cyclic response of concrete columns reinforced with SAS 670 Grade-97 steel

Open Access
Author:
Tretiakova, Ksenia K
Area of Honors:
Architectural Engineering
Degree:
Bachelor of Architectural Engineering
Document Type:
Thesis
Thesis Supervisors:
  • Dr Andres Lepage, Thesis Supervisor
  • Ali M Memari, Honors Advisor
Keywords:
  • concrete columns
  • high strength steel
  • cyclic displacement reversals
Abstract:
Since the implementation of Strength Design for structural concrete in the 1960s, US building codes have limited the use of ultrahigh-strength steel (yield strength greater than 80 ksi) for seismic applications. This has been mostly due to insufficient experimental data. The industry has been dominated by the design of concrete members reinforced with steel bars having specified yield strength of 60 ksi (Grade 60). In this study, a series of experiments was designed to investigate the cyclic response of concrete columns reinforced longitudinally with ultrahigh-strength steel bars. The experiments included two specimens, reinforced with Grade-97 steel bars. A third specimen (tested by others) represented the control specimen reinforced with conventional Grade-60 bars. All three specimens were designed to have similar flexural strengths (with nearly identical ρg fy) and were subjected to the same loading protocol consisting of reversed-cyclic displacements of increasing amplitude. The applied axial load remained constant throughout the loading protocol. The test specimens included variation in the volume fraction of hooked steel fibers, 0% for reinforced concrete (RC) and 1.5% for high-performance fiber reinforced concrete (HPFRC); and the spacing of the transverse hoops, d/4 for RC and d/2 for HPFRC. The nominal concrete strength was 6000 psi for all specimens. All of the tested columns completed the cyclic loading protocol, which targeted a maximum drift ratio of 5%. The test data indicate that, for RC and HPFRC columns, replacing conventional Grade-60 longitudinal reinforcement with reduced amounts of Grade-97 steel bars attained the target flexural strength and deformation capacity. The calculated nominal and probable moments, using conventional assumptions in Strength Design, were in reasonable agreement with the measured values.