Experimental And Theoretical Study On Fastener Steel Tube Full Hall Formwork Support System

With the development of country construction, the full hall formwork support system has been widely used as a temporary structure. The fastener steel tube full hall formwork support system is the most commonly used support system type because of its convenience, versatility, high carrying capacity and good overall stiffness. However, structural failures of this system occurred frequently, due to inadequate knowledge of relationship between construction factor and bearing capacity. In order to build appropriate computing model to reduce the accidents it was necessary to do research on fastener steel tube full hall formwork support system. In this paper, the bearing capacity and corresponding computation theories of steel tube full hall formwork support system were studied in depth. The research works included: torsion capability of right-angle coupler, effect of many erection parameters on stability bearing capacity of formwork support system, semi-rigid character of right-angle coupler, mechanical performance of super high full hall formwork support system (the overall height greater than 8m) and et al.The method that through classifying regions of connections M~*—θ~*curves to estimate the connection stiffness was put forward on the basis of the study on beam-column connection stiffness in steel structure framework theory. The semi-rigid connection character and the criterion of its critical value were studied. A 3-D finite element model of right angle coupler was established, and numerical analysis and experimental study on stiffness of it was made. The relationship between stiffness and initial bolt tightening torque was established, and the judgment of the coupler stiffness character was made.Through advanced non-linear finite element models in different geometric parameters that considering the semi-rigid character of the couplers, the critical loads and failure modes of fastener steel tube full hall formwork support system under idealized conditions were evaluated. The effect of a series of erection parameters such as lift height, spacing of upright tube, minimum building spans, length of upright tube extruding from top horizontal tube, setting of bridging on bearing capacity of full hall formwork support system was studied quantitatively, and the different characters between full hall formwork support and full hall formwork scaffold was also analyzed. On the basis of finite element analysis, a series of super high full hall formwork supports and scaffolds with and without bridging that lift height ranges from 0.6m to 1.8m and upright tube spacing ranges from 0.4m to 1.5m were tested to failure in order to examine the stability behavior and failure modes of them. The actual mechanical property of full hall formwork support system could be reflected through experimental results. Bearing capacity of full hall formwork support system with different geometric parameters were computed using the existing technical code for safety of steel tubular scaffold with couplers in construction JGJ 130-2001, and the results were higher than that of the test. Many reasons lead to the above results unsafe, and lack of systemic test research on full hall formwork support system was one of that. The problems and deficiencies of existing technical code JGJ 130 were put forward, and the improvement on bearing capacity calculation methods and corresponding construction requirements of full hall formwork support system were presented through the finite element analysis and experimental results combined with revision of code for scaffold.The research methods of columns stability in steel frames theory were referenced here to theoretically analyze the bearing capacity of steel tubular formwork support without bracing which considering the semi-rigid character of right-angle coupler, effect of adjacent horizontal and upright tubes. Distinguish of different loading modes of full hall formwork support was made according to whether full of upright tubes under loading or not, and the governing equations for determining the effective length factor were given in every loading conditions. The presented equations for calculating the effective length factor could be used not only in full hall formwork support system but also in research on columns stability in steel frames.Using the finite element analysis, experiment results and theoretical studies above, the special scaffold construction scheme of Tianjin Pole Sea Aquarium was compiled, in which every safety requirements of scaffold were calculated using several methods. It can conclude that the calculation theory presented in this paper has feasibility and applicability in forecasting the critical load of steel tube full hall formwork support system in different loading condition. The bearing capacity of actual scaffold construction scheme in which the lift height and upright tube spacing exceeding the scope of technical code were also calculated, and it proved that the technical code for safety of steel tubular scaffold with couplers in construction under revision has much safety.