Drift limits for a mill building

[tw]

I have a contractor that is bidding on a design/build for a new mill. One of the buildings is a mill building that will house an 80 ton class F crane. This thing is 82 ft high and 76' wide and they want the frames on 30 ft centers.

Anybody have a feel for what drift should be allowed due to wind/seismic. H/400 is less than 3 inches and I'm having a hard time making that happen.

tw

 

[dik]

If it's a design/build, then the parameters for drift should be specified as well as fatigue limits for the crane beam and supports. I don't have a copy of the document, but the AISC has a publication on industrial buildings with cranes. I have one for the CISC, but haven't checked it for maximum drift. I would think that L/400 is not unreasonable, but you should check with the crane supplier. For an 80 ton crane... approaching a total load of 90T... the P-Delta can be significant... also bracing the frames with longitudinal breaking/end stop forces off centre from the frames may be an issue... It may be least expensive for the design builder to put cross-bracing in areas where it is not acceptable for the end use...

Wind seismic and bracing are other issues that should clearly be stipulated in the package... as well as warranty beyond the one year... I use a fairly restrictive set of notes for metal buildings... comes from a problem with girts supporting the top of a masonry wall having an L/90 deflection... and the extra to contract for correcting this to something reasonable...

If it's an industrial building, you may want to spec additional loading for the frame and purlins (for example 1000 lbs supported from any point on a purlin or 2000 lbs supported from any two locations on the frame). Check with the owner to see what his needs are and have him sign off the loading...

Just some ramblings...

Dik

 

[tw]

From an AISC article (for this building the 1" drift at crane level suggested below will be a killer):

Lateral Stiffness for Industrial Buildings with Cranes

Drift criteria for buildings with cranes are not only dependent upon the choice of wall system, but also upon crane movements. For pendent-operated type crane systems, buildings with calculated wind drift ratios of H/100 have performed. However, crane movement can generally be observed. A structure which is this flexible should be described to the owner beforehand so he is not surprised to see his structure move and rattle when the crane is in use. It is suggested, for cab-operated cranes, that building lateral drift be limited to H/240 for both crane loads and wind loads.

In addition, the lateral sway at the elevation of the crane runway should be limited to roughly one inch. Structures supporting computer-controlled cranes will probably require more restrictive tolerances. Although not a drift criteria, it should be mentioned here that it is not recommended to tie masonry walls into crane column steel because of the frequent movement of the columns due to crane action.

 

[BSE05]

I have seen conditions where the crane columns ( set interior to the building columns) separated by a work isle, were braced back to the crane columns. This type of trussed approach would help limit deflection.