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Historic Building in Calgary, Canada[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Historic Building in Calgary, Canada
- From: Daryl Richardson <h.d.richardson(--nospam--at)shaw.ca>
- Date: Tue, 17 Jan 2006 14:07:58 -0700
I am working on the rehabilitation of an historic building in Calgary, Alberta, Canada. This building has a few structural oddities that I would like to lay before you and solicit your comments on same.
Now this posting may get a bit lengthy; so those of you who are not interested in the restoration of old (1912) steel, concrete, masonry buildings may wish to skip this posting.
The building is approximately 200 feet (east-west) by 130 feet (north-south), six stories high. The building is L shaped, with a large theatre filling in the remainder of the L to present a full rectangular footprint at the ground and basement levels. The theatre is fully connected to the office building to the west and separated from the office building to the north by an eight foot "light well" at the second and higher floors. The theatre is about the equivalent of four floors tall. The long facades of the office building are facing streets on the north and west sides. There is a public lane on the south side of the building and a private lane along the east end.
The building is located about two blocks north of the city centre. The building is surrounded by 20 to 50 stories tall with one 60 storey building proposed one block to the northeast. Back in the days when we designed buildings based on wind speed rather than wind induced pressure the design wind speed for Calgary was 85 miles per hour ( the "new" procedures haven't really changed the wind loading). For decades the seismic loading was Zone 0; it has recently been increased to Zone 1, which, out of four zones is very low.
Although the theatre is physically connected to the office building the two are on separate title and is being restored "by others". From here on reference to "the building" will mean the office building unless otherwise indicated.
The building structure consists of structural steel fully encased in concrete. The appearance of the encasement is such as to indicate that composite action is a reasonable probability. Two steel columns have been exposed and the sizes would indicate (and here I am guessing; calculations have not been completed) that steel stresses would be in the order of 13,000 p.s.i. without composite action. The perimeter walls are of brick masonry a foot or more thick. The floors, including the roof, are concrete slabs approximately six inches thick. There are no cracks or other signs of structural distress anywhere in the building.
There are no drawings of the original structure and no calculations for reference. There is no bracing, at least none yet discovered. Two or three connections have been exposed and found to be riveted moment connections. The structural nature of the elevator shaft has not yet been determined. In the absence of further evidence, the lateral load resistance is expected to be provided by the masonry (shear) walls with the moment resisting steel (composite?) frame acting as a backup.
The structural oddities I referred to earlier are related to the floor slabs. Due to a fire in the elevator penthouse one of the elevator drive units (3,000+ pounds, I'm told) fell off, went completely through the roof slab, and made a hole (about 18 inches square) in the sixth floor slab where it remained until the fire department's crews removed it. Despite the hole in the sixth floor there is little other damage to that slab bay; the roof bay was completely removed by the fire department's crew. Based on limited observations to date, the slabs appear to be one way slabs with no temperature reinforcing. The reinforcing consists of 3/4" (19mm) smooth bars at about 6" centers, bottom steel only. The facts that there are no visible cracks in any of the floors and that the sixth floor was able to "catch" a 3,000 pound elevator unit plus all of the concrete rubble from the roof slab and sustain only very moderate damage, indicate that there is very little safety concern with the structure of the building; never the less some investigative work should be carried out.
Given that some slab openings must be cut to provide for an internal exit; and an existing abandoned elevator shaft most be enlarged to accommodate a new, larger elevator there is significant opportunity to carry out a significant amount of both destructive and non destructive testing. I am planning to take cores for testing from each significant slab cut out, to map all of the main floor for reinforcing locations. I'm also planning to test some of the steel rods to confirm yield strength. I am further planning to conduct Schmidt Hammer testing of a large part of the structure.
Although I don't have any specific problems at the moment any comments or suggestions any of you might have to offer would be more than welcome.
H. Daryl Richardson
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