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Soft Storey Identification Using Storey Drift
by Ardalan Sabamehr, Ph.D.
A large number of moment frame buildings have been constructed for specific purposes and may contain large area for parking, reception lobbies, etc. These kinds of open spaces void of any infill walls are called soft storey buildings. Storeys with these kinds of open spaces are considered as having stiffness discontinuity because of its flexibility when compared to adjacent stories. One of the most common parameters used to identify soft storey is the storey drift.
The seismic force distribution is dependent on the distribution of stiffness and mass along the height of a building. The essential characteristic of soft storeys consists of a discontinuity in the strength or stiffness (Rahiman G. Khan et al, 2013).
Vertical stiffness irregularity is considered to exist when the lateral stiffness of the SFRS in a storey is less than 70% of the stiffness of any adjacent storey or less than 80% of the average stiffness of the three storeys above or below (Ventura, 2006).
The hypothetical multi storey building with 3x3 bays in X and Y directions and 4 floors is used to identify the soft storey.
A time history analysis has been applied to the building to extract the storey drift demands of the building. To simulate the soft storey floor, the lateral bracing is removed from level 3 for 8 bays.
The results show the clear spike in the third floor which confirms this floor to be a soft storey.
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