Research On Earthquake Collapse Failure Of Reinforced Concrete Frames Structures

Life safety is always the first one in any case. Under strong earthquakes, the collapse ofbuildings caused heavy casualties and property losses, especially casualties would trigger a seriesof more complex and serious social and economic problems than the property damage. In recentyears, several damage at home and abroad have shown that the strict implementation of theseismic design of buildings may also occur in varying degrees of collapse damage, thefundamental reason of the fortification objective―no collapsing with strong earthquake‖not toachieve lies in the lack of further study on failure mechanism of structural collapse, the precisedefinition of the collapse damage critical state and the reasonable establishment of quantitativecriteria of collapse. Here the failure characteristics and mechanism of reinforced concrete framestructural collapse are focused on research, besides, analysis model, the critical state and failurecriteria of collapse damage are established. The major works are summarized as follows:The existing research methods of structural collapse damage are deeply analyzed andsummarized. Existing design methods is essentially the extension of member design, while theimproved research of structural collapse into the structural thought contain the uncertainty ofmember, sub-structure and structural damage. The concentration of plastic deformation in weakareas is the fundamental reason for the collapse occurred. The plastic deformation concentratedarea of frame structure is a large number of fully developed hinge pillar area, at this point, theredistribution capacity of structural internal force is gradually decreased to form a hinge pillarfailure mechanism. Domain-failure damage model and plastic-hinge density failure criterion areproposed. It is reflection and exploration for collapse research from the three levels of components,sub-structure and the overall structure, then, the analytical ideas and methods of a feasible collapseresearch are established.The characteristics of collapse damage was analyzed, the critical state of collapse wasdefined as limit performance of incomplete structure after different degrees of injury occurredunder the action of earthquake. According to some indicators of the damaged components withinthe same layer, such as location, the degree of damage and quantity, component composition of the same type of causing the collapse of the layer and the similar extent of damage was defined as thekey areas of collapse. Analysis model of domain collapse damage was established. Domain failurewas the primary cause of collapse damage occurred. It truly reflected the degradationcharacteristics of the overall performance and applies to the different types of collapse.By analyzing the mechanism of collapse of the framework structure and the characteristics ofthe internal force redistribution, on the basis of domain model studies, the development of columnplastic hinge was selected as collapse analysis variables. According to the degree of developmentof plastic hinges, the location of plastic hinge appears, the number of column plastic hinges andother parameters, the collapse failure criterion of plastic hinges density was defined. Therelationship between the column injury and overall performance degradation of the structure wasconsidered in the failure criterion. Collapse was demonstrated and explained from three levels,such as component damage, sub-structural damage and structural collapse damage. After a certainamount of columns hinges in the weak story fully developed, the capability of redistribution ofinternal forces of the structure was lost, then substructure into variable mechanism marked thebeginning of the collapse, the critical state of collapse was accurately defined, failure mechanismwas interpreted and quantitative analysis was achieved by domain model and plastic hingesdensity failure criterion.The collapsed damage is due to the concentration of plastic deformation in the column-end,the damage and quantify of the degree of plastic deformation of frame column were studied.Effective energy theories have been proposed by considering the relationships between hystereticenergy and component damage, improved two-parameter failure criterion was established byconsidering ductility and the ratio of energy efficient, the failure characteristics of section of thecolumn were studied, on the basis of the theoretical analysis, the calculation formula of ultimatecurvature of frame column was derived by data regression, the quantization method of thedevelopment of plastic hinges was established.According to the pseudo-static test of three specimens of plane frame, fiber element modelbased on OpenSees was established, experimental verification of cyclic loading tests of framestructure were carried out, the calculation and analysis of plane frame structure collapse wascompleted based on plastic-hinge density failure criterion, the selected collapse interval (0.6,1.0) can accurately express the limits of collapse, Collapse damage index can better reflect thedeterioration of the whole performance of the structure.The framework structure’s time historyanalysis was conducted by selecting114seismic waves. According to the size of collapse damageindex,10ground motions were selected as a ground motion database for follow-parametricanalysis. The calculation and analysis of collapse damage were completed on different layers,different story height, different span length and different axial compression ratio. The resultsshowed that as the increase of layer numbers, story height, span length and axial compression ratio,collapse damage as a whole presents an exacerbated trend. Structural collapse was well defined byplastic-hinge density failure criterion based on domain-failure damage model, the impact ofground motion randomness to structural collapse damage cannot be ignored.