Effect of shear span-to-depth ratio on flexural and fracture behaviors of reinforced UHPMC beams based on four-point bending test and acoustic emission monitoring

Abstract

Ultra-high performance manufactured sand concrete (UHPMC), using manufactured sand (MS) as aggregate, belongs to a brand-new ultra-high performance concrete (UHPC). Better understanding the failure behavior of UHPMC beams reinforced with steel reinforcement bars is crucial in structural design. This study investigates the effects of different shear span-to-depth ratios (λ = 1.2, 1.6 and 2.0) on the failure modes, mid-span deflection, concrete and rebar strain, flexural toughness, initial cracking load, ultimate load, energy dissipation capacity, and crack propagation patterns based on four-point bending tests for totally twelve reinforced UHPMC beams. Meanwhile, acoustic emission (AE) monitoring is used to evaluate corresponding fracture characteristics. Results reveal that an increase in shear span-to-depth ratio leads to a significant increase in mid-span strain and better ductility but lower equivalent stiffness. The maximum strain of specimen with λ = 1.2 is 24.8 % lower than that with λ = 2.0, and specimen with λ = 1.6 exhibits 22.3 % greater equivalent stiffness than that with λ = 2.0. Beams with larger shear span-to-depth ratios demonstrate superior ductility and energy absorption capacity, specimen with λ = 2.0 showing a ductility factor 2.85 times higher than that with λ = 1.2. The presence of MS significantly improves initial cracking load by 26.9 %, ultimate load by 4.5 %, and energy dissipation capacity by 37 %. MS also enhances toughness and delays crack propagation in the early stages. This effect can make the fracture transform into more rapid energy release in the later stages, indicating that MS could alter crack propagation patterns, forcing cracks to propagate along paths with greater resistance to crack propagation. These conclusions can offer insights for the safer and economical design and application of UHPMC beams, especially the balance among shear span-to-depth ratio, MS and mechanical performance in the environmentally friendly structures design and failure prevention process.