International Concrete Abstracts Portal

Compared to conventional reinforced concrete (RC) flat-plate systems, post-tensioned (PT) flat-plate systems lack experimental studies on shear strength, and there are no studies that have been analyzed and collected with clear criteria (for example, calculation of effective depth, unbalanced moment, and measured shear strength) about experiments conducted so far. As a result, the current ACI 318-19, Section 22.6.5, for prestressed members has many restrictions based on the lack of experimental data on the nominal shear-strength equation. In this study, to reevaluate the nominal shear strength of the PT flat-plate system more reasonably and provide a reference for future studies, a total of 120 experimental data on the shear strength of the PT flat-plate system without shear reinforcement that have been conducted so far were recalculated and recompiled with clear criteria (the experimental data consists of 74 interior connections, 41 edge connections, and five corner connections). In addition, the factors affecting the shear strength and the validity of restrictions in the nominal shear-strength equation of ACI 318-19 were analyzed. The factors affecting the shear strength include: 1) method of loading; 2) presence of nonprestressed reinforcement; and 3) reinforcement ratio along the lateral load direction. The restrictions in the nominal shear-strength equation of ACI 318-19 include: 1) fc′ ≤ 4900 psi (34 MPa); 2) fpc ≥ 125 psi (0.9 MPa) (in each direction); 3) fpc ≤ 500 psi (3.5 MPa) (average in the two directions); and 4) it is applicable only for interior connections.

Advances in new lightweight self-consolidating concrete (LWSCC) mixture designs have led to the construction of new concrete structures with much lower weight and higher strengths. The integration of glass fiber-reinforced polymer (GFRP) bars with LWSCC can be used effectively in Accelerated Bridge Construction (ABC) with longer spans and less shippingcost to build durable bridges with smaller cross sections andextended service lives. This study aimed at evaluating the effectiveness of this type of concrete for building concrete bridgedeck slabs with GFRP reinforcement. Five full-scale edgerestrained concrete bridge-deck slabs were fabricated, simulating a slab-on-girder bridge deck commonly used in North America. The bridge-deck slabs were 3000 mm (118.1 in.) in length, 2500 mm (98.4 in.) in width, and 200 mm (7.9 in.) in thickness. The test parameters included reinforcement type (sand-coated or helically wrapped GFRP and steel) and reinforcement ratio (ranging from 0.44 to 1.15%). The bridge-deck slabs were designed according to the Canadian Highway Bridge Design Code. The specimens were exposed to a concentrated load over a contact area of 250 x 600 mm (9.8 x 23.6 in.), which simulates the footprint of a sustainedtruck wheel load (87.5 kN CL-625 truck), as specified in Canadian standards. The test results indicate that the failure mode of all deck slabs was punching shear. The recorded ultimate load capacities for all specimens exceeded the design factored load, which validates the use of GFRP-reinforced LWSCC for the construction of bridge-deck slabs. It was also concluded that the surface conditions of the GFRP bars (sand coated or helically wrapped) had a minor effect on the cracking, deflection, and behavior of the testedLWSCC deck slabs. In addition, increasing the axial-reinforcement stiffness in the GFRP-reinforced slabs significantly increased the ultimate capacity and reduced maximum crack width, reinforcement strains, and midspan deflection at ultimate load.

Fiber-reinforced polymer (FRP) bars have emerged as a pioneering solution to eliminate the corrosion problems associated with conventional steel bars in aggressive environments. Glass fiber-reinforced polymer (GFRP) bars are now extensively used as internal reinforcing because they are more cost-effective than other types of FRP bars. This paper presents a new design model—namely, the extended strut-and-tie model (STM)—to predict the punching-shear strength of edge slab-column (ESC) connections entirely reinforced with FRP bars. The proposed model was developed based on the failure criteria of the strut-and-tie method for symmetric punching in conjunction with an interactive approach to describe asymmetric punching-shear behavior due to moment transfer in FRP-reinforced concrete ESC connections. The extended STM is appropriate for normal-strength concrete (NSC) and high-strength concrete (HSC) ESC connections reinforced with FRP bars. The connections tested by the authors and others found in the literature were used to evaluate the proposed model. The extended STM yielded safe predictions compared with the experimental ones, giving average experimental-to-predicted punching-shear strengths of 1.19 ± 0.13 and coefficient of variation of 10.86%. Furthermore, the proposed model achieved higher accuracy and narrower scatter for punching-shear strength predictions than the equations in ACI 440.1R-15, CSA S806-17, and JSCE-97.

Ultra-high-performance fiber-reinforced concrete (UHPFRC) possesses outstanding mechanical properties and high durability, and thus can provide effective retrofit solutions for concrete walls and wall-type bridge piers. This self-leveling material can be cast in thin layers around the pier to protect it from corrosive environments and to enhance its shear resistance. However, while this is a promising solution, research has focused mostly on the retrofit of slabs and beams. To address this gap in knowledge, this paper presents results from four large-scale tests of shear-critical concrete walls with and without UHPFRC jackets. The test variables are the thickness of the jacket, the preparation of the concrete surface, and the level of axial load. It is shown that water-jetting of the surface ensures an effective composite action of the concrete and UHPFRC, while a smooth surface results in early debonding. It is also demonstrated that, while the reference reinforced concrete specimen failed in brittle shear, water-jetted walls with 30 and 50 mm jackets reached their flexural capacity and exhibited enhanced crack control. In addition to test results, the study also proposes and validates a three-degree-of-freedom kinematic model to accurately describe the deformation patterns of UHPFRC-strengthened walls.

This paper presents test results from an experimental program conducted to study the punching-shear response of reinforced concrete (RC) edge column-slab connections (ECS connections) reinforced with glass fiber-reinforced polymer bars (GFRP). Five full-scale ECS connections were tested under vertical shear force and unbalanced moment until failure. Four of the five connections were reinforced with GFRP bars as flexural reinforcement; one connection was reinforced with steel bars for comparison. All slabs measured 2500 x 1350 x 200 mm (98.4 x 53 x 7.9 in.) with a 300 mm (11.8 in.) square column stub protruding 700 mm above and below the slab surfaces. The test parameters were flexural-reinforcement type, concrete strength, and moment-to-shear force ratio (M/V). The test results revealed that all the connections failed by punching shear with no signs of concrete crushing. The high-strength concrete (HSC) directly enhanced the punching-shear capacity, load-deflection response, and initial stiffness of the connections. These connections also evidenced fewer and narrower cracks compared to their counterparts cast with normal-strength concrete (NSC). Increasing the M/V produced significant shear stresses, thereby reducing the vertical load capacity by 31% and 30% for the NSC and HSC connections, respectively. A simple design approach to predicate the punching-shear capacity of FRP-RC ECS connections is proposed. The proposed approach yielded good, yet conservative, predictions with respect to the available test data.