Staircase design according to EXC1 instead of EXC2

Slowly but surely, metalworkers are receiving their first measurements according to DIN EN 1993, i.e. static calculations according to Eurocode 3. Of course, this also means that the first errors and avoidable problems for the metalworker are appearing.

Recently, the German Metalworking Association (BVM) received an order for a check from a metalworking contractor. The job was carried out in accordance with DIN EN 1090-2 in execution class 1 (EXC1). It concerned a staircase in a residential building. The German Institute for Building Technology (DIBt), in conjunction with the BVM, has defined EXC1 for this type of construction.

The structural engineer, unaware of DIBt-Mitteilungen 2/2011, included damage consequence class CC 2 (consequence class 2) in the design, strictly in accordance with EN 1990 for residential buildings.

Therefore, the structure must be designed in EXC2 if the matrix according to EN 1090-2, B.3 is applied. It is important to note that this matrix is only a recommendation.

Unfortunately this has been overlooked by the metal fabricator.

What are the consequences for the design of the staircase?

• The documentation requirements for EXC2 are significantly higher than for EXC1 (EN 1090-2, 4.2.1).
• In EXC1, there are lower requirements for flame-cut sections.
• A radius of r = 5 mm shall be used for recessed corners.
• The basic requirements of DIN EN ISO 3834-4 are not sufficient for welding in EXC2.
• Only qualified welding procedures may be used in EXC2 (DIN EN 1090-2, Table 12).
• A butt joint of the flat steel staircase stringer with a load factor significantly above 50% must be subjected to an additional non-destructive test. The metal fabricator will need to appoint an external inspector for this project as he will not normally have his own NDT personnel.
• The requirements for weld imperfections are higher in EXC2 than in EXC1.

This short list shows how important it is for structural engineers and steel erectors to be familiar with the rules and regulations in order to ensure cost-effective execution.

Conclusion
If possible, always agree in the component specification (quotation, order, release designation) on the design class with the lowest requirements in accordance with DIBT-Mitteilungen 2/2011 or – identical in content – BVM-Merkblatt 4 “Design classes”. If there is a need for argumentation or if you have any questions, the technical advisors of the regional associations or the BVM will be pleased to help.