Cutting off bar joists; replace bottom with I-beam 2

[Thoughtclaw]

I'm the staff engineer for a smallish contractor. A customer has come to us needing more head room over a machine they want to bring in. There are 30" bar joists in the area, and they were hoping to replace those with 6" beams if possible. My analysis shows they need at least a W8x15 (it's a 20' span), and they said they can work with that. My initial approach was to put a new frame up with columns just inside each wall. Our chief estimator came up with a much less costly option, and it seems to me it could work, but as I'm still fairly green, I thought I'd run it past you folks. His idea is to weld a plate to the top chord of the bar joist, then seat the beam on an angle that's bolted to that plate. I've never analyzed such a thing and am not really sure how to go about doing so, but I'm confident I can figure it out. But before I dug into it, I thought I'd seek some outside opinions from those more experienced than I. I've attached his very rough sketch of the idea. Any thoughts?

 

[Thoughtclaw]

The building dates back to the early 1980s. So it's older, but not super-old.

 

[jimstructures]

If this is a Butler Building, is it possible that these are not Bar Joists but are actually a proprietary Butler product called Truss purlins?

If so they are not designed to meet Steel Joist Institute standards. They are a proprietary product. Get Butler involved in this redesign and modification.

Butler has a line of buildings called Landmark buildings which are long bay, up to 50' or 60' and older models could have open web beams as well.

I repeat get Butler involved if it is a Butler product.

JimStructures, a 10 year Butler employee.

 

[Wallache]

It could also be Butler Delta Joists, which would put the top chord spacing short enough for the standing seam to span directly.