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What are Ec (S),

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Ec (D)

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, and

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Ec (V)

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in composite beam design?

Answer: Values for Ec (S), Ec (D), and Ec (V) are given as follows:

  • Ec (S) is the modulus of elasticity for strength design.

    • For LRFD, Ec (S) is taken from the modulus used for deck properties.

    • For ASD, Ec (S) is calculated as 33 * gamma c1.5 * sqrt f c '.
  • Ec (D) is the deflection modulus of elasticity, given as Ec (S)/(creep factor), where creep factor is specified in the Preference menu.
  • Ec (V) is the vibration modulus of elasticity, given as 1.35 * Ec (S). This amplification coefficient is suggested in AISC Guide 11, page 12.

Since these modular ratio are different, transformed inertia varies between strength, deflection, and vibration analysis.