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Project 2010-01

Project Title:

Evaluation of the Tensile Mechanical Properties of Coiled Reinforcing Bars

Institution:

Texas Tech University
Lubbock, Texas

Researcher:

Sang-Wook Bae, Ph.D., Assistant Professor
Mahnaz Ghodsifasaei, Graduate Research Assistant

Award Period:

2010-2011 school year

Status:

Completed

Description:

The use of small diameter, #3, #4, #5, and #6 coiled reinforcing bar is common practice for fabricating repetitive items such as stirrups and ties. Fabrication is achieved by passing coiled reinforcing bars through an automated machine, generically referred to as a coil, automatic, or stirrup bender, which first straightens the coiled bar, makes the required bends, and then cuts the bar to separate the completed assembly from the coiled bar stock.

Coiled reinforcing steel is produced as per ASTM A615, Grade 60, Grade 75, ASTM A706, Grade 60, as well as a dual certified ASTM A615 / A706 Grade 60. Stainless steel reinforcing bars, as per ASTM A955, are also coiled. In the United States, there are eight major producers of coiled reinforcing steel and many international producers. The majority of coiled reinforcing steel used in the U. S., both domestic and imported production, is ASTM A615 / A706 (dual certified), Grade 60.

The physical, chemical, and mechanical properties of the reinforcing bars are tested and certified by the producing mill, with the mechanical properties based on handstraightened samples of bar cut from the coil. Specific tensile properties evaluated include yield and tensile strength, and percent elongation, as specified in the ASTM specifications. There is a significant difference between the hand straightening method utilized by the producing mill and the mechanical straightening method used in the fabrication process, which cold works the bar. Cold working will increase the yield strength, may affect the ultimate strength, and will decrease the elongation. This research will study the impact on the mechanical properties of the reinforcing bars resulting from the mechanical straightening process (cold working) of the automated fabrication equipment.

An advisory task group affiliated with the Material Properties and Bar Producers technical committee recently coordinated with the researcher to revise the research scope of the project. As such, the project will be starting in the Fall of 2011, when a new graduate student starts classes. Members of the advisory task group and the CRSI region managers will likely be working in tandem to procure samples of reinforcing bar for the researcher. These samples will be representative the population of steel mills and equipment manufacturers used in coiled bar fabrication.