Structural Engineering Slide Library

Dumbarton Bridge, San Francisco Bay, California (1982)

	Image-GoddenG61 Dumbarton Bridge. South end of main approach structure, showing the bents that support the precast concrete delta beams. The grade of the roadway in this section is 2.64% produced by bents of increasing height towards the main channel. (San Francisco Bay Area)
	Image-GoddenG62 Dumbarton Bridge. South approach structure, showing the support bents seen in the background in slide GoddenG61. The slide shows the bents in different stages of construction. The third from the front has not been constructed, but its location can be seen by the sheet piling. Note the tower of the existing lift bridge to the right. The new bridge is a high-level bridge rising 90 ft above water level over the main channel. (San Francisco Bay Area)
	Image-GoddenG63 Dumbarton Bridge. Close-up of precast prestressed hollow concrete delta beam used for the approach spans. This slide shows the pressure grouting of the prestressing tendon ducts and the anchorages of the seven tendons. The upward deflection of the beam due to the prestressing can also be seen by looking along the bottom edge of the girder: it has lifted off its intermediate supports and is supported only at the end. (San Francisco Bay Area)
	Image-GoddenG64 Dumbarton Bridge. Construction of the south approach spans. Each span consists of five delta beams plus a cast-in-place concrete deck. The beams are taken down the temporary jetty (shown) by special truck, then lifted and placed in position by the overhead traveling crane (yellow). In this slide the lifted beam is being positioned. (San Francisco Bay Area)
	Image-GoddenG65 Dumbarton Bridge. Close-up of the delta beam seen in GoddenG64 being positioned. Note the scale from the figure in red standing on the bent. (San Francisco Bay Area)
	Image-GoddenG66 Dumbarton Bridge. Top of north approach structure. Delta beams have been positioned, one beam being down the center of the slide with the rows of shear reinforcement showing on both sides. The transverse gap is directly over the support bent, and beyond it the end of the next delta beam can be seen. On each side of the beam is the formwork for casting the deck slab. (San Francisco Bay Area)
	Image-GoddenG67 Dumbarton Bridge. Top of north approach structure. This slide was taken after the slab reinforcement was placed. The four men are looking down the gap between the ends of the delta beams directly over the supports. A metal strut is fitted between the lower edges of adjacent delta beams so that the finished section will take the negative bending moment caused by continuity at the support. (San Francisco Bay Area)
	Image-GoddenG68 Dumbarton Bridge. Completed section of north approach structure. Slide taken from a car crossing the existing bridge shows a typical length of the approach structure. The five delta beams are simply supported for dead load, and act integrally with the deck slab as continuous beams for live load. The red side struts in the background are part of the falsework for casting the deck slab. (San Francisco Bay Area)
	Image-GoddenG69 Dumbarton Bridge. Transition from north approach structure to main channel crossing. Slide taken from car crossing existing bridge. On the near side of the near support are the two steel box girders for the longer channel crossing spans. (San Francisco Bay Area)
	Image-GoddenG70 Dumbarton Bridge. View above the transition support shown in GoddenG69. Near side of the bent are the two steel box girders; far side are the delta beams, and the end of one beam can be seen between the steel girders. Timbers are being placed to support the formwork for the deck slab. As continuity between the beams is not possible, this is a hinged joint in the bridge system. Note the shear studs in the top flange of the steel box sections. (San Francisco Bay Area)
	Image-GoddenG71 Dumbarton Bridge. Slide showing the section of the orthotropic steel box girders used for the main channel spans. Width at top = 29 ft.; width at bottom = 21 ft. 8 in.; depth = 9 ft. 6 in.; plate thickness (both sides and base) = 3/8 in. The transverse and diagonal bracing is only for construction purposes. (San Francisco Bay Area)
	Image-GoddenG72 Dumbarton Bridge. View of steel box girder taken from above showing the web stiffeners on the sloping sides and vertical central web, and the longitudinal stiffeners on the lower plate. Note the heavy cross-frame inside the box over the support. The free end of the girder will be a temporary hinge connection, and subsequently a fixed joint. (San Francisco Bay Area)
	Image-GoddenG73 Dumbarton Bridge. Main channel spans of the new bridge taken from half way up the south tower of the old bridge. The slide shows the difference in elevation and design between the two bridges. Note the temporary hinge on the near side of the near support in the steel box girder. (San Francisco Bay Area)
	Image-GoddenG74 Dumbarton Bridge. View of the spans in GoddenG73 taken from the top of the south tower of the old bridge. Careful study of this slide shows the stiffener design and the discontinuous shear studs on the top flanges. (San Francisco Bay Area)
	Image-GoddenG75 Dumbarton Bridge. North end of the main channel spans. View taken from deck level down the axis of the bridge shows the formwork being prepared for casting the deck slab. Note again the shear studs on the top flanges of the box girder. (San Francisco Bay Area)
	Image-GoddenG76 Dumbarton Bridge. The remaining slides, GoddenG76-G80, show the lifting of one of the long spans. It is the 240-ft. length of steel box girder just north of the central closing span. This slide shows one of the girders in place, and one on a barge waiting to be lifted. (San Francisco Bay Area)
	Image-GoddenG77 Dumbarton Bridge. The box girder is lifted vertically by two floating cranes. The girder weight is approximately 200 tons, and the location of the two lifting yokes is dictated by the capacity of the two cranes, 100 tons and 200 tons respectively. (San Francisco Bay Area)
	Image-GoddenG78 Dumbarton Bridge. The girder is lifted to its full height. This slide is included partly on account of the design of the far crane, and the interesting problem it gives in resolving the forces in the elements of the crane due to the vertical load. (San Francisco Bay Area)
	Image-GoddenG79 Dumbarton Bridge. The girder is brought horizontally into position by moving the crane pontoons. Compare the position of the pontoons in this slide with that of GoddenG77. The gap in the pontoon system enabled it to fit round the support base when lifting the previous adjacent girder. This slide is taken from the top of the south tower of the old bridge, and the north tower of the old bridge can be seen on the right with a figure on the top of the outside ladder. (San Francisco Bay Area)
	Image-GoddenG80 Dumbarton Bridge. Finally the girder is lowered into position, connected to the cantilevered end of the previous girder, and carefully aligned on the near support bent. At this stage the structure of the bridge is complete, except for closing the final span with similar steel box girders, and casting the integral concrete deck. (San Francisco Bay Area)

Set G: Structures Under Construction