Tower structure is very important in transmission line.Its security is very importantfor structure design.The current code which guide tower designing in transmission line,‘Code for design of seismic of electrical installations’ and‘TechnicalRegulation of design for tower and pole structures of overhead transmission line’ indicate that:it is not necessary that seismic checking calculation is done forself-supporting transmission tower if the seismic fortification intensity is 8 degree orunder 8 degree.There is not enough scientific basis about this define.Otherwise,alongwith the improvement of voltage grading,the height of transmission tower becomeshigher and higher,and the span of two towers becomes larger and larger.The earthquakefunction's influence to structure design turns worse,Whether carrying on anti-seismicchecking or not,controlling force play an important role.Now,one subject is the study ofcontrolling force in the course of structural design and code amendment.In this dissertation,on the basis of reviewing the study and design data available,thestructural theory of transmission tower is discussed,type tower-large span transmissiontower as engineering background and Space truss finite element method as theoreticalfoundation.Various load cases taken account such as:earthquake effect,wind load,etc,transmission tower model established by SAP2000 software,the dynamic characters andseismic response are analyzed.the controlling force of the elements on tower arecompared whether considering the earthquake effect or not.Then,compare the regularityof the elements’force with the change of wind speed and tower height.So we can getsome conclusion as following:
1)More modes should be considered according to the modal mass participation ratio when the seismic response of the structure was investinated.We suggest that numbers of the modes whether the modal mass participation ratio achieve 90%or not.
2)Force controlled by wind with wind speed variation and height below 185m,and
it don’t need seismic checking if the seismic fortification intensity is 8 degree or under 8degree.Because the span of two towers in tower-large span transmission tower is toolarge,constitution measures should be stiffened on the web materials of the cross arm.
3)Generally,whether considering seismic effect or not,the internal force of the diaphragms is not the main facts for its small value during materials selected,we usually select the materials according to slenderness ratio,but the constitution measures should be stiffened because of its confinement to tower.
Key words:High voltage transmission tower,Wind load,Seismic effect,control force
