Fatigue behaviour of non-welded wrapped composite joints for steel hollow sections in axial load experiments. (15th December 2021)

• Record Type: Journal Article
• Authors: Feng, Weikang; Pavlovic, Marko
• Is Part Of: Engineering structures. Volume 249(2021)
• Publication Date: 2021-12-15
• Subjects: Wrapped composite joint -- Bonded joint -- CHS -- Steel-composite -- Fatigue experiments -- GFRP -- Crack growth -- 3D DIC -- Welded joint -- Surface roughness; Structural engineering -- Periodicals; Structural analysis (Engineering) -- Periodicals; Construction, Technique de la -- Périodiques; Génie parasismique -- Périodiques; Pression du vent -- Périodiques; Earthquake engineering; Structural engineering; Wind-pressure; Periodicals; 624.105
• DOI: 10.1016/j.engstruct.2021.113369
• Languages: English
• ISSNs: 0141-0296

Abstract

Highlights: Bonding by a composite wrap instead of welding to connect steel hollow sections. Superior fatigue performance of bonded over welded joints in cyclic load experiments. Crack propagation monitored by 3D Digital Image Correlate system. Fatigue life and crack propagation rate characterized by nominal stress range. Higher surface roughness provide better fatigue performance of bonded interface. Abstract: Design and execution of fatigue load dominated circular hollow section (CHS) multi-membered structures, such as offshore jacket and floating structures for wind turbines, truss bridges, etc., is hinged on fatigue performance of critical welded joints. An innovative jointing technology of wrapped composite joint connects steel hollow sections by direct bonding through a fibre reinforced polymer composite wrap, which completely avoids welding and therefore has superior fatigue performance than welded joints. In this study first results on fatigue performance of the wrapped composite joints is presented. Tensile cyclic loading tests on wrapped composite X-joint specimens were carried out to characterise their fatigue performance under different constant amplitude load ranges and compare it to equivalent welded joints. In addition, the influence of surface roughness of steel tubes and re-testing (load history) on fatigue performance of wrapped composite joints, as well as the influence of fatigue loading on residual static resistance was investigated in experiments. Preliminary S-N curves of wrapped composite joints are established. The tests results showed that X45 wrapped composite joints exhibited steadier stiffness degradation and 10–100 times longer fatigue life than their welded equivalents. Through 3D DIC surface strain measurements and post-failure microscopic insights to cut specimens, different failure modes including de-bonding at glass fibre composite-to-steel interface, delamination/fracture of the composite layers and fracture of steel brace are distinguished. The relationship between joint stiffness degradation rates, crack propagation rates and nominal stress ranges in the brace are established, based on which a preliminary fatigue life prediction of wrapped composite joints can be made. The re-tested specimens exhibited superior fatigue performance than virgin ones, while specimens with poor steel surface roughness showed worse fatigue performance. After fatigue loading with 40% of stiffness degradation, the specimens were found to still have the potential to sustain its original static resistance.