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/306855
For more information on this or other projects, visit www.aspirebridge.org. The project includes the state's longest span using constant depth, precast concrete U-girder construction. each unit ready for post tensioning. After all longitudinal stressing was complete, tendons were grouted, falsework was removed, and the girders were prepared for the deck slab. The superstructure girders support the fluid weight of the fresh concrete for the cast-in-place deck in an unshored condition. This approach reduces deck cracking in negative moment regions and provides the option of a full deck replacement in the future. The success of this project and similar ones in Colorado over the last 5 years validates CDOT's vision of developing precast concrete as a viable option for complex, long-span interchange construction. CDOT has emphasized the use of standardized, commercially produced, precast concrete products to enhance the future economy and sustainability of this concept. __________ Gregg A. Reese is president of Summit Engineering Group Inc. in Littleton, Colo. A E S T H E T I C S C O M M E N T A R Y by Frederick Gottemoeller Large, multilevel interchanges are inherently confusing and stressful. Vehicles of all sizes hurtle along curved ramps in patterns that are unreadable at ground level. Drivers are continually trying to see ahead to what is coming next: sign, ramp, or merging vehicle. Within and contributing to this visual cacophony are the bridges themselves, and their phalanxes of piers. Improving a confusing and stressful scene requires simplifying it. In the case of inter- change bridges that means using fewer girders, fewer piers, and fewer columns within each pier. In addition to reducing the number of elements in the visual feld this opens up view corridors through the interchange, so that drivers can anticipate what is coming next, and improves the safety of the interchange. Simplifying the features of the bridge itself further reduces the number of visual elements the driver must absorb. Ramp A brings new techniques and new technology to these goals. First of all, the torsional stiffness of the U-girders allows only two girders in the ramp cross section. Then, splicing and post tensioning the girders allows for longer spans and fewer piers. Having only two girders to support, the piers themselves can be simple and straightforward. Since the girders are curved they can smoothly follow the curve of the ramp, so that all of the lines of the ramp are parallel to each other. Coloring the girders a darker color emphasizes this consistency, and makes the ramp appear thinner and thus the spaces below seem more open. The open, graceful appearance of this bridge will make this interchange easier and more enjoyable to use. The ends of each precast concrete girder section were notched to allow placement of an integral cast-in-place diaphragm at the abutments and expansion piers. ASPIRE , Spring 2010 | 31 SH587 Flyover Bridge_spr10-1.indd 31 4/30/14 11:11 AM