Max Bar Spacing for Tension Flexural Steel - ACI 24.3.2

[JoelTXCive]

A question came up today regarding the max bar spacing provisions of ACI section 24.3.2.

Section 24.3.2 tells you to use the attached table to compute the max bar spacing for one-way slabs & 'beams'.

Depending on your clear cover, it effectively gives you a max bar spacing of 12". (f_s = 2/3 of 60ksi which is 40 so you get 12 x 40/40 = 12")

My question is: Does this provision apply to the vertical steel in cantilever retaining walls? (they are cantilevered 'beams')

In taller retaining walls 10+ ft in height, there will often be a required steel setup for the bottom of the wall, and then a reduced setup for the top few feet. I believe I have seen 15" and 16" vertical bar spacing in this region, which would violate the table below.

Thoughts?

 

[MotorCity]

I take "beams" to be synonymous with flexural members (i.e, retaining walls).....so yes, in my opinion it applies. The purpose of a maximum spacing is for crack control, which should be a concern for retaining walls. I believe (somewhere) there is also a stipulation of 18" max bar spacing, so the 15" and 16" you have seen would comply with that.

 

[JAE]

I guess I'd take Chapter 11 of ACI 318-14 to use as the governing sections on rebar spacing requirements for walls.
Look specifically at 11.7.3.

In both Chapters 24 and 11 there is no commentary suggesting otherwise.

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[JoelTXCive]

Thank you all for the input.

I'm coming down with MotorCity on this. If a retaining wall is a flexural member; then the above table would apply.

Chapter 11's scope (11.1.1) does not include cantilever retaining walls in the list of applicable walls.

Further, 11.1.4 says for cantilever retaining walls we should go to chapter 22, which is the general sectional strength chapter.

Once we get to Chapter 22, then I believe the Chapter 24 serviceability requirements apply and voila...we are subject to the above table.

There must be room for some engineering judgement here. I pulled up TxDOT's standard retaining wall details; and every single one of them has 15" vertical bar spacing for the top several feet of wall. Those plans have been built thousands of times; and are still being used now. Perhaps AASHTO has different standards.