Appropriate Design loads for Monorail System

[FLCraneBuilder]

We are designing columns, headers & footers for a free-standing, 30 ton capacity monorail system, 32' tall. We are somewhat deadlocked on the debate as to what LATERAL load should be applied to the structure (by the lifted load).
AISC (9th edition) page 5-29 notes that 20% of lifted load & trolley shall be used for lateral load and 10% of the sum of wheel loads is used for longitudinal load.

The problem is that this paragraph applies to bridge crane runways (3 axis movment) - not monorail systems (2 axis movement); With monorails, there is theoreticly Zero lateral load.

I believe that 5% is more in order unless there is certainty that the user will be lifting off center (at which point the 30 tons will violently swing towards center)

I would appreciate your opinions on this subject
copy of dwg attached if needed

 

[SlideRuleEra]

An opinion... I consider your 5% proposal to be a very reasonable number. This is based on somewhat rough analogy with assumed forces on the girders of bridge crane:

Page 57 of "Whiting Crane Handbook, 3rd Edition" (free .pdf download from this page of my website

http://www.slideruleera.net/miscellaneous.html

) has the following statement about lateral forces that are assumed when designing bridge crane girders:

Lateral load due to acceleration or deceleration shall be considered as 5% of the live load...

Of course this has to do with fact that the girders themselves, along with the lifted load, can be accelerated down the length of the runway. My point is that the assumed 5% is apparently adequate for "ALL" lateral forces on the girders. With that being the case, I see no reason to assume lateral forces any higher that 5%, for your application. At the same time, going any lower than 5% is probably not a good idea, because of the off center load lift, that you mentioned.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[MiketheEngineer]

Seismic???

That may a much bigger concern depending on where this is going

 

[unclesyd]

Here is a free download of ANSI MH 27.1-2003 that gives the permissible loads on the monorail it's self using a patented monorail.
If the duty cycle is high I strongly recommend a patented rail in lieu of an I beam.

http://www.mhia.org/learning/resour...d-track-underhung-cranes-and-monorail-systems

 

[FLCraneBuilder]

Thank your for the comments;
To MiketheEngineer - The project is located in Florida where seismic loads are not considered. Wind loads are being considered. Thanks for the reminder.

 

[FLCraneBuilder]

Thanks your for the comments;
To MiketheEngineer - The project is located in Florida where seismic loads are not considered. Wind loads are being considered. Thanks for the reminder.

 

[civilperson]

20% is a good number if anyone proposes hooking to a weight not centered beneath the monorail. The 20% horizontal load will be experienced and then drop suddenly to zero when the load is elevated. The swing to the other side will be less than the 20% of weight when friction held the load against movement. Draw a static load diagram and assume a factor of friction of 0.4. Thus when the horizontal component of the cable tension is 40% of the remaining weight resting on grade, movement starts.

 

[unclesyd]

May I ask why would you ever permit an uncontrolled lift with a monorail?
I hope you have a RC controler.

An uncontrolled lift with two carriages is even worse. We have two single carriage monorails that we only allow around a 5 degree, measured at the carriage, off center load. We are going to a bridge crane to replace one of the monorails due to the possibility of having to pick an off center load.

 

[unclesyd]

You may want to checkout the Design of Overhead Monorails at Techclacs. This a PDH course. click on either the title or get pdf.

http://techcalcs.com/technical/civil.php

http://techcalcs.com/freepdh.php

 

[FLCraneBuilder]

Wow - thanks for the excellent responses;
The trolley-hosits will in fact be radio controlled. Duty cycle fairly light. 5 to 8 lifts per day @ 50% to 85% capacity.

Why would we permit uncontrolled lifts? - I've been in this business long enough to know it's expected rather than dis-regarded. The 5% value presented represents an 18" off center pick. To clarify, load is first picked off of a flat-bed truck (which can/should be centered(???)) and then is transferred to a large water-filled tank for testing. Load is then picked out of tank (self centering) and then put back on truck.

Bare in mind we are trying to come up with a practical design load being transmitted into the "flagpole" columns and subsiquiently the footers. The design of the monorail beam itself is much less complicated.