Research On Buckling Behavior Analysis Of Wheel-coupler High Formwork Support System Based On Semi-rigid Joints

Wheel-coupler formwork support is widely used to support the gravity load of floor slabs in buildings,the mechanical properties of connection joints are very complex,and the semi-rigid joints has a significant impact on the stability of the overall support system.In order to clarify the buckling behavior of wheel-coupler high formwork support system,taking wheel-coupler high formwork support system as the research object,the research status and development status of socket and spigot formwork support and wheel-coupler formwork support at home and abroad are summarized and analyzed in detail.The test and finite element analysis show that the connection joints of wheel-coupler formwork support are typical semi-rigid connection joints,and based on the characteristics of semi-rigid joints,the buckling behavior of the wheel-coupler high formwork support system without diagonal bracing and with diagonal bracing is analyzed respectively.The main research contents and results of are as follows:(1)The buckling behavior of the connection joints of the wheel-coupler formwork support is studied in detail through the positive and negative bending tests,it is verified that the connection joints of wheel-coupler formwork support are typical semi-rigid connection joints.Through the parametric analysis of finite element analysis,the precise numerical model of connection joints is established and verified,and the reliability of the finite element model for predicting flexural behavior is verified.The results show that the failure modes in the positive direction are relevant to the insertion depth of the socket into the wheel,the greater the depth,the more likely the socket breakage will occur,the failure modes in the negative direction are closely relevant to the insertion depth of the socket into the wheel and the bending of vertical post.The positive bending capacity is almost the same,about 0.45kN·m,and the bending capacity and stiffness in the negative direction are much larger than the positive one.(2)The finite element model of wheel-coupler high formwork support system without bracing is established,and its non-linear buckling analysis is carried out.Through a large number of parametric analysis,the effects of lateral constraint at the top,joint bending stiffness,The transverse,longitudinal distances and lift height,plane geometric size,loading mode and other factors on the overall stability are deeply studied.Finally,buckling capacity of single vertical post at different positions is studied.The results show that whether there are lateral constraint at the top has an effect on the overall stability,the stability with lateral constraint is better,and the more stories,the effect can be ignored.The greater the joint bending rigidity and the smaller the lift height,the better the overall stability.The influence of transverse and longitudinal distances on overall stability can be neglected with the increase of lift height.The plane geometry size has a significant influence on the overall buckling capacity,and the buckling coefficient of the small span is the basic criterion.The stability of central loading and corner loading is better than that of side loading,with the increase of loading area,the buckling coefficient decreases gradually under central loading and side loading,for corner loading,it is not the smaller the loading area,the larger the buckling coefficient,this rule is not affected by the lateral constraint at the top.The buckling capacity of corner post is significantly lower than central post,the buckling capacity of the central post at any position in the middle is almost the same.(3)The numerical model with diagonal bracing is established,and the effects of space layout,plane layout of vertical diagonal bracing,joint density between diagonal bracing and frame,lift height,angle between diagonal bracing and horizontal plane on the overall stability of high formwork support system with diagonal bracing on overall stability are studied.The results show that whether or not has lateral constraint at the top,it is advisable to arrange internal vertical diagonal bracing in the direction of parallel the short side.Vertical diagonal bracing should be arranged every three spans,while horizontal diagonal bracing should be set up above and below.When there is lateral constraint at the top,the optimal layout of vertical diagonal bracing is2-span,4-step,and the optimal angle is 30~o~70~o.When there is not lateral constraint at the top,the optimal layout of vertical diagonal bracing can not be determined,and the optimal angle is generally about 30~o when the lift height is not very large.Keeping the angle unchanged and increasing the joint density have little effect on the overall stability,when the angle is the same,the diagonal bracing has the same plane layout,when there is lateral constraint at the top,the denser the joint density,the better the overall stability;when there is not lateral constraint at the top,the thinner the joint density,the better the overall stability.When there is lateral constraint at the top,the larger the angle between the diagonal bracing and the horizontal plane,the better the overall stability,when there is not lateral constraint at the top,the smaller the angle between the diagonal bracing and the horizontal plane,the better the overall stability.For the formwork support system with diagonal bracing,the effect of lift height on the overall stability is almost not affected by the plane layout of vertical diagonal bracing,the smaller the lift height is,the better the overall stability is regardless of the lateral constraint at the top.