Oakland Avenue Bridge/piedmont viaduct
In 1910 when Albert Farr was designing the City Hall building, the Piedmont Board of Trustees discovered that the old wood trestle bridge over Linda Avenue needed to be replaced because it was unsafe. On July 19, 1910, the city voted to remove the wood trestle. There is a historical rumor that the police used the newer bridge for target practice.
California's Mission Revival by Weitze, Karen J., 1952- Publication date 1984:
Designed by civil engineer John B. Leonard and consulting architect Albert A. Farr, the Oakland Avenue Bridge in Piedmont was one of only a few Mission Revival bridges in California. Local real estate speculation undoubtedly had inspired the choice of style, with Piedmont civic officials seeking the fashionable Spanish imagery.
Scientific American: Supplement, 1912
A Concrete Bridge of Striking Design A Pleasing Adaptation of Old Mission Architecture
By Frank C. Perkins
Quite in keeping with the historic associations of the locality is the reinforced concrete bridge recently completed at Piedmont, California. Although built according to the most modern engineering practice, it preserves the Simplicity and quaintness of the old mission type of architecture. An attractive novel feature of the bridge is the introduction of four covered resting places supported by light concrete columns, covered with Spanish S tile
At the portals are four pylons at either end, capped with a decoration cast in concrete and and inclosing large ornamental electric lights. The total length of the structure is 362 feet 10 inch inches. including a central arch span of 130 feet with symmetrical approaches composed of reinforced slabs supported by girders and columns inclosed in 6-inch exterior curtain walls. Each transverse bent is made up of three columns.
The roadway is 22 feet wide, with an additional 6- foot sidewalk on either side. The intrados curve of the arch was chosen for beauty as well as economy. Both temperature and rib shortening were provided for. The slab of the approaches and the arch were designed to carry an interurban electric car, and the sidewalks were designed for a live load of 150 pounds per square foot, carried by ornamental brackets rigidly connected to the arch rib and approach slabs.
There was a timber trestle on the site with about 40,000 feet of lumber in the trestle. largely used for shoring and centering for the new bridge. The falsework of the arch was made of 8 by 10-inch, S by 12 inch and 10 by 12-lnch stock. The bents were on approximately 5-foot centers, and the posts of each bent on 6-foot centers. The posts were placed normal to the intrados curve, and were supported on continuous sills firmly embedded in the soil. The falsework was unusually heavy and clumsy, but the timber from the trestle was old and its strength could only be guessed at. Heavy were placed transversely on each bent, the caps in turn supporting longitudinal strings on 2-foot centers, On the stringers 2 by 4-inch pieces were blocked up and sprung to the curve. In some portions of the intrados curve where the curvature is great, 2 by 4-inch stock could not be sprung without splitting, and use was made of two 1 by 6-inch pieces nailed together. These readily took the desired spring, and the variation from the true curve was practically nil when the decking was finally placed. Constant wetting down (sometimes four times daily) kept the decking in excellent condition. Points on the intrados curve, near the crown, were built 1/4 inch higher than required to allow for settlement in the foundation of the falsework.
The bridge was designed by John B. Leonard of San Francisco, and the writer is indebted to Engineer W, P. Day of San Francisco for the photographs and data. The concrete of the rib was poured through timber chutes leading from a hoist at the center. Doors in the chute were provided in case the concrete flowed rapidly. and separated the coarser from the finer components, but their use was found unnecessary. the pitch of the chute being a minimum.
On the completion of the casting, and for several days thereafter, the arch was wet down four times. The usual buckling of the forms at the crown after pouring the haunches did not occur owing to the inclination of the posts. The falsework remained under the rib for about six weeks. It was deemed best to strike the centers before the spandrel wall forms were set in place, so as to allow the arch to take its constrained shape, without subjecting the walls to the consequent stress.
The approaches are symmetrical, each being a 15-inch reinforced slab supported on transverse girders. The entire lower approach was poured through a chute. the length of the latter from the hoist over the mixer being 180 feet. The chute was 18 inches wide and 10 inches deep, and has a drop of 2% inches per foot.
The mix was run a little wet and introduced a perfect concrete at the extreme end. On account of the depth of the girders they were poured in two parts, 4 by 12-inch blocks, and 3/8 inch rods being used to provide for horizontal shear at the plane where work was stopped. All of the side walls were poured to the bottom of the sidewalk. The upper approach could not be poured by the chute without building a very high tower, on account of the grade of the bridge, and resort was therefore had to the regulation buggies hoisting first from the mixer to a runway over the arch of the bridge.
Four expansion joins were used in the structure, each arranged so as to be hidden by the piers. The use of asphalt was originally contemplated, but was replaced by two thicknesses of heavy felt. Little or no dirt can penetrate the joint, and it is believed that a better working joint has been obtained than would have been produced with asphalt, as the latter would expand and contract with variations in temperature. About 2,250 cubic yards of concrete and 80 tons of steel were placed in this bridge.