Rehabilitation of Cracked Aluminum Connections with GFRP Composites for Fatigue Stresses

Abstract

The original design of existing aluminum overhead sign structures (OSS) did not consider fatigue as a limit state. Cracks propagate in the welds of the connection between the main chord and branches of OSS due to fatigue stresses caused by wind-induced vibration, which occasionally lead to complete fracture of the welds. A rehabilitation method for cracked aluminum welded connections using glass fiber-reinforced Polymer (GFRP) composites is investigated for its effectiveness under fatigue stresses. The results of constant amplitude fatigue tests for three types of aluminum connections from actual OSS are presented: (1) connections with no known cracks; (2) cracked connections rehabilitated with GFRP composites; and (3) connections with 90% of the weld removed and subsequently repaired with GFRP composites. The fatigue limits of the three connection types are established for four stress ranges including the constant amplitude fatigue limit threshold. The rehabilitated connections from OSS exceeded the fatigue limit of the aluminum welded connections with no known cracks. The repaired connections with 90% of the weld removed satisfied the constant amplitude fatigue limit threshold. A cumulative damage index is established which leads to a fatigue reduction factor for the rehabilitation design of cracked aluminum connections using the GFRP composites.