Unified Equivalent Rectangular Stress Block Parameters for Gfrp-Rc

Abstract

Equivalent Rectangular Stress Block (ERSB) parameters, as presented in design codes, are commonly used by designers to determine the flexural capacity of glass fiber reinforced polymer - reinforced concrete (GFRP-RC) members. However, these parameters were originally developed for normal strength concrete (NSC) and often result in errors when applied to other types of concrete, such as fiber-reinforced concrete (FRC). This is primarily due to variations in the post-peak behavior of concrete in compression. To address this issue, an analytical model was developed using concrete constitutive models and validated against experimental data on GFRP-RC flexural members reported in the previous studies. The model incorporates key variables, including concrete compressive strength, fiber aspect ratio, fiber dosage, reinforcement ratio, and reinforcement type. A parametric study was then conducted, considering a wide range of concrete strengths and post-peak degradation rates. Based on the results, new ERSB parameter values were proposed as functions of concrete strength and post-peak strength degradation rate. The accuracy of the proposed parameters was evaluated for both conventional and non-conventional concrete types, such as FRC. The results demonstrate that the proposed ERSB parameters significantly improve the accuracy of flexural strength predictions compared to existing design methods. The proposed parameters can be adopted for various types of concrete, including FRC, with differing post-peak behaviors. This study concluded that considering the strength degradation rate of concrete, especially in fiber reinforced polymer reinforced concrete members where compression-controlled failure often governs the response- is a critical parameter in predicting the flexural strength that should be explicitly addressed in design standards. This study offers a unified method and the corresponding ERSB parameters, which can be adopted not only for conventional concrete but also for non-conventional concrete. It provides a simple and comprehensive approach applicable to any type of concrete (including all types of FRC concrete, regardless of the type and amount of fibers), as long as the compressive strength and post-peak degradation are known.

Keywords: FRP, Descending branch, Rectangular stress block, Flexural strength, Interaction Diagrams, FRC