Levels-of-Approximation Approach in Codes of Practice

Civil engineering projects typically involve a number of design phases, such as preliminary design, tender design and executive design. The required degree of accuracy for the analysis of the behaviour and strength of the structural members increases as a project evolves. Codes of practice, however, seldom reflect this situation and propose a single design expression to be used at all phases of a project. This is not convenient in a number of situations, leading to lengthy analyses for initial design phases and sometimes not allowing to consider all potential load-carrying mechanisms or strength reserves for advanced analyses (design of complex structures and assessment of critical existing structures).