Distortional Buckling Analysis of I-Steel Concrete Composite Beams Subjected to Hogging Moment

Bending-torsional distortion buckling is one of the most critical buckling modes of steel–concrete composite beams when they are working under hogging moment. The rotational and lateral restraint stiffness provided by the steel web to the steel bottom flange are the key factors to determine this form of buckling. Firstly, the formula for solving the elastic rotational restraint stiffness of the composite flange of steel beam upper flange and concrete slab to the steel web is derived. Then, the equivalent lateral and rotational restraint stiffness of the steel bottom flange subjected to hogging moment are thoroughly studied. Considering the rotation restraint effect of the composite flange, this paper provides the calculation formula for the critical bending moment of I-steel concrete composite beams (I-SCCB) under hogging moment. Fifteen examples are considered to calculate the critical bending moment of the I-SCCB under hogging moment with the simplified analytical method introduced in this paper. The results are compared with the ones derived by ANSYS numerical analyses and relevant research of other scholars. The influence of the arrangement of the shear studs on the critical bending moment of the I-SCCB is investigated. It is concluded that the results given by the simplified analytical method are in good agreement with the ones obtained by the ANSYS finite element numerical method. Both methods show that the critical load of the distortional buckling of the I-SCCB under hogging moment is less affected by the member’s length. The critical bending moment of distortional buckling of the I-SCCB significantly increases with the presence of shear studs. However, once shear studs are used, it tends to be stable with the increase of equivalent restrained torsional rotational stiffness at the top edge of the steel web.