Wind-Induced Fatigue of Onshore Frame Structures

Abstract

Abstract The paper presents a proposed methodology to evaluate wind-induced fatigue of onshore slender frame structures with lattice-type design. The methodology for fatigue evaluation is based on a similar offshore industry design practice and has been repurposed for large onshore structures fabricated from tubular pipes, square tubes, and angle bars exposed to wind loading, including wind buffeting loads and wind vortex shedding. Multiple cracks resulting from wind-induced fatigue have been experienced on offshore installed flare booms and flare towers. Consequently, design codes were introduced, and it has been a standard design practice to evaluate potential fatigue damage of slender frame structures due to vibrations induced by vortex shedding, as well as buffeting loads due to gusting. This is, however, not yet standard design practice for land-based slender frame structures despite obvious similarities in terms of structural configuration, size, wind loads, and consequences of failure. Some operators have internal requirements to assess these operational risks. In this study, wind-induced fatigue design and analysis methodologies have been developed and calibrated based on offshore design practices. The proposed methodology uses a spectral analysis method that considers wind data, and includes simplified design checks as well as advanced analysis approaches. Further comparisons are presented for structural configuration and various end connection types with relevant examples. Both welded and gusset-type bolted connection of tubular members are investigated. This paper provides designers with methodology guidance to calculate structural fatigue damage due to both wind buffeting loads and vortex shedding vibrations. Key design considerations for wind fatigue analysis, typical design solutions and recommendations for improvements of fatigue life, and practical ways for the global fatigue screening are also provided.