Tilt -Up Panel Base Connection

[haynewp]

I wanted see what members here are using for tilt-up panel base connections. I have seen probably hundreds of drawings that show a typical tilt-up panel that is doweled into an adjacent pour strip and simply rests on top of a continuous footing. I started thinking about this detail the other day, particularly for high seismic areas. I am not really sure exactly what IBC/ACI intends the connection to be for tilt up panels to resist seismic.

But in general, even in non-seismic areas, it appears that engineers are either:

1. Counting on the in plane wall shear to be transferred through the rebar dowels from the wall into the pour strip

2. Relying on friction between the bottom of the panel and the top of the footing to take out the shear.

I don't think I agree with the first option, because the adjacent slab may be directly on top of a vapor barrier AND it looks like they are counting on the rebar itself to transfer shear. (Unless they are somehow justifying shear friction, but there is no intentionally roughened surface??)

I guess you could justify the second option under most cases, but I for some reason don't feel comfortable with it for high seismic.

One of the only things that I found on code requirements is this:

http://www.seaoc.org/pdfs/seismpdfs/UBC/tiltup.pdf

Which seems to be using the same concept of transferring shear through the dowels, the only difference is it also requires additional dowels going from the footing into the pour strip.

I know how to solve all of this by using embed plates and anchors into the footing. I am just looking for a discussion on this dowel into pour strip/dowel into footing stuff in high seismic areas or just using friction at the base of the panel in low seisimc areas.

 

[JedClampett]

I reviewed a tilt-up project in a high seismic area (CA) and was very impressed with the additional details required to accomodate seismic. There were hold-downs welded to grade beams at edges and openings. Beyond this there were pilasters built into the tilt-up, special "leg" reinforcing and collectors built in.
I had never seen such extensive detailing for tilt-up. We consider ourselves lucky if the contractors notice any additional bars. But I've learned that contractors in California are used to and expect such things and can build them. This applies not only to tilt-up, but CMU, concrete, etc.

 

[msquared48]

Usually I call for these panels to be welded to ebbedded steel plates in the strip footing, and with the side seam welds to provide the dead load of the adjacent panel too for uplift, the whole wall would have to move as a unit for the base to fail in shear. Years ago I got curious too, and looked in more detail at the wall system. I stisfied myself that there was not a problem and have not worried much since. More concerned with single, isolated wall panels than strings of them.

Mike McCann
McCann Engineering

 

[haynewp]

Well I looked at this again today and of course it you can use shear friction across a joint where the concrete is not intentionally roughened, you just have to use 0.6xlamba instead of 1.0xlamba. So I was wrong in assuming a roughened surface or monolithic pour was required.

Therefore, maybe the detail is alright for the dowels going into the pour strip and then other dowels going from the pour strip into the footing. But it seems like embed plates in the panel with angles anchored into the footing would be better. This is at least a direct connection to the footing. And from what you guys are saying a little more is being specified in high seismic areas anyway.

For high seismic areas when you see the direct connection into the footing using embeds etc., do you still also see the typical dowels used from the panels into a pour strip?

In my area of the country, it is normally just the dowels into the pour strip and that is it.

 

[msquared48]

I do not dowel into the pour strip - only weld to the insert in the strip footing.

Mike McCann
McCann Engineering

 

[lsmfse]

Here in CA, we use embedded plates in the footing and panel ends and field weld for uplift and in some cases shear. Occasionally, we will use embedded plates mid-height of the panel to transfer shear between the panels.

 

[MarcbSE]

I do not weld the panels directly to the footing, but install embed angles in the adjacent slab. The panels are welded together as needed and then welded to the slab embeds. In the projects I have done one side of the slab was always in place prior to erecting the panels so installing dowels from the footing into the slab was easy. However, if a pour strip was required then dowels would be needed into the pour strip as well.