However, due to the complicated section-shape and the diaphragms inside the box girder, it is difficult to calculate the torsional stiffness. When using beam element to build model for single-box steel girder, single-girder, double-girder, and triple-girder are adopted. In the construction of such a bridge, closed steel box girder is widely applied by virtue of its light weight, fast construction speed, and good aerodynamic performance. It is common that the finite element model of the long-span bridge is built by simulating girder or member based on one-dimensional two-node beam elements. This research is expected to provide reference for beam element modelling, which is conducive to accurately simulating torsional stiffness of the STSBG. According to the calculated value of the RM, ABC algorithm would satisfactorily improve the accuracy in simulating torsional stiffness of the STSBG with the IBEM. In more detail, the relative error between the torsion angle of the girder in the middle span of the BEM and the corresponding reference value in the finished state is decreased from +61.71% to +4.94%, and the relative error of torsional fundamental frequency is decreased from −17.43% to +3.66%.
The results show that the aerostatic responses and dynamic characteristics of the CBEM are close to calculated values of the RM. Finally, static and dynamic characteristics of the IBEM and the corrected beam element model (CBEM) are compared with values of the corresponding RM to evaluate the validity of the correction of the model. Then, the beam element is used for conventional modelling of the bridge, and artificial bee colony (ABC) algorithm is adopted for the optimization and correction of structure parameters of the BEM of the girder. With the reference value, an objective function of the overall residual sum of squares is constructed for the torsion angle of the girder and the frequency of the bridge. ANSYS is adopted to make a refined model (RM) of a bridge with STSBG as its girder and to calculate its aerostatic responses and dynamic characteristics in 3 typical construction states and 1 finished state. To improve the accuracy in simulating stiffness of the split-type triple-box steel box girder (STSBG) with the beam element model (BEM), a correction is made to the initial beam element model (IBEM) based on the result of a more refined finite element model. However, since the irregular cross-beams and diaphragms in the split steel box girder cannot be virtually established, the stiffness of the girder will be underestimated. In the design stage, a simple finite element model is usually established based on the beam element for wind-resistance design. Split-type steel box girders are widely used in long-span bridges because of their good wind-resistance performance.