I have a situation where a 105 kip crane (self weight) with a lifting
capacity of 90 kips, spans 79 ft across the building. The crane rails rest
on crane girders which in turn are supported on built up columns along side
the building columns. The building was an addition with one side of the
crane support along the (e) bldg. The building is in seismic zone 4, less
than 2km from a type b fault.
During installation, the contractor installed the crane rails directly over
the centerline of the crane girders at the existing building. At the new
building side, the contractor has skewed the crane rails to maintain the 79
ft center to center dimension. This meant that the had to burn the holes to
a slotted condition in order to fasten the rail to the girder. I believe the
problem was due to the new columns not being installed plumb, creating a
sweep horizontally, which shortened the span.
This creates two problems immediately recognized.
1. Burned holes... they were not reamed and the slot means that proper
tensioning of the rail clamp friction connection is essential.
2. The alignment of the crane rail creates eccentricities relative to the
centerline of the crane girder. The offset is as great a 1 1/16" Per AISC,
the max. tolerance is 1/4" from the centerlines.
Torsion is now present in the crane girder (W36x245). I am very sure the
beam can take the load under normal conditions, however, this is a fatigue
design condition which makes me cautious.
All comments are welcome along with any other issues that I may be
overlooking as a consequence to this.
Gerard Madden, P.E.
Civil Engineer/Structural Designer
The Bentley Company,
A Division of Enron Energy Services North America, Inc.
Ph: 510.661.0527 (Fremont)
Fx: 510.661.0528 (Fremont)
Ph: 925.543.3810 (San Ramon)
Fx: 925.543.3551 (San Ramon)