Mechanical Performance Research On Connection Of Concrete-filled Twin Steel Tubes Column To Steel Beams

Concrete-filled twin steel tubes (CFTSTs) column, which has been widely used in thelarge-span bridges and high-rise buildings nowadays, is characterized by its high-strength, andespecially good resistance against the strong earthquake loading. CFTSTs column, composingof an outer square steel tube and an inner circular steel tube, has the advantages of not onlygood mechanical performance but also the convenient connection. Therefore, the CFTSTscolumn has attracted increasing attention in the engineering world.Up to now, there is very limited available literature in regards to the connection betweenthe CFTSTs column and the steel beams. Thus, it is necessary to develop new types ofconnection of CFTSTs column to steel beams, investigating their behaviors under seismicload and establish the design methods accordingly. In this dissertation, six connections ofCFTSTs column to steel beams and one Concrete-filled steel tube (CFST) column to steelbeams were designed. Also, the seismic behavior of different types of connections wasanalyzed in details by means of experimental tests, numerical simulation and theoreticalanalysis.Firstly, six new connections of CFTSTs column to steel beams and one connection ofCFST column to steel beams were designed and tested under the lateral cyclic loads. The testresults showed the overhang length of vertical rib plates can adjust the position of the plastichinge for the connections. The bearing capacity for the connections of anchorage webs withribs was also shown to be better than the anchorage webs without ribs. The new typeconnection of CFTSTs column to steel beams has high bearing capacity, good energydissipation, stiffness and ductility.The seismic behavior of the suggested connections was developed and analyzed by aNon-linear finite element software ABAQUS. Comparison of results between the simulationand the test has shown good agreement. Moreover, discussion on the stress distributions of theconnections has shown good performance under high axial ratio. And the connections ofanchorage webs with ribs can transfer stress well. A series of parametric analysis have been carried out for the specimen SBJ2-2based onthe verified finite element model. Different failure modes were found when the loads wereadding at different positions i.e., the end of beam segments and the top of column. The properheight of the vertical rib plates was determined according to the results of simulation. Thecurves of moment-rotation and initial stiffness for the connection were obtained by theparameters analysis. The practical formula of this new type connection was derived accordingto the three-parameter power models, and the fitting formula of initial stiffness for theconnection was retained according to the parameters analysis. Comparison of results amongthe theoretical calculation, the simulation and the test has shown good agreement.The shear capacity of the new type connections of CFTSTs column and steel beams wereproposed, taking into the effect of the axial load and the low cyclic load at beams ends. In thetheoretical derivation, the simplified tri-linear model was used for steel, whereas the ascentstage and horizontal segment model was used for the inner and outer concrete. Additionally,the formulae of the shear capacity and the corresponding shearing deformation of theconnections were derived. Comparison of the calculated shear capacity with the experimentalresults has shown well agreement. Therefore, the proposed method could be used to derive theshear capacity of the new type of connections.