SEISMIC BEHAVIOUR OF BRIDGES WITH IRREGULAR CONFIGURATION

Abstract

Irregular bridges, i.e. bridges with skew, curved spans, or unequal pier heights, are more vulnerable to damage than regular bridges, during earthquakes. The complex behaviour of irregular bridges during an earthquake is still not understood completely. The dynamic characteristics change significantly due to presence of any irregularity in the bridge. This dissertation aims to explore the response of irregular bridges in seismic events. In the present study, behaviour of skew and curved bridges is studied by mode superposition analysis using response spectrum, linear time history analysis, and non-linear time history analysis. Different incidence angles and their effect on bridge response are assessed. The considered bridge is a curved bridge with skewed central pier. For this purpose, a 3D model of the bridge along with piers is developed assuming fixity at the base of the piers. Three other models are also developed with different combinations of skew and curvature. The girders and deck are modelled as beam elements, while the bracings and cross girders are modelled as truss elements. The pier cap and piers are modelled as beam elements, as well. The bearings of the bridge are modelled as elastic links having significant rigidity in the direction in which no movement is allowed. The seismic analysis is performed on all the four bridge models, taking incidence angle from 0° to 80° with an increment of 20° and their corresponding orthogonal angle however the 40° angle was replaced by 37.988° as it aligned with the skewed pier. The maximum response of all the bridges corresponding to the critical angle is compared in different models. The difference due to skew, curvature and their combined effect is studied. Non-linear analysis is performed by assigning inelastic fiber hinges to the pier elements simulating non-linearity in the structure. The validation of these fiber hinges is also performed to verify their behaviour under reverse cyclic loading.