Interaction buckling of tapered beams

• Lateral buckling is affected by moment distribution, taper, and restraints between segments.
• Moment distribution is allowed for in design codes by using Cbm factors.
• Taper is allowed for by using mid-segment section properties and Cbt factors.
• Restraints are allowed for by using effective length factors.
• Approximations are compared with accurate computer solutions.

There have been comparatively few studies of the elastic lateral buckling of braced or continuous tapered beams, and these are limited in their application. Lateral buckling is affected by the separate effects of moment distribution, taper, and restraints between adjacent segments.Moment distribution effects are commonly allowed for in design codes by using Cbm factors to multiply the classic lateral buckling moments Mu of simply supported uniform beam segments in uniform bending.Taper effects for linearly web tapered beam segments may conveniently be allowed for by multiplying the segment lateral buckling moments Cbm Mu computed using the mid-segment section properties by taper factors Cbt. Values of Cbt for a number of different segment moment distributions have been determined using a finite element computer program for the buckling of tapered beam structures.Lateral buckling of a braced or continuous beam is also affected the interaction between the segments into which it is divided by its braces and supports. One segment will be more critical than its neighbours, which will restrain the critical segment and increase its buckling resistance. The effects of restraints on buckling are commonly allowed for by using effective length factors to multiply the segment length used in the formulation of the elastic lateral buckling moment Mu of a uniform segment in uniform bending. Methods of determining the critical segment and of approximating its increased resistance developed for uniform beams have been adapted for web-tapered braced and continuous beams.This paper shows how these effects can be allowed for separately to develop good approximations for the elastic lateral buckling resistances of tapered braced and continuous beams. The accuracy of the approximations is demonstrated by comparisons with the predictions of the finite element computer program for the buckling of tapered beam structures.