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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 180/L is applied by default, you an change this to ensure that, in your judgment, the deflections do not damage attached "structural elements or attached non-structural elements" for your design.
The effects of each load in a load combination are used to determine total deflection.
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) , Lf == 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 will not check that permanent loads are greater than 50% of total loading in order to do this check, relying instead on the fact that the prescribed limit for total loads is twice that for permanent loads. (The 50% check allows engineers to avoid the full deflection calculation, it is not necessary in a computer program.)
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 sustained live 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 sustained live loads.