828 Transactions of the American Institute. 



" The author has long been convinced, of the importance of giving 

 to the roadway of suspension bridges the greatest possible amount 

 of stiffeness in such a mmmer as to distribute the load or the 

 effect of any violent action over a considerable extent. The plat- 

 forms of large bridges in exposed situations are acted upon in so 

 many different ways by the wind, that he had an objection to the 

 use of stays or braces to counteract movements which ought rather 

 to be resisted by the form of the truss-structure. Holding such 

 opinions, he determined to adapt a framing, which, although con- 

 nected rigidly in every direction, should nevertheless be simple, 

 composed of few parts, capable of being easily renewed, should 

 distribute its weight uniformly over the chains, not be subject to 

 change from variation of temperature, and not augment the usual 

 weight of suspended platforms." 



According to these principles, which are embraced entirely in the 

 old American inventions, but more defining the same, Rendel 

 repaired the Montrose bridge in the following way: " Instead of 

 cast-iron cross-bearers, he adopted wooden joists thirteen feet by 

 three and a half feet, bolted together and trussed with a round bar 

 of one and one-eighth of an inch diameter; every sixth beam had 

 a deep trussed frame on the under side, so as to give great stiff- 

 ness above and beneath the cross-beams; on each side of the carriage- 

 way were bolted two sets of longitudinal timbers, four in each set; 

 they were further united by cast-iron boxes at intervals of ten feet. 

 A curb of timber eleven inches by sLx inches was attached to the 

 ends of the cross-bearers, and extended the whole length of the 

 platform. To add to the stiffness afforded by this construction, 

 the author caused to be passed through the spaces between the 

 pair of longitudinal beams, a series of diagonal truss-pieces of timber, 

 six inches square, with the ends stepped in the cast-iron boxes, 

 ■which at every ten feet grasp the beams. On the other end of 

 these diagonal truss-pieces, an iroa screw bolt one inch and a 

 quarter diameter at every ten feet, and a contrivance of wedges in 

 the cast-iron boxes, enabled any degree of tension to be given to 

 the framing. The roadway was thus stiffened by two of the strongest 

 kinds of framing in parallel lines, dividing the carriageway from the 

 the footpaths." 



This truss work, with the perfect understanding of the working 

 momenta, was expressly made to resist flexures upward as well 

 as downward, an arrangement omitted in one of the greatest exist- 

 mg constructions. 



