Investigations on Live-Line Strengthening of Transmission Line Towers by Using GFRP Angle Sections

Strengthening existing transmission line (TL) towers is essential due to their aging and life extension. Further, the wind load calculations are frequently changing due to wind zone map revision by the codes of practice, resulting in extra wind and gravity loads, which leads to the over-stressing of existing tower members. Based on the state-of-the-art literature review, there is scope to propose live-line strengthening techniques that do not require site drilling of existing angle sections in TL towers. The present study proposes GFRP angle sections as strengthening members for compressive strength enhancement of leg and bracing members in TL towers. An equal angle steel section of size L 45 × 45 × 4 mm and two numbers of GFRP angle sections of size L 75 × 75 × 6 mm with slenderness ratios of 40 and 140 are considered for strengthening. The steel angle is reinforced (sandwiched) with two GFRP angle sections by using 12 mm diameter bolts spaced at 300 mm centre to centre along the length of the member through friction grip connection; hence it does not require site drilling on the existing steel angle section. The reinforced steel-GFRP angle section is subjected to the compressive load applied through the center of gravity of the steel angle to simulate the load transfer as in the field conditions. Based on the experimental and numerical investigations, it is observed that the compression capacity enhanced by 25% and 63% for slenderness ratios of 40 and 140 respectively.