Study Of Wind Load Mode On Transmission Tower Consisted Of Angle Steels

Taking220kV transmission tower consisted of angle steels as the research object, a1/2.5large scale rigid section model was fabricated and the wind tunnel measuring pressure test was performed in homogeneous turbulence flow. The wind pressure distribution and shape coefficient along main members, oblique members and auxiliary members were obtained. The characteristic of wind load functioning on each member was induced, and the law of varying shape coefficient of each member’s sections along with wind angle was summarized. It shows part of the angle steels which have both large drag and lift coefficients are under the action of double-direction distributed wind load in some specific wind directions. The shape coefficient of section model was compared between standard value and test value. The result shows that the domestic standard value is smaller than test value which tends to be unsafe to structure design, while the foreign standard value well agrees with the test value.The numerical analysis of each member under the distributed wind load was done. The result shows that diagonal members have great additional bending moment, which will result in the failure of the structure, while that in main members and auxiliary members has less influence and can be neglected. Wind-resistant design with nodal force load model that ignoring the effect of additional bending moment tends to be unsafe. The numerical analysis results of diagonal members with conventional node load model and distributed load model are compared. A correction method is carried out. It indicates that the diagonal members in finite element model, especially the longest one, should be finely modeled and load distributed wind load to consider the effect of additional bending moment. The structural mechanics principle of the correction method is given, and the accuracy of the method was verified.The internal force in main members and auxiliary members was compared between traditional nodal load mode and distributed wind load mode by establishing the modified finite element model of transmission tower. The result indicates that load mode does not make big difference on internal force of main members but make great difference on internal force of diagonal members. Each mode of the original modal and the modified one was compared. Ultimate bearing capacity of transmission tower at the action of two different wind load modes was researched. Dynamic time-history analysis of transmission tower was done. The wind vibration coefficient of local diagonal members was calculated. Compared with the traditional wind vibration coefficient calculated by the nodes of main members, the value of diagonal members’ wind vibration coefficient is bigger. It means taking traditional wind vibration coefficient as the whole section’s vibration coefficient is not proper. The local diagonal members’ wind vibration coefficient should be calculated alone. The value of diagonal members’ wind vibration coefficient calculated based on quasi-steady assumption is much smaller, which indicates that the quasi-steady assumption is not suitable to calculate the wind vibration coefficient of local diagonal members.A shell element FE-Model was established. The ultimate bearing capacity of diagonal members was compared between with and without the action of distributed wind load. The result shows that the influence of each diagonal member is different because of connection mode, and some members’ ultimate bearing capacity decreases a lot. It is pointed that calculation of ultimate bearing capacity should take both connection mode and the influence of distributed wind load into account.