Calculation method for the torsional bearing capacity of composite girders with CSW-CFST truss chords

Torsional behavior tests and a theoretical analysis were conducted on the composite girders with corrugated steel webs and concrete-filled steel tubular (CSW-CFST) truss chords. Their performance was compared with that of composite girders with circular hollow section (CSW-CHS) truss chords and composite box girders with CSW-CFST chords. The study revealed the influence of the concrete in the chord and the sectional form of the composite girders on their twist failure mode and torsional behavior. The test results showed that the sectional form of composite girders with CSW-CFST truss chords can perform as well as closed box cross-sections. The point of twist failure was found to be when the concrete roof obliquely cracked with an angle of 45 degrees between the crack and the girder axis and the rebar had already yielded. The concrete in the chord contributes to the torsional stiffness and bearing capacity of composite girders. The paper puts forward a method for calculating the compound stiffness of CFST specimens by superposing their linear stiffness. Then, on the basis of the four types of twist failure that can affect composite girders with CSW-CFST truss chords, a method for calculating their torsional bearing capacity is proposed. The deviation between the results acquired using the proposed method and the results from the tests and a finite element analysis is less than 8.5%.