March 4, 2013

The Concrete Arch Bridge over San Leandro Creek

The following article appeared in the August 27, 1903, edition of Engineering News. It is about the E. 14th Street bridge over San Leandro Creek next to Root Park near the corner of Hays Street.

THE 80-FT. CONCRETE-ARCH BRIDGE OVER THE SAN LEANDRO CREEK, SAN LEANDRO, CAL.

By William B. Barber.

The accompanying illustrations show a concrete arch bridge which is rather interesting because of its span of 8IlA ft. built of un-reinforced concrete, This bridge crosses San Leandro Creek on the line of the county road between Oakland and San Leandro, Cal. Fig. 1 is a view of the completed bridge. and Fig. 2 shows the center and some of the dimensions of the arch ring.

San Leandro Concrete Arch Bridge 1903

The bridge is a monolithic structure, built entirely of concrete, and its total length is 192 ft. No iron whatever was used in the construction of any of the parts of the bridge. It is a five-centered, elliptical arch, with a rise of 26 ft., and a span of 81 ft. 3 ins.; the arch has. a 10° skew from a right angle and its thickness at the keystone is 3 ft. The centers as shown by the original plans were intended to rest upon sand boxes, but in the construction of the bridge wedges were substituted and were found to work very successfully.

Center and some dimension for San Leandro Concrete Arch Bridge

About two miles up the stream from the location of the bridge is a dam that impounds the water supply for the city of Oakland. During the time of the construction of the bridge very little water was in the creek, but after the footings had been set and the haunches had been built about one-third the way up on each side, the filters at the dam were cleaned and the construction work flooded. The wedges under the centerings were flooded and the ground softened. In order to make the arch self-sustaining and to allow it to carry the extra weight that was to follow, a ring of the concrete, 1 ft. in thickness, was built up and keyed. Work was then continued upon the haunches and the arch was built upon the inner ring to its full thickness, as shown in the plan. Thus it will be seen that the arch is really built of two distinct rings.

The arch spans a waterway having a total area of 1,650 sq. ft. The footings of the arch have a width of 30 ft. on each side and extend 5 ft. below the bed of the creek, resting upon a bed of clay which is slightly interspersed with gravel; the footings rest on the original clay without piles. After the second arch ring had been keyed and the fill nearly completed, a 3-ft. water main that supplies the city of Oakland burst, and, cutting its way around the south end of the bridge, flooded the arch and removed a large portion of the fill. This had no effect upon the stability of the arch.

The centers were struck ten days after the keying of the second arch ring and the settling at the crown of the arch did not exceed 1 ½ ins; The main retaining walls for the approach are built also of concrete and have a length of 90 ft.

The total amount of concrete used in the bridge was 3,384 cu. yds. Scales' brand of Portland cement was used In the footings, while above the haunches and in the crown of the arch, Alsen brand was used. The concrete mixture consisted of 7 barrels of rock of varying sizes, 2 barrels of sand; and 1 barrel of Portland cement. Two winters were allowed to pass in order to allow the fill over the arch to properly settle; and the contracts, have been let for the construction of a macadam roadway, 41 ft. wide, over: the bridge and cement walks, 8 ft. wide, on each side; a granite curbing, 10 ins. in width, separates the walks from the roadway. On each side of the bridge is a parapet wall, 3 ft. 6 ins. in height.

There were 90,000 ft. of lumber in the forms used in the construction of this bridge. The finish of the exposed surface did not receive a coat of plaster, surfaced lumber being used next to the face of the bridge. It was built in 1901 from plans prepared by the County Surveyor's Office of Alameda County, California, and the construction was under the superintendency of the same office. The bridge was constructed by the E. B. & A. L. Stone Co., of Oakland, whose contract price was $25,840.

Posted by Mike Katz-Lacabe at March 4, 2013 10:37 PM | TrackBack
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