International Concrete Abstracts Portal

Despite advancements in machine learning (ML) that have boosted structural performance prediction, current ML models can still struggle to generalize to unseen situations, leading to performance degradation. This vulnerability arises from their overreliance on data, neglecting established engineering principles like mechanical priors. Models trained on specific data distributions can suffer significant accuracy degradation when encountering inputs that fall outside those distributions. To overcome the limitations of data-driven models with unseen data, A mechanics-guided Gaussian process (MGGP) for accurate prediction of shear strength in reinforced-concrete (RC) beams is proposed. The complex variation of shear strength in RC beams was captured using a Gaussian process (GP) model with a mean function derived from mechanical principles and a hybrid kernel to account for inherent prediction variability. This combination allows for accurate prediction of shear strength while considering the underlying physical mechanisms. This approach leverages domain knowledge from mechanics by incorporating a relevant design equation into the mean function of a GP model. This integration significantly enhances the model's ability to predict shear strength by capturing the underlying physical principles governing the shear strength. Cross-validation studies have shown that the MGGP offers consistent performance compared to traditional GPs in predicting the shear strength of RC beams.

This study investigates the behavior of recycled steel fibers (RSFs) recovered from waste tires and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcement types with different volume content, incorporating microstructural and macrostructural analyses. Scanning electron microscopy (SEM) is used to study the microstructure and fractures, focusing on crack initiation in the fiber interface transition zone (FITZ). The macrostructural analysis involves using digital image correlation (DIC) software, Ncorr, to analyze the split tensile behavior of plain and fiber reinforced concrete (FRC) specimens, calculating strain distribution and investigating crack initiation and propagation. The SEM study reveals that, due to the presence of hooked ends, industrial fibers promoted improved mechanical interlocking; created anchors within the matrix; added frictional resistance during crack propagation; significantly improved load transfer; and had better bonding, crack bridging, and crack deflection than recycled fibers. RSFs significantly delay crack initiation and enhance strength in the pre-peak zone. The study suggests hybridizing recycled fibers from automobile tires with industrial fibers as an optimum strategy for improving tensile performance and using environmentally friendly materials in FRC.

This paper presents the behavior of unreinforced cylindrical concrete elements confined with a hybrid system, consisting of an ultra-high-performance concrete (UHPC) jacket and basalt fiber-reinforced polymer (BFRP) grids. For exploring the feasibility of the proposed strengthening scheme, a series of tests are conducted to evaluate material properties and to obtain results related to interfacial bond, load-bearing capacity, axial responses, and failure modes. To understand the function of the individual components, a total of 57 cylinders are loaded under augmented confining conditions, including plain cores with ordinary concrete (CONT), plain cores with UHPC jackets (Type A), and plain cores with UHPC jackets plus BFRP grids (Type B). By preloading the cores at up to 60% of the control capacity (60%fc′) before applying the confinement system, the repercussions of inherent damage that can take place in vertical members on site are simulated. The compressive strength of UHPC rapidly develops within 7 days, whereas its splitting strength noticeably ascends after 14 days. The adhesion between the ordinary concrete and UHPC increases over time. While the Type B specimens outperform their Type A counterparts in terms of axial capacity by more than 18%, reliance on the BFRP grids is reduced with the growth of UHPC’s strength and adhesion because of the interaction between the hardened UHPC and the core concrete. The adverse effects of the preloading are noteworthy for both types, especially when exceeding a level of 30%fc′. The BFRP grid-wrapping alleviates the occurrence of a catastrophic collapse in the jacketed cylinders, resulting from a combination of the axial distress and lateral expansion of the core. Analytical models explain the load-carrying mechanism of the strengthened concrete, including confinement pressure and BFRP stress. Through parametric investigations, the significance of the constituents is clarified, and design recommendations are suggested.

The present study demonstrates the feasibility of using longitudinal hybrid reinforcement in concrete columns in seismic zones. In this research, four concrete columns were constructed and subjected to quasi-static cyclic loading, featuring a combination of steel and glass fiber-reinforced polymer (GFRP) longitudinal reinforcement. Two reference columns were fabricated and reinforced in the longitudinal direction with steel bars. These columns had a 400 × 400 mm (15.8 × 15.8 in.) cross-section and 1850 mm (72.8 in.) overall height. All the columns were reinforced with GFRP crossties and spirals in the horizontal direction. The variable parameters were the transverse reinforcement spacing, axial load ratio, and column configuration. The outcomes of this research clearly showed that reinforced concrete (RC) columns that are properly designed and detailed longitudinally with hybrid reinforcement (GFRP/steel) could achieve the drift limitation in building codes with no strength degradation. Further, these hybrid-RC columns displayed enhanced energy dissipation capacity, superior ductility, and improved post-earthquake recoverability compared to columns reinforced longitudinally with steel. The promising results of this study represent a step towards the use of longitudinal hybrid reinforcement in lateral-resisting systems.

This paper investigates the mechanical characteristics (encompassing compressive strength, flexural strength, toughness, and impact resistance) of ultra-high-performance fiber-reinforced concrete (UHPFRC) incorporating polypropylene (PP) and polyvinyl alcohol (PVA) fibers. An experimental program was conducted, based on which the polymer and metallic fibers were used at the same fiber content, and different sets of single and hybrid fiber reinforced composites were fabricated and tested. Despite the fact that it has been exhibited through previous research that the hybridized PVA-PP fibers do not result in the development of the mechanical characteristics of engineered cementitious composites (ECCs), the UHPC composites incorporating such hybrid fibers show augmented levels of toughness, flexural strength, and resistance to impact loads. A comparison was also made to assess the potentiality of the used fibers in terms of environmental impact and cost. Based on the results, hybridization with PVA and PP fibers leads to remarkable improvement in technical performance and mitigation of the economic and environmental impact of UHPFRC composites.