Study On Mechanical Performance And Ultimate Strength Of Multiplanar Space Joints In Tubular Lattice Tower

For steel transmission towers,the joints which are very important force transmission parts mainly include unstiffen and gusset plate connections.Tile now,the achievements of the study on performance of unstiffen joints are abundant and plentiful.However,there is little related literature on the behavior of gusset plate to joints.Especially the investigations on the multiplanar space unstiffen joints with gusset plate connections are almost blank.It is necessary to conduct in-depth research on this kind of joints considering that they have been applied in transmission towers.The behavior of two new types multiplanar tubular beam and column joints were investigated in tubular lattice tower,with the background of Youning 750 kV transformer substation engineering in Qinghai.The main research works in this dissertation are as follows:(1)In order to obtain the failure modes,stress and strain distribution characteristics,and ultimate bearing capacity of the complicated space joints,four full-scale tests were conducted.The research indicates that the main pipe is a weak part of two type joints,and the concave deformation occurs in their main pipes with no failure in branch ones or welds.(2)The nonlinear finite element models were established and their applicabilities were verified by analyzing the failure modes,load-displacement curves,strain distribution characteristics and bearing capacity obtained from the finite element.Based on parametric analysis,the failure modes and their distribution of this kind of joints show that the ultimate strength is mainly determined by that of a brace when the brace is failed.The ultimate strength of the joint depends on that of the chord when the chord is failed.The ultimate strength depends on that of the gusset plate and flapper when the unstability failure appears.(3)Furthermore,according to parametric analysis,the effects of auxiliary members on ultimate strength were investigated.The influence degree will change along with forces and failure modes of joints.(4)Based on the experimental results and finite element analysis,the calculation formulas of the ultimate strength of space joints determined via the chord are obtained by the energy method and ring-generator separation model.The complex force model is simplified and provides a reference for space joint’s design considering chord axial force effects and interaction from every branch.(5)The multiplanar space beam and column joints are simplified to Y-joints and K-joints by separating,respectively.The ultimate bearing capacity of joints separated is obtained from FEM.Based on code formulae of K-joints and Y-joints,design methods of predicting the ultimate strength of complicated joints considering interaction of every branch were proposed.