Textile-Reinforced Mortar versus FRP as Strengthening Material for Seismically Deficient RC Beam-Column Joints (original) (raw)
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SEISMIC BEHAVIOR OF TRM AND GFRP UPGRADED RC EXTERIOR BEAM-COLUMN JOINTS
Textile reinforced Mortar (TRM) was experimentally investigated in this study as a new material for strengthening and seismic retrofitting of RC beam-column joints. The results of TRM-upgraded joints were then compared with that of Glass Fiber Reinforced Polymer (GFRP)-strengthened joint specimens. Three as-built joint specimens were constructed with non-optimal design parameters (inadequate joint shear strength with no transverse reinforcement) representing extreme case of pre-seismic code design construction practice of joints and encompassing the vast majority of existing beam-column connections. Out of these three as-built specimens, one specimen was used as baseline specimen (control specimen) and the other two were strengthened with TRM and GFRP sheets respectively. All these three sub-assemblages were subjected to quasi-static cyclic lateral load histories so as to provide the equivalent of severe earthquake damage. Response histories of control and strengthened specimens were then compared. The test results demonstrated that TRM can effectively improve both the shear strength and deformation capacity of seismically deficient beamcolumn joints to an extent which is comparable to the strength and ductility achieved by well-established GFRP-strengthening of joints.
Seismic response of FRP-upgraded exterior RC beam-column joints
2010
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 Strengthening of Severely Damaged Beam-Column RC Joints Using CFRP
Journal of Composites for Construction, 2014
This paper investigates the seismic behavior of three full-scale exterior reinforced concrete (RC) beamcolumn joints rehabilitated and strengthened with externally bonded Carbon Fiber Polymers (CFRP). The specimens had inadequate detailing in the core zone and replicated joints of a real substandard building tested as part of the EU-funded project BANDIT. Seven tests were performed in two successive phases. The bare joints were first subjected to reversed cyclic loading tests to assess their basic seismic performance. As these initial tests produced severe damage in the core, the damaged concrete was replaced with new high-strength concrete. The specimens were subsequently strengthened with CFRP sheets and the cyclic tests were repeated. The results indicate that the core replacement with new concrete enhanced the shear strength of the substandard joints by up to 44% over the bare counterparts. ASCE/SEI 41-06 guidelines predict accurately the shear strength of the bare and rehabilitated joints. The CFRP strengthening enhanced further the joint strength by up to 69%, achieving a shear strength comparable to that of joints designed according to modern seismic provisions. Therefore, the rehabilitation/strengthening method is very effective for post-earthquake strengthening of typical substandard structures of developing countries.
Seismic Performance of GFRP-RC Exterior Beam–Column Joints with Lateral Beams
Journal of Composites for Construction, 2015
In the past few years, some experimental investigations have been conducted to verify seismic behaviour of fiber reinforced polymer reinforced concrete (FRP-RC) beam-column joints. Those researches were mainly focused on exterior beam-column joints without lateral beams. However, lateral beams, commonly exist in buildings, can significantly improve seismic performance of the joints. Moreover, the way the longitudinal beam bars are anchored in the joint, either using headed-end or bent bars, was not adequately addressed. This study aims to fill these gaps and investigate the shear capacity of FRP-RC exterior beam-column joints confined with lateral beams, and the effect of beam reinforcement anchorage on their seismic behaviour. Six full-scale exterior beam-column joints were constructed and tested to failure under reversal cyclic loading. Test results showed that the presence of lateral beams significantly increased the shear capacity of the joints. Moreover, replacing bent bars with headed-end bars resulted in more ductile behaviour of the joints.
FRP Strengthening of Seismically Deficient Full-Scale RC Beam-Column Joints
2012
This paper presents preliminary results of tests on three deficient full-scale RC beam-column T-joints strengthened with FRP composites. The joints were representative of existing RC buildings in developing countries, and therefore had inadequate detailing in the core zone. The bare joints were first tested under cyclic load to evaluate their basic seismic performance. After the initial tests, the damaged concrete in the core was removed and replaced with new concrete. The joints were subsequently strengthened using externally bonded FRP sheets and the tests were repeated. The results from the experiments were then used to compare the efficiency of the strengthening strategy at improving the seismic performance of the joints using existing guidelines. The results show that the strengthening with FRP sheets was very effective at improving the load carrying capacity of the deficient joints by up to 66%.
Seismic Behavior of Beam-Column Joints Reinforced with GFRP Bars and Stirrups
Journal of Composites for Construction, 2011
Reinforced concrete beam-column joints are commonly used in structures such as parking garages and road overpasses, which might be exposed to extreme weathering conditions and the application of deicing salts. The use of the noncorrodible fiber-reinforced polymer (FRP) reinforcing bars in such structures is beneficial to overcome the steel-corrosion problems. However, FRP materials exhibit linear-elastic stress-strain characteristics up to failure, which raises concerns on their performance in beam-column joints in which energy dissipation, through plastic behavior, is required. The objective of this research project is to assess the seismic behavior of concrete beam-column joints reinforced with glass (G) FRP bars and stirrups. Five full-scale exterior T-shaped beam-column joint prototypes were constructed and tested under simulated seismic load conditions. The longitudinal and transversal reinforcement types and ratios are the main investigated parameters in this study. The experimental results showed that the GFRP-reinforced joints can successfully sustain a 4.0% drift ratio without any significant residual deformation. This indicates the feasibility of using GFRP bars and stirrups as reinforcement in the beam-column joints subjected to seismic-type loading. It was also concluded that, increasing the beam reinforcement ratio, while satisfying the strong column-weak beam concept, can enhance the ability of the joint to dissipate seismic energy.
Shear Capacity of Exterior Beam-Column Joints Reinforced with GFRP Bars and Stirrups
Journal of Composites for Construction, 2016
This paper is devoted to assess the behavior of the exterior concrete beam-column connections reinforced with Glass Fiber Reinforced Polymers (GFRP) bars under cyclic loading. For this purpose, 8 different beam-column connections were experimentally investigated. In these specimens, concrete with compressive strength of 30 and 45 MPa was employed. In four of these connections, GFRP bars were used while the others were reinforced with steel bars. The confinement of longitudinal bars was different in the connections. The GFRP-reinforced beam-column connection showed an elastic behavior with very low plasticity features under cyclic loading. This resulted in lower energy dissipation compared to the steel-reinforced beam-column connections. The GFRP-reinforced beam-column connections showed lower stiffness than that of the steel-reinforced beam-column connections. Loadstory drift envelope for specimens with GFRP bars showed an acceptable drift capacity. These specimens had the essential requirements for acting as a member of a moment frame in seismic regions. In case of GFRP strengthened specimens with low and high strength concrete, increasing the cyclic loading results in flexural failure of the beam in the beam-column connection region. Increasing the confinement of concrete beams leads to the reduction of crack width. Furthermore, at higher drifts, spalling was not observed in concrete surface in beam-column connection region. In the analytical parts of the study, specimens were simulated using the SeismoStruct software. Experimental and analytical results showed a satisfactory correlation.
2009
A large number of old buildings have been identified as having potentially critical detailing to resist earthquakes. The m ain r einforcement o f lap-spliced c olumns j ust a bove t he j oint r egion, di scontinuous bot tom be am reinforcement, and little or no joint transverse reinforcement are the most critical details of interior beam column joints in such buildings. This structural type constitutes a large share of the building stock, both in developed and developing countries, and h ence r epresents a substantial e xposure. Direct o bservation o f d amaged s tructures, f ollowing t he Algiers 2003 earthquake, has shown that damage occurs usually a t the beam-column joints, with failure in bending or shear, depending on geometry and reinforcement distribution and type. While substantial literature exist for the design of concrete frame joints to withstand this type of failure, after the earthquake many structures were classified as slightly damaged and, being uneconomic to repla...
Composite Structures, 2018
This paper presents a study on evaluation of seismic performance of shear-deficient beam column joints (BCJs) strengthened by ultra-high performance fiber reinforced concrete (UHPFRC). Normal concrete BCJs having deficiencies in resisting the seismic action were cast, strengthened with a thin layer of UHPFRC, and tested under seismic loading. Two different methods were used for strengthening the normal concrete BCJ specimens consisted of: i) sandblasting the normal concrete substrate surface of BCJs and in-situ casting of a 30 mm thick UHPFRC jacket and ii) bonding 30 mm thick prefabricated UHPFRC plates to seismically deficient BCJ using epoxy resins and special fillers. The performance of UHPFRC jacketing in strengthening the seismically deficient BCJs was experimentally evaluated under reverse cyclic loading using displacement control approach keeping column axial load constant at 150 kN. The analysis of test results showed that the first method of strengthening was highly effective in terms of shear capacity, deformation capacity, stiffness characteristics and energy dissipation capacity, as compared to the second method.
Journal of Polytechnic, 2021
The Turkey includes the world's second most active faults and is geographically situated at a very high seismic activity. Research on strengthening RC (reinforcedconcrete) structures without adequate earthquake resistance has become an extremely important issue. Taking into account the objectives of this research, an experimental study is designed to strengthen the columns without adequate earthquake resistance by using carbon-reinforced-fiber-fabric (CFRP) strips and textile-reinforced-mortar (TRM) layers with two separate types of advanced composite materials. The variables evaluated within the study horizon are the composite material type used for strengthening, the width of the strip, and whether or not the anchor is used at the point of strip overlap. In this experiment, nine RC column were produced and were tested by affecting axial load, which are the reference test specimens without strengthening and eight RC column test specimens strengthened with two separate types of ...