Study On Capacities Of The Joints For The New Type Nested Steel Tubular Scaffold

In order to adapt to the current development needs of building industrialization,scaffolding system,which is essential in the construction process,is also constantly improving and innovating.It aims at achieving rapid erection and disassembly on the basis of ensuring structural safety,thereby significantly improves the efficiency of assembly and disassembly so as to save costs.The new type nested steel tubular scaffold has advantage in safety,cost and convenience compared with traditional scaffolds,but its lack of theoretical research hinders its promotion and further application.Therefore,research on compressive,tensile and torsional capacity are emphatically carried out to further improve its analysis and design theory.,with the joints of the new type nested steel tubular scaffold as the studying objects.Experimental research and finite element analysis of horizontal compressive loading cases under three different working conditions,tensile loading cases under three different working conditions,torsional loading cases under five different working conditions were carried out respectively.The research shows that:(1)the experiment results and finite element simulation results are basically consistent.The joints of compression,tension and torsion all show obvious nonlinear characteristics.Local plastic deformation during loading does not mean yielding or failure of the entire node.The capacity of joints are related to its loading method.(2)The failure modes of axial compression and biaxial asymmetric compression are bending failure and squashed section of standing tube.As for biaxial symmetrical compression,the failure mode is squashed section of standing tube and loose connection between wedge head of ledger and cruciform nested socket.Therefore,the failure mode of biaxial symmetrical compression is the real compression failure of joint area.As for the axial tension and biaxial asymmetric tension,the failure source is the bending deformation of the standing tube and the shear failure of the cruciform nested socket;for symmetrical tension,the failure form is the shear failure of the cruciform nested socket,which is real in the sense of node area tension failure.The failure modes of the five torsional conditions are basically the same,all of which show that the torsional deformation of the wedge head of ledger is too large,and the deformation can not be restored after unloading.Among them,symmetrical reverse torsion is the most representative.On this basis,the geometric parameters of the joint are systematically analyzed,and the influence of the size of the vertical bar,the size of the cruciform nested socket and the size of the wedge head of ledger on the stiffness and capacity of the joint is studied.Further combined with the actual construction of the project,a compressive,tensile and torsional stiffness model of the joints in terms of the thickness of the standing tube are proposed.Finally,through the analysis of the lateral resistance of the typical frame of the nested steel tubular scaffold considering the semi-rigid characteristics of the node,on the one hand,the rationality and feasibility of the proposed compression,tension,and torsion stiffness models are verified;on the other hand,it is concluded that the bending stiffness of the joints should be considered when analyzing the lateral resistance of the frame,and when performing refined finite element analysis,the compression,tensile,bending,and torsional stiffness of the joints should be considered at the same time to further improve the calculation accuracy and be consistent with the actual mechanical performance of the frame.Therefore,it provides a theoretical basis for the analysis,design and application of a new type nested steel tubular scaffold.