The Structural Engineer > Archive > Volume 61 (1983) > Issues > Issue 12 > Discussion on A Development in the Automated Design and Fabrication of Portal Framed Industrial Buil
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Discussion on A Development in the Automated Design and Fabrication of Portal Framed Industrial Buildings by Professor P.J. Dowling, T.F. Mears, G.W. Owens and G.K. Raven

Mr D. Beckett (Sir Frederick Snow & Partners): The design objective was to utilise the potential of automated fabrication techniques applied to non-prismatic frames to dgvelop a profile that broadly follows the form of the bending moment diagram and thus achieve significant weight reduction. An initial study of 21 span frames indicated that a weight saving of upwards of 250 kg could be achieved by using a tapered plated frame as an alternative to a plastically designed prismatic frame. This weight saving could be achieved only by adopting an unstiffened webdepth- to-thickness ratio of about 2.5 times the limit in the current edition of BS449. A departure of this magnitude from a current design standard obviously requires detailed theoretical and experimental investigations, but the precedent was set with the extensive use of tapered frames in the USA with a limiting web-depth-to-thickness ratio of 240 for grade 50 steel. The development of the design method progressed simultaneously with the test programme and the first step was to examine the elastic interaction of bending, shear and axial load effects on web plates, using the interaction formula shown in Fig Dl. The results were not encouraging but the first series of tests on frames fabricated in the USA revealed that the most significant design criterion was the stability of the compression flange. In spite of initial web distortions, web instability was not apparent. There was a subsequent shift in emphasis from considerations of web stability to the containment of lateral torsional instability of the compression flange. To achieve this, the following assumptions were made for a bending strength check.