Storey Drift

For both wind and seismic design, on each level and each direction ( E->W, W->E, N->S, S->N) Shearwalls calculates the design storey drift for each shear line and compares the maximum of these to the allowable storey drift.

Design Storey Drift

The storey drift is the lateral deflection of the top of the walls relative to the bottom of the wall.

For seismic design, Shearwalls implements NBC 4.1.8.13 and O86 11.8.8 by checking the maximum amplified storey drift against allowable limits.

For wind design, it checks the actual storey drift against the maximum allowable storey drift from NBC 4.1.3.5.(3).

Post-design Check

Note that this check is not included in the Shearwalls design routine for unknown wall materials. Shearwalls designs walls to resist shear loads and C&C wind loads, and then checks the designed walls for storey drift. So a set of wall materials that passed the shear wall design process can fail the storey drift check.

This approach is taken for two reasons -

• Different walls on a shearline can have different materials, and the design process for a single wall occurs before we know the deflection for the entire shearline.
• It is not only wall materials that influence deflection, often the largest component is the hold-down displacement term. There is not currently an iterative design for hold-downs, and even if there was, it would be prohibitively complex to optimize for both hold-downs and wall materials simultaneously.

Output

Results for the shearline with the maximum deflection for the level/direction are shown in the Storey Drift table of the Design Results. If a failure exists on any storey or direction, it is reported in the Design Summary .

For these buildings, you can suppress the output of storey drift check using either the Show/Hide menu or the Display Options settings. Doing so will also suppress any warnings that would appear in the Design Summary.

You can do so separately for wind design and for seismic design.