Design through an incremental approach: the Swiss experience

In Switzerland, the current code for structural concrete published in 2003 privileged an incremental approach for design of new members or for assessment of existing structures with respect to a number of topics (shear, buckling, reinforcement detailing through strut-and-tie modelling,...). The incremental approach is grounded on the use of general and sound theories (based on physical models) where the hypotheses performed for their application can be refined as the required accuracy increases. The approach proposes thus to adopt safe hypotheses at first stages of design leading to relatively simple and low time-consuming analyses. In cases where such degree of accuracy is not sufficient, the hypotheses are refined in a number of steps, leading to better estimates of the behaviour and strength of the member. Such approach has revealed to be very convenient for design of new structures (where different levels of detail are required as the project evolves from preliminary or conceptual design to a construction project) or for assessment of existing structures, where the structural safety may be found insufficient according to simple design rules.