Hi, Small question, does it mak

[TarikHKJ]

Hi,

Small question, does it make a difference which rebar goes above which in a slab or a footing mesh in the xy plane?

Does it depend on the rebar diameter or the length of the X or Y dimension?

 

[MIStructE_IRE]

Makes no real difference in my view provided you account for the extra distance in your calculation of the effective depth while also ensuring that cover has not been compromised.

 

[TarikHKJ]

Yes that was my guess but wanted to get expert opinion

Thank you for the reply

 

[dhengr]

TarikHKJ:
Certainly, you want to pay attention to the proper cover for the outer layer of steel. Then, you would want that outer layer, with the greater ‘d’ value, to relate to the orientation which had the greatest moment demand.

 

[KootK]

Small question, does it make a difference which rebar goes above which in a slab or a footing mesh in the xy plane?

Not unless the two layers have different demands for flexural tension capacity. Usually that is not the case for square, axially loaded footings.

 

[Rabbit12]

It absolutely can in certain applications. I was involved in a flat slab design where we were trying to keep the depth as small as possible. We needed the bottom mat running in a certain direction for it to work. Although we had several notes on the plans and details showed it correctly, the contractor messed it up and got to rip out some rebar to fix.

As KootK indicates, typically on a footing it won't matter. If you're a designer, it's all dependent on what you used as d. Unless I have no choice I try to make the direction irrelevant.

 

[BridgeSmith]

For the footings (mostly pile caps, technically) that we do for bridge foundations, we always design the bending assuming they may screw up the order of the layers in the field. We use the smaller "d" in the design for each direction.

 

[TarikHKJ]

Thanks all for the insightful replies,

The question was generally speaking not specifically footings or specific situation.

So the little bit extra millimeters in "d" for the layer that has higher demand in flexural capacity can make the difference in some situations such as the one mentioned by Rabbit.

Love this website

 

[BridgeSmith]

That's true, but as Rabbit12 gave anecdotal evidence for, and I alluded to, actually getting the extra "d" you're counting on is not a sure thing many times. For a thick footing, I suggest assuming they'll screw up the order of the layers and not worry about it. For thinner members, you just have to make sure somebody is watching them closely and assuring they get it constructed right.