Uncertainty caused variability in preliminary structural design of buildings

• Large variation in the results from engineers in a preliminary building design.
• Large uncertainties when drawings are transformed into structural models.
• Engineering modeling uncertainties (EMU) have a large effect on structural safety.

Many decisions in the everyday work of the structural engineer are taken under the influence of uncertainties. The degree of uncertainty affects the quality and variability of the outcome of the structural design work. The effect of uncertainties related to knowledge and experience of the structural engineer was studied in a round robin investigation. Despite a relatively well defined task, the results varied considerably among the 16 participating Swedish structural engineers that performed this task; a structural check, load takedown and stability calculation for a five storey concrete building. The column load of a specific position differed by a factor of three between lowest and highest suggested value. For the stabilizing forces the values varied even more. The uncertainties connected to the structural engineer were estimated by introducing the term Engineering Modeling Uncertainty, divided into a structural model part and a load part. These uncertainties are shown to have a large effect on structural safety. The significant variability in results and the consequence on structural safety of this investigation emphasizes the importance of documentation and communication of all the assumptions made by the structural engineer – even the apparently obvious ones.