International Concrete Abstracts Portal

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (i.e., a combination of bonded and unbonded (steel and/or carbon fiber reinforced polymer (CFRP)) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in the ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI PRC-440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provisions address the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the Modified Deformation-Based Approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without non-prestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI PRC-440 stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-to-depth ratio, as well as loading applications.

Progressive collapse behavior of reinforced concrete frame buildings has been studied extensively, but most of the research has concentrated on frames containing seismic details. This paper presents results from analyses of the progressive collapse behavior of reinforced concrete frame buildings containing details used in regions of low seismicity following ACI CODE-318-19. The analytical simulations presented in this paper include the effect of moment redistribution that occurs after plastic moments are reached at sections of maximum moment. Ten-story 3-D frame models were designed in accordance with ACI CODE-318-19 and analyzed under progressive collapse scenarios involving the non-simultaneous removal of an interior and a corner perimeter column following ASCE 76-23. Nonlinear material behavior in these analytical models was captured using a lumped plasticity approach using hinge properties calibrated using results from laboratory experiments of full-scale sub-assemblages representing a portion of the perimeter frame containing details corresponding to non-seismic zones. The effect of catenary action in beams after column removal was included in the analyses, and the potential for premature shear failure of beams was assessed. Furthermore, models were also constructed to investigate the beneficial effects of increased rotational capacity of perimeter beams that result from using closer stirrup spacing at beam ends. This study demonstrates the importance of incorporating properly detailed continuous longitudinal bars enclosed within closely spaced closed stirrups at ends of beams of reinforced concrete frames in non-seismic zones to provide progressive collapse resistance. The study also highlights the importance of considering three-dimensional effects in models of frames to account for out-of-plane moment redistribution after loss of supporting elements.

Controlling deflections in reinforced concrete (RC) flexural members under service loads is a serviceability requirement prescribed by design codes, such as the ACI CODE-318. Serviceability requirements are challenged by productivity requirements, such as faster construction and longer span demands, among others. This paper summarizes a parametric analysis conducted to estimate long-term deflections of one-way RC slabs. The objective of this study is to assess the effect of geometrical, concrete, and construction parameters on the long-term deflections of one-way RC slabs. The effect of these parameters on immediate deflections is also analyzed. Results of this study show that increasing the slab thickness and the area of tension reinforcement proved to be the most effective strategies for reducing both immediate and long-term deflections of one-way RC slabs. Additionally, the results of the parametric study highlight the relative influence of each studied parameter in controlling deflections.

This study presents a comprehensive field investigation into the long-term behavior of unbonded post-tensioned (PT) concrete flat slabs using Smart Strands embedded with fiber Bragg grating (FBG) sensors. The monitoring program was conducted in a real-world building in Seoul, Korea, spanning over five and a half years and capturing continuous prestressing force and deflection measurements at multiple slab locations. Results revealed that approximately 5% of nominal strength of tendon prestress losses occurred within the first year, stabilizing thereafter, and that deflection patterns were significantly influenced by slab position and construction activities. Comparison with analytical models showed strong alignment, with ACI CODE-318-25 time-dependent coefficients accurately predicting long-term deflections after the early-age period. This study contributes valuable long-term data, validating design codes and guidelines and enhancing understanding of the time-dependent behavior of PT concrete structures.

Corrosion—one of the major threats to the integrity of concrete structures—can consequently affect structure serviceability and ultimate limit state, possibly resulting in failure. Glass fiber-reinforced polymer (GFRP) can be used as an innovative alternative for conventional steel reinforcement in concrete structures, effectively addressing corrosion issues. In addition to its corrosion resistance and high strength-to-weight ratio, GFRP is commonly selected for nonprestressed bars and stirrups due to its cost advantage over other fiber-reinforced polymer (FRP) materials. The study endeavored to provide a comprehensive overview of the shear resistance in GFRP-reinforced concrete (RC) beams with short shear spans. The manuscript aims to synthesize and analyze shear test data based on published studies on GFRP-RC beams with a short shear span (a/d = 1.5 to 2.5). A comprehensive literature review was conducted to compile a database comprising 64 short GFRP-RC beams to evaluate the efficiency of using the strut-and-tie model (STM) for predicting the shear resistance of GFRP-RC beams. The findings reveal that ACI 318-19 STM yielded the most accurate predictions of the shear resistance of GFRP-RC beams with a/d of 1.5 to 2.5, because the current ACI CODE-440.11-22 and ACI 440.1R-15 design codes and guidelines do not include shear equations using the STM for predicting the shear resistance of GFRP-RC beams. Based on the findings of this study, the results could contribute to establishing shear equations in the upcoming revision of the ACI CODE-440.11-22 and ACI 440.1R-15 design codes and guidelines, specifically tailored for designing short GFRP-RC beams using the STM. The study also provides sufficient data to apply the STM in the design of GFRP-RC beams.