Influence of Width-to-Effective Depth Ratio on Shear Strength of Reinforced Concrete Elements without Web Reinforcement

The calibration of most analytical models that assess the shear strength of wide reinforced concrete members without shear reinforcement is based on simply supported beam tests, which may not be representative of slabs and wide members failing in shear. This paper addresses the knowledge on the shear strength of wide members, identification of their most important parameters, and an evaluation of the accuracy and precision of the main models presented in codes of practice and literature. A database of 170 shear tests was built on wide members loaded over the entire width, with the ratio width to effective depth b/ d > 1. This database includes members under concentrated loads (CLs) and distributed loads (DLs) in the span direction. A parameter analysis revealed such shear strength is mostly influenced by the shear slenderness and size effect rather than by the ratio b/d. Furthermore, the results show a clear decrease in the shear strength of continuous members under DLs to higher shear slenderness, similar to the behavior of members under CLs. This trend was well observed with the proposed model of shear slenderness, which assumes that continuous members with higher bending moment in the span than over the inner support behave closer to simply supported members. A comparison of the shear capacities predicted by the physical-mechanical and semiempirical approaches showed the higher accuracy and precision of models based on the critical shear crack theory and critical shear displacement theory, regardless of the ratio b/d. Therefore, the same models derived based on beam tests are valid for wide members. Apart from that, the analyses of nonslender members with some strain-based models combined with reducing factors of the acting shear load provide accurate results of shear strength for members without stirrups.Abbreviations: AVG, average value; CCCM, compression chord capacity model; COV, coefficient of variation; CSCT, critical shear crack theory; CSDT, critical shear displacement theory; CWSB, critical width of the shear band; MCFT, modified compression field theory; MIN, minimum value; SFSMM, shear-flexural strength mechanical model. Discussion on this paper must be submitted within two months of the print publication. The discussion will then be published in print, along with the authors' closure, if any, approximately nine months after the print publication.

Section: Introductionsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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One‐way shear strength of wide reinforced concrete members without stirrups

Sousa

Lantsoght

Debs

2020

Shear force redistributions and resistance of slabs and wide beams

Cantone

Ruiz

Muttoni

2021

Redistribution of shear forces in reinforced concrete members without shear reinforcement is a key aspect for the assessment of the shear capacity of wide beams and slabs. Such redistributions are due to the nonlinear response of reinforced concrete (both in bending and shear) and have the potential to significantly modify the internal forces during loading. This phenomenon allows in many cases, as for slabs linearly supported and subjected to concentrated forces, to increase the level of load even when some regions have already attained their local shear resistance. This work introduces the results of an experimental programme performed on three cantilever slabs subjected either to strip loads or to concentrated loads. Shear redistributions close to failure are investigated on the basis of refined measurements performed on the concrete surface and on the reinforcement bars. The results show the significance of several mechanical parameters, as well as how shear redistributions occur when some regions are in softening (post-peak behavior) while others have still not attained their local shear resistance. On this basis, a comprehensive approach is presented for determining the redistributions of internal forces and to predict the shear capacity of reinforced concrete slabs subjected to concentrated loads near linear supports. The performance of such approach is eventually validated against test data and practical recommendations are proposed for design and assessment.

One‐way flexural shear tests on wide reinforced concrete slab segments with simple and intermediate supports

Adam

Schmidt

Hegger

2022

Flexural shear behavior, which mainly concerns reinforced concrete (RC) slabs without shear reinforcement, is usually investigated by means of simply supported, beam‐shaped specimens. Only few tests are available where the cross‐section properties correspond to a slab (b ≫ h) or the support conditions lead to moment and shear force distributions of multi‐span slab systems. The moment distribution in the vicinity of inner supports can decrease shear slenderness and, hence, increase shear strength. An increase in member width is also often associated with a beneficial effect on load bearing behavior. Firstly, the course of the shear crack changes along the width which, both, increases the crack face area, and potentially allows for an increased interlocking effect of the two crack faces. Secondly, a (wide) slab's ability to redistribute inner stresses in lateral direction can compensate inner irregularities. However, the likelihood of irregularities to occur after all, increases with increasing concrete volume, so larger member widths. A comparison of existing investigations shows that the findings are partly inconclusive. Also, no studies addressing the influence of the member width exist with tests in the vicinity of intermediate supports despite being the typical shear‐critical section in actual members. To address related open questions, an experimental campaign comprising 20 shear tests on slab segments without shear reinforcement was conducted. Essentially, member width (b = 0.3 or 2.4 m) and support conditions were varied within the test program. Main goal of the experimental campaign was finding answers to the question whether one‐way flexural shear strength is influenced by the member's width. This has been addressed by generating results from pairs of tests which differed only in their width while having otherwise equal properties (b/h ≈ 1.0 and b/h ≈ 8.5). Eight such pairs were tested featuring different shear span lengths, rotational restrains at the support and longitudinal reinforcement ratios. In contrast to other experimental campaigns, shear tests near inner supports were incorporated in the experimental program. On average, the gain in shear capacity of the wide members compared to the reference linear member was proportional to the increase in width. It can thus be concluded that linear (beam‐shaped) specimens are suitable for representing one‐way shear capacity of RC slabs. Enhanced shear response of actual slabs can rather be ascribed to beneficial effects from loading and support conditions which enable to partially activate two‐way stress distribution or compressive membrane action. Additionally, rare occurrence of damages in RC slabs is not only to be attributed to an underestimation of capacity but probably also to an overestimation of design load.