Ductility of a shear wall designed for a future storey

[MALKOBANI]

You are asked to design a four-storey building accounting for a future additional storey. You design the shear walls for five stories using a load reduction factor R=3.5 ( for example). The owner doesn’t know when that additional storey will be added. Obviously, the shear walls are over designed and the expected ductility is less by the over-design ratio. How do you dead with such case?

Thanks

 

[morokanu]

Malkobani,

From what I know, ductility is a measure of the ability of an element/structure to yield before failure.

Even if the shear wall is over designed, the ductility may be similar: ratio of force/displacement_when_starts_yielding and force/displacement_when_fails.

If you design the structure to accommodate 5 storeys and the building will be only 4 storeys, I can not see any problem. The structure is stiffer and deflects less.