Crane Runway Beam Minor Unbraced Length
Crane Runway Beam Minor Unbraced Length
(OP)
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?
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?






RE: Crane Runway Beam Minor Unbraced Length
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RE: Crane Runway Beam Minor Unbraced Length
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?
RE: Crane Runway Beam Minor Unbraced Length
I wouldn't do it.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Crane Runway Beam Minor Unbraced Length
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.
RE: Crane Runway Beam Minor Unbraced Length
RE: Crane Runway Beam Minor Unbraced Length
Thank you all for your input.
RE: Crane Runway Beam Minor Unbraced Length
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
RE: Crane Runway Beam Minor Unbraced Length
RE: Crane Runway Beam Minor Unbraced Length
"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.
RE: Crane Runway Beam Minor Unbraced Length
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.
RE: Crane Runway Beam Minor Unbraced Length
Dik