Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Aeroplane Hanger

[Subject Prev][Subject Next][Thread Prev][Thread Next]
> From: "Jim Kestner" <jkestner(--nospam--at)somervilleinc.com>

> If the building is raised to be on 10 foot high piers, the lateral
> flexibility of these piers and how it may reduce the strength of the roof
> for gravity loads may be an issue. For a large thrust, there may be
> significant lateral deflection at the 10 foot elevation. I believe the PEMB
> frames are designed as if there is no lateral movement at the base.

A very definite issue. The more the base movement, the more deflection
to expect in the rafter (e.g. 1" horizontal separation between sidewall
bases is approximately (120'/2)/14.5'*1"= 4" vertical at the ridge for
this building). Deflection changes the first-order stress distribution.
It would be the same effect as having a less stiff column.

> From: "Effland, Greg" <geeffland(--nospam--at)butlermfg.com>

> the many comments that were sent in it appears a few important items were
> left out.
> 
> 1) Raising the building an additional 10 ft above the ground elevation
> will, per code, increase the wind loads on the building.  This will cause
> the horizontal reactions and possibly the vertical reactions under wind
> loading to increase.

The wind uplift increase due to height change will be in the magnitude
of 5%-7%. This might require minor reinforcement.

Typically, for wide clear span rigid frame projects in Canada, snow
loads control and will cause much higher horizontal base shear forces
than wind. Wind load change due to eave height will probably not be an
issue.

> 2) Assuming higher loads, this will increase the moments and shears on the
> frames lending BOTH the columns and roof beams to have potential over
> stress issues.

The greater issue will be the possibility of higher environmental load
requirements since the original building was designed.

> 3) Changing out the columns for new longer columns could also
> significantly change the moment diagram for the frame causing the roof
> beams to be over stressed as well.

The long column would need to be similar stiffness to the short column
to negate rafter issues, loads otherwise unchanged.

> Here is some contact info for the Canada office that might be of assistance
> for you:
> Butler Buildings (Canada)
> 3070 Mainway Drive, Unit 21
> Burlington, ON, Canada L7M 1A3
> Phone: 905-332-7786

Butler in Canada has been through a storied history in the last decade
(despite Butler's best efforts). They definitely do not have any
documentation prior to 1992 and, despite my good contacts there, point
any pre-1992 general inquiries toward the US head office.

Unfortunately, all of the historically knowledgeable Canadian Butler
employees (25-30 yrs, pre-desktop-computer-designed building systems)
have also retired from the Canadian office.

I think that Daryl will find that this modification to the above-ground
structure is simply more expensive than building new.

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********