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?