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/697527
C O N C R E T E B R I D G E T E C H N O L O G Y 28 | ASPIRE Summer 2016 Oregon anticipates increased use of ASTM A706 Grade 80 for the following reasons: • The stress/strain curve for Grade 80 has a similar shape compared to Grade 60. This is not the case for reinforcement grades higher than 80 ksi. • Grade 80 has an additional 33% yield strength compared to Grade 60, with only 10 to 12% additional material and fabrication cost. • Good ductility. No. 3 thru No. 11 bars have a minimum elongation of 12%. • Weldability. • Reduced congestion. • Availability. Design with Grade 80 reinforcement uses the same processes and equations used for Grade 60 reinforcement. The American Association of State Highway and Transportation Officials (AASHTO) has confirmed this and rais ed the permitted yield strength from 75 to 100 ksi in the 2013 Interim Revisions of the AASHTO LRFD Bridge Design Specifications . Availability of Grade 80 reinforcement is improving due to increased use of Grade 80 reinforcement in the building industry. At this time, a minimum order of 50 tons for each size and cut length is recommended by rolling mills in the Oregon market. This minimum order size is mentioned several times in the following discussion, but will likely differ for each rolling mill and local market. T h e f o l l o w i n g a p p l i c a t i o n s a r e good oppor tunities to use Grade 80 reinforcement: • Drilled shafts: both longitudinal and lateral reinforcement • Bridge decks: especially if design can be limited to a single bar size In 2012, two local agency projects in Oregon used ASTM A706, Grade 80 steel reinforcement in large diameter drilled shafts for crossings of the Willamette River in Portland. One is the Tilikum Crossing, a cable-stayed bridge carrying a transit line and pedestrians, which is owned by the city of Portland. The other is the Sellwood Bridge, a steel deck arch, which is owned by Multnomah County. In August of 2012, the Oregon Department of Transportation (ODOT) added guidelines for use of ASTM A706 Grade 80 steel reinforcement to their Bridge Design and Drafting Manual (BDDM). These guidelines were developed from discussions with an Oregon reinforcing bar manufacturer who confirmed both availability and the approximate cost premium for Grade 80 reinforcement. ODOT is ready to move forward with expanded use of Grade 80 reinforcement. Since those initial projec ts, only one additional projec t has used Grade 80 reinforcement. This lack of progress is primarily due to an Oregon shift in priority towards bridge repairs instead of replacements. This shift is a result of limited availability of bridge funding. However, ODOT is hopeful funding will improve in the near future. When that happens, ODOT is ready to move forward with expanded use of Grade 80 reinforcement. Use of Grade 80 Reinforcement in Oregon by Craig Shike and Dr. Tanarat Potisuk, Oregon Department of Transportation Chehalem Creek Bridge used for comparison of Grade 60 and Grade 80 reinforcement for 8-ft-diameter drilled shafts. All Photos and Tables: Oregon Department of Transportation.