I have some question about wind load in piping analysis.

for example,the combinations as followed:
1) Operation 1
2) Operation 2
3) Operation 1+ wind
4) Operation 2+ wind
5) Wind = (3)-(1)
6) Wind = (4)-(2)

now i find total wind force (ie x direction) is not same in case 5 and case 6,about 20% difference.
what is the reason for above problem?
And which one i should used for total wind force ?

Thanks

Nonlinear restraints will change the effects of your occasional load just as it can change the effect of temperature as seen in the expansion case. If you search this forum for nonlinear restraints you will find a lot of information on this subject. The bottom line is that changing your operating conditions may change the effects of the same wind load because of nonlinear conditions in your piping system.

thanks for reply.
so you mean nonlinear conditions will change restraints force,and
sum of restraints force also will be changed.

i think sum of restraints force should be same,only restraints force distribution is different

The distribution will be different surely, but not the total integrated force. However, consider a case where we have a guide with a large gap. Say in your OPE1 case the gap is closed in the positive direction and in your OPE2 case the gap is closed in the negative direction. Now add the same wind load to both load cases along the same line of action as your guide. In one case the effect of the wind load may be to close the gap by moving the pipe twice the gap distance and in the other case the wind load would not move the pipe at all because the gap was already closed. It is safe to say that the effect of wind in these two cases is dramatically different locally and that in one case you will have a much larger stress due to the same wind load than in the other case as a result. This is the effect you are seeing in your analysis.

Now i change the friction variation value,not use default value.then the result of total integrated wind force is ok.the difference is smaller between case 5 and case 6.