Steel Beams and Shear Force

[Leftwow]

Good Afternoon All,

I am looking to design a beam that can withstand 265 kips of shear force. In this situation, what would you guys consider, and what is your opinion on the best section to resist a high shear force?

I am trying to come up with the lightest per foot steel section for this.

 

[jayrod12]

My first question would be, where is this level of shear force coming from?

 

[ahypek]

Assuming this is a column transfer and you're in the U.S. why not use Chapter G of AISC360?

 

[Leftwow]

Jayrod,

It is a crane support.

Ahypek,

I looked over chapter G sir! Specifically G.2, where the area of the web is a function of shear strength for w sections.

 

[KootK]

1) you want a meaty web without excess material in the flanges.
2) you probably don't want a section so tall that shear buckling would come into play.
3) you may need to consider material lost in supporting connections etc.

Any beam software that optimizes weight should suffice. Alternately operating on a section properties spreadsheet would be pretty straight forward.

How close to the support is the load? Would a truss work? Bolted connections?

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.

 

[Stewie_]

Do you think FRP can help in this situation?

 

[Leftwow]

I have back to back MC12X50's. What you guys think?

 

[KootK]

I think that I'd need to hear a good reason or two for not using a wide flange instead. I'd think that, for the same total web area, a wide flange would provide:

1) A stockier web with better shear buckling control.

2) Laterally stiffer flanges to brace the top and bottom of the web.

3) Improved LTB control.

Are the channels really the lightest section that works? Is there a particular detailing reason to go with channels?

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.

 

[PMR06]

Don't take this personally, but shear is probably the easiest of issues to solve in a crane beam. Please tell us you've got someone experienced checking your work. Otherwise I'm keeping my eye out for back to back MC12's and staying well away!

 

[Leftwow]

Wow, it's not a crane beam, it's beams that are supporting a telescoping boom crane. Also, are these forums not dedicated to an open discussion on the best solutions possible. I'll be honest I have about 3 years of experience and I've never dealt with a crane of this magnitude.

Kootk, I was thinking that the MC channel's shear capacity was higher per pound per foot due to the web thickness, which is 13/16"*2 beams. However you could be right, since the yield strength is higher in W-sections.

 

[MotorCity]

Use a wide flange beam, probably a stocky W14. Any cost savings by using 2 lighter channels will be offset by the labor required to connect them back to back.

 

[Lomarandil]

Leftwow, do you mean beams under a mobile crane outrigger?

I don't think so (not for back to back channels), but... if that's the case, you're not really in the world of optimization -- at least not in terms of minimum steel. I design beams like that quite a bit, and my first question to the contractor is always "what do you have in your yard?". We often end up with double W or HP sections skip welded into a pseudo-box shape.

If I've misunderstood -- disregard this.


Although I'll agree with MotorCity that any saved steel weight using B-B MCs will be offset quickly by your labor and connection cost.

You might also look at an HP section for a stockier web than a W.

----
The name is a long story -- just call me Lo.

 

[Leftwow]

Lo,

It is a fixed telescoping boom crane. On top of a structure. Yea I won't go with MC channels, the majority of the forum is against it and you guys are way more experienced, so I'll take your word.

 

[Lomarandil]

No worries...

It varies by industry and client type of course (Aerospace is the exception that comes to mind), but letting constructibility and connections guide your design rather than pure efficiency is simply one of those lessons many of us have had beat into us by painful experience.

----
The name is a long story -- just call me Lo.

 

[JStephen]

I was thinking there was some variation in price per pound between channels and wide-flanges, and also some variations in lengths available, so the lightest section is not necessarily the cheapest there.
Also consider with heavy wide-flanges where the flange depth is about the same as height, you should get increased shear strength turning the beam on its side.

 

[dhengr]

Leftwow:
I am not trying to pick on you personally, but if you don’t start asking some meaningful questions, with enough basic info. to start a meaningful exchange, you really won’t get much real help. It never ceases to amaze me that you OP’ers. don’t get the concept that we can’t see what you are looking at from here, and we really can’t read your mind, just because you post no relevant design info. Reread your own posts so far, and assume that you don’t know anything about your design problem, which is our situation here. Imagine the hundreds of arrangements that any of us could conjure up, which would fit what you’ve told us. Then, say and think, “wow...” what a stupid question, instead of “wow...” they don’t seem to understand that it is not a regular crane rail beam. Of course, you still haven’t given us much meaningful design info., either. It took about 13 posts to learn, “It is a fixed telescoping boom crane. On top of a structure.” That’s a bunch of wasted time on the part of people trying to help you, as they play your guessing game.

What does the supporting structure look like? Where are the possible support points for your structure, and how do you plan to frame your structure? Dimensions, existing member sizes and orientations, etc. etc. are all important in an experienced engineer’s first impression of your problem. Does the crane weigh 265k or is this the load it can lift at some radius at any position on the compass? Does the crane start from its ring beam/bearing circle and on up; and then your structure supports this bearing ring, and takes the load out to the existing structure below?
Lomarandil (24FEB17, 22:00) is right on the money. And, I would add to his comments that sometimes in a situation like this it is easier/better to start with fabricated/welded structural elements, box beams, plate girders with heavy webs, from plates, bars, etc. which really allow you to put the meat where it is needed. Many times rolled sections are not the best starting point, although many Structural Engineers seem to think this is so.

You have to lay out this kinda stuff in some meaningful form, so others understand what the heck you are talking about. And, you should proof read your posts with this in mind. You may not have definite answers to some of these questions, I certainly don’t have all the answers. But, you have to give us a meaningful starting point with sufficient basic design info. or we’ll still be guessing at post #200. And, from this standpoint, “I am looking to design a beam that can withstand 265 kips of shear force. In this situation, what would you guys consider, and what is your opinion on the best section to resist a high shear force?” is a sophomoric question.

 

[Leftwow]

Yes, dhengr is right, I'm sorry I will reproduce this thread with the appropriate materials for you guys to make a good judgement tomorrow. Excuse my immaturity.