Study On Seismic Behavior Of New T-shaped Concrete Filled Steel Tubular Column-steel Beam Assembly Joints

The concrete-filled steel tube structure has the advantages of high load-carrying capacity,toughness and plasticity,etc.However,there are usually convex corners indoors,which affect the use function of the structure.For this reason,the special-shaped concrete-filled steel tube structure is proposed,whose column section usually adopts the T-shaped,L-shaped and cross-shaped section forms,and thus the problem of convex corner indoors is solved effectively.The special-shaped concrete-filled steel tubular column-steel beam connecting joint usually adopts the outer reinforcing ring plate joint,the inner baffle type joint and the side plate connecting joint.Among these joints,the outer reinforcing ring plate joint may affect the use function of the structure due to the existence of the outer ring plate.The inner baffle type join has the difficulty of processing and pouring concrete due to the interior diaphragm inside the tube wall.As for the side plate connecting joint,the co-stressing behavior of the side plate and wall of the side panel connected joints is questionable because of weld connection between side plate and wall.Therefore,these three facts taken together,the author proposes a new type of T-shaped concrete-filled steel tubular column-steel beam assembly joint,and the seismic behavior of the new joint and plane frame with the proposed joints are analyzed by numerical simulation separately.The results show that the new joints can meet the requirements of bearing capacity and seismic performance.What's more,only the bolts are needed while the weld is not needed during the field installation,and also the construction is simple.These advantages provide technical support for wide extension and application of special-shaped concrete-filled steel tube structure.In this thesis,the following works are carried out:(1)This paper summarizes the research progress of traditional concrete filled steel tube joints and special-shaped concrete filled steel tube joints.(2)A new type of T-shaped concrete-filled steel tubular column-steel beam assembly joint is proposed.The new type of joint is obtained on the basis of the T-shaped concrete-filled steel tubular column-steel beam joint with the outer diaphragm.One of the improvements is that the outer diaphragm is cancelled and the wall of steel pipe in the joint region is partially thickened.Another improvement is that the staggered drawing plates are arranged inside the steel pipe,and the steel beam and the steel pipeare connected with bolts through the zigzag cantilever beam.In order to compare and analyze the impacts of the improvement measures on the seismic performance of the joints,two new joints are designed on the basis of the new joint and the existing outer diaphragm joint:(1)the flanges between steel beam and cantilever beam are connected by welding and the corresponding webs are connected with bolts,instead of the full bolts connection between the steel beam and zigzag cantilever beam;(2)the steel beam connected with the new joint is changed into dog-bone type steel beam.(3)The numerical models with solid elements of the above four joints are established in the finite element software ABQUAS separately,which takes material nonlinearity,geometrical nonlinearity and contact nonlinearity into account.The analyses of the joints are conducted under low frequency cyclic loads respectively.The seismic behavior indexes including hysteretic curve,energy dissipation capacity,skeleton curve,ultimate bearing capacity,ductility performance and stiffness degradation are obtained.After that,the stress distribution of the four joints during the loading and the final failure deformation are compared and analyzed.The results show that the improved measures of the new joint can effectively improve the seismic behavior of the joint,thus meeting the seismic design requirement of "strong-joint and weak-member".(4)The seismic behavior of the plane frame with the new type of joints is studied based on fiber element model.Firstly,the solid element model and fiber element model of the planar frame with the new type of joint are established in the finite element software ABQUAS,and the analysis under monotonic load are conducted respectively.The accuracy of the fiber element model is analyzed by comparing the results of the above two models.After that,the analyses of the fiber element model of the plane frames under low frequency cyclic loads are conducted,in which the influences of the axial compression ratio and the strength of concrete are also considered.The results show that the axial compression ratio has a great influence on the seismic behavior of planar frames,and the strength of concrete has little influence on the seismic behavior of planar frames.