Mininum dimension at end of tapered cantilver beam

[ali07]

As per attached sketch, what should be the minimum dimension at the end of tapered cantilver beam. Normally it should be half of that at support. If beam depth is more than required, is there any codal requirement for minimum depth at end of cantilver.

 

[ali07]

For information at support, beam dimension is 26"x48" deep,
which is more than the required dimensions, satisfying the short and long term deflections. Lookinf for minimum 26"X? at end. Architect requires 16".

 

[InDepth]

No code requirements that I know of. You could theoretically make it zero at the end. There are recommendations on the angle of the cut before you have to account for additional stresses. Check out lincoln electric's "Welded Structures" Book.

 

[francischacko]

There is no harm in providing 16" at free end provided the moment and shear is OK at half span.As intimated the section at free end could be zero

 

[InDepth]

I thought about this a bit more, and you may want to check Lateral torsional buckling and other buckling modes at 1'-0" increments.

You want also want to look at the slope of the moment diagram....theoretically this could also be the slope of your taper.

I would also recommend checking the load case where wind provides uplift and there is a seismic load. For the wind case, I would verify a deflection criteria. Also be careful if you are in a region of snow.

More than likely, I believe you are going to be deflection controlled, so your minimum section at the end will need to be sized for deflection not strength.

I would also recommend providing a cantilever coming from the other edge to meet at the corner. This will provide redundancy and I believe will be aesthetically pleasing (two tapers joining at the corner)

The diagonal beams coming to the corner is going to be a difficult connection. You may want to offset one of them to connect into an adjacent beam rather thna at the column (check AISC bolting / wrench requirements). That, or reframe, by providing only one diagonal. Check Deck span requirements.

 

[rb1957]

what loading is being applied along the edge ?

i presume you're also putting an edge member along the other sides, ie surrounding the dark grey area, ?

 

[BAretired]

I don't think zero at the free end would be acceptable as the concrete would be subject to breaking off at the edge. Probably a minimum of 8" would be reasonable for a beam and 3" for a slab.

BA

 

[ali07]

Hi BA,

I am thinking to convince architect for a minimum of 24" at end, just for placing rebars easily.

Looking for any design literature to check slab thickness for triangular shape slabs. I am using BS code, it gives me moment formula, but not how to check thickness of slab, like l/33 or l/?.

Any material for special shapes to estimate slab thickness is appreciated.

 

[hokie66]

There is nothing wrong with the 16" edge dimension the architect requires. I don't know why you would want more at the edge. The deeper it is, the more mass you have to design for. The architects I work with would want it thinner, and I would see nothing wrong with 8".