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    Hybrid Use of Externally Embedded FRP Reinforcement for Seismic Retrofitting of Substandard RC Columns
    (Asce-Amer Soc Civil Engineers, 2023) Seyhan, Engin C.; Goksu, Caglar; Saribas, Ilyas; Ilki, Alper
    This paper discussed the effectiveness of the hybrid use of fiber-reinforced polymer (FRP) reinforcement for the seismic retrofitting of substandard reinforced concrete (RC) columns. Four columns, except for the reference, were retrofitted with externally embedded FRP (EE-FRP) bars in a longitudinal and external FRP jacket in the transverse directions. The test parameter was the configuration of the FRP bars that were used for retrofitting along the longitudinal direction (e.g., single or hybrid use of different types of FRP bars, such as aramid (AFRP), glass (GFRP), or carbon fiber-reinforced polymers (CFRP). The test results indicated that a significant enhancement in the lateral load capacity (<= 198% in the unstrengthened column) could be achieved through the hybrid use of FRP bars under reversed cyclic lateral displacement and a constant axial load without a significant sacrifice in deformability. In addition, the test results yielded insights into the strain (e) capacities of longitudinal FRP bars in tension and their contribution to compression resistance under reversed cyclic lateral loading conditions. In addition, an analytical study was conducted to predict the cyclic flexural behavior in substandard RC columns that were retrofitted through the single or hybrid use of EE-FRP bars that considered the debonding behavior of longitudinal CFRP bars with a smooth surface.
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    Post-fire Seismic Behavior of RC Columns Built with Sustainable Concrete
    (Taylor & Francis Ltd, 2022) Demir, Ugur; Unal, Goktug; Goksu, Caglar; Saribas, Ilyas; Ilki, Alper
    In this study, four full-scale reinforced concrete columns were built replacing 50% of natural coarse aggregates in concrete mix by recycled aggregates. Three of the columns were exposed to standard ISO-834 fire for 30, 60 or 90 minutes, while the reference specimen was not exposed. Sixty days after fire exposure, the columns were tested under constant axial load and reversed cyclic lateral displacements simulating earthquakes. Test results are evaluated in terms of lateral load capacity, ductility, stiffness and energy dissipation. In addition, an analytical study was conducted to predict the lateral load-displacement response of fire-damaged columns built with recycled aggregates.
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    Seismic performance of full-scale RC columns containing high proportion recycled aggregate
    (Springer, 2019) Saribas, Ilyas; Goksu, Caglar; Binbir, Ergun; Ilki, Alper
    The potential for utilizing high proportion recycled aggregates sourced from low strength waste concrete in new concrete construction is investigated in this paper. A comprehensive experimental program, consisting of ten full-scale, flexure critical reinforced concrete columns, five of which were constructed of natural concrete aggregate and five of which contained approximately 50% recycled concrete aggregate replacing the mid-sized coarse natural aggregate, was conducted to determine the effects of different axial loads and different spacings of transverse reinforcement on the seismic characteristics of columns incorporating recycled concrete aggregates. Seismic characteristics were quantified by analysis of hysteretic response, energy dissipation capacities, damage progression, residual displacement, and strain distribution of the longitudinal reinforcement. The test results indicate that the reinforced concrete columns constructed of natural aggregate concrete and those constructed of recycled aggregate concrete exhibit similar seismic performance, despite the fact that the compressive strength of the recycled aggregate concrete was slightly lower than that of the natural aggregate concrete. A theoretical study was then conducted to predict the load-displacement response of the columns. The comparison of the experimental data with the results of these theoretical calculations indicated that conventional RC design theory applied to columns incorporating natural aggregate is also valid for columns incorporating recycled aggregate. Finally, the confinement effect of the transverse reinforcement in columns subjected to low axial load were also critically evaluated for columns built with recycled aggregate concrete.
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    Seismic performance of full-scale RC columns containing high proportion recycled aggregate (vol 17, pg 6009, 2019)
    (Springer, 2019) Saribas, Ilyas; Goksu, Caglar; Binbir, Ergun; Ilki, Alper
    [Abstract Not Available]
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    Shear-flexure interaction in RAC columns under simulated seismic actions
    (Elsevier Ltd, 2021) Saribas, Ilyas; Goksu, Caglar; Binbir, Ergun; Ilki, Alper
    Inelastic flexural deformations adversely affect shear resistance of columns, and may cause building damage/collapse during earthquakes. In this paper, shear-flexure interaction on seismic performance of reinforced concrete columns constructed with recycled aggregate concrete is experimentally investigated. For this aim, reinforced concrete columns with low shear-span-to-depth ratio (2.3) were designed and constructed so that they reach their flexural lateral load capacities in accordance with capacity design principles, and the effect of shear deformations can be observed only after yielding of longitudinal reinforcing bars due to cyclic degradation. The shear-flexure interaction is characterized based on the amount of transverse reinforcement, and formulated within the framework of conventional reinforced concrete design theory during the design of the columns. These columns are then tested under the combined effects of axial and reversed cyclic lateral loads to simulate seismic loading. The recycled concrete aggregate is sourced from waste of low strength concrete, and replaced with 50% of natural coarse aggregate for the concrete mix. Comparison with columns constructed of natural aggregate is also presented in the study. The test results showed that the reinforced concrete columns either made of natural aggregate concrete or recycled aggregate concrete exhibited similar seismic performances for different interactions of shear and flexure. As the ratio of transverse reinforcement is reduced the deformation capability was reduced due to more pronounced effect of shear deformations. In addition, the load–displacement relationships determined through theoretical analysis were found to be compatible with the experimental data. Furthermore, a discussion on the minimum transverse reinforcement provisions of EN 1998-1, ACI 318-19 and TBEC-18 is also presented in order to investigate whether it is possible to reduce the required ratio of minimum transverse reinforcement per technical documents for the columns located in low to moderate seismicity regions. © 2021 Elsevier Ltd