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Concrete Cracking Moment Formula

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Hi!

I have some questions about M_cr?

What's  different between Eq 9.9 and M_ct of ACI318-02?
For example, I have a continuous prestressed girder with draped
strands.
And then, near mid section of span (i.e. shear force may not be zero),

 Which formula can I use to get cracking moment?
M_cr =  I_g / y_t  (7.5 sq rt f'c + f_pe) (Eq 9.9)
M_ct =  I_g / y_t  (6.0 sq rt f'c + f_pe) (R11.4.2)
Should I limit M_ct only for V_ci (Eq 11.11), which has M_cr term?
(So, this M_ct is not 'actually' cracking moment M_cr.)
What causes factor to change from 7.5 to 6.0?
Is that for shear or prestressing force?

I am looking forward to your clear explanaions.

Thanks!

****Wontae Kim****


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