A strongback is a beam or girder which acts as a secondary support member to an existing structure. A strongback in a staircase is usually ordinary two-by dimensional lumber attached to the staircase stringers to stiffen the assembly. In shipbuilding, a strongback, known as a waler is oriented lengthwise along a ship to brace across several frames to keep the frames square and plumb.^[1] In formwork strongbacks (typically vertical) reinforce typically horizontal walers to provide additional support against hydrostatic pressure during concrete pours.^[2]

Some rockets like the Antares (rocket), the Falcon 9 and the Falcon Heavy use a strongback to restrain the rocket prior to launch.^[3] This structure reclines several degrees away from the rocket to clear the launch, either at the moment of launch or in some case a few minutes before.