I am working on a LNG Pipeline and am running analysis of blowdown on a PIG trap. I have run the dynamic analysis, but got some strange results for support loads at the first support.

I thought this was due to the surrounding supports taking all the load, so I changed the first support to rigid from elastic (stiffness of 130000 lb/in/in) and re-ran the analysis. The results were the exact same for the dynamic time-history analysis. Has anyone else ever had this happen?

What does "strange results for support loads at the first support" signify- is that the first support is not taking any verical load or is it that it is taking excessive vertical load?

Yes, it would say that the first support was taking very little, if any, load. I found this very odd considering the blowdown force is over 200ksi.