A garage door strut is an extruded piece of metal to form a C-channel. And is cut slightly shorter than garage door width. It is used for reinforcing the garage door and to prevent the panels on the door from bending or sagging, as the opener pulls on the top panel to open the garage door. Struts will strengthen the door and help prevent damage from wind, however if you live in an area susceptible to high winds, reinforce with extra struts.
Most manufactures do not require a strut on any door up to 14ft (in width). Anything above 14ft must have at least one strut. The more struts you have on the garage door the stronger it will be. Any garage door that has an opener is required to have a strut on the top panel. The top panel is the weakest point. If you do not reinforce the door, it will damage the top section in a short period of time. The struts also help to prevent wind damage, the larger the door the more susceptible the door is to wind damage.
NOTE: WHEN IT COMES TO MOST DOORS, ADDING ONE STRUT WILL NOT AFFECT THE BALANCE OF THE DOOR. HOWEVER, IF YOU ADD MORE STRUTS THAN ONE YOU WILL MOST LIKLEY HAVE TO CHANGE OUT THE TORSION SPRINGS, TO COUNTER ACT THE WEIGHT OF THE STRUTS ADDED TO THE DOOR. IF YOU ARE NOT FAMILIAR WITH GARAGE DOOR TORSION SPRINGS YOU SHOULD SEEK A QUALLIFIED PROFESSIONAL TO EXAMINE THE GARAGE DOOR.
Replacing a Strut on the garage door:
First you will need to make sure the garage door in down, then, disconnect the opener that is plugged in on the celling close to the opener. Then, you will need to engage the slide lock (the lock on the door which slides into the tracks of the door to prevent it from opening). Remove the screws securing the top edge of the strut working toward the middle of the strut starting from each end. Then repeat previous step for the bottom. Next, remove the center screws while firmly holding the strut so it cannot fall and pull it away from the door. Screw the new strut in place starting with the center of the strut.
Finally, you will want to reconnect the opener and be sure to disengage the slide lock. Be sure the door runs smoothly, and the top panel has no stress on it while the opener is pulling it open.