Monorail Design 1

[StrP88]

Is monorail with two trolley possible?
I haven't seen monorail with two trolleys, any pics? Any publication and reference material about structural design of the monorail with two trolleys?
I appreciate if anybody had dealt with this in past helping me out

Respectfully,
Sk

 

[CCox]

Yes. I've done many of these. The two trolley rails I designed were manually powered, but I suppose they could be electrically powered as well. It is the same as a monorail with one trolley, you just have to design the runway rail and supports for two. If you know the trolley dimensions, you can figure out where the wheels will land on the bottom flange and cumulatively add the localized stresses in those areas.

You will have multiple load cases and locations you have to design for. It will take multiple attempts to find the maximum stresses in your member. I utilized RISA 3D and their moving loads to accomplish this. If you have a simply supported monorail, it will be pretty straightforward; link them together and send them running down the runway. If you have a multi span beam, it might take multiple iterations to figure where the maximum locations of hoists are located at, especially if the hoists are rated for different load capacities.

You need to get the CMAA specifications put out by Crane Manufacturer's Association of America. That is invaluable. Use this for one or two trolleys. You should perform the calcs by hand first to make sure you know what you are doing.

 

[MikeHalloran]

We had a discussion here recently where the spreader beam length was about as long as the chord of a quarter-circle of the track (i.e., the track radii were pretty tight), and there was some disagreement about side thrust and other dynamics.



Mike Halloran
Pembroke Pines, FL, USA

 

[CANPRO]

Two trolleys is common and likely required. A proper fall arrest plan requires a rescue plan and in a monorail/trolley system, you likely need a second trolley for the rescue.

 

[StrP88]

CCox (Structural): Thank you for your response and sharing your experience with me. Since, this is new subject to me first question is why they use two trolleys? Or in other words in what cases or for what purposes they use double trolley? Also, unfortunately I don't have any software to model all the cases and also don't know what are all cases with two trolleys. If you have a pic or anything of your past work that you can share that will be tremendous help to me.

Also, when a monorail is rated and labeled, is it based on one trolley or two trolleys?
The monorails I have seen just have the load rate on them and doesn't say that monorail is for two trolley operation or only one trolley operation?

Is linking the two trolleys and running them the worst case for a simply supported monorail?

CANPRO (Structural: Thank you for your response too. Do you know what are the two trolleys operation applications? Is there any minimum distance requirement when operating two trolleys? Any pictures of two trolley on a monorail? I googled and did not find any photos. Very hard for me to get any information.

Thank you gentlemen for your help.
StrP88

 

[StrP88]

Also, I forgot to ask, with two trolleys case, are there any requirement how the load is attached? If two trolleys picking one load, should be only with vertical slings or it can be angled slings to each trolley?

Is the two trolley case applicable for two separate loads each individually with one trolley?

Thanks

 

[dik]

Yup... Dik

 

[StrP88]

Did I ask too much guys? Sorry? Just try to learn and understand. Didnt mean to take too much of your time. Just dont know where to find answers to my questions.

dik (Structural), sorry I didn't understand your response.

Thanks to all reviewer of the ad and the responders.

 

[CANPRO]

Typically these systems are used where access is limited. So if a worker using this system falls or is in some kind of distress (heart attack, allergic reaction, could be anything) using the monorail and trolley is likely the only practical way of reaching him. This is called a rescue plan and is something that is required in a proper fall protection plan. You need to design the rail for its typical use, a potential fall, and the rescue. You may need to consult with the owner and/or the end-user to fully understand how this system will be used.

Where is your project located? There is very likely some codes/standards you should be somewhat familiar with before you get too far into this.

A couple of videos for example...

https://www.youtube.com/watch?v=YchefXKLyfY

https://www.youtube.com/watch?v=TNI9qmE2MTE

 

[ldeem]

Some quick comments:

Unless it is an engineered lift don't count on the user to maintain a particular distance between trolleys.

Very roughly speaking you have three main things to look at:
One: local flange bending from trolley wheel loads. Wheel spacing is a significant factor - I usually assume 1/4" inside edge of flange unless I am sure the owner will use a particular trolley. Then spacing 4 to 6" or so depending on the lift. Look up trolley dimensions on the web for guidance.

Trolley beam sizing - bending and deflection in the middle and shear on the ends near the support. There are several shear and moment examples for moving loads you can find see table in AISC. Don't forget some lateral and longitudinal loading even if not required by code.

Support sizing - connections, design for the full lifted load plus rigging plus beam weight times some factor. CMAA and AISC have some guidance. Don't forget the longitudinal and lateral loading. Even in multi span beams I usually don't consider any sharing of the load between supports. In other words as the trolley runs under a support that support must be able to take the full load.

Finally - no mater what the code minimums are the users are going to bang into the end stops (longitudal load) and pick things up off center (lateral laoding). I used to work in a steel warehouse in high school and we did this all the time.

 

[CANPRO]

Ideem,I assumed he was designing a monorail and trolley system for access, not lifting a load - this assumption was based on another recent thread started by StrP88 asking about fall arrest loads and direction of the applied loads. After reading your response I realize I may have been off the mark. StrP88 should provide more info to clarify.

 

[PaulG93]

Alex Tomanovich has developed dozens spreadsheets for different structural applications, including one for simple span monorails (see link below). This spreadsheet references AISC and CMAA No. 74 but doesn't do support sizing (but does provide reactions) and explicitly have the ability to analyze for two trolleys. You could manipulate it for two trolleys by playing with the wheel spacing. For a multispan trolley you'd have to develop your own moment and shear envelopes, but you could use the spreadsheet as a guide and to check the bottom flange bending.

Monorail Spreadsheet