Slip Connection at Top of Non-Load Bearing CMU Partition

[DaveAtkins]

I am designing a large pre-engineered steel building with frames that span about 133 feet (ice hockey rink). Part of the building has a mezzanine, really a second floor, with a sports bar and an exercise room. The non-load bearing CMU walls aroung these spaces extend to the roof above (the architect shows them butting to the roof, which of course should not be done).

I want to devise some sort of slip connection to brace the top of these walls up at the roof, but I don't know how much the roof will deflect (pre-engineered, but not designed yet). If I assume the roof could deflect as much as span/180, this would be almost 9 inches!!!

Has anyone else seen this before?

DaveAtkins

 

[MotorCity]

I would suggest designing the wall as a true cantilever (no fixity at roof) or maybe you could embed a steel plate in the top of the wall and use a slotted connection at the roof.

 

[CJJS]

Are there any perpendicular walls that you could use as bracing? Depending on the horizontal span of the masonry wall that you are concerned with, you may be able to design it as braced (pinned) on three sides (bottom, and two sides where walls frame into it).

 

[UcfSE]

You could probably devise a slip connection using a bent plate angle with slotted holes and teflon washers, provided you have some good steel at the roof to which to connect.

 

[PMR06]

I agree with part of MotorCity's response, design your structure standalone, but then stay away from the metal building entirely. The vertical deflection may be as much as 9 inches, but what about the lateral deflection? Do you happen to have a copy of the metal building spec that would list their sidesway design criteria? Unless the exterior walls are CMU, I seriously doubt the metal building engineers kept CMU cracking in mind when they designed for sidesway!

 

[ntpe]

I have ran into this before. Call out a max. deflection that you can live with for the PEMB rafter. Then attach a bent plate to the underside of the rafter to accept the top of the CMU wall; like a deflection track in a metal stud wall. The "deflection track' should come in 2 parts -a bent plate attached to the rafter before the CMU wall is ran all the way up, and flat plates welded vertically to the bent plate crating the other leg of the track. You can provide some long slots with expansion bolts in the leg of the tracks, but I feel that only provides a place to bind and I usually don't. Provide a detail for the PEMB supplier so that they can properly brace the bottom flange of the rafter.

 

[DaveAtkins]

I basically did what ntpe suggested (the drawings went out yesterday). I left a 10-1/2" gap above the CMU walls (I allowed for purlin deflection as well) with a bent plate each side of the wall welded to each purlin (will probably be 5' oc) or purlins between purlins when the wall is parallel to the purlins.

But PMR06 raises a good point as well, and I'm not sure how to deal with that. I do think that vertical deflection of the frame is more likely than lateral deflection of the entire building, however.

DaveAtkins

 

[ntpe]

Remember, you can spec a max vertical deflection and a max sidesway, the PEMB supplier will design to your imits. By specing the deflection yourself, you know exactly how much movement that you have to deal with.

 

[DaveAtkins]

Good point, ntpe.

I plan to look at the PEMB shop drawings when they arrive--if the deflection is < 10-1/2", I can revise the detail.

DaveAtkins

 

[JAE]

ntpe - We do what you have suggested. The only tough thing is that the PEMB designers really get testy when you tell them how much drift, how much deflection, etc. to use.

 

[ntpe]

JAE - You are rignt about the PEMB designers, sometimes they don't want any restrictions, but they are not the EOR. I have rejected PEMB shops for noncompliance with the contract docs, this usually brings tham back into line.

 

[PMR06]

I agree JAE. In all of the projects we've had with PEMB's, we've had nothing but hassle! In each, the PEMB contract was signed well before anyone else got involved. Of course the PEMB guys sell owners flimsy pieces of junk, and then when more stringent deflections are needed later in the design phase, they come back with outrageous back-charges.

Good luck DaveAtkins! I'd love to hear a follow up on this.

 

[j19]

Whoa PMR06. The "PEMB guys" with the AISC-MB certification design to the same criteria as the rest of the steel industry. If there is no deflection criteria specified by the EOR, the architect or the building code then they are going to design to the serviceability limits in AISC's Design Guide 3. If you want something more stringent you need to let them know up front before they quote a price or let the owner know to expect change orders when you provide your criteria. If you are working with PEMB suppliers that are not AISC certified, then I can't tell you what you will get.

 

[JAE]

j19 - good points. But I have in the past specified, on my drawings, in big letters, a requirement to minimize drift and vertical deflections where I've got brick veneer (you know - the L/600 limits) and got nothing but grief over it.

 

[Loui1]

I thought PEMB design is govnered by it's own code.

If it were me, and seeing how much PEMB's deflect (especially during snow!) I would design any CMU structure inside the PEMB as standalone. You'll never be able to force the PEMB to design it to a tighter limit.

 

[jike]

There are many other issues with metal buildings as well.
I hope the Architect is not using a hung ceiling as there will be a noticeable sag when the roof deflects and then no sag where it is connected to the walls. Also, where pipes are hung from the roof structure and then go thru walls with a sleeve. Pipes may rupture with those kind of movements if not detailed correctly!

 

[JAE]

I thought PEMB design is govnered by it's own code.

Yes, I believe they do, but these metal building codes are simply more specific to the design of the lighter thickness elements. The building still must satisfy the adopted code in the jurisdition in which it is built.

 

[j19]

The Metal Building Manufacturers Association publishes the "Metal Building Systems Manual" but it wouldn't be classified as a code. I don't think I have ever seen a building dept. or project specs (other than Corps of Engineers) require it. The 2002 Edition is based on the 2000 IBC and it provides some commentary, etc on loads and load applications. I haven't been through all of it but I don't think it provides any loopholes for PEMB's but it does give some guidance on issues that are not adequately addressed by IBC. For example, it gives some pretty good information on open buildings that just isn't covered by IBC/ASCE 7.

 

[csd72]

Have you considered providing a separate cieling at the top of the CMU? This can be designed to spread the load to cross walls avoiding the roof entirely.

This type of situation is best avoided entirly by convincing the client to use framed walls instead. I have had problems with framed partitions and less than 3 inches of roof deflection even though there had been an allowance for movement.