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The positive effect of fiber‐reinforced concrete (FRC) on shear capacity of reinforced concrete beams is well presented in many experimental studies since 1970s. However, as the main effect of fibers is in the cracking stage, it increases the complexity to analyze such structures numerically. With the increased availability of nonlinear finite element analysis software, structural designers are encouraged to use them to solve complex structural problems. In such cases, understanding and correct definition of material laws in cracked stage of FRC structures are crucial. A blind competition was organized by fib WG 2.4.2 to address this issue. It revealed that the numerical predictions of almost all of the participants overestimated the shear capacity of a T‐beam subjected to bending. The aim of the current study is to demonstrate critical aspects in the definition of input parameters of FRC analysis. A comprehensive parametric analysis is performed considering tensile softening law, shear stiffness, and shear strength definition in cracked stage as well as shrinkage effects. The results suggest that most important aspect is the correct definition of tensile softening law, which should correspond to the lower bound of residual strength obtained by standard notched prisms tests according to EN 14651 or even smaller. [ABSTRACT FROM AUTHOR]

A study on the shear model uncertainty and structural reliability of ultra‐high‐performance fiber reinforced concrete (UHPFRC) beams with stirrups is presented. Model uncertainty for the shear models given in the JSCE, AFGC and ACI 544 standards are characterized by comparison to nonlinear finite element analyses (NLFEA). In comparison to other shear basic parameters, a notable negative correlation between model uncertainty the transverse shear reinforcement ratio (ρwfywm) is observed. When combined with stochastic descriptions of the remaining parameters that describe these analytical models, reliability values for beams designed to the JSCE and AFGC specifications are found to fall 6%, and 12%, respectively, below the target values of these standards, while reliability values for the ACI 544 exceed the target value specified for this standard by 8%. [ABSTRACT FROM AUTHOR]

The shear crack width, crack behavior, and crack development of 24 reinforced concrete beams have been experimentally investigated. All the beams reinforced with longitudinal reinforcement and hooked‐end steel fibers in place of transverse reinforcement. Hooked‐end steel fibers 35 and 60 mm long are used at volume fractions ranging from 0.75% to 1.5% in the first case, and from 0.5% to 1% in the latter case. For extending the scope of the investigation, two types of concrete matrices (normal‐strength of 25 MPa and medium‐strength of 45 MPa) have been investigated. A simple mechanics‐based mathematical model is developed by determining the strains in the transverse direction of shear cracks and the average horizontal spacing between the shear cracks. The accuracy of the model has been confirmed with the experimental results and conservative predictions have been observed with mean, SD, and coefficient of variation as 0.99, 0.19, and 18.96, respectively. Based on detailed mathematical and experimental investigation, the minimum approximately observed shear crack width has value of 0.4 mm for all SFRC beams therefore the allowable shear crack width of 0.4 mm, for steel fiber reinforced concrete has been recommended. [ABSTRACT FROM AUTHOR]

Experimental research has shown the extraordinary potential of the addition of short fibers to cement‐based materials by improving significantly the behavior of concrete structures for serviceability and ultimate limit states. Software based on the finite element method has been used for the simulation of the material nonlinear behavior of fiber‐reinforced concrete (FRC) structures. The applicability of the existing approaches has often been assessed by simulating experimental tests with structural elements, in general of a small scale, where the parameter values of the material constitutive laws are adjusted for the aimed predicting level, which constitutes an inverse technique of arguable utility for structural design practice. For assessing the predictive performance of these approaches, a blind simulation competition was organized. Two twin T‐cross section steel FRC beams, flexurally reinforced with steel bars and without conventional shear reinforcement in the critical shear span, were experimentally tested up to failure. Despite the experimental data provided for the definition of the relevant model parameters, inaccuracies on the load capacity, deflection, and strain at peak load attained 40, 113, and 600%, respectively. Inadequate failure modes and highly different results were estimated with the same commercial software, indicating the need for deeper analysis and understanding of the models and influence of their parameters on their predictive performance. [ABSTRACT FROM AUTHOR]