The phenomena associated with the consolidation of fresh concrete (bleeding and plastic settlement) are commonly considered significant for the bond performance of reinforcement. However, rules to take care of such influence for design are not consistent amongst design recommendations and may lead to notable differences. With this respect, two failure modes generally govern the bond failure, namely the spalling of the concrete cover (also called splitting failure) and the pull‐out of the reinforcement. In this paper, a detailed investigation is presented on the influence of bleeding and plastic settlement on both failures modes, in an effort to understand their conceptual differences and to clarify how shall consistent design recommendations be formulated. Such investigation is based on a comprehensive experimental programme, comprising 137 pull‐out tests on specimens with different casting conditions, embedment lengths, loading arrangements and concrete covers. On the basis of the test results, the phenomenological differences between pull‐out and spalling failures are clarified, as well as the main influencing phenomena (particularly the potential presence of cracks and voids under the reinforcement and the mechanical properties of concrete). On this basis, a physically‐consistent approach is presented to consider the casting conditions on the bond performance and failure modes.
It is well known that control specimens used to assess the concrete strength of new structures have different casting and curing conditions than those of actual structures. Notably, after pouring of the concrete and before its hardening, a number of phenomena such as concrete bleeding and plastic settlement occur, influencing the in‐situ strength with respect to that of small and homogeneous control specimens (cubes or cylinders). In addition, the development of these phenomena and their structural implications are influenced by the presence of reinforcing bars, disturbing the settlement and bleeding of fresh concrete. In this paper, these aspects, with particular emphasis on the effective structural strength, are investigated by means of a testing program performed with refined measurement techniques such as tomography and Digital Image Correlation. On that basis, consistent design rules are derived to correct the strength of control specimens in order to calculate the resistance of a structural concrete member.
The compressive resistance of concrete in new structures is usually characterized on the basis of tests performed on concrete cylinders or cubes under relatively rapid loading conditions. Although efficient for material characterization, these tests do not acknowledge a number of phenomena potentially influencing the compressive resistance of concrete in actual structures. For this reason, when performing a structural analysis, strength reduction factors are usually considered in codes of practice modifying the uniaxial strength of material tests. In this paper, a detailed investigation of the influence of material brittleness and internal stress redistributions on the structural response of reinforced concrete members is presented. This work is based on a number of theoretical considerations and supported by the experimental results of more than 400 reinforced concrete columns tested with or without eccentricity and gathered from the literature. The results show the pertinence of considering a brittleness factor in the calculation of the structural resistance of reinforced concrete columns and compression zones of beams. The results of this work are eventually formulated in terms of code‐like proposals, currently considered in the draft of the new Eurocode 2 (prEN 1992‐1‐1:2018).
A large number of design approaches for structural concrete rely on the applicability of limit analysis. This is for instance the case of bending and shear design in members with transverse reinforcement, where it is assumed that plastic compression fields develop in the concrete. The behaviour of concrete in compression, however, cannot be directly assumed as perfectly plastic. In order to consistently apply limit analysis, the compressive strength of concrete is usually reduced by a number of strength reduction factors. In this paper, the factor accounting for the brittle behaviour of concrete in compression is reviewed. The aim is to assess the need for a brittleness factor when determining the capacity of concrete columns subjected to pure compression. Theoretically, the need for this factor is justified as a reinforced column is a composite system, where an interaction (redistribution of forces) potentially occurs amongst the longitudinal bars and the concrete as well as with the transverse (confinement) reinforcement. A total of 207 specimens from the scientific literature were considered in this research. They were all characterized by low slenderness (no second order effects) and presented variable concrete compressive strength (24 to 200 MPa), cross-section (square or circular), longitudinal reinforcement ratio (0.8 to 6.8 %), transverse reinforcement ratio (0.1 to 3.5 %), tie arrangement and spacing, yield strength of the longitudinal reinforcement (260 to 820 MPa) and yield strength of the transverse reinforcement (300 to 1000 MPa). Their compressive capacity was evaluated according to a rigid-plastic approach as well as to EN1992-1-1:2004. On that basis, a series of conclusions are drawn on the need for a brittleness factor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.