A Study On Seismic Performance Of Precast Prestressed Concrete Frame Structure Assembled With Dry Connections

In the 1990s,the US developed the precast seismic structural systems(PRESSS),issued relevant technical standards and carried out typical engineering practices.PRESSS adopts a hybrid beam–column connection combined through unbonded posttensioned tendons and partially unbonded energy-dissipated bars.It is characterized by high construction efficiency,low earthquake damage,good ductility,and self-centering behavior.The beam–column dry connection of PRESSS results in a weak torsional performance at the interface of the connection.The existing research on seismic performance of dry connections does not consider the influence of initial torsion at the beam end.Research conducted on the shaking table test to determine the overall seismic performance of PRESSS is limited.Moreover,further verification to confirm the impact of a precast concrete floor system on the seismic performance of a frame is required.Given this research gap in the literature,a pseudo-static test study was conducted to determine the seismic performance of a beam–column connection considering the initial torsion.Additionally,a shaking table test to determine the overall performance of the frame structure and a relevant finite element analysis(FEA)were also conducted.The main research content and results are as follows:(1)Comprehensive analyses of different connection types,including beam–column,slab–beam,column–column,and column–foundation connections,were carried out on a precast prestressed concrete frame assembled with dry connections.An analysis of the influence of a regular frame structure with a precast floor system on the lateral coordinated performance was performed.A diaphragm arrangement on the top story(located above 80% of the structure height)was proposed for better coordinated lateral deformation for the frame.(2)To determine the seismic performance,quasi-static tests of two sets of eight specimens with different reinforcement ratios and initial torsion were completed.The experimental results indicated that high reinforcement ratio,compared with medium reinforced ratio,resulted in the increase of concrete tensile and compressive damage on framed beam end,whereas concrete damage remains light,under ultimate drift ratio.As the drift ratio increased,the compression depth of the interface also decreased,the energy-dissipating steel bars yielded and dissipated energy,and the torsional performance of the connection was reduced.An interface torsional failure occurred in the loading or unloading states of the test,and the unloading state was more prone to torsional failure.After the torsional resistance failed,torsional deformation accumulated with the increasing of loading cycles and drift ratio and could not return to their initial positions.For low torsion-moment ratios,torsional deformation had limited adverse effects on the seismic performance of the connection,while high torsion-moment ratio leads to reverse effect.As the ratio of the longitudinal reinforcement increased,the torsional performance of the connection improved.(3)Based on the pseudo-static test,the FEA simulation of the seismic performance of the connection under initial torsion,and the theoretical analysis of the shear stress distribution on the compressed interface,the torsional failure characteristics and the mechanism under the moment–shear–torsion interaction of the connection interface are illustrated.Furthermore,the capacity calculation methods of the connection interface under the moment–shear–torsion interaction are proposed.(4)A shaking table test of a three-story precast prestressed concrete frame model,with a scale of 1:2,was carried out under different earthquake ground motion levels to study the seismic response of the structure,including the dynamic characteristics,acceleration and displacement response,damage distribution among others.The results revealed that the damage on the foot of the frame column was low,and the seismic damage locations of framed columns are consistent with the ‘ strong columnweak beam ' distribution of frame joints.The test model has the seismic yield mechanism featured by mixed hinges,prominent self-centering capacity,and satisfactory seismic performance under rare earthquake excitation.The precast slab could be adapted to the rotation of the beam end with no obvious residual slip.The frame with the diaphragm on the top story revealed a strong overall lateral deformation coordination performance.(5)The dynamic elastoplastic analysis of the shaking table test model under the sequential earthquake excitations was conducted based on the OpenSees.The simulation results show that the initial frequency and modal,acceleration and displacement response,and the damage distribution of the FEA model are relatively consitent with the test results,and the proposed simulation methodology of structural dynamic elastoplastic analysis is relatively rational.The FEA model built with frame joints meeting ‘strong column-weak beam' concept,performs well and exhibits the seismic mechanism characterized by framed beam-end connection yielded firstly and hinges on connection fully developed,and shows lower seismic damage on framed column.(6)According to results of the pseudo-static test of the connection,the shaking table test of the frame model and the relevant FEA simulation,suggestions for seismic design of precast prestressed concrete frame structure assembled with dry connections are proposed.