Submitted by Carter & Burgess Inc.

The third in a family of three signature pedestrian bridges, the Highland Bridge unites Denver's Lower Downtown with the Highland neighborhood across Interstate 25. This final connection helps the city and county realize its goal of improving the quality of life for visitors and residents of the Central Platte Valley by making the environment more pedestrian- and bike-friendly.

The final design features a dramatic triple-rib steel arch, rising 70 ft above the ground and spanning 320 ft over I-25 at its maximum. The flared cross-hanger arrangement for the asymmetric cable stays provides a sweeping support system for the suspended bridge deck.

The arch design and steel construction details were determined after input from fabricators and general contractors. The overhead arch was constructed in four sections and erected in phases over I-25. The plaza, ramp and abutment designs were developed with input from stakeholders to reflect the shared vision of adjacent communities.

Critical to the urban design concept was the creation of a vertical circulation area to transverse a 13-ft change in grade from the structure deck down to the existing Platte Street elevation. The need for long ramp access, in addition to stair access, drove the design toward an architecturally sophisticated and urban solution. The refined landscape and lighting design accentuates both the plaza and structure. The plaza provides direct access to the Platte Street shops and Commons Park.

Submitted by The Engineering Co.

From previous geologic studies, it was known that the CSU stadium and its field were constructed over a large expanse of bedrock. Pockets of the bedrock had been removed, leaving subsurface ground-water collections. In that state, surface drainage during snowmelt and rainstorms produced standing water and a spongy playing field.

To solve the problem, a subsurface drainage system was designed to collect groundwater and transport it to a central point at the south end of the field. The architects designed a field drain to collect surface water runoff that fell onto the field and convey it to the same central collection point. The storm sewer system was also redesigned. All these drainage systems were directed to a new collection manhole where a duplex pump system moves water to the existing storm drain and where it exits the stadium.

Because the slope of the new playing field amounts to only a 3/8-in. drop over 10 ft, the project team needed a precise method for checking the as-built conditions to get a finished subgrade tolerance of only 1/8-in. The survey team chose a combination of GPS//RTK and differential leveling methods, and surveyors made themselves available on short notice to perform checks so that no time was lost during an already-tight schedule.

To complete the new playing field, the subgrade was topped with synthetic turf that complements the university's synthetic turf practice field.

Submitted by Parsons Brinckerhoff

Spanning U.S. Highway 36 between Louisville and Superior, the McCaslin Boulevard Pedestrian Bridge provides access for transit passengers to a new RTD park-n-Ride facility and has become a landmark for local residents. With additional capacity in the planning stages for the U.S. 36 corridor, CDOT required that the bridge span the entire width of its right-of-way without a center pier. A steel basket handle arch was selected to create an architectural structure that blends with the Flatirons to the west.

The completed structure spans 234 ft and consists of 20-in.-diameter pipe tied arches and steel deck framing supported by steel suspension rods with a concrete deck. The arches were fabricated in Duluth, Minn., and shipped in four pieces. Complex connections between them and the deck framing consist of concrete thrust blocks with a post-tensioned connection of the deck framing to the thrust block.

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To minimize road closure, the entire superstructure was erected in a CDOT right-of-way parallel to U.S. 36 and lifted into place during one eight-hour, overnight closure. Three cranes were used. One stationary crane lifted and stabilized the north bearings, then a second one lifted the south end of the structure and boomed out over the westbound lanes reaching to a crawler crane waiting in the eastbound lanes. At this point the structure was "handed off" to the crawler crane, which then walked the south end of the structure into place and lowered it onto the south abutment - eliminating any destruction to the median and barrier during erection.

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