Static strength of simple and grouted tubular X-joints subjected to in-plane bending

Abstract

Tubular X-joints are used extensively in leg assemblies of jackup platforms and jacket structures. As a result of Hurricanes Katrina and Rita in 2005, existing platforms will be required to resist significantly higher loads with associated demand on the critical tubular members and joints. For older platforms, there is a corresponding need to retrofit crucial joints to ensure adequate static strength. This paper presents results of an experimental and numerical investigation on the effect of strengthening the chord with ultra high strength grout on the enhancement of static strength of tubular X-joints. Two pairs of tubular X-joints, consisting of as-welded and grout in-filled chord were tested under in-plane moment. These X-joints are fabricated with chord diameters d 0=406 mm or 508 mm, and brace diameter d 1=406 mm. The geometric ratios of the tested specimens comprised of chord radius-to-thickness ratio γ=9.2 to 16, and brace-to-chord diameter ratio β=0.8 and 1.0. Based on the test results, the Densit Ducorit D4 grout is found to provide significant strength enhancement to the as-welded X-joint, with the static strength ratio of the grouted to aswelded joint at 2.58 for β = 0.8, and 1.68 for β = 1.0 respectively. The nonlinear finite element results which account for the interaction of the grout and chord interface are found to be in close agreement with those obtained from the four experimental tests.