HomeMy WebLinkAbout11/17/1992, 2 - CLARIFICATION OF SEISMIC ZONE TO BE USED FOR REQUIRED STRUCTURAL ANALYSIS OF UNREINFORCED MASONRY BUILDINGS. 1I1h@NIIIIV11111111 X11:1 jj� city of San . 1S OBISPO MEETING /-7 -
COUNCIL AGENDA REPORT ITEM NUMBER:
FROM: Arnold Jonas, Community Development Director
PREPARED BY: Tom Baasch, Chief Building Official
SUBJECT: Clarification of Seismic Zone to be Used for
Required Structural Analysis of Unreinforced
Masonry Buildings.
CAO RECOMMENDATION:
Introduce ordinance to print amending Appendix Section A111(b) of
the Uniform Code for Building Conservation as adopted clarifying
that Seismic Zone 4 criteria is to be used for the structural
analysis required for unreinforced masonry (URM) buildings.
DISCUSSION:
Current City ordinance establishes an unreinforced masonry building
strengthening program through adoption of Appendix 1 of the 1991
edition of the Uniform Code for Building Conservation (UCBC) . The
administrative regulations added to the Appendix, which originated
with the passage of Ordinance No. 1203 on February 4, 1992 , require
that owners of URM buildings have a structural analysis conducted
to determine extent of compliance with the strengthening provisions
and a cost estimate prepared to achieve compliance if remedial work
is necessary, both to be completed for all URM buildings within 18
months beginning January 1, 1993 .
The technical standards were developed after a seismic hazard
analysis performed by a geotechnical engineering firm concluded
that the seismic forces likely to be encountered in the City of San
Luis Obispo would be in the moderate range. Although the City is
technically located in Seismic Zone 4 , the consultant recommended
that a strengthening ordinance be developed utilizing Zone 3
criteria. Due to concern that the Seismic Safety Commission is
reluctant to endorse the creation of subzones, City Council
approval included addition of a requirement in the regulations that
any question regarding use of Seismic Zone 3 factors be resolved
prior to initiating the 18-month structural analysis period.
A written response has been received from the Seismic Safety
Commission regarding the technical and administrative components of
the City's strengthening ordinance. While the Commission is
opposed to the use of reduced criteria, there is no authority for
their denial. However, the situation remains unresolved and
confusing. A change to the UCBC Appendix, to be published in the
1994 edition, was recently approved by the International Conference
of Building Officials. The amendment will allow a force reduction
factor with Zone 4 criteria that effectively accomplishes the same
result as use of Zone 3 in the current design equations. This
change was unsuccessfully challenged by the Structural Engineer's
Association of California. The content of the challenge may be
considered again, since the UCBC will go through an additional code
change cycle before the next edition is published in 1994. There
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00% COUNCIL AGENDA REPORT
is also the possibility of additional amendments through the State
adoption process. The uncertainty as to the final conclusion of
this technical issue has caused the City Attorney to strongly
recommend that the best course of action is to promote the more
conservative approach during the structural analysis phase.
The Seismic Task Force recently studied this issue and received
testimony from local engineers and architects indicating that the
cost to prepare a Zone 4 conclusion compared to the Zone 3 work
would be negligible. In fact, it was suggested that the analysis
could address requirements for both Zones at a maximum additional
cost of only a few hundred dollars. The Task Force concluded that
it would be in the best interest ofaffected property owners to
proceed conservatively with the structural analysis. Staff will
continue to monitor State adoption of, as well as future revisions i
to, Appendix 1 of the UCBC.
i
CONCURRENCES:
The Chamber of Commerce Board of Directors, upon recommendation of
the Seismic Task Force, unanimously endorsed the use of Zone 4
criteria for the required structural analysis. The Downtown BIA
will be acting on a resolution of support on November 10, 1992 .
ATTACH14ENT:
1. Seismic Task Force Membership
2 . Letter from Seismic Safety Commission
3. Legislative Draft
4 . Proposed Ordinance
I
_ Attachment l
= MEMBERSHIP OF THE SEISMIC TASK FORCE
Lynn Block Businiess Improvement Association
r' Linda.Stahl Mid-State Bank
Chris Ford RRM Design Group r.t;
Ed`Nolan SLO Co:.Building Contractors Association
Rod Levin Ross Levin MacIntyre & Varne_r Architects
=-Alex Gough Adobe Realty '
;r.
- Rob Rossi Rossi Enterprises
:.Pierre Rader Pierre Rademaker Design
z Charlie Frait Commerce Bank of San Luis Obispo
1 ' ` Tom Baascl Chief Building Official, City of San Luis Obispo
Lon'Lundberg Lundberg & Co.
William Thoma Thoma Electric, Inc.
' ' .Howard Carroll Carroll Properties
Robert,Vessely Robert S: Vessely Engineering
:Scott Jay Smaby Tiens
j
Attachment 2
STATE OFCALIFCINIA PETE WILSON,GOVERNOR
SEISMIC SAFETY COMMIS6I0N
1900 K STREET,SUfTE 100 �m
SACRAMENTO,CA 95814
'916)322-4917
(916)322-9476 FAX C E V O
SEP 2 S 1992
CITY OF SAN LUS&OSISvb
September 23, 1992 BUILDING OIYISIO.'J
Mr. Thomas Baasch
Chief Building Official
PO Box 8100
San Luis Obispo, CA 93403-8100
Dear Tom:
On behalf of the Seismic Safety Commission, thank you for
sending a copy of your city' s new ordinance that requires a
seismic evaluation of URM buildings . It certainly represents an
important step in the right direction . This new program is
likely to be more effective than programs that stop at notifying
owners of unreinforced masonry buildings that their buildings
are hazardous . While falling short of the stringency of
mandatory or voluntary hazard mitigation, it may nevertheless
result in some hazard reduction over time .
We have stated in several publications that voluntary
strengthening will have some effectiveness in cities with strong
economic conditions and financial incentive programs . Without
these, very little hazard reduction will likely be realized.
Ordinances in cities with caps on remodeling similar to yours
have not done much more than discourage remodeling.
with regards to your concerns about reducing the city ' s Seismic
Zone for URM buildings, I can offer you a few suggestions, but
the Commission has no authority to issue legal opinions .
The NEHRP maps you referenced in your letter of September 15,
1992 are a series of twelve maps . Maps 1 through '4 indicate San
Luis Obispo is in seismic zones consistent with Seismic Zone 4
which is defined differently in the Uniform Building Code . Maps
6 and 8 show San Luis Obispo is in an area of lower seismicity.
However, Maps 6 and 8 are titled "Preliminary Maps" and include
a note stating: "They should not be used for design at this time
but should be evaluated by trial design . " These maps are
referenced in Appendix Chapter 1 of the NEHRP Provisions which
is intended to be applicable to new construction - not the
retrofit of existing buildings . This new appendix is labeled
preliminary and it was included "to obtain broad professional
review and comment . " Much of the review and comment to date
within the national Building Seismic Safety Council regarding
3aasch SLO 1tr 9/23/
these maps has b negative . At any rate, t NEHRP provisions
are preliminary iccommendations absent the t�.-ce of law.
The UCBC Appendix Chapter 1 does not define the Seismic Zone
Factor Z. but it states that "all other provisions (including
the Z factor) of the (Uniform) Building Code shall apply. " You
might consider asking your legal counsel or the Building_
Standards Commission if adding your new definition of Z impacts
Section A102 or impacts the Uniform Building Code, the
provisions of which I understand can be increased but not
decreased by local governments . The issue of fairness between
new and existing buildings may be called into question since the
Z factor is intended to apply to both in the Uniform Building
Code .
Finding 2 of your ordinance states that the city is ."situated
near three major fault each capable of generating earthquakes
with a magnitude of 7 . 5 . . .subject to becoming active at any
time . . .The city of San Luis Obispo is particularly vulnerable to
devastation should such an earthquake occur. The potential
effects include . . .the need_ for rescues from collapsed
structures . " I agree with this finding, but it may appear to be
inconsistent with Finding 8 which states "seismic forces . . .may
be less than normally anticipated in Seismic Zone 4 . "
The boundary between Seismic Zone 3 and 4 was set at 25 miles
from a fault considered capable of generating an earthquake or-
magnitude
fmagnitude 7 . 0 or greater and 15 miles from a fault that could
generate an earthquake of magnitude 6 . 0 and 7 . 0 . The distances
were based on the Schnabel-Seed attenuation curve and a value of
0 .3 g for the peak acceleration at the boundary on a rock site .
For issues as critical as this, it may be in San Luis Obispo ' s
interest to have the city-wide seismic hazard analysis reviewed
by a panel of independent peer reviewers .
I can suggest five other alternatives, the legality and
political viability of which you might consider exploring. The
first would be to amend your ordinance and adopt the 1992
amendments to the UCBC . Note that the amendments adopted by ICBO
at this year 's Annual Business Meeting have lowered some of the
key requirements addressed by your city's amendments . This would
circumvent some of the potential concerns that might exist about
modifying seismic zones .
The second alternative would be to forego amending the 'Seismic
Zone factor and introduce new factors within the city ' s UCBC
amendments to reflect a lower desired seismic performance
objective for retrofitted URM buildings than currently exists in
the UCBC . This would perhaps clarify the intent of the city ' s
ordinance .
The third alternative would be to submit a successful code
change proposal to ICBO to lower your Seismic Zone defined in
the Uniform Building Code .
Baasch SLO 1tr 9/23/
The fourth alters. Ave is to adopt a more coi..r,lete voluntary
strengthening program which can be modeled after the City of
Palo Alto' s program. This would allow the public to be disclosed
of the hazards and would allow the city council to be disclosed
of and monitor the owners ' intentions to retrofit . The
Commission has published a report on this program titled
"Earthquake Hazard Identification and Voluntary Mitigation. "
The fifth alternative is one that the Commission recommends,
which is to require full compliance with the UCBC Appendix
Chapter 1, to provide incentives to encourage compliance, and to
work with owners to establish reasonable time frames for full
compliance .
Whether you choose to continue with your existing ordinance or
use the above alternatives, I recommend that San Luis Obispo
explore financial assistance for building owners . A recently
chaptered bill SB 1464 (Mello) increases the flexibility of
using Mello-Roos Assessment districts for the seismic retrofit
of buildings . A similar bill still awaiting Governor Wilson' s
signature is AB 1965 (Areias) which modifies the special
assessment district laws for more flexibility. These types of
districts are proving successful in big cities like Long Beach,
San Jose and Santa Barbara . They are also successful in small
cities like Torrance with as few as four buildings in the
district .
For more information about financial assistance alternatives,
the Association of Bay Area Governments has recently completed a
handbook on seismic retrofit financial incentives and options
for local government use . You can reach them through Dari Barzel
at 510-464-7900 .
If I can be of help to you, please feel free to call me .
Veryy truly yours,
Fred Turner
Staff Structural Engineer
FT/ft
9aasch SLO 1tr 9/23/ /
Attachment 3
LEGISLATIVE DRAFT
Revisions to Unreinforced Masonry Building
Strengthening Ordinance
Section 15.04 .050 of Title 15 of the San Luis Obispo
Municipal Code amending the Uniform Code for Building
Conservation is hereby further amended as follows.
A. Delete the following amendment to Appendix Section
A104:
The-Se!smle-3enezaeter €eeSe}ssieZene-4
B. Amend Appendix Section A105 (a) to read as follows:
(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. Fer--the purr_ges of this ehapte ,
Selsmie-gene--3 eElterla maybe sed.
C. Amend Appendix Section A111(b) 1 to read as follows:
(b) Compliance Requirements.
1. The owner of each building within the scope
of this 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
hail Utiliae 5e.... Zor►e . crate a. and. shall
include the'prep'aratlori 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.
Attachment 4
ORDINANCE NO. (1992 Series)
AN ORDINANCE OF THE CITY OF SAN LUIS OBISPO AMENDING
TITLE 151 CHAPTER 15.04 OF THE MUNICIPAL CODE TO
CLARIFY THE SEISMIC ZONE CRITERIA
TO BE USED FOR THE STRUCTURAL ANALYSIS OF
UNREINFORCED MASONRY BUILDINGS
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 buildings in the most cost
effective manner; and
WHEREAS, confusion exists concerning the appropriate seismic
zone factors to use for strengthening unreinforced masonry
buildings, and the City Council desires to clarify the issue.
NOW, THEREFORE, BE IT ORDAINED by the Council of the City of
San Luis Obispo as follows:
SECTION 1. Section 15. 04. 050 of Title 15 of the San Luis
Obispo Municipal Code amending the Uniform Code for Building
Conservation is hereby further amended as follows.
A. Delete the following amendment to Appendix Section A104:
Z = The Seismic Zone Factor for Seismic Zone 3
specified in Table 23-I of the Building Code.
B. Delete the amendment to Appendix Section A105 (a) to read
as follows:
(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.
C. Amend Appendix Section A111 (b) 1 to read as follows:
(b) Compliance Requirements.
1. The owner of each building within the scope of
this 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 utilize
Seismic Zone 4 criteria and 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
Ordinance No. - (1992 Series)
Page 2
structurally alter the building to conform to such
standards. The Building. Official shall establish a
basic outline for the format of the report.
SECTION 2. 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 3. This ordinance, together with the names of
councilmembers voting for and against, shall be published once in
full 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 30 days after its
final passage.
INTRODUCED AND PASSED TO PRINT by the Council of the City of
San Luis Obispo at a meeting held on the day of
1992, on motion of ,seconded by ,
and on the following roll call vote:
AYES:
NOES:
ABSENT:
MAYOR RON DUNIN
ATTEST:
DIANE GLADWELL, - CITY CLERK *********
APPROVED:
City A inistrative Officer
ttte ---
Director of o unity Development
12 , 11 JA A A P.4
Chief Buildin4 Official