Effect of Vertical Motion of Earthquake on RC Bridge Pier

Abstract eng:
In seismic design of RC piers, designers usually don't consider effect of vertical motion, however, measurements of ground motion during past earthquakes indicate that the vertical acceleration maybe exceed the horizontal acceleration. Analyses of actual bridges indicate that, in general, the vertical motion will increase the level of response and the amount of damage sustained by a highway bridge. Vertical motion generates fluctuating axial forces in the columns, which cause instability of the hysteresis loops. Furthermore, vertical motion can generate forces of high magnitude in the abutments and foundations that are not accounted for by the current seismic design guidelines. Also, the impulsive vertical motion induces the circumferential crack on RC piers. This paper presents analytical study for investigation of vertical motion effects on actual RC bridge. In this study, linear and nonlinear time history analysis (Tabas, Northridge and Kobe scaled records ) under two case of loading; in the first case, bridge was subject to horizontal motion of earthquakes whereas in the second case bridge was subject to horizontal motion of case1 in addition to vertical motion. Analyses indicate vertical motion will increase the axial loads, axial and shear strain and variation of longitudinal displacement and shear force are negligible.

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