Seismic Resilience Analysis Of Precast Concrete Frame Structures With “Dry” Connections

Precast concrete frames(PCFs)have been widely put into engineering practice in China given their advantages such as construction efficiency,rapid repair speed,energy conservation,and labor saving.According to the assembling method at the beam-column connections,PCF structures can be divided into two categories,namely the “wet” connected PCFs and the “dry”connected PCFs.Compared with the “wet” connected ones,the PCFs with “dry” connections are subject to very limited engineering applications.The reasons are threefold:(1)there is no existing seismic design code applicable to PCFs with “dry” connections;(2)the mechanical properties and design methods are still in research stage for this structural system;and(3)doubts arise from both the academia and the industry on the seismic performances,especially on the behaviors of panel zones under strong ground motion excitations,of this structural system.To manifest the rapid post-earthquake recovery and excellent seismic resilience of PCFs with “dry” connections,this study proposed a resilience incorporated seismic risk quantification framework.The uncertainties are coherently integrated into this framework from seismic hazard,structural seismic demand and capacity,damage and loss,and recovery path.The current study aims to provide reliable and practical seismic resilience methods for single building structures.This framework is demonstrated through a comprehensive comparative study in a specific engineering case,where three structural seismic design alternatives located at a highly seismic fortification zone,namely: two “dry” connected precast frames and one conventional cast-insite one,are designed and simulated as prototype structures.A comparative study is comprehensively conducted in terms of probabilistic seismic demand and capacity,earthquake loss,post-earthquake recovery,and seismic risk of the three prototype structures.Specifically,the research contents involved are as follows:(1)Numerical models of the RCF and the PCFs in this study are developed in Open Sees platform.The numerical modeling of the “dry” connection is validated by comparing the simulated responses with the experimental results.Three alternative structural systems are designed for a five-story archetype building,namely a conventional ductile RCF and two PCF structures(one with web friction devices and one without).The PCF structures are designed through a displacement-based seismic design method,where two design phases are involved.Nonlinear time-history analyses with quadruple seismic performance levels are performed to demonstrated the structural alternatives satisfy the requirements of seismic fortification,whilst the prototype structures are comparative in probabilistic manner.The established structural models are used for seismic evaluations in the subsequent chapters.(2)Site-specific seismic hazard analysis,along with probabilistic seismic fragility and demand analyses are conducted based on the site information and structural models.Separately considering the collapse and demolition events,fragility functions are established based on the results of incremental dynamic analysis.Based on the probabilistic deformation responses in each story,the deformation hazard functions are established both in the story level and in the building level.(3)A comprehensive capacity model is established for both structural and non-structural components for the repair event.Considering the lack of a capacity database for “dry”connected structures,the current study utilizes a story-based probabilistic pushover analysis to establish the capacity model for the PCFs in a story-wise manner.For this end,a detailed literature review on experimental observations is performed to determine the limit states for both PCFs and RCFs.According to the definitions of limit states,the story-wise pushover analyses considering the uncertainty in structural parameters are conducted to identify the capacity parameters for the PCFs in each story.For non-structural components,a thorough capacity database is compiled through literature review.(4)A resilience-incorporated seismic risk analysis framework is proposed.The conventional “performance-based” seismic assessment framework is extended where the invariable decision variables,namely the economic loss and downtime,is propagated to the seismic resilience analysis procedure.Two main efforts are made in the resilience analysis procedure:(1)the resilience loss is evaluated as an additional decision variable besides economic loss and downtime;(2)the estimated story-wise repair costs and time are converted to represent functionality increments along the repair actions.The functionality increments are accumulated according to their completion time to form the step-wise recovery process for calculating the resilience loss.As such,the recovery process established in this way does not rely on any empirical judgment and reflects the contingency of the repairs in different stories.Additionally,the uncertainties in the repair costs and time propagate into the recovery process and consequently into the resilience loss.(5)Separately considering the contribution from the repair,the demolition,and the collapse events,estimations for three types of earthquake losses(i.e.,economic loss,downtime and resilience loss)are conducted.For the non-repair event,the estimation is performed in the building level;whilst for the repair event,considering the differences of seismic damage in building components,the estimation is conducted in the component level based on a comprehensive damage-loss database.In light of the information of repair time and cost regarding different repair stages,the post-earthquake functionality recovery process is stochastically sampled for probabilistic seismic resilience analysis.Lastly,the seismic risk quantification is performed based on the results of earthquake loss and seismic hazard information.(6)The above seismic resilience analyses in the preceding five chapters are based on twodimensional models,which cannot fully reflect the interactions for real structures under bidirectional ground motion excitations.The last chapter takes one of the prototype structures as an example,a pilot study is carrid out for the three-dimensional model under bi-directional horizontal ground motion excitations.Additionally,in view of the randomness of ground motion directionality,the ground motions are randomly rotated to different incidence angles as structural inputs,in an effort to quantitatively evaluate the effects of directionality on seismic resilience and functionality recovery.Lastly the findings of the full article and are summarized,along with a brief discussion of several directions for future research.