Design of FRP-RC Rectangular Columns with Nominal Curvature Method and Universal Interaction Diagrams Applicable to Various FRP Bar Types

Abstract The design method for slender fiber-reinforced polymer (FRP) reinforced concrete (FRP-RC) rectangular columns based on the nominal curvature is not yet included in the new Eurocode 2 Annexure R. However, a proposal to expand Eurocode 2 in this regard is presently being considered and would also be included in the new DAfStb guideline for nonmetallic reinforcement. Additionally, other national codes, such as ACI 440.11-22 and CSA S806-12, also require load–moment capacity curves for the design of FRP-RC column cross sections. However, distinct load–moment capacity curves are required for each type of FRP bar in FRP-RC columns due to their different modulus of elasticity and ultimate design strain limits. This paper presents a novel concept of universal interaction diagrams, which can be used regardless of the type of FRP reinforcement bar such as glass, carbon, basalt, or aramid FRP. This significantly enhances both its usability and practicality in structural design. These diagrams only depend on the concrete strength, reinforcement configuration, and cover-to-depth ratio. This paper introduces provisions to expand Eurocode 2, provides universal interaction diagrams for rectangular cross sections for cross-section design, and provides universal interaction diagrams for slender FRP-RC columns with slenderness ratios of 40, 60, and 80, all of which are based on the nominal curvature method. The universal interaction diagrams for slender columns bypass the iterative solution of the presented equations and therefore have high practical value. Finally, the paper provides three worked examples that illustrate how to analyze and design short and slender FRP-RC columns using the presented diagrams.