International Concrete Abstracts Portal

Advancements in AI and computational models have significantly enhanced the predictability of concrete performance by leveraging extensive datasets. Recently, machine learning models have been developed to predict concrete’s compressive strength based on its mixture proportions. However, these models treat supplementary cementitious materials (SCMs) as a categorical (as opposed to quantitative) parameter and do not account for the significant impact of the SCM reactivity on concrete’s strength development. In this study, we assembled a dataset of binary (cement-SCM) mixtures, incorporating SCM reactivity measured by the R3 (ASTM C1897) test. Utilizing a random forest machine learning model, we demonstrated that integrating SCM reactivity significantly enhances the model's predictive performance with the fewest input parameters (w/cm, SCM/cm, SCM R3 heat, Agg/cm, cement CaO%). Further, we implemented a multi-objective Bayesian optimization framework to assist in the mixture proportioning of low-carbon low-cost concrete utilizing cement(s) and SCM(s) available to a concrete producer. This framework proposes concrete mix designs to meet a target 28-day compressive strength while minimizing cost and CO2 emissions, by leveraging SCMs with varied reactivity levels. The proposed mix designs were further validated with experiments. The work demonstrates how to avoid model extrapolation and erroneous predictions by utilizing a multi-dimensional convex envelop algorithm. Overall, the outcomes of this work provide a valuable tool for the concrete industry which can be expanded to predict and incorporate other metrics of concrete performance (e.g., workability, durability) and develop optimized mix designs accordingly.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio reinforced concrete (RC) shear walls when designed using normal-strength reinforcement (NSR) versus high-strength reinforcement (HSR). Such studies demonstrated that the use of HSR has the potential to address several constructability issues in nuclear construction practice by reducing the required steel areas and subsequently reinforcing bar congestion. However, the response of nuclear RC shear walls (that is, aspect ratios of less than 1) with both HSR and axial loads has not been yet evaluated under ground motion sequences. As such, most nuclear design standards restrict the use of HSR in nuclear RC shear wall systems. Such design standards do not also consider the influence of axial loads when the shear-strength capacity of such walls is calculated. To address this gap, the current study investigates the influence of axial load on the performance of nuclear RC shear walls with HSR when subjected to ground motion sequences using hybrid simulation testing and modeling assessment techniques. In this respect, two RC shear walls (that is, W1-HSR and W2-HSR-AL) with an aspect ratio of 0.83 are investigated. Wall W2-HSR-AL had an axial load of 3.5% of its axial compressive strength, whereas Wall W1-HSR had no axial load. The test walls were subjected to a wide range of ground motion records, from operational basis earthquake (OBE) to beyond design basis earthquake (BDBE) levels. The experimental results of the walls are discussed in terms of their damage sequences, cracking patterns, ductility capacities, effective periods, and reinforcing bar strains. The test results were then used to develop and validate a numerical OpenSees model that simulates the seismic response of nuclear RC shear walls with different axial load levels. Finally, the experimental and numerical results were compared to the current ASCE 41 backbone model for RC shear walls. The experimental results demonstrate that Walls W1-HSR and W2-HSR-AL showed similar crack patterns and subsequent shear-flexure failures; however, the former had wider cracks relative to the latter during the different ground motion records. In addition, the axial load reduced the displacement ductility of Wall W2-HSR-AL by 18% compared to Wall W1-HSR. Moreover, the ASCE 41 backbone model was not able to adequately capture the seismic response of the two test walls. The current study enlarges the experimental and numerical/analytical database pertaining to the seismic performance of low-aspect-ratio RC shear walls with HSR to facilitate their adoption in nuclear construction practice.

This paper proposes new procedures for determining allowable loads for power-actuated fasteners that are consistent with ASCE/SEI 7-22. Thirty new load test data sets for single fasteners in shear and tension and fastener groups in shear are analyzed statistically. The current ICC-ES AC70-2021 procedure yields allowable loads that are quite variable, even negative, and very sensitive to “reject-as-outlier” decisions. In addition, ICC-ES AC70 procedures to determine allowable loads can currently not be clearly linked to the reliability requirements of ASCE/SEI 7-22. Monte Carlo simulation demonstrates that the proposed simplified method, derived from the described detailed method, is robust for sample sizes as small as 10 specimens. It yields allowable fastener loads that are 10 to 25% greater than those obtained using the current ICC-ES AC70 procedure yet are typically 60 to 90% of the actual allowable fastener loads, derived from the described detailed method to assess allowable loads in line with ASCE/SEI 7-22 reliability requirements. The new provisions are extended to cases where the coarse aggregate hardness in the test specimens differs from that in the structure, which is not addressed in ICC-ES AC70.

This paper presents the implications of variable bond for the behavior of concrete beams with glass fiber-reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded reinforcing bars, which are intended to represent sequential bond damage. Conforming to published literature, three shear span-depth ratios (av/d) are taken into account: arch action (av/d < 2.0), beam action (3.5 ≤ av/d), and a transition from arch to beam actions (2.0 ≤ av/d < 3.5). When sufficient bond is provided for the element-level testing (over 75% of 5db, where db is the reinforcing bar diameter), the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the av/d from 1.5 to 3.7, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams by up to 40.2%, and the slippage of the partially bonded reinforcing bars dominates their flexural stiffness. Compared with the case of the beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of reinforcing bar stress is dependent upon the av/d and, in terms of using the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of reinforcing bar stresses with bond damage when subjected to arch and beam actions.

The bond property between deformed bars and concrete plays a significant role in the safety of construction. Numerous database-dependent empirical models are proposed to evaluate the bond behavior without considering the effect of additional confinement, whose application range is quite limited as a result of unstable accuracy. In this paper, a new model was established based on the thick-walled cylinder model and fictitious crack theory, which can predict bond strength and bond-slip response with fiber-reinforced polymer (FRP)-steel confinement. The effects of various factors on the bond behavior such as concrete strength, concrete cover, reinforcing bar diameter, bar surface geometry, and FRP/steel confinement were comprehensively discussed. According to radial crack radius, the radial stress and displacement induced on bond interface can be calculated, and thus analytical formulae of bond strength and slip were respectively developed in conjunction with deformed bar surface geometry. Finally, a new analytical model was proposed, which can simulate the bond-slip curves of the specimens with different confinement levels, covering unstrengthened, FRP-strengthened, stirrup-strengthened, and FRP-stirrup dually strengthened specimens. Compared with existing models, the proposed model can provide better agreement with existing test results.