Separating CMU stair and elevator from lateral load resisting system

[jplay2519]

I'm designing a 3 story storage center with light framed cold formed shear walls, elevated composite deck concrete slabs and metal roof. The foundations and cmu stair/elevator walls are designed by others. I haven't had any correspondence with the other engineer and we got comments back from the municipality. The engineer stated that his walls are not to brace the structure. I have not had to deal with this situation before,but I'm trying to determine how I'm going to separate the walls from the floor laterally. Just provide bearing angles attached to the walls with slotted connections to the floor system and compressible joint fillers between the edge of floor and wall? This changed my whole design of the building pretty much (I know I know why wasn't there a conversation between the other engineer and myself?). I didn't talk to the engineer because when I sent the drawings to the client for review I never got anything to coordinate with and they just sent them in so now here we are. Any ideas on separating the walls from the lateral system? I have the ideas but feasibility/construct-ability are HUGE components that I'm not sure I'm hitting.

 

[JAE]

Slide bearings and slip connections are tough to really get to work. To really separate them you may have to simply provide an expansion joint around them.

Alternatively, there is the concept of deformation compatibility - you provide the stair engineer with assumed story drift values and their stair needs to be checked for that imposed drift.
Under that drift, the stair does end up taking load, perhaps more load than your drift would suggest because the stair is probably more stiff than your system.

The two really should be designed as one system by one engineer unless there is a pure separation joint.


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[haynewp]

I recently reviewed a project that had this separation of shaft CMU and structure. Any separation joints would need to be sized for seismic including Cd to preclude impact.

 

[jplay2519]

So we'll just have to build walls around the shafts and have the deflection accounted. Their details will have to change, I was confused about how they had the floors bearing directly on the shaft walls but stated that they designed it separate from the lateral system. sigh, I'll get to it.

 

[P205]

haynewp how big of a separation did you see built into the separation joints, 25mm, 50mm? Also, these would need to build with each successive storey, would it not?

 

[haynewp]

I don't know if they ended up using the joints or redesigning the lateral to include the CMU shafts. This was a project we were hired to provide review comments at 90% stage and were not engaged after that. For seismic joints, it depends on the seismic values of the site and the lateral system's drift and amplifier. Isolation joints in higher seismic areas can get larger than a couple of inches and I don't think such isolation around the interior of a building's CMU shafts is very practical.

 

[Teguci]

A 3-story building shouldn't need more than a 2" EJ. I'd think keeping the structures separate (no slide bearings) would be the cleanest way to deal with this design mistake. Whoever designs the foundation needs to account for how loads are handled and should document how elements relate between different lateral bracing systems.

As an aside, who is the Engineer of Record?

 

[haynewp]

If H/50 drift is applicable then that can result in more than 2" of a total joint at the upper floor.

 

[jplay2519]

The building engineer is the EOR, the foundation engineer is a sub. Not sure why this is even a thing. I think it's the way the owner does his projects. We need to provide a better coordination.

 

[JAE]

For a three story in a high seismic area you could get joints at the roof of 6 to 8 inches (150mm to 200mm).



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