The analysis and design of concrete structures is essentially an iterative process. The magnitude of permanent gravity loads, for instance, is dependent on the member sizes and hence an initial estimate of member sizes is required before the structure can be analysed. If, however, the final dimensions required to resist, say, bending moment in a member differ from the initial estimate of the member size, then the design process may be repeated with revised member dimensions until these initial assumptions are satisfied. The more accurate the initial size estimates, the less iteration that will be involved as the solution will converge more rapidly to the precise requirements.