Energy-based Damage Assessment,retrofitting Design And Resilience Research Of Earthquake-damaged RC Frames

As a country with frequent earthquakes,earthquake disasters have caused a large number of casualties and economic loss.The arrival of aftershocks and even earthquake swarms will lead to increased damage to houses,which will seriously affect production and life in the earthquake area.Correct and rapid assessment of structural damage under earthquake and safety assessment of earthquake-damaged structures is helpful for rescue and production recovery,as well as providing a basis for decision-making on earthquake-damaged structures.For seismically damaged frames that do not meet the current seismic codes in the earthquake zone,it is obvious that the retrofitting measures are more in line with the requirements of economy and safety,and the retrofitting methods for seismically damaged structures deserve further study.Recoverability can evaluate the ability of a structure to recover under an earthquake,which has guiding significance for the recovery of the disaster area to a normal state,and can also evaluate the economics of the structure in relation to the structural loss.In this paper,the research on the seismic performance of the structure under the action of the mainshock-aftershock sequence is carried out to carry out the retrofitting design,and the research on the recoverability of the structure is carried out.The main contents and achievements are as follows:(1)The energy-based earthquake damage index is used to evaluate the structural damage,and a theoretical framework for holistic damage assessment under the action of the mainshock-aftershock sequence is established.Then,the structural damage under the mainshock-aftershock sequence is quantified based on the I_V damage index,the collapse capacity curve of the damaged structure is obtained,and the remaining capacity of the structure to withstand strong aftershocks is determined.The results show that compared with an earthquake,the mainshock-aftershock sequence will significantly increase the structural damage;the initial damage index of the earthquake-damaged structure is bigger,the smaller the aftershock intensity leads to the collapse of the structure;it decreases with the increase of the initial damage index of the earthquake-damaged structure,and the decreasing rate gradually accelerates until the remaining collapse capacity decreases to 0.(2)Analyzing the retrofitting of seismic damaged RC frames from the perspective of energy,extending the energy balance analysis of seismic structures to the retrofitting of the structure,obtaining the energy method of the retrofitting design of the structure,and giving the retrofitting suggestions from the perspective of energy.On this basis,the process of strengthening the seismic damage RC frame with FRP and BRB strengthening the seismic damage RC frame is described in detail.The results show that the seismic damage RC frame reinforced by FRP can meet the setting damage limit,and it is found that the key retrofitting in the weak part can reduce the damage and save the retrofitting cost at the same time;the energy-based BRB retrofitting design method is used to determine the parameters of the BRB required for each floor,the analysis results show that this method can basically achieve the seismic capacity of the intact frame and limit the lateral movement of the structure for BRB retrofitting of the seismically damaged RC frame,which also shows the effectiveness of the energy-based BRB retrofitting design method.(3)Numerical models of intact RC frame,earthquake-damaged RC frame,damage-based FRP-retrofitting earthquake-damaged RC frame and energy-based BRB-retrofitting earthquake-damaged RC frame were established,and the vulnerability analysis under the mainshock was extended to the mainshock-aftershock by defining the vector ground motion intensity IM=(IM_m,IM_a).For the seismic vulnerability analysis under the sequence,the cloud image method is used to analyze the vulnerability of the intact RC frame and the energy-based BRB-retrofitting earthquake-damaged RC frame under the mainshock-aftershocks and the earthquake-damaged RC frame under the aftershocks.The results show that compared with the intact RC frame,the earthquake-damaged RC frame has a greater probability of IO,LS,and CP states under the same ground motion intensity,especially the surpassing probability of the CP state decreased more.Compared with the earthquake-damaged RC frame,the energy-based BRB-retrofitting earthquake-damaged RC frame has a significantly lower probability of IO,LS,and CP states under the same ground motion intensity.The energy-based BRB retrofitting design method can improve the seismic performance of the earthquake-damaged RC frame to the undamaged state,which is helpful to improve the collapse resistance of the earthquake-damaged RC frame.(4)Based on the analysis of vulnerability under mainshock-aftershocks,and considering the uncertainty of residual function,recovery function,and recovery time,the structural recoverability assessment process considering the influence of mainshock-aftershocks is given.The results show that compared with the intact RC frame,the recoverability index of the earthquake-damaged RC frame under the same ground motion intensity is significantly smaller,which also shows that the earthquake-damaged RC frame needs more resources to restore its function in subsequent earthquakes;Compared with the earthquake-damaged RC frame,the recoverability index of the energy-based BRB-retrofitting earthquake-damaged RC frame under the same seismic intensity is greatly improved;the energy-based BRB retrofitting design method can improve the recoverability of the earthquake-damaged RC frame to the undamaged state,it contributes to the sustainable development of the building structure.The energy-based BRB retrofitting design method improves the recoverability value of the earthquake-damaged RC frame slightly more than the damage-based FRP retrofitting design method;the recovery cost and recovery time of the structure increase with the increase of the earthquake intensity,until the reconstruction cost and reconstruction time.After BRB retrofitting of the earthquake-damaged RC frame,the structural recovery cost and recovery time are significantly reduced,and the retrofitting benefit increases with the increase of the service period,indicating that the energy-based BRB retrofitting method has high cost performance.