Generally, steel buildings performed favorably during past major earthquakes that hit the country. A major reason for this is the exploitation of structural steel’s property to be plastically deformed without a fracture, or its ductility. In other words, popular designs of steel buildings that are earthquake-resistant concentrate on the capability of the structure to develop and maintain its bearing resistance in the inelastic range.
Ductility is very vital for local building codes relating to seismic movements. Common designs of steel buildings strictly follow these regulations, resulting in structures that are able to endure large earthquakes with no building collapse; moderately strong earthquakes with no substantial structural damage; and mild earthquakes with no damage at all.
Playing very significant roles in seismic design of steel buildings, are three kinds of ductility, which may be observed in a material itself, in a structural element, or in the whole steel building.
Ductility of a material measures its ability to tolerate large plastic deformations. Steel, as a construction material, has a high value of ductility since it can be deformed without breaking.
Ductility of a structural element or joint, measures it ability to redistribute stresses within the structural system, in the inelastic range, without loss of resistance. For example, common joint solutions for steel buildings are made more ductile by allowing the placement of plastic hinges into the joints.
The last kind of ductility essential in the design of steel buildings is structural ductility or the measure of the ability of the whole structure to deform in the inelastic range after some of its components have gone beyond their linear elastic range.
In the design of earthquake-resistant steel buildings, the three measures of ductility must meet the following condition: material ductility should be greater than joint ductility, and joint ductility should be greater than structural ductility.