A brace separated from the chord on an offshore platform during a hurricane. Our client developed a novel repair involving a clamshell-like clamp. We were asked to develop a detailed finite element model of the clamp halves, the grout, the chord, and the brace so that the fatigue life of the design could be determined.
The clamp halves are attached with threaded rods. In the analysis, the rods are pre-tensioned to the specified bolting torque.
Between the clamps and the chord, grout is injected. Shear keys are provided between the brace and chord. For the ultimate load cases, the grout is modeled with a damaged plasticity model in which the grout can fail in tension and compression. When all of the integration points of a grout element fail, the element is removed from the model. Using this analysis methodology, the ultimate capacity of the repair clamp can be assessed.
With some modification, the design was found to be acceptable for ULS and FLS load cases.