What is a Cantilever Beam?

PrintPrintEmailEmailSaveSave
Image Credit: 
Creative Commons
Main Image: 
Image of a cantilever bridge (under construction)

A cantilever is a beam supported on only one end. The beam transfers the load to the support where it has manage the moment of force and shear stress. Moment of force is the tendency of a force to twist or rotate an object. Shear stress is defined as a stress which is applied parallel to the face of a material. In other words, the beam bears a specific weight on its open end as a result of the support on its enclosed end, in addition to not breaking down as a result of the shear stress the weight would generate on the beam's structure. Cantilever construction allows for overhanging structures without external bracing / support pillars. Cantilevers can also be constructed with trusses or slabs. Cantilever construction is famous in many kinds of architectural design and in other kinds of engineering, where professionals use terms like end load, intermediate load and end moment to find out how much a cantilever will hold.

 

What is the formula for calculating the maximum load for a cantilever beam?

For a cantilever of length L, the moment at the support of a cantilever beam due to a uniform load ‘w’ (kg/m) is given as

  • M1 = (1/2) * w *(L)2

The moment at the support due to a point load P (kg) at the end is given as 

  • M2 = P * L

The formula for the maximum stress a cantilever beam can tolerate is given by

  • σmax = (Mmax ) * (y) / (I), Where Mmax is the maximum moment (which is equal to M1 + M2), y is the distance from the center to the outer edge, and I is the area of the cross-section of the beam

 

Once you have the max stress, σmax, for the beam, the Mmax can be calculated, which can then be used to determine the maximum load P (from the second equation above, for M2)

 

How is Cantilever design used in various building construction?

Cantilevers are widely found in construction, particularly in cantilever bridges and balconies. Carpenters often think of cantilever beam design in terms of wooden beams, but in other kinds of projects a cantilever design is applied to a concrete slab (foundation of a house or building in construction, made using concrete) or a metal girder.

  •  In cantilever bridges: In cantilever bridges, the cantilevers are usually built as pairs, with each cantilever used to support one end of a central section. The “Forth Bridge” in Scotland is a popular example of a cantilever truss bridge. The Forth Bridge is a railway bridge towards east of Scotland.
  • In Architectural application: In an architectural application “Frank Lloyd Wright’s Falling water” used cantilevers to project large balconies. Frank Lloyd Wright was an American Architect, interior designer who designed more than 1,000 projects. Falling water is a house designed by Frank Lloyd in 1935 in rural southwestern Pennsylvania.

 

The East Stand at Elland Road Football Stadium in Leeds, England, is the largest cantilever stand in the world, which can hold 17,000 spectators.

 

What is the use of Cantilever in Aircrafts?

Another use of the cantilever is in fixed-wing aircraft (aero plane) design, pioneered by Hugo Junkers in 1915. Early aircraft wings typically bore their loads by using two or more wings in a biplane (fixed-wing aircraft with 2 main wings) configuration braced with wires and struts (cable). They were similar to truss bridges. The advantage in using struts or cables is a reduction in weight for a given strength, but it causes additional drag which reduces the maximum speed and increased fuel consumption. Hugo Junkers endeavored to eliminate all external bracing, after many years of Wright Brother’s initial flights to decrease airframe drag in flight, with the result being the Junkers “J1” pioneering all-metal monoplane of late 1915, designed from the start with all-metal cantilever wing panels. The most common current wing design is the cantilever.

 

 What is the role of Cantilever beams in Micromechanical systems?

Cantilever beams are the most omnipresent structure in the field of micromechanical systems (MEMS). An early example of a MEMS cantilever is the “Resonistor”. It is an electromechanical monolithic resonator. MEMS cantilevers are commonly fabricated from silicon (Si), silicon nitride (SiN) or polymers.

 

How are cantilevers used in storage applications?

  • In Warehouse storage: a cantilever rack is a type of warehouse storage system consisting of the vertical column, the base, the arms and the horizontal and /or cross bracing. These components are fabricated from both roll formed and structural steel. The horizontal and /or cross bracing are used to connect 2 or more columns together. They are commonly found in wood working shops, and plumbing supply warehouses.
  • In Portable storage: A folding cantilever tray is a type of stacked shelf that can be unfolded to allow convenient access to items on multiple tiers at the same time. The shelves can be collapsed when not in use for more compact storage. Due to these properties, folding cantilever trays are often used in luggage and tool boxes.

 

How is cantilever design applied in overhangs?

Architects use cantilever beam structures for the overhangs that are found in airports, university campuses, office complexes etc. These overhanging elements can provide shelter from the elements or decorative aspect to a building. In few cases, an “open-style” cantilever design fits into a modern or artistic design for a space, where planners have blended practicality with artistic appeal.



Individuals who are interested in observing how cantilever design in used in modern engineering can easily find many visible examples of this engineering method at work in their local communities. A detailed study of this kind of design can prepare a student in a better way into an engineering or architectural program. 

External References
Related Videos: 
See video