Research On Seismic Performance Evaluation Method Of Earthquake Damaged RC Frame Structures

Destructive earthquakes occur occasionally in our country, and these earthquakeshave led to a large number of damaged engineering structures; meanwhile, the earlymassive concrete structures, especially the earthquake-damaged buildings, have thephenomenon of premature deterioration thatneed to be maintained or strengthened, andsome buildings even face the situation of early retirement. Therefore, it is significanceto evaluate the seismic performance ofearthquake-damaged reinforced concretestructures.This paper took RC frame structure as the object，and three research contentsfor the earthquake-damagedstructures, includingearthquake action calculation, damagemodel determine and seismie performance evaluation method were deply studied in thispaper.The main contents and resultsof thispaper as following:①The Homogeneous Poisson distribution modelsand the Inhomogeneous Poissonprobabilistic models for earthquake occurrencewere established to characterizeif theconstruction site will consider the history earthquake informations.The seismicappraisal criteria of structures in different seismic risk were established based on theearthquake occurrenceprobabilistic models.Considering the different residual servicelives of structures and the different exceeding probability of earthquake in different sites,the calculation formulas of exceeding probability of assessment intensities were derived,while the exceeding probability based on the residual service life was converted to thewell-matched exceeding probability based on the design reference period (i.e.,50years);The values of small earthquake intensity and major earthquake intensity of three zoneswith different seismic hazard characteristics were studied in this paper, then theconversion among maximum horizontal earthquake influence coefficient, peak groundacceleration and seismic intensity were derived; the modification factors of seismicaction of buildings at the three zones with different seismic appraisal assessment criteriaand different residual service lives were provided in this paper.②The hysteresis curve datas of47compression-flexure concrete columnswereselected in the study, and the damage index values corresponding to different damagestatus of each damaged concrete column were calculated usingthe Park-Ang damageindex calculation formula.Through regression analysis, the fitting relations betweenstiffness degradation coefficient(strength degradation coefficient)and damage index values of damaged members were obtained. The restoring force model of damagedmembers only considering seismic damage was established in this paper, and on thisbasis, restoring force model determining method of earthquake damaged membersconsidering the durability of material was given. Noticed the close relationship betweenconcrete carbonation depth and concrete material deterioration constitutive relationship,Bayesian Updating was incorporated to reevaluate the results obtained viawell-established models, and its accuracy and objectivity is enhanced extensively byBayesian updating.③In the methods of seismic performance evaluation of existing structures,thestatic elastic-plastic analysis method is oneofimportant method. Based on the modalelastic-plastic theory, considering the advantagesof dynamic time history analysismethod and static elastic-plastic analysis method, the determination of targetdisplacements for buildings under the earthquake action and the load pattern ofpushover analysis considering higher mode effects were improved in this paper, andthen the detailseismic performanceevaluating processof the new improvedmethodpropose by the authorfor structures was given. Make the modified pushovermethod applying to the performance evaluation fortwoundamagedframestructures(five-story and ten-storyframe structure) and a seismic damageten-storyframestructure. The results show that the modified pushover method can efficiently simulatethe seicmic response of structure under earthquake action and also can embody thenonlinear behavior of the earthquake-damage structure during the subsequentearthquakes.④Considering that seismic fragility analysis is an essential content of theperformance-based seismic assessment on existing structures,and the groups of structureperformance objective on three traditional levels of horizontal earthquake action can’treasonably describe the five seismic performance objectivesdefined by the current codeof seismic design, especiallycan’t provide a basis for seismic performance assessment ofslight earthquake damaged structure. In order to perfect the performance-based seismicperformance assesment system of existing reinforced concrete structures, the authordefined a new earthquake action level with exceeding probability of40%in50yearsnamed medium-small earthquake aimed at the different seismic risk level characteristicswhich may be encountered for the existing structures. Based on the available actionlevel of small, mediumand strong earthquake, and established the seismic performanceobjectives corresponding to different earthquake action levels of exciting RC structures, in order to perfect the performance-based seismic performance assesment system ofexisting RC structures.⑤A theory system and basic procedure of evaluating the seismic performance ofRC structures after earthquake was established. And then, a10-layers RC framestructure was taken to explain the damage model in seismic performance evaluationprocess, and how to confirm the assessment earthquake action of earthquake damagedstructures. And the influence of the different damage locations to the reliability andapplicability of different evaluation methods were checked.