In the meantime, here is an overview of the general design considerations for composite hydraulic structures:

Identify Design Requirements

The requirements of a new FRP structure are usually based on the requirements of the existing structure made of conventional materials, including the geometric boundary conditions and various loads on the structure. Geometric boundary conditions focus on the dimension of the structure, fatigue cycles, sustained stresses and environmental conditions, such as the range of operating temperature. The loads considered may include complex wave loads, dead load, torsion and longitudinal loads, ice loads, wind loads, water flows and potential barge collisions.

Consider Material Selection

The properties of composite materials and their manufacturing process usually drive the selection of FRP composite materials. The lamina properties of FRPs, including the properties of core materials (if involved), are calculated, and the material safety factors and design values are determined. Manufacturing methods suitable for the proposed structure should be selected to achieve high fiber content and to enhance the strength and stiffness of the material. Designers also can take advantage of the fact that composite materials are anisotropic, so they can be designed and manufactured with properties varying in different directions to suit the application needs, dependent on load paths.

During the material selection process, designers should consider numerous factors, including corrosion, weathering and the material safety factor. With regard to safety factor, uncertainties due to a combination of effects corresponding to various knock-downs (under temperature, moisture, sustained stress/creep and fatigue) should be taken into account. In addition, uncertainties regarding targeted material design properties should be considered. It is extremely important to note that proper selection of the manufacturing process, as well as the constituent materials (resins, fibers, additives) for a tailor-made composite structure, are essential to meet minimum design and performance requirements.

Define the Structural Concepts

The next step is to define the structural concepts of the proposed FRP structure. Usually, a minimum of three important aspects should be considered: 1) use of a limited number of connections, 2) optimal design under water or barge impact loads and leakage flows and 3) uniform load transfer over the entire structure. The design includes guiding principles for the structural concepts, description and calculation of different options, such as sandwich structure versus box beam. Then, the most suitable option of optimal design is selected to meet the strength and deflection requirements.

Take Deflection Requirements into Account

In some cases, the maximum deflection requirement influences the design of a composite hydraulic structure since the stiffness of the GFRP composite is low. To meet the stiffness requirement, CFRP can be used at a different cost scenario, recognizing that the potential for galvanic corrosion exists when in direct contact with steel.