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/306882
Loop 202 over Indian Bend Wash, Tempe. (Seven-span prestressed concrete I-girders). All photos: Arizona Department of Transportation. Early bridge over I-17, Central Phoenix. (Two-span prestressed concrete I-girders). Loop 202 and Interstate 10 Interchange, Chandler. (Post-tensioned box girders). Early bridge on I-10 over St Mary's, Tucson. (Two-span prestressed concrete I-girders). 58 | ASPIRE , Spring 2008 S TAT E H istorically, concrete has been the material of choice for bridge construction in Arizona. Raw materials needed to produce concrete are readily available within the state. Prestressed I-girder and post-tensioned box girder bridges have been the most commonly constructed bridge types on Arizona's highways for the past several decades, especially in urban settings. Examples of early precast I-girder bridges dating to the 1950s can still be found throughout the state. Over time, Arizona bridge construction has followed the industry trends to use larger precast, prestressed I-girder shapes that can span longer distances, thus eliminating costly substructure units and providing plausible solutions to complex bridge sites. Historical Overview The use of precast concrete girders began in Arizona in the late 1950s. Precast girders of various types can be found on all of Arizona's interstate and state highway routes. The earlier types of precast girders consisted of small I-girder shapes, voided slabs, and box beams. The AASHTO Type II girder appears to be the primary precast girder used in many bridges in the original construction of I-10 and I-17 in the Phoenix and Tucson areas. For economical reasons, similar span and girder arrangements were used as frequently as possible. Voided slabs and box beams with asphaltic concrete overlays were used on the I-40 and various state highways. Construction plans for these girders often allowed the contractor a choice between prestressing methods: either pretensioned or post-tensioned. In most instances, as-built drawings did not document which method was used. High profile vehicle collisions with such girders, exposing ducts or strands, offered some clues to the mystery. Current Practice Today, the more commonly used precast girders are those that can span 90 to 135 ft, such as the AASHTO Type IV, V, and VI girders. Concrete Bridges in Arizona by Jean A. Nehme and Tina Sisley, Arizona Department of Transportation ASPIRE_spring08.indb 58 3/24/08 1:09:58 PM