Why isn't my total reaction force correct after a PSD analysis? When I list reaction forces with the PRNLD, PRRSOL or PRRFOR
commands, all forces are positive and the sum is unrealistically high. This is also the case when i do a shock response spectrum
analysis (SinglePoint Response Spectrum (SPRS) Analysis)
After a PSD analysis the reaction force at each support is a 1 sigma value. There is no sign associated with it, so the sum of such reaction forces is meaningless, unless they happen to all be in phase. A possible workaround is to connect all the support points together with stiff beams or constraint equations and then support a single node. The situation is similar in a single point spectrum. The SRSS combination process removes the sign of the reaction force at each location. For a more detailed discussion of this issue, and for a more general workaround, please see the following presentation from the 2006 ANSYS Conference: <a target=_blank href="http://www.padtinc.com/docs/lit/psd_reactcalcmethod(2).ppt">http://www.padtinc.com/docs/lit/psd_reactcalcmethod(2).ppt</a>http://www.padtinc.com/docs/lit/psd_reactcalcmethod(2).ppt . This presentation was given at the 2006 ANSYS International Conference in Pittsburgh. The presentation title is: "A Method for Calculating Accurate PSD Reation Loads". 

