Design a rectangular post tensioned concrete beam to carry a uniform live load of $14\mathrm{.}60$ KN$/$m in addition to its own weight. The beam is simply supported over a $15$ m span. It is required that depth should not exceed twice the width. Using the Approximate Design Method, determine the dimensions at midspan and amount of prestressing steel needed. Allowable stresses for concrete and steel are $17\mathrm{.}23$ MPa and $1035$ MPa respectively.