The levels-of-approximation approach in MC 2010: application to punching shear provisions

In order to address how new knowledge influences design expressions, design codes have in most cases become significantly more complex over the last decades. However, this tendency is leading to codes that are too complicated for preliminary design but still not sufficiently accurate for assessing existing structures (where even more realistic models of behaviour are sometimes required). An alternative code strategy is that proposed by codes based on a levels-of-approximation (LoA) approach. This approach is based on the use of theories based on physical parameters where the hypotheses for their application can be refined as the accuracy required increases. The approach proposes adopting safe hypotheses during the first stages of design, leading to relatively quick and simple analyses. In cases where such a degree of accuracy is not sufficient (e.g. design of complex structures, assessment of existing structures, significant potential economic savings), the hypotheses can be refined in a number of steps, leading to better estimates of the behaviour and strength of members. This approach, recently adopted in the first complete draft of Model Code 2010 for a number of design issues, is discussed within this paper with reference to punching shear provisions.