Seismic Strengthening of Severely Damaged Beam-Column RC Joints Using CFRP (original) (raw)
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Seismic response of FRP-upgraded exterior RC beam-column joints
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Shear failure of exterior beam-column joints is identified as the principal cause of collapse of many moment-resisting frame buildings during recent earthquakes. Effective and economical strengthening techniques to upgrade joint shear-resistance and ductility in existing structures are needed. In this paper, efficiency and effectiveness of Carbon Fiber Reinforced Polymers (CFRP) in upgrading the shear strength and ductility of seismically deficient exterior beam-column joints have been studied. For this purpose, two reinforced concrete exterior beam-column sub-assemblages were constructed with non-optimal design parameters (inadequate joint shear strength with no transverse reinforcement) representing pre-seismic code design construction practice of joints and encompassing the vast majority of existing beam-column connections. Out of these two, one specimen was used as baseline specimen (control specimen) and the other one was strengthened with CFRP sheets (strengthened specimen). These two sub-assemblages were subjected to cyclic lateral load histories so as to provide the equivalent of severe earthquake damage. The damaged control specimen was then repaired using CFRP sheets. This repaired specimen was subjected to the similar cyclic lateral load history and its response history was obtained. Response histories of control, repaired and strengthened specimens were then compared. The results were compared through hysteretic loops, load-displacement envelopes, ductility and stiffness degradation. The comparison shows that CFRP sheets improve the shear resistance of the joint and increase its ductility.
Seismic Behavior of Exterior RC Beam-Column Joints Retrofitted using CFRP Sheets
Latin American Journal of Solids and Structures, 2020
The seismic behavior of full-scale exterior reinforced concrete (RC) beam-column joints retrofitted with externally bonded Carbon Fiber Polymers (CFRP) is examined in this paper. Casting and testing of two similar reinforced concrete beam column connections in the absence of transverse reinforcement at the joints took place under opposing cyclic loading with regulated displacement so as to examine their fundamental seismic performance. The first joint was examined as the control specimen and the other specimen was then retrofitted with CFRP sheets, with rounded border of the column and beam at and close to the joint region to change them from square to squircle segments. It is demonstrated in the experimental findings that the retrofitted beam column joint shows significantly greater strength, energy dissipation and ductility in comparison to the control specimen. There was a shift in the failure from the joint region to the beam ends in the retrofitted specimens, which would help in preventing the structure from disintegrating progressively. Because of the change in the beam and column from square to squircle segments, the debonding potential of the CFRP decreased and the restrictive impact of the CFRP increased. As a result, the experimental findings were verified using a 3D nonlinear finite element (FE) model. When the finite element and experimental findings are compared, it is determined that the suggested model is quite accurate.
Repairing And Strengthening Earthquake Damaged Rc Beams With Composites
2013
The dominant judgment for earthquake damaged reinforced concrete (RC) structures is to rebuild them with the new ones. Consequently, this paper estimates if there is chance to repair earthquake RC beams and obtain economical contribution to modern day society. Therefore, the totally damaged (damaged in shear under cyclic load) reinforced concrete (RC) beams repaired and strengthened by externally bonded carbon fibre reinforced polymer (CFRP) strips in this study. Four specimens, apart from the reference beam, were separated into two distinct groups. Two experimental beams in the first group primarily tested up to failure then appropriately repaired and strengthened with CFRP strips. Two undamaged specimens from the second group were not repaired but strengthened by the identical strengthening scheme as the first group for comparison. This study studies whether earthquake damaged RC beams that have been repaired and strengthened will validate similar strength and behavior to equally ...
Behavior of Damaged Exterior RC Beam-Column Joints Strengthened by CFRP Composites
Latin American Journal of Solids and Structures, 2016
This paper presents an experimental investigation on the behavior of retrofitted beam-column joints subjected to reversed cyclic loading. The experimental program comprises 8 external beamcolumn joint connection subassemblages tested in 2 phases; one was the damaging phase and second was the repairing phase. The Beam-column joints were designed only for gravity loads. The joints had no beam-column joint transverse reinforcement and special stirrups in beam and column critical zones. These Non-Seismically designed (NS) joints were damaged with different levels at the first phase of the experiment. In the second phase, the damaged joints were strengthened with externally bonded carbon-fibre-reinforced polymers (C-FRP) sheets. From the observed responses of the examined specimens it can be deduced that the technique of externally bonded retrofitting (EBR) using C-FRP sheets is appropriate for the rehabilitation of the joints seismic capacity. This technique had a significant improvement of the energy dissipation and the performance level and finally it leads to improved type of damages compared with the damage modes of the specimens during the initial loading. Shortcomings of the application of C-FRP sheets for practical use are also pointed out.
Repairing and strengthening of earthquake-damaged RC beams with CFRP strips
Magazine of Concrete Research, 2010
This paper summarizes the results of an experimental investigation into earthquake-damaged (damaged in shear under cyclic load) reinforced concrete (RC) beams repaired and strengthened by externally bonded carbon fibre-reinforced polymer (CFRP) strips. Eight specimens, apart from the reference beam, were separated into two distinct groups. Four experimental beams in the first group were subjected to cyclic load up to failure then properly repaired and CFRP strengthened. Four undamaged specimens from the second group were repaired and strengthened following the identical scheme as the first group for comparison. This study examines whether earthquake-damaged RC beams that have been repaired and strengthened will demonstrate similar strength and behaviour to equally strengthened, undamaged RC beams. In the absence of steel stirrups, increases of minimum 57% and maximum 72% in shear capacity according to the reference were obtained from the strengthened specimens. Accordingly, a streng...
Seismic Retrofitting of Reinforced Concrete Columns using Carbon Fiber Reinforced Polymer (CFRP)
2007
Reinforced concrete columns with non-seismic detailing are often vulnerable to the effects of a major earthquake. In this study, the structural behaviour of undamaged and moderately damaged columns, which were retrofitted with carbon fiber reinforced polymers (CFRP) is investigated. The experimental program consists of four specimens having inadequate tie spacing, 90 degree hooks and plain reinforcing bars that were tested under lateral cyclic displacement excursions under a constant axial load of approximately 27% of the axial load carrying capacity. One reference specimen without any strengthening and one strengthened specimen with strengthening but without any pre-damage were tested. In addition, two similar specimens tested to moderate damage level of 2% drift ratio were repaired and retested. In one of the pre-damaged columns the repairing process was performed in the presence of constant axial load. The main parameters investigated in this study were the presence of axial load on the column during repairing, effect of pre-damage on ultimate displacements and the effect of CFRP wrapping on strengthened and repaired columns. The ultimate drift ratio for retrofitted columns increased to 6% which was only 3.5% for the reference column. Severe stiffness degradation was observed in both of the repaired columns due to the moderate level of pre-damage. For the repaired columns, the presence of the axial load during repairing did not significantly affect the ultimate drift ratio significantly however the enhancement in strength was not observed as compared to its companion specimen.
Journal of Engineered Fibers and Fabrics, 2016
It is known that the vast majority of buildings in Turkey are made out of reinforced concrete (RC). The 1999 Kocaeli and Düzce, the 2010 Elazig, and the 2011 Van earthquakes that occurred in Turkey revealed that the most significant factor in causing damage to buildings, or their collapse, was the use of low quality concretes, i.e., concretes with low strength values, in their construction This reveals that the load bearing members of these structures should be reinforced against the effects of possible earthquakes. The aim of the present study is to investigate the effect of carbon fiber reinforced polymer (CFRP) usage on the behavior of beams made out of low strength concrete. Within the scope of the study, the results of the experimental and numerical analysis for 14 RC beams, to which CFRP plates were applied on their lower surface, as well as for two reference beams, were presented for the case of collapsing. From the start of the test to the end, load, deflection and deformati...
Materials and Structures
13 Purpose 14 This study evaluates the effectiveness of a new method for seismic strengthening of exterior RC 15 beam-column connections and develops a joint shear strength model for the strengthened 16 connections. 17 Methods 18 Four RC exterior connections without transverse reinforcement at the joints were cast and tested 19 under reverse cyclic loading. The first connection was tested as the control specimen while the 20 three remaining connections were glued with concrete covers around the columns at the joint 21 area to modify them from square to circular sections and then they were wrapped with different 22 Due to their superior performance, the proposed strengthening method and the proposed model 38 are expected for practical application. 39
Full Scale Reinforced Concrete Beam-Column Joints Strengthened with Steel Reinforced Polymer Systems
Frontiers in Materials
This paper presents the results of an experimental campaign performed at the Laboratory of Materials and Structural Testing of the University of Salerno (Italy) in order to investigate the seismic performance of reinforced concrete (RC) beam-column joints strengthened with steel reinforced polymer (SRP) systems. With the aim to represent typical façade frames' beam-column subassemblies found in existing RC buildings, specimens were provided with two short beam stubs orthogonal to the main beam and were designed with inadequate seismic details. Five members were strengthened by using two different SRP layouts while the remaining ones were used as benchmarks. Once damaged, two specimens were also repaired, retrofitted with SRP, and subjected to cyclic test again. The results of cyclic tests performed on SRP strengthened joints are examined through a comparison with the outcomes of the previous experimental program including companion specimens not provided with transverse beam stubs and strengthened by carbon fiber-reinforced polymer (CFRP) systems. In particular, both qualitative and quantitative considerations about the influence of the confining effect provided by the secondary beams on the joint response, the suitability of all the adopted strengthening solutions (SRP/CFRP systems), the performances and the failure modes experienced in the several cases studied are provided.
Engineering Structures, 2008
Reinforced concrete columns lacking transverse reinforcing steel do not possess necessary ductility to dissipate seismic energy during a major earthquake. The study reported herein investigates the use of carbon fiber-reinforced polymer (CFRP) wrapping as a method of retrofitting nonductile square reinforced concrete columns with low strength concrete and plain bars. Five specimens representative of transverse steel deficient flexure dominated columns in existing buildings were tested under lateral cyclic displacement excursions and constant axial load. The main parameters under investigation were the number of layers of CFRP wrap and presence and absence of the axial load on the column during strengthening. It was found that upon CFRP retrofit, deficient columns were able to withstand larger deformation demands without strength degradation. The test results were also compared with the results obtained from the analytical study that was conducted using a simple plastic hinge model considering the effects of FRP confinement and slip of plain bars. A good agreement between analytical and experimental results was observed.