I'm building a murphy bed. I've build a box out of plywood that holds the mattress (the box is shaped like a sandbox. See image below). I plan on putting 5 different 25lb springs across the long side of the bed frame, but want to know if the frame can withstand 125 lbs of constant force.
So, what I did was build three different L-shaped test pieces, joined the same way I did the box (rabbit joints + dowels + screws + glue), to test their breaking force. (I'm going to use a similar setup to http://woodgears.ca/joint_strength/).
Here's my question. Does each of those L-shaped test pieces need to withstand 125 pounds of force? Or do they need to withstand only 25 pounds (assuming the L-shaped pieces are the same length as the average distance between springs)?