Seismic Design And Performance Research Of R.C Frame Under Fortification And Major Earthquakes

The damage of the earthquake occurred in recent years indicated that structures designed according to the criterion "no damage under moderate earthquake" could not avoid the enormous economic loss. It became to be a concerned problem whether structures could be designed "strong" enough to be "no damage" and then to avoid huge loss under fortification intensity or even under major earthquakes; and the ductility, or the seismic performance of structures designed according to the criterion "no damage under moderate earthquake" has no measurement index. So it would be theoretical and practical to study the seismic design and performance of structures at fortification intensity and at unusual earthquake. In this paper, the author discusses the design possibility and the behaviour of structures under fortification intensity and under major earthquakes, researches the simplified calculating method of the section ductility and the structure ductility, compares the various empirical formulas about plastic hinge length. The main content and results are as follows:The references about fortification criterion and ductility of sections, members, structures are summarized firstly, the problems unsolved are pointed out and then the research topics are determined.The vulnerability matrices and the ratios of various seismic losses to the direct economic losses used in this paper are presented with summarizing the related literature. The various target function expressions corresponding to the three design criteria of "no damage under moderate earthquakes", "no damage under fortification intensity" and "no damage under major earthquakes" are deduced using method of cost-benefit analysis and the isoline figures of various buildings in areas of intensity grade 7 are calculated. Then, an example of an R.C frame is presented to illustrate the application of the figures.The calculating expressions for the section curvature ductility are deduced on some assumptions and validated with trial data, which takes the influence of the stirrups into account. The influence of ignoring rebars in web area on the column section ductility is discussed. The curves and tables are presented which reflect the changes of column section ductility coefficient along with the axial compression ratio and the concrete ultimate strain, and the changes of beam section ductility along with the ratio of reinforcement respectively. It is convenient for designers and owners to consult.The various empirical formulas about plastic hinge length are studied by comparing the formula themselves and the influence on the element ductility. The appliance of some main formulas under various axial-compression ratios and various shear-span ratios are pointed out.The issue is presented that the two key points, namely the first yielding point and the last yielding point on the force-displacement curve of R.C frame structures, are corresponding to the maximal value and the minimum value of the ratio of loading moment to yielding moment of the sections. The influence factors of the structure are determined by using dimension analysis. The method for calculating the force and displacement of the two yielding points is put forward. The trend of structural ductility which changes with the changing of the influence factors are analysed by using orthogonal test, and the order of the factors are ranked. Then the ductility coefficients tables are calculated by using the former calculating method and by changing the main influencing factors, and the ductility formulas are regressed.In the finality, the contents in this paper are summarized and the problems requiring further studies are discussed.