MITIGATION OF LATERAL SPREADING EFFECTS ON BRIDGES

Transcription

1 MITIGATION OF LATERAL SPREADING EFFECTS ON BRIDGES Professor Ross W. Boulanger Arash Khosravifar, Graduate Student Researcher Thang Nguyen, Graduate Student Researcher PEER TransportaHon Systems Research Program (TSRP) August 11, 2010

2 Title: MiHgaHon of Lateral Spreading Effects on Bridges Consider an exishng ordinary bridge: 1. Assess the potenhal of liquefachon and lateral spreading 2. If needs to fix: I. Add more piles II. Use large diameter extended pile shavs Arash s work III. Use ground improvement techniques, like DSM shear box wall Thang s work IV. Decision making

3 InelasHc Response of Large Diameter Extended Pile ShaVs in Laterally Spreading Ground during Earthquakes

4 Statement of Problem Large diameter extended pile shavs (2 to 3 m) can be an effechve choice in areas of potenhal lateral spreading. How to design for effects of shaking and lateral spreading? Loose Sand Dense/SHff Soil

5 Research Approach 1. Nonlinear Dynamic FE Analyses (NDA) 3. Evaluate Current Caltrans Equivalent StaHc Analysis (ESA) 4. Develop an Improved Guidance

6 Nonlinear Dynamic FE CG 1. OpenSees FE framework 2. Soil elements (far field) ConsHtuHve models (MYPD and 10m 2m RC shav MYPI) 2Dim Up elements 3. Pile elements Fiber sechons Flexibility based nonlinear beam column elements 4. Soil springs PY and PYLiq 5m 3m 12m SHff Clay S u = various Loose Sand (N 1 ) 60 = 5 Dense Sand (N 1 ) 60 = 35 PySimple TzSimple PyLiq TzLiq PyLiq TzLiq... every 0.5 m TZ and TZLiq... QZ α=0.1 TzLiq PyLiq QzSimple

7 Ground MoHons 40 ground mohons from Professor J. Baker They were selected so that their response spectra match the median and log standard deviahons predicted from Boore and Atkinson (2008) model: (from J. Baker, Stanford U.) Magnitude = 7 earthquake Source to site distance = 10 km Site Vs30 = 760 m/s Earthquake mechanism = strike slip

8 Results

9 Results

10 Conclusions: Dynamic FE analyses show that: coupling of inerhal and kinemahc demands during lateral spreading can be the governing load case, and that is not enveloped by analyzing the inerhal and kinemahc loading cases separately. Caltrans DRAFT ESA criteria: The ESA undereshmate the peak displacement and duchlity demands, The criterion for M LS being less than 20% M p did not correlate well with either good or poor performance.

11 Conclusions (Cont d) DraV proposed ESA includes: 1. Analyze the non liquefachon case. 2. Analyze the liquefachon case by: i. Removing springs from liquefied and crust layers, ii. Applying full passive earth pressure from the crust, iii. Imposing an addihonal superstructure displacement Δ 2 = C ΔL Δ NL, where Δ NL is the demand predicted in the absence of liquefachon. Currently, we use C ΔL =1.0 based on the NDA results. iv. AdjusHng the predicted deck displacement if significant shear strains are eshmated to occur in the underlying dense/shff soils. The proposed ESA appears to work equally well for structures that do not yield (μ φ 1) and do yield (1 μ φ 3.5). We are currently performing a broader set of parametric analyses, which may lead to revisions in the ESA procedures.

12 Results

13 Ground Improvement Methods: Cement mix shear box

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15 Next Tasks: 1. 3D vs. 2D simulahon using OpenSeesPL How much do the results change? Do the findings change? What are the important factors/parameters? 2. Decision Making Compare the efficiency and cost of different mihgahon techniques Extended pile shav vs. pile group Extended pile shav vs. ground improvement

16 AnimaHon Nonlinear Dynamic Analysis (NDA)

17 Thank you Any queshon?

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19 EQUIVALENT STATIC ANALYSIS (ESA): CALTRANS DRAFT GUIDANCE

20 ESA Caltrans DraV Steps include: 1. Pushover analysis without liquefachon Use non liquefied and t z springs V CG 2. Pushover analysis with liquefachon (no LS) Use liquefied springs (p mul2pliers) crust Loose sand 3. Apply lateral spreading (LS) force alone Check that M LS < 0.20 M p Dense sand Tz Qz

21 ESA Deck Displacement Demand w/o LiquefacHon (Example) ElasHc period T e (non liq) = 3.2 sec ground surface for outcrop PGA=0.6g 10 (Non liquefied) For 0.6 g at rock outcrop PSa = 0.11 g Δ e = PSa/ω 2 = 0.28 m Use R μ T relahonships High T e equal displacement Δ e p = 0.28 m PSa (g) Period (sec) 3.2

22 ESA Caltrans DraV Steps include: 1. Pushover analysis without liquefachon Use non liquefied and t z springs V CG 2. Pushover analysis with liquefachon (no LS) Use liquefied springs (p mul2pliers) crust P mulhplier Loose sand 3. Apply lateral spreading (LS) force alone Check that M LS < 0.20 Mp Dense sand Tz Qz

23 ESA Caltrans DraV Steps include: 1. Pushover analysis without liquefachon Use non liquefied and t z springs CG Moment 2. Pushover analysis with liquefachon (no LS) Use liquefied springs (p mul2pliers) crust P mulhplier Loose sand LSF M LS <0.20M p 3. Apply lateral spreading (LS) force alone Dense sand Check that M LS < 0.20 Mp Tz Qz

24 ESA Caltrans vs. FE Nonlinear Dynamic Analysis ρ s = 4%, Axial P = 10% A g.f c μ φ 1 (low duchlity) max Deck Disp (m) max Curvature (1/m) Crust S u = 80 kpa Crust Su= 80 kpa PGA (g) PGA (g) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Mpd=0.20*Mp (0.73 m) P Δ criterion 1% driw (0.18 m) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) (capacity) (allowable: 3.5 duc2lity) (yielding)

25 ESA Caltrans vs. FE Nonlinear Dynamic Analysis ρ s = 4%, Axial P = 10% A g.f c μ φ 1 (low duchlity) max Deck Disp (m) max Curvature (1/m) Crust S u = 80 kpa Crust S PGA (g) u = 80 kpa PGA (g) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Mpd=0.20*Mp (0.73 m) P Δ criterion 1% driw (0.18 m) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) (capacity) (allowable: 3.5 duc2lity) (yielding)

26 ESA Caltrans vs. FE Nonlinear Dynamic Analysis ρ s = 4%, Axial P = 10% A g.f c μ φ 1 (low duchlity) max Deck Disp (m) max Curvature (1/m) Crust S u = 80 kpa Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Crust S u = 80 kpa Equiv. Sta2c (liq case) Crust S PGA (g) u = 80 kpa Mpd=0.20*Mp (0.73 m) % driw (0.18 m) 8000 Dynamic Analysis (wliq_wss) 4000 Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) (capacity) Lateral Spreading case (allowable: 3.5 duc2lity) 20% of Mp (10400 kn m) (yielding) PGA (g) max Moment (kn m)

27 EQUIVALENT STATIC ANALYSIS (ESA): DRAFT PROPOSED GUIDANCE

28 ESA DraV Proposed Guidance Steps include: V 1. Analyze for non liquefachon case CG Use non liquefied and t z springs 2. Analyze the liquefachon case i. removing springs from liquefied and crust layers and applying full passive earth crust ii. pressure from the crust Imposing an addi2onal superstructure Loose sand displacement Δ 2 =C ΔL Δ NL, where Δ NL is the Dense sand demand predicted in the absence of liquefac2on. Currently, we use C ΔL =1.0 based on the NDA results. Tz Qz

29 ESA DraV Proposed Guidance Steps include: Δ 1 1. Analyze for non liquefachon case CG Use non liquefied and t z springs 2. Analyze the liquefachon case Crust passive pressure i. removing springs from liquefied and crust layers and applying full passive earth crust ii. pressure from the crust Imposing an addi2onal superstructure Loose sand displacement Δ 2 =C ΔL Δ NL, where Δ NL is the Dense sand demand predicted in the absence of liquefac2on. Currently, we use C ΔL =1.0 based on the NDA results. Tz Qz

30 ESA DraV Proposed Guidance Steps include: 1. Analyze for non liquefachon case V Δ 1 CG Δ 2 Use non liquefied and t z springs 2. Analyze the liquefachon case Crust passive pressure i. removing springs from liquefied and crust layers and applying full passive earth crust ii. pressure from the crust Imposing an addi2onal superstructure Loose sand displacement Δ 2 =C ΔL Δ NL, where Δ NL is the Dense sand demand predicted in the absence of liquefac2on. Currently, we use C ΔL =1.0 based on the NDA results. Tz Qz

31 ESA DraV Proposed (Example) i. Applying full passive earth pressure from the crust (Crust S u = 80 kpa) Δ 1 =0.06 m CG Moment V (kn) 2750 kn kn.m Δ 1 =0.06 m Δ deck Tz Qz

32 ESA DraV Proposed (Example) ii. Imposing an addihonal superstructure displacement Δ 1 =0.06 m V CG Δ 2 Moment V (kn) kn Δ 1 =0.06 m 1 m Δ deck Tz Qz

33 ESA DraV Proposed (Example) AddiHonal Disp: V (kn) Δ 2 = C ΔL Δ NL = 1.0(0.28 m)= 0.28 m 1600 Global Disp demand: Δ 1 + Δ 2 = 0.34 m Δ 1 =0.06 m Δ 2 =0.28 m 1 m Δ deck From pushover analysis: Local curvature demand = (1/m) 0.1 Curvature (1/m) m Δ deck

34 ESA DraV Proposed Adjust displacement for dense sand layer shear strain V 0.34 m CG crust Loose sand Dense sand Tz Qz

35 ESA DraV Proposed Adjust displacement for dense sand layer shear strain 0.36 m For 0.6 g shake: Avg. γ = 1.2% L = 30 m γ L = 0.36 m V 0.34 m CG crust Loose sand Dense sand Tz Qz

36 ESA DraV Proposed results max Deck Disp (m) ρ s = 4%, Axial P = 10% Crust S u = 80 kpa max Curvature (1/m) Crust S u = 80 kpa PGA (g) Crust S u = 80 kpa PGA (g) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Proposed ESA Mpd=0.20*Mp (0.73 m) P Δ criterion 1% driw (0.18 m) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Proposed ESA (capacity) (allowable: 3.5 duc2lity) (yielding)

37 ESA DraV Proposed results max Deck Disp (m) ρ s = 4%, Axial P = 10% Crust S u = 80 kpa PGA (g) Crust S u = 80 kpa 0.2 max Curvature (1/m) Crust S u = 80 kpa Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Proposed ESA Mpd=0.20*Mp (0.73 m) P Δ criterion 1% driw (0.18 m) PGA (g) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Proposed ESA (capacity) (allowable: 3.5 duc2lity) (yielding)

38 ESA DraV Proposed results max Deck Disp (m) ρ s = 4%, Axial P = 10% Crust S u = 80 kpa Crust S u = 80 kpa PGA (g) max Curvature (1/m) Dynamic Analysis (wliq_wss) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Proposed ESA P Δ criteria Crust S u = 80 kpa Caltrans 3 rd step max Moment (kn m) Mpd=0.20*Mp (0.73 m) 1% driw (0.18 m) Crust S u = 80 kpa Dynamic Analysis (wliq_wss) Lateral Spreading case 20% of Mp (10400 kn m) Equiv. Sta2c (no liq case) Equiv. Sta2c (liq case) Proposed ESA (capacity) (allowable: 3.5 duc2lity) PGA (g) (yielding)