Douglas Harper's Etymology Dictionary
type of framework shaped like the letter "A," 1909; as a type of building construction from 1932.
Wiktionary
n. An architectural structure, in the shape of an "A", having two straight sides meeting at the top.Brown, Lesley (2003)
Wikipedia
An A-frame is a basic structure designed to bear a load in a lightweight economical manner. The simplest form of an A-frame is two similarly sized beams, arranged in a 45-degree or less angle, attached at the top. These materials are often wooden or steel beams attached at the top by rope, welding, gluing, or riveting.
Because they have only two "legs", A-frames are usually set up in rows so that they can have good stability. A saw horse is a good example of this structure. More complex structures will have a crossmember connecting the two materials in the middle to prevent the legs from bowing outwards under load, giving the structure the appearance of the capital letter A.
Usage examples of "a-frame".
The rope whipped off the winch, its coils fell into the water and the buoy caromed off the A-frame and disappeared.
Pitt pointed to the walking beam mounted above the high A-frame that tilted up and down, one end driven by a connecting rod from the steam cylinder, the other driving the crank that turned the paddlewheel.
She felt his seekersense flick over her as soon as she stepped onto the walk leading to his hut, but the convenances governing polite behavior between nonintimate operants forbade that he take any notice of her arrival until she actually tapped on the door of the A-frame.
He cruised up to a buoy, grabbed it with a boat hook and hauled it aboard, fed its rope through a block and tackle suspended from a steel A-frame, wrapped the rope around a winch and brought the wood-and-wire lobster pot up onto his bulwarks.
The Council Hall was a ferro-concrete A-frame thirty meters to the roof peak and a full hundred meters along that beam.
She looked up at the huge A-frame that supported the walking beams, and then to the great cylinders, steam condensers, and boilers.
He climbed up the engine to the top of the steam cylinder and then took a Jacob's ladder to the top of the A-frame before stepping off onto the top deck of the ferry just aft of its twin smokestacks.
After the submersibles were swung over and released to float away, the huge A-frame on the stern of the ship that was used to launch and recover oceanographic equipment was unmounted and dropped over the sides as well.
A kid named Leon, one of the other pole vaulters, told Kevin he was renting an A-frame out in the jungle.