Strut: A solid one piece of molded sheet metal cut to the same length as the width of your garage door. This reinforcement at the top of your door is there to keep the opener arm that attaches to the top panel of the door from bending top panel when opener pulls on panel to open door. Any garage door with an opener that has an arm and pulls door open from the top panel has to have some kind of strut to protect top panel from damage, no matter how wide the door.
Garage door is over 16 ft?
When you have a garage door that is over 16 ft. wide than you should have a strut on every panel. This is necessary because when a garage door panel is longer than 16ft. wide it will sag or be concave when the door is in the up position. Struts eliminate this from happening when the door is up. When a garage door is constructed of wood it is even more necessary to have multiple struts even on smaller garage doors 8-10 ft. wide. If you have a custom carriage door made of all wood or metal panels on the inside and wood overlay on the outside it is also necessary to have sometimes 2 struts on each panel. Steel and wood combination doors really sag a lot when in up position because of the extra weight of the wood on outside.
Damage to top panel
The most common reason for damage to top panel of a garage door even with the reinforcement of a strut is someone locking door with a mechanical locking system and someone tries to open with opener and forgets or doesn’t know door is locked. This will do damage immediately. Or the same outcome will happen if the door won’t move because something won’t let it like broken springs or object in garage is in the way of the travel of the door.