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Building Width for Low-rise Restriction (Change 112, Bug 2466)
When determining the height-to-width ratio of the structure for use in the low-rise load restriction in NBC Structural Commentary I-26, that is, height/ width < 1, the the smallest of the two plan dimensions of the storey with the largest such dimension is now used as the width.. Previously the smallest plan dimension of the smallest storey was used, leading to situations whereby this ratio might be determined by a small penthouse. Judgement must now be exercised in using this method for a structure that has an extensive one-storey base with a narrow multi-storey tower above.
Building Depth for All-heights Cp (Change 112, Bug 2466)
In determining H/D for Commentary Figure 1-15, the program uses the storey with the largest plan dimension. Note 1 to Figure 1-15 says to use the dimension of the building at the base, which in almost all cases will be the largest storey.
Application of All-heights Restriction (Bug 2432)
When generating wind loads using NBC Commentaries I-15 all-heights design procedure, if the structure has a height-to-width ratio greater than 4, the wind loads were generated even though NBC 4.1.7.2 states that dynamic analysis is needed, so that the methods currently in Shearwalls are not applicable. (Dynamic analysis was not implemented due to the rarity of such buildings that also adhere to height restrictions for wooden buildings.) Now, an error message is displayed and the wind loads are not generated for height to width rations greater than 4.
Building Width for All-heights Restriction (Bug 2466)
When determining the height-to-width ratio of structures with unevenly sized storeys for the purposes of the I-15 all heights restriction, the program now uses the procedure given in 4.1.7.(3), that is, w = ∑hi wi / ∑hi , where hi = height above grade to level i; and wi = width at height hi .
All-heights vs. Low Rise Building Width
Note that the building width definition in 4.1.7.2 (3) when considering the applicability of dynamic analysis to all buildings is not used for low-rise height-to-width ratios because the NBC Structural commentaries in Figure 1-1 assign two separate symbols to these dimensions, w, and Ds, respectively, and they have different descriptors – the minimum building width in each wind direction, and the smallest plan dimension in each direction.