SDC Torsion Design

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AIST Torsion Design

Structural Design Corporation has inspected thousands of EOT Crane Girders.  It has been a challenge to either repair existing crane girders or design new girders that would prevent the same types of failures that we see in the field.  This challenge came to a head in 1992 when inspecting a Slab Yard Shipping Building.  The building and crane runway were 8" out-of- gauge from the ends of the building due to the heat generated from 20 foot tall stacks of hot slabs.

The cranes were binding as they bridged down the crane runway.  The binding forces were causing brittle fractures of the crane girders.  SDC informed the mill that they could either continue to live with a sudden fracture of the crane girders and risk dropping a crane to the ground or they could move the crane rails 2 1/2" off the girder centerlines and slowly cause the crane girders to warp.  Engineering chose to move the crane rails and buy time to rehabilitate the entire Shipping Building.

SDC performed its first complete torsional analysis of a crane girder to check the girder stresses.  As part of our analysis we reviewed the torsional design requirements of AIST Technical Bulletin 13.  SDC needed to know the limitations of the AIST procedure.  We found that the AIST procedure is conservative for doubly symmetrical girder cross sections. but may not be conservative for singly symmetric and unsymmetrical cross sections. 

Attached is a paper written by John Fong, SE that describes the Classical Torsion and AIST Torsion Theory.  It may be helpful to understand these theories before trying to understand the SDC Torsion Design that is based on Warping Torsion Theory.

AIST Torsion.pdf