International Concrete Abstracts Portal

Creep and shrinkage affect a range of design considerations, from serviceability to the stability of slender reinforced concrete columns. Yet most structural engineering software lacks the tools to integrate these time-dependent effects into concrete constitutive models. To address this limitation, CreepShrinkageACI209 was developed as a modular uniaxial material wrapper and implemented in OpenSees. This wrapper superimposes creep and shrinkage strains calculated per ACI 209.2R-08 onto any user-selected base concrete constitutive model. Its modular architecture separates time-dependent effects from mechanical behavior, allowing users to add creep and shrinkage capabilities to existing material models without altering the underlying code. To validate its accuracy, a database of slender reinforced concrete column tests was developed, and the long-term behavior of these columns was compared against the predicted behavior using the CreepShrinkageACI209 wrapper. Comparisons showed that the wrapper accurately predicts both the evolution of time-dependent deflections and the reduction in load-carrying capacity observed in the tests, demonstrating its viability for long-term analysis of reinforced concrete structures. The implementation approach is extensible to other software, alternative creep and shrinkage models, and multi-axial concrete constitutive models.

This study examines shortcomings in current modeling approaches for reinforced concrete (RC) columns with short, non-yielding lap splices. A database of such columns was compiled, and nonlinear fiber-based modeling was conducted in OpenSees, with Hysteretic material calibrated for peak strength, deflection, degradation, and pinching. Key findings include: 1) a significant positive correlation between lap-splice stress and axial load ratio, quantified through the factor λ1. Additionally, it was noted that this factor is not currently accounted for in the development length provisions of ACI 318-19; 2) the proposal of a constant λ2 value of 2.0 to model additional deformation due to bar slip, observed across a range of column geometries; and 3) the identification of improved ductility with reduced axial load ratios and longer lap-splice lengths, as reflected in the post-peak response slope Er. Moreover, updated hysteretic behavior parameters pinchX (0.70), pinchY (0.22), and damage (0.01) were proposed that better capture energy dissipation and pinching effects compared to existing models. Validation using experimental data demonstrated the effectiveness of the proposed modeling strategy and expressions in predicting initial stiffness, peak capacity, and strength degradation.

This study investigated the flexural behavior of innovative precast self-consolidating concrete stadium bleacher units with an L-shaped cross section and reinforced with glass fiber-reinforced polymer (GFRP) bars. Six full-size reinforced concrete stadium bleacher specimens with a width, height, and thickness of 950, 390, and 150 mm (37.4, 15.35, and 5.9 in.), respectively, and with a total length of 4200 mm (165.4 in.) were tested under four-point bending load up to failure. Six specimens were fabricated: three with normal concrete and sand-coated GFRP reinforcement with three different reinforcement ratios, and three with fiber-reinforced concrete (FRC) and sand-coated GFRP reinforcement. The test parameters included GFRP reinforcement ratio and concrete type. The test results were analyzed based on the cracking and ultimate moment specified in the existing FRP design codes. The comparison shows that the experimental moment capacities of the bleachers were generally conservative in the design standards. Moreover, the reinforcement ratio had a substantial impact on the serviceability performance of the bleacher specimens. Increasing the ratio of flexural reinforcement led to reduced crack widths and decreased deflections. Changing the concrete type from normal to fiber with the same bar size showed improved serviceability and moment capacity results. This research enhances the understanding of precast self-consolidating concrete stadium bleacher units with an L-shaped cross section reinforced with GFRP bars subjected to flexural load and supports their use in infrastructure.

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.

The combined use of recycled aggregate concrete (RAC) and glass fiber-reinforced polymer (GFRP) reinforcement raises concerns regarding deflections, cracking, and shear resistance. This study investigates the serviceability and shear behavior of GFRP-reinforced RAC slabs. Eight slabs were tested in a four-point load setup: RAC slabs of two strength levels, reinforced with varying ratios of longitudinal reinforcement, and one control natural aggregate concrete (NAC) slab per concrete grade. All slabs failed in shear following significant flexural deflections. Results indicate that recycled coarse aggregates (RCA) use did not significantly impact service load deflections and maximum crack widths but slightly reduced the shear strength of the higher-strength slab. Furthermore, RCA use did not alter behavioral trends observed in NAC slabs, such as bilinear load-deflection curves, proportionality between crack width and GFRP bar strain, and increased resistance and decreased deflections with higher reinforcement ratios. Observed shear strength was conservatively estimated by ACI CODE-440.11-22 and CSA-S806 equations, and deflections were accurately predicted. ACI crack control provisions effectively limited crack widths to under 0.7 mm.