Seismic Performance Enhancement of RC Columns Using Thin High-Strength RC Jackets and CFRP Jackets

Abstract

The existing non-ductile RC structures built prior to the 1960s–1970s were mainly conceived to carry only vertical loads. As a result, the columns of these structures demonstrate poor overall hysteresis behavior during strong earthquakes, dominated by brittle shear or/and premature excessive slipping of the inadequately lap-spliced reinforcement. In the present study, the effectiveness of two different strengthening systems (including either the wrapping of the columns by carbon-fiber-reinforced polymer textile or the use of thin high-strength reinforced concrete jackets), was experimentally and analytically investigated. The main variables examined were the strengthening material, the length of the lap splices and the amount of confinement provided by the jackets. Three cantilever column specimens were constructed without incorporating modern design code requirements for preserving seismic safety and structural integrity. Subsequently, the specimens were strengthened and subjected to earthquake-type loading. Their hysteresis performances were compared, while also evaluated with respect to the response of two similar original specimens and the behavior of a control one with continuous reinforcement, tested in a previous study. The predictions of the proposed analytical formulation for the hysteresis behavior of the strengthened specimens were satisfactorily verified by the experimental results.

Hysteresis Behavior of RC Beam–Column Joints of Existing Substandard RC Structures Subjected to Seismic Loading–Experimental and Analytical Investigation

“…Moreover, Kalogeropoulos and Tsonos [18][19][20] recently proposed a modified version of the analytical model which allows for the prediction of the seismic behavior of RC columns by controlling the adequacy of the length of lap-spliced reinforcement. The modified formulation is also used to precisely determine the necessary confinement to be provided by the strengthening material to prevent premature lap splice failure and allow for the yielding of reinforcement and the development of the column's nominal flexural moment capacity.…”

“…Kalogeropoulos and Tsonos experimentally investigated the seismic performance of original column subassemblages typical of substandard RC buildings built prior to the 1960-1970s with deficient lap splices, as well as the behavior of similar specimens retrofitted using thin steel jackets, RC jackets and CFRP jackets. They also proposed an analytical formulation for calculating the necessary confinement to achieve yielding of the deficiently lap-spliced rebars [18][19][20]. Anagnostou et al [21] used a database with experimental results of 67 RC columns with lapspliced steel bars, strengthened externally with FRP jackets subjected to pseudo-seismic loading to investigate the predictive performance of EC8.3 [22] and KANEPE [23] in calculating VR and θu.…”

Innovative Seismic Strengthening Techniques to Be Used in RC Beams’ Critical Zones

“…Research works emphasise the significant improvements in the seismic behaviour of RC sub assemblages by increasing the compressive zone deformation capacity, such as the use in beam-column joints of HPFRC-High Performance Fibre Reinforced Concrete-Dogan [25]; Ficher [26]; Parra-Montesinos [27]; Shannag [28,29]; Konstantinos [30]; Chalioris [31,32]; Kalogeropoulos [33]; Bencardino [34]; Fares [35]. Muhaj (2020) [36] presented an experimental study of seismically reinforced concrete beams strengthened with post-tensioning with anchorages by bonding, which presented reduced residual deformation and anenhanced load capacity.…”

Retrofitting of Shear Compression Failure-Critic Short Columns with a New Technique

“…Hosseini [11] found that the presence of FRP anchors provides extra ductility. Kalogeropoulos [12] and Kalogeropoulos and Tsonos [13] used steel fibers and thin RC jackets, in addition to FRP, for jacketing of the column. Different researchers have used different test methods for the shear test [14][15][16].…”