When advanced models can lead to lower safety: Codified design of structures against wind loads

In modern structural design standards, reliability requirements are verified following a semi-probabilistic approach, in which the safety of a structure is controlled by the selection of characteristic values and partial safety factors. These standards are typically based on simplified models of load and structural performance, whose parameters are selected conservatively, which leads to additional "hidden" safety. If these models are replaced by more advanced and potentially more accurate models, some of this hidden safety might be lost. This study investigates the hidden safety associated with the wind load model of the Eurocode. In particular, we estimate the hidden safeties included in the wind velocity pressure maps and the gust-, the pressureand the roughness-coefficient. In order to make general statements, a generic portfolio representing the most common design situations is analyzed. The effect of advanced models (e.g. a "virtual wind tunnel") on these hidden safeties is considered. First, we estimate how the application of advanced modeling techniques influences the material usage and the reliability of structures. In a second step, we recalibrate the partial safety factor regarding wind, so that designs gained by advanced modeling techniques lead to the same avarage level of safety as designs following the Eurocode. With this recalibrated partial safety factor we reevaluate the effect on the material usage and the reliability.