I can be a little bit more specific on the iterative method. A cross-section is cracked only when the bending moment exceeds the cracking moment M r. This mehtod is true if the out of plane loads are significantly high such that the concrete cracks. Delta_u is calculated by using eq 14-5 and then applied in eq 14-4 to get M_u. Whereas in direct design method, the concrete is assumed to be cracked.
In iterative method(ACI318-08) the value of Delta_u is varied using equations 14-8 & 14-9, until the value of M_u converges in eq. Once a reinforced concrete beam is cracked, the section reduces dramatically from the gross moment of inertia to the cracked moment of inertia. And, the article clearly explains why ACI has decided to adopt the method given in UBC.Īlso, there is difference between using the iterative method and direct P-Delta analysis method.
Here's an interesting article on why the slender wall design section in ACI318-02 &05 has been modified in ACI318-08.Īs you all know, the method given in ACI-318 is similar to what's given in Unified Building Code.
