In-situ retrofit strategy for transmission tower structure members using light-weight steel casings

A practical technique to increase the robustness of existing light truss electric power transmission towers by restraining the buckling of their critical members is presented in this paper. Such buckling-critical members are enclosed by a tight-fitting rectangular casing comprised of two identical light gauge steel C- or U-shapes connected using screws. The steel casing was designed to postpone a decrease in the compression load-carrying capacity of the tower truss member by restraining its lateral-torsional and weak-axis buckling. Five full-scale restrained specimens and one unrestrained base-line specimen were manufactured and tested. One of the restrained specimens was loaded cyclically, while the other ones were tested under monotonic compression. Numerical models of the specimens were built by ABAQUS, and the simulation results were found to match the test observations. A parametric study was conducted using the validated numerical model to investigate the effect of the restraining casing thickness on the behavior of the restrained member. It was revealed that a steep drop in the compression capacity of the restrained member could not be substantially postponed when the thickness of the restraining casing was less than half of that of the restrained member legs. Conversely, the compression capacity of the restrained member could approach its yield strength in case that the thickness of restraining casing was set to be larger than 85% of that of the restrained member legs. The outcome of both experimental and numerical investigations demonstrates the feasibility of the proposed buckling restrainers for use in practice to enhance the mechanical robustness of light truss electric power transmission towers.