STRESS-STRAIN RELATIONSHIP OF CONCRETE: HOW IMPORTANT IS IT?

Radical Concrete Technology. Edited by R K Dhir and P C Hewlett. Published in 1996 by E & FN Spon, 2-6 Boundary Row, London SE1 8HN, UK. ISBN 0 419 21480 1. ABSTRACT. For normal strength concrete with compressive strengths between 20 and 50 MPa, there are several well established reliable models to predict the stress-strain relationship of concrete. Recent developments in concrete technology has facilitated production of high strength/high performance concrete with compressive strengths over 100 MPa. Developing a unified stress-strain model which predicts the behaviour of reinforced concrete with a reasonable accuracy and valid for the full range of compressive strengths of concrete, is a challenging task. Most important consideration should be given to the degree of influence of the assumed stress-strain relationship of concrete on the prediction of the structural behaviour of reinforced concrete. This paper reports the early results of an investigation of the influence of the stress-strain curve assumed for concrete on the predicted behaviour of structural members. Structural elements studied include reinforced high strength concrete columns under axial compression, high strength concrete beams and slender high strength concrete walls. Keywords: High Strength Concrete, Stress-Strain Relationship, Moment-Curvature Behaviour, Instability Analysis, Axial Compression, Lateral Confinement Dr Sujeeva Setunge is a Lecturer in Structural Engineering, Monash University, Gippsland School of Engineering. Her main research interests include the structural behaviour of high performance concrete with particular reference to the triaxial behaviour and time dependent deformations. Dr Priyan Mendis is a Senior Lecturer in Structural Engineering at the University of Melbourne. He worked as a Structural Engineer with Connell Wagner Ltd. before joining the University in 1991. His research interests include high strength/high performance concrete, Earthquake Engineering and multi-storey buildings. INTRODUCTION In ultimate strength design of concrete structures, the stress-strain relationship is one of the main material properties required. Since part of the concrete compression zone at ultimate strength is subjected to strains beyond the strain at the peak stress, information on both the ascending and descending portions of the curve are of importance. For normal strength concrete (with compressive strengths up to 50 MPa) the shape of the curve in uniaxial compression is well established. There are a large number of analytical expressions proposed to predict the stress strain curves of normal strength concretes in uniaxial compression (1, 2, 3, 4, 5, 6) and under lateral confinement (4, 7, 8, 9, 10).