International Concrete Abstracts Portal

The influence of lap splices on the seismic behavior of low-rise reinforced concrete (RC) walls was studied through tests of four 1:2 length-scale bridge pier wall specimens subjected to constant axial load and quasi-static cyclic loading sequence. The study parameters were horizontal reinforcement ratio (0.25 to 0.34%), splice length-shear span ratio (≈ 0.2 to 0.3), and wall-end confinement. Specimens lost 20% of maximum lateral strength at drifts between approximately 1.2% and 1.8%, increasing with horizontal reinforcement ratio, wall-end confinement, and splice length-shear span ratio. Splice failure, bar fracture, or their combination, caused abrupt strength loss and transition from flexure- to rocking-controlled behavior. Flexure-compression failure in the specimen with a splice length-shear span ratio of approximately 0.3 resulted in gradual strength degradation without transition to rocking. All specimens sustained drift demands of almost 2% without loss of axial load-carrying capacity.

Conventional anchor-bolt-confined flexible formwork concrete walls for gob-side entry retaining have clear inherent technical limitations, including incompatible deformation between steel anchors and concrete, low construction efficiency, and grout leakage. However, existing studies have not fundamentally solved the core mechanical problem of confinement efficiency loss caused by deformation mismatch, nor have they established a complete theoretical design framework for new high-compatibility confined systems, which severely limits their application in complex underground conditions. This study develops an innovative prefabricated stirrup-confined flexible formwork concrete system, identifies two primary surrounding rock fracture modes through theoretical analysis, establishes corresponding mechanical models for support design, and verifies the system through laboratory tests and full-scale field trials. The high-strength fiber stirrups achieve tensile strength equivalent to that of deformed steel bars, with an elongation of ≤6%, significantly improving deformation compatibility with concrete. Field results show that the optimized system delivers excellent surrounding rock control, with a maximum roof subsidence of 65 mm, wall displacement of 30 mm, and floor heave of 35 mm. This study provides a validated design framework for high-efficiency confined concrete underground support structures.

Concrete, as a typical heterogeneous particulate composite material, leads to complex mechanical properties. The significant differences in mechanical properties between the reinforcement and the incorporated aggregate further exacerbate the complexity of the mechanical performance of reinforced concrete and aggregate concrete. This study investigates the variation in strength characteristics and failure mechanisms of reinforced concrete beams under static and dynamic loads through static three-point bending tests and drop hammer tests. The research findings indicate that: (1) adhering to the principle of similarity in load-bearing capacity during design ensures a comparable load-bearing capacity between the prototype and the model. Following the principle of similarity in deflection during design ensures comparable deformations between the prototype and the model; (2) under static load conditions, as the reinforcement ratio and concrete strength increase, the maximum load-bearing capacity of the beam also increases; however, the deflection decreases correspondingly, demonstrating an inverse relationship between the concrete strength and deflection of the RC beam; and (3) under dynamic load conditions, the maximum residual deflection of the beam is proportional to the impact energy of the hammer. Excessive hammer energy can result in the beam's residual deflection exceeding allowable limits, thus affecting the stability and serviceability of the structure. The slope of this relationship primarily depends on the static bending load-bearing capacity of the beam, and as the load-bearing capacity increases, the corresponding slope decreases.

Projectile impact on reinforced concrete (RC) slabs fabricated using steel fiber-reinforced concrete (SFRC) and slurry infiltrated fiber concrete (SIFCON) has been benchmarked through 2-D and 3-D analyses using advanced computational tools. In the simulations, the importance of concrete compressive and tensile strengths, the presence of reinforcement bars, target thickness, and fracture energy were investigated with respect to target deformation and projectile residual velocity. The obtained results were compared with experimental outcomes from three regular reinforced concrete, two SFRC, and two SIFCON specimens in terms of target crater geometry and projectile residual velocity. In general, the simulations showed that the 3-D analysis results provide good agreement with the experimental data and also better correlation compared to the 2-D analysis results. It was also observed that the compressive and tensile strengths of the concrete specimens significantly influence the crater diameter. Additionally, incorporating reinforcement bars into the models leads to improved results. The study concludes that conducting detailed material tests on specimens is essential for achieving higher simulation accuracy.

Concentrated shear deformation near the base of a wall, referred to herein as sliding shear, is one of the major mechanisms that can limit the strength and deformation capacity of reinforced concrete (RC) low-rise or squat walls. This paper reports tests of five large-scale RC squat wall specimens without axial load to investigate the effects of: 1) longitudinal reinforcement layout; 2) shear stress demand; 3) high-strength materials; and 4) aspect ratio (hw/lw) on the sliding shear behavior of squat walls. All specimens were tested under lateral displacement reversals. Test results indicate that the maximum strength of all test specimens with an aspect ratio of 0.5 was primarily associated with, or limited by, sliding shear at the wall base. For specimens with an aspect ratio of 0.5 and negligible axial load, the presence of special boundary elements did not have an apparent influence on wall behavior. Increasing the amount of longitudinal reinforcement, which also increased wall strength, resulted in less sliding deformation before 1.0% drift ratio. Beyond 1.0% drift ratio, all specimens with an aspect ratio of 0.5 exhibited a substantial pinching of the hysteretic response, where sliding along the wall base accounted for approximately 80% of the overall deformation. The specimen with high-strength materials exhibited less deformation capacity than other specimens due to bar fracture at the wall base. As the aspect ratio increased to 1.0, the relative contribution of sliding deformation to overall drift decreased substantially to less than 20% of the overall deformation. Based on the response characteristics of the test specimens, a sliding shear strength model for walls with negligible axial load is proposed. A database consisting of test results from 55 specimens (including five from this study) was developed to verify the proposed strength model.