Improved LJF equations for the uni-planar gapped K-type tubular joints of ageing fixed steel offshore platforms

Riaz Khan, Kenneth Smith, Ivana Kraincanic
2017 Journal of Marine Engineering & Technology  
SYNOPSIS The distribution of fixed steel offshore platforms around the world reveals a global fleet that has exceeded or is approaching the end of the design life of the facility. In many operating areas, there is an attraction to continue using these ageing facilities due to continued production or as an adjoining structure to facilitate a new field development or expansion. To justify continued life extension of the fixed platform, various integrity assessment techniques are often used. One
more » ... the major techniques used is based on the phenomenon of Local Joint Flexibility (LJF). While the phenomenon of LJF has been well known in the offshore industry since the early 1980s, there has been little experimental data available. In 1983, Amoco conducted an experimental study primarily to determine stress concentration factors associated with gapped K-type steel tubular joints. The LJFs were also calculated as part of the study by using the chord and brace displacements observed of two specimens under eleven load cases. The LJFs calculated were based on the effects of in-plane bending, out-of-plane bending and axial compression and tension. Presently there are at least ten sets of LJF equations that have been used since the 1980s to predict fatigue life estimation and ultimate strength of the jacket structures. Their derivations have evolved in many ways including use of finite element methods to predict the joint behavior. There has been no benchmarking exercise to large-scale experimental data. This paper provides an improvement on existing LJF equations by benchmarking the Amoco K-joints test results to a finite element model and through a detailed parametric study. Improved formulations are provided for local joint flexibilities for gapped uni-planar K-type tubular steel joints. Authors' Biographies Dr Riaz Khan is a chartered engineer with over twenty years of experience in the civil engineering discipline. He has particular expertise in the structural integrity management of fixed and floating offshore structures and has assumed responsible positions on a variety of projects ranging from major offshore and onshore field developments. He has developed particular skills in the area of life-cycle integrity management for energy related. His experience also includes conceptual field development studies, detailed design and analyses of both onshore and offshore structures including fatigue, seismic, vessel impact, decommissioning and ultimate strength considerations in a variety of operating regions including the Gulf of Mexico, North Sea, Latin America, Asia and the Far East. He also serves as a Task Group Leader and Member of the OGP (ISO 19901-9) Code Committee for the Structural Integrity Management of Fixed Offshore Structures. Kenneth Smith is a Reader of Structural Engineering at the London South Bank University and a chartered civil engineer. He has over thirty years of both industry and lecturing experience with his research interests including forensic engineering and conservation, asset integrity management and structural engineering. Dr Ivana Kraincanic is a Senior Lecturer at the London South Bank University who specialises in finite element analysis, dynamic analysis and earthquake engineering. Her research interest also covers diverse topics of steel cables, offshore flexible pipelines, reinforced concrete slabs, and steel fibre-reinforced concrete. Open
doi:10.1080/20464177.2017.1299613 fatcat:xgvssplydjgmzngfwsemzgxh7a