Stability Theory And Field Measurement Of Fastener Type Tall Formwork Support System

Tall formwork support system(High Support Mold for short)is widely used in high-rise construction,and safety accidents occur frequently.At present,the design and construction personnel have insufficient understanding of the stability of the system.The semi-empirical and semi-theoretical method is adopted to design the system,and the boundary and physical conditions considered are quite different from the construction site.The formulas for checking the stability of bending bars in relevant codes are not uniform.In addition,there are few practical studies on high support formwork,and most of them are limited to the monitoring of the frame itself,so the data cannot provide reliable scientific basis for the codes.Therefore,it is necessary to carry out systematic theoretical research and field test on high support die.For high modulus calculation method is not unified and poling stability coefficient φ of ready-made technical specification for the cold bending thin-wall steel structure(GB50018-2002)partial unsafe problem,based on the fastener type high modulus as the research object,statistics and analysis on the major of high collapse,comprehensive use theoretical analysis,numerical simulation and field test method to study on the stability of high modulus.The initial defects affecting the stability of high formwork support,the problems existing in the analysis principle and model of high formwork support,the stability buckling analysis method and the basic calculation method are systematically analyzed.Nine codes which are mainly referred to in the calculation of high formwork support for construction are compared and analyzed,and suggestions for practical codes are given.Through field measurement and finite element simulation,the measured defects and theoretical defects affecting the stability of the vertical rod are obtained.The stability coefficient of the vertical rod which is in line with the actual engineering is calculated by the analysis correction method,and the high support mold with fastener in a certain project is checked.Through field measurement,the maximum stress values at different positions of the vertical rod of fastener type high support die under normal working condition are obtained.Through comparative analysis,the differences between the measured maximum stress values,the stress values calculated by the standard stability coefficient and the critical values calculated by the recommended stability coefficient are found out.It is found that the stability coefficient given by the code is too large,which leads to the small stability calculation result,so the stability coefficient given by the code is not safe.When v0=L/400 is used as the initial bending value of the vertical rod,the initial defects are almost close to those obtained from the measured defect data,and the calculated stability coefficient of the vertical rod is also less than that given by the code,and the calculated stability value of the vertical rod is about 44%less than that given by the code.The measured maximum compressive stress of the vertical rod is greater than the stress calculated by the standard stability coefficient,but less than the stress calculated by the recommended stability coefficient in this paper,and is closer to the stress calculated by the recommended stability coefficient in this paper.Therefore,it is suggested to use the stability coefficient given in this paper to check the stability of the vertical rod.The monitoring found that:the position of the maximum stress of the vertical bar is uncertain,and there is a danger point mainly at the upper end.The horizontal bar also bears a considerable part of load in the actual working state,which is close to the calculated value in the code.The danger point of scissor brace mainly appears at the upper end and the stress curve varies greatly.In the process of concrete construction,the horizontal load generated by the impact of the pump pipe on the high formwork will be 1.9%of the maximum axial force of the vertical rod.Through the real-time monitoring of the stress in the whole construction process of a high-support formwork in Xi ’an,the difference of the stress conditions of the high-support formwork under the actual load and the design load is compared,which provides a detailed stress data reference for the design,installation and construction of similar high-support formwork projects in the future.To high stress data monitoring and regulating the stress calculation value,this article suggested that stable coefficient calculation,comparing the stress value at the beginning of this paper calculate bending for L/400 poling stability factor φ’ to improve the current specification about the safety of high modulus design theory has scientific theoretical support,applied to the project will reduce the occurrence of safety accidents and promote the healthy and orderly development of construction industry.