International Concrete Abstracts Portal

The weakness of concrete in tension can be mitigated by developing fiber-reinforced concrete (FRC) to induce pseudo-ductility. However, enhancing the intrinsic tensile strength of the matrix in FRC has received little attention. In this regard, nanofibers, which can improve the intrinsic tensile properties of the matrix, were used in conjunction with microfibers to enhance intrinsic tensile strength. Different volumes of nanofibers (0.0–0.6%) and microfibers (0.0–2.0%) were tested, and various fresh and hardened properties were analyzed. Test results show that the superplasticizer dosage increased with both nanofiber and microfiber volume and that strength increased with microfiber volume, reaching an optimum point at a certain nanofiber dosage. Moreover, incorporating nanofibers and microfibers to develop multiscale FRC (MSFRC) significantly improved direct tensile strength and energy absorption. The synergy between nanofibers and microfibers was revealed both qualitatively and quantitatively, contributing to the advancement of FRC.

There is a need to model the complete responses of shear-critical beams strengthened with embedded through-section (ETS) fiber-reinforced polymer (FRP) bars. Here, a strategy is proposed to integrate two separate approaches, flexural‒shear deformation theory (FSDT) for element fields and a bonding-based method for ETS strengthening, into a comprehensive computation algorithm through localized behavior at the main diagonal crack. The use of force- and stress-based solutions in the algorithm that couple fixed and updated shear crack angle conditions for analyzing the shear resistance of ETS bars is investigated. The primary benefit of the proposed approach compared to single FSDT or existing models is that member performance is estimated in both the pre-peak and post-peak loading regimes in terms of load, deflection, strain, and cracking characteristics. All equations in the developed model are transparent, based on mechanics, and supported by validated empirical expressions. The rationale and precision of the proposed model are comprehensively verified based on the results obtained for 46 datasets. Extensive investigation of the different bond‒slip and concrete tension laws strengthens the insightfulness and effectiveness of the model.

Accurate prediction of the cyclic response of reinforced concrete (RC) shear walls is critical for performance assessment of buildings under wind and earthquakes. Over the past few decades, various macro-models have been developed, based on different formulations and simplifying assumptions, to facilitate large-scale modeling of RC walls. However, there is limited research on the accuracy of these models for walls with different characteristics. This study evaluates the accuracy and application range of five prevalent macro-models using experimental results from 39 wall specimens with a wide range of design variables. Analytical and experimental results are compared in terms of cyclic load-deflection responses, failure modes, and a set of structural performance measures. The results indicate that while the evaluated macro-models can predict the behavior of shear walls reasonably well, there are important limitations that may restrict their application range. Strengths and weaknesses of each macro-model are identified to help engineers select the most suitable analysis method based on the characteristics of the wall.

This paper presents a statistically based expression derived from the existing ACI provision for determining the development and lap splice length of glass fiber-reinforced polymer (GFRP) reinforcing bars in concrete elements subjected to flexure. Missing parameters such as confining reinforcement and the differentiation between development and lap splice strength were incorporated into the base expression available in ACI CODE-440.11-22 to enhance its reliability. A database of 201 tests was used to formulate the proposed equation, aiming to prevent a splitting failure mode and resulting in a reduction in the required embedment length for typical values employed in a GFRP-reinforced concrete beam, as compared to the ACI 440 expression. The analysis of bond strength revealed an unconservative aspect in the current ACI 440 expression, particularly noticeable in lap splice tests. The proposed expression achieved an experimental-to-predicted ratio of 1.01 with a coefficient of variation of 0.180. Finally, recommendations for adoption in the next version of the Code are presented.