The axial compressive elastic- plastic behaviour of a tubular beam with combined damages of out-of-straight and local dent has been studied. An incremental -iterative computation procedure is employed to trace the shortening deformation, axial stiffness and stress of a damaged beam at each of axial compressive steps. The effect of initial overall deflection of a beam on the plastic hinge at dent center is discussed. The elastically fixed boundary condition as well as bending moments at beam ends has been introduced into the analysis of ultimate strength of a damaged beam. A method is presented for the strength assessment of a platform with damaged members.
The structural strength of offshore platforms must be checked at design stage against the new state of platforms to confirm their safety in service. But it becomes suspectable when some structural members of a platform are damaged by accidental loads which make the state of structure obviously deviate from design condition. A reanalysis of platform structure considering damages of members becomes necessary to assess the safety of an aged platform. Most structural members of a platform are tubular beams. Damages are typically combined by local dent and permanent overall deflect ion. Many works written by Ellinas, C. P. [6], Smith, C. S. [7], Ueda, Y. [3.8], Moan, T. and Taby, J. [1. 2] etc. for predicting the ultimate strength of damaged tubular beam under axial compressive loads have been published. In their works, several calculation models of dented beam have been set up. The behaviour of tubular members subjected to axial compression was investigated. A wide range of parameters and the good correlation between the theoretical analysis and test results were obtained. The first step of analysis is to determine the axial force under which a plastic hinge appears at bottom of dent.
