Design procedures for high-strength concrete cross-sections

The use of high-strength concrete (HSC) is more advantageous in structural elements under compression and the compressive stress-strain relationship is a relevant characteristic of the concrete required for behaviour analysis and design of those elements. For cross-section design, the codes of practice usually allow curved-rectangular and/or simplified rectangular idealised concrete stress blocks. Comparisons between idealised concrete stress blocks of different codes are presented and examples of their influence on the cross-section theoretical axial load-bending moment interaction diagram are given in this paper. The theoretical strengths obtained considering those compressive stress diagrams for the concrete are compared with experimental strengths of 403 elements subjected to pure axial load or to combined axial load and bending moment. Besides the cross-section type (square or rectangular), the elements had the variables of dimensions, steel and concrete strengths, load eccentricity and reinforcement ratios and configuration. The analysis of the comparisons between experimental and theoretical strengths considering different stress diagrams for the concrete under compression provides an insight to the level of safety related to the different design procedures, which is highly relevant for those who want to design HSC structures.