Seismic drift check
By default this check is applied to all columns (of all materials), and all walls at every level in the model.
Results are presented in terms of levels, with detailed results for individual column/wall stacks/panels also being available.
For levels set as floors a Reporting Level option is displayed in Level Properties. By unselecting this option, individual levels can be excluded from the check reporting.
In this check the seismic stability coefficient θ in each direction is checked against the limit θmax and then the stack design story drift Δdes is determined in each direction and checked against the allowable story drift Δa
A workflow for running the check is outlined below:
Configure the check and set the limit
The check is configured on the Localization page of the Seismic Wizard.
An option is provided to override the allowable story drift factor and a second option allows for the seismic drift check to be skipped entirely if required.
Run the check
Seismic load combinations are automatically checked on a level by level basis for drift by running an appropriate analysis or design.
Review the check status and details
Once the check has been run, an overall status is reported in the Design branch of the Status Tree, the overall status being the worst status from each of the individual levels.
Right clicking on the status opens a context menu.
From this menu you can display the seismic drift check summary in a Review Data Table, an ASCE example of this table is shown below.
By unselecting the Summary Only option in the ribbon, the table can also display detailed results on a stack by stack basis if required.
By unselecting the Summary Only option in the ribbon, the table can also display detailed results on a stack by stack basis if required.The individual checks can be investigated in more detail by clicking the Details button at the end of any row.
Review the check graphically
From the right click menu in the Status Tree you are also provided with an option to graphically review the checks in a Show/Alter State View.
The color coded legend makes it easy to see individual failing members. By hovering the cursor over a member, its seismic drift results are displayed in the tooltip.
From the same Show/Alter State view, by changing the Mode in the Properties window, you also have the option to switch off checks for specific stacks if you require.
Switching off inappropriate checks and merging stack lengths
After reviewing you might choose to switch off checks for selected columns and walls, or individual stacks/panels within selected columns and walls: this can be done directly via the Properties window, or graphically in a Show/Alter State view (as described in the previous section).
You might also choose to take advantage of the option to merge short stacks automatically where they are less than a specified limit. Stacks check lengths can also be be manually adjusted by merging them together if required.
An option is also provided which allows you to switch off checks for specific levels if you decide they are inappropriate, (for example if the story height is very short). The checks at that level are still performed, but they are excluded from the tabular review data display.
Printing calculations
The seismic drift check results table is available either by creating a Seismic Design report, or by including the Analysis>Seismic Drift chapter in a custom report.