11.4.5 - Spacing Limits for shear reinforcement 2

[eit09]

I have an 18" square concrete column that has very little uplift and shear forces (couple kips). According to section 11.4.5.1 in 318-08 taking d/2 would require tie spacing of 7" c-c. This seams excessive as I normally see these ties spaced at 16" c-c. Could anyone provide more insight or is the d/2 pretty solid?

 

[rapt]

Are you designing this as a column or a beam. Chapter 10 might be more appropriate if it is a column!

 

[JAE]

If you are designing the column as a beam (i.e. very little axial load and more a flexural element) then the shear design for a "beam" follows this way:

1. If the shear Vu is greater than φVc then you must provide shear stirrups based on Equation 11-2 and Section 11.4.7 (i.e. Vs is calculated)
2. If the shear Vu is greater than φVc/2 but less than φVc, then you must meet 11.4.5 (your stated situation)
3. If the shear Vu is less than φVc/2 no shear reinforcement is required. (based on 11.4.6.1)

So if you are under condition 3 above, then you can essentially do what you like - providing ties or whatever to facilitate construction or to give you a level of warm fuzzies.

If you are in condition 2, then yes - you must meet the limits in 11.4.5.



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[eit09]

rapt: Currently I am designing it as a column. I looked through chapter 10 and the only guidance I found on tie spacing was section 10.13.8.4 but that is for composite section. Is there a section I missed that you could refer me to on tie spacing in Chapter 10?

JAE: With such low Vu values I thought shear ties would be more to facilitate construction/warm fuzzies also, but when I read 11.4.5.1 it seemed to be saying these are minimum spacing regardless of shear values. Thanks for your post made much sense and now am able to rationaliz vs tossing extra ties at the column.

 

[rapt]

Probably 10.9.3

 

[JedClampett]

Try 7.10.5.
They put it there to trick you.