Plasticity Spread in Columns Reinforced With High-Strength Steel

Abstract eng:
The demand for higher strength reinforcing steel in concrete construction is rapidly increasing in the United States and worldwide. Economic, environmental, and contractibility incentives are fueling the demand, particularly in highly congested seismic designs. Nevertheless, current code limits on the strength of reinforcing steel in the U.S, combined with a lack of understanding of the effects of higher strength steel on the performance of concrete members, are hindering progress in structural designs. Steel grades higher than Grade 80 (80 ksi specified yield strength [540 MPa]) and having relatively high ductility (>10% fracture strains) are just emerging in the U.S. However, the steel industry is producing the high-strength steels with varying mechanical properties. Test results are presented from an experimental program carried at the University of Texas at Austin aimed at evaluating the effect of the tensile-to-yield (T/Y) strength ratio of high-strength reinforcement on the plasticity spread in concrete columns subjected to seismic demands. Comparisons are made between the performances of columns reinforced with various grade bars including Grade 100 bars (100 ksi specified yield strength [690 MPa]) produced using the leading production techniques in the U.S. and having different T/Y strength ratios. These tests were conducted as part of a research effort aimed at setting the minimum acceptable T/Y ratio in new ASTM specifications for seismic Grades 80 and 100 reinforcement. Column specimens were tested under constant axial load and reverse cyclic lateral loading until significant loss in lateral load carrying capacity. Conclusions are drawn with respect to the effects of higher strength reinforcement on the seismic performance of concrete columns and strain demands on reinforcing bars.

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