FRP Strengthening of Seismically Deficient Full-Scale RC Beam-Column Joints (original) (raw)
Related papers
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 strengthening of deficient RC buildings using externally bonded FRPs
A full-scale RC building with poor detailing in the beam-column joints was tested on a shake table. After initial tests which damaged the structure, the frame was strengthened using FRPs and re-tested. This paper studies analytically the efficiency of the strengthening at improving the seismic performance of this frame. The experimental data from the initial shake table tests are used to calibrate analytical models. To simulate deficient beam-column joints, steel-concrete bond-slip and bond-strength degradation models are considered. The analytical models are used to assess the efficiency of the FRP rehabilitation using real seismic records. The FRP intervention enhanced the behaviour of the substandard joints, and resulted in substantial improvement of the seismic performance of the damaged RC frame. It is shown that after strengthening, the damaged building would experience on average 65% less global damage compared to the original structure if it was subjected to a set of real seismic records.
Seismic Behaviour of Beam-Column Joint in R/C Frames and Strengthening with FRP
2nd Croatian Conference on Earthquake Engineering ‒ 2CroCEE
Multi-story reinforced concrete structures in previous periods, in general, do not meet current seismic design code requirements, including the poor materials and execution of civil engineering works. In the scope of this, is analyzed the behavior of the structures during the Earthquake of November 2019, in Albania, specifically in different building stocks. Typical structural deficiencies observed in reinforced concrete (R/C) frame buildings affected by the 2019 earthquake reveal that many collapses occurred could be attributed to the poor quality of construction and use of non-ductile detailing and during the assessment that deficiency beam–column joints can jeopardize the integrity of structures. In general, it is accepted that beam-column joints are critical elements of reinforced concrete buildings subjected to lateral loads and that they may require specific design. Assessment reports have often indicated that beam-column joints, which are one of the most vulnerable and critic...
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...
Seismic upgrade of beam-column joints with FRP reinforcement
2000
Many opportunities are becoming available for using composite materials to strengthen/upgrade existing reinforced concrete (RC) structures. This paper focuses on a new technique for the seismic upgrade of RC beam-column connections in gravity load-designed (GLD) frames by the application (combined or not) of FRP rods and laminates. The FRP rods provide flexural strengthening, whereas the lay-up laminates provide confinement and shear strengthening. Along with the modeling of such upgraded connections to assess the increase of strength and/or ductility provided by the composite reinforcement, an experimental program was planned and it is being undertaken. A preview of it is given in this paper together with an explanation of its philosophy; furthermore, interesting preliminary results are presented and discussed. It appears that the proposed upgrade method will have a significant impact of the engineering practice in the near future.
Seismic behavior of RC columns flexurally strengthened with FRP sheets and FRP anchors
Composite Structures, 2018
In this paper, an experimental study has been conducted on strengthening of reinforced concrete (RC) connections by FRP sheets. The innovation of this research is using narrow grooves on critical regions of connection to increase the adherence of FRP sheets and prevent their early debonding. Therefore, four RC connections were made and tested under a constant axial load on the column and an increasing cyclic load on the beam. The first specimen, as the standard reference specimen, had close tie spacing in ductile regions of beam, column and panel zone based on seismic design provisions, and the second specimen, as the weak reference specimen did not have these conditions in all regions. Two other weak specimens were strengthened using two different strengthening patterns with FRP sheets; one by ordinary surface preparation and the other with surface grooving method for installing FRP sheets on the connection. The results showed that ultimate load and ductility of the weak specimen compared to standard specimen decreased 25% and 17%, respectively. The shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened specimens. Also, it was observed that early debonding of FRP sheets was prevented in the strengthened connection with grooving pattern and so had desirable ductility and bearing capacity similar to the standard specimen.
Applied Composite Materials, 2004
The use of FRP as reinforcement in concrete structures has been growing rapidly due to its advantages over conventional steel reinforcement (e.g., corrosion resistance, light weight, magnetic neutrality). A potential application of FRP reinforcement is in structural concrete frames. However, current seismic design standards and detailing criteria for beam-column joints were established for steel reinforcement and may be unsuitable for FRP reinforcement due to its different mechanical properties. During recent earthquakes, many structural collapses were initiated or caused by beam-column joint failures. Since there are no detailed specifications for the application of FRP reinforcement in seismic zones, research is needed to gain a better understanding of the behaviour of FRP-reinforced concrete under seismic loading. In this study, two full-scale beam-column joint specimens reinforced with steel and GFRP, respectively, were tested in order to investigate their performance in the event of an earthquake. The control steel-reinforced specimen is detailed according to the Canadian Code (CSA A23.3-94) recommendations. The GFRP-reinforced specimen is detailed in a similar scheme but using a GFRP grid. The behaviour of the two specimens under reversed cyclic loading, their load-storey drift envelope relationship and energy dissipation ability were compared. The GFRP-reinforced specimen showed a predominantly elastic behaviour up to failure. While its energy dissipation was low, its performance was acceptable in terms of total storey drift demand.
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.