question about load case

The standard method of C2 to determine wind load is:
L1: W + P1 + T1 (OPE)
L2: W + P1 + T1 + WIND (OPE+WIND)
L3: W + P1 (SUS)
L4: L1 - L3 (EXP)
L5: L2 - L1 (OCC,WIND EFFECT)
L6: L5 + L3 (SUS + OCC)

Why cann't we get wind efffect directly by add a case L7: Wind,
then: get L8: L3+L7 (sus+occ)?

Because running a load case with just "WIND" won't properly account for any non-linear restraint changes due to other loads.

For example, say due to "W+P1+T1", you have some gaps that close and some +Y supports that lift off. This is the restraint configuration you want the wind to see, hence you need "W+P1+T1+WIND". This yields an OPE case with wind. (Running just WIND, wouldn't have gaps closed or +Y supports lifted off.)

Now you subtract your typical operating case from this to get "the effects of wind considering non-linear boundary conditions". You then add the stresses from this case to those from Sustained for your occasional code compliance.

Dear Peter,

The Caesar II documentation - technical reference manual - page 6-21 describes the possible effects of nonlinear restraints in occasional loadcases.

Hope that helps a bit,

Veit Bockemühl
vb@esn-gmbh.com
www.esn-gmbh.com