The strain demand of reinforced concrete bridge columns under seismic loading

Abstract

The steel in reinforced concrete (RC) members that form plastic hinges must possess sufficient strain capacity to dissipate seismic deformation demands. Unfortunately, there is limited information on the seismic strain demands of bridge column plastic hinges. Instead, designers rely on a perception of cyclic strain capacity that is an approximate rule of thumb. A standard methodology needs to be established for quantifying the strain demand on these structural members as a function of the expected seismic hazard. To develop this methodology, 1944 columns were analyzed with nonlinear time-history analyses (NLTHAs) using ground motions from a range of earthquakes. This study evaluates the strain demand on RC bridge columns by defining the relationship between the strain demand and earthquake intensity. The results of the model are defined in terms of the peak tensile strain of the reinforcing bar, ${\epsilon }_t$ . The earthquake intensity with the highest correlation to the ${\epsilon }_t$ was determined to be the elastic spectral displacement at the optimal period ( $S_{\mathrm{de}}(T_{\mathrm{opt}})$ ), which is defined as 75% of the effective period. The relationship between ${\epsilon }_t$ and $S_{\mathrm{de}}(T_{\mathrm{opt}})$ can be used to predict the strain demand for an RC bridge column at a given geographic location. Results are presented as a probability density function (PDF), representing strain demand, compared to a PDF of the column capacity. The intersection of the capacity curve and demand curve represents the maximum acceptable strain given as a function of $S_{\mathrm{de}}(T_{\mathrm{opt}})$ . This methodology can help understand the demand placed on a structural system given a region’s seismicity.