Displacement-based strategies for the performance-based seismic design of 'short' bridges considering embankment flexibility

This study focuses on the transverse (or skew) response of ordinary reinforced concrete bridges having integral abutments and relatively stiff decks that lack intermediate joints for thermal expansion, termed “short” bridges. Empirical observations and analysis of the recorded response of two such “short” bridges indicate that the flexibility of the bridge embankment has a significant effect on the displacement demands sustained by the substructure column during earthquakes.; An existing approach embankment model was refined to account for embankment flexibility by explicitly representing nonlinear behavior of embankment soil. The refined embankment model was used to represent embankment flexibility in MDOF models of two short bridges in a calibration study, to determine a range of embankment length that best represented the recorded response. Using findings from the calibration study, a simple technique was developed to account for embankment flexibility, for estimating the displacement demands sustained by the substructure columns of “short” bridges responding to earthquakes. The technique makes use of an “equivalent” SDOF model of the bridge. Embankment flexibility is accounted for using capacity curves developed for common embankment fill properties and dimensions.; The significant role of embankment flexibility has implications for the seismic design of the substructure columns. Existing procedures, based on force reduction factors, do not account for the significant role played by the embankments. A displacement-based approach for the design of the columns is proposed, in which smaller diameter columns, possibly with higher axial load ratios, are shown to result in improved performance relative to that computed for conventional designs. Guidelines are presented for proportioning the substructure columns to improve their seismic performance.