Influence of diaphragm stiffness on distortional behavior of composite box girder with corrugated steel webs

To investigate the influence of diaphragm stiffness and number on the distortional behavior of composite box girders with corrugated steel webs (CSWs), a distortional beam element (B2D-CSW) that incorporates both diaphragm stiffness and shear deformation effects was developed. Based on the generalized coordinate method, expressions for distortional warping displacement in composite box sections with CSWs were formulated, incorporating the influence of distortional shear force on shear deformation. The physical relationship between distortional shear force and distortional bimoment was derived theoretically. By enforcing displacement compatibility between diaphragms and the composite box section, deformation expressions for different diaphragm types and their geometric relationships with the distortion angle were established, thus revealing their mechanism for resisting distortional deformation. Using the energy variational method, governing differential equations for composite box girders with CSWs that account for distortional shear deformation were derived, and interpolation functions for generalized displacements were constructed based on homogeneous solutions. Based on the finite element method, a two-node, four-degree-of-freedom distortional beam element considering distortional shear deformation was developed, and the stiffness matrix and equivalent nodal load vector considering diaphragm stiffness were derived. Through numerical examples, the computational accuracy and wide applicability of the proposed B2D-CSW beam element were verified. The results indicate that, compared with solid finite element models, the B2D-CSW beam element can accurately predict the distortional response of composite box girders with CSWs under varying diaphragm stiffness and number of diaphragms, using only a small number of elements and thus significantly improving modeling and computational efficiency. The analysis shows that the anti-distortional stiffness of diaphragms provides significant elastic restraint on the distortional deformation of composite box girders with CSWs. As the diaphragm stiffness or number reaches a critical threshold, the restraining effect on the distortional deformation of the main girder tends to stabilize. The proposed B2D-CSW beam element provides a reliable computational method for the design and analysis of diaphragms in continuous prestressed concrete (PC) composite box girder bridges with CSWs.