ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306966
ASPIRE , Winter 2008 | 45 A E S T H E T I C S C O M M E N T A R Y by Frederick Gottemoeller For many precast concrete girder bridges, particularly low ones, the biggest aesthetic problem is often the size and shape of the pier caps. They can break up the horizontal lines of the bridge, creating a visual stop at each pier line. On very low bridges, they can look like a series of transverse walls segmenting the space under the bridge. The Daggett Road Bridge avoids these potential problems. Driven by the necessities of the site, the designers have come up with innovative techniques to raise the pier caps into the plane of the girders. The method also creates structural continuity across the piers, allowing the girders to be shallower than usual. Shallow- ness is especially appreciated in a structure that is low to the water like this one. The result is a graceful, well-proportioned structure that sweeps cleanly from bank to bank while leaving a signifcant opening below. There is a tendency to downplay the appearance of small, out of the way bridges, like the Daggett Road Bridge. However, almost all bridges are important features in somebody's neighborhood or somebody's park. They all deserve attention to their appearance. Our goal should be to achieve effciency, economy, and elegance on every structure. The structural innovations used in this structure would beneft the appearance of other precast concrete girder bridges, as well as create functional advantages such as longer spans. They should be considered wherever precast girders are being designed. For more information on this or other projects, visit www.aspirebridge.org. However, extensive analysis and verifica- tion was necessary to ensure that this solution was structurally viable and safe. Consultation with the precasters and crane companies yielded information about the crane's required capacity and the magnitude of its maximum anticipated reactions. This information was then used to delineate the physical limits of the permissible crane operations that did not violate the girders' tem- porary stress limits. The project plans and specifications provided adequate detail to the contractor to devise an erection scheme within these limits. As an example, the plans required that intermediate diaphragms be centered under the crane outrigger pads, as determined by the contractor. This requirement was there to protect the deck slab and distribute the crane rear outrigger loads evenly among the girders. The design plans provided a variable dimension to locate the intermediate diaphragm, since the dimensions of the crane were unknown at the time of design. This process proved to be effective in avoiding potential problems and construction went exceptionally well. _______________ Ahmad Abdel-Karim is Associate Vice President, Thomas Barnard is Vice President, and Orin Brown is Senior Bridge Engineer with DMJM Harris | AECOM, Sacramento, California. Construction sequence. Illustration: DMJM Harris. 10973_ASPIRE_win08.indb 45 12/12/07 3:32:32 PM