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Re: Toronto wind speeds and ice requirements

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Neil,

        I'm back, Neil.  The information I provided earlier in not suitable for
anything like a 100' flagpole; when you said "pole structure" I visualized
something much closer to the ground.  The following will be much more
appropriate.

        The National Building Code of Canada (1995 edition) lists four
Toronto suburbs, all with the same reference wind loading (as Peter pointed out,
there may be others which I don't recognize as suburbs of Toronto), namely

(1/10) (ten year)  . . . . . . q = 0.39 kPa = 8.07 p.s.f.
(1/30) (thirty year) . . . . . q = 0.48 kPa = 9.94 p.s.f.
(1/100) (hundred year) . . q = 0.59 kPa = 12.21 p.s.f.

Note: these are reference wind pressures, based on average hourly wind
speeds.  Do not attempt to use any American codes based on this information.

        Canadian wind loading calculations are based on

                f = q * Ce * Cg * Cp

where        f = wind pressure applied on the projected area of the structure

                 q = reference wind pressure (indicated above)

                Ce = exposure factor
                       = (Z/10)^0.28 >= 1.0 for exposure A (open exposure)
                       = (Z/12.7)^0.5 >= 0.5 for exposure B (centre of large
towns)
                       = (Z/30)^0.72 >= 0.4 for exposure C (centre of large
cities)
where Z = height from grade to the point under consideration (not the total
height of the stack) in meters.  Note: this gives a continuously increasing
curve which we use in place of the familiar step function which we've all used
in the past  It also gives roughly the same values as the step function (which,
by the way, can still be used if you really want to).

                Cg = gust factor
                        = 2.0 for structures (using simplified procedure)
                        = 2.5 for cladding
                        = As determined by detailed dynamic procedure.

                Cp = 0.7 for tall cylinders with height/diameter of 25 or so.

        The gust factor is the main variable that will give you problems.  It's
a rather complicated function of geometry, natural frequency and damping ratio
in addition to including some of the above data.  I estimate (without doing any
calculations) that it will be about 3.5 for a free standing pole and about 2,8
for a guyed pole.

        I have some information on this which I will send to you privately
because it will be too large for the seaint list.

        To answer your original question about the wind speed, you could get an
estimate of the equivalent constant wind speed from the equation

            0.0027 * v^2 = q * Cg
                                = 9.94 * 2
                              v = 86 mph (for simplified analysis)

and        0.0027 * v^2 = 9.94 * 3
                               v =  105 mph (for estimated Cg = 3.0)

Other considerations:

1.)    In Canada we do not use a 1/3 increase in stress (or 25% reduction in
loading) for dead + wind with no other loads.

2.)    We do use a 0.7 load combination factor with any two of live, wind or
earthquake, thermal (but not on the dead load portion).


3.)    We use a 0.6 combination factor when all three act together.

Regards,

H. Daryl Richardson.


Neil Moore wrote:

> 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.
>
> At 02:55 PM 7/24/02 -0400, you wrote:
> >> -----Original Message-----
> >> From: Neil Moore
> >>
> >> I'm reviewing a pole structure for Toronto, Canada and need the following
> >> information:
> >>
> >> 1.   Design wind speed
> >> 2.   Ice requirements
> >> 3.   Low temperature requirements.
> >>
> >
> >Neil:
> >
> >Is this an electrical utility pole, a highway (lamp standard) pole, or
> >another kind of pole which would likely come under the jurisdiction of the
> >Ontario Building Code?
> >
> >Peter James
> >Ottawa
> >
> >
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