Stochastic Evaluation of Offshore Carbon Fibre Reinforced Concrete Platforms on Aluminum Girders

ABSTRACT

A stochastic evaluation of the performance of the Carbon Fibre Offshore Plastics (CFRP) offshore platform considering submerged and partially submerged environmental conditions was analyzed using Swedish code, Boverket (2004).
A Probability-based analysis using First Order Reliability Method (FORM) was used to determine the safety index of the deck considering varied load ratios, effective depths of the deck, and ultimate strength of Fibre Reinforced Plastics (FRP) tendons.

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The results generated from FORM indicate that the theoretical framework for risk assessment based on the Joint Committee for Structural Safety JCSS (2003) showed that the maximum safety index of the CFRP deck was shown to be 3.49 which is higher than the limit set by the JCSS (2003) code. Hence the deck can adequately transmit the given loading conditions when designed in accordance with Boverket (2004).
Also, the results of the Finite Element analysis carried out on the deck showed that the von Mises stress was within acceptable limits, implying that the resisting moment of the CFRP deck was adequate.
Hence, it is shown that the CFRP deck can be used in the marine environment with increasing tidal loading as the CFRP was also able to resist failure due to compression.
The flexural, as well as shearing resistance, are also within safety limits; and are about 500% greater than that of a steel-reinforced concrete platform.
However considering the serviceability limit state of deflection, the CFRP platforms did not show noticeable deformation in the geometry of the deck from the finite element analysis.

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INTRODUCTION

Background of Study
Corrosion is a major problem on reinforced concrete structures especially in the case of macrocell formation because it can cause local loss of the reinforcement cross-section in conjunction with subsequent cracking and spalling of concrete cover in the structure.
With increasing deterioration, the serviceability will be impaired and the load-bearing capacity decreases. The inspection and maintenance strategies to detect such damages can be costly and economic planning is mandatory.
In off-shore structures, structural components are built to be embedded in water as in the case of harbours, oil rig platforms just to mention a few. It is however essential that proper design to safely carry the imposed loadings be considered.
Most importantly, design for the durability and resistance to chloride effect, salty water, de-icing salt, freeze-thaw, etc. must be thoroughly considered (Humphrey, 2003).
Once corrosion gets started due to chloride ingress, anodic areas can be detected through potential mapping. Potential mapping provides two-dimensional information about a structure.
This kind of information can be used for a spatial evaluation of corroding areas. It has to be considered that potential fields are influenced by several parameters such as concrete cover and resistivity, which always will have an effect on the spatial variability.
The potential consequences of the corrosion problem can be summed up in the continuous reduction in strength, stiffness, durability, and designed lifetime of the concrete structural elements reinforced with conventional steel.
Considerable percentages of many national budgets are assigned either for innovative research works that can come up with radical solutions including corrosion problems or for repair, strengthening, and in some cases reconstruction of damaged concrete structures (Humphrey, 2003).

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REFERENCES

AASHTO, (2004):―LRFD Bridge Design Specifications‖, American Association of State Highway and Transportation Officials, Washington, D. C.
AASHTO, (2007):―LRFD Bridge Design Specifications‖, American Association of State Highway and Transportation Officials, Washington, D. C.
AASHTO, (2010):“LRFD Bridge Design Specifications”, American Association of State Highway and Transportation Officials, Washington, D. C.
Abejide, O. S (1997): “Solid soilcrete blocks for low-cost buildings: a Nigerian case study”.Building Research and Information, Building RES INFORM. Vol 25, no 2, pp 115-119, DOI: 10-1080/09613219730516.
ACI Committee 318 (1995): “Building Code Requirements for Reinforced Concrete (ACI318-99)”. American Concrete Institute, Farmington Hills, MI.
ACI 318-02 and ACI 318R-02, (2002): “Building codes Requirement for structural concretes and commentary”, American Concrete Institute, Farmington Hills; Michigan,USA.