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RE: Toronto wind speeds and ice requirements

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> -----Original Message-----
> From: Neil Moore
> Peter:
> It's a 100 foot high flagpole.
> Neil Moore, S.E.
> We've done a number of poles in the northern areas where at least 1/2" of
> ice was required.  In other parts of Canada, I've had to consider brittle
> fracture from low temperatures.


A flagpole probably doesn't strictly come under the scope of the Building
Code. The loads defined by the OBC, which flow from the NBCC, would be
appropriate (but see below).

Daryl provided the reference wind pressures. The Toronto values are higher
than most Ontario locations because of the proximity to Lake Ontario - but
there are a couple of nearby municipalities with slightly higher values.

OBC and NBCC dodge the issue of ice accretion by referring to local
experience. The Ontario Highway Bridge Code (which applies to all highway
structures including signs) provides a map that shows 31 mm - again it's the
lake effect - many Northern regions have 12 mm or 4 mm - no moisture
available in the air. The density is the same as water(!).

The OBC/NBCC provide design temperatures for heating systems. The January 1%
temp is -22°C - warm compared to just about everywhere in Canada - most of
Alberta would be in the -30 to -40 range. The Bridge Code gives a minimum
daily mean of -30°C - this figure would be a better choice for an exposed
structure (I'm comparing the values given for Ottawa, where I live, and the
Bridge Code chart is a better representation of the actual lows).

The Ce value Daryl quoted is only applicable up to certain heights - for
Exposure Class A the equation is:

Ce = (Z/10)^0.28 (min 1.0)

where Z = height in metres

Both the OBC/NBCC and the OHBDC require a dynamic analysis for sensitive
structures. Both documents have detailed requirements for this. I don't have
any experience in this area to compare the two.

Peter James

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