Structural analysis and optimum design of GRP pipes based on properties of materials

Despite their three-layer-composite cross section, the stability of glass fiber reinforced plastics (GRPs) pipes has been evaluated only through the allowable deflection and nominal stiffness (SN) in the design stage without considering the fracture characteristics of materials. This study suggests a safety evaluation method based on the strength and fracture characteristics of pipe wall materials. Also, the present study proposes a formula to calculate an optimum pipe wall thickness and a method to determine the total bending moment (the sum of moments due to vertical earth pressure, horizontal earth pressure, and live load). To this end, the present study conducted a quantitative evaluation on structural behavior of GRP pipes using the assumptions of earth pressure distribution proposed by Spangler and Howard as well as the theories of mechanics of materials and structural analysis. Also, the equations to calculate the total moment coefficient, minimum pipe wall thickness, and optimum GRP layer thickness were derived by analyzing the characteristics of bending moment distribution in GRP pipes. By proposing a reasonable total bending moment calculating equation and optimum design method, this study intends to provide useful basic data for economical manufacturing and valid structural safety evaluation of GRP pipes.