Experimental Study of Glass Fiber–Reinforced Polymer Composite Crossarms for Power Transmission Towers

Glass fiber–reinforced polymer (GFRP) composites have emerged as a promising alternative to conventional steel and aluminum in energy transmission tower construction due to their superior mechanical strength, enhanced resistance to chemical degradation and creep, and excellent electrical insulation properties. This study aims to evaluate the mechanical behavior of pultruded GFRP composite box-section crossarms for use in 154-kV energy transmission towers under realistic loading conditions. The first phase of the investigation focuses on characterizing the bearing strength of the GFRP composite material through a series of experiments on single-bolted double-lap joint configurations with varying edge distance-to-bolt diameter ratios (e/d ranging from 3 to 8). The bearing strength and service stiffness were determined by following three distinct approaches: 4% hole elongation, 1 mm hole elongation, and stiffness degradation. In the second phase, full-scale GFRP composite crossarms were experimentally tested under two critical loadings to evaluate the effects of loading conditions and connection details on their structural performance. Under the critical loadings, crossarms with final connection details exceeded target loads by 18% and 8%, respectively, demonstrating satisfactory structural integrity. The enhancements, including epoxy-bonded resin blocks and additional bolts, were observed to significantly increase the overall load capacity. The findings indicate that bolted connections in pultruded GFRP box sections reinforced with woven mat layers exhibit superior load capacity and stiffness. Therefore, GFRP composite crossarms offer a viable, structurally efficient alternative to conventional steel components in power transmission towers, proving their suitability for 154-kV transmission lines.