Maximum Reinforcing Steel in Concrete Beam 3

[SlideRuleEra]

Have been looking high & low for the maximum reinforcement allowed per ACI 318-02 (need to use that particular revision for this project). All that I can find is the minimum (paragraph 10.5).
Advice appreciated.

http://www.SlideRuleEra.net

 

[JAE]

Looks like they revised section 10.3.3 - removed the 75% x rho(balanced) limit and now use a strain limit in the steel.

Read 10.3.3 through 10.3.5. Specifically 10.3.5 is the new limiting provision.

 

[UcfSE]

Just to add some to what JAE wrote, you have a minimum steel strain et of 0.004 in stead of the maximum reinforcement ratio. In order to use the phi factor for flexure of 0.9, you have to have a minimum et of 0.005. With f'c = 4ksi and fy = 60 ksi and using et_max = 0.004, you get a maximum reinforcement ratio of around 0.72*rho_balanced. The new limit is similar to the old 0.75*rho_balanced and is slightly more conservative, for these numbers anyway.

 

[JAE]

I just did a few rough calcs and got the following:

[ρ](maximum) = (0.3643(f'c)([β]1)) / fy

This is for a rectangular, singly reinforced beam. Someone want to check me on this?

 

[WillisV]

JAE is correct, this method was moved from the appendix to the main body in '-2. As noted in the commentary of 10.3.5 0.75rho balance was approximately a strain limit of 0.00376 as opposed to the 0.004 in the new code.

 

[UcfSE]

I have the same 0.3643 factor.

 

[SlideRuleEra]

Thanks to each of you on your timely advice.

http://www.SlideRuleEra.net

 

[miecz]

Looking at PCA notes on 318-02 (page 6-17), it seems that the factor is 0.85*ec/(ec+es), where ec=.003 and es=.005. The factor is then 0.319.