Maximum Span of Cantilever Beams

A question we get fairly often is what is the maximum span that we could cantilever this beam? Thankfully CVL Engineers has worked on a number of projects involving cantilever beams and we have a good understanding of them. Although they aren’t overly complex, there are some special calculations we need to understand in order to find the maximum span of cantilever beams for specific projects.

What is the Function of Cantilever Beams?

A cantilever beam is supported at one end and unsupported at the other end. Instead of bracing or support structures under the length of the beam and extending to both ends, there is clear space under the beam.

Cantilever beams are often used in construction, and there are two main examples of structures that use them: balconies and cantilever bridges. Although cantilevers can be extremely durable and structurally sound, there are some considerations.

What is the Maximum Span for a Cantilever Beam?

A question we’re often asked is what the maximum span for a cantilever beam is when no length has been specified.

To answer this question, we have to look at the load that the beam will be subjected to. When analyzing the load, we’ll look at several different measurements:  

  1. What is the magnitude of the load? 
  2. What is the type of load (i.e. is it uniformly distributed or concentrated)? 
  3. What is causing the load? (i.e. a live load, a snow load, etc.) 

Once we understand the load, there are still several considerations.

Other Factors that Contribute to Maximum Cantilever Length

All of these factors need to be studied by a structural designer before permitting the proposed cantilever length:

  1. The maximum span depends on the deflection at the extreme end that can be tolerated. The deflection limit for cantilever beams set by most design codes is L/180 for live load and L/90 for combined dead & live load.
  2. The maximum span depends on the material of the beam (wood, steel or concrete).
  3. The maximum span depends on the depth (and incidentally, the moment of inertia) of the cross-section of the beam. 
  4. The maximum span depends on the connection strength at the supported edge of the beam. 

There is one other note for specific situations: If the cantilever span is an overhanging extension of an adjacent, simply supported span, and subjected to the same uniformly distributed load, then the beam can safely cantilever up to a quarter of the simply supported span without needing special checks.

Learn More

If your project involves a cantilever beam and you have questions, get in touch with CVL Engineers Inc. We can run scenarios and calculations based on your projections to provide you with a well-rounded plan for building.

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