To reduce the environmental impact or cost of a civil engineering structure their designs are optimized. A
promising method to optimize are iterative optimization algorithms. If both the design calculations and the
iterative optimization algorithm are automated, an optimized de
...

To reduce the environmental impact or cost of a civil engineering structure their designs are optimized. A
promising method to optimize are iterative optimization algorithms. If both the design calculations and the
iterative optimization algorithm are automated, an optimized design solution can be found within a feasible
timeframe. To be able to automate the design calculations they need to be fully parameterizable. In this context
it becomes interesting to research whether yet unparameterizable calculation processes can be made
parameterizable. One of these processes is the determination of the locations in which the fatigue resistance has
to be determined in a steel orthotropic bridge deck. This location is the location where the first fatigue crack is
expected. Therefore, Antea Group requested if a study could be performed with the objective to answer the
following research question:

**How can the determination of the location of the first fatigue crack in the deck, at a stiffener to deck plate
weld toe, be parameterized?**

To answer the research question, the (in the Netherlands active) regulations are studied. Based on the
regulations the process of determining fatigue damage of a point in the bridge can be understood. As well as the
reason why, this process is too computational demanding and complex to be able to be applied to all points in
all welds.

In response to this an alternative method is proposed. This method reduces the complexity and the
computational budget that is needed, by using 1D elements instead of the currently prescribed 2D elements. To
determine if this method can be used it was decided to apply it on a case study. The bridge which served as the
case study was the Goereese bridge. The alternative method was applied to determine the expected distribution
of fatigue damages in all welds in the case study. Based on this obtained distribution a limited number of
interesting locations in the deck could be identified. At these points to regulatory required method was used to
obtain results which can be compared with the alternative method.

It is concluded that the predicted location of the first fatigue crack of both methods is directly next to each other.
However, the distribution of the remaining points suggest by the alternative method does not agree with the
obtained results of the regulatory method. Remarkable enough, both these methods predict a location which is
counter intuitive to the structural engineers participating in the research.

Therefore, the following general recommendations are given:- Research if the regulatory method, to determine the location of the first fatigue crack, can be simplified.
- Research the cause(s) of the differences between the regulatory method and the alternative method.
- Increase the awareness of structural engineers regarding their intuition on the location of the first
fatigue crack.