Strengthening the grid: hybrid-bonded bolted joints for retrofitting weathered power-line structures

The escalating demand for renewable energy had necessitated the retrofitting of ageing power-line structures so that their resilience to increasingly frequent extreme-weather events might be improved. Within this engineering context, particular emphasis had been placed on minimising operational downtime, preserving existing assets and avoiding costly full-scale replacements. A central obstacle in such retrofit projects had been the presence of weathered, deteriorated coatings on the steelwork. These coatings were exhaustively characterised and were found to comprise a complex, multi-layer build-up that adversely affected the performance of conventional adhesive bonding. To determine practicable retrofitting routes, several surface-preparation strategies were investigated, and distinct test series were subsequently manufactured and mechanically tested. Untreated hybrid joints (H0), combining bonding and pre-loaded bolting, attained a sliding load of 38.0 kN, representing roughly a 171% increase over the maximum load of untreated adhesively bonded joints (A0: 14.0 kN) and about a 99% increase over the sliding load of preloaded bolted joints (B0: 19.1 kN). When moderate surface treatments were applied, further gains were realised: bristle-blasted hybrids (H1) reached 68.15 kN – an improvement of approximately 79% relative to H0—while laser-treated hybrids (H2) achieved 69.99 kN (≈84% over H0). From an engineering-retrofit perspective, these results demonstrate that a relatively simple hybrid solution could be deployed directly on the existing weathered surface with only minimal preparation, thereby shortening installation time, reducing cost, and limiting disruption to the power supply operation. For moderately loaded joints, it is even possible to facilitate the hybrid joint without any surface treatment. The substantial load-bearing capacity and enhanced reliability afforded by the hybrid approach therefore promises a practical, scalable means of strengthening critical power-grid infrastructure and, in turn, of facilitating a timely transition to sustainable energy sources.