Effect of tensile residual stresses on fatigue crack growth and S–N curves in tubular joints loaded in compression

The influence of welding tensile residual stresses on fatigue crack growth in bridge tubular K-joints is investigated through experimental testing of large-scale specimens. Crack development is monitored using the alternating current potential drop method. Crack shape, propagation rate, and the stress intensity factors, are analyzed based on measurements. Current CIDECT design guidelines devoted to K-joints recommend to use the fatigue strength S–N curve category 114. Based on experimental investigations, this category is shown to overestimate the fatigue life of bridge K-joints presenting a low chord slenderness γ value (γ < 12). CIDECT guidelines also neglect fatigue from compressive loading; however, the fatigue test results prove that cracks propagate up to a critical size for details loaded in compression. The detail category 100 is proposed to design bridge K-joints loaded in tension or compression.

► We measure the crack growth in large-scale specimens using the alternating current potential drop.
► We compare crack propagation in details loaded in compression and tension during fatigue tests.
► We explain why and how cracks can propagate under compression (residual stress influence).
► We propose new recommendation for designing K-joints using a fatigue strength curve category 100.