What are E_c (S), E_c (D), and E_c (V) in composite beam design?

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

• E_c (S) is the modulus of elasticity for strength design.
  
  
  • For LRFD, E_c (S) is taken directly as the modulus of elasticity of the material assigned to the composite section.
    
    
  • For ASD, E_c (S) is calculated as 33 * gamma_c^1.5 * √f '_c (ksi), where gamma_c is the weight per unit volume (kips/in³) of the material assigned to the composite section.

• E_c (D) is the deflection modulus of elasticity, given as E_c (S) / (creep factor), where the creep factor is specified in the Preference menu.

• E_c (V) is the vibration modulus of elasticity, given as 1.35 * E_c (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.