Influence of constructing transverse concrete diaphragms in different distances on the dynamic and static behavior of prestressed concrete T-beam bridge structure.

Structure of diaphragm was defined as a transverse strengthener beam which was located between beams or girders to keep section geometry. It plays a significant role to provide the stability of bridge girders and to distribute the vertical and axial loads. The main objective of this study was to investigate the influence of construction transverse concrete diaphragms between T-beams at different distances on the dynamic and static behavior of T-beam bridge structure. The methodology of this research includes five case studies. The first case had no transverse diaphragms, the second case had transverse diaphragms at the supports of the bridge (abutment and piers), the third case had transverse diaphragms at the center of each span of the bridge, the fourth case had transverse diaphragms at 1/4 of each span of the bridge, and the fifth case had transverse diaphragms at 3 m of each span of the bridge. Three analysis methods were used to determine the dynamic responses by using finite element analysis method in CSI-Bridge ver. 20. These methods included modal analysis, time history analysis, and spectra responses analysis. Dynamic responses consisted of unloaded frequency, loaded frequency, and dynamic displacement. Static analysis was done to find static responses such as bending moment and vertical deflection. The results of dynamic analysis shown that the using of concrete diaphragms has not important effect on the improvement of unloaded frequency (natural frequency) in vertical and horizontal directions, but they had an important effect on the reducing of loaded frequency (vibration frequency) in vertical and horizontal direction and dynamic displacement. For static state, the construction of concrete diaphragms causes to increase bending moment and downward vertical deflection because of these cross diaphragms lead to increase in the dead load (self-weight of structure), resulting the increasing in the static responses due to service loads (dead load, prestressed load, and trucks load). Therefore, there is need to increase the prestressed load to resist the over load due to the construction of transverse diaphragms. [ABSTRACT FROM AUTHOR]