The NESC-2012 has wind maps from older ASCE-7 so you can get the right loading. In my part of the world, the hurricane winds are much more severe than the ice loads. The latest version will allow you to have the redundants in the structural model but analyze the tower as if they are not there. Of course you have to account for the missing area for the wind drag by adjusting the section parameters.
You typically leave out the redundant bracing members and adjust the leg and lacing KL/r to assume that the redundant will brace the leg. I've been analyzing towers since 1973 so I can answer most questions about this very narrow subject. There is another forum for these questions and I just came across this thread by accident. The de facto standard program for analyzing towers is from PLS-CADD from Power Line Systems. We do not apply ice on members of the tower (not required by ASCE 74 or NESC), we just load up the conductors with ice. Everything is assumed as pinned connections in lattice towers and we adjust the KL/r based on connection fixity. RE: Transmission tower analysis/design BAretired (Structural) 6 Jul 12 13:39ĪSCE 10 is the standard you need for transmission towers. We have modeled this tower in RISA 3D, not the RISA TOWER.
Is it typical to design these braces as pinned at the joints, we would have expected so. moments that are within the joints design capabilities. We did change all of the bracing to fixed connections and only SMALL moments are generated at the joints. Should the loads be applied to the joints of the structure only? If so, are both the wind and ice loads translated to the joints only?
Are these braces typically designed as "Tension Only"? When we make them tension only the model will not converge which is our next problem. We are finding the Euler Buckling is exceeded for the long braces when they are modeled as two way members. we applied the wind loads and the ice loads to each individual member including the bracing members. We have calculated the wind and ice loads per ASCE 7 and built a Finite Element model of the tower. We are analyzing the existing condition of an existing transmission tower having long (30 ft plus) L2x2x1/4" braces.
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