Seismic design in the Hungarian context
The relationship between mass and force
Section titled “The relationship between mass and force”An earthquake arises from movement of the ground, and the force on the structure comes from inertia: the greater the mass, the greater the force.
Hence one of the natural advantages of light gauge steel construction: in the same situation a substantially smaller seismic force arises than in a masonry or in-situ building.
It still has to be checked
Section titled “It still has to be checked”The smaller force does not mean the question can be ignored:
- the structure has to move together — bracing and continuity of the load path are conditions here too,
- the fixing of the non-structural elements — heavy finishes, plant, partitions — is a separate question,
- an irregular plan or mass distribution causes unfavourable behaviour regardless of weight.
What gives an advantage in design
Section titled “What gives an advantage in design”A regular plan
Section titled “A regular plan”A symmetrical, evenly braced plan behaves better than one prone to twisting and braced on one side.
Even distribution of stiffness
Section titled “Even distribution of stiffness”Stiffness changing abruptly from storey to storey — an open ground floor beneath closed upper storeys, say — concentrates the forces.
A continuous load path
Section titled “A continuous load path”The same requirement as for wind load. Load path continuity.
Ductile connections
Section titled “Ductile connections”A screwed connection can take large deformation before failing, which is a favourable property in an earthquake.
The Hungarian situation
Section titled “The Hungarian situation”Hungary is not among the highest seismic risk areas, but it is not free of it either: the zone map in the national annex gives the base value for a given location.
In practice that means that for many ordinary dwellings the wind is the governing horizontal action, not the earthquake — but that has to be checked, not assumed.
Non-structural elements
Section titled “Non-structural elements”In an earthquake a significant share of the damage comes not from the structure but from finishes falling and equipment overturning. Fixing these is part of the design, in public buildings especially.
The point
Section titled “The point”A light structure has a natural advantage here, but the advantage only materialises if the structure moves as one: with bracing and a continuous load path.