Study On Mechanical Properties Of Key Joints Of Bolt Connections Of Narrow Base Angle Steel Towers

The narrow base angle steel tower in power transmission line engineering is one kind of tower with small footprint and relatively compact channel,which is mainly used in urban area and limited corridor.Because of the convenient construction of bolt connection,simple disassembly and less welding work on the sites,the angle steel towers are widely used in transmission tower structure.For the sake of the assemblies,the diameter of screw hole is larger than the diameter of bolt.Due to the bolt clearance,the bolt will yield the slippage in the screw hole.And the randomness and accumulation of bolt clearance may lead to large deformations of the structures from the bolt connections.Thus,the overall structural security of the tower will be deteriorated.On the other hand,due to the complexity of the interaction between the joint members of the bolt connections and the stress concentration,it is difficult to accurately analyze the local stress fields in the joint structures.Then the evaluation of the stress strength and safety of the joints will be difficult.The narrow base angle steel tower is more flexible than the conventional angle steel tower.Then the size of the bolt clearances of the joint connections will have a greater influence on the mechanical properties of the tower structures.Therefore,it is necessary to study the effect of bolt connection on the mechanical properties of the narrow base angle steel towers.In this thesis,the typical key joints of the narrow base angle steel tower are selected.The rigid frame model of the angle steel tower structure and the joint local model are established by reasonable mechanical simplifications,in which the details of the bolted connections are considered.Then a multi-scale finite element model is proposed by using multi-point constraint equation(MPC)to implement the connections between the beam elements and three-dimensional solid elements.Consequently,the joint model,the frame structural model and the multi-scale structural model are analyzed by finite element method respectively.Through the comparative analysis of the computed results among the rigid-framed model,multi-scale model and full-scale model test,the reasonability of the multi-scale structural model is verified.According to the analysis of the joint model and multi-scale model,the deformation and stress fields of the joint structures with different bolt clearances in the narrow base angle steel tower are studied by changing the bolting gaps at the joint.In addition,the reasonable suggestion for the sizes of the bolt clearances are given for the bolt connections of the towers.The multi-scale analysis method and the computed results in the present work are beneficial references to the mechanical analysis and the designs of bolt connections of the angle steel towers.