Scale-Model Structure tests with Particular Reference to All-Welded Plate Girders

AT the World’s Fair to be held in New York during 1939, there will be seen two structures of outstanding interest; they are the Trylon and the Perisphere. The Trylon, which is a three-sided steel tower 610 ft. in height tapering to a point at the top, has been referred to by the steelworkers as the "Needle." There are approximately 39 lengths of column in each of the three legs. Starting at the base, heavy box sections are employed. The fist section which is attached to the column footing, although only a little over 12 ft. in length, weighs 26 tons. As the legs taper upward they gradually become lighter, a variety of box sections being used with cover plates laced and battened ; the top leg sections are formed of straight beams. Two types of construction are used, and at a height of 480 ft. the framework of the Trylon changes from column legs, braced with diagonals and struts, to plate construction. The complete 130 ft. of plate tower section was assembled as a whole, a task which presented difficulty to both the erectors on the site and to the fabricators in the workshops, on account of the triangular shaped piece being less than 15 ft. across the base and only 2 ft. 7 in. at the top. Also the holes in this part of the tower were all countersunk, making it harder to pin and assemble the material. The work involved an unusual amount of bending and welding, and in the plate sections at each corner a large heavy angle section had to be closed for its full length from the usual right angle as received from the rolling mills, to 60 degrees.

Mr. J. TAYLOR THOMPSON (L.N.E.R.) proposed a hearty vote of thanks to Mr. Bruff for his interesting paper, and particularly for the lantern slides by which he had illustrated it, some of which had disclosed steelwork in a condition which was almost startling. Another reason why Mr. Bruff merited the thanks of engineers was that he was the outstanding enthusiast in this country, if not in the world, for the application of welding to the repair of bridges.

THE PRESIDENT (Professor J. Husband, F.R.C.Sc.I., M.Inst.C.E.), following the presentation of the paper, said that Mr. Bowie had made out a very good and probably a very closely approximate case. All structural engineers knew that in dealing with reinforced concrete it was impossible to derive absolutely accurate mathematical theories. The amount of mathematical formuls which had accumulated during the last 30 or 40 years was simply colossal. Probably we approached a little nearer the truth in the course of time, but the assumptions that had to be made when dealing with so complicated a material rendered it impossible - and it would always be impossible -to make exact calculations in respect of reinforced concrete structures. That was true even for the simplest element of reinforced concrete construction. When we came to cases such as slabs and dropped slabs carried by variously shaped column caps, the exact theory, if it were accessible, would be staggering. The only way in which to approach problems of that kind was the way in which the author had approached them in the paper. Certain common-sense assumptions were made in the paper, just as it was necessary to make common-sense assumptions in a great many other engineering problems, and the assumptions made in the paper appealed to the President as being perfectly sound and rational. He urged that those who agreed with the author’s statements should say so, and that those who considered that any of the author’s conclusions were wide of the probable truth should also express their views. Having read the paper very carefully before the meeting, it seemed to him that the author had given his problem a very sound, closely approximate and sufficiently practical treatment. He congratulated the author on having dealt with a comparatively dry but very important practical subject in so satisfactory a manner.