Comparison of Seismic Demands on RC Bridge Columns Using the AASHTO Guide Specification, DDBA, and Nonlinear Analysis for Shallow Crustal and Subduction Tectonic Regimes

Abstract

An accurate estimation of displacement demand is essential to predict structural performance. However, the calculated displacements will vary depending on the analysis procedure. This paper shows the differences between the seismic demands of reinforced concrete (RC) columns calculated by using three analysis procedures: (1) AASHTO Seismic Guide Specifications (SGS); (2) direct displacement–based assessment (DDBA); and (3) nonlinear time history analysis (NLTHA). The demands were evaluated using two different response spectra definitions (3-period and 22-period representations) of the 2018 USGS seismic hazard model for structures located in shallow crustal and subduction tectonic regimes. Nonlinear time history analyses were performed using spectrally matched records for five design spectra from both tectonic regimes. This paper shows that the AASHTO-SGS significantly underpredicts the demands (compared with NLTHA) as the displacement ductility increases. In contrast, the predictions of the DDBA agree well with those of NLTHA, with mean differences of 10% for ductility higher than μΔ = 3. Lastly, equations are proposed to improve the accuracy of displacement demands for the AASHTO-SGS and the DDBA methodologies.