Study On Construction Safety Monitoring And Early Warning Technology Of Full Hall Support

Due to the use of less auxiliary equipment,various forms of vertical and horizonta l spacing structure,low requirements of foundation bearing capacity,and lower cost,the full hall support has been widely used in the project.However,on account of the lack of attention to the full support and the complexity of the construction process,the collapse of the full hall support system has occurred frequently in recent years.In this paper,the internal and external factors that affect the construction safety of the full hall support are analysed by means of numerical simulation,and the influe nce rules of different factors on the stability bearing capacity of the structure are obtained.In view of the differences of experts’ experience and level,a method of using expert confidence index to modify the different evaluation results of experts is proposed.Based on the theoretical and experimental research,the content and scope of the full hall support monitoring are pinpointed,and a multi factor comprehensive early warning method considering the interaction of factors is proposed on the basis of single factor early warning.The details are as follows:(1)Studying the influence of internal factors on the stability of the full hall support,such as support scale,longitudinal slope and cross slope,horizontal curve radius,spacing of different tubes,density of diagonal braces,joint connection and initial defects of materials,the general change rules are obtained.The change of the longitudinal length of the support has little influence on its stability;with the decrease of the transverse width of the support,its buckling load shows a downward trend,while its stability of the full hall support varies inversely with the height.The support slope is controlled by apical extension length(a),and the stability of the support decreases with the increase of apical extension length,there is a remarkable change while a>0.2m,the full hall support gradually converts from the overall large wave buckling instability to the partial transverse instability.The bearing capacity of the support reduces with the decrease of the radius of horizontal curve,no less than 300 m is recommended.With the increase of the distance between the tubes,the buckling load of the formwork support is greatly reduced;the change of the distance between horizontal tubes has no obvious influence on the buckling load of the formwork support;the erection density of the diagonal braces also directly affects the bearing capacity of the formwork support.As the density increases,the bearing capacity of the formwork support is gradually enhanced,especially in the longitudinal direction.With the increase of the joint stiffness,the bearing capacity of the structure is steadily enhanced.The increase of fastener unbuckled ratio will lead to the decrease of frame stability.The initial defects of materials have a great influence on the bearing capacity of the structure,with the increase of the material correction coefficient,the buckling load of the formwork support decreases little by little.(2)Studying the influence of external factors on the safety of full hall support,such as terrains,foundation conditions,wind loads,environments and man’s activities,the relevant erection suggestions and notable points in construction are given.Diverse terrains have different influence on the safety of the formwork support,and the order of safety coefficient is: flat > slope > Λ-shaped slope > V-shaped valey.The bearing capacity of the full hall support varies inversely with the height(b)of bottom reinforc ing tubes from the ground,it is recommended that the b value is no more than 0.3m.The bad foundation has a great influence on the stability of the full hall support,so the foundatio n treatment must be done strictly in the actual construction.With the increase of wind pressure,the maximum tensile and compressive stress and the maximum displacement of the full hall support increase linearly.Besides,attention should be paid to the influe nce of environment and man’s activity on the formwork support safety during construction.(3)This paper defines and classifies the construction risk of the formwork support,analyzing the risk factors that affect the construction safety of the formwork support from the internal and external factors,establishing the index system of construction safety assessment,and introduces the calculation process of using AHP to determine the index weights.The grading standard of construction risk is determined based on the accident possibility and severity,then the risk matrix is used as the risk evaluation criterion.Finally,the expert confidence coefficient is proposed to modify the assessment conclusion of different experts and get the comprehensive risk level.Put forward different measures for different risk levels.The construction that reaches moderate risk(level 2)or above should be monitored,and the application scope of monitoring and early warning of full hall support is defined.(4)Through consulting literatures and regulations,and comparing the outdoor trial,the content of monitoring of formwork support should includ ing supporting force,axial force of upright tubes,vertical and horizontal displacement of upright tubes,sedimentation of foundation and formwork support etc.Based on the analysis of load distribution of the box girder structure and the finite element simulation of the trial model,obtaining the location or area of the maximum value of each monitoring index.Combined with relevant regulations,the location of each index in the monitoring content on the longitudinal bridge direction,transverse bridge direction and height interval is proposed.A method of the monitoring data de-noising is given.The threshold of each monitor ing parameter is determined reasonably.The working state of full hall support is divided into normal,abnormal and dangerous.Realizing the early warning by stages and levels.On the basis of the method of single factor early warning,considering the influence of the superposition of parameters,a grading method of multi factor comprehensive early warning is proposed to achieve more accurate and timely early warning of the unsafe status for the full hall support.(5)According to the research results in this paper,the risk assessment of the supporting project was carried into execution.Contrasted the assessment results in this paper with the results in traditional index system,the feasibility of the index system in this paper has been verified,and it is concluded that the construction risk level of the full hall support was higher than level 2.For this reason,the monitoring and early warning analysis of the concrete pouring process were carried out.In the single factor analysis,the support was in the Yellow early warning state at 19:00 of the second concrete pouring.In the multi factor analysis,the abnormality of the support was discovered about 1 hour earlier than the single factor analysis.Arranging professional personnel to check and solve the causes of support abnormality in time.During the subsequent pouring process,the support was perpetually in a safe state.It conforms to the actual situation of the project.The fair utilization of the research results in this paper can effectively help managers know the safety situation of site in real time,discovering and eliminating the constructio n risks as early as possible,and it greatly improves the ability of accident prevention.