Deflection checking on Cantilever beams & columns

[jochav5280]

Hello All,

I've got a fundamental question regarding deflection checks on cantilever columns or beams. In short, when a spec of L/400 for instance is placed on a cantilevered beam or column, what is to be used for L? Is it to be twice the actual cantilever or just the cantilever dimension itself. I'd appreciate some explanation to help me understand this.

Thank you,

jochav5280

 

[jayrod12]

columns and beams are two different arguments as I see it.

For columns they are generally trying to limit building drift therefore the h/400 or h/500 limitation is the actual height.

For cantilevers, it's generally 2L/400 or L/200 where L is the actual cantilever length.

The denominators in this example are for example and may be different based on application.

 

[KootK]

Usually it is as you've suggested, 2L. The rationale is that a cantilevered beam end will have about the same curvature, slope, and displacement as 1/2 a non-cantilevered beam would. Some finer points to watch out for:

1) Beam rotation at the support can have a large impact on both slope and absolute tip displacement for a cantilevered beam.

2) As a result of #1 cantilevered beams can often have upwards absolute displacements. That can be problematic at times.

3) Again, because of #1, cantilevered beams can be particularly sensitive to vibration concerns.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.