NEWS Vol. 6, No. 3 July 2005 Steel Bridge N A T I O N A L S T E E L B R I D G E A L L I A N C E New Central Viaduct for downtown San Francisco uses steel girders with integral concrete bent caps for vertical clearance By Yong-Pil Kim, Senior Bridge Engineer, Caltrans A new Central Viaduct will soon direct built bent cap to eliminate need for false- stretches to 58 m (190 ft). The design fol- traffic into San Francisco from the work during the deck pour. After the deck lows LFD specifications. Contractors bolted Bay Bridge in the east and from Highway concrete reaches its strength, additional underlying girders end to end via field 101 in the south. The new steel viaduct post-tensioning will be applied to each splices to create a set of continuous paral- replaces a previously retrofitted viaduct bentcap for final service loads. lel girders that matched the entire length of whose structural integrity came into ques- the viaduct. Various factors for this project dictated tion after the 7.1 magnitude Loma Prieta San Francisco Central Viaduct steel for the viaduct’s superstructure. The earthquake in 1989. After the earthquake, superstructure streets below run parallel to a major por- Caltrans removed the upper deck portion tion of the viaduct and had to remain open of the viaduct in the interest of safety. Number of continuous steel girders 7 during construction. One intersection below the viaduct in particular required a Weight of steel girders 2,362 tons long span with a limited area for falsework. Space was sufficient only for falsework to Number of crossframes 376 construct the bentcap beam. Vertical clear- Weight of crossframes 392 tons ance requirements, a curvature in the hori- zontal alignment, and one particularly long Number of spans 10 span where falsework was prohibited virtu- ally ruled out either cast-in-place or precast Longest span 190 ft concrete design. Oregon Iron Works fabri- Viaduct length 1423 ft cated the steel for the project. Viaduct configuration Figure 1 Tight vertical clearance require- Three concrete columns topped by a trans- ments and the curvature in the horizontal The new portion of the Central Viaduct verse concrete bent cap support the alignment tipped the decision for a steel, consists of ten spans that achieve a total viaduct’s superstructure. The columns rather than precast concrete, superstructure length of 434 m (1424 ft). The longest span extend from concrete pile shafts that run as for the Central Viaduct in San Francisco. Standard V-shaped cross frames connect the deep as 94 ft below the surface. Columns girders laterally. are supported by cast-in-place drilled con- crete pileshafts, 6 ft and 7 ft in diameter. The new steel viaduct replaces the lower Some interruption of traffic could not be elevated deck, and touches down on avoided. The contractor set up falsework Market Street, a main thoroughfare within adjacent to bents to set the girders in their the city. The viaduct provides two lanes in final configuration and to bolt-splice the each direction plus shoulders. The steel steel girders together, making them contin- superstructure has a hybrid girder design, uous. This required closing a portion of the combining high performance grade 70 ksi street below. A minimum set number of steel with standard 50 ksi steel. The steel hours were allowed for this operation. Figure 2 Workers for Adams and Smith, Inc. girders are integral with the concrete bent begin splicing two steel girders to make them cap to maximize vertical clearance. The continuous. This operation required partial - continued on page 5 closing of the street below. contractor post-tensioned the partially n s b a s t e e l b r i d g e n e w s • j u l y 2 0 0 5 • p a g e 1
Steel Bridge News is a newsletter of Message the National Steel Bridge Alliance and is published quarterly. National Steel Bridge Alliance One East Wacker Drive, Suite 700 from the Chicago, IL 60601-1802 Executive Director: Phone: 312.670.7010 Fax: 312.670.5403 www.nsbaweb.org Conn Abnee Conn Abnee Executive Director Phone: 312.670.7012 abnee@nsbaweb.org I would like to take a moment to provide an update on the National Steel Bridge Mike Moffitt Alliance federal government relations’ agenda. We have had many accomplish- Director of Engineering Services Phone: 312.670.7013 ments that I would like to share. moffitt@nsbaweb.org As you are aware, the National Steel Bridge Alliance has been working closely Jody Lovsness with several members of Congress to push for an amendment to the Marketing and Membership Coordinator Transportation Equity Act (TEA bill) for a dedicated high performing steel 11708 Jackson Road Omaha, NE 68154 research program. Our request would direct research at developing new, longer Phone: 402.758.9099 lasting coatings and low cost, corrosion resistant steels. This program would Fax: 402.778.9499 lovsness@nsbaweb.org have benefits to the steel industry that would extend beyond the bridge indus- Calvin R. Schrage try and would contribute to the development of a new generation of steel that Regional Director will combine strength and reasonable cost. In short, there is no single develop- 5620 Harding Drive ment that will contribute more to the life cycle of steel benefits or reduce the Lincoln, NE 68521 Phone: 402.466.1007 need to replace current infrastructures than the advancements that will be sup- Fax: 402.466.1027 ported through this program. schrage@nsbaweb.org William F. McEleney After many long hours and a number of meetings with key Senators and their Regional Director 45 Pasture View Lane staffs, I am pleased to inform you that Senators John Thune (R-SD) and Barrack Cranston, RI 02921-2732 Obama (D-IL) agreed to sponsor the NSBA amendment. Soon thereafter, the Phone: 401.943.5660 Fax: Same as phone Senate passed their version of the TEA bill that included our amendment at a mceleney@nsbaweb.org funding level of $5 million per year for the next five years. This is excellent news for not only steel bridges, but for the entire steel industry. As the Senate and House now meet in conference to resolve the differences in Regional Directors’ Territories the TEA bill, we will need to continue working together to ensure that the NSBA amendment is kept in the final language of the legislation. With this amend- ment we can propel the steel industry into an age of lower costs and higher quality. Best wishes. We’re on the Move nsba On July 5th, the Chicago Office of the National Steel Bridge Alliance moved from the 31st floor at One East Wacker Drive to the 7th floor. Please note the new suite number and zip for your records: NATIONAL STEEL National Steel Bridge Alliance BRIDGE ALLIANCE One East Wacker Drive, Suite 700 Subscription requests, address changes should and correspondence regarding newsletter con- Chicago, Illinois 60601-1802 tent should be sent to the attention of Mike Moffitt.
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