The Suspension Bridge

The Suspension Bridge

COL. GREENE'S ARTICLE IN SCIENTIFIC AMERICAN: In June of 1908, Supt. Greene had the wire suspension bridge completed and most likely thought that it was a uniquely designed structure for he wrote an article for the Scientific American describing its construction.

We always thought the bridge was a special addition to the early Park and hope you do too. Here is the article submitted by Col. Greene. It is titled WIRE SUSPENSION FOOT BRIDGE AT BROMIDE SPRINGS, PLATT NATIONAL PARK, SULPHUR, OKLAHOMA.

"The accompanying out shows the latest addition to the attractions of Platt National Park, in the form of a wire suspension bridge across Rock Creek, by which visitors have easy and safe access to the waters of its principle springs. The span is 112 feet, the width of the roadway three feet in the clear and the height above the water is twenty-four feet The towers consist of four 70-pound rails each, set in concrete base and joined at the top by portal plates of boiler iron bolted through the flanges of the rails.

These towers are set three feet in the concrete and have a net height of 27 feet to the top of the portal plate. Concave caps or 'saddles' are fastened to the top of the towers to receive the supporting cables. The cables are ¾" Swedish iron with hemp center. The anchorage at the north end of the bridge is on a level with the floor and consist of a pit 5 X 12 feet and 7 feet in depth, at the bottom of which the cables are passed around 2 inch iron rods and secured with clips.

The pit was filled with concrete of the proportions of 1-2-4 and was reinforced with a network of ½ inch iron rods at intervals of one foot. The south anchorage consists of iron rods 1 inch in diameter and 6 feet in length, with welded eye to receive cable hook, threaded for five feet and supplied with 6 hexagonal nuts. These rods were set 6 feet into the solid rock of Bromide Cliff, the holes being filled with plastic cement mortar of the proportion of 1 to 2.

At the north anchorage the cables are 9 feet apart at the surface, the distance at the top of the tower being 70 feet. At the south anchorage the cables are somewhat less, owing to the shorter distance to the fastenings. The width at the top of the tower is 6 feet. The width of the cables in the center of the bridge is 5 feet. Soldered to these cables at intervals of three feet are loops or 'stirrups' of No. 8 galvanized wire, graduated in length from the ends to the center of the bridge so as to give a camber of six feet. Into these stirrups are placed floor beams 2 X 6 inches and 8 feet length, upon which the superstructure of wood is placed. Drawn taught over the upper edges of these floor beams and fastened to iron rods in the concrete of the tower bases, and 5 No. 8 wires placed as a precaution against an uplift by the wind.

Four planks 2 x 8, with spaces of 2 inches, are laid lengthwise on the floor beams and upon these three layers of one-inch floor boards, the first two layers are placed at angles of 45 degrees and the last straight across, all layers having space for the free circulation of air. The stringers are 2 x 8 dapped to 5 inches and strengthened by stays 2 x 4, 18 inches in length. On top of the stringers are the post for the lattice, 2 x 4 and 36 inches in length. These are braced by 2 x 4 braces spiked to the ends of the floor beams.

On top of the lattice posts are caps 2 x 4 set on edge, on top of which is the handrail 2 x 6, with beveled edges. All dimension fastened by #40 spikes; all inch stuff by #10 nails. Lateral vibration is overcome by guy wires running from intervals of 28 feet on the bridge to the anchorages on either bank of the stream. These and the supporting wires are adjusted by simply twisting them with an iron rod, care being taken to avoid kinks.

The total weight of the bridge is 8,790 pounds. Bridge and 20 persons at 150 pounds each, 11,790 pounds. Safe strain on the two cables is 64,000 pounds. Safe load on bridge including the bridge itself, 11,860 lbs. The bridge was designed by H. V. Hinkley, Consulting Engineer, Sulphur, Oklahoma and constructed by the government on force account, under the supervision of A. R. Greene, Superintendent of Platt National Park. The estimated cost was $630.00 but the actual cost somewhat exceeded this amount.