How to find worst case of concentrated forces?

Question

Hi, 
 I am modelling a pipe system where concentrated forces and moments are applied (in Gravity case) at the interface connection points. Is there a way to check which sign combination that gives the worst result regarding stresses and restraint forces? F.ex. for applied F1, F2, M3, M4, the worst combination could be -F1, +F2, -M3, +M4, etc. 
 
 Appreciate any answer. 
 HJ

Bilal Shah · Answer

Heidi, 
 
I think in this case you would probably need to define the combinations of these applied concentrated loads/moments using different load cases. For example, if you had two input force values say FX and FY, both of which could reverse in direction you can do either of the following: 
 
Insert the forces in individual load cases: 
U1 = FX 
U2 = -FX 
U3 = FY 
U4 = -FY 
 
Then you can create the following result non-code combinations (Load > Combinations > Non-Code combinations) with Combination method as Sum: 
Summation method: Sum 
+FX+FY [Case 1 = U1, Case 2 = U3] 
+FX-FY [Case 1 = U1, Case 2 = U4] 
-FX+FY [Case 1 = U2, Case 2 = U3] 
-FX-FY [Case 1 = U2, Case 2 = U4] 
 
You may then be able to output the maximum load on your support out of these combinations using another combination with combination method set to say Sign Max: 
 
Summation method: Sign Max 
MaxFXFY [Case 1 = +FX+FY, Case 2 = +FX-FY, Case 3 = -FX+FY, Case 4 = -FX-FY] 
 
Alternatively, you may define the input load combination +FX+FY in your load case U1, +FX-FY in load case U2 and so on. And then create another combination with U1, U2, U3 and U4 to get your worst case scenario. 
 
From post processor I meant the combination dialog, which is part of all AutoPIPE editions. 
 
Hope this helps.