Experimental Study On Specially Shaped Columns With 500MPa Reinforcing Steel Bar

Owing to low bearing capacity,poor seismic performance and lack of ductility in plastic hinge near the column base,the employment of specially shaped column structure in seismic zone was restricted.However,the application of high strength reinforcement in the structure show a way to solve these problems.Experimental and analytical research on the mechanical propertities of the specially shaped column with high strength reinforcement,such as the seismic behavior,the ductility in the plastic hinge and the crack width which is the primary issue in restricting the application of high strength reinforcement is conducted to figure out the impact of the high strength reinforcement to the overall mechanical behavior of the specially shaped column,to prove and find out the enhancement level and provide the basis for the application of this material.The seismic performance of specially shaped columns with reinforcement with different strength is contrasted through experimental and anylatical research procedure,the ductility of the plastic hinges is also studied baed on the plastic hinge element.The test and analytical results indicate that the employment of high strength reinforcement could greatly improve the bearing capacity while maitain the ductility of the specially shaped column.The bearing capacity of members with 500 MPa steel bars are 30%~36% and 8%~11% larger than members with 335 MPa and 400 MPa steel bars respectively.However,the overlarge crack width of the specially shaped column with high strength reinforcement have a negative impact on the durability of the members so measures restricting the crack width should be applied.The analytical results of plastic hinge length and curvature ductility indicate that the curvature ductility ratio of L-shaped columns range from 5.43 to 13.19,while the curvature ductility ratio of +-shaped columns range from 8.52 to 13.41 and Tshaped columns from 7.54 to 11.76,all of them possess good ductility.Corner columns in the ground floor possess the poorest ductility and is the weak key part of the whole structure.The curvature ductility of the members with 500 MPa steel bars is almost idenctical with the members using 335 MPa or 400 MPa steel bars,while the ultimate curvature is increased by 15% and 10% repectively.The impact of the axial compression ratio and the reinforcement ratio on mechanical behavior of the specially shaped column with high strength reinforcement is investigated through experimental and analytical research.The results indicate that high reinforcement ratio provides better mechanical capacity,including increasing the bearing capacity by 17%~45%,yield displacement by 6%~15%,ultimate displacement by 17%~79% and displacement ductility ratio by 10%~63%.The ultimate displacement and ductility of the members decreased with the increase of the axial load,wherein the ultimate displacement is decreased by 11%~18% and the displacement ductility ratio decreased by 14%~18%.The analysis on the frame indicates that failure mode of beam hinge happen in specially shaped column structure with high-strength reinforcement.The story drift ratio exceeds 1/50 and meet the requirements for plastic deformability of frame structure.High strength reinforcement provides longer elastic stage,retards the appearance of the plastic hinges,decreases the residual deformation of each floor in contrast to structures using,the residual deformation in ground floor could be decreased by 17% and 10% respectively,but meanwhile the story drift ratio has no obvious change.