What are Ec (S), Ec (D), and Ec (V) 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 directly as the modulus of elasticity of the material assigned to the composite section.
- For ASD, Ec (S) is calculated as 33 * gammac1.5 * √f 'c (ksi), where gammac is the weight per unit volume (kips/in3) of the material assigned to the composite section.
- For LRFD, Ec (S) is taken directly as the modulus of elasticity of the material assigned to the composite section.
- Ec (D) is the deflection modulus of elasticity, given as Ec (S) / (creep factor), where the 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.
