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The floor of the bridge, as has been remarked before, is suspended to thecables by means of suspenders, placed four feet apart, and made of the bestcharcoal iron. The thickness of these suspenders differs; they are to be ofround iron, one inch in diameter within 200 feet from the centre tower, one andone-eighth inch in diameter within the next 100 feet, and one and three-sixteenthinch thick for the rest of the floor. They will all terminate at the lower end inscrewbolts of one and one-fourth inch thick. All suspenders over 15 feet longare made in joints. Their connection with the cables is formed by straps,which nearly encircle them, in a manner similar to the plan applied on theMonongahela bridge. The reason of the reduced size of the suspenders nearthe pier is, because their tension will be almost entirely relieved by the stays.
7. STAYS.
On inspection of the plan, thirty lines will be observed on each side of thetower, descending from its summit to the floor in a diagonal direction; theseindicate the stays which I propose to employ as an additional means of supportto the floor, as well as one of the most effective means of guarding againstvertical vibrations, and to check them when they do take place. Another, anda most important object to be accomplished by these stays, is to counteract theeffects which heavy loads may have upon one span, while no load is on theother. In that part of my report where I treat of the practicability and safetyof the structure, this action will be more fully explained. Each pair of stays,occupying a corresponding position on the two sides of the centre tower, isformed of one single wire rope. Each group of stays is divided into four parts,each part resting upon a separate saddle, on the summit of the tower. Thereare, therefore, eight saddles, each allowed to move independently of the other,on rollers , so as to regulate the tension of the several divisions of stays whenthey are affected by heavy loads, and in proportion as these loads proceed uponthe floor. It must be observed, that the stays are to act entirely independent ofthe cables. The latter are stationary, fastened upon the summit of the tower,and not allowed to move. When one of the spans is overloaded its floor will bea little depressed, and consequently act upon the stays, which in their turn willyield a little, and in proportion tighten those on the other span, until the latterbecome so much strained by the resistance of the floor, that their tension will bebalanced by the tension of the others. The effect upon the tower will be noother than a quiet vertical pressure, the result of the tension of the stays, directedthrough the centre of the masonry.
I am aware that several remarkable specimens of suspension bridges havebeen erected, where no use at all has been made of stays, while on some othersthey have been applied to an excess. Theoretical investigations, as well asexperiments lately made, have convinced me of the utility of stays when judi-ciously applied. As regards their power to support, it may be observed here,that they can, in all cases, be applied to advantage, if not extended far beyondthe limit of the tangent of the cables. The objection has been made to staysthat they do not act in concert with the cables. This may be correct when