Structural Engineering Slide Library

Set G: Structures Under Construction

This set of slides shows the construction of eight different structures. They represent different forms of construction, in different materials, and of different spans. The earliest is the Forth Road Bridge near Edinburgh in Scotland, a major suspension bridge completed in 1964; and the most recent is the multi-span Dumbarton Bridge across San Francisco Bay, opened in 1981. The structures are given in chronological order and are as follows:

Forth Road Bridge, Scotland (1964)

This suspension bridge has a main span of 3300 feet and two side spans of 1340 feet each. It is shown at four different stages of construction: During the erection of the main towers, during cable-spinning, during the construction of the stiffening truss, and completed. In spite of the fact that the great Forth Railway Bridge was constructed in 1889 (see slides D28 and D29), it was not until 1964 that an equivalent highway crossing was constructed.

Oakland Coliseum Arena (1966)

The Oakland Coliseum Arena was constructed in 1966, seats 15,000 and is used for a variety of sporting events and exhibitions. The roof is a 420-foot diameter circle consisting of 96 prestretched bridge strands, each 2-3/16 inches in diameter and 196 feet long. The cables are connected on the outside to a reinforced concrete ring beam supported on 56-foot high X columns, and on the inside to a 45-foot diameter steel tension ring. The steel cables support precast concrete ribs, 90 feet long, each weighing 13 tons. Inside, the arena is 106 feet high. The building is shown during construction at the stage when the cables have been installed and the stiffening beams are being placed. The complete building is shown both inside and outside.

Prestressed Concrete Beams for the BART System, San Francisco, California (1968)

Three slides showing the construction of a typical 75-foot span prestressed concrete beam used in the elevated rapid transit system for the San Francisco Bay Area. The complete system in which these beams are used is shown in slides A4 and A5.

Composite Highway Bridge, Switzerland (1971)

Three slides show the long multi-span bridge during construction. The section of the bridge will consist of a constant depth steel plate girder with shear keys, acting integrally with a concrete deck made of precast units. These slides were taken after the erection of the steel girder and before the precast concrete deck sections were placed.

Kocher Valley Viaduct, Neuenstadt, Germany (1972)

This highway bridge across the Kocher Valley, 60 kilometers north of Stuttgart, is included because of its interesting construction procedure. It consists of two separate bridges side by side, each 478 meters long, and each incrementally launched from one end. Slides taken by the author in 1971 show the partially completed structure. The designers are Leonhardt and Andrä.

Neckar Valley Viaduct, Weitingen, Germany (1978)

This is an interesting structure, a five-span cable-stayed continuous steel box girder bridge, with the cables below, rather than above, the girder. The cables, which are used only for the long end spans, are quite unobtrusive. The slide shows the construction phase when the steel box girders were cantilevered out from the sides of the valley and supported on temporary columns. One end span is shown, with the king post in position, but before the cables were added. The design is by Leonhardt and Andrä. Slides taken by the author in 1977 show the bridge in the early stages of construction.

Highway Overcrossing, Richmond, California (1980)

A multi-span concrete highway bridge using both cast-in-place reinforced concrete box girder spans and precast prestressing delta beams for the two spans crossing railway tracks where supporting falsework from the ground was not possible.

Dumbarton Bridge, San Francisco Bay, California (1982)

An 8800-foot multi-span bridge crossing San Francisco Bay. The short approach spans consist of precast prestressed concrete delta beams, and the long spans over the navigation channel consist of steel box girders with the concrete deck acting as the top flange of a composite section. Slides were taken at different stages of construction showing the placement of the prestressed concrete delta beams, and the lifting and placing of the long steel box girders.

The projects selected show a variety of different constructional procedures, in different materials, and in structures large enough for the erection procedure to be a major consideration. By studying these projects, students will become aware of the importance of constructional stresses and deflections, and the need for precise analysis at all stages. Further, the effective structural systems for dead load are often quite different from those that support live load. Examples of this can be seen in the cases of the Composite Highway Bridge, Highway Overcrossing, and Dumbarton Bridge, where by adding the deck, both the girder section and the degree of indeterminacy are changed. In two cases involving cables, deflections can be seen during construction. In the case of the Forth Road Bridge, the gross displacements of the unfinished truss are easily seen during the construction of a long-span suspension bridge. In the case of the Neckar Valley Viaduct, the cantilever deflections of the steel box girder can be seen during the construction phase.