Does doubling the vertical web double the load bearing capacity of a beam/girder?

[edison123]

Assuming proper fabrication, does the box girder on the left have twice the load bearing capacity of the I beam?

Muthu

http://www.edison.co.in

 

[hokie66]

No. The capacity in shear and web crippling may be approximately doubled, but the "load bearing capacity" depends also on the flange size.

 

[edison123]

Thanks, hokie66. So the bottom flange thickness has to be doubled?

Muthu

http://www.edison.co.in

 

[jayrod12]

Not just that either. Perhaps you should consult a local structural engineer.

If you are wanting to put more load on an existing beam there's many aspects that need to be checked, the beam itself, its connections, its supporting framing, foundations, etc.

 

[IFRs]

There are many failure modes and things to be checked. Some are quite dependant on the web material, others not so much.

What do you mean by load bearing?
Bending?
Web crippling?
Torsion stress?
Combined bending and compression?

Load capacity in bending is based on the section modulus of the profile, which is highly dependant on the top and bottom flanges size and distance apart and much less dependent on the web thickness or quantity.

Web cripling is very dependant on the amount of material in the web and nearly indepandant on the material in the flanges.

Defletion is base on Young's Modulus and the Setion Modulus

Torsion is based on another property of the section.

You need to understand the loading and failure modes, then go after what could be changed to make the beam stronger.

 

[edison123]

Thanks, guys.

Two separate I-beams on the right are being used as crane beams with bottom hung 10 ton hoists in each beam for over 25 years. The plan now is to upgrade to 30 tons with 2 of box girders (shown on the left) with the crab running on top with 2 of 15 ton hoists.

Due to space constraints in z axis, I would like to maintain the original beam height of D. The columns have been designed for 40 tons when the shop was built. This is just a preliminary budgeting exercise. I will approach a good crane supplier eventually. Just needed to know if the box girder concept is correct.

Muthu

http://www.edison.co.in

 

[Lomarandil]

Just needed to know if the box girder concept is correct.

It is possible to put a new crane beam in with twice as much capacity while maintaining the original beam height.

A box beam may be the correct concept (economically) to use. (It may not, depending on other details -- span length, connections, crane arrangement).

Estimating the cost/weight of this new crane beam is not as simple as doubling any specific dimension. (If it was, there would be no need for structural engineers).

If you find a local structural engineer, they are likely to visit your site and offer enough free advice to develop a good budget estimate -- in return for getting the call when you are ready for design.

----
just call me Lo.

 

[edison123]

Ok, thanks guys. I will check with structural engineers in my area.

Muthu

http://www.edison.co.in