Accidental actions and robustness

What it means

Robustness does not mean the structure survives everything. It means that if something unexpected happens — a vehicle impact, an explosion, the failure of a member — the consequence stays proportionate: the whole building does not come down because of a local event.

Why many small members help

A light gauge steel wall has many studs at relatively close centres. If one is damaged, the neighbours can take its load — provided there is something to hand it over: the track, the lining and the connections.

That is the capacity for load redistribution, and it is a natural property of this structural type.

In a long-span structure of few members it is harder: there the loss of a single member is more serious.

What it takes

Tying connections

Horizontal and vertical ties ensure the structure behaves as a system rather than as members set side by side.

Alternative load paths

Where possible, the load can come down by more than one route. That is a matter of design outlook.

Ductile connections

A screwed connection fails with large deformation rather than brittlely. That gives time and warning.

Where it needs separate attention

The standard distinguishes buildings by the severity of the consequences. For a house the usual structural arrangement is enough; for a larger building, one holding many people or a taller one, a specific check is needed.

Accidental actions

A separate part of EN 1991 deals with accidental actions: impact, explosion, and the general robustness requirements.

In practice the most common case is not dramatic: during an alteration somebody removes a member. Which is another reason the documentation has to survive and the bracing role has to be unambiguous. Load-bearing and non-load-bearing walls.

The point

Robustness is not extra material but a good system: many members, good connections, alternative load paths. Light gauge steel is good at this — if the connections get made.