Crane Girder Bidding

[haynewp]

Do these sizes sound reasonable?

I sized a girder for a 5 ton crane (crane bridge span=60')at W18x40 with a C12X20.7 on top. This was a 32.5' span girder with 2-wheel loads of 9kips (including impact) with a wheel base of 8.25'. My approximate deflection was about 0.82" or l/475. Max stress is 19.3 ksi (tension)for the bottom flange (21ksi allow.).

I also sized a girder for another 5 ton crane (bridge length=40') at a W16x26 with a C10X15.3 on top. This had a girder span of 25' and wheel loads of 7.1kips (including impact) with a wheel base of 6'-7". My approximate deflection was 0.78" or l/380. Max stress is 20ksi also in bottom flange tension (21 ksi allow.).

Both girders were designed as simple span. I think my fatigue limit fluctuation is about 18ksi by ASD appendix K.
I took the unbraced length for compression at the total girder length and the compression stresses have a few more ksi to spare. Weak axis didn't seem as a problem either. The longitudinal axial seemed negligible as well. The girders are going to sit on top of their own columns.

I had to figure out how to do this-including finding all these built up properties today in about 1.5hr to get a bid out.

Any help on this one is extremely appreciated.

 

[haynewp]

I guess my main concern is that my deflection and my stresses would be considered too high for a crane beam?

 

[ishvaaag]

Haste is not a good companyon in design. Proportionate time for design allows the designing parties to mentally review all or most of the relevant issues that to the case pertain. Then, what can one say about any design of this practical kind but ensure you are meeting at least what a pertinent code demands? This is what codes are mainly for, to ensure a basic sets of procedures available to expert and less than expert design and construction parties, normalizing the industry about the item. So if you had the time to make all the verifications required in 90 mins, how good.

I posted one freely available worksheet in Mathcad for the design of crane bridge beams -to my own surprise (I have never had to closely focus on crane design) one of the more sucessful- but is for box shaped bridge-beams. A tool like this gives the design in minutes. If you are satisfied with it, you may adapt it to other sections. I'd rather recommend yorself make your own tools if you think you are going to have such haste in producing repetitive designs.

 

[haynewp]

I agree, haste is not good for design, now if I can just convince my boss of that. And to stop hitting me with that whip.

 

[dlew]

haynewp,

In crane runway design, connection details are also critical. For a good review of crane runway design, I would recommend "Light and Heavy Industrial Buidings" by Fisher and Buettner (published by the AISC), and two old articles from the AISC's Engineering Journal: "Lessons from Crane Runways" (Jan 1965), and "Tips for Avoiding Crane Runway Problems" (4 quarter 1962).

AEF