Performance-based Seismic Resilience Assessment And Improvement Of RC Frame Structures

Earthquake is a natural hazard that could be a great threat to human communities.Some recent earthquakes indicate that grate earthquake could induce a large number of casualties as well as the destruction of many structures and infrastructures.The great earthquake could also cause huge economic losses and hence hinder the development of the society.Seeking the methods to ensure the security of structures under earthquake and reduce the economic losses and social impacts caused by the earthquake have been a main issue for researchers for a long time.Recently,research interests of researchers have shifted from the traditional seismic capacity to seismic resilience of the structures after earthquakes and they try to reduce the long time impacts to society of the earthquake by improving the seismic resilience of structures.There are many districts near the fault in China and these districts have high probabilities experiencing earthquakes.Hence it is of great importance to conduct researches regarding seismic resilience assessment and improvement of structures as it can help to ensure the safety of people's lives and properties as well as social development.This thesis mainly focus on the reinforced concrete(RC)frame structures as they are widely used in China.This work tries to establish a more systematic method for evaluating and improving seismic resilience of existing RC frame structures.Addressing the present research drawbacks,this work will conduct studies regarding the seismic modelling method for concrete columns,seismic fragility as well as seismic losses analysis of the buildings.And based on these theoretical tools,this work will try to propose methods for evaluating and improving seismic resilience of existing RC frame structures.Detailed research works are summarized as below:(1)This study will firstly investigate the seismic modelling method of RC columns that can consider the corrosion induced deterioration effects and the flexure-shear interaction behaviours of column under seismic loadings.Based on the macro-element coupling method,a new shear element is proposed and added to the flexural element and hence the flexure-shear interaction can be considered.The shear hysteretic model is developed based on the Modified Compression Field Theory(MCFT)and test data of 25 corroded RC columns failed in shear,respectively.The modeling accuracy of the proposed model is verified through comparing the predicted and test results for several corroded RC columns.Moreover,based on the proposed numerical model,the corrosion effects on failure mode and seismic performance of column are investigated and discussed.(2)This study investigates the time-dependent seismic fragility of RC frame structures considering corrosion effects.The traditional seismic fragility analysis method for RC frame structures is extended in time-scale in order to consider the corrosion effects.Based on the proposed modeling method for RC column,the building numerical model of RC frame is developed in order to consider corrosion induced deterioration effects and then,the timedependent seismic fragility analysis method is proposed.Seismic fragility analysis is conducted for a case RC frame and the effects of corrosion and ground motion characteristics on seismic fragility of RC frame structures are investiagetd and discussed.(3)The evaluation method of earthquake induced economic losses of RC frame structures is investigated.Based on the building-based losses evaluation method in HAZUS,this work considers the losses induced by the demolition of the building due to the large residual deformation.Then a simple and accurate seismic losses evaluation method for RC frame structures is developed.Seismic losses analysis is conducted for a case RC frame and the effects of residual deformation and ground motion characteristics on losses evaluation results are discussed.(4)Based on the developed theoretical analysis tools,this work investigates the seismic resilience analysis method for existing RC frame structures.The residual functionality,seismic losses and restoration time are adopted as the resilience index for RC frame structures.The uncertainties from ground motions,structures,residual functionalities as well as repair strategies after earthquake are considered in the resilience evaluation framework in order to provide more reliable evaluation results.Seismic resilience analysis is conducted for a case RC frame and the effects of corrosion levels and ground motion characteristics on evaluation results are discussed.(5)A seismic resilience improvement method for RC frame structures that can consider the near fault seismic hazard and corrosion hazard is proposed in this study.The seismic resilience is adopted as the index for evaluating the retrofit effectiveness.The probabilistic near fault seismic hazard analysis is used in order to consider the near fault seismic hazard and is adopted in calculating the damage and resilience of the structures.The corrosion modelling method is used in order to consider the corrosion hazard.Comparison analysis of the seismic resilience is conducted for a case RC frame before and after seismic retrofit and the “fault effect”of the seismic resilience for RC frame structures located in near fault region is discussed.Finally,the main conclusions are summarized and a brief discussion on the future works is given.