner, specific detailing has been omitted to complete the shear transfer. During our January 17, 1992 meeting with Mr. Bob Neumann, City Fire Chief, we discussed several options regarding the extent of seismic upgrading, all of which were centered around the anticipated future service life of the facility. Based on his opinion that there will be a high likelihood to extend the service life of the facility beyond the next 20 years, we recommend that regardless of the results of the additional structural analysis, a supplemental G HOWARD F. STUD 8 ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIVE • SUITE 205 • CAMARILLO, CA 93010 • 805.987-7887' • FAX 805.388.2041 City of San Luis Obispo 910042 Summary Report/Field Investigation Phase Fire Station #2 and 43 January 30, 1992 Page 3 framing system should be installed across the apparatus bay to mitigate load transfer to the east and west masonry shear walls. Mr. Neumann concurred with our position. Final drawings for the seismic upgrading effort will address work similar to that shown on our preliminary drawing SK-3 (dated November 11, 1991). As a result of our field investigation and discussions, we will modify our design of the steel frame from that of a shear-resisting element to that of an energy-absorbing element. This will eliminate the need to install a concrete grade beam, thereby reducing construction costs and facility disruption. The lack of positive roof shear transfer at the southeast corner is a simple item-to correct. It will also be detailed on the drawings. With regards to the attachment of the floor framing to the masonry walls, we feel that the close proximity of the floor to the adjacent grade serves to confine the diaphragm, thereby mitigating the need to control displacements. No correction work is recommended. . Sincerely HOWARD F. STUD & ASSOCIATES �N' ,4i ohn P. Nelson, S.E. C- 1313 HOWARD F. STUP &ASSOCIATES CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIVE • SUITE 205 - CAMARILLO, CA 93010 • 805-987.7887 • FAX 805-388-2041 HOWARD F. STUP & ASSOCIATES January 30, 1992 CONSULTING STRUCTURAL ENGINEERS - City of San Luis Obispo Department of Public Works 990 Palm Street P.O. Box 8100 San Luis Obispo CA 93401 Attn: David Elliott Administrative Analyst Re: Summary Report for the Field Investigation Phase Mitigation of Seismic Hazards to San Luis Obispo City Hall HFS&A #910042 Gentlemen - On December 5, 1991 and January 8 through 11, 1992 a field investigation of the facility was completed. Our work on December 5, 1991 addressed issues related to Phase I work within • the basement. During January our field investigation addressed bracing the tops of non- bearing masonry walls in the attic and documenting the construction of the existing horizontal roof truss. Information obtained during our field investigation was used to compare the existing construction to the original contract drawings, clarify issues identified by the structural analysis and Degenkolb's report, and verify the constructability of upgrading design proposals. Phase I - Basement Level Column Strenzhenine The results of the structural analysis were reported to you by our correspondence dated December 2, 1991. At that time we verified the need to strengthen all eight basement level columns as identified by Degenkolb's report, and recommended utilizing pneumatically-placed reinforced concrete as the appropriate technique for completing the task. The concrete would be used to encase new confinement reinforcement placed around the existing column. This reinforcement would be designed to meet current minimum code requirements for reinforced concrete columns subject to seismic axial loadings. Additionally, the analysis also identified certain concrete beams; framing into the subject columns and below the masonry wall above that would be overstressed when subjected to moderate seismic loadings. At the request of the City, we performed additional analyses and research to identify a simpler and less disruptive methodology for confining the existing column reinforcement. To this extent we pursued a methodology that would incorporate a steel lining around the exterior of the column. During our meeting of January 10, 1992 we discussed our findings, specifically: C 601 DAILY DRIVE - SUITE 205 - CAMARILLO, CA 93010 • 805-987-7887 City of San Luis Obispo 910042 Summary Report for Field Investigation Phase San Luis Obispo City Hall January 30, 1992 Page 2 1. A steel liner can be designed that analytically will provide the same area of confinement steel that would be required by current code provisions; however, the method is not recognized by the code. This is not to say that it is technically unacceptable -- just not addressed by current code provisions. 2. The steel liner would be constructed of bent 1/8" or 3/16" steel plate, fabricated in two halves, wrapped around the column, and field-welded. The liner would extend the full height of the column with the collar joint between the column and liner grouted solid with epoxy. 3. CALTRANS is actively utilizing a similar methodology to retrofit their existing bridge columns. Their retrofit designs have been supported by a laboratory testing program currently being conducted at UCSD under the direction of Professor Nigel Priestly. We have conducted extensive conversations with CALTRANS regarding this test program; however, they are reluctant to release any information regarding the . analytical results of their testing. 4. The need to strengthen certain existing beams is not necessary when the reserve capacity of the masonry elements above are mobilized to absorb additional seismic loads. However, when using this technique, all eight columns, in lieu of specific columns subjected to orthogonal loadings, should be strengthened. This will account for the redistribution of loads due to the potential weakening of masonry walls during long duration ground shaking. Based on the recommendations of this office, the City requested that we prepare Phase I drawings utilizing the steel liner design proposal. Subsequently, we prepared City plan No. S32-X and issued originals to your office for City Engineer's signature on January 22, 1992. Phase 1I - Attic Partition Bracine and Dianhratmt Strengthening Our field investigation work confirmed the need to complete strengthening work identified by Degenkolb's report, specifically: 1. Non-bearing masonry partitions are not braced. Bracing to the top of these walls needs to be provided. 2. The horizontal roof trusses were not constructed per the original drawings. Large eccentricities have been built into the connections. 3. Support plates that secure the roof trusses to the exterior masonry walls have been C- I�y • IS HOWARD F. STUP &ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIVE • SUITE 205 • CAMARILLO, CA 93010 • 805.987.7887 • FAX 805-388.2041 City of San Luis Obispo 910042 Summary Report for Field Investigation Phase San Luis Obispo City Hall January 30, 1992 Page 3 constructed with elongated bolt holes to facilitate field erection. The slots are orientated perpendicular to the walls. Take-up in the elongated hole will have to be realized prior to mobilizing loads into the plates. .. - Additionally, during field work performed on January 17, 1992, the attachment of the cementious roof panels was investigated by destructive techniques. The investigation determined that the panels are not secured with any positive attachment to the supporting steel angles. Panel joints at the steel angles are grouted solid with a lime-base mortar._ The mortar is easily dislodged, has minimal strength, and is not bonded to the panels. At the request of the City, mortar samples from the panel joints were retrieved and tested for asbestos content. No asbestos was identified with the mortar, however, roofing felts do contain 3% to 5% chrysotile. A copy of the test report is attached for your review. As a result of our field investigation work, we have been able to complete our structural analysis of the horizontal roof truss system. Our analysis confirmed that the existing system is inadequate to resist seismic loadings, specifically: 1. Eccentric connections to the bottom roof truss will overstress the existing chord • member by a factor of eight. 2. Positive truss connections to transfer seismic loads to the masonry bearing walls are either non-existent or, if present, are overstressed by a factor of three. To mitigate this structural condition, two options are proposed: Strengthening Option No. 1 This option would require that the horizontal truss system be strengthened. Connections and struts would be added as necessary to enhance the performance of the existing framing and provide a continuous load path for seismic forces. It is anticipated that a majority of the work could be completed within the existing attic space; however, some selective demolition work to interior ceilings is anticipated. Option No. 1 does not address the issue of securing the cementious lay-in roof panels. Because of their asbestos content, it is difficult to envision attaching any type of mechanical fastener to the panels without creating a considerable amount of airborne friable particulate. With limited ventilation within the attic, safe working conditions would be difficult to achieve. The cementious lay-in panels represent a moderate risk of seismic hazard exposure. Individual panels weigh approximately 20 pounds each and, if separated from the roof framing, would likely penetrate the suspended ceiling below. C'm Ila HOWARD F. STUP 8 ASSOCIATES • CONSULTING STRUCTURAL ENGINEERS 601 DAILY DRIVE - SUITE 205 • CAMARILLO, CA 93010 • 805.987.7887 . FAX 805.388-2041 City of San Luis Obispo 910042 Summary Report for Field Investigation Phase San Luis Obispo City Hall January 30, 1992 Page 4 To eliminate this hazard and, at the same time, address the structural strengthening requirements identified by our analysis, we recommend that the City consider and implement an alternative upgrading program, specifically: Strengthening Option No. 2 For this option the structural upgrading work will require the removal of the cementious lay- in panels and replacing them with a fluted metal decking. The decking would be welded to the existing steel angles that currently support the panels. The existing roof tiles and new membrane would be installed over plywood furring attached to the decking. Advantages of this option are: 1. Hazards associated with the cementious panels will be eliminated. Aside from seismic issues, the problem of asbestos contamination will be gone. When exposed, the roof panels are easily dislodged and can be removed as complete units. .The friability of the materials should not become an issue during selective demolition.. 2. Installation of the metal decking will create a contiguous competent roof diaphragm. Strengthening of the horizontal roof truss will not be necessary. 3. Installation of interior wall bracing, seismic struts and anchors can be easily performed with open access from the "top down." While the cementious panels remain in place, the building will continue to present a moderate seismic risk to the occupants. Unanchored gravity-supported framing elements traditionally provide poor seismic performance, even during the lower bounds of ground shaking (magnitude 4.0 to 5.0). Anchorage of these elements is always a high priority of any seismic upgrading program. Option No. 2 provides a method for not only eliminating the hazard, but efficiently addressing the other upgrading efforts from a constructability standpoint. We recommend that the City pursue this course of action. Sincerely HOWARD . STUP & ASSOCIATES 7ttac P. elson, S.E. hment: Asbestos Test Result HOWARD F. STUD &ASSOCIATES - CONSULTING STRUCTURAL ENGINEERS Cels ` 11 601 DAILY DRIVE • SUITE 205 - CAMARILLO, CA 93010 • 805-987-7887 • FAX 805-388-2041 8tc - 2978 SEABORG AVENUE,VENTURA,CA 93003 • 805/656{074 tabomtodn Project: Howard Stup&Associates JOB NUMBER: 92-2548-VOI 601 Daily Drive LAB NUMBER: 920036 Suite 205 DATE: January 30, 1992 Camarillo, CA 93010 REPORT OF TESTS On January 21, 1992, a representative of this laboratory received 1 bulk sample of material suspected of containing asbestos. The sample was identified by the client as roof mortar from the San Luis Obispo City Hall. The sample was found to contain asbestos in the tar mastic layer(see attached report). Because this material contains asbestos, a potential health hazard exists. This hazard can only be eliminated by complete removal of all asbestos containing materials. • Respectfully submitted, BTC LABORATORIE ,1NC Ir 6s,� Darin J. Copies: i Howard Stup&Assoc. 1 File DJF:hra Asbes. C - 13- Ig OXNARD!CAMARILLO SUELLTON THOUSAND OAKS (605)656.6074 (605)68&3273 (805)497.2401 ESSTEKINCe • A1vIembCOfSfiCL�1CGBC)UP.INC Data Reoelved: an 23 92 nn Seaborg Ave. 1>am Analyzed: Jan 24 92 vcra l 6 CA 93003 Data Reported: .tea 24 92 666�607s Reported To/vm Maobine Steed BY/vis: us 81x9 Accotud#: #901300 Report Nrrnber: PMa1 70oSIS Contact Darin 1 FrarMa pose Order# Not Provided Prcie= Sam Luis Obispo City NO cow m:mee rMUM are Manxcm/tr me�ts�e a�ad�d ate mum.4s ae�e�d aab� Laboratory Dirs dor•,Aobert A WoeAW Arsh"4 Alan Gitano H25I P�at Type Layer Chert Sam�pie# Lab Saarple# Peraerd A Typo of Nor AsbeV= Sample Appesamcc alA�ertos Sample Locadon/DescrWon #MOW PL700516A None Des ed 35%Yermt uft L FAMM 30%G'Dsurn Root;Mortar LAM 20%Carboraa Binders 15%Callalosa 092DO36 PL700516B 34%Ciaysots-le AD, OrganIe Binders i Fibrous 2VA VermiocMs Rood Tar 81asSc LaYW 10%Centrlaw 10%mica ar a.reua d �d amt gra mord for asneta Mcca irL a1G IM 1dl0rrs @l4 aa�+ee tTt CU.t p-7�R 70S s F Ago.A.dais wm Mov eom kw ismer a teem SQaa i arboam0e at agaosiffinocaOf WE m ML omr+m wo e+a�t r umphobw sad taeeG fs eesi0t resat b®eed a a*0 vM a wwwc rduc*a bee& 'tba aataaya+�a.saesa me r W tam a low raemea mfoeee ws wit a Mtflrs Cbosa ee Swift aablrm+a adr stmt asap �d ma earoa mmdd wst e�mad m Oieemla ma a>�d ma sIDrt Sbe almerosa Yd4�+ertea ire d e Ogee d e od efpeaas erakft adore- ; mems is Awwound by avow comate me*Mvt r d aroma aamrid m a�.�m.s Eld6 aaamap. b COITAL me:hboomi 1�km as lms era rmeaer MM ae m ea<•emt tarata¢ts d¢eemeL aamed+0 br so Pia a td Nid daa�rabef�f AeQeaaram Faepem- Or sm7lD.amenr'1 d�aneambea m m CWM Ra*=aem�br K*w or ae!ava AwW aadta tbc�idlUCn ae lead aaadt N bd®r a hemwEn"ra saa<1a • 7.1431 S n9bTires=%day E-agk v=c&Coloedesot12 �1 HOWARD F. STUP & ASSOCIATES CONSULTING STRUCTURAL ENGINEERS January 31, 1992 City of San Luis Obispo Department of Public Works - 990 Palm Street P.O. Box 8100 San Luis Obispo CA 93401 Attn: David Elliott, Administrative Assistant Re: Project Status Report #4 Mitigation of Structural Seismic Hazards to San Luis Obispo City Hall Fire Station #2 and Fire Station #3 HFS&A #910040 Gentlemen During the month of January we completed field investigation work at all three (3) buildings. Summary reports of our field work have been previously submitted. Contract drawings were also completed and submitted for Fire Station #3 and City Hall Phase] strengthening work. Strengthening design for Fire Station #3 was completed cognizant of our January 17, 1992 meeting with Bob Neuman, City of San Luis Obispo Fire Chief. During the early part of February we will be completing contract documents for Fire Station #2 strengthening work. As you are aware, this facility will require a more extensive effort than Fire Station #3. At the same time we hope to resolve open issues related to the strengthening of the City Hall roof. Contractually, our scheduled completion date is February 1992. Depending on (when or how) outstanding City Hall issues are resolved, we anticipate project completion near March 1, 1992. If this timing is unacceptable to the City, please notify us immediately. Sincerely HOWARD F STUP & ASSOCIATES i Jo)sn el on, S.E. C 601 DAILY DRIVE • SUITE 205 CAMARILLO, CA 93010 • 805-987.7887