Performance based design of offshore topside structures subjected to blastloading
Author(s)
Mohamed Ali, Rafee Makbol
Type
Thesis
Abstract
Topside structures of offshore installations have to support heavy process plant dealing with
large volumes of oil and gas under high pressure. Many of these platforms have to be operated
in very remote areas in a harsh environment with little supporting infrastructure. It is therefore
necessary to design these high risk installations to various types of extreme loadings. One of
these extreme scenarios is blast loading from a possible hydrocarbon explosion. Although this
is a comparatively low frequency accidental event, it has the capability to cause major fatalities
to personnel and serious structural damage which could lead to the complete loss of the
platform. At present, most topside structures are designed based on working stress design
(WSD), or load and resistance factor design (LFRD), which is quite safe but not economical
due to the uncertain extent of the levels of protection. For these reasons, a Performance Based
Design Methodology is proposed, which emphasizes the structure’s predictable behaviour and
the protection of personnel and assets. The end result will be an optimum design which satisfies
the function of a system without compromising safety.
A performance based design guideline for the assessment of topside structures subjected to
blast loading is proposed. The guideline, which reasonably incorporated some statistical
findings, simplifies the evaluation of performance levels for the topside structure without
quantitative risk assessment (QRA) data. The assessment of topside structures is not complete
if the proper behaviour and response is not fully understood. It has been shown in the study that
the roles of secondary structural members i.e. deck plates and stringer beams cannot be
overlooked. Having substantial deformations on secondary members averts severe damage on
primary members. A simplified deck plate analytical model is proposed and the optimum
slenderness ratio for deck plate design is recommended. Although accuracy of the proposed
analytical method is found slightly offset from the finite element result at extreme overpressure,
the model is straightforward and provides a quick method to assess the deck plate capacity. The
study has also highlighted the weakness of sniped bottom flanges for stringer beams, a
necessary condition to facilitate practical fabrication. This shortcoming is overcome by
strengthening with angles, a novel idea which is simple and practical with minimum
interference to the existing structural configuration.
Based upon a typical topside framing, the performance level of the topside is evaluated for
reference which can be applied to other topsides. The study has investigated a number of
mitigation techniques for improving beam to beam connections. The techniques comprise
studies based on some conventional approaches, typical fabrication methods and a new
proposal with tubular braces. Finally, the effect of equipment on the topside structure is
investigated and recommendations are made to minimise unnecessary damage.
large volumes of oil and gas under high pressure. Many of these platforms have to be operated
in very remote areas in a harsh environment with little supporting infrastructure. It is therefore
necessary to design these high risk installations to various types of extreme loadings. One of
these extreme scenarios is blast loading from a possible hydrocarbon explosion. Although this
is a comparatively low frequency accidental event, it has the capability to cause major fatalities
to personnel and serious structural damage which could lead to the complete loss of the
platform. At present, most topside structures are designed based on working stress design
(WSD), or load and resistance factor design (LFRD), which is quite safe but not economical
due to the uncertain extent of the levels of protection. For these reasons, a Performance Based
Design Methodology is proposed, which emphasizes the structure’s predictable behaviour and
the protection of personnel and assets. The end result will be an optimum design which satisfies
the function of a system without compromising safety.
A performance based design guideline for the assessment of topside structures subjected to
blast loading is proposed. The guideline, which reasonably incorporated some statistical
findings, simplifies the evaluation of performance levels for the topside structure without
quantitative risk assessment (QRA) data. The assessment of topside structures is not complete
if the proper behaviour and response is not fully understood. It has been shown in the study that
the roles of secondary structural members i.e. deck plates and stringer beams cannot be
overlooked. Having substantial deformations on secondary members averts severe damage on
primary members. A simplified deck plate analytical model is proposed and the optimum
slenderness ratio for deck plate design is recommended. Although accuracy of the proposed
analytical method is found slightly offset from the finite element result at extreme overpressure,
the model is straightforward and provides a quick method to assess the deck plate capacity. The
study has also highlighted the weakness of sniped bottom flanges for stringer beams, a
necessary condition to facilitate practical fabrication. This shortcoming is overcome by
strengthening with angles, a novel idea which is simple and practical with minimum
interference to the existing structural configuration.
Based upon a typical topside framing, the performance level of the topside is evaluated for
reference which can be applied to other topsides. The study has investigated a number of
mitigation techniques for improving beam to beam connections. The techniques comprise
studies based on some conventional approaches, typical fabrication methods and a new
proposal with tubular braces. Finally, the effect of equipment on the topside structure is
investigated and recommendations are made to minimise unnecessary damage.
Date Issued
2008-03-31T14:39:22Z
Date Awarded
2008-03
Format Extent
5282756 bytes
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Louca, Luke
Sponsor
MARA, Malaysia
Creator
Mohamed Ali, Rafee Makbol
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)