Effect of joint flexibility on the nonlinear static and dynamic behaviour of offshore jacket platforms / Hamidreza Golabi

Hamidreza, Golabi (2015) Effect of joint flexibility on the nonlinear static and dynamic behaviour of offshore jacket platforms / Hamidreza Golabi. Masters thesis, University of Malaya.

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Abstract

Offshore steel jacket structures consist primarily of tubular members and associated joints. Tubular members have been widely used due to their excellent properties in respect of resistance in compression, tension, bending and torsion forces. In computer analysis, connections between the elements are assumed to be rigid, which means that there would be no axial rotational or deflection at the end of the secondary member against the main member’s axis. Nevertheless, the tubular joints have a remarkable amount of flexibility in the elasto-plastic range. Designing these structures based on realistic conditions is important due to the high costs of design and construction. Several studies based on numerical and experimental work have been done on tubular joints in 2-Dimensional states. In this study, finite element (FE) modelling of tubular connections is carried out in 3-Dimensions, to account for the actual platform performance. In this study a 3-D model of a fixed steel platform existing in the Persian Gulf has been modelled using a nonlinear finite element program. The joints and platform members are modelled using a SHELL element and PIPE element, respectively, through ANSYS software. Moreover, to investigate the effect of joint flexibility on these models, the analysis of rigid and flexible models of the platform and comparison of their static and dynamic behaviours are presented. In addition, push-over analyses were carried out for several joints with and without Joint-cans and also a comparison of M  curves in these two conditions is reported. The result of the non-linear static analysis shows that the static response of the structure changed considerably with respect to the joints’ flexibility in the nonlinear range. The modal features of the structure with flexible joints have significant differences compared to the rigid joints structure. In addition, performing the dynamic time-history analysis and investigating the exact effect of flexibility based on the flexible model shows that base shear values are reduced by about 30% compared to the rigid model. It is proven that local joint restraint has a considerable effect on the nonlinear static and dynamic behaviour of offshore structures.

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