Shear design for column with shear on both axes? Biaxial shear 1

[S275]

Hi,
If there is a column subjected to shear forces along both axes (Biaxial shear) - (It is also subjected to biaxial moment)- I have no problem for the flexural design of the biaxial moment, but I'm not sure about the shear, should I simply take the resultant shear force = sqrt([Shear_x]^2+[Shear_y]^2)
then consider it to be applied along the axis subjected to maximum shear?

I hope my question is clear enough.
Thanks in advance

 

[S275]

By the way, the column is rectangular in cross section.

 

[S275]

By having further thought, the shear force applied in each side of the column is resisted by the stirrups cross section area perpendicular to the force direction, hence each side to be designed separately and choose the lower spacing.

It is a situation when thinking loud helps to reach the solution.

Have a nice day everybody

 

[ishvaaag]

As you see the thing is under active research. Since we are dealing more and more with 3D models, every kind of solicitation is showing and we need simple models and tools that help us to do well the thing.

The separate addtion you perform will be safe as long due to the biaxial behavior neither stirrups, rebar or concrete strut don't exceed their limit design values. This is not discernible directly from the two separate orthogonal shear designs, even if taking the worse stirrup schedule.

http://ww2.integer.it/Web_1/database_locale/Fib Praga_2011/pdf/025 477 345 1 Mark SE.pdf

 

[ishvaaag]

Another reference

http://es.scribd.com/doc/47265631/589-CORTANTE-BIAXIAL-EN-COLUMNAS

 

[ishvaaag]

the previous project can be downloaded from 4shared.com freely.

http://www.4shared.com/get/SdcjtLzr/589_CORTANTE_BIAXIAL_EN_COLUMN.html

A modern simplified approach

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc52622.pdf

 

[S275]

Thanks Ishvaaag for these valuable references I didn't find any useful material about this topic while searching.

The first reference is saying you should use a reduction factor of 0.75 for a circular section, isn't this strange? because circular section will always be having uni-axial shear and moment!

Second reference is in Spanish which I don't understand. Third one needs more careful study.

I am not sure that I understood your opinion above:
"The separate addtion you perform will be safe as long due to the biaxial behavior neither stirrups, rebar or concrete strut don't exceed their limit design values."

Do you mean if I took the resultant shear force =sqrt([Shear_x]^2+[Shear_y]^2), it will be safe while if I considered each side separately it won't?

I'm using BS8110, and as I know it doesn't mention the case of biaxial shear, is it?

Best regards

 

[ishvaaag]

Hi, S275, well, taking the vectorial sum separately for each side might work if in each case uniaxially leads to a satisfactory design; the main problem I would have with such approach is that doesn't bear relation with the actual solicitation, even if for most cases (if the separate checks and designs are satisfactory) appears should lead to a conservative design.

In any case, there being some literature out there the wiser approach would be to examine it to see what it has about.

Respect the particular case of a circular column I like you see it perfectly reducible to one uniaxial shear case. Other thing is that most tables and procedures of design address the rectangular shapes in uniaxial shear. Then we must start a search for the correct design in shear of circular members, for it is clear that exactly the same procedure is not warranted, and may end in the recommendation there given of such reduction in capacity when compared with the same stirrups laid on a rectangular shape of the same depth, or whatever it states.

Let's make some searches on the capacity of circular members in shear.

 

[ishvaaag]

For a start

http://publik.tuwien.ac.at/files/pub-bi_7783.pdf

 

[ishvaaag]

http://www.crpd-hk.com/Publications/TechnicalNotes/Technical Note TN01.pdf

Quote of following article

"According to ACI Code 11.2.3, for circular members, the area used to compute c V is taken as the product of the diameter and effective depth of the concrete section. It is permitted to take d as 0.80 times the diameter of the concrete section."

http://site.iugaza.edu.ps/aalmadhoun/files/Chp5-Shear.pdf

enough for the matter...

 

[S275]

Thanks a lot Ishvaaag I appreciate your help

Yesterday I have done some extra searching and one interesting finding is in the JSCE "Japan Society of Civil Engineers" - Standard specifications for concrete structures, 2007

http://www.jsce.or.jp/committee/concrete/e/Standard_specification/JGC15_Design_1.0.pdf

Bottom of [Page 161] equation C9.2.1, gives a relation that: sum of design shear force to design shear capacity along each side squared should be less than 1.

Anyway, The first reference you posted gives easy way to determine the reduction factor.

Thanks again
Regards