Longitudinal reinforcement on retaining wall footing or foundation 1

[COEngineeer]

All of the examples I have for retaining wall design never show any calc on longitudinal rebars in the footing. My supervisor always tell me to put #5 @ 12 or close to 12" for foundation wall. What do you guys usually do? What do you check usually on longit. rebars?

Never, but never question engineer's judgement

 

[Lion06]

Just check it for Temperature and Shrinkage.

 

[COEngineeer]

shrinkage for the footing crossection only right? Thats what I thought too but I have been doing what the boss told me. I ll tell him.

Never, but never question engineer's judgement

 

[Lion06]

Yes, just T & S for the foting. I guess if you wanted to check the footing to span over a soft spot in the soil you could, but I can't see any reason to do that, unless you know of a problem (maybe they excavated under the footing and didn't grout it solid). Either way, that would be a construction issue, not a new design issue.

 

[COEngineeer]

How about the transverse top reinforcement on the footing (for heel reinforcement), is there a limit on the spacing from ACI?

Never, but never question engineer's judgement

 

[Lion06]

I would follow the spacing limitations for slabs - 3h or 18", whichever is less.

 

[JKW05]

I usually provide the T&S based on the footing section with spacing limits similar to what StructuralEIT says above. I also usually provide a couple of #4 or #5 bars at the hooked bar as well, just so they have something to tie it to.

 

[COEngineeer]

Another question, does my transverse reinforcement need to exceed T&S (.0018xAg)? Or can I just use the As I got for flexural?

Never, but never question engineer's judgement

 

[Lion06]

If you have tension, you can't use less than T&S steel. You can use T&S, but not less.

 

[hokie66]

In reality, the longitudinal bars in a retaining wall footing are not really necessary except to support the main reinforcement and to serve as distribution steel. Providing the code required amount of T&S steel is appropriate, if that gives you enough support for the main bars.

The place where more bars can do some good is in the bottom of the wall, because the wall is restrained by the footing and will tend to crack at about 10 ft centers.

 

[spats]

BULL! hokie66 that longitudinal bars are not necessary... minimum reinforcing is 0.0018 x Ag. The only other thing you can do is design the footing as plain concrete (ACI 318, Chapter 22), but how would you determine bending moments in the longitudinal direction to check concrete stress?

Treating a continuous wall footing as plain concrete for transverse bending, however, is common, if it's not a cantilevered wall. This usually results in a thicker footing, but it's better than having to put 0.0018 x Ag transverse. Also keep in mind that reinforcing, to do the most good, needs to be fully developed. Often, continuous footings are not wide enough to fully develop the transverse bars.

 

[hokie66]

In the longitudinal direction, a reinforced retaining wall is normally much stronger than the footing in bending, so the footing doesn't need to be reinforced in that direction. Many concrete basement walls are built on unreinforced footings.

In a cantilevered retaining wall, I didn't object to the use of .18% steel in the longitudinal direction, although providing adequate support bars for the main bars in some cases can require more than this amount. The OP's supervisor who uses #5 @ 12 sounds like me.