huangyhg

hybrid crane runway beam, fb?
when analyzing a "hybrid" crane runway beam that is a combined section with different grades of steel (s-shape- 50ksi, strong axis, with a channel-36ksi at top flange, weak axis), how do you account for the combined different grades of steel when computing the allowable bending stress, fb?
would it be similar to the hybrid girder factor, re, in plate girder design, when the flanges and webs are made up of different grades of steel.
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i would figure out the engineering properties of the combined section, calculate the stresses and compare the stresses in the c part of the member to the 36 ksi allowable and the stresses in the s part of the
you can be conservative and assume grade 50 is 36!!! i am sure you are using grade 550 because that is all is available these days. you can get grade 50 dual certified.
regards,
lutfi
oops grade 550 = 50.
at any rate, i designed countless crane runways using same section combination you are talking about using a36 steel.
good luck
regards,
lutfi
since your channel is the lower grade material and it is at the extreme fiber, it will govern the design of the upper flange in vertical bending and the entire design for weak axis bending. you can use the 50 ksi to check the bending stress in the lower flange. if you were questioning whether there would be some type of equivalent crossection like there is if your are combining separate materials like steel & concrete or steel and wood, there isn't because both grades of steel have the same young's modulous.
the channel will yield until the 50 ksi kicks in... <g> it's an interesting problem, though... i would suggest that the limit state capacity of the combined section would be the entire c section at (or near) 36 and the w at 50...
dik

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