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Re: Aeroplane Hanger

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> From: Daryl Richardson <h.d.richardson(--nospam--at)shaw.ca>

>         I have been asked to provide engineering services for the
> lifting of an aeroplane hanger roof by ten feet.  This sounds like the

>         My question is: how would one proceed to physically do the work
> in the field, keeping in mind that not only must it be done but it must
> be done safely?

I'd be asking cost questions before I got too excited about raising the
building. It MAY be feasibile to simply demolish the existing (possibly
saving some of the cladding and secondaries - purlins/girts, windows,
doors, sprinklers, etc.) but buy new rigid frames and endwalls to suit
the taller structure. There is a good chance that the foundations will
be adequate.

You will need to have an adjustable support at mid-span of the
clear-span frames, as well, since the columns will spring outwards when
the building is lifted from the foundation. The centre jacking can be
used to control the column spreading. Alternately, move the side
supports in to the rafter points of inflection and cable across between
opposite sidewall columns.

>         The building is a pre engineered rigid frame steel building 120
> feet square by about 18 feet high with tapered beams and columns.  There
> is a horizontal bolted joint between the columns and the beams.  It has

Horizontal haunch joints sound like a Butler signature. Do you know the
manufacturer? You MAY be able to get some assistance from the
manufacturer as to the capacities of standard components and materials
from that era.

I'm guessing that the haunch connection is about 5' deep. This would
make your haunch node about 18'-1'- 5'/2 = 14.5 ft. Adding 10 ft is like
raising the structure 10'/14.5' = 70%.

> the pre engineered package.  The building is 25 plus years old and
> appears to be in excellent condition.

The plate and mill sections are PROBABLY 44 ksi if from a Canadian
manufacturer at that time. This was pre-desktop-computer-design and will
probably be almost standard from the manufacturer.

> One contractor's proposal (very preliminary, in fact discussion
> only) is to secure the roof with cable or rod bracing against wind; use
> adjustable telescopic columns to support the roof; jack each column in
> sequence a few inches at a time until ten feet is achieved; insert
> prefabricated column sections into place and bolt it down; finally

You would be attaching to a small (exisiting) column base that would
likely have minimal moment capacity. See my suggestion below.

> reinforce the frames for the new design loading (I know from past
> experience that pre engineered buildings have virtually no reserve
> strength so substantial reinforcement will be required).

There is always reserve strength but it is rarely in the place that you
want it.


> From: Clifford Schwinger <clifford234(--nospam--at)yahoo.com>

> I'm just shooting from the hip here, but how about
> building some concrete new foundations and concrete
> piers (or walls) on each side of each column and
> jacking the whole building up onto new piers. Design
> the piers to take all the forces in a way that no
> modifications to the existing hanger structure would
> be required.
> 
> Cliff

I think that this is the most practical possibility if the same building
envelope must be used. You may have issues with the building bracing due
to the higher door tributary height.

Another option would be to investigate the possibility of raising the
building and COMPLETELY REPLACING ONLY THE COLUMNS of the rigid frames.
The rafters should be adequate if the new tall columns are similar
stiffness to the shorter originals. The girts could be unfastened at
each frame while the column is replaced (cladding will hold the girts in
position). The new column would not be much more expensive than the 10'
extension after the labour is added.

This kind of job is as much a detailing nightmare as the engineering
analysis.

Field reinforcing is rarely cost effective for PEMBs except for very
localized situations (probably not this case).

New pre-eng building is about CDN$10/sf erected (about CDN$150,000 for a
replacement plus demolition/disposal less scrap recovery).

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

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