Shape and laminate optimization of fiber-reinforced-polymer structures

Fiber Reinforced polymer (FRP) composites, or advanced composite materials, which have shown outstanding mechanical characteristics, such as high strength-to-weight and high stiffness-to-weight, and high chemical and environmental endurance compared to conventional materials, have been adapted from aerospace and defense industries to civil infrastructure applications. The nature of FRP composites makes them strong and stiff in planes along fiber orientations but rather weak through their thickness. Thus, they are most efficient when used under global in-plane stress demands. Due to their high material costs, a way to employ their high material stiffness and strength is to use them in structural forms in which the structural efficiency is maximized by shaping the structural geometry to achieve mainly in-plane behavior under the applied loads. Therefore, an approach is needed to develop the structural forms where the in-plane properties of FRP composites can be used efficiently.; An integrated approach is developed for the shape and material optimization of laminated FRP structures. The integrated approach is implemented in a two-level uncoupled procedure: shape and material-property optimization followed by material design optimization, where structural shape and laminate design are optimized simultaneously with the aim of maximizing structural stiffness.; Examples of optimizing laminated FRP shell structures are provided to validate the procedure. The performance of the integrated approach is evaluated by comparing a shape-and-material optimized FRP shell with two shape-only optimized FRP shells. The numerical results show that the proposed integrated approach is reliable and provides a useful tool for designing optimized laminated FRP structures.; The integrated approach is also used to aid the rational implementation of FRP composites in civil infrastructure by developing innovative bridge design concepts. Innovative FRP composite membrane-based bridge systems were explored through analytical studies of the integrated approach. Two types of bridge systems are developed, FRP membrane beam bridges and FRP membrane suspension bridges. Both bridge systems consist of a shape-and-material optimized laminated FRP membrane/shell carrying the in-plane tensile and shear forces together with a conventional reinforced concrete deck providing the live load transfer. The analytical studies of optimizing the FRP membrane bridges provide the initial development of innovative systems that use FRP composites in their inherent behavioral characteristics for new high-performance structures.; Results from this work demonstrate that FRP composites can be used with higher efficiency in new structural systems as long as their advantageous properties of directional strength, lightweight, and tailored properties are properly considered in the design process. The work further discusses the feasible implementation of the optimum design for composite membrane-based bridges in practical engineering construction. The work also provides insight to further development and applications of the integrated optimization approach.