Experimental And Theoretical Research On Seismic Performance Of Concrete Frame With Special-Shaped Columns Reinforced With Polypropylene Fiber

RC frame structure with special-shaped columns is used more and more widely with the satisfactory architectural functions in engineering application. But in seismic zone with earthquake intensity of degree 8, because of the weak seismic performance caused by the weak cross section in special-shaped columns, the height of the frame structure has been limited. Some joints and lower parts of the special-shaped columns are weak according to the result of experimental and theoretical research. So polypropylene fiber was adopted to reinforce local parts of the structure, and pseudo-static test study and theoretical analysis were completed to study the seismic performance of the reinforced structure in order to study polypropylene fiber's reinforcement to the seismic performance of the structure. Also this can provide some basis for the application of polypropylene fiber to the structure with special-shaped columns. The detailed work of this paper is stated as follows:Based on practical project of six-story residential structure with special-shaped columns in seismic zone of earthquake intensity of degree 8, a pseudo-static test study was conducted on a frame model with special-shaped columns, which is 1/3 in size of the prototype and reinforced with polypropylene fiber in parts of joints and column legs in first two stories. The seismic performance such as failure characteristics, plastic hinges of beams and columns, bearing capacity and ductility, hysteretic properties and energy dissipation of the specimen are studied. The result show that frame structure with special-shaped columns reinforced with polypropylene fiber has good seismic performance. The specimen's failure process belongs to a beam-hinge failure mechanism, and the specimen has good initial rigidity and bearing capacity. Also the structure's ductility and energy dissipation capacity is fine in ultimate failure.Comparison is made between the partially reinforced structure with special-shaped columns and the general RC structure with special-shaped columns about the pseudo-static test results. The effectiveness of reinforcement with polypropylene fiber to the weak parts of the structure and also to the entire structure is studied. The result show that polypropylene fiber has reinforcement in different degrees in seismic performance like cracking, bearing capacity, hysteretic properties, ductility and energy dissipation capacity. Fiber can improve the weak parts of special-shaped columns, and the effectiveness of reinforcement with fiber is obvious.To make a further study about seismic performance and help analysis with experiment, structural design and analysis program SAP2000 is adopted to build analysis model to make a static elastic-plastic analysis for the general RC frame with special-shaped columns and that partially reinforced with fiber. Based on the static elastic-plastic analysis and the idea of Performance-Based Seismic Design (DBSD), the capacity spectrum method was applied to find the performance point and evaluate the seismic performance of the frame reinforced partially with fiber. The result indicate that the seismic performance of partially reinforced frame with special-shaped columns is fine under the frequent and infrequent earthquake action.Finally, some suggestions for design of RC frame with special-shaped columns are mentioned from the above study.