Anyone have PCA notes on ACI 318-05?

[blackmaddog]

I am using the PCA notes on ACI 318-99 and am questioning if something is right. I am following example 23.4 - "Design of Precast Panel by the Alternate Design Method (14.8)". The book uses Ase (effective tension reinforcement) to calculate 'a' and Mn. I question whether this should be As instead of Ase.

Comparing the moment capacity I calculate vs. an Enercalc model of the same wall, I get much closer to the Enercalc moment capacity using As instead of Ase. Can anyone explain what Ase is and why you use it instead of As? I assume it may be a way to account for the interaction of compression + bending.

 

[Lion06]

I have PCA Notes for '05. I'll look for the example you reference, but Ase is typically reserved for the effective area of an anchor (i.e. one that is threaded).

 

[ishvaaag]

have not but ... Might it be that the ultimate capacity of some prestressing steel present is recommended to be accounted for ultimate failure?

If the tensile unitary deformation puts both steels at their yield capacity, you may account both for the flexural strength by whatever appropriate method. Or the tensile stress the presstressed steel shows at the analyzed ultimate stage, anyway. It uses to happen at disgusting deformations with sections quite cracked but I have seen as accepted practice for prestressed sections and always in limit moment strength.

 

[blackmaddog]

To clarify, this is a reinforced (not prestressed) design based on ACI 318 14.8.

 

[ash060]

It is the effective area of steel used to calculate you effective moment of inertia and for calculation of "a". It has been revised in the 2008 code because in previous codes it was to liberal.

The new formula = As + (Pu/fy)(0.5h/d)

 

[blackmaddog]

Thanks for pointing out the revised equation Ash. Although the 2008 ACI code isn't adopted by the 2006 IBC, since the original equation is liberal, I think I will use the new one.

After reading the commentary of the 2008 14.8.3, I am still wondering which equations to use the Ase in. The last sentence of the commentary section indicates that it is used to calculate 'c' in Eq (14-7). But should we be using Ase or As to calculate Mn and corresponding 'a' value? Since the code doesn't give us the Mn equation, my gut says use As (more conservative) but the PCA notes say Ase.

 

[ash060]

You should use Ase becuase your N.A. will be lower becuase of the axial force.