Analysis of the structural behaviour of grouted pile/sleeve connections for offshore structures
Existing experimental results are studied to determine the factors (including those not previously identified) affecting the strength of grouted connections. The current bond strength formula is evaluated and its limitations noted. Previous analytical work is examined and strengths and weaknesses investigated. A nonlinear finite element analysis is developed using a friction gap element to model the steel/grout bond. This includes a dilation effect when slip occurs and successfully simulates the behaviour of plain pipe connections up to ultimate load. An elastic-plastic, work-hardening, cracking and crushing constitutive model is developed to represent the behaviour of grout material. This is used for a detailed finite element analysis of the load-slip behaviour of individual shear keys of various shapes. The friction-gap element is adapted to give a representation of the shear keys using data derived from the detailed shear key analysis. A confinement factor is used to give higher ultimate shear key loads when the bond opening is small. This accounts for the observed fact that higher key loads are achieved with increased sleeve and pile dimensions due to greater confinement of the grout. Load-slip behaviour and strains up to ultimate load for shear keyed connections are successfully simulated using the friction-gap element. Bond stress distributions show that high normal bond stress concentrations are necessary to balance the bending moments in the grout annulus. Various extreme geometries are analysed and their failure modes determined. The effects of connection length, stiffeners, alternative loading arrangements, scale and shear key geometry are also fully investigated. Results are used to produce a new bond strength formula which takes into account most factors affecting bond strength and is stle to give good results over the full rang of geometries. Experimental tests have been conducted to determine the coefficient of friction between shot-blasted steel and grout for use in the numerical analyses.