Study On Semi-rigidity And Stability Bearing Capacity Of Fastener Steel Pipe Formwork Support Joints

Fastener-type steel pipe formwork support has the advantages of low cost,convenient erection and high bearing capacity,and its usage ranks first among many formwork support systems.However,at present,the value of joint stiffness is inconsistent with the actual joint working condition and the research on joint semi-rigidity lacks systematic accumulation,so it is necessary to carry out joint semi-rigidity research and improve the design theory.In this paper,the torsional stiffness performance of right-angle fasteners under different working conditions is studied by taking the bolt torsional moment as the main research parameter,and the mechanical performance and rotational characteristics of semi-rigid joints are studied by establishing the joint bending moment-rotation relationship model According to the joint stiffness value determined by experimental study and the theory of semi-rigid connection frame with lateral displacement,the formulas for calculating the stiffness correction coefficient au of the cross bar and the restraint coefficient k of the end of the vertical bar are derived,and the stable bearing capacity of the vertical bar under different erection parameters is calculated according to the theoretical calculation formula and the current code calculation method respectively.Using finite element software,the finite element analysis model of fastener-type steel pipe formwork support is established,and the parametric analysis is carried out by using the finite element model.By considering the influence of scissors support on the stable bearing capacity of vertical pole,the stable bearing capacity of vertical pole without support formwork support is revised Combined with the actual project,the stress monitoring of the key upright post of the tall formwork support is carried out,the actual stress of the upright post in the concrete pouring process is studied,and the stable bearing capacity of the upright post in the measured project is calculated.The main research results are as follows:Experimental study on torsional stiffness performance of right-angle fastener shows that when the torsional moment of right-angle fastener bolt increases from 20 N·m to 30 N·m,the initial stiffness value of joint increases the most,and the initial stiffness value of joint has nothing to do with the length of crossbar.According to the established joint bending moment-rotation angle relationship model,the initial stiffness values of joints under different working conditions are obtained,and the relationship between bolt torsion moment and initial stiffness values of joints is put forward.Based on the theoretical study of the stability bearing capacity of fastener-type steel pipe formwork support,the simplified formulas of the bar stiffness correction coefficient αu and the end restraint coefficient k of the upright are derived,and the theoretical values of the calculated length coefficient μ and the stability bearing capacity of the upright under different working conditions are given.Compared with the standard values,it is found that the theoretical calculation results of the percentage increase of the stability bearing capacity of the upright are 3～4 times larger than the standard calculation results under the same condition of decreasing the step distance,and the theoretical calculation method can better consider the influence of semi-rigidity of joints and adjacent members on the stability bearing capacity of the upright.Through finite element parametric analysis,it is found that the stable bearing capacity of the vertical pole with horizontal scissors support only increases by 2%,but the maximum lateral displacement can decrease by 20.3%～50.2%;Setting vertical bracing has a significant impact on the bearing capacity of vertical poles,and the percentage of vertical bracing to improve the stable bearing capacity of vertical poles is related to the step distance.With the increase of step distance,the percentage of setting bracing to improve the stable bearing capacity of vertical poles becomes larger.When the height to width ratio of the frame meets the requirements of the current code,the height to width ratio is small,which has a great influence on the stability of the frame bearing capacity.The stress monitoring of the key upright posts in the actual project shows that the stress of the upright posts at the bottom of the beam is greater than that of the upright posts on both sides of the beam in the process of concrete pouring,and the stress of the upright posts at the upper part of the frame body is the greatest,and the concrete measures to strengthen the upper upright posts in the construction are given.At the same time,combined with the calculation method in this paper,the theoretical value of stability bearing capacity of stud under different torsional moments of fastener bolts in practical engineering is given.