Story Drift
Story Drift
(OP)
I'm designing a 1 story retail building approximately 75'x230' in size. I'm providing moment frames on the ends to accomodate my wind loads (no seismic in this area). Is it too conservative to say that both the deflection of the roof diamphragm and the story drift from my frames should be accumulative when looking at the overall drift of the building? Or should they be assumed as seperate entities?






RE: Story Drift
I had a similar project where I felt the diaphragm was deflecting too much, so I designed the interior columns as "flagpoles" to help resist lateral loads.
DaveAtkins
RE: Story Drift
At 75'x230', assuming a reasonable roof height, you probably can still get 1 1/2" roof deck to work. May need to beef up you fasteners towards the ends to get the diaphragm shear strength rrequired. But nothing to to far out of the ordinary.
RE: Story Drift
RE: Story Drift
You say that you have no seismic in your area, but under the IBC, everywhere has seismic, just to greater or lesser degrees.
With seismic design with SDC B or higher, you check lateral drift (with limits) for a seismic load on your building (which may be less than the wind), but this is the "design" seismic. To check drift, you also have to include the Deflection Amplification Factor, Cd in your diaphragm and frame drifts which can get large with a long diaphragm like you have.
So be sure to check that as well unless you are an SDC A.
RE: Story Drift
1. Is it possible to put another frame near the center?
2. A rep from Loadmaster came to give our company a lunch seminar. The system uses a composite roofing system to gain much higher shear loads and span distances. Here's their webiste: http://www.loadmaster.net/ Might be something you can look into.
RE: Story Drift
Or, if your contractor is on board already, ask them how much it would cost to use a 36/7 pattern fastening for the whole building. It may surprise you how relatively inexpensive this is. Particularly if you allow them to use fasteners instead of welding. I've had to do 36/7 fastening before, and have been surprised how little the extra attachments cost.
RE: Story Drift
RE: Story Drift
RE: Story Drift
haynewp,
Take a look at the ASCE 7-02 commentary section CB.1.2 for Drift of Walls and Frames from the effects of wind. They suggest limits between 1/600 and 1/400. I've generally used 1/400 and have had pretty good luck. I would think H/240 could me a litte excessive. But thats just my 2 cents.
RE: Story Drift
RE: Story Drift
RE: Story Drift
If so, you need a separate set of columns at the center. Now you have 2 separate roof diaphragms and 4 moment frames.
RE: Story Drift
RE: Story Drift
RE: Story Drift
It is approx. H/450