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It’s applied to diaphragm in-plane shear strength. Φ is obtained automatically as 0.75. For a diaphragm that is entirely cast-in-place, Vn is calculated according to Eq. (12.5.3.3).
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Cross-sectional dimensions is selected to satisfy Eq. 12.5.3.4, for a diaphragm that is entirely cast-in-place where the value of √f′c used to calculate Vn is not exceed 100 psi.
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