Study On The Behavior Of Load-bearing Disk Button Type Steel Tube Formwork Supports

The disk button type steel tube formwork supports have the advantages of high bearing capacity,convenient assembly and disassembly,self-locking under normal operation,being suitable for different actual working conditions,good economy and high comprehensive benefits.However,at present,there are few reports on this type of load-bearing formwork supports,and their ultimate bearing capacity,stability and failure mode are still unclear.Obviously,such studies are obviously insufficient,which will affect the safety and application in engineering.In this thesis,7 groups of single-span two-step full-size tests on the load-bearing disk button type steel tube formwork supports have been carried out under different actual working conditions.Based on the finite element simulation and parameter analysis,the mechanical performance of the frame under different parameters are further investigated.The detailed research contents are as follows:(1)In order to study the behaviro of the disk button type steel tube formwork supports,the full-scale tests were conducted on 7 sets of frames with different diameters of steel tubes,different specifications of vertical inclined bars,and different spacing of vertical bars.Strain gauges and displacement transducers were arranged on vertical,horizontal and vertical inclined bars to measure the forces exerted by these bars during loading.The results show that the first,second,fifth,sixth and seventh steps of the frame lost its bearing capacity due to buckling,and the third and fourth step of the frame lost its bearing capacity due to buckling.The large strain appears on the vertical bar,while the strain on the vertical inclined bar and the horizontal bar is small,which indicates that the vertical bar is the main stress bar of the frame.The ultimate bearing capacity of frame 1 is increased by 102% compared with that of frame 7,indicating that the vertical inclined bar plays a very important role in the bearing capacity of the disk button type steel tube formwork supports,and it is related to whether the vertical bar can give full play to the material strength of steel and has a great influence on the ultimate bearing capacity.(2)The finite element software ABAQUS was used to develop models of 7 groups of different working conditions to simulate their buckling modes,and the initial defect of L/500 bar length was introduced to simulate their ultimate load,instability mode,and load-displacement curve.The deviation between the predicted ultimate load and the test results is within 15%.The simulated instability modes agree with the experimental results.The load-displacement curve is consistent with the test,which verifies the finite element model.(3)Based on the model,a parameter analysis was conducted to study the effets of the initial defect of the frame,the diameter of the vertical steel pipe,the wall thickness of the vertical steel pipe,the distance between the vertical bars,the step distance of the horizontal bars,the setting form of the vertical inclined bar of the frame and the height of the frame and other influencing factors.According to the experimental results and finite element analysis,the practical conclusions on disk button type steel tube formwork supports,the corrected coefficients on poling stability calculation length correction coefficient accounting for the initial defects and the height of supports were obtained,which provides a valuable reference for the engineering practice,promotion and application of the disk button type steel tube formwork supports.