Research On Seismic Performance Of RC Frames With Specially-Shaped Columns Reinforced By Polypropylene Fiber

RC frames with specially-shaped columns, i.e. columns with L, T or X-shaped cross section, have been considered to be a structure suitable for residential buildings. However, due to the weak seismic performance caused by the specially-shaped columns, the application of this structure is limited in high seismic intensity zone. Compared to normal frame structure, some joints and bottom parts of the columns have been found weaker in the experimental research. So polypropylene fiber is adopted to reinforce those local parts of the structure and improve the seismic performance. This paper has completed pseudo-static test and theoretical research in order to study the function of polypropylene fiber in the concrete in the seismic performance.Firstly , pseudo-static tests were conducted on concrete joints and specially-shaped columns reinforced by polypropylene fiber. Two interior joints, two exterior joints, two columns with T section and two columns with L section were designed in the test. All of the specimens were divided into two groups, and the specimens in first group were normal concrete members and the others were concrete members reinforced by polypropylene fiber. Seismic property including the Hysteretic Behavior,Ductility,plastic hinges of beams and columns has been obtained. The results were followed:(1) With the reinforcement of polypropylene fiber, the failure characteristics were changed. The development of the crack was limited and narrowed, so the rigid of the specimens was strengthened;(2) The strength of the specimen, the yield load and the failure load were improved sharply;(3) The seismic performance such as cracking, bearing capacity, hysteretic behaviors, ductility and energy dissipation capacity is improved obviously.Furthermore, based on practical project of six–story residential RC frame with specially-shaped columns in seismic zone of earthquake intensity of degree 8, a pseudo-static test study was conducted on a frame model in 1/3 size of prototype and reinforced with polypropylene fiber in parts of joints and column legs. Seismic property including the hysteretic behavior,ductility,plastic hinges of beams and columns were also obtained. So comparison was made between the two type frames according to the pseudo-static test results. The deformations of the two type frame were all shearing type, and the specimen's failure process belongs to a beam-hinge failure mechanism. But polypropylene fibre has reinforcement in different degrees in seismic performance like cracking, bearing capacity, hysteretic properties, ductility and energy dissipation capacity. Fibre can improve the weak parts of specially-shaped columns, and the effectiveness of reinforcement with fibre is obvious.Finally, to make a further study about seismic performance, structural analysis program ANSYS is adopted to build analysis model to make a static elastic-plastic for the general RC frame with specially-shaped columns and that partially reinforced with polypropylene fibre. The result is very satisfying.