Moment capacity of bolted connection to top flange

[lostmeche]

Hello.

I'm new the community and this is my first thread. So forgive me in advance for any mistakes I make. I am designing a double overhung monorail for an electric motor and gearbox. Only one overhang will ever be loaded. Due to the location of the motor and gearbox, I am limited to how the monorail is supported. I've already sized up my monorail and and I know it can handle the load. However, I'm stumped on how I can make my support connections moment resistant. At this time, I'm thinking both supports will be u-frames with the top flange of the monorail bolted to two angles that are welded to the side of the u-frame cross member but my concern is how do I determine if this connection will safely hold?

I've attached a sketch. The lines going through the W6x12 and angles represent the bolts. I'm not a structural engineer, btw. I'm a noobie MechE and the only one in my department.

 

[mmarlow]

When you say "U frame" do you mean like an upside down "U"? Two columns and a beam? Or is it hanging from structure above? I think you should get a structural engineer involved.

Questions and considerations
-How much does the gearbox weigh? This will effect the following remarks.
-You have two frames correct? why do you have moment connections in the title of the thread? Are these monorail connections also intended to brace the frame? If so, I dont like that Idea.
-Frame considerations:
*lateral stability of frame? Cantaleivered columns? Braces (I like bracesd frames for something like this)?
*Impact loads per ASCE 7 (see above)

-Connection considerations
*Flange Bending or toe bending at the connection and the monorail location
*Prying action
*Welds
*bolts in tension
* etc..

I might be missing your approach on this, however I feel you have a lot to consider, not just the connection at the monorail. Unless these are things you didnt mention in your post.

I hope some of this information helps get you started. You say you're the only Mech. in house, do you have structural engineers in house?






-MMARLOW EIT

 

[lostmeche]

mmarlow,

It is an upside down u-frame with columns and a beam.

The motor has 1308lbs on the badge and the gearbox is about 900lbs. We label our monorails so I'm designing for 3/4 ton. It's manual driven so the chain fall and trolley shouldn't be more than 100lbs.

Yes, there are two frames. I have moment in the title because at the support location, when the load is at the end of the overhang the maximum moment occurs at the nearest support.

I know I have a lot to consider but I'm doing one thing at a time and if it isn't adequate down the road I can fix it. My approach is like this: size monorail, design support connections, design frames, design frame anchoring.

I'm the in house Mech and there are no structural engineers. There's 5 other engineers but they are electrical and chemical. Thanks for your response!

 

[mmarlow]

Lostmeche,

If you have something that looks like the attached image, you dont need moment connections. you can Idealize them as pinned at each location. Even with the cantilever. The moment is in the monorail beam, and I dont see any reason to transfer it into the carrier beam (tube)? If you design the connection as a moment connection you will just be causing your carrier beam (tube) to want to twist. When your load is at one end of the cantilever you will see axial compression loads in your closest frame columns, and possibly some uplift in your further away frame (Unlikely being that your load is relatively light.).. But I dont really know the dimensions of your frame.

The way I see it, the connection should be designed for vertical loads and shears caused by impact loads


This is all assuming you have something Like the image I have attached.




-MMARLOW EIT

 

[lostmeche]

mmarlow,

That is something that I considered but didn't quite grasp. I know the moment is internal to the monorail beam but I thought that if it happened at a support location that it would transfer it to the connection. And your sketch is correct. Thanks for your help!

 

[Ron247]

I am a little lost about what you are designing. When you say monorail, I assume you have 2 assemblies as mmarlow depicted that has a monorail spanning between them. A sketch of the entire system would be helpful.

 

[lostmeche]

Ron247,

I have attached a sketch of the whole assembly. The motor and gearbox assembly are not to scale. They are close though.

 

[mmarlow]

lostmeche,

Looking at the image attached, I stand by my original posts. This does not appear to be a stable structure. Understanding you are still in the design phase and you didnt ask for help on other aspects, Id still like to mention based on your sketch, overturning from impact loads and vertical loads out at the right end will probably be a design concern. I also like S shapes for monorails They tend to be better in flange bending from wheel loads.

One of my first Structural projects, 2 years ago, was something very similar to this, I opted to use different sections than you, and my loads were closer to 3000#. But it was close.

These are the types of projects that really develop young engineers like us. Getting thrown to the wolves and figuring it out. Just make sure someone with experience reviews the final deign.

-MMARLOW EIT

 

[Ron247]

So I assume there are 4 columns. I can see 2 in your sketch. The upper tubes run from column to column into the page. Your column bases need to be fixed-base OR your upper tubes need to be moment connections 90 degrees to what you show. I do not think your monorail beam connection to the upper tubes has to be moment connected. In the direction of the monorail beam, you must have fixed bases OR x-bracing. If not, you need another set of beams that connect each U-frame to each other, and that connection must be a moment connection unless you are fixed base in that direction.

If you cannot have X-braces, fixed base in both directions is your most direct solution if you can put in foundations if needed. Given a thick enough slab and a light lateral hoist load, you may get by without foundations. What is your estimated lateral load?

Also, I would not refer to this as "double overhung", I would say it cantilevers on both ends. Cranes are referred to as top running and underhung, so overhung sounds like you are referring to a top running.

 

[lostmeche]

@mmarlow,

The way it is set up is so that the motor or gearbox can be lowered on the right side. Are you saying that the support system is not laterals stable? I checked my flange bending and I'm all good there.

haha yeah. Definitely thrown to the wolves. I was hired a year ago and for the first 6 months I worked under a PE before he retired. As I've been told numerous times "sink or swim". I'm managing to stay afloat.

@Ron247

Yes, there are four columns. Basically two upside down u-frames. I can't have x-bracing in both directions due to the amount of room that is available. The concrete flooring is 8" thick. I'm using 20% of my lifted load as a lateral load. I called it double overhang because with one, my textbook calls it single overhang. But that is good to know.

 

[mmarlow]

Yes, I am speaking to lateral stability. Are you on ground level? A cantilever column could work fine, just do your checks. However, Id try to avoid it, maybe run your columns straight up to the diaphragm above? If its another concrete floor, you could have a really good setup. Just my thoughts.

Keep swimming! Good luck!

-MMARLOW EIT