Earthquakes and Structures

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Rapid retrofit of substandard short RC columns with buckled longitudinal bars using CFRP jacketing

  • Marina L. Moretti (School of Architecture, National Technical University of Athens)
  • Received : 2022.11.19
  • Accepted : 2022.12.18
  • Published : 2023.02.25
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Abstract

This experimental study investigates the effectiveness of applying carbon fiber reinforced polymer (CFRP) jackets for the retrofit of short reinforced concrete (RC) columns with inadequate transverse reinforcement and stirrup spacing to longitudinal rebar diameter equal to 12. RC columns scaled at 1/3, with round and square section, were subjected to axial compression up to failure. A damage scale is introduced for the assessment of the damage severity, which focusses on the extent of buckling of the longitudinal rebars. The damaged specimens were subsequently repaired with unidirectional CFRP jackets without any treatment of the buckled reinforcing bars and were finally re-tested to failure. Test results indicate that CFRP jackets may be effectively applied to rehabilitate RC columns (a) with inadequate transverse reinforcement constructed according to older practices so as to meet modern code requirements, and (b) with moderately buckled bars without the need of previously repairing the reinforcement bars, an application technique which may considerably facilitate the retrofit of earthquake damaged RC columns. Factors for the estimation of the reduced mechanical properties of the repaired specimens compared to the respective values for intact CFRP-jacketed specimens, in relation to the level of damage prior to retrofit, are proposed both for the compressive strength and the average modulus of elasticity. It was determined that the compressive strength of the retrofitted CFRP-jacketed columns is reduced by 90% to 65%, while the average modulus of elasticity is lower by 60% to 25% in respect to similar undamaged columns jacketed with the same layers of CFRP.

Keywords

Acknowledgement

The tests were performed in the Laboratory of RC Technology and Structures at the University of Thessaly, Greece. The author would like to thank Mr. E. Miliokas and Mr. I. Paparizos who have undertaken the tests as part of their undergraduate thesis in the School of Engineering, University of Thessaly, Volos, Greece, under the supervision of the author who served as Assistant Professor. The contribution of Mr. A. Koutselinis and Mr. T. Papatheocharis in manufacturing the specimens and technical advice at testing, respectively, as well as Sika Hellas SA for supplying the composite materials, are also gratefully acknowledged.

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