Deflection Limits

In Beam view, and in the Concept mode groups dialogs, the program allows you to input live, permanent, and total deflection limits based on ratio of span length, and optionally a single absolute limit in inches or mm, for each project. These limits apply to the current project only.

In addition, there is a Default Values Setting that allows you to specify the default limits that appear for new files, or upon change in member type, for each deflection criterion and each type of member.

"Factory" Defaults

The default limits when the program is shipped or the limits are reset are as follows

• Floor beams, solid floor joists and CLT floor panels: Live = L/360, Permanent = L/360, Total = L/180, Absolute = 0 (not active)
• Floor I-joists: Live = L/480, Permanent = L/360, Total = L/240, Absolute = 0 (not active)
• Roof beams, roof joists and CLT roof panels: Live = L/240, Permanent = L/360, Total = L/180, Absolute = 0 (not active)
• Columns, wall studs and CLT wall panels: Live = L/180, Permanent = L/360, Total = L/180, Absolute = 0 (not active)

For roof beams, a checkbox called "With ceiling" allows you to quickly change these defaults to L/360 for live L/240 for total deflection, values recommended when the beam supports a gypsum-based ceiling.

The sources for these recommended deflection limits are:

• Total deflection, except I-joists,CSA O86 5.4.2.
• Permanent deflection: CSA O86 5.4.3
• Live deflection, beams, solid joists, CLT roof and floor panels: NBC Table 9.4.3.1, roofs not plastered or with gypsum wallboard
• Live deflection, columns, wall studs and CLT wall panels - CWC Wood Design Manual, Table 2.1
• I-joists – Recommendations of an I-Joist manufacturer.

Absolute Deflection

Sizer allows you to enter an absolute limit for the amount the member can deflect, that is independent of the span length, for those situations in which movement of cladding or other non-structural elements must be confined to a certain value. If this is limit proves to be less than the live, permanent or total deflection limit based on span length, the program checks the deflection criteria based on it and output shows this limit rather than the one based on span length.