| Reinforced concrete(RC)frame structure is one of the common structural forms of buildings.In the past earthquakes,RC frame structures all have experienced damages in different degrees in a large scale,which greatly endangered life safety and caused huge economic loss.Being the force transmission centers of a frame structure,beam-column joints are the embodiment of the overall structural seismic performance.Bad seismic behavior of the joints will result in poor function of the whole structure.So,seismic research about beam-column joints is particularly important.In our country,a major design requirement of frame structures is "strong column and weak beam".However,a number of seismic damage data showed that,frame structures had not fully achieved the expected "strong column and weak beam" goal,beam hinge mechanism had not overally formed,strength gradients corresponding to different fortification levels lacked solid data references,and the probability ensurence of column-beam capacity amplification factors and fortification standards lacked concrete research foundations.In view of the above problems,this study seeks to explore the performance of beam-column joint of RC frame structures by way of pseudo-static tests.So,firstly,12 frame structure beam-column joints were constructed in reduced scale of 2:3 according to the standards of GB50011-2010,including 3 interior joints of fortification degrees of 7,8,and 9,and 3 exterior joints of fortification degree of 8.Capacity amplification factors of these beam-column joint models were calculated and verified,pseudo static tests were conducted,failure patterns of the joints were analyzed,hysteretic energy dissipation,ductility,strength degradation and deformation capacity etc.,were analyzed and compared.The influence of different factors,such as the fortification levels,the position of the contra-flectural point,the interior and exterior locations,etc.,on the joints' performance were compared and studied.Experimental and analytical results showed that,beam-column amplification factors conform to the code's requirement specifications;the joints' damage all results from beams' bending behavior;all joints have realized the beam hinge mechanism;exterior joints and fortification 9 joints have higher energy dissipation capacities than other joints;higher fortification joints have higher strength but slightly lower ductility;position of contra-flectural point does not impact much on beam-hinge mechanism and beam bending ability.According to the experimental data and conclusions,it is found that,there exists a 2-4 times beam strength gradients between dififferent fortification levels.Second,the probabilistic seismic capacity analysis of structures needs to consider the uncertainty of the structure and ground motion.Thus,based in the performance parameters from the tests,the nonlinear constitutive models of joints with different fortification levels were determined,and damage indices that correspond to different performance levels were put forward.On the basis of these and the "strong column and weak beam" design,the probability seismic capacity was analyzed,and capacity vunerabilty curves were constructed,so that the uncertainty of the joints was understood.Using experiental ways to perform the probability capacity analysis of structural components is the innovation point of this study,and also is the verification and quantification of the design regulations of the codes.By this study,the design capacity of the joints that conform to “strong column weak beam” under different fortification conditions has models to use;and the reliability to achieve the design performance have been understood to some content.The above obtained constitutive model and vulnerability curves will be used for further analysis of the overall vulnerability of frame structures,non structural components,and to provide a research basis for futural seismic research of the medical buildings. |
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