Abstract
Reinforced concrete (RC) columns typical of existing structures often exhibit premature failures during seismic events (i.e., longitudinal bars buckling and shear interaction mechanisms) due to the poor quality concrete and the absence of proper seismic details in the potential plastic hinge region. The Fiber Reinforced Polymers (FRP) externally bonded reinforcement is known to be a valid technique to improve the shear capacity or the ductility of existing RC columns. However, few experimental tests have proven its effectiveness in the case of columns affected by shear interaction mechanisms. In this work, the behavior of existing RC columns with border line behavior between flexure and shear have been investigated in the case of poor quality concrete and light FRP strengthening with local jacketing and medium quality concrete and strong FRP strengthening with local jacketing, in order to highlight the effect of concrete strength on the effectiveness of the retrofit intervention. As an alternative to FRP jacketing; the effectiveness of the Fiber Reinforced Cementitious Composite (FRCC) jacketing for the seismic strengthening of columns with highly deteriorated concrete cover or columns already damaged by an earthquake is also evaluated. Six full-scale RC columns have been tested under cyclic loading: one was used as a control specimen; four were strengthened in the potential plastic hinge region with carbon FRP (CFRP); and one was fully jacketed with FRCC. The comparison between poor and medium quality concrete columns showed that the CFRP local jacketing is more effective in the case of poor quality concrete. The FRCC jacketing appears to be a sound repair strategy and a suitable alternative to the FRP jacketing in case of poor quality; however, more experimental research is needed for improving this retrofit technique.
Highlights
Post-earthquakes reconnaissance [1,2,3,4] and experimental research [5,6,7,8,9,10,11,12], among many others have evidenced that existing reinforced concrete (RC) columns, designed according to old standards and construction practice, often show premature failures due to many phenomena
The last part of the present work investigates the use of the Fiber Reinforced Cementitious Composite (FRCC) jacketing for the repair/strengthening of poor quality concrete RC columns already damaged by a seismic event, as an alternative to the externally bonded Fiber Reinforced Polymers (FRP) technique
The notation of specimens is CX_Y, where C stays for column, X refers to the concrete compressive strength (L, low or M, medium) and Y denotes the strengthening system adopted (FRPa, FRPb or FRCC)
Summary
Post-earthquakes reconnaissance [1,2,3,4] and experimental research [5,6,7,8,9,10,11,12], among many others have evidenced that existing reinforced concrete (RC) columns, designed according to old standards and construction practice, often show premature failures due to many phenomena (i.e., buckling of longitudinal bars, loss of bond, shear interaction, etc.). The cyclic loading caused by earthquakes weaken the concrete shear resisting mechanism in the plastic hinge region of existing RC members, characterized by poor quality concrete and large spacing of transverse reinforcement, leading to brittle shear failures after the flexural yielding [13,14]. The last part of the present work investigates the use of the FRCC jacketing for the repair/strengthening of poor quality concrete RC columns already damaged by a seismic event, as an alternative to the externally bonded FRP technique. The performance of jacketed specimens was compared in terms of failure mode, lateral capacity and ductility, stiffness degradation, energy dissipation and damage evolution
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