Basement wall @ slab on grade

[WWTEng]

Typically there is exp joint/bond break between slab-on-grade & bottom of the basement wall. Yet, the wall is assumed to be pinned at this location (not designed as cantilevered). Does this mean that the joint/bond break is assumed to be compressed to the point where the force is transferred into SOG?

 

[hokie66]

If I have a slab on grade which has to resist a horizontal force, I don't want a soft joint. I would turn the plastic up the wall to try to establish a bond break, but wouldn't want to use a compressible material.

 

[BAretired]

It is normal practice to consider the wall laterally braced by the grade slab. I recall that a common practice forty or fifty years ago was to use 3/8" A.I.F.B. (Asphalt Impregnated Fiber Board)between the slab and the wall. The fiber board would compress as required under the lateral force, but the amount of movement was not very large and I do not recall any problems resulting from that movement.

Today, many engineers, like hokie, avoid a soft joint so the wall movement is limited to the amount of slab shrinkage.

There does not appear to be a problem with either detail.

BA

 

[WWTEng]

Hokie, so what is the correct way to call out the joint at this location? I guess I am asking how you would note that on the drawings.

Thanks.

 

[hokie66]

I would show it in section, show the plastic turned up the wall, and further note that no compressible material is to be used in this case. But I do agree with BA that it is not a big deal.

 

[RFreund]

What about a shear key between wall and footing?

EIT

http://www.HowToEngineer.com

 

[Quanski]

Agree with RF, shear key is a must.

 

[BAretired]

You may use a shear key if you wish, but it is by no means a must. Dowels from the footing into the wall are usually more than enough for the horizontal shear.


BA

 

[hokie66]

The reaction at the footing is not the question here. The OP wants to resist the wall by using the slab. We don't even know what kind of footing is used, and if it is capable of resisting the force.

 

[BAretired]

Right, hokie the slab is deemed to be the reistance.

BA

 

[focuseng]

So how much growth are we talking about for a basement slab? Temperature expansion and contraction is probably nill due to a temp variation of 10-20 deg. Moisture shrinkage is contraction only. I can see a bond break but is the EJ material going to do anything? WFIW, I always show the detail at the slab and wall with the EJ in my drawings out of habit but I can't ever remember seeing one installed -EVER! (including my own home not designed by a professional).

I have doweled the slab to the wall in the case of ICF walls due to this issue where the form is 2+" thick and the contractor doesn't want to remove/cut the forms (and ties).

MAP

 

[hokie66]

focuseng,
The purpose of a soft joint in an interior slab on grade is not to allow movement perpendicular to the wall, but parallel to it, thus limiting restraint which leads to shrinkage cracking. The soft joints are used frequently because they are easy to install, but turning the plastic up will do the same thing. If in an exterior situation where debris is likely to accumulate, then a joint for movement perpendicular to an obstruction like a wall or curb is necessary.

 

[focuseng]

Right Hokie66. I don't disagree and think you are spot on from your very first response post. The point from the OP is regarding compression of the joint in idealizing the situation where the slab is used to resist inward pressure forces WHEN an EJ is used. I am simply trying to talk out loud about why the EJ isn't necessary in a typical basement situation even though it is so readily drawn that way (including by office many times) by force of habit. Also trying to relate it to what I see in the field about the EJ never getting installed anyway (residential projects).

I think I need to pay more attention to this "boiler plate" detail. I can already dread the discussions with the architect bosses about why it is missing from the drawing... <shrug>.

MAP