Effects of fling step on the seismic response of reinforced concrete arch bridges

Many arch bridges have been built in near-fault regions around the world and may be affected by fling step, which is the permanent ground displacement caused by the long-period pulse within the frequency content of an earthquake. This study investigates the effect of fling step on reinforced concrete deck-type arch bridges with short to medium spans. Three-dimensional non-linear models of three existing reinforced concrete arch bridges in Iran, with span lengths of 23, 35 and 60 m, were developed. The structures were subjected to seven near-fault earthquakes in longitudinal and transverse directions, once with the fling-step pulse included and once with it removed. The results showed that fling step has a noticeable effect on the seismic response indicators investigated, but may increase or decrease the seismic demand. The maximum curvature in the presence of fling step in relation to that without fling step ranged between 0.54 and 2.06. Unseating in the longitudinal direction was most sensitive to the fling step, and showed a more than 200% increase in some cases. Effects of the fling step were correlated with the ratio of the period of the fundamental mode of vibration of the structure to that of the fling-step pulse.