R/F for Increased Wall Thickness

[marinaman]

Here's one for you guys!

I've got a large concrete basement wall that I designed for a building. It was to have been 18" thick.

The GC, in his layout process, incorrectly placed the vertical wall dowels when he poured the footings. He misplaced the wall dowels by 18" when he installed them. The footings are large, and due to the schedule of construction, I need to work with what the guy has installed.

Ironically, the footing is in the right place...just the dowels are in the wrong place.

I was going to use the dowels that he has installed already, thicken the wall of 36" thick (original 18" thickness plus the layout error of 18"), and install another layer of vert and horz bars on the inside face.

My concern is.....the wall is now 36" thick! That's a thick wall! I'm thinking of using 0.0025 percentage area of steel, in each direction, on the inside face, to help control shrinkage and temperature cracking. He only did this for a 32' length of wall....and the other couple hundred feet of wall are ok.....so I didn't want to change the concrete type (normal 4,000 psi).

What is your gut reaction to the wall thickness and reinforcing needed to thicken the wall to 36"? At 0.0025, that's 1.1 square inches per foot. I was going to go with (1) #6 at 6" o.c. horizontally and (1) #6 vertically at 10" on the inside face.

 

[jayrod12]

Seriously cutting the dowels and epoxying new ones sure seems much easier and faster.

 

[KootK]

I like the drill and epoxy dowels too. If you went 36" and didn't do proper T&S, I'd worry that you'd be inviting undesirable, vertical shrinkage cracking in your wall. In reality, your wall probably pushes against a slab on grade for lateral restraint so the dowels aren't doing much. I doubt many engineers would be willing to omit the dowels entirely on that basis however. I wouldn't.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[marinaman]

I appreciate the input.

I am going to keep the cast-in-place dowels. The reason is that the walls are designed as cantilevered concrete retaining walls. The building is long and narrow with limited stabilizing elements that could have taken the lateral force of a pin-pin retaining wall into the floor diaphragm, so the perimeter walls were designed as cantilevered retaining walls.

For this reason, I want to keep the already poured-in-place fill side dowels. Cutting off the dowels and epoxying new dowels will not work on the tension face of these walls. I also checked, in the original design, the inside face of steel necessary should there be some pin-pin action that occurs.

That being said, I'm really more interested in opinions regarding a 36" thick wall and the reinforcing that would need to be present on the inside face. I have ample r/f on the outside face.

 

[jayrod12]

If it's on the fill side, could you do an upside corbel type detail to minimize the actual height of the 36" thick wall?

 

[Sawbux]

See ACI 318-14 16.3.1.2 & 16.3.4

16.3.4.1 gives minimum As = 0.005Ag, which is your 0.0025 for each face.

I think there was a provision in ACI 350 that allowed you to consider only the outer 12" of the wall for calculating the minimum reinforcing. (Tanks commonly have very thick walls.) But I couldn't find that in the newer ACI 318.

 

[hokie66]

Just thicken the wall up a ways, not full height. Would have helped with answers if you had originally said the wall was cantilevered.