Need A Simple Beam Selection Program?? 2

[BronYrAur]

Anyone know of a simple calculator, table, or "cheat sheet" for sizing beams? This would be for simple point loading on beams supported on both ends. I'm in construction and had to recently choose a 10' long beam that would be supported at each end and point loaded in the center with 5,500 Lbs. It was to be used for rigging up some equipment with a chainfall. I have a person to call for help with this, but it would be nice to be able to do it myself. He advised me to go with a W8x31 for that application. Anyone have a simple guide or reference for someone who is not well-schooled in structural steel?

 

[UcfSE]

Meaning no disrespect, but someone who is not well-schooled in steel should not be sizing beams.

In light of that, you may find some text books and information to help you become better able to size beams. Schaum's outlines may help. If you purchase the AISC manual, you will find many charts and tables but you'll need to understand which apply and when, and why others are inappropriate. There's enough that goes into beam design that one simple chart that could capture all the necessary conditions and assumptions wouldn't be very simple.

You mentioned you had to size a beam (unless I misunderstood). How close was your answer to your advisor's?

I think you should start reading up on steel beam design if you are truly insterested in doing it yourself, but keep in mind it's not something you can learn overnight.

 

[COEngineeer]

The deflection usually controls so it is kinda hard to have a list which section to use. You have to calculate minimum I to meet your deflection limit then just use the AISC to find the size you want.

So find out what I you need and it will be easy to just use the AISC.

 

[BronYrAur]

Thanks for your feedback. I actually have the "Manual of Steel Construction - 7th Edition" from AISC, but I find it too cumbersome.

I also have a 1-page sheet on beams from an unknown reference. That sheet works through a problem similar to mine. It shows an equation for the moment on a point loaded beam supported at each end as M=1/4*L*W. Plugging in my 120 in and 5,500 Lbs, the Moment comes to 165,000 in-lb. It then identifies a "safe stress" as 20,000 psi and divides by this number to get the "Minimum modulus". In my case, I came up with 8.25.

I didn't question my advisor, but it seems to me that his choice of W8x31 is overkill, since it looks like that beam has a modulus of 27.4. Would not a W8x17 have worked just fine? He may have thrown in a safety factor.

Again, my needs for structural knowledge are very limited and are generally just for small rigging jobs such as this. That's why I am wondering if there is a "simple" reference that shows some typical beam sizes and how much they can carry at various spans?

 

[MiketheEngineer]

I agree with the above posts that steel beam design is not a quickly learned thing. Basically that and column design took most of a college semester.

That said - Archoneng.com has a very good steel beam design program for about $40 or $50.

Always be careful about providing lateral bracing as required!!! Also, working around construction - be leary of load numbers provided by others - sometimes correct - often way too low!!!

 

[UcfSE]

You would have to know what unbraced length is associated with that "safe stress" and adjust accordingly if you are greater than the unbraced length that allows you to use 20,000 psi. Your helper may have used a different unbraced length than you did, and you see the results of changing that value first hand.

I suppose it will be no comfort to know that bending equations have gotten quite a bit more complex since the AISC 7th.

What you'll find though, as far as diagrams and charts, is that the AISC is probably the easiest you'll get that covers what needs to be covered. Even then you'll still need to know what went into those charts to know if you can use them in your case.

 

[COEngineeer]

Ok I guess you were not really listening to what I said because you ignored 2 responses. Do not look at the stress because on this scenario, your deflection controls. Your deflection at the middle should be less than .25" (L/480). Since you are a 1st year structural engineer, you should be able to calculate the deflection at the middle.

 

[IceNine]

You need to learn how to check deflection AND stress.
Then, buy yourself a new steel manual as I don't think you can get a W8x17 anymore.

 

[BronYrAur]

Thanks all for your replies. Your suggestions were very helpful.

Please consider this thread closed.

 

[PEinc]

There is more to sizing a beam than checking the bending moment. Also, deflection may not be important if the beam is for a temporary application such as "rigging up some equipment with a chainfall."

The "designer" also needs to consider the unbraced length, web crippling and yielding, and flange buckling. If the rigger wraps a chain or cable around the beam in order to hold the hoist, the highly concentrated load could damage the beam even though the bending stress is OK.

 

[desertfox]

Hi BronYrAur

Try this calculator

http://pergatory.mit.edu/2.007/software_tools/Excel/springs/Beam_simply_supported.xls

regards

desertfox

 

[Lion06]

BronYrAur-
The higher size may be a result of an allowable bending stress of less than 20,000psi assuming your unbraced length is 10 ft. It seems unlikely that deflection would be an issue in a use such as this, but should be checked nonetheless.

 

[JStephen]

"It was to be used for rigging up some equipment with a chainfall."

Be aware that OSHA may require higher factors of safety than used in normal steel structural design. Also see ASME B30.20.

 

[csd72]

If this is for temporary rigging then the deflection is not an issue, in fact for shock loads a higher deflection is better as it reduces the maximum force on the beam.

The issue here is buckling.

For rigging beams this is an exceptionally bad situation for buckling as there is nowhere along the length that is properly restrained.

This situation is much more complex than you realise and I would stay within your expertise (as your PE licence dictates) and let the structural engineer take his small fee (and the liability).