where £] and s2 are the strains in the top and bottom surfaces of the beam, respectively. They are also indicated on Fig. 3.23(a).

Since b and R are constant then the position of the neutral axis must be such that:

i.e. the total area under the cr-£ curve between £i and £2 must be zero. This is achieved by marking the length er on the horizontal axis of Fig. 3.23(a) in such a way as to make the positive and negative areas of the diagram equal. This identifies the appropriate values for £i and £2 with:

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