Study On The "Strong-Beam-Weak-Column" Failure Pattern Of RC Frame Structure

In the 5.12 Wenchuan earthquake, the seismic damage of reinforced concrete frame structure is quite serious, especially the "strong-beam-weak- column" failure mechanism causing damage to column-ends had led to serious damage of the structures or even made them collapse, and then resulted in heavy casualties and property losses, which were unexpected to occur.The author made reference to massive literature on this issue,and analyzed the typical damage of reinforced concrete frame structure in the earthquake. Seven types of spatial finite element analysis models which were non-floor-structures, floor-structures and flange-considered-structures had been established using ABAQUS, to simplify a four-story building on the earthquake site. By the modal analysis and nonlinear dynamic analysis of the models under three strong ground motion, the influence of casting slab and plate reinforcement on the failure mechanism of reinforced concrete frame structure was deeply discussed, and the main conclusions obtained are as follows:1. Typical seismic damage of reinforced concrete frame structure in the 5.12 Wenchuan earthquake is analyzed and summarized.In the low-intensity areas, mainly damage occured in masonry infill walls and very few damage of the frame structure. The reinforced concrete frame building suffered serious damage in the high-intensity region, and the structural damage is summarized such as infill walls damage, the collision damage in the deformation joints, floor slab and staircase destroyed, damage of major load-bearing component such as beams and columns, structural collapse and so on. From the major load-bearing components damage and structural collapse, the"strong- beam-weak-column" type of failure mechanism is very obvious.2. The numerical simulation for reinforced concrete frame structure which destroyes as a "strong-beam-weak-column" type of failurepattern is achieved. Through comparative analysis of various concrete constitutive models, concrete damage plasticity model is choosen, which can be used for a good simulation of structural damage and failure process. Considering under strong ground motions, the structure may be into the highly nonlinear phase because of severe plastic deformation, which would causing numerical convergence difficult, the explicit integration method is adopted. Besides, three-dimensional reduced integration finite element is used in this paper which is well applied to the calculation method.3.The influence of the casting slabs and plate reinforcement within it on the "strong-beam-weak-column" type of failure pattern in reinforced concrete frame structure is investigated.It is the floor slabs and plate reinforcement that make difference to the acceleration and velocity response, the displacement of top floor, story drift, story shear force and the the components damage ,which to a large extent causes structural damage to performance as the failure mode of "strong beam-weak-column".4. The design idea that by increasing the beam section stiffness to indirectly take into account the role of floor slab in the seismic design code, to some certain extent, can heighten the beam lateral Stiffness ,although it has little effect on the change in failure pattern of the structures, which still shows a very typical damage of "strong-column-weak-beam" type.Thence, to take into account the actual contribution of the floor slabs and the reinforcement directly when desig and analyze afterwards is proposed in this paper.