Adjustable Beam Clamp 3

[shinerttu]

Hello All, thank you for viewing my post.

I am a new (entry level) engineer and I have my second assignment which I have no clue on how to approach. I have been asked to design an adustable beam clamp for 3-tons to fit a beam with a flange 12" wide and a flange thickness of 1.5". All I have to work with is what a previously designed beam clamp looks like. I KNOW they sell these but my company tends to make everything in house and I just need some direction. Does anyone have an example or can someone get me started in the right path? I started by assuming some dimensions and calculating shear and moment diagrams for the lower arm, the center vertical member, and upper arm...thats about it.

 

[theonlynamenottaken]

You've got quite a few things to check and design on this, but lets separate them into two main categories: the supporting W-beam and the clamp itself. With the supporting W-beam you'll need to check flange local bending right at the clamp location, and then check the overall member bending and shear. To check the overall member you'll need to know its length and what other loads may be on the beam, such as if its an existing floor or roof beam.

There are many aspects to the clamp design, such as hole tearout for the shackle and bending in the "upper arms", but first lets look at the general approach. Unless there are some details missing from the example drawing you posted it looks like the clamp assembly is unstable. If the only thing tying the two halves of the clamp together is the shackle pin then you could essentially idealize the clamp assembly as a simply supported beam with a hinge in the middle. When the sling is loaded the two halves of the clamp will rotate and bind on the tips of the supporting beam's bottom flange. You'd need to fill atleast another one of the holes with a pin or bolt to keep the two halves tied together. Make sense?

 

[briancpotter]

I don't think shear/moment diagrams are going to be particularly helpful. With a shape resembling that, you're going to encounter rather severe stress concentrations in the corners that won't be easy to calculate. Barring any sort of specific design guide for beam clamps, I'd say this needs to be thrown in a FEA model.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[shinerttu]

How about ASME BTH (Below the hook lifting device) is this applicable here?

 

[msquared48]

You need to put a minimum 1" radius on all the interior corners, and I would add a small bearing plate each side to spread out the load to the beam flange better. It will also help to stabalize the clamp from rocking.

Mike McCann
MMC Engineering

 

[rb1957]

so you'd make 6 of these 1/2 ton brkts to lift 3 tons ?

how spread out along the beam ? or close spaced (against each other) ?

where do the 4 3/4 ton shackles fit ? on either side of each brkt ?

then 1 bar between the bottoms of the shackles and 1 wire (good for 3 tons * x) ?

what happens at the three holes in the brkt ? clamp the plates together ? adjustment (for wider flange beams) ??

Quando Omni Flunkus Moritati

 

[shinerttu]

@rb1957,

No I am to design something similar to this with a 3-ton capacity...this is a design someone at my company did in the past for (1 ton load). This is all I was given and asked to design something for a 3-ton load on a 1.5" thick flanged beam 12" wide.

 

[BAretired]

Why not start by analyzing the 1/2" plate on the 1/2 Ton clamp to see what the shear stress and bending stress is? Find out what code you are supposed to be using. I would imagine for something of that sort you would likely be using a safety factor of 4 or 5, maybe even more.

Talk to the guys in the shop and find out how the adjustable feature works. Maybe they would have some valuable suggestions for you.

Sketch out the dimensions of the clamp you would require for a 12"x1.5" beam flange. When you know the span of the bottom plate, make a rough calculation of the size of components which would result in approximately the same shear and bending stress as in the previous design.

I agree that sharp corners should be avoided and the idea of using a spreader plate to rest on the beam flange is good. Put it all together in the form of a rough drawing and discuss it with your boss. He may have some further requirements which he forgot to tell you.

BA

 

[BAretired]

It might be a good idea to consider a single plate from one side and a double from the other. That way you avoid eccentricity. You also receive the benefit of double instead of single shear on each of the three bolts or pins.

As detailed, the 1/2 Ton clamp does not seem to have any adjustment for varying the flange width. To do so, it would need more holes.

Also the 1.25" dia. holes are spaced at 1.5" centers, leaving only 1/4" between them. I would consider reducing the diameter of hole or, if that is not possible, spacing them further apart.

BA

 

[XR250]

Why would your company pay you to design one of these and then build it when they can simply buy one?

 

[dhengr]

shinerttu:
IMHO, that is an awful detail unless someone, at your company, can explain its purpose to you, and you to us, some sound reasons for its configuration. And, I think whoever gave you that as a good design to follow should be very careful about mentoring young engineers on good structural and mechanical design. That detail makes very little real engineering sense at first glance. What holds this thing in place on the length of the beam, or is it o.k. that it can move up and down the beam length, or do you want it to do that? As someone mentioned, the square notches are not a good detail condition, those square corners are stress raisers. They should be cut and ground as a 3/4" dia. notch end shape. Grind a 1/16" radius on the edges of those half circles too. What prevents the two halves from just hinging about the shackle pin, and loading the beam flg. at the inner/top of flange tips of the 1/2" pls.? The 1.25" dia. holes are not compatible with the 7/8" pins/bolts on that 4.75 ton shackle. You will likely have pin bearing issues on those holes in the plates. The two moving 1/2" pls are not compatible with the inside width of the shackle at the pin, and you could have pin bending issues. As BA mentions the hole size, spacing and edge distances need more study. You can use the next smaller size shackle for your 3 ton load, and then smaller pin holes. The ASME BTH codes would give you some good insight about this type of equipment. Draw some free body diagrams (FBD’s) of that hanger and try to understand how it works and moves. Does it do what you want it to do?

Why don’t you explain how this beam clamp is supposed to work and what it is intended to do. That’s part of getting started on the new design. Can the beam flanges take those point loadings so far from the beam web, or should they be applied closer to the web? Obviously, you have to analyze the entire beam for this new load. Also, it would be slightly more clear in your presentation if you showed the part detail on the left in the same orientation it shows up in the beam section/side view. Then, the shop wouldn’t paint the ½ ton marking upside-down on the parts. Otherwise, the sketch is good and helps explain what you are looking at.

I believe I’ve seen a beam clamp which acts like an ice tongs and has a couple hinge pins and a scissors lift type action; clamping in and down tighter as it is loaded by the shackle.

 

[TLHS]

They literally make the exact thing you're looking for, targeted for lifting applications even.

i.e.

http://www.lkgoodwin.com/more_info/screwlok_clamps_and_trolleys/screwlok_clamps_and_trolleys.shtml

I know you've said you're aware that you can buy them, but doing something that requires custom design and fabrication that you could otherwise buy for $300 is pretty hard to justify from a cost perspective. Are you sure you couldn't call some vendors up for information, then go to a boss and say that in the course of your research you found that there are specialized manufacturers that already make these things and that costs are <NUMBER> and delivery could happen within <TIME> which would be a net gain.

Personally, I'd be happy if someone came to me with something that was both cheaper and reduced my liability.

 

[BAretired]

I totally agree with dhengr. TLHS has provided a link to a company which makes exactly what your company is looking for. It is not worth the hassle to re-invent the wheel. Buy the clamp and spend your time doing something more useful, like playing a game of golf.

BA

 

[shinerttu]

The more you guys point out the flaws the more I realize this is a terrible design, and its bulky compared to products available online. Please understand I just graduated with my degree in civil engineering, and I just began my career 2 weeks ago. The lack of guidance I am getting is frustrating and is making me second guess whether I picked the right company to work for. I will bring up all the points you guys have made, but I did want to show some initiative to try and solve the problem considering every time I ask a question they act as if this is the easiest thing in the world.

However I would like to show you the work I have done and at least critique whether I make any sense at all. I came across a padeye design using ASME BTH-1-2008 "Design of Below-the-Hook Lifting Devices" and followed that as a guideline.

The purpose of this is to lift something while the clamp is connected to the I-beam...I assume it is acting like a spreader bar??? Not sure though and will try and get some more clarification if anyone around here actually gives me some time.

I have yet to conduct the pin hole design or check whether the flange can support the point load. The design I have attached is for the plate only so far. My Free body diagram was for my first attempt (why the dimensions differ then my design) but its maximum moment is higher then the design I went with so it can be considered conservative.

Thanks for all your input, I appreciate you guys putting up with "rookie" questions...

OH BTW I AM USING 1" PLATE

 

[BAretired]

I couldn't download your file.

BA

 

[shinerttu]

Trying again...I noticed an issue with my FBD...I'm having to add an external moment to keep it stable...having a brain fart

 

[dhengr]

shinerttu:
We all started out, only two weeks out of school at some point, and quick realized we had a awful lot to learn. So, don’t be discouraged on that account. E-Tips is a good place to come with your questions, and get lightly beaten-up once in a while, but also to learn a lot from some pretty knowledgeable and experienced older engineers. It is a serious shame that companies are not doing a better job of guiding and mentoring their young engineers, because they sure aren’t getting a lot of that basic understanding, intuition, feel for real world design problems in college. Keep after the boss, show him/her you are willing to work hard and want to learn all you can. You might look elsewhere for a mentor, maybe through a professional association, at meetings which you’ll learn from and develop freindships, maybe future job contacts; or even at another company or office if you have any personal relationship or interaction with that person. Older engineers are usually willing to help, if you come well prepared and show progress. Once in awhile, make those meetings lunch or a beer after work, with a sketch pad, or some of your own details to be red-lined. You’ll find this mentoring interaction to be a rewarding experience, we certainly do.

You are well on your way on this particular design problem. Think about what various people have suggested, kinda read btwn. the lines for the full meaning of what they are saying. TLHS shows one of the devices I was thinking of. You’ve been given a bunch of areas you should check for a good design. Make a list of your questions, sketches, possible solutions and approx. member sizes, some off-the-shelf solutions; and take them to your boss as a progress presentation and question session. However, 1" plates are too thick, you’ll need at least a 12 ton shackle to fit over them.

 

[shinerttu]

dhengr thank you for your advice, that has motivated me to find a chapter of ASCE in the town I work in (Corpus Christi, TX) which I just moved to. I am passionate about engineering and my goal is to achieve becoming a PE. I have my EIT currently and if you guys know anyone in the Corpus Christi area who likes to teach... I love to learn!

 

[BAretired]

Okay, now I have downloaded your file. I was under the impression that there was a bolt or pin in all three holes, not just the central one. With three pins, the statics are clear. If the only pin is in the center hole, the assembly is unstable. This was pointed out in the second post above.

Trying again...I noticed an issue with my FBD...I'm having to add an external moment to keep it stable...having a brain fart

You can't simply add an external moment unless there is some means of applying it. You would need an equal and opposite horizontal reaction at the hinge and bearing point of the upper arm. The pin could take it, but the bearing point would be relying on friction against the beam flange which is not acceptable. If you had pins in all three holes, the two outer holes could supply the necessary moment to resist the 4.5"k moment imbalance.

BA

 

[dhengr]

shinerttu:
You say.... “but I did want to show some initiative to try and solve the problem considering every time I ask a question they act as if this is the easiest thing in the world.” If Good Design were really so easy, they wouldn’t have given you such an awful example to follow. And, I’ll bet that if the truth be known, they can’t explain that original, in-house, design and detail. All they know is that it hasn’t failed yet. But, then, you are much too quick to start calculating, without thinking through the problem, and doing some sketching; and your sketch shows that you don’t read very carefully for our full meaning. A bunch of people have told you not to use that square inside corner, and there is plenty of reading material on that design detail, but what does your sketch show. Secondly, draw an end view of a beam with a 12" x 1.5" bot. flg. and a flg./web fillet of about .75 - 1" radius. That’s one honkin big beam. The lower tip of your upper leg can’t encroach on the flg./web fillet, and you have to account for the 1" rad. to fix that sq. inside notch end; so your upper leg can’t/shouldn’t be longer than about 4" on the inside (not 8.5"). Anything longer just increases the bending stresses for no good reason. Your lower leg load point won’t be at 12" if those bot. legs overlap, as on the original design. But, the two 1" overlapped plates make for the need for a might large shackle. There just isn’t anything nice and clean about that original design, unless there is a real reason for its arrangement. Slow down, read for meaning, not for speed, do your layout to scale, but quickly, so you can see how things fit and work together, then start your calcs. On your second page the top moment may be (4 or 5")(3k) and the bot. moment may be (7 to 9")(3k), on the vert. leg, and it varied over the length of the vert. leg. And, the entire system will be in equilibrium when you add a horiz. force at the shackle pin center. The lower legs will try to pull apart, clockwise to the left and counter-clockwise to the right. It’s still a bad design.