One long beam VS several shorter beams
One long beam VS several shorter beams
(OP)
I'm a new mechanical engineer, and one of the projects I’m working on involves a good amount of structural steel for a suspended platform/walkway. It has one main beam that spans the length of the platform, and several cross members connecting that beam to another parallel beam for support. (Imagine your typical horizontal truss/walkway, where the cross members are all perpendicular to the main supports.) My question is this:
Assuming the beam is supported at the same points along its span either way, is there a significant difference/benefit to breaking the beam (which is wide flange by the way) up into shorter pieces bolted to one another? Would this eliminate additional bending moments, or is this already taken care of by the intermediary supports?
Thanks in advance!
Assuming the beam is supported at the same points along its span either way, is there a significant difference/benefit to breaking the beam (which is wide flange by the way) up into shorter pieces bolted to one another? Would this eliminate additional bending moments, or is this already taken care of by the intermediary supports?
Thanks in advance!






RE: One long beam VS several shorter beams
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.
RE: One long beam VS several shorter beams
RE: One long beam VS several shorter beams
RE: One long beam VS several shorter beams
RE: One long beam VS several shorter beams
There is a difference structurally. If the girders are continuous, they will be more efficient and a lighter section can probably be used. However, this is often offset by the need for bottom flange braces which is why I inquired about the elevation of the cross beams. With the set up you have, the cross beams would brace the girders and additional bracing would be required.
For small stuff like this, I find that ease of assembly is much more important to economy that section weights. Ergo the comment regarding handling. Another consideration may be ability to stuff the pieces in a galvanizing tank if it's to be that kind of structure.
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.
RE: One long beam VS several shorter beams
about beam length:
I have seen W sections up to 133 feet long, but they had to be shipped by barge.
I think 60 foot lengths are truckable and usually available, but check with your local steel suppliers before specifying a particular section or a particular length.
Some stuff that's in stock lists is only available if you buy really big lots and can afford interminable delays for ocean shipping or setup of mills.
OTOH, for small projects, you may be able to find a local stock of offcuts that are just what you need. You discover this kind of thing by sending an RFQ to each of the suppliers in your area, including a list of exact lengths and sections that you want, maybe with a note describing any flexibility you may have.
I used to do this with a group email of an Excel .xls file that was set up to look like (and print like) a paper form. Be sure to use an older Excel format like 2003 or earlier; lots of businesses are using very old computers. The really old school guys still use fax.
Mike Halloran
Pembroke Pines, FL, USA
RE: One long beam VS several shorter beams
another day in paradise, or is paradise one day closer ?
RE: One long beam VS several shorter beams
RE: One long beam VS several shorter beams
Because of the width, you should include a load case where a police car crosses the bridge from time to time. ... and in some locales, a fire truck.
Did you know that there are several outfits that specialize in repurposing old railroad flatcars into short bridges?
Mike Halloran
Pembroke Pines, FL, USA