Page:Popular Science Monthly Volume 92.djvu/957

 Popular Science Monthly

��941

��� ��A Rope Suspension Bridge for a Garden

SUSPENSION bridges present a very artistic structure for spanning small streams or a brook on the grounds or in a park. The illustration gives the details of such a bridge and tables of proportions for construction of the different lengths.

The concrete posts which hold the upper cord of the bridge are built and reinforced as shown in Fig. 1. The suspension cable is secured to a drive anchor, expanding anchor or dead man and then run across the ravine and se- cured on the opposite side in the same manner. Both suspension cables should be the same length and have the same amount of slack or sag. The lower cord is drawn as taut as possible and then hung perfectly level by the supporting vertical cables, which should be spaced about 1 ft. apart. When all vertical cables are se- cured to both the upper and lower cords the latter is drawn up again and secured at each end.

Planks are laid across the lower cord and held in place by driving large staples over the rope and into the bottom of the plank. The tables should be studied closely. Table 2 gives the size of the post, length above and below ground and size of spread footing, while Table 3 gives the size of the ropes to use for the various lengths of the span. In the last column

��of this table is given the size of the bottom cord of round iron bar, which is used in place of manila rope, and in Table 4 is given the number and size of the bars necessary to reinforce the columns shown or mentioned in Table 2.

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����■r^y FIG 3

��A cross section of the completed bridge and the detail of the anchor post and its base

The illustration. Fig. 2, gives a cross- section of the completed bridge, while Fig. 3 shows a little more detail of the

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