Limit states design of crane runway girders

Steel crane runway girders are subjected to torsion by their eccentric loads. The twist rotation of the principal axes caused by torsion induces additional bending moments, and reduces the resistance to lateral-torsional buckling. There is little guidance on how to design for torsion, and design procedures are often intuitive, with varying degrees of rationality and precision. This paper seeks to establish a logical procedure for designing crane runway girders which is based on an extension of the limit states methods of designing for biaxial bending. An additional term for the ratio of the design torque to the section torsion resistance is included in the interaction equations. Proposals are made for determining this section resistance. Research has shown that this addition can allow for the reduction in the lateral-torsional buckling resistance caused by the twist rotations. A linear elastic analysis of the twist rotations is used to determine the moment increases caused by torsion. An example of the proposed method is developed and illustrated by a design example. The design is governed by the member capacity, which is mostly affected by the lateral-torsional buckling capacity. Torsion has a very small effect, and the twist rotations are small. The twist rotations cause a significant increase in the minor axis bending moment, but this has only a minor effect on the member capacity.