These are the basic assumptions and in the actual design to find the amount of reinforcement required we can use: (a) design charts: (b) design formulae; or (c) strain compatibility.

These are in Part 3 of the Code and have been prepared using the rectangular-parabolic stress block for the concrete and the bilinear stress-strain curve for the reinforcement. The charts are for rectangular sections reinforced in tension only (singly reinforced), or in tension and compression (doubly reinforced). Appendix A of Part 3 gives notes on the derivation of the charts and in the equation for the concrete compressive force at failure it can be seen that 0.45/cu has been used rather than 0.67/cu/1.5. As in the previous charts, the full area of concrete in compression has been assumed even where compression reinforcement is present. The singly reinforced charts are for reinforce­ ment Grade 250 and Grade 460 with different concrete grades.