Fiber beam-column element for circular concrete filled steel tube under axial–flexure–torsion combined load

• The test on CFST subjected to compression–bending–torsion combined load was carried out.
• A nonlinear element was developed based on the proposed fiber beam-column element.
• The high modeling speed and solution precision can be achieved using the proposed element.

When subjected to the horizontal earthquake load, compression–bending–torsion combined actions often exist in the piers of curved bridges because the center of stiffness and the center of mass of curved bridges do not locate at the same position. A new fiber beam-column element considering the nonlinear torsion behavior for concrete filled steel tubes with circular section was developed based on the traditional fiber beam-column model, which had widely been used. The calculation and solution procedures of the proposed fiber beam-column model were also illustrated. The reasonable geometrical relations, material constitutive law and force equilibrium equations were all applied. Based on the principles of fiber beam-column element considering torsion effect, a nonlinear solution program was developed using FORTRAN language. The entire loading history of concrete filled steel tube columns subjected to combined compression–bending–torsion load could be predicted with good agreement with test results. Using the proposed fiber beam-column model for the time-history analysis of curved steel–concrete composite girder bridges, the high solution precision and efficiency could be obtained, compared with the traditional finite element model.