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Sizer performs deflection design for three separate deflection criteria:
Total Deflection
This check is performed to conform to CSA O86 5.4.2, for elastic deflection. The absolute deflection limit of L/180 is applied by default, you can change this to ensure that, in your judgment, the deflections do not damage "structural elements or attached non-structural elements" for your design.
The program issues a warning in the Design Check output if you have entered a limit larger than L/180 and the member deflections more than L/180.
The effects of each load in a load combination are used to determine total deflection.
For CLT panels, a factor Kcreep from O86 A8.5.2 is applied to the deflections due to long-term loads and the sustained portion of live loads when calculating total deflection. Refer to Design Code Load Options for more details.
"Live" Deflection
This check is performed to limit damage to non-structural elements due to the deflection that occurs in addition to permanent deflection, as specified for example in NBC 9.4.3.1 for residential construction. Default deflection limits are given for each member type, and you can change these according to the application, for example if a fragile covering is to be applied to the structure.
The program includes the effects of L = live (use,occupancy), Ls = live (storage,equipment) , Lt = live (liquids in tanks) , S = snow, and W = wind loads in the "live" deflection calculations.
Permanent Deflection
This check is performed to conform to CSA O86 5.4.3 for permanent deformation. Default deflection limits of L/360 are used, and they too can be changed for a particular application to provide for "a more accurate evaluation of the acceptable deflection limits."
The program reminds you with a note in the Design Check output if you have entered a limit larger than L/360 and the permanent deflections are larger than L/360.
The program includes the effect of long-term loads D = dead, Ds = dead load due to soil, H = earth,groundwater, Ls = live (storage,equipment) and Lt = live (liquids in tanks) load types in the permanent deflection calculations.
Permanent + Live
Note that Live Storage loads are to be included in both the “live” deflection check, and the permanent deformation check, so that “live” deflection and “dead” deflection will not add to total deflection in the presence of live storage loads.
Cambering
You can indicate that the member is cambered, so that permanent deflection is not considered or included in the total deflection calculation.
This is allowed by O86 5.4.2, Elastic Deflections, and by NBC 2015 Structural Commentaries, Table D1, Note 5. Notes 1 and 3 of NBC 2020 Table 4.1.3.4 permit the exclusion of dead load from total deflection if allowed by the referenced standard.
If Cambered is selected, only "Live" deflection is checked by Sizer and included in the Design Check output.