Welded Steel Truss Tolerance 1

[Mistieats]

Hi fellow structural engineers,

My team just designed a steel truss roof with a 50' span and 10' width, with some tight clearance (1-1/4") with adjacent steel structures. We received some pushback regarding the manufacturability of the steel truss: the contractor is worried about the shop welding of the truss connections. What's the normal tolerance we should expect for a 50' steel welded roof truss?

Thanks!
JC
EIT

 

[DrZoidberWoop]

The connections at the truss ends need to be bolted up (or something), so I'd expect the acceptable/rough tolerance to be approximately the wiggle room allowed by the end connections. An experienced shop should be able to handle that without issues. Otherwise, The general tolerances are per AISC Code of Standard Practice and ASTM A6.

During fabrication, the weld joints are supposed to be inspected via AISC 360 Table N5.4-1 "Inspection Tasks Prior to Welding", which covers the alignment and preparation details of the joint in question, and for compliance w/ AWS D1.1 4.17.5 (2020) (weld tab requirement at possible welded chord splices. No weld dams). The truss will be laid down on the bucks in the fab shop and inspected before welding commences.

For a 10' tall truss, spanning 50', you likely don't need to consider pre-set elevations, camber, or diagonal member shortening/lengthening. If you do need to account for those, things become more complex to detail, but still something an experienced shop should be able to deliver and erect.