A-frame is a structure that is fitted at each transverse girder in the crosshead engines to support the cylinder block from the bedplate. They also have holes to accommodate the tie rods which hold the entire entablature, A-frame, and bedplate together.
Flat steel plates are welded together to fabricate the A-frame columns. Nowadays the frame box is built as a separate fabricated construction and the mating surfaces are machined. The stress is relieved before the frames are mounted on the bedplate.
When the frames are aligned on the bedplate they are secured together by drilling and reaming and using fitted bolts. the A-frame also serves as a mounting point for various engine components such as the fuel pump, oil pump, and water pump.
These components are typically mounted on brackets or mounting plates that are attached to the A-frame, allowing them to be easily accessed for maintenance and repairs.