The best way to answer this question is to relate things in the <em>static</em> sense first. Consider the case (shown in the figure below) where two elements share a support, and a vertical load is applied.





For this model, assume the load on the restraint from each of the two beams is also 100. Viewing the static restraint report will show a reaction of 200, not 300! Why? Because the applied load of 100 goes straight out the restraint (it doesn't load the beams).

Now, in the case of dynamics, each element's mass is determined, then this value is split equally between the two nodes (of the element). So any given node will have a mass equal to 1/2 of each element framing into it. This mass is then accelerated (F=Ma), to determine the system load(s).

The system of equations is solved and the nodal movements are determined. From these movements, elemental forces and stresses are determined. The restraint report may differ from the sum of the element forces based on whether or not the sum of these forces is equal to (Ma) - it doesn't have to be. This is the same idea as in the static example above.


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Regards,
Richard Ay (COADE, Inc.)

[This message has been edited by rich_ay (edited January 26, 2000).]

[This message has been edited by rich_ay (edited January 26, 2000).]