Lateral Stability and 4" Settlement Difference
Lateral Stability and 4" Settlement Difference
(OP)
We are designing a 3 story external stair tower adjacent to a structure. The specifications require that the two structures allow for 4" settlement difference. The aluminum stair tower requires an enormous amount of bracing to be free standing.
How can I attached to the adjacent structure for lateral stability and still have the vertical movement required?
How can I attached to the adjacent structure for lateral stability and still have the vertical movement required?






RE: Lateral Stability and 4" Settlement Difference
RE: Lateral Stability and 4" Settlement Difference
All kidding aside, that's a tough one, but you wouldn't be here otherwise.
Could you "clamp" a member to the structure, and provide an elastomeric bearing pad between the surfaces that have to move? You wouldn't develop friction forces this way, allowing the pieces to move vertically relative to each other. The clamping pieces would keep your stairs from pulling away from the building.
RE: Lateral Stability and 4" Settlement Difference
I have considered a bolted connection to the adjacent structure, with 8" vertical slot. But, there is not a structural application for bolts in slots longer than "long-slots". So can this transfer and load orthogonal to the slot? Obviously it can, but is it allowed
http://www.FerrellEngineering.com
RE: Lateral Stability and 4" Settlement Difference
I have considered vertical elastomeric pads. But this would allow for free movement vertical and horizontal. Thus, no lateral restraint.
And again, a very long vertical slot could provide horizontal control. But, there is no design reference for the shear capacity of the bolt. There could even be bending of the slot edge, due to the long size.
http://www.FerrellEngineering.com
RE: Lateral Stability and 4" Settlement Difference
RE: Lateral Stability and 4" Settlement Difference
RE: Lateral Stability and 4" Settlement Difference
Something's wrong with the criteria. First of all the structure itself is not likely capable of handling a 4" settlement. All the plumbing connections would go, and most other utilities would be affected.
4" of differential settlement is generally an unacceptable site condition and would require remediation of the soil conditions. If your building is on deep foundations and the stair tower is supported by poor soil conditions at the ground level, then consider ground remediation for the stair tower.
4" differential would also mean that the stairs won't match the landings. That's a life safety issue and a code compliance issue.
A slip connection could be done, but could you guarantee it would still slip in a year, two years...
This just doesn't sound right...are you sure it isn't a typo or missing a decimal point??!!
RE: Lateral Stability and 4" Settlement Difference
RE: Lateral Stability and 4" Settlement Difference
We have designed two as self-supporting structures and no attachment to the adjacent structures. But, as usual we are discussing the options for a more efficient design. Using aluminum we are trying to minimize welding and are using primarily bolted X bracing.
http://www.FerrellEngineering.com
RE: Lateral Stability and 4" Settlement Difference
RE: Lateral Stability and 4" Settlement Difference
A little elaborate but I had not considered it. Your detail allows vertical movement. But is there enough horizontal resistance to provide lateral stability?
http://www.FerrellEngineering.com
RE: Lateral Stability and 4" Settlement Difference
That being said, something seems off with the criteria. 4"
seems like way too much.
RE: Lateral Stability and 4" Settlement Difference
I know the 4" is ridiculous, it may have been their indirect way of keeping me from connecting to their building.
http://www.FerrellEngineering.com
RE: Lateral Stability and 4" Settlement Difference
The piles looked like WF sections, maybe 18" deep, and up to 135 feet long.
Funny thing is, when they set the pile in the guide frame and attached a vibrating hammer, many of the piles slid down and drove themselves, upwards of 50 feet, just from the weight of the pile and the hammer.
"Ground" is just a concept in South Louisiana. I believe the 4" spec is realistic.
Mike Halloran
Pembroke Pines, FL, USA
RE: Lateral Stability and 4" Settlement Difference
ht
RE: Lateral Stability and 4" Settlement Difference
You can figure out if I'm serious or not. Even I don't know.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask