Softening of Normal Strength and High-Strength Concrete Frames

Abstract

In the 21st century, computing facilities will make it possible to opt on a regular basis for more accurate rigorous methods of analysis. A rigorous collapse load analysis requires a knowledge of the behaviour of plastic hinges up to advanced curvatures. Concrete sections characteristically soften, that is the bending moment capacity decreases with increasing curvatures after the end of the plastic plateau while steel sections undergo a hardening phase. Consideration of softening is essential in a rational analysis. In this paper, the important aspects of softening of concrete frame structures are reviewed. High-strength concrete (f'c>50 MPa) is a more brittle construction material than normal strength concrete. High-strength concrete sections show a steeper softening slope when compared with similar normal strength concrete sections. An example is presented to demonstrate that a HSC frame structure with steeper softening slopes will have a lower collapse load.