Lattice Transmission Tower Analysis: Beyond Simple Truss Model

In the early years of transmission tower design, the transmission engineer used graphical analysis methods that were developed to a professional-art for application to three dimensional space truss towers. The method of analysis for transmission line towers has advanced since the use of these graphical procedures. With the introduction of the computer, mainframe computer analysis capabilities using structural matrix algorithms were developed. BPA's Tower computer program was one of the original programs developed specifically for transmission line latticed structures. Now with the analytical power of personal computers, PC, the availability of tower analysis computer programs are numerous, such as BPA's Tower, PLS Tower, GT Tower, etc. The standard of practice for analysis of lattice steel transmission line towers is a three-dimensional truss analysis. The structural computer model is based on the tension and compression behavior of the individual tower members. These tower analysis programs are based on linear elastic structural performance, whereby members are assumed to be axially loaded and to have pinned connections. The member forces determined from the computer model are compared to the allowable member capacities. In special cases, a three-dimensional frame model may be required to provide necessary information on the member forces, including bending moments. With the maturity of the transmission tower engineering profession and the advances in PC analytical solution power, the transmission engineer can now push the margin of analysis beyond the simple truss model. The uses of the simple truss model is still the main analysis tool of the transmission engineer, but advanced tools for evaluating the performance of space truss towers, including effects other than simple truss action, are now being utilized. This paper presents three advanced transmission tower analysis computer programs.