Hollowcore Slab + Cold Formed Steel Walls 1

[srazahz]

Hello,

Please refer to the attached sketch, the hollowcore slab is falling slightly short of the actual bearing length and I am looking to fill in the void properly and provide proper bearing and connection for jack and king studs that are taking larger loads. What would be the best way to do that?

 

[MIStructE_IRE]

Can you cut out the top of the cored, drop a bar in and fill as shown?

 

[Agent666]

Move wall over?

Replace wall with narrower studs at closer centers?

Put additional narrower studs in till it works, and pack out exterior face?

Can bearing at other end of hollowcore be reduced/extended?

Can you give some actual dimensions, is the wall 4" wide or 12", how much is slightly short of the bearing length (1/2" or 3"), etc?

 

[srazahz]

@MIStructE_IRE: I do not think that would be possible, the client is suggesting to put straps on the outside and screw them to the wall both above and below the slab.

@Agent666: Moving or changing the wall would be an issue since this situation is already existing.
The wall is 8" wide and about 1.5" short.

 

[Celt83]

check out this thread: Link
was a rough slab edge condition but some of the options there could be modified to work with planks.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[srazahz]

Thanks for the link, it is very helpful.

 

[KootK]

I'd recommend designing the tracks, studs, jambs, and their connections to simply deal with the bearing shortfall. Realistic tolerances always need to be considered in these systems and, unless you're willing to detail the plank running out past the studs, there's really no way to get the plank consistently out under the outer flange of the track which would be ideal structurally.

Some additional questions to help us help you:

1) Is there a concrete topping? Will it run beneath the studs?

2) Is there any kind of bearing pad/strip between the plank and the studs below?

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[srazahz]

1) Is there a concrete topping? Will it run beneath the studs?

2) Is there any kind of bearing pad/strip between the plank and the studs below?

Truth is, I am unable to definitively answer both of these questions, but I would assume (from the limited information that I have) that there is no concrete topping and that the plank is bearing directly on the top track of the wall.

 

[KootK]

Bearing directly on the studs has always unnerved me a bit. When you see it in the wild, two things will always happen:

1) There will be some transverse dishing/cupping in the planks and;

2) If the walls are panelized neighboring panels will never be exactly the same height.

This unfortunately means that uniform plank bearing on the wall is a myth.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[bones206]

I was thinking the same thing about the bearing pad. If there is one and it's centered on the wall, then the load eccentricity should be zero from the wall's point of view, right? As long as the plank is at bearing over the full width of the bearing strip.

 

[KootK]

If there is one and it's centered on the wall, then the load eccentricity should be zero from the wall's point of view, right?

It would improve eccentricity greatly but not eliminate it. The front of the bearing pad would compress more than the back as it matched the plank end rotation. I usually assume that the load is applied about 1/3 the width in from the edge of the bearing pad.

Unfortunately, I don't believe that there are often bearing pads with this system. Often the planks are embed welded to the top track or an HSS on the top track which precludes the gap created by the bearing bad unless clip angles etc are used.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[srazahz]

I have seen HSS sections being used as load distribution members for open web steel joists and trusses.

In this case, the CFS tracks are bolted together using bolts going through the plank. But there isn't a bearing pad or a load distribution member between the tracks and the plank.

 

[MIStructE_IRE]

Is hollowcore on cold formed stud a common construction technique over there? Its not something I’d be terribly keen to do I must say..

 

[KootK]

Less common that HC on steel, concrete, or CMU but happening often enough to show up on the radar screen a couple of times each year. It can make for some pretty icky diaphragm situations in my opinion as well.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[jayrod12]

It can make for some pretty icky diaphragm situations in my opinion as well

I still think it's cute that you are of the opinion most people pay attention to this.

 

[KootK]

I still think it's cute that you are of the opinion most people pay attention to this.

Simultaneously accurate and patronizing. I wish I could turn of the the part of me that "sees diaphragm failures" like that kid in the Sixth Sense.

I worked on a forensic thing a year or so back that was six stories untopped plank on CFM. Corridor and unit thing with the plank perpendicular to the corridor and nothing for chords other than, I guess, the perimeter walls acting as shear walls. All I could see was the accordion action. And the monster P-delta impact of a zillion pound concrete deck 70' in the air flexing like Ronald McDonald's smile. Thankfully the CFM engineer refused to supply until a third party engineer took a look at the lateral.

Another one I see a lot is untopped, hollow core roof decks with jogs in plan where the chords should be (plank perp to chord). If you think that's tough in steel / wood, imagine what form it has to take in untopped hollow core.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[MIStructE_IRE]

I completely agree. How are these guys justifying the diaphragm action? Or is it ignored/forgotten as jayrod alludes to..?

 

[KootK]

You can do a plank diagram with the right attention to detail, even untopped (there's even a NEHRP guide). It's just that nobody really seems to put forth that attention to detail. I see a lot of what I call "in betweeners". They tell me, as the precaster, to supply XXX PLF shear capacity in the panel. So I do. And I ignore the glaring lack of chords, struts, and the associated detailing.

Personally, I hate not having a topping on my plank jobs when I'm EOR. I always push hard for it on the floors at least.

MISEIRE's attachment...

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[MIStructE_IRE]

Interesting guide! Thanks, always good to have these things up the sleeve..

 

[jayrod12]

In my experience, locally there's maybe a dozen or so designers that pay any attention to diaphragm detailing when it's hollowcore. It's sad really.

The problem is, we haven't seen any specific failures that can be attributed to poor diaphragm detailing.