Rotational capacity and optimum bracing point of high strength steel I-girders

The rotational capacity of I-girders in the negative bending moment region is a crucial design parameter, since a large negative bending moment occurs near bridge piers where plastic hinges are first formed. Thus, the continuous girders on the intermediate supports must have sufficient rotational capacity (or flexural ductility) to redistribute the negative bending moment into an adjacent positive bending moment region to ensure ductile behavior of the girder. Furthermore, the rotational capacity of I-girders built up with high strength steel plates is usually smaller than that of I-girders built up with normal strength steel plates; the rotational capacity therefore needs to be improved. High strength steel with yield stress of 690 MPa was used for this study. A theoretical model to predict the rotational capacity of the I-girder with high strength steel was proposed based on the analytical model of a flexural curvature distribution diagram. The theoretical model was verified through a series of tests and parametric studies. Further, the optimum arrangement of bracing points to maximize the rotational capacity was derived, and the proposed optimum bracing point was successfully verified.