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An attempt is made to theoretically and experimentally verify the shrinkage curvature models presented in Eurocode 2 and BS 8110. These codes claim that the models originally derived and proven for uncracked sections are suitable, with modification, for predicting the behaviour of cracked sections, although this claim has never been proven experimentally. To achieve verification, an alternative theoretical approach is initially proposed in this paper. In this theoretical model, the effect of shrinkage, creep and the variation in the neutral axis position of the section are taken into account. The stresses developed in the steel and concrete at a cracked section according to this theoretical model are then applied to a finite-element (FE) model representing a portion of the beam from the crack to mid-way between the crack and an adjacent crack. Ultimately, the mean curvature is determined. Experimentally, pairs of beams were cast and subjected to a level of flexural loading to produce a stabilised crack pattern in the constant-moment zone. The behaviour of the beams was monitored for up to 180 days. For any pair of beams, one beam was cast using a high-shrinkage concrete and the other with a low-shrinkage concrete. Each concrete type, however, exhibits similar creep. Therefore, shrinkage curvature can be obtained by subtracting the long-term movements of one beam from the other. These experimentally defined curvatures were compared with the mean curvatures obtained from the FE analysis. The comparison showed reasonable agreement. The curvatures were also compared with uncracked and cracked curvatures predicted by the codes. The curvatures derived in this investigation fell within the boundaries of the uncracked and cracked curvatures predicted by the codes and, for the fully cracked case, the curvatures were closer to the uncracked boundary. [ABSTRACT FROM AUTHOR]

This paper aims to further the understanding of the interaction between reinforcement in tension and the surrounding cracked concrete. This is achieved using the elastic analysis of axisymmetric prisms reinforced with a single central bar. As a preliminary to the analyses, the behavior of axially reinforced prisms is described based on previous experiments. This preliminary analysis confirms that the elastic analysis adopted in this investigation is reasonable. Two analytical exercises are described: the first assumes no slip, plasticity, or internal cracking at the interface between the steel and the concrete; the second introduces internal cracking and debonding between ribs. The first analysis indicates that shear deformation of the surrounding concrete accounts for a substantial proportion of the surface crack width, and therefore that this form of deformation cannot be ignored in crack prediction formulae. The second analytical exercise shows that the internal cracking model described by Goto is appropriate. [ABSTRACT FROM AUTHOR]

Professor Beeby's 2004 paper questioned the basis of the widely cited 'classical' model for estimation of crack widths in reinforced concrete elements. It provides a valuable reminder of the need to verify the predictions of theoretical models against experimental data, a task which he has performed to the benefit of our understanding on several occasions in the past. Professor Beeby will therefore not be surprised to learn that others have subjected his own ideas to similar scrutiny. In the several contributions below, members of fib Task Group 4.5 'Bond Models' raise questions over the validity of conclusions in the paper, based on a wider range of experimental data and more recent developments in theoretical modelling. (John Cairns, Convenor, fib Task Group 4.5 'Bond Models'.) [ABSTRACT FROM AUTHOR]

Long-term tension-stiffening effects in beams and slabs were investigated by a comprehensive series of laboratory tests. Most tests used square prisms reinforced with a single, central bar loaded in pure tension but, in addition, a small number of slabs were tested to confirm the applicability of the tensile results to flexural situations. Three load levels and three concrete strengths were used and loads were sustained for periods of up to 4 months. Some specimens contained strain-gauged reinforcing bars to obtain very detailed data concerning reinforcement strain distributions. The results indicated that tension stiffening decayed much more rapidly than was previously thought, and that by 20 days, or sooner, after loading, it had reduced to its long-term value. The paper describes the test program in detail and discusses the important implications of the results on the current design rules for deflection control. [ABSTRACT FROM AUTHOR]

Many formulae for the prediction and control of crack widths in reinforced concrete members assume that the transfer length over which force is transferred by bond from the reinforcement to the concrete on either side of a crack is proportional to the parameter φ/Peff where φ is the bar diameter and Peff is an effective reinforcement ratio. This paper aims to examine the validity of this assumption by comparing the predictions of the theory which leads to the derivation of the parameter φ/Peff to data from experimental programmes where crack widths were measured. These comparisons strongly suggest that φ/Peff has minimal influence on rack widths. [ABSTRACT FROM AUTHOR]

Presents the author's comments on a paper related to constructions. Criteria for loading slabs during construction; Interpretation of data from the Cardington building case; Deflections of real slabs under real loads.