Great Exhibition Building — Testing the Girders. The Illustrated London News (1850): 413. Source: An Internet Archive online version of a copy in the University of Michigan Library. Click on image to enlarge it.

Text from The Illustrated London News

Among the various objects of interest which present themselves to the mind of the risitor to the building, one of the most Attractive is the method of testing the test-iron girders (1141 in number, each 14 feet span) which ere used throughout the building. This is effected by means of the hydraulic press invented by Mr. Bramah; an apparatus which, as our readers will doubtless remember, avails itself of the peculiar properties of fluids, which being submitted to compression, the whole mass is equally affected, and the compression operates in all directions. A given pressure, for instance, made by a plug forced inwards upon a square inch of the surface of a fluid confined in a vessel, is suddenly communicated to every square inch of the vessel's surface, however large, and to every inch of the surface of any body immersed in the fluid. The apparatus used in the present instance is a modification of Mr. Bramah's invention, and consists of a very strong cylinder, with double pistons of proportionate strength attached to the under aide ot the frame in which the girder to be tested is fixed, and through openings in which the ends of the pistons pass, so as to apply the pressure upon the exact spots on which the load to be ultimately borne will be placed. Connected with this cylinder is a pipe, leading from the force-pump, below which is placed a tank for the reception of the water, if the area of the bore of the force-pump stands in a certain ratio to the area of that of the testing cylinder, whatever pressure in pounds weight may be brought to bear upon the lorce-pipe, the power of the water acting upon the testing pistons will be equivalent to as many times that weight as the area of the testing cylinder exceed* that of the force-pump. A valve is attached to the pipe leading to the force-pump, on which a weight, regulated by the proportion of the areas to which we have alluded, is placed. As soon as the pressure upon the testing piston has reached the desired force, the compressed water presses through the force-pipe and raises the weight. If the action of the pump be still continued, a safety-valve in the blinder of the force-pump is immediately raised, and the surplus water returns to the tank The amount of pressure used in testing the girders vanes according to their strength, and the positions they will occupy in the building: those supporting the galleries are tested at 22 and 15 tons; and those which bear the root at 9 tons. Althoagh the weight required to break any of these girders would probably be at least double that to which they are respectively tested, the latter, or testing weight, far exceeds any strain to which the most liberal calculation can imagine they are ever likely to be exposed. [414]

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Last modified 21 August 2017