URGENT: question about rebar detail around windows in basement wall

[DavidButler]

I'm in the process of building the basement for my own new home. As an engineer myself, I understand each engineer develops their own prescriptive or 'template' designs for certain common details. In that context, there's a detail in my structural engineer's wall rebar design for which I'd like a 2nd opinion. Not that it matters but my structural engineer is acting only in an advisory role, as I don't need a stamped design.

The basement is fully below grade with 6" poured-in-place walls just under 10' in height (9' below grade). The rebar mat is #5 in an 18x18 grid, with closely spaced vertical members on either side of the 60x48 windows, which will have deep window wells. My question is about the terminus of the lateral rebar members that abut the windows. The engineer's detail calls for 180-degree hooks wrapped around the twin vertical members (see attached diagram). My concrete crew somehow missed that detail and say they can't do this bend in the field (should have been done by the rebar supplier). The rebar matt is installed and the forms go up tomorrow.

I wasn't able to reach the engineer today so I contacted a couple of colleagues (builders) who have lots of basement experience and neither had ever seen that detail before, casting doubt on its necessity. I obviously want to avoid sending the forms crew home tomorrow and halting construction to have these members fabricated per spec. The site is rural so logistics is an issue (1-1/2 hr drive to rebar supplier). On the other hand, I don't want to ignore the detail. I would be grateful for any informed opinions.

 

[dik]

OP: I can attach the actual *.dwg file, if you can use it. The drawing was incomplete, and was updated because I had some time to do it.

Dik

 

[DavidButler]

As noted in any earlier comment, my structural engineer made it clear that the floor diaphragm, which is set inside and anchored to the basement wall, is a key part of getting the 6" wall to pass. Even without that detail, I wouldn't dream of backfilling without the floor system in place.

BTW, the plan calls for a (perpendicular) partition wall roughly midway on the longest span (47 ft). Would building that wall with 6" reinforced CMU's (i.e., as a buttress) buy anything in terms of performance margin? When I brought this up during our initial conversation, my structural engineer seemed to discount any benefit, which seems counterintuitive.

 

[XR250]

I am not a big fan of using framed partitions for the sustained loads of backfill. The loads will be substantial. If you can, use masonry or concrete with a proper collector on top.(I usually use a a dbl. LVL floor joist that is cont. across the building) The collector is key to making these function as intended.

 

[jayrod12]

I would side with your engineer on the idea that a partition, evenly properly detailed, will not provide much in terms of help. Your foundation wall spans vertically, so unless you provide partition walls at a tight enough spacing to force the exterior wall to span horizontally, they may never see any load.

Although it would cut down your diaphragm size, and therefore may stiffen the building as a whole. But in terms of direct benefit to the exterior wall, I don't see any.

 

[XR250]

Although it would cut down your diaphragm size, and therefore may stiffen the building as a whole. But in terms of direct benefit to the exterior wall, I don't see any.

Jayrod, I believe the IRC requires 'em every 50 ft.

 

[jayrod12]

Agreed, but he said it's 47ft long, within the allowable. I'm indicating that the presence of that demising wall makes no effect on the retaining capacity of the exterior wall.

 

[XR250]

I agree

 

[DavidButler]

Correct, the distance between end walls is 47 ft.

Your foundation wall spans vertically, so unless you provide partition walls at a tight enough spacing to force the exterior wall to span horizontally, they may never see any load.

If I understand this correctly, you're saying the dominant (constraining) load is along the height of the backfill, not the width of the wall, right? I'm curious why the IRC would stipulate buttress every 50 feet?

 

[jayrod12]

My bet on the 50ft would be diaphragm strength.