Experimental Study On Seismic Performance Of Bolted Prefabricated Concrete Joint With Single-sided Open Steel Boxes

Compared with cast-in-place concrete structure,prefabricated concrete structure has the advantages of high industrialization level,high production efficiency and energy saving,which is in accord with Chinese building industrialization.Beam-column joint is the critical part in fabricated concrete frame structure.The configuration of beam-column joint determines seismic performance,cost and production efficiency of the whole structure.Prefabricated concrete frame joints can be divided into the following three main categories: assembly integral joints,prestressed joints and total-prefabricated joints.Based on analysis of advantages and disadvantages of the three types of joints,a new type of total-prefabricated concrete frame joint based on embedded steel pieces,single-sided open steel boxes and bolts is proposed in this paper.The new-type fabricated joint has the advantages of fast assembly and clear force transmission.In order to study the seismic performance of the new-type fabricated joint,low cyclic loading tests are carried out on one full-scale cast-in-place concrete joint and two fullscale new-type fabricated concrete joints.A numerical model is established,on which the parametric research is based.Force transfer analysis of the joint is carried out,on which the proposed design formula is based.The main work and conclusions are as follows:(1)Based on the classification of fabricated concrete frame joints,the previous representative studies are summarized,and then a new type of total-prefabricated joint is proposed.(2)The configuration of this proposed fabricated joint is introduced in detail,and the force transmission of the new-type fabricated joint is qualitatively analyzed.It is pointed out that the critical components of the joint are single-sided open steel boxes and bolts.(3)Based on a side joint at the middle floor of a five story reinforced concrete frame structure,two new-type fabricated joints and one cast-in-place joint are designed,and low cyclic loading tests are carried out on these joints.Failure mode,bearing capacity,ductility,stiffness degradation,and energy dissipation capacity of the joints are analyzed.The results show that the bearing capacity of the new-type fabricated joint is better than that of the cast-inplace joint;compared with the cast-in-place joint,stiffness degradation of prefabricated joints is faster in the initial stage of loading,but it is slowed down in the subsequent loading;the interstory drift angle at the moment of the joint failure meets the limit value of elastic-plastic interstory drift angle of reinforced concrete frame specified in the Chinese code,Code for seismic design of buildings.(4)The finite element model of these joints is established based on ABAQUS software.Hysteretic curve,backbone curve,stress contour plot and concrete damage plasticity contour plot are analyzed and compared with experimental results.The research shows that this finite element model can reflect the mechanical properties of the new-type fabricated joint.Based on the proposed finite element model,the influence of concrete strength grade,axial compression ratio and embedded depth of the embedded steel pieces in precast beam and column on the mechanical properties of the new prefabricated joint is further analyzed.The results show that the higher the concrete strength grade,the greater the bearing capacity of the joint;the influence of axial compression ratio on the bearing capacity of the joint is very small;joints with small axial compression ratio have larger initial stiffness;the greater the embedded depth of the embedded steel pieces in the precast beam and column is,the greater the bearing capacity of the joint is;increasing the embedded depth of embedded steel pieces in the precast column is more obvious for the improvement of joint bearing capacity than increasing the embedded depth of embedded steel pieces in the precast beam.(5)Based on the results of experiment and finite element analysis,the force transmission of the new-type fabricated joints is quantitatively analyzed,and the force acting on single-sided open steel boxes,bolts,beam and column when the precast beam rotates around the joint is obtained.On this basis,the design formula of the joint is established,which provides a reference for the design of the proposed fabricated joint.