Strip Footing: Transverse Steel Slways Necessary?

[sgunn]

Let's say you have a small continuous strip footing (wall footing), with a very nominal (small) load. Something like 16" wide x 12" deep with an 8" CMU wall bearing upon the footing.

Granted you'll have at least 2 continuous #4 bars longitudinally, but is it really necessary to have transverse bars perpendicular to the longintudinal steel? Do the shrinkage & temperature requirements apply here, even though the footing is below frost depth? Granted there is shrinkage taking place during drying/curing, but it seems a small issue given the small cross section of the footing.

The ACI code doesn't seem to properly address this type of situation. Upon reviewing similar constr. docs. on various projects, sometimes the transverse bars will be spec'd, sometimes not.

Of course, the contractor never wants to put these in, and many times they just leave them out.

This is a question I've been trying to answer for some time, but cannot find any definitive info.

I welcome anyone's input.

Thanks.

 

[sgunn]

Obviously I made a typo in the thread title. It should read "Strip Footing: Transverse Steel Always Necessary?"

Thanks.

 

[jike]

For nominal strip footings that work as unreinforced footings, I use two longitundinal bars and require that they be wired together with a transverse bar at 4 feet oc. I have seen too many times where the longitundinal bars roll off the brick support into the sand as the concrete is being poured.

It is not an ACI requirement but I think that it is needed to assure that the longitundinal bars wind up where you want them.

 

[whyun]

ACI 318-99 Section 7.11 addresses lateral reinforcement for flexural members. (Latest edition I own...)

Shrinkage/Temperature steel requirements per Section 7.12 seems to be intended for "slabs" although I see it as a general practice by many to use these ratios for elements other than slabs.

 

[dik]

We often use strip footings without transverse reinforcing - nearly all houses on strip footings. One of the latest projects was a 4 storey condo. The soil bearing capacity of 10KSF, the footing concrete as plain concrete with 2-15M longitudinal and no transverse steel. One of the old tables from ACI Design Handbook has values for design using plain concrete footings.

Dik

 

[dik]

Forgot to add that any shrinkage cracking will be at right angles to the wall and not likely interfere with the flexural strength.

Dik

 

[14159]

I second jike. That's exactly what we did at my old firm.

DBD

 

[miecz]

I put longitudinal reinforcing (2#5s) in the bottom of the wall (and the top), not in the footing. The footing can be unreinforced. This way, your wall is a deep beam, reinforced top and bottom.

 

[sgunn]

Thanks for all the replies. Its interesting that many of you have your own way of doing it, and there doesn't seem to be a consensus as far as the 'proper' way to do it. This, of course, is also what I find in practice when reviewing drawings produced by other A/E firms.

Another thing I have noticed is that the structural design software we use at our firm always calls for transverse bars in a strip footing design no matter how small of a footing or light of a load. It always puts in .0018 x gross area for the transverse steel. I guess the engineers at the software company are being ultra-conservative.

 

[PSlem]

.0018 is the temp steel requirement, but if you check ACI 318 you will see footings are exempt. I don't spec transverse.