Partially loaded areas in reinforced concrete: Mechanical modelling

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The structural behavior of concrete hinges under general loading is far from being properly understood, which is to a large extent due to the lack of pertinent experimental data. This paper contributes to filling this knowledge gap by presenting and discussing the results of an experimental campaign on one‐way Freyssinet concrete hinges. Seven large‐scale concrete hinges were tested in the Large Universal Shell Element Tester, which allowed the investigation of their behavior under general loading by all six stress resultants. A combination of digital image correlation and distributed fiber optic measurements allowed a deeper insight into the structural behavior of the specimens. The tested hinges could sustain very high axial stresses exceeding 4.5 times the uniaxial concrete compressive strength, large rotations of over 60 mrad, and shear stresses in transverse and longitudinal directions up to 2.24 times the axial compressive stress. The resistance to bending moments about the strong axis and torques also proved to be significant. A moderate amount of reinforcement crossing the hinge throat considerably increased the shear resistance at low axial stresses and produced a ductile shear behavior.

Section: General Observations On Load-bearing and Cracking Behaviorsupporting

confidence: 90%

Large‐scale experiments on concrete hinges under general loading

Markić

Kaufmann

2022

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“…In order to ensure this confinement, the hinge shoulders (recession) should not be more inclined than strictly required to facilitate the manufacturing of the hinge (e.g., extraction of the throat inserts during demolding), thereby allowing the placement of confinement reinforcement in the blocks as close as possible to the throat. This confinement reinforcement should consist of a fine grid of closed ties (or adequately anchored bars such as headed bars) and ensure sufficient reinforcement in the longitudinal direction (e.g., ρ z ≥ 0.5 ρ y ) 20,21,23 ; see, for instance, Figure 1f.…”

Section: General Considerations and Recommendationsmentioning

confidence: 99%

“…Their bearing capacity, which corresponds to the confined concrete strength in the throat region, can be reliably determined with the Dual-Wedge (DW) stress field (Figure 3c), a mechanically consistent and experimentally validated model developed by the authors in a previous study targeting partially loaded areas. 20,21,23,35,36 The reader is referred to References 21 and 23 for a detailed model description.…”

Section: Confined Concrete Strength F CCmentioning

confidence: 99%

“…Here, only the main stress-field-related aspects and expressions are summarized. Where applicable, the general expressions reported by Markic et al 21 are simplified for the conditions typical for concrete hinges.…”

Section: Confined Concrete Strength F CCmentioning

confidence: 99%

“…). Following Markic et al, 21,23 d 2 is chosen equal to the width d cs of the confinement core, see Figure 1f. The confining stress σ conf , where 0 ≤ σ conf ≤ f c0 , is assumed to be constant along the height of the stress field and can be determined from expressions contained in design codes, typically depending on the content and layout of the confinement reinforcement.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Modeling and design of concrete hinges under general loading

Markić

Kaufmann

2023

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Despite their successful applications in practice for over a century, the design of concrete hinges still entails considerable modeling uncertainty. Their dimensioning still relies on semi‐empirical recommendations originally proposed for admissible stress design, based on limited experimental data and generalized with engineering judgment. This presumably results in overly conservative designs in many cases, particularly when applied with modern design codes based on partial safety factors. This paper addresses these issues by revisiting the analytical modeling for one‐way Freyssinet concrete hinges under general loading based on approaches compatible with current design codes. A cross‐sectional analysis with confined concrete properties is proposed for the behavior under axial forces and bending moments, where the strength of the triaxially compressed concrete in the hinge throat is determined with a discontinuous stress field. The hinge resistance to shear forces is investigated with failure mechanisms inspired by failure modes observed in experiments. Based on the shear strength, a simple approach to estimate the torsional resistance of the throat is proposed. Remarks are also made on the analysis of combined actions. The predictions of the proposed models are validated against a wide range of test data, including a series of recently conducted own experiments. Overall, the proposed models agree better with the available experimental data than the existing approaches, potentially allowing for a more efficient design of new and assessment of existing concrete hinges.

Passive confinement of reinforced concrete members revisited

Morger,

Kenel,

Kaufmann

2024

Passive confinement provided by transverse reinforcement is taken into account in the design of reinforced concrete structures subjected to high compressive loading such as columns, piers, or tunnel lining segments. In current guidelines, several models exist to account for this beneficial effect. However, these approaches lack mechanical consistency regarding the three‐dimensional load dispersion of the confining forces. The article addresses this knowledge gap by introducing a new model based on a lower‐bound solution according to the theory of plasticity, along with a simplification regarding the governing confined concrete area. The proposed model and its simplified version are compared to the design approaches proposed by current guidelines, and both are successfully validated against experimental data. The simplified new model is a valuable alternative to existing models in current guidelines, as (i) it is mechanically more consistent, (ii) its application is more straightforward, and (iii) it allows the comprehensive treatment of rectangular and circular cross‐sections using the same equations.