Design of Reinforced Concrete Bridge Columns for Near-Fault Earthquakes

Report No. CCEER-13-13Bridges are key components in the transportation network providing access for emergency response vehicles following major earthquakes. The strong and long period velocity pulse in the fault-normal component of near-fault ground motions exposes structures in near-fault regions to high input energy that could result in high residual displacements in bridge columns. The residual displacement in bridges plays a key role in assessing whether a bridge should be kept open to traffic or closed for repair or replacement. Currently there are no reliable provisions to account for residual displacements caused by near-fault earthquakes in design of reinforced concrete bridge columns. The main objective of the study was to develop a new guideline for the design of reinforced concrete bridge columns subjected to near-fault earthquakes. The goal of the study was achieved through the following tasks: (1) determine the adequacy of existing computer models to estimate residual displacements by comparing the results of the experimental data for six large-scale reinforced concrete bridge columns to those of nonlinear dynamic analyses, (2) determine the residual moment capacity of reinforced concrete columns as a function of maximum displacement ductility, (3) determine critical residual displacement limit with respect to structural performance, (4) develop a simple method to estimate residual displacement, (5) develop residual displacement spectra for different displacement ductilities, soil conditions, and earthquake characteristics, (6) develop a step-by-step design guideline to control the residual drift ratio utilizing the simple method or residual drift spectra with an illustrative example, and (7) evaluate the impact of the proposed design guidelines in terms of cost by redesigning several representative bridges from different parts of the United States. The analysis of residual drift ratio limits indicated that circular bridge columns meeting current seismic codes are able to carry large traffic loads even when the permanent lateral drift is 1.2% or higher, depending on the column strength and geometry. It was found that residual drift ratio is negligible (less than 1%) when one-second spectral acceleration is less than 0.4g. Also, utilizing the proposed design method to control residual drift ratio has negligible effect on the overall cost of the bridge

Parametric study of seismic performance of super-elastic shape memory alloy-reinforced bridge piers

One of the important measures of post-earthquake functionality of bridges after a major earthquake is residual displacement. In many recent major earthquakes, large residual displacements resulted in demolition of bridge piers due to the loss of functionality. Replacing the conventional longitudinal steel reinforcement in the plastic hinge regions of bridge piers with super-elastic shape memory alloy (SMA) could significantly reduce residual deformations. In this study, numerical investigations on the performance of SMA-reinforced concrete (RC) bridge bents to monotonic and seismic loadings are presented. Incremental dynamic analyses are conducted to compare the response of SMA RC bents with steel RC bents considering the peak and the residual deformations after seismic events. Numerical study on multiple prototype bridge bents with single and multiple piers reinforced with super-elastic SMA or conventional steel bars in plastic hinge regions is conducted. Effects of replacement of the steel rebar by SMA rebar on the performance of the bridge bents are studied. This paper presents results of the parametrical analyses on the effects of various design and geometric parameters, such as the number and geometry of piers and reinforcement ratio of the RC SMA bridge bents on its performance