Influence Of Initial Defects On Stability Of Steel Tubular Scaffold Structure

In the process of engineering construction,due to the non-uniformity of scaffold construction conditions and improper use and management,accidents of scaffold collapse occur frequently.Among them,because design and construction personnel on the fastener type steel pipe scaffold defect identification is not enough,the influence of initial defects on the stability of the fastener type steel pipe scaffold can not be ignored.In order to ensure the safety of fastener type steel pipe scaffold construction,this paper studies the initial defects of fastener type steel pipe scaffold.400 fasteners were randomly selected at the construction site,and the weight of each fastener was measured.200 pieces of 6m and 3m pipe with diameter ofΦ 48.3mm×3.6mmwere randomly selected to measure the wall thickness,pipe diameter and initial bending.From the perspective of fastener weight,only about 5%of the fasteners used on site meet the specification requirements.From the perspective of steel pipe size,only a small part of the steel pipes used on site meet the specification requirements.With the help of SAP2000 finite element software,the fastener type steel pipe scaffold model is established,and the fastener tightening torque,measured steel pipe defects,initial bending and comprehensive initial defects are analyzed.With the increase of tightening torque of fastener,the stability of steel pipe increases gradually.Under the condition of uncertain n-times reuse of fastener,it is suggested that the tightening torque should be 40 N·m.The stability of fastener type steel pipe scaffold decreases with the decrease of outer diameter and wall thickness of steel pipe.The uniform defect mode method is used to analyze the initial geometric defects(ideal defect free state,maximum allowable bending of 3L/1000 and measured maximum bending of L/305)of steel pipe,and it is concluded that the initial bending has a great impact on the stability of scaffold.Finally,this paper attempts to synthesize a variety of defects into one defect to study the overall bearing capacity of fastener type steel pipe scaffold.In order to ensure the safety of the scaffold,it is suggested that the comprehensive initial defects should be controlled less than 1.5%of the ultimate load.