By Henry Karpinski
By 1928 it was obvious that a new bridge over the great river was needed. The 1921 bridge danced in the winds that regularly came roaring through the inner gorge and on at least one
occasion it was reported to have capsized. The new crossing must be built to maintain rigidity in all conditions
so as not to frighten (or kill) the many tourists that were expected to ride or walk upon it. Since 1922, when Phantom Ranch opened, ever-increasing numbers of visitors were clamoring to ride the mules
down and it did not take long before the inadequacy of the first bridge became apparent; only one rider at a time
was allowed to cross and the delay--while not the imposition that the old cable and cage presented-was nonetheless
prolonged and irksome. On January 4th, 1928, F. A. Kittredge, Chief Engineer for the National Park Service, wrote
Grand Canyon Superintendent, Miner Tillotson; "Your letter of December 3rd regarding proposed Kaibab Trail suspension bridge is at hand and we have given
it a great deal of study. A camp accommodating nine skilled laborers and an (all-important) cook was established at the confluence of
the Colorado and the Bright Angel Creek-later the crew was increased to twenty. Construction commenced on March
9th, 1928. The site selected for the new structure was about sixteen feet directly over the 1921 bridge, the use
of which was uninterrupted throughout the duration of the project.. |
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Now, the north cable supports, north approach, and north abutment, could be readied. Work on the south anchorage
pits, cable supports, and approach also progressed and a storage yard, assembly platform, and canvas-covered blacksmith shop were set up at the foot of the South Kaibab Trail. Work was also begun on the south approach tunnel with excavation commencing at both the north and south portals simultaneously. The compressors used for this project were not entirely adequate and, eventually, it was decided to add another shift working 6pm to 2am in an attempt to make up for the delays. When finished, the tunnel ran one hundred and five feet with the north portal leading directly on to the bridge. |
The extraordinary location of the span made for some interesting logistics:
Suspension cables were put in place-air hoisted into position on the north anchorage, and, on the south anchorage by means of a thirty ton hand-operated stump puller. Once these main cables were in place, a rigger moved out on the cables by means of a "boz'nz" chair to mark where the hanger cables were to be secured.
Attachment of the hanger cables began at the south end of the bridge. As the hangers were placed, aligned, and attached, a group of six men would carry onto the old bridge-directly in position below the new span-a transom assembly (consisting of a floor beam and two verticals). Once carried to the proper location the transoms were hoisted by means of tackle sets and attached to the hanger cables. The riggers suspended high above, would then permanently attach the transoms to the main cables. As the transoms and hangers were connected, structural workers at the assembly platform near the south portal of the tunnel were assembling and riveting steel floor beams and plates for placement and installation. Carefully, though not so slowly, the bridge began to take shape. The presence of the old bridge certainly assisted in the construction (especially with the transoms) and for a while there existed an irony in that the old structure was invaluable in the creation of its successor…which would hasten its removal. The width of the span (5 feet) was chosen with consideration to the movement of mules. It was felt that a narrower
walkway would interfere with the pack loads and that a wider one would allow the animals to potentially maneuver
enough to turn around and cause much confusion. Because of the bridge's isolation, it was decided to construct
the flooring in a manner that would warrant a minimal amount of maintenance. To that end the flooring system was
made up of flat steel plates, ¼" thick, riveted directly to the floor beams and girders. On top of
this system was spread a layer, 2" thick, of an asphaltic concrete called "Laykold", that would
provide a durable surface and sure footing for pack and saddle animals. |
Approaching the bridge in any fashion, hikers, riders, or boaters, are struck by the graceful wind cables (or,
side sway cables). After delivery by train at Grand Canyon the nine hundred foot long cable was trucked to the
Kaibab Trailhead and cut to length there. A "go-devil" in the fashion of a sled with iron wheels was
built to transport the cables down the trail (The remarkable and well-known instance where forty-two men walked down the main suspension cables, centipede style, was employed just once- due to time pressures; it took only a long day for the crew to walk the cables down. Because it was not necessary to transport the wind cables as quickly, it was decided to sled them down. Additionally, this method was favored because it saved a considerable amount of revenue since mules work cheap.) The location of the south upstream wind cable anchorage was especially problematic. Engineer Lawrence wrote that, "It was necessary for the jack hammer operator to hang in a sling from two ropes one hundred and twenty five feet below where the rope was secured and with a seventy foot sheer wall to the river below him." |
DRILLING FOR NORTH UPSTREAM CABLE ANCHOR |
BOTH KAIBAB SUSPENSION BRIDGES - VIEW LOOKING NORTHEAST - 1928 |
Work continued into the summer of 1928 and throughout this time the old bridge remained open to foot traffic. Photographs taken during various phases of (pre-OSHA) construction show clearly the dangers that the men were routinely exposed to. Consider the summer heat of the Inner Gorge and the inherent dangers of climbing the cliffs or hanging seventy feet (or more) above the river while drilling by hand through granite, and one can see that the hazards were everywhere. To the everlasting credit of all involved Engineer Lawrence could, when the project was complete, state in his February 1929 final report that, "There were no serious injuries on this construction job, the most serious being a broken bone in a rigger's foot."
Also in his February 1929 report, Engineer Lawrence enumerated some interesting points:
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With the bulk of the new bridge in place the main cables were adjusted for final position and the wind cables
were connected to the wind cable guys and were also adjusted to their correct length. When these tasks were completed,
the temporary field bolts in the truss were replaced with field rivets and the guardrails were bolted into position.
There remained only the application of the "Laykold" surface and positioning the stiffing truss to the
abutments.
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JOHN H. LAWRENCE |
BUILDING
THE KAIBAB TRAIL BUILDING THE 1921 SWINGING BRIDGE Return to
Photographic Exploration |