Reattaching a Sofa Bed to Its Frame

Find out how it was originally attached.

If it is a matter of screws through a metal frame into a wooden "box spring" you can fortify the whole and screw it back in.

If it is metal on metal with broken rivets just rerivet or use nuts and bolts.

Your best bet is to figure out exactly how it had been attached. Take some digital pictures of it that you can print out or just show on the camera. Go to a Home Depot or a Lowes and talk to some of the people there. There is usually one or two handy/creative workers in each store that could give you some ideas but they really need to know what you are working with. Hence the pictures. Take many at different angles to answer all the questions they might have that you wouldn't remember the answer to.

Good luck.