Boundary Steel In Shear Walls

[CURVEB]

We have a concrete shear wall with vertical concentrated steel at the ends (something like boundary elements). My question is related to the spacing requirements for ties in these elements.

I was told that ties for these elements would only be required if:
1) The reinforcement is required for compression
- or -
2) The reinforcement ratio is greater than 1%.
(per ACI Chapter 14)

I was also told that if the ties are required by either of the above provisions, there is no code-prescribed spacing limitation (IE you wouldn't need to meet the detailing requirements of ACI 318-08 7.10.5) . So in this example, even if we have a 10" wide wall the ties could be spaced 12" OC.

I'm not sure I buy this however. Section 10.10.3.6 implies that if you include your compression steel in a wall, even if it is less than 1%, you need to provide code-minimum ties.

To simplify my questions:

If I have a compression member integral with a wall with greater than 1% steel, do my ties have to meet 7.10.5?
If my steel is only required for tension, but is greater than 1%, do I need to provide ties and do the spacing limitations of 7.10.5 apply?

Ultimately, I'd like to match my tie spacing to my horizontal wall spacing. I have horizontals at 12" OC, but in a 10" wall if I have to meet 7.10.5 for my boundary ties those would need to be at 10".

This is in Seismic category B.

 

[CURVEB]

Bump. Any thoughts?

 

[KootK]

For walls not specifically detailed for high seismic ductility, I think that it's as simple as this:

If a compression load creates a demand for reinforcing in excess of 1%, you need ties meeting the column provisions. Otherwise, you don't need the ties.

I'll do a little more fact checking when I'm back at the office and have ACI handy.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Section 10.10.3.6 implies...

Are you sure about this section reference? My 318-08 doesn't have this clause.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

Looking over this I agree that it does appear ACI 318 begins by stating that walls need to be designed for compression with ties on the longitudinal reinforcement. Then, ACI 318-08 my interpretation is section 14.3.6 overrides this previous implication that ties are always required. In the past I've considered long, lightly loaded bearing walls with in-plane bending to fall under 14.3.6 if I can ensure they have sufficient compression strength considering plain concrete only and thus do not need transverse ties.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[CURVEB]

Koot - my apologies: I believe I was looking at 10.3.6.2.

 

[KootK]

Thanks for the clarification CurveB. With that in mind, I stand by my original comments. While not explicitly stated in ACI, I'm confident that 10.3.6.2 is meant to apply to discrete members like beams and columns rather than walls.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CURVEB]

Thanks KootK. Your insight is very much appreciated.