Methodology For Assessing Life-cycle Seismic Resilience Of Structures

Earthquakes can usually lead to immense economic losses,casualties,and serious socioenvironmental impacts,and China is one of the countries that are most seriously affected by earthquakes.With the increase of the service time,chloride ions induced corrosion in the concrete structure can cause cross-section reduction of the corroded bars,the degradation of the mechanical properties of the reinforcing steel,and the crack and spalling of the concrete cover,which will lead to the decrease of the seismic performance of the concrete structure.The corrosion in steel structures can also cause cross-section reduction of the steel components and the degradation of the mechanical properties,which will lead to a decrease in the load-carrying capacity and seismic performance of the steel structures.A large number of investigation results show that structural damage caused by corrosion can cause huge economic losses,making it more difficult to recover after earthquakes.It is of theoretical and practical significance to consider the deterioration effect of corrosion on the seismic performance of structures.Seismic resilience is a comprehensive measure to evaluate the seismic performance,post-earthquake loss,and post-earthquake recovery of structures.Reliable and comprehensive resilience evaluation of new or existing building structures before the earthquake and repair or retrofitting the buildings that do not meet the expected performance goals can effectively reduce the postearthquake loss of structures,shorten the post-earthquake recovery time,and control the negative impact due to earthquakes.Based on the existing studies associated with corrosion tests,the life-cycle seismic resilience of building structures is investigated comprehensively and systematically by combining experimental study,theoretical analysis,and case study.The detailed works are as follows:(1)To address the problem associated with insufficient research on seismic resilience assessment for structures with different service times,this paper proposes a comprehensive framework for assessing life-cycle seismic resilience.This framework can evaluate postearthquake losses for structures with varying service times,and enable direct application in assessing their seismic resilience.Additionally,a loss prediction model for RC frame structures concerning service time is presented in this study.By utilizing this model,the life-cycle seismic resilience indicators for structures with different service times can be efficiently derived,which provides valuable reference information for post-earthquake disaster assessment with similar structures and offers crucial risk decision-making insights for policymakers such as governments.(2)To deal with the problem concerning inaccurate resilience assessment due to excessive simplification of the recovery model,a modified recovery model is proposed in the paper.According to the properties of differentiable functions and power series,the form of power series is adopted for the modified recovery model.The traditional recovery model can only be used to evaluate the seismic resilience of structures under certain assumptions.However,the modified recovery model does not require too many assumptions.Besides,this model can not only take into account the characteristics of traditional recovery models but also describe other complex recovery processes,allowing for the inclusion of more recovery paths.Thus it has a wider application.(3)Traditional methods may usually lead to the inaccurate assessment of functionality,which can cause inaccurate and unreliable resilience assessment finally.To this end,this paper proposes 8 different methods to evaluate functionality losses and seismic resilience.The seismic resilience of uncorroded and corroded multi-story steel frames is studied by using the proposed methods and the modified recovery model.The effects of 8 different methods on the resilience of steel frame structures with different service times are studied and compared.The results show that different seismic resilience is obtained for the selected 8 methods.This can be attributed to the fact that these 8 methods are used based on different performance measures.Performance measures are the basis for resilience assessment,and thus the accurate and reliable resilience assessment should consider economic loss(direct and indirect economic loss),downtime(rational and irrational downtime),casualties,and probability of incurring unsafe placarding.The improper performance measures used in the functionality assessment can cause an inaccurate resilience assessment.(4)To solve the cross problem of fragility curves for structures with different service times, an improved fragility analysis method that considers the corrosion effects is proposed in this paper.A new functionality loss ratio assessment model that considers the contribution of direct and indirect economic losses,rational downtime(repair time),irrational downtime(e.g.,inspection time and engineering mobilization time),casualties,and unsafe placarding is proposed to study the seismic resilience of self-centering energy dissipation braced steel frame structures with different service times.Besides,the method suggested in HAZUS is also used to evaluate the seismic resilience of self-centering energy dissipative braced steel frame structures with different service times.The proposed method and the HAZUS method are compared,and the feasibility of the proposed method is validated.(5)To overcome the problems concerning low energy dissipation,poor ductility,and difficulty in replacing the damaged wall after earthquakes,a resilient precast self-centering energy dissipative shear wall is designed and manufactured.The pseudo-static tests are performed for the full-scale resilient precast self-centering energy dissipative shear wall specimen and cast-in-place RC shear wall specimen,and the results show that the hysteretic curve of resilient precast self-centering energy dissipative shear wall specimen has a typical flag shape,which shows good self-centering capacity.Compared with the cast-in-place RC shear wall,the resilient precast self-centering energy dissipative shear wall has a slightly lower load capacity,higher stiffness,larger energy dissipation capacity,stronger deformation capacity,and smaller residual displacement.(6)To study the improvement level of seismic resilience of RC frame-resilient precast selfcentering energy dissipative shear wall structures,the seismic resilience of RC frame-resilient precast self-centering shear wall structures and RC frame-shear wall structures with different service times is evaluated based on the proposed modified recovery function model,functionality loss assessment method,and the new time-dependent functionality loss assessment model.The results show that resilience improvement of RC frame-resilient precast self-centering shear wall structures is positively correlated with ground motion intensity and service time;RC frame-resilient precast self-centering shear wall structures have smaller earthquake losses,shorter recovery time,and higher seismic resilience when compared to RC frame-shear wall structures under the same disaster level,and the impact of corrosion on RC frame-resilient precast self-centering shear wall structures is less than that of RC frame-shear wall structures.For rare earthquakes,the resilience of RC frame-resilient precast self-centering shear wall structure is increased to 0.45% when considering the service time of 0 years,while the resilience is increased to 5.89% when considering the service time of 55 years.(7)To illustrate the generality and universality of the proposed methodology,life-cycle resilience assessments of the RC frame,steel frame,self-centering energy dissipation braced steel frame,RC frame-resilient precast self-centering shear wall structure,and the traditional RC frame-shear wall structure are performed.The results show that the corrosion will reduce the structural stiffness,increase the fundamental period,increase the peak inter-story drift ratio and the residual drift ratio,and decrease the peak floor acceleration.Besides,the corrosion can lead to an increase in the seismic fragility.The corroded structures are easier to damage under earthquakes,and post-earthquake recovery is more difficult due to the larger losses and longer recovery time,and the decrease in resilience can be achieved with the increase in service time.The greater impact of corrosion on the losses,recovery time,and resilience can be observed when considering the higher ground motion intensity.