From the STAAD technical reference, section 5.31.2.1 UBC 1997 Load Definition
"Ct< 0.42 if the units are in feet, and Ct> 0.42 if the units are in meter."
From UBC 1997
WHERE:
Ct = 0.035 (0.0853) for steel moment-resisting frames.
Ct = 0.030 (0.0731) for reinforced concrete moment-resisting
frames and eccentrically braced frames.
Ct = 0.020 (0.0488) for all other buildings.
Alternatively, the value of Ct for structures with concrete or masonry
shear walls may be taken as 0.1/ √Ac (For SI: 0.0743/ √Ac
for Ac in m2).
The value of Ac shall be determined from the following formula:
Ac = ∑Ae [0.2 + (De/hn)2]
My question is: where did the 0.42 limit come from in the STAAD technical reference? From the above, Ct is always less than 0.1 whether in SI or imperial units.
Another question, regarding the equation Ac = ∑Ae [0.2 + (De/hn)2], will STAAD detect vertical plates or surfaces modeled as shear walls to apply this equation if Ct was not user defined? Consequently, will it detect the first floor height and calculate De, and Ae?
