| At present common construction scaffolds are fastener type,bowl buckle type,socket type,door type,etc,where fastener-type steel tube scaffolds have been applied the most extensively.Current studies on fastener-type scaffolds mostly concentrate on single and double-row forms while there lacks studies on full support system,especially in aspect of full-scale destruction test;due to semi-rigidity of fastener connection,fastener-type steel tube full support has complicated stress bearing conditions.Fastener-type steel tube full support collapse accidents happen now and then due to unreasonable design in engineering,which results in severe economic loss and personal casualties.Based on a large quantity of full-scale test,theoretical analysis and numerical simulation,this paper conducted a systematic and in-depth study on bearing characteristics and design method of fastener-type full scaffolds.Influencing rules of fastener tightening torque,quantity of anti-skidding fasteners,fastener newness,layout form of load-transferring horizontal bars,quality difference between manufacturers and other factors on anti-skidding load-bearing properties of fastener connection were obtained through a large quantity of full-scale anti-skidding tests;according to statistical analysis of test data,design values of anti-skidding load-bearing capacities of different fastener connection types like single fastener,double fasteners and three fasteners were proposed.Influencing rules of fastener tightening torque,fastener and steel tube newness,quality difference between manufacturers and other factors on rotational stiffness of fastener connection were obtained through a large quantity of full-scale tests;degradation laws of rotational stiffness of fastener connection during repeated loading-unloading process were revealed.Based on torque-corner curves obtained through the tests,average rotational stiffness of fastener connection was obtained under all kinds of working conditions,semi-rigidity characteristics of fastener connection were defined,and numerical values of structural properties of fastener-type steel tube full scaffold as well as values of rotational stiffness in theoretical analysis model were put forward.In consideration of semi-rigidity of fastener connection and anti-skidding performance of top-layer fastener connection,a parametric finite element model of fastener-type steel tube full scaffold was established;after verification of the numerical model through test data,influencing rules of structural measures of the scaffold body in horizontal and vertical directions like non-loading region,height to width ratio,scaffold height,step of upright tubes,spacing between upright tubes and vertical diagonal bracing on bearing capacity of fastener-type steel tube full scaffold were revealed,and then non-uniform distribution coefficient of vertical frictional force of fastener connection at top layer of fastener-type full scaffold was proposed.According to full-scale test and numerical simulation results,typical failure mode of fastener-type steel tube full scaffold was defined and simplified calculation model of ultimate bearing capacity was put forward;in consideration of semi-rigidity and anti-skidding performance of fastener connection,a simplified calculation formula of ultimate bearing capacity of fastener-type steel tube full scaffold was derived and verified through test data.Improved steel tube full scaffolds like truss reinforced type,weak truss reinforced type and mortise and tenon joint reinforced type were put forward,their load-bearing properties were studied and analyzed through numerical simulation and full-scale destruction test,and then it's found that ultimate bearing capacities of three reinforced steel tube full scaffolds were improved by 69%-235% when compared with those of traditional fastener-type steel tube full scaffolds;finally the design method for mortise and tenon joint-reinforced steel tube scaffolds was proposed. |
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