huangyhg

existing runway beam reinforcement
we are upgrading shop cranes and existing runway beams (w beam & channel on top) need to be reinforced. the easiest fix for our shop is to weld another w beam (channel will not be sufficient) under existing one (flange to flange). my question is how to calculate allowable bending stress for this "strange" section. how to check bending about y-y axis in the top flange. any suggestion would be appreciated.
ibro v.
check out our whitepaper library.
go back to basics. take the shape and your first year materials and sections book and figure it out.
richard a. cornelius, p.e.
while adding another wf beam is easy, it is not the most efficient way to reinforce crane runway beams. you should be concerned with the compression flange. adding another beam will place the neutral axis lower from the top flange (compression flange) which will not buy you much top section properties.
i suggest adding two angles and weld them to the top flange. this way you can "lift" the neutral axes closer to the top flange while increasing its section modulus.
to compute the properties, as stated above, you need to go back to basics. if you can not do it by hand, you really have no business in attempting to reinforce a beam. the stress calculations are simple but rigorous. you have to have a good understanding of how to compute the allowable compressive strength. i doubt that the tensile stress will govern. you add area to the bottom flange very easily.
another concern is the weld between the existing section and the new section to ensure composite action. that needs to be studies carefully.
if you do not know how to do this, it is ok to get expert help and expect to pay for it.
aisc has several article sin the engineering journal that addresses this topic. they also have a design guide that deals with industrial buildings which has a section on over head crane design. gaylord and gaylord have some write up and examples on crane runway and bridge design. whiting crane handbook is one of the best texts written on overhead cranes. unfortunately, it is out of print. i happen to have one copy in my library and i would not part with it for any price.
i have designed many cranes and written masters鈥?thesis on overhead crane and runway design. i could share some information with you if you need more help.
regards,
lutfi
lufti-
i agree that adding angles to the top flange is the best method to increase section modulus, but the existing beam has a cap channel. would you add these to the flanges on the channel? i've seen w-sections added to the bottom flange of existing runways before, but the runways also had horizontal trusses for the lateral force.
ibro-
your y-axis bending will not be any better than what you currently have by adding an additional w-shape to the bottom of the existing runway. is there enough room to provide a horizontal truss on the outside of the runway or is there a maintenance catwalk at runway level?

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