Research On Reliability And Risk Control Of High Formwork Support System During Construction Period

Fastener-style steel tube high formwork support system is one of the most commonly used formwork support forms in China.However,due to many uncertainties in the design calculation and actual erection of such structures,collapse accidents occur.In view of the problems existing in the formwork support system in actual construction projects,this paper adopted the theoretical research and risk analysis methods to study the reliability of the formwork support system based on the entire construction process of the building structure.On this basis,according to various risk factors,effective improvement measures are put forward to reduce the occurrence of collapse accidents as much as possible.The main research results are as follows:In the static test,9 sets of template support frame test models are proposed,and the effects of the bridging setting,the load application and the fastener damage on its bearing capacity are discussed.Through experimental analysis,the results show that the horizontal bridging setting,eccentric load and fastener damage in the static test are more important for the bearing capacity of the formwork support.When the three risk factors are coupled,the bearing capacity of the formwork support frame decreases sharply.This is a process from quantitative change to qualitative change,and then collapse occurs.In the dynamic test,it is proposed to set up a formwork support frame model with a height of more than eight meters,taking into account the influence of insufficient bridging setting,different concrete pouring amount and fastener failure on the stability of the frame system,it shows that the various structural factors make upright stanchion of dynamic axial force change.Especially when the fastener fails suddenly during concrete pouring process,the maximum upright stanchion of dynamic axial force increases by 120%,which seriously affects the structural stability.Therefore,it is necessary to consider the influence of eccentric load,insufficient X-bracing,failure of some fasteners and concrete pouring amount on the bearing capacity of the frame,and provide strong evidence for the subsequent risk analysis.On the basis of the theoretical model,considering the performance difference of the components and the semi-rigid properties of the fasteners,the bearing capacity reliability of the fastener formwork bracing system under different setting conditions is calculated and analyzed.Select"the wall thickness of steel tube","the modulus of elasticity","the rotational stiffness of fastener"and"the diameter of steel tube"as the main uncertain factors,and regard it as random variables.The effects of these random variables on the bearing capacity of steel tube formwork support system are investigated respectively.By analyzing the calculation results,it can be found that,considering the influence of a single variable,when the vertical and horizontal spacing of vertical bar is constant,the coefficient of variation increases with the decrease of step gridding.As the number of random variables considered in the calculation increases,the distribution density of the bearing capacity appears to be dispersed,while the mean value of the bearing capacity decreases.The influence of the erection parameters on the reliability of the bearing capacity of the formwork support system is not decisive.Even if the parameter design is advantageous,the performance of the component and fitting can’t meet the requirements and the target reliability can’t be met.It can be seen from the reliability calculation that the reliability indexβdecreases with the increase of L_n/D_n,the reliability indexβincreases with the increase of the resistance coefficientΦ.Finally,risk study of concrete and formwork support project based on WBS-RBS and AHP.The influence degree of fourteen risk factors on its bearing performance is discussed.The results show that the total risks of formwork erection and concrete pouring in the basic work package is relatively high,which should be paid more attention to.Three risk factors such as short demolition time,human error,and incorrect casting sequence in the construction works are more important,and emphasis should be placed on strengthening prevention.According to the various risk factors existing in the formwork support system,control measures are proposed from three aspects of design,construction and management.