Seismic Behavior And Design Of Step Joints In A Reinforced Concrete Frame

During recent years, the researches of step floor structure have been paid closeattention to by academic and engineering circles as the structure itself is increasinglyapplied in the civil industry. The key of the problem focuses on step joint. The intricatenatures of the step joint cause the research more arduous than those on common joint.Therefore, only a few researches on the mechanisms of shear transfer and seismicresistant behaviors about step joint for empirical needs have been accomplished so far.Based on earlier step joint research by postgraduates of Chongqing University theauthor discovered unsolved problem in those research and did four reinforced concretebeam-column assembly supplemental experiments. Then by analyzing all testing results,the author focused attention on the influence of staggered height, different loadingdirection, shear compression ratio and axial load ratio on the seismic resistant behaviorsof the step joints. Further, according　to the reinforced concrete nonlinear finiteelement analysis, the author present the mechanism of the step joint and suggestfeasible design method of concrete frame step joint.After the test and nonlinear finite analysis on the step joint, the conclusion aredrawn as following:1)　According to supplemental experiments, the author further studied transfermechanism and deterioration performance of the step joint, and present new designmethod of the step full joint. In new design method, the height of joint is whole heightof the full step joint.2) The better quality of anchor behaviors is beneficial to the seismic behavior ofthe step joint, making the beam reinforcement over strength. Corresponding to the test,the author proposed a feasible amplified factor of the beam reinforcement over strength.3) High shear compression ratio is unfavorable to behavior of the step joint. Underhigh shear compression ratio, significant deterioration in bearing capacity occurs beforeductility or deformation capacity is maintained. So the computation of shear resistancecapacityof the step joint should consider the influence of shear compression ratio.4) On the basis of the test and the reinforced concrete nonlinear finite elementanalysis, the author advanced the mechanisms of the full step joint and the part stepjoint.5) Again on the basis of the testing results and the mechanisms, author suggestedthe formulates of shear resistance capacity and designed shear of step joint.