April 8, 1999
Challenging the Traditional Concepts of Torsion in Open and Hybrid Open/Closed Cross Sections
by
Dr. K.T.
Kavanagh
Head
Department of Civil and
Resource Engineering
Torsion in civil engineering structures is an area which has traditionally been relegated to secondary importance, and engineering solutions frequently rely on avoiding the problem rather than analyzing the problem. One of the classical examples of avoidance occurred in the early AISI Specifications for Cold Formed Steel, where quarter-point bracing was adopted to effectively eliminate torsional effects. Engineers can unknowingly commit serious design errors when they rely upon strength models to design for torsion (i.e. the lower bound theorem of plasticity). Strength design assures safety but does not prevent problems associated with serviceability.
This talk examines the role of
the shear centre in the analysis of open and combined open/closed cross
sections. Examples are given for thin walled beams and building core walls. A
simple finite element-based method is proposed for determining general
properties of such sections, and the traditional location of the shear centre
is examined. Implications of the analysis are given in terms of a modified
linear element for warping and uniform torsion in complex cross sections.