A Beam Finite Element Model Considering the Slip, Shear Lag, and Time-Dependent Effects of Steel–Concrete Composite Box Beams

A beam finite element model considering the slip, shear lag, and time-dependent effects of steel–concrete composite box beams have been proposed in this study. The element is employed to a one-dimensional analytical method that is solved involving an expression of spatial and time-dependent variables. A step-by-step method that does not involve storing the stress and strain histories, which is more accurate than the single-step algebraic method, is employed to solve the time variables. A recursive method was elaborated to determine spatial and time-dependent variables through the above method. The validity of the proposed method in instantaneous analysis is attested by the numerical data of the elaborate finite element model established in a commercial software, ANSYS, and that of the time-dependent analysis is verified by the existing test results on the long-term performance of composite beams. The proposed beam finite element model is applied to predict the time-related behavior of simply supported composite beams after validation. The results show that concrete shrinkage and creep significantly influence the structural responses of the composite box beams. From the initial load on the 28th day to that in the 3rd year, the vertical deflection at the cross-section of the mid-span increased by 47.01%. The interface slip at the end increased by −10.99%. The warping intensity function of the concrete slab and the steel beam at the end caused by shear lag increased by 111.64% and 7.01%, respectively. The maximum compressive stress on the concrete slab and the maximum tensile stress at the steel bottom flange increased by −6.75% and 4.56%, respectively.