Storey Drift Calculation

For seismic design, the shear wall deflections amplified using NBC 4.1.8.13 are compared to the allowable drift limits. For wind design, the actual maximum deflections from are used. Deflections are calculated for each shear line and the results for the one with the largest deflection are shown in the Storey Drift table of the Design Results. The following are the data that appear in that table.

Deflection Amplification Factor

For seismic design, non-constant deflections are multiplied by the amplification factor from 4.1.8.13.(2) = R_d R_d / I_E. The R values can be input into the Site Dialog, but unless they were over-ridden, they are the values from NBC Table 4.1.8.9. The importance factor I_E is calculated from the Occupancy category entered in the site dialog, and is shown below the table.

Constant Deflection

The deflection due to the contribution to hold-down displacement of oversized boltholes, miscuts, gaps, and shrinkage. For seismic design, this deflection is not multiplied by the deflection amplification factor, because it is independent of the base shear force, which was generated using the inverse of that factor. The purpose of the deflection amplification factor is to remove the influence of the R_d R_d and I_E factors in the generation of seismic loads.

The constant deflection for the shearline corresponding to the maximum deflection is shown.

Maximum Deflection

The maximum deflection is the largest deflection on any shear line. If deflections on a line have been equalised, it is the common deflection of all wall segments on the line. If not, it is the largest deflection for any segment on the line.

Amplified Deflection

Defining the constant deflection as D_c and the maximum deflection as D_max the amplified deflection is D_c + (D_max - D_c ) R_d R_d / I_{E .}