框架中钢-混凝土组合梁等效弯曲刚度分析

In the frame system, the bending moment distribution of steel-concrete composite beam under vertical loads is closely related to the rotational constraint condition at the beam ends. In addition, the flexural rigidity of the cross section at different direction is significantly different. The rotational constraints at beam ends should be considered to accurately calculate the equivalent flexural rigidity of the composite beam under vertical loads, which are related to the deformation of the beams and columns connected to it. A theoretical model for the equivalent flexural rigidity of the composite beam under vertical loads in the frame was established by segmenting the flexural rigidity of the composite beam. This considered the influence of rotational stiffness of beam end constraints and sectional characteristics before and after the cracking of concrete slab on the equivalent flexural rigidity of the composite beam. Based on this theoretical model, a parametric analysis was carried out to identify two key factors affecting the equivalent flexural rigidity of the composite beam: the ratio between rotational constraint stiffness and section line stiffness and the ratio between section stiffness of the beam before and after the cracking of the concrete slab. A design formula for the equivalent rigidity of the composite beam under vertical loads was also obtained, which accounts for the effect of rotational stiffness of beam end constraints. The proposed design formula can be easily used in the frame design practice. The computational accuracy between the proposed design formula and some existing formulas was compared, and the rationality of the proposed design formula was also validated by a series of numerical results of whole-process nonlinear analysis of a structural system. The theoretical analysis and design methods show that the length of the negative moment region and the equivalent flexural rigidity of the composite beam under the vertical uniformly-distributed loads changed significantly with the changing of end rotational constraints, which should be accurately considered in the design.