The Effect Of Bolt Joint On The Mechanics Characteristic Of The Transmission Tower

With the development of electric power construction and economic growth in China,more and more transmission towers will go through the areas,where the foundations are easy to sink,or the extreme weathers frequently happen.The changeable environments will easily cause tower damage,even collapse.In addition,with the improvement of voltage classes,the heights and spans of transmission towers increase quickly.Large span transmission towers are more sensitive to dynamic environment loads.In the practical application,it is increasingly urgent for the prediction of dynamic response.As high lattice structures,transmission towers usually consist of structural steels and steel tubes,etc.The bolt joints,which are used to connect the members,are mainly eccentric connections.They are easily to slip because of the fitting clearance between bolts and holes,when under high shear forces.The effects of bolt joints on the mechanical behavior of lattice transmission towers have continuously attracted the attention of researchers and engineers,as the conventional analysis results usually possess large discrepancies in comparison with actual measurements.The estimations of ultimate bearing capacity remain to investigate.In dynamic aspects,it also has a large deviation for the forecast of natural frequencies.All the reasons are oversimplified modeling of bolt connections.Rigid or pinned connections are both inaccurate for bolt joints.Our research group has finished axial extension tests of the typical bolt connections,as well as a full-scale test of ZM-11 transmission tower.In this study,using ANSYS software,the bolt joint effects are introduced in from parts to parts.Numerical results are compared with the test measurements,emphasizing on studying the important parameters,the micro-slip stiffness and the macro-slip length of the nonlinear slippage curve of bolt joint.Furthermore,the different effects of the bolt joints in the bracing members,the tower legs,and the tower head are obtained.Analysis will be described in static and dynamic aspects.In engineering practice,transmission towers often operate well when failure in forecast.The reason can be found in this dissertation,since the differences between traditional models and slip models in non-uniform settlement conditions are presented clearly.In order to ensure the safety operation of the transmission lines,it is necessary to have a comprehensive understanding of meteorological conditions along the route and accurate analysis in the design process.This dissertation also examines the effect of bolt joints in four biggest working load conditions.The results can further prove that considering bolt slip is meaningful for engineering applications.Through this study,the effects of bolt joint on mechanics characteristics can be clearly observed.The improved model will provide reasonable advertisement on design of deform resistance,anti-vibration,safety assessment and control,and will also lay the foundation for future study of tower-line systems.