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/306858
The ribs were precompressed with hydraulic jacks placed in jacking frames at openings at the rib crowns. This compensated for the second-order load effects in the arch ribs and longitudinal beams from displacements in the foundations during development of the foundation resistance. Jacking occurred at an optimum step in the construction sequence, with the jacking frames cast into a closure placement at the crowns. T h e b r i d g e i n c o r p o r a t e s s e v e r a l pedestrian-scale features designed for compatibility with the recreational use of the canyon area. Overlooks are located at each abutment, allowing pedestrians to step off the sidewalk to enjoy the canyon's scenery. Similar areas are provided at the interior bents of the arch spans. Raised cantilever sidewalks on each side have tubular steel rails. The rails meet the strength requirements for both vehicles and pedestrians while allowing freedom of view for all bridge users. Recessed step-lights concealed within the rail bottom tube provide low-level sidewalk lighting. The open rail also facilitates an accurate perception of the superstructure depth when the bridge is viewed from the side, adding to the slender and graceful appearance. The design offers a majestic presence both from a distance, with its sleek, flowing arches, and from close up, where visitors can admire the canyon and the careful way that the new Maple Avenue Bridge fits into its surroundings. ____________ James N. Bollman is senior bridge engineer, OBEC Consulting Engineers, Eugene, Ore. For more information on this or other projects, visit www.aspirebridge.org. A E S T H E T I C S C O M M E N T A R Y by Frederick Gottemoeller In the last issue, I quoted the renowned twentieth century architect Mies van der Rohe's famous dictum, "Less is More." This time I'd like to quote another of his famous sayings, "God is in the Details." On the Maple Avenue Bridge, one has only to look at the proportions of the joint where the arch ribs, bent column, and bearing come together to see what van der Rohe was driving at. The arch ribs appear to narrow to almost a single point as they reach the bearing. The bridge seems to barely touch the ground. That feature alone gives the whole structure an incredible lightness of being. However, the same kind of attention is applied to the spandrel columns, the bracing, the railings, and all of the other features of the bridge. Each part has an elegant slenderness and simplicity. Each is smoothly and logically connect- ed to the others. Every element appears competent to do its job without wasted effort or materials, giving the whole structure a sense of calm transparency. This bridge really does deserve that often-stated praise: it lies lightly on the land. Achieving this result required a lot of sophisticated engineering. It is good to see such engineering being done in the service of visual goals, not just cost re- duction. Calling the bridge a "signature bridge" creates the impression that only the rare structure deserves this atten- tion to detail and to visual goals. Actu- ally, all bridges deserve that attention. It ought to be a standard part of bridge engineering. Then we wouldn't have to identify "signature bridges," because they would all be signature bridges. The series of photos illustrates the construction sequence including arch falsework, arch forms, arch columns, and deck falsework. 20 | ASPIRE , Winter 2009