Effect of impact damage on the capacity of tubular steel members of offshore structures

The effect of axial pre-loading on the behaviour and instability of a cylindrical member of an offshore structure struck by a supply vessel has been investigated. Numerical models have been used to analyse a tubular member with and without axial pre-loading. It has been found that axial pre-loading has a marked effect on the lateral collapse load of the member and more dramatically on the level of energy that the member can absorb prior to its collapse. The effect of different end conditions on the behaviour of the tubular members has been examined and four distinct modes of deformation for a cylindrical member under quasi-static concentrated lateral loads have been defined. The finite element model was validated using available test results from the literature. These were mostly static tests, carried out on cylindrical members with no axial loading. Good agreement was obtained between the finite element model and the test results. Significant differences have been found between the results presented in this study and previous results by the other workers who represented the impact damage as an imperfection effect