Effect of Open-Loop or Closed-Loop Deflection Control on Measured Toughness of FRC

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Title: Effect of Open-Loop or Closed-Loop Deflection Control on Measured Toughness of FRC

Author(s): R. Gupta and N. Banthia

Publication: Special Publication

Volume: 248

Issue:

Appears on pages(s): 67-82

Keywords: closed loop; fiber-reinforced concrete; open loop; toughness

Date: 9/1/2007

Abstract:
Effect of open- or closed-loop deflection control on the measured flexural toughness of fiber reinforced concrete (FRC) was investigated. Third-point loading tests were performed as per ASTM C1609M on several high strength concrete mixtures containing low volume fractions of single, double and triple-fiber blends. A 3-stage loading sequence was adopted for the closed-loop deflection control tests to fully capture the load vs. deflection response immediately after the peak-load. The results indicate that the open-loop tests produce high instability in the load deflection curves after the peak-load. However, contrary to general belief, the open-loop tests also overestimated the flexural toughness compared to the closed-loop deflection control tests. Manually removing the instability from the open-loop curves helped bring the open-loop toughness values closer to the closed-loop toughness values.