Comparison of Critical Bending Moment in a Bridge Based on Influence Line Diagram (ILD), FOSM Method and Optimization

The location of critical section in any civil infrastructure viz., bridges, trusses etc., that experience maximum value of design parameters for the subjected moving loads is imperative in order to design a safe structure. Traditionally these locations are evaluated by constructing the influence line diagrams (ILD) for the structures subjected to moving loads. In general the variations of these critical parameters viz., deflections, bending moment, shear force etc are evaluated at different locations while designing the configurations of the members of bridges, trusses etc. The location of critical parameters for instance the location of absolute maximum bending moment in a structure, may not coincide with the location of maximum deflection for a given position of load. Hence, in this paper an alternative probabilistic approach based on first order reliability principles is proposed for evaluating the location of critical section for the bridge structures subjected to moving loads, subsequently critical parameters can be evaluated at that location. In order to illustrate the approach, the following cases are considered.