Tension stiffening response of high-strength reinforced concrete tensile members

The purpose of this research was to experimentally determine if any relationship exists between the concrete strength and the post-cracking behaviour of a reinforced concrete member. A total of nine large-scale reinforced concrete tension specimens, using either high or normal-strength concrete, were constructed and tested in addition to a series of six small-scale reinforced high strength concrete specimens (pilot specimens). High strength concrete refers to a material meeting the requirements of the Canadian specification CSA A23.1-94 ({dollar}fsb{lcub}c{rcub}' > 70{dollar} MPa).; The extension response with respect to increasing tensile load of all specimens was measured, adjusted to account for shrinkage, and subsequently presented as bond performance ({dollar}betasb{lcub}c{rcub}{dollar}) factor values. Shrinkage corrected response curves more appropriately evaluate the post-cracking behaviour, which would otherwise underestimate the tension stiffening potential. In addition to concrete strength, other variables were tested for influence on post-cracking behaviour and included: the steel reinforcing ratio, grade of reinforcement (deformed bar or prestressing strand), and concrete section and bar layout (effective area). A series of comparative based results regarding specimen variables were then produced from the accumulated research data. Observation of crack width and spacing developments were also made for the large scale specimens during testing.; It was found that, although the high strength specimens were indeed stronger (ie. larger cracking load) and stiffer than the normal strength members, concrete strength had little or no effect on the relative post-cracking behaviour (ie. {dollar}betasb{lcub}c{rcub}{dollar} was largely unaffected by concrete compressive strength). Perhaps the only variable influencing the {dollar}betasb{lcub}c{rcub}{dollar} values obtained was the steel reinforcing ratio. A {dollar}betasb{lcub}c{rcub}{dollar} function (for reinforced concrete in tension) is suggested which better fits the experimental data than other published models do. The effective area of concrete in tension given in the CEB-FIP code is found to reasonably agree with the information collected under this programme.