Research On Deformation Ability And Collapse Resistance Of Reinforced Concrete Frame Structure Under Strong Earthquake

The seismic performance of frame structures under strong earthquakes was primarily affected by the failure mechanism.In order to facilitate the formation of strong-column weak-beam failure mechanism,the design method that improving the column flexural capacity is adopted in seismic code.However,the actual structures tended to present the column-hinge failure mechanism under earthquake in the past.Only the elastoplastic deformation of building structures is checked according to current design code,where the specified limit value of elastoplastic inter-layer drift angle was used as the criterion for structure collapse.This specified parameter is defined based on the concept of member design essentially,lacking the theoretical analysis and experimental data validation of whole structures.In this paper,the typical reinforced concrete frame structures were taken as the research object.The influence of member deformation on the structural stability is considered comprehensively and the relationship between structural deformation and collapse is discussed through theoretical analysis and experimental study.The major contributions of this thesis are listed as follows:(1)Based on the mechanical model of regular plane frame,the beam-to-column linear stiffness ratio was defined to reflect the relative restraint of beams and columns,then a governing equation achieving the strong-column weak-beam failure mechanism was proposed.The limit values of beam-to-column linear stiffness ratio for different seismic grades were proposed subsequently.By comparing the plastic hinge distribution of structures with or without considering the limit values of beam-to-column linear stiffness ratio,the effectiveness of the component stiffness matching on achieving the beam-hinge failure mode was discussed;(2)A pseudo-static test of three 3-layer,3-span reinforced concrete plane frame specimens with 1:3 scale ratio was carried out.Then the failure process,the plastic hinge formation,the deformation ability,and the stiffness degradation of specimens were systematically analyzed.The results showed that the initial lateral stiffness of frame structure was improved with the increase in vertical load,but the development of plastic hinge at beam end and the deformation capacity of frame structure were decreased.For the fame structure with lager beam-to-column linear stiffness ratio,the plastic hinge at beam end was not fully developed,but the plastic hinge at column end is easier to achieve.The structures with beam-hinge failure mode still had a certain vertical bearing capacity even the inter-layer drift angle reached the specified limit value 1/50,far from the ultimate state of collapse;(3)Taking the beam-column subassemblages as the objects,the constitution of structural inter-story drift and the evolution law of individual nonlinear deformation in the overall deformation were analyzed.By defining a reduction coefficient,the relationship between the inter-story drift of frame structures and the deformation of members was established in elastic state and elastoplastic state;(4)Taking the influence of multiple factors,such as component types,component importance,damage degree and storey position on structural stability into consideration,a damage model was established,which could reflect the relationship between members damage and structural collapse.The collapse mechanism of structures under strong earthquake was revealed by analyzing the damage distribution in member-level,storey-level and structure-level.Meanwhile,a seismic vulnerability assessment method was conducted by regarding the integral damage index as demand parameters;The deformation ability of reinforced concrete frame structures under strong earthquake is studied in this thesis.The relationship between structural collapse and member deformation is established.The measures to make the deformation capacity and energy dissipation of frame structures fully played were improved.This research provides experimental data and theoretical basis for further understanding the seismic collapse characteristics of reinforced concrete structures and optimizing the anti-collapse design method.