Design and Construction of Prestressed Concrete Vessels
Authors: Gerwick Ben C. 
Published: October 2008

The proper utilization of prestressed concrete £or ocean vessels and floating structures demands the integration of many complex and interacting considerations: naval architectural, structural engineering, concrete technology, and construction engineering. While the excellent properties of prestressed concrete have been pointed out by many authors, for cryogenic transport and storage, for Arctic Ocean service, and for floating storage vessels, many of these efforts have had to be abandoned because of inability to efficiently integrate the numerous aspects. Now the demand for special purpose vessels has again focussed attention on prestressed concrete construction.

Factors requiring consideration include wave action, hydrostatic pressure, variable cargo loading, stability in a damaged and undamaged condition, grounding, resistance to collision, impact, fatigue, temperature stresses, including shock from a ruptured liquefied gas tank, and behavior in fire. Combined loadings and appropriate load or safety factors at various limit states must be established.

Procedures for construction inspection, quality: control and quality assurance in service inspection, and repair must be developed, all to meet the approval of applicable regulatory bodies. Stability and stress levels at various stages of construction, launching, and during immersion must be determined.

Multiaxial prestressing, shell configuration, and new concrete materials of greater tensile and compressive strengths must be thoroughly evaluated in order to maximize their contribution to better deadweight/displacementratios, construction simplification, and improved service performance.

Recent experience with several large ocean projects has required the development of improved construction concepts and design criteria. This paper is presented as a guide to the further development of prestressed concrete vessels.

INTRODUCTION

Prestressed concrete vessels are being increasingly considered for large-scale offshore operations, such as floating storage vessels, ocean transport of special cargo such as liquefied gasses, and for the transport and support of complex processing facilities, such as LNG plant units. Prestressed concrete offers the advantages of economy, low maintenance, fire resistance, nonbrittle behavior at low temperatures, good impact resistance, and a favorable mode of failure under accident conditions. Repairs can be effected easily, usually while afloat. Suitable materials, techniques, and adequately skilled personnel are widely available.

At the same time, prestressed concrete is not yet widely employed for such vessels due in large part to lack of well-established criteria for design and construction which have been accepted by regulatory'agencies, insurance groups, and user industries, and which would serve as a standard to which the manufacturer of the vessel must conform.

Interestingly, the first use of reinforced concrete was a boat, built by Lambot in 1850 in France, only shortly after iron was first used for ship hulls and well before the first steel vessel. One of Lambot's boats is still afloat in the Amsterdam Zoo. Reinforced concrete ships were used extensively in both World Wars I and II, but with few exceptions, designs were based on imitating steel vessels, and construction was based on uneconomical (high labor cost) practice.