Experimental Study On Seismic Behavior Of Fabricated Special-shaped Column Joints

As an important structural form for realizing the industrialization and green development of new buildings in China,the fabricated reinforced concrete structure provides the possibility to promote the sustainable development of economy and society in China.The post-assembly and pouring monolithic frame structure has the characteristics of equivalent cast-in-place,quick construction and low cost.It can be widely used in schools,hospitals and residential low-rise buildings,and the prefabricated special-shaped column frame structure is concealed by its column.The wall layout is flexible,and the advantage of using a large area is easier to promote.Beam-column joints are the main factors affecting the overall performance of the structure.Due to the relatively complex mechanism of the jointed frame structure,the node safety is more difficult to guarantee,and domestic and foreign scholars have studied the concentration of conventional rectangular section column assembly nodes and traditional cast-in-place shaped columns.Seismic theory study of nodes.Therefore,it is very important to study the seismic performance of assembled special-shaped column joints.This paper summarizes the development history of fabricated buildings at home and abroad,and introduces the research status of assembled concrete frame beam-column joints at home and abroad,and analyzes the urgency and feasibility of developing the frame structure of special-shaped columns.This experiment relies on the actual project,selects the side column node and the middle column node,the node area is post-cast concrete,the beam and the plate are all superimposed members,and the beam and column longitudinal bars are respectively passed through the straight threaded sleeve and the grouting sleeve.Connection,quasi-static test of constant axial pressure ratio full-scale test piece for two assembly-shaped column nodes and two cast-in-place joints with equivalent reinforcement.Among them,one group is a middle node and one group is an edge node.By observing the cracks of the four specimens,the failure process was carried out,and the seismic index parameters such as displacement ductility,bearing capacity,stiffness degradation and energy dissipation capacity,as well as the internal strain of steel strain were analyzed.The test results show that:(1)The failure process and type of the assembly-shaped side column node J03 and the comparison cast-in-place node J01 are basically the same,both are beam end bending failure,and the failure process and type of the two center column nodes are obviously different.The cast-in-place node J02 is the beam end bending.Destruction,the column node J04 in the assembly is the core area shear failure.The cracks in the assembly nodes are mostly concentrated in the post-cast concrete area,and the damage is serious compared with the cast-in-place nodes.(2)The longitudinal ribs of the assembled node beam are made of straight threaded sleeves and steel bars.In the case of a certain bond slip,the bidirectional stress of concrete and steel bars can be effectively transmitted,and the core area stress performance is improved,thereby changing the node damage.The longitudinal ribs of the upper and lower columns are connected by a grouting sleeve,which is not pulled out at all times,and can achieve good force transmission.(3)Compared with the cast-in-place node,the relative slip of the steel bar and the concrete during the large displacement loading and the slippage of the laminated plate lead to the decrease of the bearing capacity of the assembled joint,indicating that the strength and rigidity of the assembly joint are slightly worse than the cast-in-place node,but Early yielding,similar damage displacement,its ductile deformation is better than cast-in-place joints,and can meet the life-resistance seismic performance requirements of 2% of the ultimate displacement angle limit.In the case of failure,the positive and negative ultimate bearing capacities of the assembled side column nodes and the column nodes in the assembly are different from those of the equivalent reinforcement.The forward ultimate bearing capacity can reach more than 85% of the cast-in-place nodes,while the negative limit bearing The force is about 80%.(4)Compared with the cast-in-place node,before the node yields,the assembly node stiffness and strength degradation laws are basically the same,consistent,and the energy consumption is not much different.After yielding,because the assembly side column J03 breaks earlier,the strength,the strength decreases rapidly,the damage displacement is small,and the energy consumption is low.The plastic hinge is formed at the J04 beam end of the column node in the assembly,and the strength and degradation curves are basically coincident,and the difference is not large.The energy consumption is basically the same.(5)According to the traditional design method of "strong column weak beam,strong shear weak bend,strong joint weak member",and at the same time ensure the prefabricated component fabrication and on-site construction quality,the assembly of special-shaped column nodes can achieve the "equivalent cast-in-place" seismic performance.(6)The ABAQUS finite element simulation can truly reflect the bearing capacity and crack propagation of the special-shaped column joints in a certain range.However,the nonlinear plastic deformation behavior of the reinforced concrete structure is complicated and difficult to simulate.There are still some limitations and differences.