Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Subarea: Original Author: Bentley Technical Support Group Logged Nov 2014, AutoPIPE V8i 09.06.01.10 Problem: Can you please explain the forces and moments, why in the middle of a segment the magnitude of the forces flip from (-)ve to (+)ve at the same node point. Answer: Please see the following AutoPIPE help section: Help > Contents> Contents Tab> Reference Information> Results Interpretation> Pipe Forces and Moments: Global Option, read this entire document. As mentioned in the document: In order to interpret the meaning of pipe forces and moments it is important to understand the cross section on which the forces act. consistent procedure to define the cross section all pipe segments have a segment direction at any point there will be two cross sections to consider, namely the - side, which is immediately before the point, and the + side, which is immediately after the point the cross section for pipe force output is obtained by removing all of the segment up to that point. The pipe forces and moments act on the exposed cross section positive forces and moments act on the cross section in the positive X, Y and Z directions With that said, let us consider the following example: Cantilever beam made up of 1 segment (A), Origin point = A00 segment direction (+)ve to the right (A01, A02), and finally a Force = +1000 acting on the Example #1, first off consider the restraint reaction as a force (Red arrow facing left on A00 ). For determination of Global Forces and Moment for the pipe, the Segment Direction is very important. Consider Segment A, and suppose we want to obtain the forces and moments acting on the cross section of the pipe at node A01. What you will basically do is that moving in the segment direction from start point (A00), remove all the previous points leading up to A01 (Boxed in Red rectangle and light red fill). So now you will have an exposed section of the pipe available to you at node A01. Now for that remaining piece to remain in equilibrium, a force of magnitude 1000 acting in the negative X direction would be required (Green arrow). This is your Global Force reported by AutoPIPE for A01. Example #2, now suppose the segment direction was reversed, as seen below on Segment B: Similarly for segment B, suppose we want to find Global forces and moments acting on B01. Moving in the direction of the segment from start point (B00), remove all the previous points leading up to B01 (Boxed in Red rectangle and light red fill). You will have an exposed section of the pipe available at node B01 (You will need to look left). For the remaining piece to remain in equilibrium, a force of magnitude 1000 acting in the positive X direction would be required (Green arrow). This is your Global Force reported by AutoPIPE for B01. Example #3, now suppose the the cases above were combined where these example was composed of 2 segments Segment A origin was at A00 progressing to the Right at A01, and Segment B origin was B00 progressing to the left joining segment A at node point A02. as seen below: Furthermore suppose we want to find Global forces and moments acting on A01. Looking at the (-)ve side of A01 from segment A point of view the force is -1000, However, looking at the (-)ve side of A01 from Segment B point of view the Force is +1000. Thus giving the affect of the force changing at the same point but in reference to how AutoPIPE calculates the forces and moments, the results are correct. If you have concerns about how the forces and moments are calculated in this 3rd example, reverse one of the segments (A or B but not both), so that both segments are progressing in the same direction. Then the calculated forces will have similar signs. See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? Bentley's Technical Support Group requests that you please submit any comments you have on this Wiki article to the "Comments" area below. THANK YOU!
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