Long term tension stiffening effects in concrete.

Abstract

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.