nucstructural012
Structural
- Jun 8, 2020
- 8
Anyone worked on a base plate type design where you can't fix the base and must rely on friction to maintain some stability?
I'm working on a design to modify an existing ladder mounted at the top of a concrete deck, extending down about 25 ft to the floor at the base of the ladder. The problem with the existing configuration is that when analyzed for seismic forces vs the requirements for our plant, the ladder deflects too much and fails the anchors at its top side; this is due to a 5 inch gap from the ladder base plate and the stainless steel floor. The hurdle Im facing is that any new attachment to the ladder base can NOT be bolted or welded to the floor below, and therefore must rely on friction/sliding resistance to stabilize the ladder in a seismic event.
The conceptual modification idea is the bridge the gap by welding a few new members to the ladder base (likely a little metal working or shims to bridge the gap perfectly). I thought of adding short circular HSS sections to the ladder bottom for this concept.
However, I've thought about it and wondered if the best solution isn't some type of adjustable column(s) sitting on the floor with a top plate welded to the ladder base underside. Theoretically, I'd think the most stable attachment would be one exerting the most Normal Force back on the floor, giving the most sliding resistance. Since the gap is so small, wouldn't an adjustable column(s) (basically a floor jack) provide the most resistance? Wondering if anyone has dealt with: a base design not allowing fixity? Design using a wedge or relying on friction? Permanent jacking type design?
I've never ran into this type of design problem before. Hoping there are some thoughts out there!
Thanks!
I'm working on a design to modify an existing ladder mounted at the top of a concrete deck, extending down about 25 ft to the floor at the base of the ladder. The problem with the existing configuration is that when analyzed for seismic forces vs the requirements for our plant, the ladder deflects too much and fails the anchors at its top side; this is due to a 5 inch gap from the ladder base plate and the stainless steel floor. The hurdle Im facing is that any new attachment to the ladder base can NOT be bolted or welded to the floor below, and therefore must rely on friction/sliding resistance to stabilize the ladder in a seismic event.
The conceptual modification idea is the bridge the gap by welding a few new members to the ladder base (likely a little metal working or shims to bridge the gap perfectly). I thought of adding short circular HSS sections to the ladder bottom for this concept.
However, I've thought about it and wondered if the best solution isn't some type of adjustable column(s) sitting on the floor with a top plate welded to the ladder base underside. Theoretically, I'd think the most stable attachment would be one exerting the most Normal Force back on the floor, giving the most sliding resistance. Since the gap is so small, wouldn't an adjustable column(s) (basically a floor jack) provide the most resistance? Wondering if anyone has dealt with: a base design not allowing fixity? Design using a wedge or relying on friction? Permanent jacking type design?
I've never ran into this type of design problem before. Hoping there are some thoughts out there!
Thanks!