Sizing Bar Joists

[johnny watt]

I see my local Lowes/Depot both have roofs over their contractor loading areas and both went about the design completely differently. Both I assume should have a 70lb snow load design. One uses bar joist and the other uses light gauge 2x10 or so, in combination with more I-beams. I guess at some point, trucking permits are a factor and the crane size needed too, but I would think they should have come to similar solutions.

Building commercial structures between 50’ and 80’ deep and I started wondering what is the most cost effective depth of a building for clear span bar joists. When should I make the decision to go with a wider building instead of deeper one or when should the architect decide to spec a decrease O.C. spacing or when is it worth it to add some internal columns instead of trying to clear span, or how much of a premium am I paying for the flexibility that clear spans give to the interior floor plans?

Deeper is Cheaper according to the literature, but I don’t see any pricing readily available on line to help determine the optimum spans. I guess you have to get a quote each time or guess by the pound?

[dave_k]

The general rule is the longer the span the more $/sf to build. You pay for bay width. Means assemblies cost data book is a valuable resource for answering such questions. http://content.reedconstructiondata....0Sheet2013.pdf It's an expensive book and I wouldn't use it to bid work but it's a great planning tool. The $ amounts go out of date but unit number rarely change. You can plug in current numbers if need be. I threw out my 1992 copy just a couple of years ago.