NZSEE CONFERENCE Jack Moehle University of California, Berkeley

Transcription

1 NZSEE CONFERENCE 2009 Jack Moehle University of California, Berkeley

2 Why do we still tolerate buildings that are unsafe in earthquakes? > Can we really identify the unsafe buildings? > What can earthquake professionals do? > What do we expect of our cities after the next earthquake?

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5 Can a trained engineer spot the differences between a good building and a bad one?

6 Can you spot the differences?

7 Tension lap splice Compression lap splice Can you spot the differences? s1 h 1 14 h 6 in x so 4 3 h 1 4 h 2 4 s 1 6 d b lo s o 4 in h 1 s2 s1 s 2 6 d b 6 in h 1, h 2 lc l o h 1 h 2 l c 6 18 in lo s1/2 Figure Column transverse reinforcement spacing requirements

8 O P E N O P E N O P E N Damage Threshold Collapse Onset IO LS CP FEMA 356 Deformation Rare (10%/50yr) MCE (~2%/50yr) FEMA 356/ASCE 41

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10 Percentage Otani (1999) Kobe, 1995 Erzincan, Luzon, 1990 Operational Mexico City, 1985 Heavy Collapse Older Concrete Building Damage Rating

11 Behavior of older-type columns Axial failure Flexural yield Onset of shear failure

12 NCREE

13 PEER movie

14 Constitutive Model for Column Failure Column Shear Flexure strength Shear failure envelope Axial failure point D y D s D p Column Lateral Displacement Column Axial Load Axial failure envelope Column Lateral Displacement

15 lateral force Improved ASCE 41 a b collapse a - new b - new a - old b - old plastic rotation (rad) displacement

16 Technical advances unimportant if unimplemented

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19 California Inventory Project 4 pieces of information: > # of total buildings > # of pre-1980 buildings > # of concrete buildings > # of pre-1980 concrete buildings

20 Hollywood Wilshire Corridor Downtow n

21 Hollywood Wilshire Corridor Downtow n

22 Usage summary 400 Industrial, Manufacturing, Warehousing Commercial/restaurant Offices / professional services Residential Vacant Church/ Theatre Education Hospital Government Hotel Recreation Parking structure

23 We need your help to really understand the nature of this problem

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27 The Resilient City: Defining what San Francisco needs from its seismic mitigation policies

28 SPUR s Disaster Planning Initiative > Hazard Mitigation Hazard Mitigation Task Force > Emergency Preparedness > Rebuilding

29 Hazard Mitigation Task Force > Overarching Framework > Existing Buildings > New Buildings > Lifelines 120,000 existing buildings ¼ could be damaged beyond repair in expected earthquake Existing Buildings New Buildings Lifelines Overarching paper

30 Simple and direct approach: > Define resilience in the context of disaster planning and recovery > Establish performance goals for the expected earthquake that supports our definition of resilience > Define transparent performance measures that help us reach our performance goals > Suggest next steps for new buildings, existing buildings, and lifelines

31 What is seismic resilience? Seismic resilience is the ability of the city to > contain the effects of earthquakes > carry out recovery activities in ways that minimize social disruption > rebuild in ways that mitigate the effects of future earthquakes.

32 Performance goals for the expected earthquake Phase Time Frame Condition of the built environment I 1 to few days Initial response and staging for reconstruction II few to 30 days Workforce housing restored ongoing social needs met III Several years Long-term reconstruction

33 Transparent Performance Measures for Buildings Category Category A Category B Category C Category D Category E Performance Standard Safe and operational: Essential facilities such as hospitals and emergency operations centers Safe and usable during repair: shelter-inplace residential buildings and buildings needed for emergency operations Safe and usable after repair: current minimum design standard for new, non-essential buildings Safe but not repairable: low end of acceptability for new, non-essential, buildings. Unsafe: damage that will lead to significant casualties in the expected earthquake

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36 What are the next steps? > Existing buildings > New buildings > Lifelines

37 Define the unique attributes of your existing building stock > For San Francisco. Prevalence of soft-story, multi-unit buildings and house-over-garage conditions. Non-ductile concrete frame buildings probably house every critical occupancy. Need more complete inventory..

38 Target time to recovery Compliant unreinforced masonry Soft-story wood frame Non-ductile concrete frame Unbraced cripple wall Rigid wall-flexible diaphragm Pre-Northridge steel systems Steel or concrete frame w/ URM infill Major falling hazards (chimneys, cladding) Vulnerable gas lines and gas-fired equipment Vulnerable nonstructural components What are your building occupancies? VULNERABLE CONDITION SERVICE/OCCUPANCY First responders Medical services Singe-family residences Multi-family residences Emergency shelters Essential city services Schools Social services Retail Businesses 4 hrs 12 hrs 24 hrs 24 hrs 24 hrs 3 days 30 days 30 days 30 days 4 mos Critical: The vulnerability is prevalent for the occupancy and is likely to hamper response and recovery. Potentially critical: The vulnerability is unknown but could be prevalent enough to hamper response and recovery. Possibly critical: The vulnerability is common for the occupancy and could affect response and recovery. Not critical: The vulnerability is not typically associated with the occupancy or critical to its response and recovery.

39 Policies for achieving resilience > Existing Buildings - A balance of voluntary, triggered, encouraged with incentives, and mandatory requirements > New Buildings - Add transparency, almost free > Lifelines Community developed program based on new national standards and incentives

40 Policies for Existing Buildings > Recommended for San Francisco. Mandated retrofit of soft-story woodframe multi-family housing Mandated retrofit or redundancy for designated shelters Mitigation program for essential city services Inventory of pre-1980 concrete structures of all occupancies. Retrofit of gas lines and gas-fired equipment Assessment of the unreinforced masonry program

41 Paying for mitigation > In general, whoever owns the risk and benefits from mitigation should pay for it. > but why should the owner have to bear the cost if the object is to improve resilience of the city? > Clearly, the city should bear some portion of the mitigation cost.

42 100 years of planning and still not ready > Seismic risk is clearly understood > Building codes protect lives and can do more > Dangerous buildings can be rehabilitated > Major lifelines are being rehabilitated but more consistent regional strategies are needed > Need for resilience is being discussed