Strip foundation problem 3

[strathclydeo]

Using the shear stress for strip footings per the CERM it seems that negative stresses are frequently calculated. They give no reference for the equation, is there something I'm missing?

The equation is Vu=(qu/d)*((B-t)/2-d) where (B) is the footing width, (t) is the wall thickness and (d) is the critical depth.

 

[BAretired]

What is CERM?
What is Vu?
What is qu?



BA

 

[dhengr]

BA.... You and I are not going to be able to call ourselves Structural Engineers much longer, we just don’t speak the right language any longer. If you can’t speak in acronyms with a few adjectives and adverbs thrown in for seasoning, along with some special nomenclature symbols, and still not really explaining your actual problem in common language terms, you can’t be a modern engineer, any longer. We both need all the newer (gooder) engineering cookbooks. Never mind being able the define your problem or understanding the fundamentals, the recipe takes care of all of that, assuming you keep the salt and the sugar in different colored containers so you don’t get them mixed up. Screw fundamental understanding.

I’ve gotta tell you, I’ve given up even trying to participate in half the questions here on E-Tips, because you have to guess at what the real question and real problem are, and may be wasting your time at that. Then you probably don’t have the latest Ed. of the code or the software that they are plucking the obscure equation or nomenclature symbols from, even though the design of strip footings has been going on long before that Ed. of the code was foisted upon us, and some of those structures are still standing too. I often wonder if it makes any difference if they don’t understand some obscure formula, when there is every evidence that they don’t understand the fundamentals of the problem, by the nature of the way the question has been asked, without being able to define the problem.

 

[JoshPlumSE]

Vu is a standard ACI (Americant Concrete Institute) term for strength level shear on an element (beam, column, footing). Most US concrete texts will use this terminology.

Most US soil texts, I believe, will use the term q for the maximum calculated soil pressure in the footing. With the u subscript referring to the fact that this term was calcualted at ultimate strength force levels. That's not quite so widely accepted, but common enough that I would think most currently practicing engineers in the US would get it.

However, I do not know what CERM refers to.

 

[msquared48]

http://www.cerm.utep.edu

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[RFreund]

Civil Engineering Reference Manual?

EIT

http://www.HowToEngineer.com

 

[RFreund]

I still enjoyed DH's response though.

EIT

http://www.HowToEngineer.com

 

[BAretired]

JoshPlum,

I would have expected Vu (using capital V) to be a shear, but the units don't make sense. In this case, the OP probably means v_u, meaning a shear stress in the strip footing.

If he is getting negative values, it means that d>(B-t)/2 which would suggest shear is not an issue.

BA

 

[BAretired]

I should have added that the formula is no longer applicable when d>(B-t)/2 as it is out of range, so negative shear stress is meaningless.

BA

 

[paddingtongreen]

@JoshPlum, this is not an American forum, it is an international forum. We have similar problems when other nationals fail to identify their basis and nomenclature. Plus, I have been retired now for ten years, and some formulae have changed in that time although they do virtually the same thing.

I am amused, the spell checker doesn't like "formulae" it wants "formulas", my old English teachers must be rolling in their graves.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[SAIL3]

dh has sruck a nerve again...where are you, Julia Child, when we need you?

 

[BAretired]

dhengr

 

[spats]

Boy, did this thread get sidetracked! Strathclydeo needs to understand the principles involved, and forget about the formula.

 

[DST148]

@strathclydeo - Ref CERM 11th Ed, Eqn. 55-7: To make this formula work, the units will have to be consistent.
For example vu and qu in psf; B, t, and d in feet. The same thing applies to eqn. 55-8.

@spats - I concur