Cantilever Beam on both side of Column

[DaveHolder]

I just was wondering when you design Cantilever Beam with the same span on both side of the Column, what is the bending moment going to be on the column?

Many thanks

 

[JAE]

If the load is balanced, then zero moment on the column.

But usually you would consider the possibility of an unbalanced load condition and design accordingly with some moment getting into the column.


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[DaveHolder]

Thank you for a quick response. When I designed the symmetrical canopy, the section size of the beams is larger than the column which is quite sensible since the moment is zero on the column. I applied different load on both sides of the canopy; the moment is still relatively small on the column resulting in slight column section. As far as I know the column section size should be 30% greater than the beam or at least equal, in my case the column size is quite tiny compared to the beam. Please correct me if I am terribly wrong.

 

[JAE]

I'm not sure if you are "terribly" wrong - due to your general, non-detailed question. You might elaborate on your situation and post a sketch as it would help others understand what you are doing.


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[cliff234]

Your question is vague. What are the loads on the cantilevered beam? As JAE said, if the loads are balanced, then there is no moment on the column - however loads are seldom exactly balanced. Most building codes require investigation of pattern loads or partial loading which can often create bigger moments, reactions and shears than full loading. What is on your cantilevered beam? Floor load? Wind load? Snow load? Always assume the worse case.

 

[XR250]

Also depends on the relative stiffness of the beam and column. A noodly column will see very little moment where a stiff column will attract more.

 

[dhengr]

Leoelfarra:
This sounds like a “T” or a “Y” shaped canopy to me, a simple determinate structure. So, the column will take whatever moment is induced into it, by the worst case loading condition from the roof structure. And it better be able to take that moment, irrespective of the relative stiffness of the beam and the column. And, you don’t want the roof system fluttering in the wind like a loose sail.

 

[prasadrmb]

When there are cantilevers in both sides, fists you have to find the worst case. This is actually depends on the axial load and the bending moments.

you can consider three cases.
01 one side loaded
02 other side loaded
03 both side loaded

each case find the bending moment and axial force. Design separately.

http://structuraldesignbs.blogspot.com/

 

[XR250]

Also depends on the relative stiffness of the beam and column. A noodly column will see very little moment where a stiff column will attract more.

I guess I was assuming one of the beams was supported at the opposite end. If not, what dhengr said.

 

[IDS]

Also don't forget to use a maximum load factor on all loads on one side, with a minimum load factor (i.e. less than 1) on permanent loads only on the other side, combined with whatever wind loading will give the maximum overturning moment.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[jayrod12]

My first run would likely check as if a single beam existed only (whichever beam has the highest moment) and then if that becomes unmanageable, I would account for the reduced dead load of the other cantilever.

 

[Ron]

If you have any wind load you will have an unbalanced condition with moment in the column

 

[Guastavino]

I would agree with the unbalanced load case. I would model it in an FEA program with all the various load combinations and then "sanity" check it with hand calcs.

With all that said, check out this by one of my Favorite designers Eladio Dieste...If only this could be done in the U.S.

 

[Ron]

Here's one with unbalanced wind loading at 130 mph. All aluminum.

 

[dhengr]

I’m glad you two guys posted those great big, great
wide, photos, except I still can’t count the blades
of grass, so not big enough. But, now I do have to
run into the next room to my right to read the right
2/3rds of every line of print on the thread. That
kind of scrolling is a pain in the A$$, it dooms this
thread for me. And, the people who’ve been improving
the E-Tips site just don’t seem too interested in
fixing this problem. The photos would have shown
everything intended, at a scale which would fit in the
normal thread format width, and this could be
automatically accomplished when you post those photos,
or plans or sketches. Then, there might be a feature
which allowed us to increase the scale if we wished and
then scale (click) back, without screwing up the whole
thread.

 

[Trenno]

I've never had a problem with photo scaling or text alignment on Eng-tips.

 

[IDS]

I've never had a problem with photo scaling or text alignment on Eng-tips.

It's probably browser related; the pictures in this tread do cause the scrolling problem for me.

It's pretty easy to scale an image down to screen size; that or attach the file rather than embedding.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[jayrod12]

They look fine on chrome. regular size, and super impressive canopies.

 

[Trenno]

What's the material of the first one? Almost looks like masonry.

 

[hokie66]

The horizontal scrolling thing must be browser related. I have had it in the past, but this one looks fine.

I hate njlutzwe's canopy. As for Ron's, I like his car.