Research On The Seismic Performance Of The Existing Structures Retrofitted By The External Pbspc Frame-brace

Industrial and civil buildings will encounter problems such as reduced load-bearing capacity,reduced use functions,and substandard safety after a certain service period.Under these circumstances,if these structures are going to be used continually,they have to be upgraded and retrofitted.The current reinforcing process emphasizes on the component-level,but lacks the design principles and methods from the overall-level;the existing reinforcing process from the overall-level is mostly conducted by cast-in-place construction,and the structural form often relies on the damage of the beam and column to consume energy,thus the post-disaster deformation is severe and difficult to repair,which leads to the lack of applicable new system with high efficiency;although the existing precast technology is efficient,it is mainly used in new structures.Based on the aforementioned background,this paper proposes a new type of external precast bolt-connected steel plate reinforced concrete(PBSPC)frame-brace system,which combines the additional sub-structure technology,prefabrication-assembly technology,postearthquake self-recovery technology and damage control technology.The proposed system collaborates with the original structure to achieve the improvement of the existing structures from the overall-level.This paper discusses the retrofitting performance of the new system in detail from five levels,based on the research ideas of partial component-overall structure,testsimulation-design,deterministic analysis-probability analysis.The related calculations and data comparisons can be used for the promotion and application of the precast bolt-connected steel plate reinforced concrete frame-brace system.The specific research contents of this paper includes:(1)Propose a new type of assembled bolt-connected buckling restrained brace(AB-BRB).Specifically,it focuses on analyzing the hysteretic performance and post-disaster repair /replacing capabilities,and the design method of this new type of brace is put forward.Twelve specimens are manufactured for experimental verification,and the out-of-plane constraint amplification factor is introduced.The quasi-static experiments are conducted to study the hysteretic performance,and six types of performance evaluation indexes are given to evaluate the hysteretic trends.A numerical model of the AB-BRB is established,considering the impact of concrete damage parameters on the hysteretic performance.This research can provide a basis for the application of the precast buckling restrained brace,and provide data for the research of the novel frame-brace retrofitting system.(2)Carry out the experimental research of the precast bolt-connected steel plate reinforced concrete frame-brace.Specifically,quasi-static experiments are carried out based on seven sets of specimens,and the failure mechanism and force characteristics are studied from the aspects of retrofitting principle,test plan,failure mode,and result analysis.Each group of specimens is compared in pairs to analyze the parameter influences in the overall performance,including the precast / cast-in-place construction,with / without external frame,with / without external brace and with / without external prestressed tendons,etc.This study explores the test results of the retrofitting system and provides a data basis for the numerical simulation and design theory.(3)Establish a numerical model of the precast bolt-connected steel plate reinforced concrete frame-brace,and carry out the corresponding evaluation research on the static response.Specifically,detailed local models of two types of precast concrete joints(wet and dry)are established,and the efficient overall models of two-dimensional and three-dimensional retrofitted systems are established.The influence of factors such as assembly / post-casting,steel plate slip,and bolt connections are considered,and parameter analyses are carried out to expand the test data to predict the impact of various variables on the overall upgrading performance.The research supplements with the experimental data mutually and provides the model / static base for the subsequent dynamic analyses.(4)Propose the design method of the precast bolt-connected steel plate reinforced concrete frame-brace,and carry out the corresponding evaluation research on the dynamic response.Specifically,combined with the test-simulation data,the design process is divided into 3modules and 12 steps,and during the process the assembly reduction factor is proposed.Two retrofitting cases(single and multiple)are considered,and the numerical models before and after upgrading are established.The dynamic time history responses and performance indicators are evaluated,and the contributions of external components are compared to verify the effectiveness of the design method.The research summarizes the theoretical methods of the retrofitting system,and provides a dynamic basis for the subsequent probability analysis.(5)Establish a probabilistic seismic assessment process for the precast bolt-connected steel plate reinforced concrete frame-brace.Specifically,for the seismic capacity analysis,the average median value and average logarithmic standard deviation of the damage indicators are given,corresponding to each limit state;for the seismic demand analysis,the displacement demand,exceeding probability and the overall reliability of the structure before and after upgrading are analyzed,combined with the two previous cases;for the seismic loss analysis,the overall structural indicators are adopted from the structural-system perspective.The proportions of repair,demolition and collapse losses are discussed,and the corresponding function / resilience indicators are evaluated.This research provides reference for the substructure optimizations,performance improvements and economic evaluations of the retrofitting system.Based on the above-mentioned experimental analysis,numerical analysis,theoretical analysis and probabilistic analysis,this paper conducts a detailed and in-depth study on the seismic performance of the new external precast bolt-connected steel plate reinforced concrete frame-brace.The performance changes and development trends of the existing structures upgraded by the novel frame-brace system are evaluated comprehensively,and the applicability conclusion and mechanism description are given subsequently,which provides references for the promotion and application of the external retrofitting system in the seismic-prone regions.