pile foundation

Hi all,

I am working on Abaqus 6.8. I am doing a pile loading
analysis in dense sand. I am not understanding how to plot
load-displacement plot by using static general step. I mean where i
should assign reaction forces and displacement in output request. i have
assigned a set at middle of pile and requested for disp. in output
request also i have made a set of bottom which is fixed and ask for
reation force in output request. i summed up all reaction forces and
combine with displacement. but i am getting zero force and graph becomes