Research On The Mechanism Of Joint In The Ribbed Flat Beams With Concrete Filled Steel Tubular Column

Abstract:The joint of beam connected with the column is a key part of concrete filled steel tubular structures, and there is no perfect calculation theory and practical method at present. Now there are several simple joint types of concrete filled steel tube provided by national codes. In this paper, the researches on the static test and theoretical analysis of joint made with thin reinforced concrete(RC) ring plate and stiffened RC beams with concrete filled steel tubular column is fulfilled. The main works finished are as following.1. The joint models with three and four corbels by the ratio of1:2reduced scale are completed along with the design of loading system and test system. The yield load and ultimate load of stiffened beams, the mechanism and strain variation with load in pipe wall, core concrete, upper and lower horizontal steel ring plate, upper and lower vertical steel ring plate and stiffened girders in RC beams are obtained from the experimental research.2. After introducing constitutive relationship of concrete and steel, treatment of concrete crack and crushing and failure criterion which are adopted in ANSYS software, the mechanism of joints from loading to the destruction are analyzed.3. The comprehensive comparison of the test results and theoretical values for steel pipe wall, core concrete, upper and lower horizontal steel ring plate, upper and lower vertical steel ring plate and stiffened girders shows that the mechanism of force is almost same, and the ultimate load of stiffened RC beams is almost same. The mechanism of pipe wall and closing core concrete is familiar though the strains in core concrete lags behind the pipe wall. The pipe wall and core concrete keep in elastic phase during loading show that the design of joints is reasonable as "strong column with weak beam". 4. It is difficult to ensure accuracy in calculating cracking load of RC beams (the microscopic analysis in concrete structures) by ANSYS while it is relatively agreeable in calculating the deflection of RC beams at elastic stage(the macro analysis of concrete structures). The accuracy of calculation of rigidness in the state of ultimate load reduces comparing to the elastic state for which the numerous cracks results in larger different between theoretical displacement and experimental values. The theoretical ultimate loads of stiffened RC beams are close to the experimental values, showing that ANSYS has good precision in calculating the bearing capacity of steel srtuctures.