Thrust and pull are the forces exerted by a wall-mounted jib crane on the wall. Most of the time the phrase “wall-mounted” actually means the jib crane is mounted to a steel building column as if that building column were a wall. A standard steel building column is engineered to support the weight of the building roof as well as anything that hangs from that roof: lights, ducts, fans. Typically these extra items are light weight and inconsequential to the building design. However, when one mounts a heavy jib crane capable of lifting 4,000 pound loads, the building column must be specifically designed or adapted to support the jib crane.
Jib Crane Thrust and Pull
Who can design or adapt a building column to support a wall-mounted jib crane? Typically this person is an architect, engineer, or general contractor with engineers on staff. A safe rule of thumb is to have a Professional Engineer or “PE” stamp the drawing showing the modification or design.
So what exactly is thrust and pull? All wall-mounted jib cranes have a beam and a beam support device, usually either a tie-rod or vertical-mounted mast. There will be two hinges to allow the jib to swivel 180 degrees. One hinge is always at the place the beam meets the wall. The beam is the running beam for the hoist/trolley. The other hinge is always where the support device meets the wall: either the end of the tie-rod or vertical mast. The tie rod is above the beam, while the vertical support member hangs below the beam, like an inverted “L”. Because the load is hanging off the beam, the beam is like a lever being pulled by the load.
If one envisions the beam as a lever being pulled down, it’s not hard to imagine the top hinge is effectively fighting to pull out of the wall, while the bottom hinge is effectively fighting to go thru the wall. Pull and Thrust. See the drawing. The wall or column must be engineered to withstand the pull on the top hinge and thrust on the bottom hinge.
