A Composite Steel-Concrete Monopole for Electrical Transmission Lines

A new electric transmission line mono pole structure has been developed to provide a more efficient load carrying capability for limited or restrictive diameter pole applications. The primary feature of the new pole is the placement of concrete at strategic locations along the pole, and hence the designation "concrete-filled steel tube" (CFST). Since tubular steel poles have relatively thin walls that eventually buckle under high compressive stresses due to bending loads, the placement of concrete inside the tube will provide lateral stability to the wall as well as added flange area in compression. Additional longitudinal steel reinforcement may be embedded in the concrete to provide additional flexural strength to the cross section. One form of longitudinal reinforcement that was successfully used is standard deformed steel reinforcing bars. This paper addresses the design and testing activities that were performed in developing the CFST transmission pole. Data comparing the strength of the CFST to the strength of conventional tubular steel poles will be presented. Potential benefits of the CFST pole structure include the ability to carry significantly higher loads, using longer spans, and reduction in pole dimensions at ground line.