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THE CHAIRMAN, proposing a vote of thanks to Mr. Etches for his excellent paper, said it was clear in the first place that the conception of the project as a whole, and also the development of the details gave evidence of much care and thought. The problems which had to be solved were considerable, because they had included not only the usual difficulties relating to the design of a new building, but they also included
many particularly difficult problems associated with altering existing buildings and making them serve other pulposes. He thought that Mr. Etches and all concerned with that project should be congratulated on the success which they had achieved in their solution to these many and varied problems. He had found it very interesting to compare the slide of one of the original buildings (roofed with Belfast trusses) with
the slide of the new structure which had replaced it. The fuss and complication of the old structure had given way to the simple and finely proportioned portal framed structure, which he felt sure that everyone would agree was very satisfying to the engineering eye. It was also clear that a great deal of ingenuity had been shown in the development of the details, for example, the specially shaped gutter, with its overflow weir just beyond the end wall-which would effectively prevent flooding inside the building in the event of particularly heavy rain or a blocked downpipe.
The development of satisfactory design rules for beams of slender proportions, which are prone to lateral instability, has taken place gradually since the introduction of the first rolled sections, over a century ago. Until the presentation of rational data in the recently revised B.S. Code of Practice for the "Structural Use of Steel in Buildings", design formulae have been of an empirical nature. These were based on the
conception that lateral buckling was entirely due to collapse of the compression flange of a beam, as a strut under variable end load. In consequence the formdlae
gave estimates of load carrying capacity which were often considerably in error, as a result of neglecting the torsional stiffness of the member.' The new design rules
are based on the mathematical theory of stability and will give reasonable estimates of the limiting stresses in beams whose slenderness ratios exceed a certain minimum value, in the same way that the Euler formula proves satisfactory in calculating the critical stresses in slender struts.