RAM Elements - Forces at Member Ends Sign Convention

I am trying to understand the forces at members ends sign convention. I've started with a simple example - simply supported beam to confirm the direction of "shear in 2". Based on the sign convention diagram I would expect to get two negative values because the direction of force at the ends of the beam is downward (aka in the negative 2 direction). Meaning that is applying a force in the negative, local 2 direction. However, I get a positive value. See images below:

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  • The sign convention for member forces at the end have always been a bit confusing.  For on-screen display, and for most of the reports like "Member Forces at Significant Points" we use the same sign convention. 2 positive values in your example, sign reversal for a uniformly loaded beam (see below). But for the report "Forces and Ends" the output is at the node (point of view from the node you might say) and opposite hand at the K (end) node. 



    Answer Verified By: RFreund 

  • Thanks for the response. A couple follow up questions:

    1. When performing the connection design, it seems like this report would be the most useful though, right? Assuming you were going to create some sort of program that takes forces from one of the reports, it seems like this would be what you would want so that you always understand which direction the force is going. Using the on screen display or significant points sign convention would seems like it would be harder to program which direction the force is going, but maybe I'm wrong here. Does RAM Connection pull these forces from "Member forces at ends"?

    "point of view from the node you might say" - So would you say this is a "reaction" at that node? If so, am I saying this correctly - The output "Member forces at ends" is actually the force applied to the end of the member? 

  • We already have fully integrated connection design with Ram Connection, and the member end force sign convention or translation is fully automated in all modes. I refrain from using the term "reaction", except for external supports and springs and in the global axis. This has more to do with which free-body diagram we are looking at. The End Forces report is similar to what we show in STAAD.Pro, by the way, but I prefer the member forces at significant points report myself. 



  • "I refrain from using the term "reaction", except for external supports and springs and in the global axis."

    - OK that's fair. However, if you were to replace the other members that frame into that joint with equivalent springs/supports and then look at the reactions report you would get the same results, correct?

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