MODEL OF THE KEY BRIDGE.

Wanganui Chronicle, Volume 5, Issue 270, 28 November 1861, Page 4

MODEL OF THE KEY BRIDGE.

The model of Mr. "Woore’s “ Key Bridge” in the exhibition has attracted a considerable amount of attention, and numerous inquiries as. to its principle and construction have been made of the machinists, Messrs. James and Davis, whc are in attendance for the purpose' of giving explanations to visitors. The peculiarity of the bridge was recently described by its inventor in a paper read ai a meeting of the Philosophical Socsjatj; and which appeared in our columns. We subjoin a few particulars respecting the principle of the bridge, premising that its construction can only be understood by an inspection of the model. The distinguishing feature of the key bridge is stated to be “ a new disposition of timbei struts arranged in a series of triangles tc form a trussed beam in such a mannei that the strain rests solely on the longitudinal fibre of the timber, and that the whole is incapable of longitudinal expansion.” The main design of the inventoi was to construct a strong timber bridge adapted for crossing the creeks and ravines of this colony, and capable of being carried over a considerable span without any intermediate supports. The piers oi the proposed bridge are of stone, and upon either of these rest the ends of three diagonal struts, the lower one of which meets at about a right angle the corresponding strut from the other pier; the other two extend at different angles, and are joined at their opposite ends to smallei struts so as to form triangles, the uppei angles of which are right angles and fil into grooves prepared for their reception in the girders. These press consequently against the fibre of the struts, and the whole weight of the bridge falls perpendicularly on the piers. The struts and the girders are secured to each other by duplex vertical braces, fastened at tlieii ends with iron straps. The planking foi the roadway rests upon the girders as in ordinary bridges ; and in addition to the piers for the struts, there are to be uppei piers, or some other kinds of support for the ends of the superstructure. -The model is made of rosewood very cleverly executed 5 it represents a bridge of a hundred feet span, the scale being threequarters of an inch to. the foot. The thickness of the scantling for a bridge oi that size would ha six inches; in the model the thickness, is only three-eighths of an inch. In order to test the strength of the bridge, weights . amounting to five and a half hundred weight were placed upon it, which were occasionally increased, with scarcely any perceptible deflection. The weight of the,model is less than nineteen , pounds; it consequently sustains more than, thirty; times its own weight, and. by comparing the condition of the ends, of th.c Struts before and aftei the weights are put on, It is evident there

is no lateral thrust. The experimental ilot yet been: put to tile test on d large sbale, but the bdbstructidii tif a bridge neat CaifldeH, td be of eighty feet spaii) is cdtitempiatdd, the iibst bf which is estimated by Mi\ Wddi*e itt <£3oo. Ail Application litis beeii iliade td the Govern* riieilt by Mil Wdbre for,a patent for his invention, and it is now under consideration. The difficulties which have been experienced in internal communication in this colony, in consequence of the number of creeks and ravines, render it desirable that Mr. Woore’s structure, which appeal's to combine lightness of material. with extreme strength, as well as to bn adapted to any locality, and to be economical in cost, should be fairly tested- — Sidney Morning 11 eraid.