Intensity measures (IMs) are used as a link between seismic hazard and seismic demand analysis and therefore have a key role in performance-based earthquake engineering. To the best of our knowledge, no study has been carried out on the determination of suitable IMs to evaluate the seismic demand of plain concrete arch bridges. In the present study, the efficiency, sufficiency, scaling robustness and practicality of 34 potential IMs for evaluating the seismic response of two old railway plain concrete arch bridges in km-23 and km-24 of Tehran–Qom railway are investigated. The considered bridges are simulated using finite-element method and subjected to incremental dynamic analysis (IDA) using 22 far-field earthquake ground motion records. Complete response of the models is obtained through IDA method in terms of engineering demand parameter measured by the maximum displacement of the bridges. The optimal IMs among the considered intensity measures for evaluating seismic demand of the investigated plain concrete arch bridges are recognized using the concepts of efficiency, sufficiency, scaling robustness and practicality. Using the results of the regression analysis, it is concluded that root mean square acceleration is the optimal IM based on efficiency, sufficiency, scaling robustness and practicality for seismic response evaluation of plain concrete arch bridges under far-field ground motions.
