Estimation of Ultimate Strength of Concrete Box-Girder Bridges Using Space Truss Analogy

The box section has high torsional stiffness and bending stiffness which makes it a very efficient structural system to resist different forces acting on it. Owing to its complex geometry, the analysis and behavior at the ultimate stage of a box-girder bridge are not yet completely understood. Among the existing theories, Space truss analogy is the basic theory to understand the behavior of box sections at its ultimate stage. For reinforced concrete box-girder bridges subjected to a combined action of bending and torsion, space truss analogy visualizes the structure as a space truss formed by inclined diagonal concrete elements as struts and reinforcing cage as ties. In the present study, box-girder bridges are modeled and their ultimate strength is predicted using the theoretical formulations of space truss analogy and strut and tie model. In analysis, the various load patterns are considered to incorporate the actual bending and twisting effects which are generated due to eccentric load. The numerical computations for the space truss are performed using STAAD, and the results are compared with those available from literature.