Sources of uncertainty and design values for field-manufactured FRP

Development of design codes for the use of fiber reinforced polymer composites as externally bonded reinforcement demands the definition of design values for the materials. Externally bonded reinforcement is frequently applied through use of the wet-layup process in field settings. The conditions present during field manufacture can affect the properties of the finished composite and introduce sources of uncertainty that should be considered in the design process. This paper describes sources of uncertainty that may be present in field manufactured FRP materials. Results from tensile testing of several different sets of field-manufactured FRP are presented and discussed. Based on a review of current methods for the determination of design values and the results of material testing a rational definition of material design values for field-manufactured FRP is proposed. This definition is developed for simple integration with reliability-based design procedures, such as load and resistance factor design (LRFD). It is based on the use of the anticipated mean in-situ value as the design value with a separate composite specific resistance factor that considers the potential for different levels of material uncertainty depending on circumstances specific to individual applications of the material. The proposed design values are intended to have a high level of traceability and yet be flexible enough to capture the specific variations in each application in order to prevent the blanket use of excessive knock-down factors used conventionally to capture the worst levels of variation and uncertainty possible.