Research On Seismic Performance Of RC Frame Structure In Villages And Bracing Schemes

Structural seismic resistance has always been a maj or scientific issue.The survey of strong earthquake disasters of the past two decades in China shows that the seismic damage of building structures in villages is more severe than that in urban areas.The RC frame structure is particularly damaged during earthquakes in villages,while it is always considered with good seismic performance.The reasons for the insufficient seismic capacity of village buildings during earthquakes are complicated.The most important reasons include random layout of the structure,insufficient size design of structural components,and non-standard building materials Research on the evaluation and enhancement of the seismic performance of buildings in villages is not systematic currently.Moreover,the seismic performance evaluation of seismic-damaged structures is a great challenge,as the quantitative relationship between structural damage and structural performance degradation have always been a technical problem.Based on the above research background,this thesis conducts research on seismic performance of RC frame structures with insufficient cross-section sizes of components in villages and seismic-damaged RC frame structures.Contents of this study are as follows:1)A typical poorly design RC frame structure model with insufficient component crosssection size is established to study the seimic performance of typical poorly design RC frame structure(PDS)in villages.A method for improving the seismic resistance of PDS with external braces is proposed,and the influence of external braces on the seismic performance of PDS is quantitatively analyzed.40 ground motion records are selected for dynamic analysis and collapse fragility analysis in this study.The seismic performance of PDS,standard design frame structure(SDS)and PDS with three groups of external braces are analyzed.The results show that the collapse resistance of PDS is obviously lower than SDS,which cannot meet the safety requirements during earthquakes.The appropriate external bracing scheme can improve the seismic performance of PDS structure significantly,especially the collapse resistance of the structure under earthquake can reach the level of SDS.2)In order to quantify the relationship between the damage of RC members and mechanical degradation,a restoring force model of seismic damaged compression-bending RC members based on damage index is proposed.Firstly,strength and stiffness reduction factors are introduced using hysteretic energy consumption based strength reduction,restoring force model based on the ModIMK material model is constructed for seismic damaged compressionbending RC members.Secondly,the relationship between strength and stiffness reduction coefficients based on damage index is regressed using the data of RC column cyclic reciprocating test in PEER database,which means that the relationship between RC component damage and seismic damage RC members performance degradation is realized.Considering the random nature of RC members and earthquakes,the probability distribution curves of strength and stiffness reduction coefficients of seismic-damaged compression-bending RC members are proposed.Finally,the damage index based restoring force model for seismicdamaged compression-bending RC members is proposed.3)A seismic-damaged RC frame structure model based on the damage areas is propose,the accuracy and effectiveness of which are verified by the comparison of shaking table test.Currently,the establishment of numerical models of seismic damaged RC frame structures is usually carried out based on materials or components,which have problems such as complex calculations,heavy workload,and low accuracy.The damage mechanism of the RC frame structure during earthquakes determines that structural damage is concentrated on the two ends of columns,the two ends of beams and the middle of the beams,while the damage levels are different in different areas.A seismic-damaged RC frame structure model based on the damage areas is propose according to the seismic failure phenomenon and mechanism of the RC frame structures.The preparation and applicability of the method is verified by a shaking table test of RC frame structure in this paper.4)Quantitative analysis of the seismic performance of the seimisc-damaged PDS and the influence of the external braces on the seismic performance of seimisc-damaged PDS are performed.Firstly,damage indexes of damaged areas are determined through nonlinear timehistory analysis under earthquakes with different intensities.Then,the seismic-damaged PDS models are established using the damage-area based model.Seismic resistance of two differently seismic damaged PDS structure are assessed.The influence of the external braces on the dynamic response and seismic collapse fragility of the damaged PDS is quantitatively analyzed,which provides a scientific basis for improving the seismic performance of the seismic-damaged PDS.