The influence of the parameterϕ/ρeffon crack widths

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’.)