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One-way slabs under concentrated loads may fail by one-way shear, two-way shear, flexure, or a combination of these modes. This paper reviews shear and punching shear-failure mechanisms of one-way slabs under concentrated loads tested from the literature and investigates the accuracy of different approaches to predict the ultimate capacity for such slabs using the ACI code expressions. A database with 160 test results was evaluated. Shear and concentrated loads measured at failure were reviewed according to parameters such as the load position, slab width, and reinforcement ratios. The load position and slab width play a marked influence on the failure mechanism and tested loads. The analyses improved the understanding of the main parameters influencing the behavior of one-way slabs under concentrated loads. Finally, the proposed effective shear width expression enables accurate shear capacity predictions using the ACI code expressions.

Reinforced concrete one-way slabs under concentrated loads can develop different shear failure mechanisms: as wide beams in one-way shear, punching shear around the load or a mixed mode between them. Until now, most publications presented recommendations to assess the shear capacity considering only the one-way shear failure mechanism. This study proposed developing recommendations to assess both the one-way shear and punching shear capacity of such slabs. Different codes of practice were addressed, including the current Eurocode and fib Model Code 2010 expressions. The recommendations were validated against 143 test results from the literature. Following these recommendations, one-way shear and punching capacities predictions achieved enhanced and almost the same level of accuracy.

Currently, the evaluation methods and design codes for predicting the shear strength of FRP-RC members are being continuously developed and updated. The revision draft of the Korean Standard KDS 14 20 22 (KDS 14 draft) adopts the compression zone failure mechanism theory to predict the one-way shear strength of slender steel-reinforced concrete members. This study extends the application of the KDS 14 draft model to slender concrete members reinforced with fiber-reinforced polymer (FRP) rebars. The model performance was evaluated using a comprehensive database of slender FRP-reinforced concrete (RC) specimens, including 304 and 110 specimens without and with FRP stirrups, respectively. The strength prediction of the KDS 14 draft model was compared with those of the existing state-of-the-art international design guidelines and of other recently developed models for FRP-RC members. The KDS 14 draft model demonstrated promising performance over a wide range of design parameters, exhibiting the lowest scatteredness among the evaluated methods. It exhibited a strong correlation with the dataset while maintaining an acceptable level of safety and reliability. Among the investigated design models, the ACI 440.11-22 design method exhibited the highest scatteredness and conservatism for specimens without FRP stirrups. However, the JSCE model provided overly conservative predictions for specimens with FRP stirrups because of the rigorous adoption of a strain limit for FRP stirrups. In addition, parametric analyses were conducted, and design examples were presented to further understand the influence of key design parameters and the applicability of the KDS 14 draft model for FRP-RC beams.

This article shows a model for the design of circular isolated footings and the column placed anywhere in the footing under minimum cost criteria. Some designs for obtaining the diameter, effective depth, and steel areas of the footing under biaxial bending assume the maximum and uniform pressure at the bottom of the footing supported on elastic soils. All these works consider the column placed at the center of the footing. Three numerical problems are given (each problem presents four variants) to determine the lowest cost to design the circular footings under biaxial bending. Problem 1: Column without eccentricity. Problem 2: Column with eccentricity in the direction of the X axis of one quarter of the diameter of the footing. Problem 3: Column placed at the end furthest from the center of the footing on the X axis. The results are verified by the balance of moments, one-way shear or shear and two-way shear or punching. The new model shows a saving of 17.92% in the contact area with soil and of 31.15% in cost compared to the model proposed by other authors. In this way, the proposed minimum cost design model for circular footings will be of great help for the design when the column is placed on the center or edge of the footing.

Steel reinforcing bars conforming to ASTM A1035 have enhanced corrosion resistance and significantly higher tensile strength compared to conventional reinforcing steel grades. However, the impact of the unique stress-strain characteristics of this steel on the failure modes and strength prediction models is not yet fully understood. This paper reports on the laboratory testing to failure of eight large-scale specimens having small shear span to effective depth ratios and containing or omitting web reinforcement. All specimens were longitudinally reinforced with deformed A1035 steel bars with measured stresses at the peak load from 695 to 988 MPa (100 to 143 ksi)-significantly higher than the design stress limits defined in current codes of practice. Members without web reinforcement failed in a brittle manner after the formation of diagonal cracks joining the loads and supports. For members containing web reinforcement, the shear span to effective depth ratio and the longitudinal reinforcement ratio were both found to influence the failure mode and post-peak ductility. It was possible to develop designs that could exploit the high reinforcement strength while exhibiting acceptable service-ability characteristics and adequate ductility at failure. The safety of capacity predictions using ACI ITG-6R-10 provisions is presented.

This study investigates the effectiveness of using Hairpin shaped stirrups to increase the shear capacity of beams and slabs. The hairpin system consists of inverted U-shape stirrups welded to flexural corner rebar. Previous research works proved the increase of the hairpin system in increasing the two-way shear capacity compared to conventional punching reinforcement. However, the system’s ability to increase the shear capacity of beams has not been explored. This paper presents the results of Finite Element simulation of two beams performed using ABAQUS Software; one beam is reinforced with conventional shear stirrups, and the other is reinforced with hairpin stirrups. The load capacity, deflection and damage pattern of the two beams were compared. Results showed that beams reinforced with hairpin stirrups have higher load capacity and ductility compared to beams with conventional stirrups. However, the reinforcement type had little effect on the shear damage pattern.

Stud rails systems (SRSs) are prefabricated reinforcement elements with headed steel studs welded to a steel base rail. SRSs can affect construction efficiency and can be used in members that are too small for hooked bars. Provisions for using SRSs in slabs and footings were introduced in ACI 318-08; however, there are currently no provisions in ACI 318 for using SRSs as shear reinforcement in one-way members. Accordingly, an experimental program was conducted to evaluate SRSs as shear reinforcement in one-way beams and slabs. Variables in the program included specimen dimensions, shear span-depth ratio, and type and spacing of shear reinforcement. Details of the program are presented, and experimental results are compared with provisions from ACI 318 to evaluate their applicability to one-way members reinforced with SRS. Experimental results from other researchers are also included in the code comparison.

It has been shown previously that the use of shear reinforcement improves the strength and ductility of large beams and thick slabs. The corresponding impact on member constructibility and economy from provisions of code-specified minimum shear reinforcement ratios can be significant. In this paper, the viability of a system of headed shear reinforcement assemblies for one-way shear is examined. Three large-scale laboratory tests were conducted on members containing high-strength longitudinal reinforcement and headed shear stud assemblies of varying configurations. Member performance at the serviceability and ultimate limit states were examined and compared against predictions in accordance with design code models for flexure, shear, and deflection. Member capacity was predicted well by existing models, but significantly larger-than-predicted deflections occurred due to shear deformations associated with diagonal cracking and the smooth shear reinforcement legs. [PUBLICATION ABSTRACT]

The shear strength and stiffness of granular materials are crucial parameters for evaluating both stability and sustainability in geoenvironmental engineering. Two types of shear loading, static and cyclic, may directly influence the mechanical properties of granular materials; however, the investigation of stiffness improvement of granular materials has not yet been sufficiently investigated using a loading method. The one-way repeated loading method described in this study may overcome the drawbacks of classical testing approaches. One-way repeated direct shear (DS) and direct simple shear (DSS) tests were conducted on a series of poorly graded bead gradations to investigate the shear strength and stiffness of granular materials under a drained and strain-controlled condition with a shear velocity of 0.1 mm/min. All samples in the two tests were prepared using the same method and initial geometry. Three types of samples referring to different curvature coefficient (C u ) values of 1.8, 3.3, and 5.8 and normal stresses (σ n ) of 50, 100, and 150 kPa were applied. The test results show that an increase in C u results in an increase in the shear stress of the granular materials at the peak and ultimate states for both the DS and DSS tests. The peak shear stress ratios between the two tests (τ DSS /τ DS ) ranged from 0.75 to 0.95 when C u and σ n were increased. The angles of shearing resistance from the DS test were in a wide range of 25.7°–33.7° at the peak state and 24.9°–31.3° at the ultimate state, whereas those found in the DSS test were in narrow ranges of 26.0°–28.4° and 23.6°–27.9° at the peak and ultimate states, respectively. It should be noted that an increase in C u led to the increase in the stiffness ratio in both test methods. The difference in stiffness ratios determined from the DS and DSS tests was approximately 14%. Under one-way repeated shear loading, the DS test is recommended to determine the residual shear strength generated along the shear plane, whereas the DSS test is recommended to determine the maximum shear stress at the weakest shear zone developed horizontally owing to repeated shearing.

Recent research data was evaluated with the aim of extending the applicability of using deformed steel fiber-reinforced concrete (SFRC) to enhance the shear strength of beams and one-way slabs. Experimental results were assessed for influences on the shear strength of SFRC members that do not contain stirrups of factors, including size effect, concrete density (normalweight and lightweight) and compressive strength, fiber-volume fraction (Vy), and the longitudinal steel reinforcement ratio. Estimates of steel stresses in longitudinal bars at the time of shear failure were carried out to identify differences in members with distinct longitudinal steel ratios and bar grades, consistent with the range of flexural design parameters in ACI 318-19. Results of these analyses and a reliability investigation of design equations applicable to members without fibers were used for proposing new provisions for the shear design of SFRC beams and one-way slabs based on the ACI 318-19 shear-strength model.