International Concrete Abstracts Portal

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-to-depth ratios are taken into account: arch action, beam action, and a transition from arch to beam action. When sufficient bond is provided for the element-level testing, the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the shear-span-to-depth ratio 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 bar 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 on the shear-span-to-depth ratios, 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.

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 non-prestressed bars and stirrups due to its cost advantage over other FRP materials. The study endeavored to provide a comprehensive overview of the shear resistance in GFRP-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 the ACI 318 (2019) STM yielded the most accurate predictions of the shear resistance of GFRP-RC beams with shear span-to-depth ratios of 1.5 to 2.5, since the current ACI 440.11 and ACI 440.1R design codes and guidelines do not include shear equations using the strut-and-tie model 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 440.11 and ACI 440.1R design codes and guidelines, specifically tailored for designing short GFRP-RC beams using the strut-and-tie model. The study also provides sufficient data to apply the strut-and-tie model in the design of GFRP-RC beams.

This paper presents the effectiveness of various reinforcing schemes in the end zones of prestressed concrete bulb-tee girders. The default girder, provided by a local transportation agency, includes C-bars and spirals intended to control cracking, and is analyzed using three-dimensional finite element analysis. The formulated models are used to evaluate the breadth of end zones, strain responses, cracking patterns, damage amounts, and splitting forces, depending upon the configuration of the end-zone reinforcement. The number of C-bars is not influential in developing strand stress along the girder. The maximum principal stresses exceed the conventional limit within h/4 of the girder end, where h is the girder depth; however, the 3h/4 limit adequately encompasses the stress profiles, particularly in the web of the girder. The maximum tensile strain in the concrete varies with the elevation of the girder, and the inclined strands cause local compression in the C-bars, while spiral strains are independent of the number of bars. By positioning the C-bars, the vertical strain of the concrete decreases by more than 15.9%, which can minimize crack formation. Whereas the short-term crack width of the girder may not be an immediate concern, its long-term width is found to surpass the established limit of 0.18 mm (0.007 in.). In this regard, multiple C-bars should be placed to address concerns about undesirable cracking. The splitting cracks in the girder, resulting from the strand angles and eccentricities, can be properly predicted by published specifications within the range of 0.2h to 0.7h, beyond which remarkable discrepancies are observed in comparison with a refined approach. From a practical perspective, two to three No. 6 or No. 7 C-bars spaced 150 mm (6 in.) apart are recommended in the end zones alongside welded wire fabric.

Engineered cementitious composites (ECC) represent a significantinnovation in construction materials due to their exceptionalflexibility, tensile strength, and durability, surpassing traditionalconcrete. This review systematically examines the composition,mechanical behavior, and real-world applications of ECC, with afocus on how fiber reinforcement, mineral additives, and micromechanical design improve its structural performances. The present study reports on the effects of various factors, including different types of mineral admixtures, aggregate sizes, fiber hybridization, and specimen dimensions. Key topics include ECC’s strain hardening properties, its sustainability, and its capacity to resist crack development, making it ideal for high-performance infrastructure projects. Additionally, the review discusses recentadvancements in ECC technology such as hybrid fiber reinforcementand the material’s growing use in seismic structures. The paper also addresses the primary obstacles, including high initial costs and the absence of standardized specifications, while proposing future research paths aimed at optimizing ECC’s efficiency and economic viability.

Thirty-nine large-scale reinforced concrete beams were testedunder monotonic three-point bending to investigate the use of stirrups with mechanical anchors (heads) or hooks and Grade 80 (550) reinforcing steel. Grade 60 and 80 (420 and 550) No. 3, No. 4, and No. 6 (0.375, 0.5, and 0.75 in. [10, 13, and 19 mm]) bars wereused as stirrups, which were spaced at one-quarter to one-half ofthe member effective depth. Other variables included beam depth(12 to 48 in. [310 to 1220 mm]), beam width (24 and 42 in. [620and 1070 mm]), longitudinal reinforcement strain correspondingto the nominal beam shear strength (nominally 0.0011, 0.0017, or0.018), and concrete compressive strength (4000 and 10,000 psi[28 and 69 MPa]). Headed stirrups that: a) engage (are in contactwith) the longitudinal bars; or b) have a side cover of at least sixheaded bar diameters and at least one longitudinal bar within theside cover, produce equivalent shear strengths as hooked stirrups,and both details allow stirrups to yield. The results affirm thatbeams designed for the same Vn with either Grade 60 or 80 (420 or550) stirrups exhibit equivalent shear strengths. A nominal shearstrength based on a concrete contribution equal to 2 √ fc bwd may beunconservative when ρtfytm < 85 psi (0.59 MPa) in members witha/d = 3, h ≥ 36 in. (910 mm), ρ < 1.5%, and no skin reinforcement.