Wind-Induced Dynamic Performance and Fatigue Life of a Flat-Jib Tower Crane Across Various Operating Conditions

This study systematically investigates the effects of rope length, lifting position, and load on the dynamic behavior and wind-induced fatigue life of flat-jib tower cranes. Firstly, natural frequencies of a representative crane (40 m tower, 66 m jib) were accurately identified via on-site stress measurements. Subsequently, a finite element model was developed to analyze free vibration characteristics under various operational conditions. Fluctuating along-wind loads were simulated using harmonic synthesis, and transient dynamic analysis provided the wind-induced response. Finally, fatigue life of critical components was assessed through rain-flow counting, S–N curves per Chinese and European standards, and Miner’s linear damage rule. The results indicate that the first-order natural frequency in the along-wind direction decreases by approximately 12.5% and 14.2% with increasing lifted load and rope length, respectively, while the frequency at the jib tip is reduced by up to 37% compared to that at the jib root. Structural responses are more pronounced in the along-wind direction, predominantly exciting the first-order mode. Under operational conditions, stress in the jib’s main chord increases by approximately 30% to 50%, whereas stress fluctuations in other jib sections remain minimal. The fatigue life of tower crane components decreases by 13% to 21% relative to the unloaded state, with rope length exerting a greater influence than lifting load magnitude.