Performance of the effect of fractured member of an old steel truss railway bridge: A case study of Hardinge bridge

Hardinge Bridge is the first railway bridge in Bangladesh which is made up of prefabricated trusses. As an old steel bridge, fatigue crack and rust can affect steadily on truss members. Steel truss bridges have the determinate system and which have not any redundancy, can progressively collapse over the entire span, if a single primary member or gusset plate connection of the main trusses is damage. Beside this, as it is a railway bridge, it is very important to know the dynamic behavior of this bridge. A train at high speed can cause large vibration of the bridge super-structure and this large vibration might be affect on truss members. This paper describes the redundancy analysis and the free vibration analysis of Hardinge bridge truss after fracture of its different primary members. In this paper redundancy is described with respect to change in axial stresses before and after fracture of different members. From free vibration analysis, vibrational behavior of the bridge structure before and after fracture of different members can be observed. From these analyses it is observed that increase of axial stress of the adjacent members and natural frequencies of corresponding mode shapes varied with different damage scenario. Fracture of diagonal member drastically increased the axial stress of one of its adjacent member and the lowest natural frequency was obtained. Therefore, the fractured diagonal condition is the most critical condition.