Comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges

This paper presents a comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. Boğaziçi (The First Bosporus) and Fatih Sultan Mehmet (Second Bosporus) suspension bridges built in Istanbul, Turkey, are selected as numerical examples. Both bridges have almost the same span. While Boğaziçi Suspension Bridge has inclined hangers, Fatih Sultan Mehmet Suspension Bridge has vertical hangers. Geometric nonlinearity including P-delta effects from self-weight of the bridges is taken into account in the determination of the dynamic behavior of the suspension bridges for near-fault and far-fault ground motions. Near-fault and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of 1999 Chi-Chi, 1999 Kocaeli, and 1979 Imperial Valley earthquakes are selected for the analyses. Displacements and internal forces of the bridges are determined using the finite element method including geometric nonlinearity. The displacements and internal forces obtained from the dynamic analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that near-fault ground motions are more effective than far-fault ground motion on the displacements and internal forces such as bending moment, shear force and axial forces of the suspension bridges.