Capacity‐based inelastic displacement spectra for reinforced concrete bridge columns

Abstract

SUMMARYCapacity‐based inelastic displacement spectra that comprise an inelastic displacement ratio (CR) spectrum and the corresponding damage index (DI) spectrum are proposed in this study to aid seismic design and evaluation of reinforced concrete (RC) bridges. Nonlinear time history analyses of single‐degree‐of‐freedom (SDOF) systems are conducted using a versatile smooth hysteretic model when subjected to far‐field and near‐fault ground motions. It is demonstrated that the Park and Ang damage index can be a good indicator for assessing the actual visible damage condition of columns regardless of its loading history, providing a better insight into the seismic performance of bridges. The computed spectra for near‐fault (NF) ground motions show that as the magnitude of pulse period ranges increases from NF1 (0.5‐2.5 seconds) to NF2 (2.5‐5.5 seconds), the spectral ordinates of the CR and DI spectra increase moderately. In contrast, the computed spectra do not show much difference between NF2 and NF3 (5.5‐10.5 seconds) when the period of vibration Tn≤ 1.5 seconds, after which the spectral ordinates of NF3 tend to increase obviously, whereas those of NF2 decrease with increasing Tn. Moreover, when relative strength ratio R = 5.0, nearly all of the practical design scenarios could not survive NF3. On the basis of the computed spectra, CR and DI formulae are presented as a function of Tn, R, and various design parameters for far‐field and near‐fault ground motions. Finally, an application of the proposed spectra to the performance‐based seismic design of RC bridges is presented using DI as the performance objective.