Projects : Task Order 25

Use of High-Strength Flexural Reinforcement in Reinforced Concrete Seismic Design

SUMMARY

The ATC-57 report, The Missing Piece: Improving Seismic Design and Construction Practices (ATC, 2003), which defines a roadmap for the NIST problem-focused research and development program in earthquake engineering, recommended that NIST examine new technologies that can improve construction productivity. One improvement already being utilized is that of High Performance Concrete (HPC), which can be used to reduce member sizes, dead loads, and construction costs, and has had the effect of improving performance and the competitiveness of reinforced concrete structures, especially in mid- and high-rise buildings. Unfortunately, reductions in member sizes can create problems with reinforcing steel congestion, especially in high seismic regions. The potential use of high-strength reinforcing bars along with HPC offers a possible solution to this problem, along with the added benefit of improved construction efficiency through lower material and labor costs.

Nominal yield strengths of 100 ksi, well above the traditional limit of 60 ksi, are available in commonly used ASTM A615 and A706 bars, as well as the newer A1035 chromium steel corrosion resistant bars. An important question is how reinforced concrete structures would behave when reinforced with high-strength bars. Nearly all of the research conducted over the past four decades has utilized standard Grade 60 reinforcing bars for reinforcement. The application of high-strength steel deformed bars is only now being studied, mostly by producers, and on a limited basis. Basic behavior questions, and the knowledge gaps that are present when considering use of these higher yield strength bars, need to be identified and addressed.

The primary objective of this task is to perform the work required to study and make recommendations concerning the utilization of high-strength steel reinforcing bars in concrete structures subjected to earthquake ground motion. Work will investigate the potential savings in construction costs and time, and will review available information in the literature regarding potential difference in behavior.

Work to be carried out under this task order includes: (1) project management and oversight, including the selection and confirmation of key project personnel; (2) preparation of a Project Work Plan and progress reports; (3) update of a NIST project description; (4) identification of existing knowledge and research needs; (5) application to building prototype designs; (6) conduct of a limited program of laboratory testing; (7) development of recommended code changes; (8) preparation of a project report; and (9) presentation of in-person progress reviews at NIST offices in Gaithersburg, MD and at the ATC offices in Redwood City, CA.

Project Director: Laura Samant, ATC Director of Business Development, Arlington, VA

Project Technical Committee members:

• Dominic Kelly (Project Director, Chair), Simpson Gumpertz & Heger, Waltham, MA

• Cary Kopczynski, Cary Kopczynski & Co., Bellevue, WA

• Andres Lepage, Pennsylvania State University, University Park, PA

• David Mar, Tipping + Mar, Berkeley, CA

• Jose Restrepo, University of California, San Diego, CA

• Joseph C. Sanders, Charles Pankow Builders, Ltd., Pasadena, CA

Project Review Panel Members:

• Tony Ghodsi, Englekirk & Sabol Consulting Structural Engineers, Santa Ana, CA

• James Jirsa, University of Texas at Austin, TX

• Conrad Paulson, Wiss, Janney, Elstner Associates, Inc., Chicago, IL

• Mete Sozen, Purdue University, West Lafayette, IN

• Loring A. Wyllie. Jr., Degenkolb Engineers, San Francisco, CA