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Effect of Load Path and Failure Modes on Seismic Response of Regular Bridges.
Title
Effect of Load Path and Failure Modes on Seismic Response of Regular Bridges.
Creator
Darwash, Haider, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Bai, Yuanli, University of Central Florida
Abstract / Description
Bridges are essential infrastructure constituents that have been studied for centuries. Typically,seismic bridge design and assessment utilize simplified modeling and analysis techniques basedon one-dimensional spine elements and zero-length springs/hinges. The geometry of the elementsand calibration of parameters are based on assumptions for the lateral load path and failure modes,e.g., sacrificial backwall and shear keys, neglecting wing walls, and strength based on backfillalone. These...
Show moreBridges are essential infrastructure constituents that have been studied for centuries. Typically,seismic bridge design and assessment utilize simplified modeling and analysis techniques basedon one-dimensional spine elements and zero-length springs/hinges. The geometry of the elementsand calibration of parameters are based on assumptions for the lateral load path and failure modes,e.g., sacrificial backwall and shear keys, neglecting wing walls, and strength based on backfillalone. These assumptions have led to observations of underestimated resistance, overestimateddisplacement demands, and unpredicted damage and failure mode. The focus of the study is onordinary standard bridges with continuous reinforced concrete box girder superstructures and seattypeabutments.A bridge component calibration study was conducted first using simplified (spine models with 1Delements and springs) and three-dimensional nonlinear continuum finite element models (FEM).Model responses were compared with experimental results to identify the drawbacks in the simplifiedmodels and verify the adequacy of the material nonlinearities and analysis procedures. Thecomponents include a T-girder, abutment backfill, abutment shear key, elastomeric bearing pad,and a bridge pier. Results show the simplified models do not capture damage propagation andfailure mode in the shear key case, nonlinear behaviors in beams with high aspect ratios (or deepbeam action), and underestimate the strength and overestimate the stiffness for the backfill case.The component models (both simplified and continuum) were then used in studying the nonlinearstatic behaviors of key bridge lateral-load resisting substructures, namely abutments and bents.For the abutment subsystem, cases with and without backfill and several back wall constructionjoint configurations for the longitudinal direction, with monolithic shear key and shear key withconstruction joint for the transverse direction, and boundary conditions in the transverse direction were considered. Abutment subsystem results showed simplified models underestimate the resistanceby 10-60%, neglect back wall and wing wall structural contributions, and localize damagein the back fill relative to the continuum models. For the bent subsystem, a full bridge systemthat considers material nonlinearity and damage in the bent segment only was adopted to determinethe effect of the finite bent cap or superstructure-to-column connection. Inelastic behaviorand damage was included in the columns, bent cap, and a superstructure segment with a lengththat correspond to the dead load moment inflection point. The other superstructure segments andthe pile cap were modeled as elastic. Bent subsystem results showed simplified models overestimatethe stiffness, induce excessive flexibility and deformation in the cap beam, and overestimatecolumns' deformations.Due to the differences observed in the abutment subsystem, and the potential impact of the abutmentbehavior on the seismic response of the whole bridge system, dynamic studies on the bridgesystem were conducted using four abutment parameters: abutment stiffness and strength in eachof the longitudinal and transverse directions. Two models were developed to conduct nonlineartime history analysis: an equivalent single-degree-of-freedom (SDOF) model for each of the longitudinaland transverse directions, and a 3D spine bridge model. Constant ductility analyses wereconducted using the SDOF systems, while standard probabilistic seismic demand analysis wasused on the spine systems.Results revealed that, besides the columns yielding, the abutment has an early and significant contributionto the behavior. The SDOF system results showed that increasing the abutment stiffnessor strength reduces the system displacement demand and increases the system forces. The consequenceof such increase in the forces is mobilizing significant amount of force in the abutments,causing inelastic response. The full bridge study also confirmed the SDOF results and showedthat the abutment forces are more than 200% of the columns forces that would result in the sameaftereffect observed in the SDOF system.
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Date Issued
2017
Identifier
CFE0006869, ucf:51759
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006869