IRC 2015 Foundation Reinforcing 2

[BSE05]

Table R4041.2(1) is new to code and requires one #4 bar top and middle of 8 ft high concrete basement walls.

I am reviewing a homeowners claim against the builder that this was not done for his new home construction. Does anyone have a theory on what this reinforcing does for the wall? It is not enough area of reinforcing to offset concrete shrinkage.

Thanks for any input.

 

[WARose]

Are you sure you don't mean Table R404.1.2(1)?

My guess: it probably accounts for some sort of differential movement/settlement.

 

[KootK]

This is the thread that you want: Link. That thread took a lot of twists and turns but, for me at least, the conclusion was that the rebar is to temporarily allow the walls to span horizontally and not collapse on construction workers before the floor deck is installed to brace the tops of the walls. That that seems to go back to some incidents that occurred long ago that we don't wish to repeat. Viewed in that context, the owner's claim may well be unjistified unless the walls actually did collapse during construction.

 

[r13]

Is this a basement/foundation wall? Per the State of Washington's "Plan Review General Requirement" in the Building Safety section, "3. Foundation walls supporting more than 4 feet of unbalanced backfill shall be constructed in accordance with Table R404.1.(2) (1 through 9)." I think the purpose could be made clear through reading this provision entirely.

 

[r13]

For the basement/foundation wall, it seems IRC does not prescribe horizontal reinforcement, but mandate the minimum. So from the perspective of code compliance, if no horizontal reinforcing shown in your client's wall, the designer may be held liable for any damage occurred after the construction.

 

[StrucDesignPE]

This is the thread that you want: Link. That thread took a lot of twists and turns but, for me at least, the conclusion was that the rebar is to temporarily allow the walls to span horizontally and not collapse on construction workers before the floor deck is installed to brace the tops of the walls. That that seems to go back to some incidents that occurred long ago that we don't wish to repeat. Viewed in that context, the owner's claim may well be unjistified unless the walls actually did collapse during construction.

Does that really make sense though? IRC 2015 Section 404.1.7 prohibits placement of backfill against the wall until it has reached design strength AND it is anchored to the floor above or braced at the top of the wall. Regardless, I have seen many poured basement walls with cracks and horizontal bows in the middle third of the wall because a) the builder backfilled too early or b) the builder used crappy sill plate ties that are never installed correctly (I'm looking at you Simpson MAB15 - not Simpson's fault, just the folks installing it wrong).

 

[KootK]

Does that really make sense though?

If you read that other thread carefully, you'll know that I really have no idea if it makes sense or if that is actually even the intent. Clearly, nobody knows with much certainty. It simply is the most plausible of the available explanations in my opinion based on the information provided in the thread. That said, it sure does make a ton of sense if:

1) You question the diligence of your average residential contractor with respect to following the "no-backfill" rule and/or;

2) You have zero confidence in 90% of the floor deck to wall connections floating around out there to actually resist backfill loads.

And you can put me quite solidly in both camps.

Regardless, I have seen many poured basement walls with cracks and horizontal bows in the middle third of the wall because a) the builder backfilled too early or b) the builder used crappy sill plate ties that are never installed correctly (I'm looking at you Simpson MAB15 - not Simpson's fault, just the folks installing it wrong).

Soooo... does that not justify the very kind of belt and suspenders approach that the horizontal bars may well be provided to accomplish? Just looking it it from a practical standpoint, what other possible function could such a ridiculously small amount of horizontal rebar possibly accomplish? It 'aint crack control, that's for sure. Maybe some ability for the wall to span soil soft spots with the wall acting as a very deep, horrifically under-reinforce beam? In my experience, neither residential nor commercial codes expend much effort worrying about serviceability issues like differential settlement. That's the kind of thing you higher some engineers for.

 

[r13]

My previous call "the designer is liable" was a mistake, it is the builder's feet have to be held over the fire, as design drawings, specifications, typical details do not require professional seal, if IRC provisions are followed.

 

[BSE05]

Thanks for the feed back.

The wall is an 8 foot high 10 inch non reinforced concrete wall on a strip footing for a two story residence.

The structural engineer for the home owner is stating that the wall will now without the horizontal reinforcing, require steel perimeter plates bolted to the top and bottom of the wall around the entire perimeter to compensate.

The ultimate goal (my guess) is to run up a huge cost for repairs for a law suite or settlement agreement.

 

[r13]

I wonder why to omit two #4 bars to start with. Quite a saving for 100 units, maybe.

 

[StrucDesignPE]

Just looking it it from a practical standpoint, what other possible function could such a ridiculously small amount of horizontal rebar possibly accomplish? It 'aint crack control, that's for sure. Maybe some ability for the wall to span soil soft spots with the wall acting as a very deep, horrifically under-reinforce beam? In my experience, neither residential nor commercial codes expend much effort worrying about serviceability issues like differential settlement. That's the kind of thing you higher some engineers for.

That seems to be what the horizontal reinforcing is for. It's my understanding that the IRC code requirements are based on ACI 332. See 2015 IRC R404.1.

This is a quote from ACI 332-08:
"R7.2.8 Horizontal wall reinforcement is placed to reduce cracking that can result from restraint against volume changes due to shrinkage and temperature change. The
serviceability requirements of residential concrete allow for crack development. "

 

[r13]

This requirement can be traced back to 2009 IRC. It was modified from the 2006 IRC, section R404.1.4, which stated:

 

[KootK]

@StructDesignEIT: yeah, we discussed the ACI332 some in the other thread too. Looking at it again, with fresh eyes, I'm especially curious about the bit highlighted in yellow. What do you make of that?

1) What exactly are "the serviceability requirements of residential concrete"?

2) Is not all reinforced concrete design predicated on crack development? Or are we implying that especially huge crack development is okay for residential concrete?

I'd actually be pretty okay with wall restraint cracking if only it would remain vertical, as planned. It seems as though all the ones I get to look at in the field wind up being at 45deg wich, obviously, doesn't make one feel too great about the vertical spanning capability of a vertically unreinforced wall.