The method of analysis for transmission line towers has advanced since the use of graphically procedures. Before the advent of the computer, the transmission engineer used graphical analysis developed to a professional art for determining member forces in three dimensional space truss towers. With the introduction of the computer, analysis calculations using structural matrix techniques were developed. BPA's Tower computer program was one of the original programs developed specifically for transmission line lattice structures. Now with the power of the personal computer (PC) the availability of tower analysis computer programs are numerous, such programs include BPA's Tower, PLS Tower, GT Tower, etc. The standard method of computer analysis for a lattice steel transmission line tower assumes three-dimensional truss behavior. The structural computer model is based on the tension and compression behavior of the individual members. These tower analysis programs are based on linear elastic structural performance, whereby pinned connected members are assumed to be axially loaded. The member forces determined from the computer model are compared to the allowable design capacity.
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