Wow, a lot of progress!
Below is the split in the face that is needed to make the Fixed Joint. Go to SpaceClaim. Use the Split button and Ctrl-click all the horizontal faces in one column then click the Cut button and select of of the vertical faces at the center to split the faces. Repeat for the other 3 columns. Then go and repair each fixed joint and change it from using a face to using only edges. The reason for this edit is that the Fixed Joint with behavior Rigid makes the whole horizontal frame rigid instead of flexible.
Below is the Rigid Elements that cover your structure, you can see it covers way too much compared with the example I provided in one of my previous comments. This is why your F vs D is not correct. Look carefully at which edges are included in each joint. This plot can only be seen after the solver has run on the model. Click on the Solution Information folder where you see the Force Convergence Plot, except the main graphics window automatically switches to Worksheet. Click the Geometry tab at the bottom left of the main window to see this plot.
I will send this now and keep looking at the rest of the model. What time zone are you in? I am in the Eastern US Time Zone. I posted this at 7:08 AM. What time does it show for you?