Experimental Study On Mechanism Of Scaffolding Supporting The Cast-in-place Reinforced Concrete Beam And Floor Structure

Disk lock steel tubular scaffold has the advantages of convenient assembly and disassembly,component shaping are applied in practical engineering,but DLOSTS field test is not sufficient,the design theory is not perfect,which will lead to the collapse,result in the loss of personnel and property.Therefore,it is theoretical and practical significance to study the field performance of the formwork support system.According to the practical project investigation,there are two forms of the floor supporting system H-type(the horizontal bar is directly subjected to the construction load of the main beam,and which is supported by the stander on both sides of the main beam)and T-type(the girder is supported by the stander which directly under the main girder).Based on the project of Heng Da future city in Kai Feng City,we monitored the internal force of two different forms of formwork support system in the whole process of concrete pouring,including stander,pledger and diagonal bar(scissors brace).the field test results and numerical simulation results are compared with the National Code calculation results,and the internal force distribution and development tendency of the support members are summarized,and the applicable boundaries of the two different support types are determined,analyze the influence factors of the bearing capacity of the bracket system,and provide technical basis for the design and construction of DLOSTS.The main research results are as follows:(1)Both standers under slab and girder,they are compressed axially,and the bending moment can be neglected.The pressure on the upper section of the same pole is greater than the lower part.(2)The internal force of the upright pole on both sides of the H-type support beam is greater than that below the plate,the internal force distribution is not uniform,the average value of the internal force on both sides is-9.96 k N,and the vertical bar is-8.75 k N.It is recommended that the beam bottom poles be encrypted(half the spacing),and that every two poles and the lower pole of the panel pull the structure into a whole force system.(3)The supporting poles at the bottom of the V-type support are compressed more than on both sides,the axial force distribution is uneven,the intermediate axial force is large,the two sides are small,the bearing capacity exertion factor(0.202)of the top support stander is larger than that of the two sides(0.176).According to the actual material characteristics of the project and the construction technology and management level,it is recommended that the coefficient of the formwork support pole ? be controlled between 0.2 and 0.3.(4)The pledger of H and V type supports are complex and closely related to the erection position of the scissors.When the pledger are restrained by the scissors supports,the internal forces are under pressure,otherwise they are under tension.the horizontal and vertical horizontal rods are approximately the same in force,and there is no significant difference in the internal force between the beam bottom and the horizontal rod under the panel,both showing that the upper internal force is greater than the lower.(5)Determination of H and V-type supports based on beam height h=630mm as selection limits by field measurement and calculation,but considering the actual height of the beam with 100 mm module,it is suggested that the H-type support for maximum beam height h=600mm.(6)When the actual concrete is poured,the construction load is complicated,and part of the rods are changed in tension and pressure.After pouring 8h,the scaffold has certain strength due to the early pouring of concrete and the “unloading phenomenon” of the formwork support occurs,which reduces the force of the pole.(7)The comparison between the numerical simulation results and the field measurement results validates the rationality of the modeling analysis,and shows that it is feasible to analyze DLOSTS based on the semi-rigid joint model,and the buckling analysis of the two types support shows that the H-type may happen that the overall lateral displacement of the longitudinal section(YOZ plane)is unstable,indicating that the longitudinal section is a weak surface,and the cross section of the V-type support(XOZ plane)is a weak surface.(8)As the vertical and horizontal unbalanced loads caused by pouring of concrete during construction are gradually increased,the critical load is graduallyreduced,and the laterally unbalanced pouring has greater influence on the bearing capacity of the support;the longitudinal section of the H-type support is a weak surface,and the instability of the support first turns from the longitudinal section to the transverse section.Therefore,the pouring of concrete should ensure uniform symmetry.