Evaluation of the Strength of High-Strength Concrete Columns

Due to the different characteristics of higher strength concrete, this paper describes how some procedures traditionally used in the design of structures made of lower-strength concrete have to be changed. In order to evaluate the behavior of high-strength concrete (HSC) elements (fc > 50 MPa) with reasonable accuracy, an adequate compressive stress-strain relationship of concrete should be adopted. This is particularly important for predicting the behavior of columns—elements where the use of HSC is most advantageous. Different types of stress-strain relationships for HSC have been proposed for the nonlinear analysis of member behavior and for the ultimate state analysis of cross sections of elements under combined flexure and axial load. In this work, simplified rectangular stress blocks for the design of cross sections by different codes applicable to HSC structures are presented. It is shown that those concrete stress blocks can lead to quite different bending moment-axial load interaction diagrams and comparisons between experimental and calculated strengths of 403 tested columns give an idea of the level of safety related to the use of various concrete stress blocks.