Crane Runway Beam Minor Unbraced Length 2

[waytsh]

Hi All,

I am interested in getting your opinions as to whether or not it is acceptable to consider the wheels of the crane as minor axis brace points for the runway beam. I have always considered the minor axis unbraced length to be the full length of the runway beam but it has just come to my attention that there is a school of thought which calculates the minor axis unbraced length using the crane wheels as brace points with the crane located in a position which generates the maximum moment. It is my understanding that the reasoning behind this is that when the crane beam is fully loaded the opposite crane beam is minimally loaded and therefore has reserve strength to brace the fully loaded beam.

What do you think?

 

[SlideRuleEra]

Interesting concept. IMHO, I would disregard it when designing the structure for the crane's rated load (100%), but consider allowing it for the maximum 125% TEST load required by OSHA (in the USA).

http://www.SlideRuleEra.net

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[JAE]

I would wonder if the far beam would have the required stiffness (laterally) to brace the main beam. I also wonder if there is a concurrent lateral thrust at the same time if the far beam would really be doing any good.

I would also wonder how I'd sleep at night if I counted on that far beam to brace my fully loaded beam...but that's just me.

Can you check the stiffness required based on AISC Appendix 6?

 

[paddingtongreen]

It is a strange idea that the object delivering the lateral force should be considered to provide lateral bracing at the same time. Further, would there be enough friction on the unloaded side, the flange doesn't help on that side.

I wouldn't do it.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[weab]

Most cranes wheels that I deal with have only one flange. Depending upon which way the bucking flange chooses to fail, the wheel on the opposite rail will likely slide rather than grip the rail.

You are also assuming that the internal hardware of the crane is stiff enough. I don't know about the stiffness of wheel bearings and such and their abilities to transmit sufficient lateral load.

I wouldn't do this.

 

[JAE]

I think weab really has a good point. Agree.

 

[waytsh]

I agree, I think weab had a really good point as well. All of your comments have mirrored my feelings. This came up as an optional setting in some design software which suprised me because I had never heared of it being done before. Apparently it is common enough to warrant such a setting and I was curious to learn a little more about how common it really is and how exactly the justification for a lateral brace is made.

Thank you all for your input.

 

[Neilmo]

waytsh

There is a clause (which escapes me at present) somewhere in the British Standards, which states words to the effect that - you are not allowed `mutual dependency` of any restraint, there must be a positive connection to something solid. Your crane is effectively a mutual restraint to two runway beams with no fixed connection to anything solid and is therefore not acceptable. So I agree with the other comments and yourself, that you should take the full length of the runway beam. If this length is to great for minor axis bending, one solution is to place a channel section member (toes down) over the top flange of the beam, thereby increasing the section modulus in the lateral direction.

Neil

 

[CTW]

Where does the school of thought originate and what is the design software? I agree with the others here, although it is an interesting concept.

 

[apsix]

From AS1418.18 'Crane runways and monorails' Appendix C2

"The method of verification for lateral buckling shall be in accordance with the procedures given in the nominated structural standard.
The limited interaction between the 2 opposite runway girders may be taken into account by increasing the ry value by 20%."

It's not quite using the wheel locations as brace points, but it does recognise some benefit.

 

[hagi10]

Dear all,

Could you please, suggest softwares for "CRANE RUNWAY BEAM DESIGN" with advantageous and disadvantageous? One of my concern is I need a software only for runway beam design, and I don't want to pay for a full steel design software which I already have.

Thanks much.

 

[dik]

Unless I had a moment connection between the crane wheels and the crane beam <G>, I would not consider these as being good lateral support braces...

Dik