COLLAPSE ASSESSMENT OF RC BRIDGES CONSIDERING SOIL STRUCTURE INTERACTION_REW 1.pptx

Seismic response of bridges

1. COLLAPSE ASSESSMENT OF RC BRIDGES CONSIDERING SOIL STRUCTURE INTERACTION (SSI) K. Ashkani Zadeh 1 , C. Ventura 2 , L. Finn 3 1 Research Associate, Dept. of Civil Engineering, The University of British Columbia 2 Professor, Dept. of Civil Engineering, The University of British Columbia 3 Emiritus Professor, Dept. of Civil Engineering, The University of British Columbia September 27 to October 2 , 2019

2. Outline Introduction Proposed “Simplified Bridge Seismic Performance Evaluation Procedure” (SBSPEP) General Workflow The Methodology Features Technical Skills and Competencies Requirement Case Study: Collapse Assessment of The Meloland Road Overcrossing (MRO) Developed MRO Nonlinear Models Calculating Curves and Parameters Evaluation Seismic Performance of The MRO Concluding Remarks 2

3. Introduction Motivation Lack of understanding nonlinear response and consideration of the effect of Soil-Structure Interaction (SSI) has resulted in unsafe design which has led to collapse of many bridges worldwide Lack of practical procedures and guidelines in the code provisions to assist engineers performing collapse assessment of the bridge structures. Main Goal Proposing a simplified procedure for performance evaluation of the bridge structures Approach Adopting performance-based earthquake engineering approach in seismic Hazard Analysis, Structural Analysis, and Damage Assessment Considering ground motions’ spectral shape effects and total system collapse uncertainty Using simulated and non-simulated collapse modes in simulation of collapse Performing collapse assessment of Meloland Road Overcrossing (MRO) as a case study 3

4. Proposed Simplified Bridge Seismic Performance Evaluation Procedure (SBSPEP) - General Workflow

5. The Methodology Features 5 The methodology is: Proposed for seismic assessment of bridges using analytical and statistical approaches within a performance-based seismic design framework. Applicable to both design or retrofit of existing RC bridge structures and can be used in discrete or continuum approaches. Allowing consideration of an acceptable probability of collapse (P acceptable ) Accounting for ground motion characteristics and various aspects of data and modeling uncertainties. Able to incorporate SSI effects when needed. Sensitive to level of detail and fidelity of the models employed and highly dependent on the assumed value of total system uncertainty.

6. MRO Case Study: Developed MRO Nonlinear Models 6 A schematic view of developed models: (a) Viscoelastic embankments and center bent, (b) and (c) Elastic support at embankments and center bent, (d) Pile support at abutments and bent (a) Zhang and Makris, 2002 (b) Douglas, Maragakis and Vrontinos, 1991 (c) Caltrans Method A, 1989 FFM: Free Field Motions FFM FFM D 1 Model D 2 Model D 3 Model FFM FFM FFM FFM FFM FFM (d) Ashkani et al., 2020 D 4 Model

7. MRO Case Study: Calculating Collapse Margin Ratio (CMR) 7 Task 1: Selecting a sufficient number of ground motions Task 2: Performing IDA analyses and calculating the IDA curves Task 3: Calculating the Collapse Fragility Curve (CFC) Task 4: Determining the Maximum Considered Earthquake (MCE) based on the relevant soil site class and Calculating Collapse Margin Ratio (CMR)

8. MRO Case Study: Calculating the Collapse Fragility Curve (CFC) 8 D 4 Model FFM D 1 Model FFM FFM For a given spectral acceleration, the probability of collapse is higher for model D 4 For a given probability of collapse, the spectral acceleration associated with model D 4 is smaller compared to D 1 , resulting in a lower CMR value for D 4

9. MRO Case Study: Calculating Adjusted Collapse Margin Ratio (ACMR) 9 Estimated β and β 1 coefficients for the model D 4 where, is the expected or target value for the site and hazard-level of interest obtained by seismic deaggregation. is the mean epsilon value of the Far-Field ground motion set, evaluated at period.

10. MRO Case Study: Total System Collapse Uncertainty (𝛽 TOT ) 10 Proposed total system collapse uncertainty (𝛽 TOT ) based on quality of model and design for the period-based ductility, (FEMA P695, 2009) Quality of Test Data Quality of Design Requirements (A) Superior (B) Good (C) Fair (D) Poor (A) Superior 0.425 0.475 0.550 0.650 (B) Good 0.475 0.500 0.575 0.675 (C) Fair 0.550 0.575 0.650 0.725 (D) Poor 0.650 0.675 0.725 0.825 Relationship between total uncertainty of the system ( β TOT ) and acceptable collapse margin ration (CMR acceptable )

11. MRO Case Study: Calculating ACMR acceptable 11 Fragility curves: (a) reflects record-to-record collapse uncertainty ( β RTR ) or (b) reflects total system collapse uncertainty ( β TOT ), which is square root of record-to-record, design requirements-related, test data-related, and modeling-related collapse uncertainty.   P Collapse Sa (T 1 ) [g] 0.5 1 (a) (b) 1 2 3 4 5

12. MRO Case Study: Evaluation Seismic Performance 12 T he bridge model does not satisfy the performance requirements of the proposed methodology! Index Archetype Model     SSF     ACMR Aceptable Probability of Collapse ACMR acceptable Ratio ACMR acceptable Ratio D 1 1.33 1.04 0.95 1.10(Y) 0.86 1.21(Y) D 2 1.35 1.04 0.96 1.08(Y) 0.87 1.19(Y) D 3 1.38 1.04 1.00 1.04(Y) 0.90 1.16(Y) D 4 1.22 0.81 0.98 0.83(N) 0.89 0.92(N) Average 1.32 0.98 0.97 1.01(Y) 0.88 1.12(Y) Note Green : Methodology requirement is fulfilled Red : Methodology requirement is NOT fulfilled To achieve acceptable performance, the following two criteria need to be satisfied: The average value of adjusted collapse margin ratio for each performance group exceeds ACMR 10% Individual values of adjusted collapse margin ratio for each index archetype model (ACMR i ) within a performance group exceeds ACMR 20% (ACMRi ≥ ACMR 20% )

13. Concluding Remarks A FEMA-based methodology is proposed for seismic assessment of bridges using performance-based seismic design approach. The methodology was based on the comparison of the calculated value of the ACMR for each model with its corresponding acceptable value. The proposed evaluation procedure is applicable to both design or retrofit of existing RC bridge structures and can be used in discrete or continuum approaches The methodology allows for consideration of an acceptable probability of collapse (Pacceptable) The methodology accounts for the ground motion spectral shape effects and total system collapse uncertainty To achieve a better understanding of the structure’s performance, it’s best to choose a set of models to cover the modelling uncertainty. The MRO was used as a case study to demonstrate the workflow of the proposed methodology. 13

14. Thank You! Questions? 14