on the basis of the parabola - rectangle approach and the bilinear approach. The figure shows that there is good overall consistency. It could be argued that for the lowest concrete strength classes (see the figure for C20 in Fig. 3.12), the bilinear approach is slightly less accurate. This could be improved by reducing the values £c3 for the lower strength classes. This would however have a considerable disadvantage since then the shape of the design stress strain curves for all strength classes < C55 would be different which would render substantial complications for practical design (different shape factors and distance factors, large sets of design diagrams for various cases, where now only one diagram is sufficient). Since the loss of accuracy for practical calculations is very small the constant value £c3 = 1.75 % should be maintained.

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