CRC 87: Part 2 Columns: Defining Structurally Acceptable Properties of High-Strength Steel Bars through Material and Column Testing


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Title: CRC 87: Part 2 Columns: Defining Structurally Acceptable Properties of High-Strength Steel Bars through Material and Column Testing

Author(s): The University of Texas at Austin, Drit Sokoli, Albert Limantono, and Wassim M. Ghannoum

Publication: CRC



Appears on pages(s):


Date: 2/3/2017


Economic, environmental, and constructability incentives are fueling the demand for higher strength reinforcing steel in concrete construction, particularly in highly congested seismic designs. In response, steel mills in the United States are developing highstrength reinforcing bar (HSRB) that can be used in seismic as well as non-seismic applications. However, different manufacturers are achieving higher strengths using different techniques (i.e., micro-alloying, quenching, etc.), leading to HSRB having differing mechanical properties. Such differences have raised questions about what the minimum acceptable mechanical properties should be for HSRB to achieve acceptable structural performance in various members and for various loading types. An experimental program was undertaken to assess the influence of the tensile-to-yield strength (T/Y) ratio and ductility of HSRB on the behavior of concrete columns under cyclic lateral loading. Four column tests were conducted in this study that was part of a broader research effort aimed at setting the minimum acceptable T/Y ratios and elongations in new ASTM specifications for seismic grade 80 and 100 reinforcing bars. Three of the specimens were reinforced with grade 100 bars produced by different manufacturers and therefore having different mechanical properties. The fourth column was reinforced with conventional grade 60 ASTM A706 bars. Column specimens were tested under constant axial load and reverse cyclic lateral loading of increasing amplitude until fracture of longitudinal bars. Conclusions are drawn with respect to the effects of the higher strength reinforcement on the seismic performance of concrete columns, strain demands on reinforcing bars, plasticity spread, and energy dissipation. In this report, HSRB are defined as those having a yield strength in excess of 80 ksi (or grade 80 and higher).

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