The I-25 Bridge over the South Platte River (aka Bronco Bridge) has been a Denver landmark structure since its initial construction in 1951. The steel arches, supporting the bridge superstructure, became known as the Bronco Arches after the Denver Broncos began playing football in the adjacent Mile High Stadium in 1960. Today, the bridge carries more than 200,000 vehicles per day. After many years of service, the bridge deteriorated to the point of needing replacement.
To address this issue, the Colorado Department of Transportation (CDOT) designed a replacement bridge to accommodate four through lanes of traffic in each direction, as well as acceleration lanes and on- and off-ramps. The selected contractor, Lawrence Construction Co., requested that CDOT consider a value-engineering (VE) proposal prepared by Summit Engineering Group (Summit) that would enhance the constructability and accelerate the construction schedule of the bridge. Working in concert with CDOT and the contractor and Summit provided designs that maximized the use of precast concrete thus reducing the number of construction stages, shortening the schedule, and greatly reducing the impact on existing traffic. The VE proposal provided a substantial benefit that prompted CDOT to approve the VE proposal and promptly issued notice-to-proceed. At this point, Summit became the Engineer of Record for the bridge. All the constructed designs were prepared by Summit in cooperation with the contractor and CDOT.
Summit’s innovative solution featured a completely precast rigid frame, which enhanced the structural efficiency and stiffness of the system while optimizing the use of precast, prestressed concrete elements. The piers were all precast and consisted of slender, arched shafts that are connected with a strut at mid-height. The addition of the strut reduced bending moments in the pier shafts by 60%, which resulted in a more slender design and reduced overall weight. This made precasting, handling, and erection possible. The superstructure consists of precast, post-tensioned concrete deck slabs supported on 8 continuous spliced precast concrete girder lines. The extensive use of precast concrete elements greatly reduced the construction time, minimized the number of construction phases, and reduced cost for CDOT.
The design and construction of the Bronco Arch Bridge is an excellent example of efficient accelerated bridge construction. A signature structure was built within budget and schedule. When all project stakeholders work together, new and innovative design/construction methods can be executed with minimum inconvenience to the traveling public.
"Thanks to the use of precast concrete in this project, a vital urban structure was rebuilt within budget and schedule with minimal inconvenience to the citizens of Colorado." - www.pci.org
Gregg A. Reese, PE (Project Principal)
DeWayne D. Hansen, PE (Project Manager)