International Concrete Abstracts Portal

Design recommendations are presented for calculating the immediate deflection of cracked prestressed concrete members under service load. Inconsistency and sometimes confusion regarding the calculation of immediate deflection for the different approaches presently available highlight the need for a rational approach to computing deflection. The ACI 318-19 approach for reinforced (nonprestressed) concrete is broadened to include prestressed concrete. This involves the implementation of an effective moment of inertia taken together with an effective eccentricity of the prestressing steel used to define the effective curvature and/or camber from the prestressing force. Proposed revisions to ACI 318 are presented for prestressed Class T and Class C flexural members and clear steps are provided for calculating immediate deflection. The effectiveness of the new approach is validated against an extensive database of test results, showing reasonable accuracy and reliability in predicting deflections. The paper concludes with practical recommendations for implementation and a worked-out example to illustrate the proposed methodology. These findings aim to enhance the accuracy and consistency of deflection predictions in prestressed concrete design, contributing to better serviceability and performance of concrete structures.

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 study investigates the behavior of recycled steel fibers (RSFs) recovered from waste tires and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcement types with different volume content, incorporating microstructural and macrostructural analyses. Scanning electron microscopy (SEM) is used to study the microstructure and fractures, focusing on crack initiation in the fiber interface transition zone (FITZ). The macrostructural analysis involves using digital image correlation (DIC) software, Ncorr, to analyze the split tensile behavior of plain and fiber reinforced concrete (FRC) specimens, calculating strain distribution and investigating crack initiation and propagation. The SEM study reveals that, due to the presence of hooked ends, industrial fibers promoted improved mechanical interlocking; created anchors within the matrix; added frictional resistance during crack propagation; significantly improved load transfer; and had better bonding, crack bridging, and crack deflection than recycled fibers. RSFs significantly delay crack initiation and enhance strength in the pre-peak zone. The study suggests hybridizing recycled fibers from automobile tires with industrial fibers as an optimum strategy for improving tensile performance and using environmentally friendly materials in FRC.

Portland cement has played a significant role in the construction of major infrastructure and building structures. However, in light of the substantial CO2 emissions associated with its production, there is a growing concern about environmental issues. Accordingly, the development of eco-friendly alternatives is actively underway. Geopolymer represents a class of inorganic polymers formed through a chemical interaction between solid aluminosilicate powder with alkali hydroxide and/or alkali silicate compounds. Concrete made with geopolymers, as an alternative to portland cement, generally demonstrates comparable physical and durability characteristics to ordinary portland cement (OPC) concrete. Research on the material properties of geopolymer concrete (GPC) has made extensive progress. However, the number of large-scale tests conducted to assess its structural performance is still insufficient. Additionally, there is a shortage of comprehensive studies that compile and analyze all the structural experiments conducted thus far to evaluate GPC’s potential. Therefore, this study aimed to compile and analyze a number of bond, flexural, shear, and axial strength tests of GPC to assess its potential as a substitute for OPC and identify its distinctive characteristics compared to OPC. As a result, it is considered that GPC can be used as a substitute for OPC without any structural safety issues. However, caution is needed in terms of deflection and ductility, and additional experiments are deemed necessary in the aspect of compressive strength of large-scale members.