Tarea

Seismic Vulnerability of Bridges Susceptible to Spatially Distributed Soil Liquefaction Hazards


Authors:

Bayram Aygün, Rice University, Houston, TX, ba2@rice.edu
Leonardo Dueñas-Osorio, Rice University, Houston, TX, leonardo.duenas-osorio@rice.edu
Jamie E. Padgett, Rice University, Houston, TX, Jamie.Padgett@rice.edu
Reginald DesRoches, Georgia Institute of Technology, Atlanta, GA,reginald.desroches@ce.gatech.edu


ABSTRACT:

Among the multiple highway structures such as box culverts, chambers, retaining walls and bridges, the latter are among the most critical components of modern transportation networks. Although these networks provide the foundation for vibrant economies, a lack of understanding persists about the role that individual bridges play in networkperformance when subjected to unforeseen natural hazards. This paper concentrates on bridge-soil system analyses and probabilistically investigates the complex behavior of multi-span continuous steel bridges (MSCS) typical of the central-eastern U.S. (CEUS) when exposed to earthquake-induced soil liquefaction. MSCS bridges are among the most vulnerable bridge classes owing to their bearing and abutmentinability to accommodate excessive demands. Due to the large mass and relatively small bearing stiffnesses at the abutments, this bridge type experiences the largest deck displacements of all bridge types common to central-eastern U.S. Sophisticated bridge models developed in OpenSees -the computational platform of the Pacific Earthquake Engineering Research Center (PEER)- are coupled with liquefiablesoil models. To account for the effects of soil-pile interaction on bridge response, nonlinear P-y springs sensitive to excess pore water pressure are embedded in the models. Uncertainties in bridge response propagating from soil liquefaction to structural performance of bridge systems are synthesized as parametric fragility functions. The developed fragility curves for complete damage showconsiderable amplifications on vulnerability of rocker bearings and piles. Moreover, depending on the soil profile, liquefaction decreases the fragility of bridge columns. These vulnerability assessments result in more accurate regional prioritization and maintenance programs that are useful to U.S. departments of transportation and related infrastructure agencies.

Introduction

UNCERTAINTYTREATMENT IS A CENTRAL COMPONENT IN STRUCTURAL DESIGN AND RESPONSE EVALUATION METHODS. FOR THE STRUCTURAL RESPONSE EVALUATION OF A SIMPLE REINFORCED CONCRETE FRAME BUILDING OR A COMPLEX TRANSPORTATION NETWORK, A PROBABILISTIC APPROACH IS NECESSARY FOR THE ANALYST TO EXPLICITLY ACCOUNT FOR UNCERTAINTIES OF SYSTEM DESIGN AND OPERATION PARAMETERS. HOWEVER, IT IS PECULIAR THAT MANY BRIDGE VULNERABILITYANALYSES IN THE LITERATURE HAVE BEEN CONDUCTED WITHOUT ANY SIGNIFICANT CONSIDERATION OF UNCERTAINTY CHARACTERIZATION OF THE SUBSTRUCTURE. A DETAILED STATISTICAL DESCRIPTION OF THE UNDERLYING SOIL AND THE BRIDGE PILES IS NECESSARY FOR ADEQUATE UNCERTAINTY TREATMENT IN BRIDGE SYSTEMS.
Previous studies either focused on the superstructure neglecting the soil underlying it or they concentrated on thesubstructure representing the complex superstructure in a simplistic way. Boulanger et al. (1999) studied the seismic soil-pile-structure interaction via dynamic P-y analysis where they represented the superstructure as a lumped mass. Zhang et al. (2004) investigated the behavior of a 330 meter long, 9-span composite structure with four precast, prestressed concrete I-girders and cast-in-placeconcrete slabs underlain by liquefiable soil in a probabilistic framework where they neglected friction effects between soil and piles and gapping between soil and piles near the ground surface for the sake of simplicity. Nielson (2005) did a comprehensive fragility analysis on the bridge inventory of CEUS where the bridge foundations were modeled as simplified springs. Dueñas-Osorio and DesRoches...