Damage Observations in an Industrial Plant Affected by the Sichuan-China Earthquake

Transcription

1 Seismic Design Risk Assessment Structural Dynamics Yaron Offir Engineers LTD Damage Observations in an Industrial Plant Affected by the Sichuan-China Earthquake By Yaron Offir Engineers LTD Emad Nsieri (M.Sc) Yaron Offir (M.Sc) Daniel Dubois (B.Sc) מרכז קונגרסים אווניו, קריית שדה התעופה

2 Outline Earthquake Details, Damages and Casualties Seismic Activity Recorded Ground Motions and Response Spectrum Observations of Structural and Non-Structural Damages in a Chemical Plant Conclusions and Recommendations 2

3 Earthquake Details Epicenter Location Epicenter at Wenchuan County Epicenter CHINA N N 3

4 Earthquake Details Date-Time 12/05/2008 at 14:28 Region Eastern Sichuan Province, China Epicenter Wenchuan County Magnitude M w = 7.9 Intensity XI in Wenchuan area Focal Depth 20 km Fault Longmen Shan fault Fault rupture 300 km Distances 90 km N-W of Chengdu 545 km S-W of Beijing Map of Main Faults Sichuan Province Aftershocks 235 Aftershocks greater than 4.0 M w Affected area ~450,000 km 2 4

5 Damage and Casualties Damage Chemical plants: Heavy damages caused extensive shutdowns Buildings: 24 million damaged, destroyed including 7,000 school buildings Bridges: 4840 totally or partly damaged Roads and railways: ~50,000 km damaged Tunnels: 98 totally or partly damaged Landslides: 10 million m 3 of slide materials, and falling rocks Surface rupture: Vertical displacement of at several locations Death ~90,000 Injured ~375,000 Homeless people Economic loss ~5.0 million billion USD$ 5

6 Seismic Activity Past earthquakes Sichuan Province Destructive earthquakes within the past century close to Sichuan Province (Agha et al., 2008, 14WCEE) 6

7 Strong Ground Motion Records (Xiaojun et al. 2008, 14WCEE) N 7

8 Strong Ground Motion Records Wolong station, 19 km from epicenter (Xiaojun et al. 2008, 14WCEE) PGA=0.97g PGA=0.67g Two main shocks!! PGA=0.97g very high! 8

9 Strong Ground Motion Records Wolong station, 19 km from epicenter (Xiaojun et al. 2008, 14WCEE) PGA=0.97g PGA=0.67g Sa=3.0g!! PGA=0.97g very high! 9

10 Strong Ground Motion Records Qingping station, 88 km from epicenter (Xiaojun et al. 2008, 14WCEE) PGA=0.84g PGA=0.82g PGA=0.64g 10

11 Seismic Zoning Map in China (GB ) PGA=0.20g for return period of 475 years N 11

12 Response Spectrum and Chinese code Spectral acceleration (g) Wolong station in Wenchuan during the main shock of 12 May % damping (Intensity XI) East-West component North-South component Vertical component Chinese Seismic Code 1989, years, 5% damping, Intensity VII Design spectrum substantially underestimated spectral acceleration (base shear strength) Fundamental period (seconds) 12

13 Response spectrum from site specific study in Israel vs. Israeli code IS 413 (5% damping and return period 475 years) New design spectrum substantially underestimating spectral acceleration at short periods!!! 13

14 Damage Observations: Chemical Plant Hundreds of people have been buried under two chemical plants collapsed in Shifang (Deyang prefecture) and more than 80 tons of ammonia have spread into the environment (source: Chinese Government News Agency Xinhua). Facility damages caused extensive shutdowns and business interruption. Location: Shifang town, Deyang ~150 km from epicenter ~60 km fault rupture Damage: 1. Structures 2. Piping Systems and Tanks 14

15 15 Damage Observations: Structures

16 Response Spectrum and Structure Response Assumption: Stiff structures with low fundamental periods were highly vulnerable to this earthquake due to the high seismic force demands 16

17 Damage Observations: Stiff Structures Poor seismic performance Destruction of low rise masonry infilled frame RC buildings Out-of-plane failure of masonry infill walls In-plane failure of masonry infill walls 17

18 Damage Observations: Stiff Structures Structures with poor seismic performance 0<T <0.5 Members at stiff structures collapsed/experienced severe damage during the earthquake event 18

19 Damage Observations: Prefabricated Structures Collapse of prefabricated structure with pre-cast elements Inadequate connection between pre-cast beams and supporting columns led to very low seismic resistance 19

20 Damage Observations: Residential Buildings Catastrophic collapse of pre-cast hollow core plank floors and roofs widely used in school and residential buildings due to low cost, simple and rapid construction. Poor seismic performance Poor connection between floor/roof slab and supporting beam 20

21 Damage Observations: Existing Construction Details Pebble aggregate used in columns (poor inspection): low compression and shear strength Column ties: smooth bars, wide spacing (30-40cm), insufficient endhooks (unconfined concrete section) Rebars: buckling, tearing 21

22 Spectral acceleration (g) Damage Observations: Poor Constructions Details and High Seismic Demands Poor construction details Non-ductile behavior Low quality of construction material Low strength Poor seismic performance Strong ground motions 22 High seismic force demands Fundamental vibration period (seconds)

23 Evaluation of ductility seismic demand SDOF structure 23

24 Evaluation of ductility seismic demand T=2 (M/Keff)=0.3 sec., Sa=2.6 md R=Sa/(Vy/Wt)=7.0 (high ductility demand) Cross Section Yield of column ties Ductility Capacity md=1.0 (brittle) md=6.0 (ductile) 24

25 Damage Observations: Flexible Structures Structures with good seismic performance 25

26 Damage Observations: Flexible structures Structures with good seismic performance 0.5<T <1.0 Flexible RC frame structure remained intact 26

27 Damage Observations: Piping Systems and Tanks 27

28 Damage Observations: Piping Systems RC structure collapsed on ammonia tanks: damage mainly to pipelines and release of 80 tons of ammonia 28

29 Damage Observations: Piping Systems Pipeline damages due to stiff connection supports No damage Pipeline fractured 29

30 Damage Observations: Piping Systems Pipeline damages due to large relative displacement between pipeline ends 30

31 ALA (2002): seismic design and retrofit of piping systems Piping systems need to be designed for two effects: 1. Inertia forces 2. Relative displacements between supports 31

32 Damage Observations: Unanchored Tanks Poor Performance Sliding of ammonia tank from its support 32

33 Damage Observations: Tanks Poor Performance Pipe rupture due to large displacement Low quality of construction material: concrete floor crushed due to rocking of tank 33

34 Damage Observations: Spherical Tanks Poor Performance Braced sphere tank: non-ductile seismic response of steel tie-rods (buckling and tension failure) 34

35 Proposed Seismic Upgrading Measures Existing Sphere Seismic Upgrading of Sphere by Installing Viscous Dampers 35

36 Conclusions and Recommendations Observed large scale destruction of industrial plant caused casualties, high financial loss and extensive shutdowns. Follows are actions to significantly reduce public risk and financial loss from the damaging effects of a potential earthquake: Increase awareness of earthquake risks Identify seismic hazard (site specific study) Identify problematic structures in industrial plants lacking seismic resistance and defining their seismic failure modes Provide effective and practical retrofitting techniques and develop cost-effective retrofit program 36 Implementation of retrofitting techniques

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