Composite beam studs/rib

[ARKeng]

I have a question on designing composite steel beams. RAM steel will give a minimum number of studs but I'm not sure how to make proper use of it.

For example, I'm designing a 30' long beam with deck perpendicular to the beam. The deck has rib spacing of 12" oc. But RAM tells me the number of studs as 42, and I've seen a number of engineers basically just call that number out.

My question is, how do they figure out how to "uniformly" space 42 studs in 30 deck ribs? Do they automatically just say "that's more than 1 stud per rib so let's put in two studs per rib"? If so it would make sense to automatically jump from 30 studs to 60, no? I'm just trying to figure how to do this economically since RAM gives you the bare minimum (sometimes with less than 0.1 kip*ft to spare on the moment capacity) and I'm trying to balance upsizing the beams one size versus more studs.

Thoughts?

 

[ishvaaag]

In your case and if sure of the number of studs, I would place 30 in 1 per rib and (except for quite unsymmetrical shear solicitations) 6 from supports, each side, in the first 6 ribs. This way you will be following closer the kind of elastic shear transfer at the interface, giving a better service life.

 

[a2mfk]

upsize your beam until you get < 30 studs

There is a rule of thumb for how much an installed stud equals in pounds of steel, worth googling under current economic conditions. Sometimes its better to upsize, studs are not free.

 

[BAretired]

I think you can take either alternative as presented by ishvaag and a2mfk. It seems to me that adding studs near each end of the beam makes good sense as you will be following the VQ/I diagram more closely.

In the end, economy will dictate your best option.

BA