Research On The Robustness Of Cuplock Steel Tube Formwork Support Based On Semi-rigid Joints

With the rapid development of China’s construction industry,all kinds of steel tube formwork support have been widely used,among which cuplock steel tube formwork support is widely used in construction,bridge and other projects because of its simple structure,easy disassembly,high bearing capacity,small initial defects and other advantages.Given that the formwork support is a temporary facility in the construction process,its design and construction are often easily neglected,and safety accidents caused by the collapse of the formwork support occur from time to time.Therefore,it is particularly important to study the overall stability of the cuplock steel tube formwork support and enhance the stable bearing capacity of the formwork structure.Because experimental research on the rotational stiffness of the cuplock joints with different structural forms and the quantitative evaluation of the overall stability of the cuplock steel tube formwork support are relatively few,this paper first conducts experimental research on the rotational stiffness of the cuplock joints and discusses the quantitative evaluation method of the stability of the cuplock steel tube formwork support and its influencing factors.The main research work is as follows:Firstly,this paper makes an experimental study on the rotational stiffness of the joints of the cuplock steel tube formwork support.Based on the rotational stiffness test of the coupler joints,a test scheme is proposed to determine the rotational stiffness of the cuplock joints.Four groups of tests were designed to measure the rotational stiffness of the two-tube,three-tube and four-tube joints and to compare the group coupler joints,and to study the influence of different structural forms on the rotational stiffness of the cuplock joints.According to the strain of each component measured by the test,the elastic modulus of the component purchased randomly from the market is calculated.The results show that:(1)The rotational stiffness of the corner joints and side joints of the cuplock steel tube formwork support is77.93% and 92.14% of the middle joints respectively,and both are higher than the recommended value of 25 k N·m/rad given in the code.The rotational stiffness of corner joints and side joints is relatively weak,which has a significant influence on the overall stability of frame.(2)The elastic modulus of cuplock steel tubes randomly purchased in the local market has decreased to varying degrees compared with the new test pieces,with a maximum decrease of about 30%;(3)The order for the failure of cuplock joints is the horizontal tube,the bell shape cap,the standing tube,and the bowl shape socket.The failure of the joints occurred at the joint of the horizontal tube,and the quality control should be strengthened here.Secondly,according to the above test results,the finite element models of the cuplock basic structures without diagonal bracing and with diagonal bracing with different standing tube spacing and horizontal tube lift height were established.The eigenvalue buckling and nonlinear buckling analyses were carried out respectively.The influence of standing tube spacing and horizontal tube lift height on the stable bearing capacity of the basic structure was studied,and the robustness of the two basic structures was evaluated respectively.The results show that: With the increase of the standing tube spacing and horizontal tube lift height,the eigenvalue buckling load and nonlinear buckling load of the frame show a decreasing trend;Under the condition that the horizontal tube lift height is constant,the standing tube spacing of basic structure without diagonal bracing increases from 600 mm to 900 mm,and the robustness coefficient decreases.If the standing tube spacing continues to increase,the robustness coefficient shows an upward trend.The standing tube spacing remains unchanged,and the robustness coefficient increases with the increase of horizontal tube lift height;The robustness coefficient of the basic structure with diagonal bracing increases when the standing tube spacing increases from 600 mm to 900 mm.When the standing tube spacing continues to increase,the robustness coefficient shows a downward trend.When the standing tube spacing remains constant,the robustness coefficient increases with the increase of horizontal tube lift height.Finally,based on the formwork project of the gate of a university in Wuhu City,the cuplock steel tube formwork support is designed.Three groups of working conditions are designed according to different standing tube spacing and horizontal tube lift height.The standing tube spacing and horizontal tube lift height are 600mm×600mm,1200mm×1200mm and1500mm×1800mm respectively.According to the code,the stability and bearing capacity of the three groups of working conditions were checked,and the eigenvalue buckling and nonlinear buckling analysis were carried out,and then a transverse frame in the span of the three groups of working conditions was selected for robustness evaluation.The results show that: the robustness coefficients of the three groups of models are 0.676,0.707 and0.735,respectively.The results show that the robustness coefficients of the three groups of models are 0.676,0.707,and 0.735,respectively,which means that the reduction of the horizontal tube lift height improves the bearing capacity of the structure to some extent,but reduces the antiinstability robustness of the structure.