Cushing Street Bridge over Santa Cruz River
Structural Design
Tucson, Arizona
The Cushing Street Bridge over the Santa Cruz River, designed by Structural Grace, Inc., is the first segment to break ground on the 3.9 mile Modern Streetcar project for the City of Tucson. Structural Grace Inc. provided the preliminary and final design for the new bridge which features significant historical detailing and carries two traffic lanes, two modern streetcar tracks, two bicycle lanes and pedestrian ways over the Santa Cruz River.
Engineering efforts began in March 2007 after initial meetings with the City of Tucson, Pima County, Rio Nuevo Development Staff, numerous neighborhood associations and the general public. Per the direction of Rio Nuevo Leadership and the City of Tucson, five bridge design alternatives were developed and presented in a Structure Selection Memo. Rio Nuevo Leadership and the City approved a 3-span bridge with an overall length of 315 feet. 30% design documents, a preliminary estimate and reports were then completed and submitted to the City in early April 2008.
Upon approval, Structural Grace, Inc. began the 60% design for the selected bridge type and incorporated a design process change from a conventional design-bid-build delivery method to a construction manager at risk (CMAR) delivery method. In August 2008, 60% design documents with all ancillary elements, including developed art elements, were submitted to the City of Tucson.
In October 2008, with a goal of reducing the impact of the structure on the high-water elevation, the City requested the design team revisit the bridge type selection. Ultimately the City approved a new bridge type consisting of a 2-span bridge with an overall length of 315 feet. The client also desired the appearance of the new bridge type to remain fundamentally consistent with the designs of the previous bridge alternatives. Additionally, the City returned to a design-bid-build delivery approach.
The final design of the structure evolved to a fairly typical structural system of Super VI Modified AASHTO girders, two spans with a center pier consisting of a two column bent with cantilevered sidewalks, retaining historical detailing, a complex form, architectural quality and proportion which makes for a very unique structure. Integrated public art that grew from an involved public participation process also graces the bridge with meaningful and locally historic motifs.
The consultant team consisted of AMEC, prime consultant; Structural Grace, Inc., bridge design; Sage Landscape Architecture, Inc., landscape architecture and environmental reporting; R.A. Alcala & Associates, Inc., electrical engineering; and Terracon Consultants, Inc., geotechnical analysis.
Read more about this project at http://www.downtowntucson.org/news/?p=3354.
