Title:
Hebron Offshore Concrete Gravity-Based-Structure: Novel Design and Construction Techniques
Author(s):
Widianto; Jameel Khalifa; Kåre O. Hæreid; Kjell Tore Fosså; Anton Gjørven
Publication:
Symposium Paper
Volume:
337
Issue:
Appears on pages(s):
21-39
Keywords:
Hebron, Offshore, Design, Construction, Gravity Based, Slipforming, Crack Width, Grouting
DOI:
10.14359/51724545
Date:
1/23/2020
Abstract:
The Hebron platform is the latest major offshore integrated oil drilling and production platform supported by a concrete gravity-based-structure (GBS). It was successfully installed in the Grand Banks (offshore Newfoundland) in June 2017. The design of the platform was challenged by arctic-like and extreme metocean conditions. This paper presents development of extreme loads on the GBS such as 10,000-year iceberg impact and wave loads. It also describes novel design and construction techniques used, which resulted in a capitalefficient platform.
From an analysis and design perspective, in addition to linear-elastic finite element analysis typically used in design of offshore concrete GBS, the innovative use of non-linear finite element analysis (NLFEA) technique to calculate internal forces is presented. Such analyses more accurately capture the structural behavior and result in more realistic internal forces. In addition, a new crack-width calculation method accounting for the effect of a significant number of layers of transverse reinforcement was implemented. Also, a novel method to assess the complex interactions between solid ballast, embedded pipes, and concrete structures was applied.
From a construction perspective, the use of slipforming panels that are taller than those used in past GBSs and a system to allow slipforming of the shaft wall with a complex geometry and curvature, that is much larger than that employed in the past GBS, are presented. A novel method to minimize the risk of concrete adhering to slipforming panels by cooling the panels with cold water is presented. An innovative method to ensure that highstrength grout completely filled the space underneath one of the largest Topsides footings is discussed. Full-scale constructability tests of various complex GBS components, which provided invaluable information for design, increased execution certainty, and improved construction safety, is presented.
Related References:
Canadian Standards Association. 2006. CAN/CSA-ISO 19900:06 Petroleum and Natural Gas Industries — General Requirements for Offshore Structures. 28 pp.
Canadian Standards Association. 2010. CAN/CSA-ISO 19906:10 Petroleum and Natural Gas Industries — Arctic offshore structures.
Norwegian Standard, NS 3473E:2003, “Concrete structures – Design and Detailing Rules,” Standard Norge, Norway, 2003, 128 pp.
Oberlies, R., Khalifa, J., Huang, J., et al. 2014. Determination of Wave Impact Loads for the Hebron Gravity Based Structure (GBS). Presented at the 33th International Conference on Offshore Mechanics & Arctic Engineering, San Francisco, California, USA, 8-13 June. OMAE2014-23503.
Tistel, J., Eiksund, G. R., Hermstad, J., et al. 2015. Gravity Based Structure Foundation Design and Optimization Opportunities. Presented at the Twenty-fifth (2015) International Ocean and Polar Engineering Conference, Kona, Hawaii, USA 21-26 June. ISOPE-I-15-767.
Widianto, Khalifa, J., Younan, A., Karlsson, T., Stuckey, P., Gjorven, A. 2013. Design of Hebron Gravity Based Structure for Iceberg Impact. Proceedings of the Twenty-third (2013) International Offshore and Polar Engineering, Anchorage, Alaska, USA, 30 June – 5 July. ISOPE-I-13-036.
Widianto, Khalifa, J., Taborda, G., Bidne, K. 2016. Concrete Gravity-Based Structure: Construction of the Hebron Offshore Oil Platform. Concrete International, American Concrete Institute, 38(6):29-36.
Widianto, Khalifa, J., Åldstedt, E., Hæreid, K.O., Fosså. K.T. 2020. Design and Construction Overview of Offshore Concrete Gravity-Based-Structures: Past, Present, and Future. ACI Special Publication, ACI.