huangyhg

retaining wall: critical section for flexural design
been looking at the design codes for the design principle relating to the section where design should take place for flexure:
while retaining walls are not specifically adressed, the following:
base: on the face of the column/wall
wall: considered to be a slab => use standard cantilever span => h + d/2 i.e half an effective depth into the base.
these two principles are contradictory. i have seen example calcs where design is done at the face and others where it is doneat the centre of the attached member.
can anyone assist in defining what the correct position for design is? i am looking for a design code definition, not a principle.
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if you are looking for a design code definition, you need to include the design code you're looking for! there are lots of jurisdictions where design is based on performance, not prescription. in such a jurisdiction the principle governs by definition.
in my opinion the design for flexure occurs upon a plane cut through a section, not at the face.
i could only help you with the principles involved. i suggest you post the code you work to, and hope someone can help!
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
i suggest it is too much to expect of a code that it tell you where the critical sections are for every type of structural element. but even though you don't want it, i will tell you anyway: retaining walls are normally designed for bending at the top of the footing, and the footing for bending at the faces of the wall.
thanks guys
the critical sections you mention, hokie66, are what i also normally use.
the question arises from what the definitions in the bs 8110 code we are working to indicate. as i mentioned, the code specifically refers to the critical section in regards the base and refers one to normal flexure design of cantilever slabs for the wall. if one interprests the code in that manner, ther are quite a few engineers who are designing incorrectly.
i was considering whether i have interpreted the matter incorrectly, hence the question.
fot that matter the aci 318 code seems to imply the same thing.
hokie66-
for the design of the heel, i take the critical section at the location of the vertical bars at the back of the stem, around 2-1/2" in from the back face. not a big deal, really, but i'm surprised to read that it is normal to take the section at the back face.
miecz,
you are correct, of course, that when the bars are in tension, the lever arm should be from the bars rather than the face. but there are so many variables involved in retaining wall design and construction that i don't think it matters much.

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