Mechanical Analysis And Structural Study Of Gravity Second-order Effects Of Narrow Base Angle Steel Towers

The narrow base tower in power transmission line engineering is one kind of tower which occupies small space and relatively compact channel.This kind of tower is mainly used in urban area and the place where the corridor is limited in a narrow area.The use of the narrow base towers are mostly narrow base steel tube towers in China until now.Steel tube is used as the main structure and angle steel members are used in the second parts.However,the bearing capacity of the steel tube tower can not be fully utilized,so the economy is worse.A new type of narrow base angle steel tower has been proposed.The narrow base angle steel tower consists of the angle steel members,which can reduce the cost of constructions to a large extent.At present,there are no authoritatively technical regulations for the design of the narrow base angle steel tower both at home and abroad.Therefore,it is urgent to pay the study on key technique of the narrow base angle steel tower.In this thesis,the rod element model,beam-rod element model and finite element analysis model of the narrow base angle steel tower are established through reasonable mechanical simplification.The analysis method of gravity second order effect(P-Δ effect)is given in the engineering design of the narrow base angle steel tower.A comparative analysis of structural strength,stiffness and stability.of the narrow base angle steel tower is carried out by means of finite element analysis and theoretical analysis in order to investigate the influence degree of the gravity second order effect(P-Δ effect)to the new narrow base angle steel tower.The results of the analysis are compared with those of the conventional tower.At present,the relevant softwares used in the conventional design of the electric power design institute consider all the members as two-force members,which are calculated and analyzed as rod elements.In the rod element model,the axial force is only considered and the bending effect of the rod end is ignored.In fact,the mechanical model of the main components of the narrow base angle steel tower should be closer to the beam characteristic.Based on the comparison rerults of the two kinds of models in the thesis,the reasonable mechanical model is that the main components in the finite element analysis of the narrow base angle steel tower should be acted as the beam elements.It has been suggested that the main components should be strengthened based on the design of the conventional rod element,for the main components is more dangerous than the slant components and the sub components.Meanwhile,some design suggestions are given for the top displacements of the towers which are not specified in the published design code of the towers.