Research On Seismic Performance Of Function-recoverability Prefabricated Concrete Joints And Its Frame Structure

Prefabricated concrete joints and connections are weak in prefabricated structures.The seismic performance of prefabricated concrete joints and frame structural systems needs to be optimized and improved.This paper proposes an innovative prefabricated concrete joints and its frame structural system with the function of recoverability.Function-recoverability prefabricated concrete joints was mainly composed of replaceable energy-dissipation hinges with weakened constrained steel plate dampers,the core area of joints constrained by steel sleeves,precast concrete beams and columns.Function-recoverability prefabricated concrete joints are installed in the prefabricated frame structure,forming a function-recoverability prefabricated frame structure system,which achieves the seismic requierments about“strong column weak beam,strong shear weak bending,strong joints weak members of the seismic requirements”.Meanwhile,the joints are easy to assemble,exhibiting the performance of the plasticity-controllability,restoration and recoverability after a seismic event.This paper conducts the following research focusing on the function-recoverability prefabricated concrete joints and its frame structure:(1)The mechanical characteristics of replaceable weakened constrained steelplate dampers are the key of the force-transmission and plastic energy-dissipation of function-recoverability prefabricated concrete joints.Axial low cyclic reciprocating loading tests of 4 replaceable weakened constrained steel-plate dampers were carried out,in which the effect mechanism of weakened steel-plate dampers were analyzed.The failure modes,hysteretic curves,stiffness degradation,strength degradation and energy dissipation capacity were investigated.The finite element models of replaceable weakened constrained steel plate dampers were established and analyzed.The results showed that the weakened steel-plate damper cracked or broke at the hole-opened weakening part,achieving the controllability of plastic energy dissipation and failure mode.The damper's hysteretic curve was full and its equivalent damping coefficient was approximately 0.4,which exhibited good bearing capacity.The average ductility factor of all dampers were greater than seven performing good ductility.The entire stress process was divided into three stages,including elastic stage,plastic ultimate stage and fracturing failure stage.(2)Parameter analysis of replaceable weakened constrained steel-plate dampers was carried out.The hysteretic restoring force model was proposed.Finite models of different steel-plate weakened-form dampers were conducted to analyze the effect of variable parameters,including the hole-opened weakened size,the width-thickness ratio,and the thickness direction gap.The reasonable parameter range was provided.Simultaneously,a simplified mechanical model was established and the hysteretic restoring force model by value reversion was proposed.The results showed the reasonable parameter range was that the weakened length a/L was 0.25?0.55,the weakened width b/B was 0.2?0.5,the width-to-thickness ratio is not less than 12.50,and the gap in the thickness direction can't exceed 2mm.The proposed hysteretic constitutive model of replaceable weakened constrained steel-plate dampers can accurately simulate the mechanical performance of dampers.(3)The hysteretic behavior experimental research of function-recoverability prefabricated concrete joints was carried out under the axial low cyclic reciprocating loading.The first experimental study on the hysteretic performance of function-recoverability prefabricated concrete joints was implemented.Then,on the basis of the previous test,the second test was carried out by only replacing the weakened constrained steel-plate dampers damaged in the energy dissipation hinge.Finally,hysteretic performance tests of the cast-in-place reinforced concrete joints were conducted.Through three tests,the seismic performance of each joint such as the failure modes,component bearing capacity,crack development,stiffness degradation,strength degradation,ductility and energy-dissipation capacity was investigated.The bending moment capacity,sloping ductility and energy-dissipation capacity of replaceable energy-dissipation hinges was discussed.Two tests of assembled joints and cast-in-place joints were compared.The results showed that function-recoverability prefabricated concrete joints exhibited the rational failure mode with the mode-controllability,appearing that about seventy percent energy dissipation focused on the replaceable energy-dissipation hinges.Observing the second joint test,in addition to the decrease in stiffness in the early stage,the performance in the later stage was basically same.It showed that joints could restore original functions by easily replacing damaged dampers after an earthquake event which verified the feasibility of function-recoverability prefabricated concrete joints.The seismic performance of function-recoverability prefabricated concrete joints was superior to that of cast-in-place reinforced concrete joints.(4)The numerical analysis of function-recoverability prefabricated concrete joints and its frame structure carried out.The mechanism of function-recoverability prefabricated concrete joints was discussed.The finite element model of the cast-in-place concrete structure and the reinforced cast-in-place concrete frame structure was established,containing the exploration of seismic performance and failure modes for three kinds of structural systems.The results showed that the numerical calculation results of hysteretic curves and skeleton curves are basically consistent with experimental results for function-recoverability prefabricated concrete joints,exhibiting the difference between bearing capacity and stiffness was within 5%.The energy-dissipation,plastic development,damage of function-recoverability prefabricated concrete joints and its frame structure all concentrated on weakened constrained steel-plate dampers in energy-dissipation hinges,achieving the controllability of plastic development.It made structural system appear the better bearing-capacity,rational failure mechanism and good ductility,implementing “strong column weak beam,strong joints weak members” of the seismic requirements”.