Constitutive Relations for Modelling Macro Synthetic Fiber Reinforced Concrete

The increasing utilization of Fiber-Reinforced Concrete (FRC) within the construction industry signifies a pivotal shift towards enhancing structural integrity and durability. Despite the predominant use of steel fibers, exploring macro synthetic fibers has gained momentum due to their potential to address critical challenges, such as workability reduction and corrosion resistance in FRC, without markedly affecting its structural performance. Among the forefronts of FRC research is developing an accurate constitutive model encompassing the diverse behavior of fibers, particularly synthetic ones. This discrepancy necessitates a distinct constitutive model for synthetic fibers to precisely characterize their tensile postcracking behavior and regulate their design specifications. In this research, a preliminary constitutive model is derived through an inverse analysis procedure employing a Generalized Reduced Gradient (GRG) optimization method to the loaddisplacement results of the experimental testing of twenty ASTM C1609 beam samples. The results of the inverse analysis are used to correlate the ASTM C1609 residual flexural tensile strength parameters, f(L/600) and f(L/150) to the stress-strain points defining the uniaxial tensile curve of macro-synthetic fibers, achieving coefficients of determination exceeding 98.5%. The model is statistically confirmed to be a valid constitutive relation for macro-synthetic fibers via successfully representing the post-cracking load-deflection behavior of standardized concrete beams, thereby outperforming traditional constitutive models in simulating the post-cracking behavior of FRC. Moreover, the model demonstrates robust predictive capabilities for the load-deflection curve of externally standardized samples, showcasing its potential for broader application in FRC design and analysis.