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Abstract
The fracture of transverse hoop reinforcement can lead to the collapse of a reinforced concrete column, as has been observed in concrete bridges and buildings attacked by severe earthquakes as well as in laboratory tests. To predict the longitudinal concrete strain at the stage of first hoop fracture a theoretical method based on considerations of strain energy referred to as "Energy Balance Theory" has been proposed by Mander et al. This paper reviews the "Energy Balance Theory" and then proposes several modifications for this theory based on a failure model of a reinforced concrete column subject to axial compression. These modifications take into account significant energy factors neglected in the theory by Mander et al and correct some unrealistic assumptions made in that theory. The predictions of the modified theory are then compared with the results obtained from concentric loading tests on 18 reinforced concrete columns conducted at the University of Canterbury and the validity of the modified theory is assessed.
Highlights
When a reinforced concrete column well confined by hoop reinforcement is loaded to failure, fracture of the hoop reinforcement eventually occurs and results in a sudden drop in load carrying capacity of the section due to a reduction in confinment of the core concrete and a loss of buckling restraint for the longitudinal bars
In order to provide such a restriction to the column deformation, a method for the prediction of the available maximum deformation of the column section limited by the occurrence of hoop fracture is required > The available maximum deformation of a column section could be expressed in terms of an ultimate longitudinal compressive strain of the core concrete at an associated curvature
To estimate the ultimate concrete compressive strain, defined as that strain where first hoop fracture occurs, a theoretical method using an energy principle model was established in this study
Summary
When a reinforced concrete column well confined by hoop reinforcement is loaded to failure, fracture of the hoop reinforcement eventually occurs and results in a sudden drop in load carrying capacity of the section due to a reduction in confinment of the core concrete and a loss of buckling restraint for the longitudinal bars. The strain distribution of the spirals or hoops along the column axis needs to be taken into account for the estimation of the U This is because the corresponding strain energy stored in the core concrete has to be calculated from a theoretical or a measured stress-strain relation of confined concrete over a defined gauge length. Total height of column is 3d_ and the gauge length of the concrete"" core strain measurement is d , the gross buckled shape of the longitudinal bars may be approximated by a sinusoidal curve expressed by the following equation. The average lateral displacement within the gauge length 1 of d c in the middle third of the column San be expressed in the form
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