A cantilever balcony of the Fallingwater house, by Frank Lloyd Wright

Cantilever – a beam anchored at only one end. The beam carries the load to the support where it is forced against by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.

Nearly all cable-stayed bridges are built using cantilevers. Many box girder bridges are built segmentally, or in short pieces. This type of construction lends itself well to balanced cantilever construction where the bridge is built in both directions from a single support. These structures are highly based on torque and rotational equilibrium.

In an architectural application, Frank Lloyd Wright’s Fallingwater used cantilevers to project large balconies. For the cantilevered floors, Wright and his team used upside down T-shaped beams integrated into a monolithic concrete slab which both formed the ceiling of the space below and provided resistance against compression.

Another use of the cantilever is in fixed-wing aircraft design, pioneered by Hugo Junkers in 1915. A single large beam, called the main spar, runs through the wing, typically nearer the leading edge at about 25 percent of the total chord. In flight, the wings generate lift, and the wing spars are designed to carry this load through the fuselage to the other wing.

Cantilever chair is an example of cantilever used in furniture design. It has no back legs, relying for support on the properties of the material from which it is made. In the early 1930s, Marcel Breuer come up with the idea to use metal tubing like that used in bicycles. This was the first light-weight mass-produced metal chair.
That’s engineering

  • bracing – a support used to steady, strengthen or stiffen a structure. Many buildings, bridges and other constructions have bracing structures.
Euler-Bernoulli beam

Engineering ideas

  • cantilever, hydraulic, counterweight, torque, rotational equilibrium, beam, anchor, load, force, moment, shear stress, statics

Do it
Now it is your turn. Here are some challenges for you to work on…

  • suggest some other uses for cantilever structures. When would it be important to have part of the structure just sticking out in midair?
  • design and build a model to show how cantilevers work and what the limitations are.

Learn more…

  • Fallingwater house by Frank Lloyd Wright makes extensive use of cantilever balconies throughout.