Improved softened truss model for prestressed concrete composite box girders with corrugated steel webs under pure torsion

This paper aimed at developing a theoretical model for prestressed composite box girders with corrugated steel webs (CSW) under pure torsion, based on the combined action softened truss model (CA-STM). The equilibrium equations and materials' constitutive laws were modified, considering the relationship between the initial stress and strain generated by prestressing. According to the yield state of the CSW, proper shear flow conditions were also introduced to describe the deformation coordination relationship between the CSW and concrete slabs. The effect of the width of cantilever slabs on the torsional performance of composite box girders was investigated. An optimized algorithm was employed to solve the CA-STM, resulting in a more efficient and stable solution procedure. The validity of the model was confirmed through the available experimental data. Results showed that the prediction accuracy of the improved CA-STM for depicting entire torsional behavior is great, when considering the reasonable shear strain relationship and modified initial torque calculation formula.