Strip Footing

[strawhats2000]

Hi,

This is typical strip footing drawing used here. In Chudley's Contruction Technology, it is the reverse which is true and I believe he is right as B1 bars should span along the shortest distance.

Actual Typical Drawings per Structural Engineers and Actual Practice

Roy Chudley's Construction Technology instruction

Thanks for your comments.

 

[jayrod12]

Those two details appear to have the steel oriented the same way... am I missing something obvious?

 

[strawhats2000]

No in typical detail, the main bars are made up of R6 mild steel and the main bars are made of T10 main bars. In Chudley's book, it is just the contrary, the longitudinal bars are actually the distribution bars whereas the shortest bars along the width of the strip footing are the main bars.

 

[jayrod12]

I think the bar size is irrelevant when comparing details. You size them as required for your performed analysis. I know a few engineers who design the longtiudinal bars assuming they've lost a certain length of bearing and the footing then needs to span a gap. Depending on what size of gap they used in their design, those bars may need to be larger diameter than the transverse bars if the bearing capacity is good.

You should not be picking bar sizes straight out of other people's typical details.

 

[strawhats2000]

Hi Jayrod12,

Here is the 2 design compared:

https://ibb.co/g7NG2PC

 

[JAE]

I think this is just random labeling of bars.

"Main" bars vs. "Links" or transverse bars. The design is the same. The labeling is inconsistent.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[jayrod12]

I agree with JAE, what you call the bars, i.e. main, links, longitudinal, frank, bill, sally, joe.... doesn't matter. As long as they are depicted in the appropriate direction for the analysis it really doesn't matter what you call them. To me, the bars going the short direction would be the "main" bars if someone asked. But that type of confusion is why I use the terms longitudinal and transverse, there's no ambiguity there.

 

[dhengr]

Strawhats2000:
I think that what you may not be seeing is that there are sorta to different design problems/approaches here, which end up looking much alike but meet two different needs. As
Jayrod12 suggests, one issue is that the strip footing be able to bridge over (span over) soft spots in the soil, over its length of run. This favors the long rebars being in the bottom layer. And, we see plenty of cracked found. walls which indicate this should be considered; there has been some differential settlement (movement, bending) at soft spots. We seldom put longitudinal rebars in the tops of strip ftgs. at corners, but we often see differential settlement cracking at corners of the walls, which indicated maybe we should have. Alternatively, when the allowable soil bearing pressure is low and the wall loads are higher, this will cause you to need a wider strip ftg. to carry the loads. And, then the ftg. bending action perpendicular to the wall length will favor the short bars (perpendicular to the wall axis) being the bottom layer of rebars. Even so, I can put these short bars in as the upper layer, and just increase their size or reduce their spacing to accomplish the same design objective. And, this may have some constructability advantages in that you can support 2 or 3 of the long bars every 10’ and lay (and tie) the short bars on top of them, as apposed to having to hold the short bars up to tie them. It’s pretty much a matter of engineering judgement and experience, and your pictures and question don’t really show this aspect of the problem.