Pre-Damage Strengthening of Heavy-Duty Steel Crane Girders Using Bonded CFRP Plates for Fatigue Life Enhancement

In recent years, premature fatigue issues in heavy-duty steel crane girders have occurred frequently, underscoring an urgent need to establish targeted life extension methods. Compared with post-crack repair after macroscopic fatigue cracks have appeared, it is more practical to delay or even prevent the formation of such cracks in fatigue-sensitive zones of the crane girder. Extensive research has demonstrated that bonding Carbon Fiber-Reinforced Polymer (CFRP) plates can significantly enhance the fatigue life of defective components. However, most existing studies focus on thin plates with pre-existing macroscopic cracks, with limited attention given to scenarios involving thick plates or intervention before crack initiation. Therefore, this study focuses on the fatigue problem around bolt holes in the lower flange of heavy-duty steel crane girders. It investigates the life extension method of bonding CFRP plates prior to macroscopic crack formation. Through finite element analysis and comparative fatigue tests, the fatigue life enhancement mechanism was preliminarily interpreted. The effectiveness of this method is validated, and a practical CFRP bonding strategy is proposed to significantly improve the fatigue life of the lower flange in heavy-duty steel crane girders.