Lateral Thrust - in under-running monorails systems

[SM3225]

Hello Everyone,

I have one question as to the applicability/feasibility of lateral forces (?) on the bottom-running monorails systems - travelling along the bottom flange of the supporting beam.

Understandably, in case of top running crane girders lateral surge force is mainly derivative of the thrust from sudden application of brakes attached with crab(trolley) motor... estimated as 20% of the combined weight of the lifted load and trolley.

However, my feeling suggests that in the case of bottom running system the load to be lifted is constrained to move along the bottom flange of the supporting beam, since for an under-hung and under-running system the end trucks operate on lower flanges of the runway beams.

Since there is no movement of the lifted weight in the lateral direction which could result in zero lateral force in the design of under-hung and under-running monorails systems.

Does this sound legitimate to anyone in this forum?

Please let me have your opinion.

Thanks & Regards.

 

[Ingenuity]

So you have a underhung monorail hoist with NO orthogonal runway beams?

Since there is no movement of the lifted weight in the lateral direction which could result in zero lateral force

The lifted load may not be centered vertically below the hook, so upon lifting there is a horizontal load component and also the load swings and therefore laterally loads the hoist girder.

Last month (May 2017) AISC conducted a live webinar by Lucas Pachal, entitled "Design of Underhung Hoist and Crane Girders". The stated lateral crane loads, acting horizontally at the traction surface of runway beam (top of bottom flange) perpendicular to the beam were 20% of sum of [rated load capacity + hoist weight + trolley weight] but NOT including bridge weight as the bridge is NOT moving. If there are runway girders, 60% of the 20% to be assigned to one runway girder to control differential stiffness of the runway girders.

 

[SM3225]

@ Ingenuity :=

Thanks for the prompt response.

You are absolutely correct I am concerned only with under-hung/under-running monorail hoist without any orthogonal runway beams. Me too have come across a similar literature that suggests consideration of lateral force as high as 20% - also ASCE7-10 is silent about the possible treatment for monorail hoists (Ref cl 4.9) - in other words much focused onto the Overhead travelling cranes on crane runway beams - I believe.

In reality I am dealing with a monorail beam which is supposed to carry 20 tonnes over a span 20'-0" ... client advocate using of S shapes only... they do have a similar facility where monorail beams are "S-shapes"... Indeed I have made the system workable against all odds for instance Flange buckling, local flange stresses under the wheels and tip-deflection etc - lower flange bending controls the scenario.

Consideration of 20% lateral load results into considerable torsion on the monorail beam - as well as making the situation worse in terms of monorail beam lateral deflection - permissible limit of L/400 is achieved if full weak axis moment of inertia would be utilized else engaging the top flange properties alone against the probable weak axis displacement - resulting into bumping up the member size enormously- well beyond the expected limit.

On a precise note what I am looking for any justifiable reason which could waive this 20% criteria, per current situation the monorail system is extended by an amount of 1'-0" beyond the column line to get the monorail hoist directly over top of the load ... eliminating the possibility of picking up a load sideways - reducing the danger "swinging of the load".

Also please let me know any special connection requirement to cater for this lateral load - presently it is 4-3/4" dia bolts on gauge.

Looking forward for your response.

Thanks & Regards.

 

[mtu1972]

I've designed monorail's for many industrial facilities and do agree with Ingenuity. You should include some lateral load.

The "clowns" doing the work will not worry about the load being "centered" under the monorail. I've seen them have several workers pulling sideways when trying to position the load onto the vehicle/trailer brought into remove/replace the lifted device.

When lifting it off, they hook up the hoist and lift, just letting it swing.

I used 10% lateral load (approximately 5 degrees out of plumb). Don't know if it can be found in any code. The 20% is too high and not relevant as the "load" is not traveling perpendicularly.


gjc

 

[SM3225]

@mtu1972: Your explanation is perfect. 10% lateral load is quite reasonable would not load the monorail beam too much. Thanks.