Recently, the stretch of cable-stayed bridges-CSB span and the more slandering of stiffening girder make these bridge vulnerable for nonlinear behavior. The damage suffered during 1995 Hyogoken-Nanbu earthquake led to increased awareness concerning bridges response and emphasized the need for sophisticated research to provide new procedures and specifications. A nonlinear time-history analysis has been conducted to complete the seismic design and establish expected seismic performance. An analytical model is developed for CSB towers to accurately understand 3D nonlinear dynamic response of...