Effects of Extreme Events on FRP Reinforced/Strengthened Structures (ACI Spring 2024, New Orleans, LA) This paper presents experimental and theoretical investigations on the residual tensile and bond response of polypara-phenylene-benzo-bisthiazole (PBO) fabric reinforced cementitious matrix (FRCM) composites after the exposure to elevated temperatures ranging between 20 °C [68 ºF] and 300 °C [572 ºF]. Experimental results obtained from direct tensile (DT) and single-lap direct shear (DS) tests carried out respectively on PBO FRCM specimens and PBO FRCM-concrete elements were reported and discussed. Overall, specimens exposed to temperatures up to 200 °C [392 ºF] did not present significant reductions of both bond and tensile properties. This result can be attributed to the thermal shrinkage underwent by the inorganic matrix, which may enhance the bond between the fibers and the matrix. On the other hand, when the specimens were heated at 300 °C [572 ºF], marked reductions were observed, primarily stemming from the degradation of both mechanical properties of the FRCM constituent materials and the fiber-to-matrix bond. Subsequently, the experimental results were used for the following purposes: (i) to assess whether the Aveston–Cooper–Kelly (ACK) theory is able to describe the tensile behavior of FRCM materials at elevated temperatures; (ii) to define temperature-dependent local bond stress vs. slip law and (iii) to evaluate the ability of degradation models to simulate the variation with temperature of the FRCM tensile and bond properties. The results obtained from the theoretical analyses showed that, for all the tested temperature, the relative differences between predicted and experimental results are very low, confirming the accuracy of the proposed approaches.

Fiber Orientation in Ultra High-Performance Concrete: Quantification, Characterization, and Implications for Design and Performance, Part 1 (ACI Spring 2024, New Orleans, LA) The alignment and uniform distribution of steel fibers within ultra-high-performance concrete (UHPC) are essential for optimizing its structural performance. These factors are determined during the casting phase when the concrete is still in its fluid state. To comprehensively analyze how variables such as fresh UHPC rheology, fiber type, reinforcing bars, and casting equipment influence fiber orientation and distribution, a robust predictive tool is required. This tool should be capable of simulating the microscale interactions between the fluid mortar and the embedded fibers. To this end, we will employ a synergistic approach that integrates Computational Fluid Dynamics (CFD) with Discrete Element Methods (DEM), a combination proven effective in elucidating complex multiphase flows. The accuracy of the CFD model will be initially confirmed through comparisons with controlled laboratory experiments. Subsequently, advanced imaging techniques will be employed to register the fiber movements, providing a basis for comparing and validating the DEM predictions. The findings from this comprehensive evaluation will constitute the main focus of the forthcoming presentation.