community action plan for seismic safety – the...
TRANSCRIPT
Community Action Plan for Seismic Safety – the Soft-Story Program
SEAOSC Buildings At Risk │ EQ Loss Reduction SummitPutting Earthquake Loss Mitigation Solutions into Practice
Keith Porter, PE, PhD
University of Colorado at Boulder and SPA Risk LLC
Acknowledgments
• LT Tobin, LD Samant, K Cobeen, CR Scawthorn, HA Seligson, C Poland, ML Zoback, W Holmes, S King, J Moehle, L Kornfield … (CAPSS)
• Holly Bonstrom & Ross Corotis (risk communication)
Outline
• CAPSS-1 and CAPSS-2• Impetus for the soft-story effort• Engineering analysis• Policy formulation• Lessons learned from CAPSS
CAPSS-1 and CAPSS-2• “The CAPSS project of the
San Francisco Department of Building Inspection (DBI) was created to provide … a plan … to reduce earthquake risks in existing, privately-owned buildings, … and also to develop … guidelines that will expedite recovery….”
• CAPSS-1 completed 2003, unpublished
• Restarted 2006• Published in 2010
Engineer, reporter, mayor
June 29, 2008 Sunday, Main News, Page A-1, Robert Selna, Chronicle Staff Writer: “S.F. disregards danger of weakest buildings; Classic structures abound - many on unstable ground.”
• Selna: “Tens of thousands of San Francisco homes and businesses are built in a way that will probably cause them to collapse in the next big earthquake, yet city leaders and building officials have largely ignored the danger for decades.”
• Pat Buscovich: “’Almost every apartment building in the Sunset District and the Richmond District with ground-floor grocery stores and shops. ... They're toast! … they'll kill a lot of people.’”
• Selna: “San Francisco building-safety experts wonder why it's taking so long for the city to craft a soft-story building retrofit plan.”
One week later: Mayor issues Executive Directive 08-07
• Expedite study of soft-story buildings under CAPSS
• Include retrofit guidelines• Waive related fees• Outreach campaign• Create an emergency
planning exercise
The engineering analysis
San Francisco Planning and Urban Research Association (SPUR) performance levels
• SPUR recommends policy to ensure 95% shelter in place• CAPSS to estimate buildings and housing units in each
performance level, for several scenarios & retrofit options • What up-front construction costs & scenario repair costs?• No attempt to estimate casualties
Label Description Tag A Safe and Operational Green B Safe and usable during repair Green C Safe and usable after repair Yellow D Safe but not repairable Red E Unsafe: Partial or complete collapse Collapse
4 scenario earthquakes
• Focus on 1• 2-4x as 1989
Sa(1.0)• Acknowledge
uncertainty• “Could
happen at any time”
T=360 yr T=?
T=130 yr T=520 yr
4 index buildings
Figure 1. Representative index buildings 1-4 (from left to right) studied as part of the CAPSS project. Table 1. Description of index buildings selected for study. Building Location Stories Sq ft/floor Replacement
cost, $1000 Housing
units Interior finish
1 Corner 3 3,610 $3,600 6 Plaster & wood lath 2 Corner 4 5,800 $7,700 8 Plaster & wood lath 3 Mid-block 4 2,270 $3,000 6 Plaster & wood lath 4 Mid-block 3 1,750 $1,700 4 Gypsum Wallboard
As-is + 3 retrofits
Building 1 retrofit 2
Retrofit Performance level target
Average cost per Total cost, $M Building Housing unit
1. Structural sheathing at ground-story walls with inadequate bracing length
D $65,000 $11,000 $180
2. Structural sheathing at ground-story walls and steel moment frames at garage openings
C $105,000 $17,000 $290
3. Structural sheathing at ground-story walls and steel cantilever columns with lower R factor and same seismic force level as 2
C to B $93,000 $16,000 $260
We created pushover curves…Sheathing Yield capacity Yield
deflection Peak capacity Deflection at
peak Plaster over wood lath 350 plf 0.5” 400 plf 0.7” Straight horiz. sheath. 160 plf 0.8” 200 plf 3.0”
Gypsum wallboard 67 plf 0.1” 100 plf 0.5” OSB sheathing 67% peak
capacity per ASCE 41
Per SDPWS deflection equation
Per SDPWS tabulated
nominal capacity
Per SDPWS deflection equation
Building 1
Derived new fragility functions …Wood lath & plaster wallsWood lath & plaster walls•• TrayerTrayer (1956), Schmidt (1984) tests(1956), Schmidt (1984) testsStraight sheathing:Straight sheathing:•• TrayerTrayer (1956), (1956), ElkhoraibiElkhoraibi & & MosalamMosalam (2007)(2007)•• Connections fail at Connections fail at ∆∆ ~ 3%~ 3%Brick veneerBrick veneer•• Failure modes from lab tests (Failure modes from lab tests (KlingnerKlingner, , etc.)etc.)•• JalilJalil et al. (1992) veneer et al. (1992) veneer delamdelam. at . at ∆∆ < 1%< 1%StuccoStucco•• CUREECUREE--Caltech: delaminates at Caltech: delaminates at ∆∆ ≈≈ 1%1%Red-tag fragility• Deierlein et al. (2007) 5% PTD 2%
residual drift (red-tag in woodframe)Collapse fragility• Harris and Egan (1992): estimated Sd and
damage of 44 buildings 0.00
0.25
0.50
0.75
1.00
0 5 10 15
Spectral displacement, in.C
olla
pse
prob
abili
ty
4 collapsed on soft soil2 collapsed on failed ground0 collapsed on firm soil
3 of 7 on firm or soft soilcollapsed at S d ≈ 12.5"
1 of 11 on firm or soft soilcollapsed at S d ≈ 10"
θ = 13 in, β = 0.2
Related damage states to tag colors…Experimental observations Median
Sd, in. HAZUS structural damage
Small cracks appear near corners of openings in lath and plaster walls
0.06-0.07 Slight: Small plaster or gypsum-board cracks at corners of door and window openings and wall-ceiling intersections; small cracks in … masonry veneer. (Green tag under ATC-20.)
Small cracks appear throughout the ground-floor lath and plaster walls; brick veneer begins to fall off
0.4-0.5
Moderate: Large plaster or gypsum-board cracks at corners of door and window openings; small diagonal cracks across shear wall panels exhibited by small cracks in stucco and gypsum wall panels…. (Green tag under ATC-20.)
Ground-floor stucco delaminates from wood lath; ground-floor lath and plaster walls exhibit large cracks
1.5-1.9
Extensive: Permanent lateral movement of floors and roof… partial collapse of “room-over-garage” or other “soft-story” configurations…. (Yellow tag under ATC-20.) Nails heavily deformed in exterior
straight sheathing 2.9-3.6
Complete: Structure may have large permanent lateral displacement, may collapse, or be in imminent danger of collapse …. Approximately 3% of the total area of W1 buildings with Complete damage is expected to be collapsed. (Red tag under ATC-20.)
Residual drift in the ground floor ≥ 2 inches; no collapse
5-8
Collapse occurs 13-?
Related shaking to tag color…
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Sa(1.0 sec, 5%), g
Red
-tag
prob
abili
ty M7, 10 km, soil D
IB1 as-is
Retrofit 3
Retr 1
Retr 2
(a)
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Sa(1.0 sec, 5%), g
Red
tag
prob
abili
ty M7, 10 km, soil D
IB2
(b)
Retrofit 3
Retr 1Retr 2
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Sa(1.0 sec, 5%), g
Red
tag
prob
abili
ty M7, 10 km, soil D
IB3 as-is
Retrofit 3
(c)
Retr 1 Retr 2
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Sa(1.0 sec, 5%), g
Red
tag
prob
abili
ty
M7, 10 km, soil D
IB4 as-is
Retr 2, 3
(d)
Retrofit 1
Estimated shaking intensity…
Estimated scenario losses…
In an inevitable earthquake that could happen tomorrow:• 8 in 10 buildings red tagged, of which 2 collapse• Retrofit reduces red tags to 1 in 10, collapse to 1 in 200 • Retrofit costs $16k/housing unit—a small bathroom reno• After retrofit, many buildings require substantial repair,
but on average at lower cost than retrofit
Estimated Distribution of 2,800 Buildings with Large Openings by Post-earthquake Safety Tagging Category
Scenario Retrofit Dollar Loss ($ Billions)* Green Tag (%
of Buildings) Yellow Tag
(% of Buildings)
Red Tag (% of Buildings)
Red Tag - Collapse (% of
Buildings) As-is $4.10 6 – 35 9 – 23 32 – 54 11 – 31
1 $3.40 36 – 48 28 – 34 14 – 28 4 – 8 2 $2.90 57 – 64 24 – 27 9 – 18 0.5 – 1
Magnitude 7.2 San Andreas Fault
3 $2.60 67 – 71 21 – 23 6 – 12 0.3 – 0.7 * Total exposed value of buildings and contents: $14 billion, not including land
Produced useful graphics…
And presented them to CAPSS Advisory Committee
• Volunteer owners, tenants, & other community stakeholders; met 30 times
• At 8th meeting 10 Dec 2008 we presented:– Community demographics & economics– Engineering risk study results– But no policy advice
Policy formulation
Advisory Committee discussion• Scope: these the right buildings to focus on first?
– Yes, but there are other vulnerable buildings• Performance objectives
– General agreement on 95% shelter-in-place objective– Fatality risk addressed by preventing collapse
• Intervention strategy– Broad consensus for a mandatory program; seismic risk “a
community issue that outweighs individual concerns”• Priorities
– Focus on large corner buildings on soft soil first• Incentives
– Low cost loans, general obligation bonds, DBI fee rebates– Pass through costs to tenants, even in rent controlled buildings
CAPSS policy recommendations1. Require evaluation of all large
woodframe buildings2. Inform the public (education &
outreach)3. Update standards for
evaluation & retrofit4. Require seismic evaluation of
all buildings5. Require retrofit of vulnerable
buildings6. Assist community service orgs
to be resilient7. Assign a City official to
manage seismic risk8. Improve post-earthquake
repair standards
9. Offer incentives to retrofit buildings
10.Require gas shut-off valves on select buildings
11.Track evaluations & retrofits12.Provide retrofit technical
assistance13.Enact façade ordinance14.Promote risk-reduction
technology15.Evaluate measures to address
FFE16.Address nonstructural hazards17.Periodically assess progress
Press followup
A Serious Temblor would Crush HomesKatie Worth, 12/10/2008
• “An analysis … by The City looked at the consequences of a serious earthquake on … large, wood-framed, soft-story … buildings.”
• “Kornfield: ‘Everyone was aware that this particular class of buildings are … at risk…. The surprise is just how at-risk they are…. We’ll make recommendations, but… we don’t make the policy. That’ll be up to the mayor and the supervisors.’”
• Later press talks about Newsom supporting retrofit, e.g., “San Francisco leaders are well aware that a devastating earthquake could happen at any moment…. They’re painfully aware that building owners aren’t just going to up and retrofit their buildings on their own.”
Eventual policy
• 2009: Mayor Newsom proposes mandatory retrofit ordinance; fails
• March 2010: SF Supervisors pass voluntary retrofit ordinance 54-10 with incentives – Fewer retrofits the year after than before (26 vs 40)
• Nov 2010: Measure A, bond to pay for retrofit of most-vulnerable buildings fails (64% voting for)
• 2011: SF continues to struggle with a mandatory retrofit ordinance
Lessons • Inform but do not recommend policy
– Let stakeholders produce policy advice• Use scenarios; minimize talk of probability
– Acknowledge uncertainty then move on• Focus on community values
– CAPSS: collapse & functionality, not BCR etc.• Make government officials accountable
– Media alarm addresses “incompatibility of lifetimes”– Mayor punished for inaction, faintly praised for action
• Anticipate funding and regulatory info needs
