A Study On Seismic Performance Of Precast Post-tensioned Concrete Structure With Additional Energy Dissipaters

Earthquakes are one of the natural disasters that cities and residents may suffer.Their destructive effects on building structures and secondary disasters have become the main natural disasters in human history.China is one of the countries with the most serious earthquake disasters in the world.The Wenchuan earthquake with magnitude 8.0 in 2008,Yushu earthquake with magnitude 7.1 in 2010 and Ya'an earthquake with magnitude 7.0 in 2013 all caused huge casualties and economic losses.It is one of the important needs and urgent tasks of civil engineering to improve the seismic performance of building structural systems,study the theory of new structural systems and performance design,disaster effects,structural failure mechanism and dynamic control,and minimize earthquake hazards to the most extent.At present,the structural vibration control has attracted more and more attention from domestic structural engineers and researchers,among which the most prominent is to improve the seismic performance of structures by using various energy dissipation devices.Developing low-cost energy dissipation dampers with stable energy dissipation performance to improve the energy dissipation capacity of assembled concrete structures is considered as one of the key technologies to promote the application of assembled concrete structures in high intensity areas.At the same time,a series of earthquake damage studies show that the failure and ductility deficiency of the fabricated concrete beam-column joints are the main reasons for the more damage and catastrophic damage of the fabricated concrete structure,so it is very important to improve the reliability and ductility of the fabricated concrete joint area.In view of the above problems,this paper,by means of theoretical analysis,experimental research and numerical simulation,the bamboo-shaped energy dissipater,partially-restrained energy dissipater,precast self-centering concrete connection with additional energy dissipater and precast self-centering concrete frame with additional energy dissipater are systematically investigated from the aspects of the development of new energy dissipater,new precast concrete connection and precast frame fragility,respectively.All achievements in this paper are helpful to promote the formation of structures that can be repaired quickly after the earthquake,and to promote the research process of seismic resistance of sustainable development engineering structures.The main contents and conclusions of this paper are as follows:In the Chapter Two,a new type of bamboo-shaped energy dissipater with high durability is proposed by conceptual design.The hysteretic performance and low cycle fatigue life of the high performance aluminum alloy bamboo-shaped energy dissipater suitable for small strain conditions are evaluated by tests.The effects of design parameters on the deformation mode,failure mode and compression adjustment coefficient of the aluminium alloy bamboo-shaped energy dissipater were investigated through tests.The experimental results show that each performance index of the aluminium alloy bamboo-shaped energy dissipater is higly influenced by the above geometrical configurations and loading patterns.Besides,the effects of key design parameters on the hysteretic performance,low cycle fatigue life,deformation and failure mode and compression adjustment coefficient of all-steel bamboo-shaped energy dissipater are compared through tests.It is proved that it still has stable and reliable hysteretic performance,good fatigue life and controllable deformation and failure modes under large strain conditions.The torsional and contact states of bamboo-shaped core are evaluated by refined finite element analysis.The failure mechanism of bamboo-shaped energy dissipater is analyzed based on the cumulative plastic deformation.The multi-wave buckling behavior of bamboo-shaped core is discussed according to the buckling theory and the correction formula of core wavelength considering slub rotation is given.In Chapter Three,after analyzing the problems of the bamboo-shaped energy dissipater studied in Chapter Two,a new partially buckling-restrained mechanism is introduced,and a partially buckling-restrained energy dissipater characterized by high material utilization ratio is proposed,and the calculation formula for evaluating the material utilization ratio of the buckling-restrained energy dissipater is given quantitatively.Through theoretical deduction,the design methods related to the torsional buckling,anti-section expansion and local failure of the partially buckling-restrained energy dissipater are given.The reliability of the above theoretical design methods is verified by tests.The effects of the above parameters on hysteretic properties,low cycle fatigue life,deformation and failure modes,and basic mechanical properties are analyzed.The experimental results show that the partially buckling-restrained energy dissipater has excellent performance,which improves the material utilization ratio and hysteretic performance at the same time.The buckling response,contact state and plastic deformation of partially buckling-restrained energy dissipater are evaluated by the validated refined finite element model.In the Chapter Four,based on the previous research of energy dissipater,the all-steel bamboo-shaped energy dissipater is attached to the precast post-tensioned concrete connection in order to ensure the self-resetting capacity of the connection and improve the energy dissipation capacity of the connection.Five groups of static cyclic cyclic tests were carried out to study the effects of different loading patterns,initial prestressed force,geometric dimension,number and configurations of the energy dissipaters on the seismic performance of the precast connection.Deformation and failure modes,load-displacement responses,prestressed force variation during the whole tests,equivalent damping ratio and self-centering capacity of the precast concrete connection with additional energy dissipaters were analyzed and evaluated.The test results show that the new precast concrete connection presented in this paper have the characteristics of good energy dissipation,small residual displacement and controllable prestress loss.There is no degradation of strength and stiffness during loading process,and the connection can still maintain sufficient bearing capacity and energy dissipation capacity without repair under the directly repeated loading,which shows the ability of the precast connection to withstand strong aftershocks.The strain variation of steel bars reveals that the main structure of prefabricated beam-column basically retains elasticity during the loading process.At the same time,the calculation value of the height of the compression zone of the precast connection is given according to the test results.In Chapter Five,based on Open Sees,the numerical model of the precast post-tensioned concrete connection with additional energy dissipaters is established,and the numerical model is validated by using the experimental data of the precast concrete connection in Chapter Five.Combined with numerical parametric analysis,the effects of initial prestressed force,number of energy dissipaters,yield strength of energy dissipaters,installation location of energy dissipaters,column axial compression ratio,geometric dimensions of prefabricated beams on the bearing capacity and energy dissipation capacity of connections were studied.Finally,on the basis of numerical analysis and theoretical analysis of force equilibrium mechanism of the precast connection under loading and unloading,the proposed design formulas for the bearing capacity of the precast concrete connection and the criterion for the self-centering control of connection are given.In the Chapter Six,in order to deeply study the mechanical and hysteretic characteristics of the precast post-tensioned concrete connection with all-steel bamboo-shaped energy dissipaters,the connection is decomposed into two sub-systems: precast concrete beam and column-post-tensioend tendons and precast concrete beam and column joints-additional energy dissipater.The whole process of hysteretic loading of the connection is thus analyzed theoretically,and the macro hysteretic model of the precast concrete connection is established on the basis of the above analyses.Through the force analysis of free body,quantitative analysis and explicit formulas for calculating the rotational stiffness of the hysteretic model of the connection and the bending moment and rotation angle at the characteristic points are given.Combining with the experimental phenomena,each limit state of the precast connection is defined and derived.The characteristic loads and displacements corresponding to the limit states are quantitively given.In Chapter Seven,in order to widen the application of additional energy dissipater and improve the utilization efficiency of additional energy dissipater,a new type of precast posttensioned concrete connection with knee-braced energy dissipater is proposed.The relevant experimental studies are carried out and compared with precast post-tensioned concrete connection with additional horizontal energy dissipater.The bearing capacity of the precast post-tensioned concrete connection with knee-braced energy dissipater is theoretically analyzed.Based on the force mechanism,the theoretical hysteretic model of the knee-braced connection is established,and the three-dimensional numerical model of the knee-braced connection is established based on ABAQUS.The parameters of the angle between the axis of the knee brace and beam surface and the total length of the knee brace are analyzed with the calibrated numerical model.The formulas for calculating the positive and negative bearing capacities of the knee-braced connection are given.In Chapter Eight,in order to make up for the lack of consideration of the influence of floor slab on the performance of the precast post-tensioned concrete connection with additional energy dissipaters in the previous chapter,systematic experimental studies are carried out on the composite slab-precast post-tensioned concrete connection.The effects of the existence of composite slabs and multiple loads on the performance of the precast connection are evaluated.Systematic studies are conducted to study the variation law of the load-bearing capacity,energy dissipation capacity and self-centering ability of the composite slab-precast post-tensioned concrete connection under different test parameters.The reliability of the energy dissipaters subjected to multiple loads under full-scale test is investigated.Based on test results,it is found that the strength of the composite slab-precast post-tensioned concrete connection does not deteriorate during loading,but the strength of the connection decreases gradually with the increase of the number of loading cycles at the same drift ratio.The positive and negative strengths of the composite slab-precast post-tensioned concrete connection will decrease obviously without repairing under the condition of secondary loading.The residual deformation of the composite slab-precast post-tensioned concrete connection after once loading will increase the prestressed force after loading compared with the initial prestress.The energy dissipation capacity of the composite slab-precast post-tensioned concrete connection decreases gradually with the increase of loading times,and the cumulative energy dissipation of the secondary loading decreases significantly compared with the cumulative energy dissipation of the initial loading.In Chapter Nine,the pushover analysis is carried out for the precast post-tensioned concrete frame with additional energy dissipaters.And,the ultimate state and failure state of the structure are defined according to the capacity curve of the structure.The dynamic response of the structure is studied by dynamic elastic-plastic time history analyses,and the parameters of the probabilistic demand model of the structure are obtained by logarithmic linear regression method.Finally,based on the reliability theory,a structural failure model is established,and the fragility curve of the frame is drawn.