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Seismic Retrofit of Reinforced Concrete Columns With Post-Tensioned Metal Strips

Samadi, Maysam | 2010

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40542 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Moghaddam, Hassan
  7. Abstract:
  8. This thesis presents the results of an experimental and analytical study on the application of the strapping technique for seismic retrofit of reinforced concrete columns. In this technique, the columns are externally confined by post-tensioned metal strips. In the first phase of the experiments, the compressive stress-strain behavior of strapped cylindrical and prismatic specimens was studied. Effects of several parameters were studied including shape and size of specimens, strength of plain concrete, mechanical characteristics of confining strips and the level of pre-tensioning of the strips. The second phase of the tests included studying the lateral performance of strapped RC columns. Eight poorly designed 2/3 scale models of building columns with square cross-sections and with were tested under constant axial load and cyclic reversals with increasing amplitudes. Two levels of axial load were considered in testing the eight columns including 0.19 f’c Ag and 0.38 f’c Ag. In addition to the axial load level, the effect of the volumetric ratio of confining strips on the lateral behavior of six specimens of these eight columns was studied. Test results showed the excellent performance of the strapping technique in improving the lateral behavior of brittle RC columns. In the seventh specimen, the strapping technique was applied together with the addition of a near surface mounted longitudinal reinforcement that results in considerable strength gain, as well as lateral ductility. The eighth specimen was damaged and repaired with the strapping technique that showed the successful performance of strapping in repair of severely damaged RC columns. In addition, four 2/3 scale RC columns with short lap-spliced longitudinal reinforcements with circular cross-section were tested. The strapping technique could provide considerable improvement on the behavior of these columns. In addition, the premature slippage that was the predominant failure mode of control specimen was effectively prevented in the strapped specimens and higher lateral strength was achieved. A confinement model was proposed for concrete confined with post-tensioned metal strips, which was successfully applied in predicting the stress-strain of tested specimens. This model was also used in section analysis of the tested columns that resulted in reasonably predictions.

  9. Keywords:
  10. Concrete ; Seismic Rehabilitation ; Columns (Supports) ; Metal Strips ; Lap-Splice Length

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