Grand Canyon Bridge Opens New Route Across Greatest of All Natural Barriers

VACATION LAND, 1929 ARIZONA HIGHWAYS Page Thirteen Grand Canyon Bridge Opens New Route Across Greatest of All Natural Barriers By RALPH A. HOFFMAN, Bridge Engineer

ALL of the Great Southwest welcomes the completion of the imposing span over the Grand Canyon of the Colorado which is soon to be dedicated. It is of especial interest to the states of the Rocky Mountain Region, as it opens a new route across the greatest of all natural barriers. This bridge is the only crossing by either highway or railroad between the town of Topoc, Arizona, and the junction of the Green and Grand Rivers in Utah, a stretch of 600 miles of rough mountains and deep canyons. It is of more especial interest to the sister states of Utah and Arizona, as the immediate benefits of the opening of this new route of scenic grandeur will accrue to these two states. It is fitting, therefore, that these sister states should enter into the preparations for a great celebration at the dedication of the structure on the 14th and 15th of June, 1929.

Many of our citizens and visitors from other parts will view with awe this gigantic gorge, which has kept those of us connected with the building of the structure spellbound for hours. I have sat on the rim during the progress of the work, trying to get a picture in mind that would dispel the awe and trepidation that comes upon one who is in any degree responsible for such an undertaking.

An old Indian, one of the many typical of that section, looking at the mass of steel lying around and understanding for the first time what we were trying to do, said: "Humph! No can do. Him too big."

The gap is not nearly so big now, and the same Indian, along with many others, delights in parading back and forth across the bridge with their chests stuck out in pride of ownership.

It will be fitting at this time to review briefly the historical and design data given in previous articles published in ARIZONA HIGHWAYS.

The present site of the bridge is about six miles below what is known as Lee's Ferry and about four miles below the mouth of the Paria Creek. Many years ago a crossing was proposed about 1,000 feet from the present site by the Denver and Rio Grande railroad, and traces of the preliminary work still exist.

The original location and triangulation of distance from rim to rim of the site was made by Captain J. B. Wright, county engineer of Coconino County, and the present alignment corresponds almost exactly with his location. It was upon the basis of this data that the congressional appropriation of $100,000 was authorized and was estimated to be one-half the cost of a suspension type with a timber floor. This appropriation was to be matched with a like amount by the stat of Arizona.

Subsequent surveys and estimates showed the estimate to be too low and the final result was an appropriation by the state legislature of $185,000, making a total available for the job of $285,000. This was still inadequate for the type of bridge recommended by the Highway Department and after the bids were taken other funds were added to make the recommended arch type with a concrete floor possible.

Experiences of neighboring states with timber floors made it highly desirable that the fire hazard be eliminated on this structure. The cost of maintenance was another factor to be considered in this extremely remote and desolate location.

The extra cost of building the structure for modern highway traffic was justified by the importance of the route and proposed developments of Bus and Freight lines through this territory and has vindicated the judgment of the department in insisting on the higher type of structure. The route has also been established as one of the Federal Highways and it is expected that it will soon be included in the Federal Aid System for participatioin in a program of road construction.

The original plan, as before stated, was for a light suspension bridge. The deck arch type was suggested by the writer in 1923, at the time the bill was in Congress, but the suggestion went no further than the immediate department at the time; however, when estimates were requested of the department by the State Legislature, they were made upon the basis of the deck type arch and sketches were made to show the adaptability of the type to the location.

When the task of preparing plans was finally turned over to the Highway Department work was immediately started on the basis of a 600-foot arch. This was changed to a 616-foot span after some development work had been done on the foundation.

The final result was a plan for the present bridge consisting of a 616 foot main arch span, two 84-foot and one 50-foot approach spans, with a concrete floor having a clear width of 18 feet The design was based on a loading for two 12½ ton trucks or one 15 ton truck, which will meet the requirements for the primary Federal Aid System.

As estimates based upon actual design proved that our funds were short of the amount required, bids were taken with an alternate for a timber floor, but the main structure based on a concrete floor load.

Four bids were received June 7, 1927, the low bid of $310,000 being offered by the Kansas City Structural Steel Company for the structure, with a concrete floor.

By taking over part of the concrete and excavation work with other funds the state was able to award the contract on the bridge with a concrete floor. Government approval was given by the U. S. Indian Service and the contract awarded June 17, 1927.

The first excavation was done at the site during the period of design by a small crew working with hand drills. This work was done only on a narrow face on the proposed line of each shoe to determine the stability of the rock and the distance back from the rim which would be safe for such a span. The actual excavation was started June 23, 1927, on the northrim, after many days of hardships in hauling a compressor and other equipment through the sand washes and ferrying it to the north side of the river. The excavation on both sides was completed by November, 1927, and the concrete arch foundations commenced. These were completed by April 5, 1928, the south foundation being poured first in order to allow the steel company to begin work. They had established a camp and begun work on the anchorage duringPage Fourteen

ARIZONA HIGHWAYS VACATION LAND, 1929

the first half of March, while the concreting was in progress.

The first car of erection equipment was shipped from Kansas City January 5, 1928, and the first car of structural steel was shipped from the same place The first steel was set on the Flagstaff end on April 16, 1928, and the progress was quite rapid from that period. The eleven panels of the first half were completed June 15, only two months after setting the shoes. The by reason of a faulty toggle screw which fortunately was discovered before placing it in the structure.

January 19, 1928. The hauling to the site, a distance of 130 miles was started immediately upon the arrival of the first car at Flagstaff.

The entire haulage required a period of four months and was accomplished entirely with two trucks, one a six wheeler 12 ton capacity and a standard five ton. The total haulage contract amounted to more than $58,000, a total of more than 1600 tons of equipment, cement, steel, etc. Eleven hundred tons of this amount was structural steel.

The big surprise to many contractors and engineers who saw the road will be the fact that the hauling contractor made an excellent profit on the job at $35.00 per ton for material delivered on truck at the site. The general contractor unloaded the trucks but the material was loaded by the hauler. He also had to do his own road maintenance for 80 miles of the distance, usually carrying a heavy dray behind the truck on both trips. It was also necessary that he do some special road work with tractor equipment in some of the tight places. Car shipments were arranged for convenience of the haulage and no delay was experienced by either contractor because of the arrangement.

The north half was completed August 11, 1928, a total elapsed time of less than four months for the main span. During this time some delay was experienced The two great halves of the arch span, erected by cantilever method, on August 12, 1928, were lowered together, as described in a previous article published in this magazine and others. The screws were started at 11 A. М., with an opening of about nine inches between the pin sockets at the crown and both sides were bearing on the center pin at 5:30 P. M. The operation of the screws had to be continued for four hours longer to keep up with the contraction of the steel, due to the falling temperature almost as rapidly as the screws could be let out and the operation was continued until there was no possibility of the toggles again taking the load of the spans.

The erection traveler was dismantled the following day and work begun on changing the tie back steel into approach spans and setting the floor system steel on the main span.

The steel work was finished and the crew moved out October 20, 1928. There remained only the concrete floor to place and approach fills to build. The hazardous part was over but still much work to be done to complete the structure. Forms for the concrete slab were made up during the time the steel crew were setting the approach spans. These forms were set and the rein(Continued on page 57)