Seismic Retrofit of Defective RC Beam-Column Joints

2010

Beam-column joints are recognized as the critical and vulnerable zone of a Reinforced Concrete (RC) moment resisting structure subjected to seismic loads. During an earthquake, the global response of the structure is mainly governed by the behaviour of the joints. If the joints behave in a ductile manner, the global behaviour generally will be ductile, whereas if the joints behave in a brittle fashion then the structure will display a brittle behaviour. The joints of old and non-seismically detailed structures are more vulnerable and behave poorly under the earthquakes compared to the joints of new and seismically detailed structures. Therefore, more often than not, the joints of such old structures require retrofitting in order to deliver better performance during earthquakes. Various researchers have proposed different methods to retrofit the beam-column joints of existing RC structures. This paper reports a few experimental investigations carried out for seismic retrofitting of RC beam-column joints using different techniques. The concepts behind each of them and their practical usefulness have been brought out.

International Journal for Modern Trends in Science and Technology, 2020

Earthquakes are one of the biggest life-threats in the world. The effect is immediate, with little to no warning about damage plans and the collapse of buildings/structures. Prevention of earthquake-related disasters has become more and more important in recent years. Preventing disasters involves reducing seismic risk by retrofitting existing buildings. Seismic retrofitting has now become a crucial issue. Retrofitting helps improve the structure's strength, resistivity and overall lifespan. Recent occurrences of earthquakes in various parts of the world have clearly shown the urgency of repairing deficient seismic structures. The paper summarised many past studies in the form of a seismic strengthening solution, based on the type of beam-column joints, retrofitting technology and fiber reinforced polymers (FRP).

2017

Existing reinforced concrete (RC) building structures constructed until the mid-1970's, prior to the enforcement of modern seismic design philosophies, are expected to behave poorly when subjected to earthquake actions. The response and damage evolution of RC structures when subjected to severe cyclic loading, such as the ones induced by earthquakes, are highly influenced by the beam-column joint behavior, as they are responsible for the force transfer mechanism between columns and beams and restrain the lateral displacement of the columns. The seismic response of existing RC structures with inadequate reinforcement detailing in the beam-column connections can be improved by retrofitting these connections. In the literature several joint retrofit techniques are presented, including concrete or steel jacketing, carbon fiber reinforced polymer (CFRP) wrapping and strengthening with steel profiles, plates or angles. These retrofit techniques aim to avoid the weak-column/strong-beam mechanism by increasing the flexural capacity of the column and also, in some cases, to improve the joint shear capacity. In this paper a series of unidirectional cyclic tests carried out on four full-scale interior beam-column joints with transverse beams and slab, with typical detailing of structures built until the mid-70's, are described. One specimen is tested without retrofit (control specimen), another is retrofitted with CFRP and the other two are retrofitted with steel profiles and plates. Both retrofit solutions aim to increase the flexural strength of the columns and the joint shear capacity and to avoid the weak-column/strong-beam mechanism identified in the control specimen test. The selective weakening technique is applied to all retrofitted specimens by cutting the slab in both directions around the joint. The main results in terms of lateral forcedisplacement, equivalent damping, ductility and dissipated energy evolution diagrams, as well as damage description at the end of the tests are presented and discussed. The experimental results show that the adopted retrofit solutions can significantly increase the maximum lateral strength, the ultimate ductility and the energy dissipation capacity. Therefore, the improved seismic performance of the retrofitted specimens is evident when compared with the control specimen and consequently demonstrates the need of retrofitting beam-column joints in order to improve the global seismic behavior of existing RC structures.

2017

An innovative and efficient technique is presented for the seismic retrofit of reinforced concrete beam-column joints using prestressed high-strength steel wires (PHSW). This method is to improve the seismic performance and enhance the shear strength of beam-column joints with non-seismic design as well as to overcome the shortcomings of traditional seismic retrofitting techniques for the joints. Five interior beam-column joints that were tested under reversed cyclic loading. The specimens included one un-retrofitted control specimen and four strengthened joints using proposed PHSW technique including two joints without transverse beam and two with transverse beams. Test results showed a significant increase in the joint shear capacity and reduction of the cracks on the joints in retrofitted specimens. In addition, energy dissipation and ductility level of beam-column joints were improved in retrofitted specimens compare to control specimen. The failure mode of the retrofitted speci...

This paper presents the progress of a NCREE's research program on seismic retrofit of existing RC bridge columns during the last three years. More than sixty large-scale specimens were designed and constructed to simulate the worst scenario of the construction practice in Taiwan prior to 1987. Twenty-four of the test columns were used as the benchmark for comparison with other specimens retrofitted or repaired using the carbon fiber reinforced plastics (CFRP) jacketing, steel jacketing, and RC jacketing. Experimental results showed that, in general, the retrofit methods used in the U.S. and Japan are effective also effective for the existing RC bridge columns in Taiwan. However, due to the poor concrete compressive strength and the lap splicing at the plastic hinge zone, the retrofit measures developed for better ductility and shear strength are not always effective. More research effort is necessary to develop effective methods for RC columns lap-spliced at the plastic hinge zones. assumed in the specimens, such as the double U-shaped transverse reinforcements with large spacing, and the lap-spliced of main reinforcements at the plastic hinge zone. Retrofit techniques used in the specimens include steel jacketing, FRP wrapping, and RC jacketing. In addition, seismic performance of column-foundation connections, beam-column connections as well as the wall type piers are also studied. Details of the test specimens are listed in Tables 1-3.

Innovative Materials and Techniques in Concrete Construction, 2011

The main target of this study is to develop simple, realistic and applicable retrofitting techniques by using innovative materials for existing deficient beam-column joints. By retrofitting, it is targeted to overcome deficiencies such as usage of low-strength concrete, absence of stirrups in the joint and poor anchorage of beam longitudinal bars at the joint.

IRJET, 2022

Tall structures are necessary in big cities owing to the high cost of land, the shortage of open space and the scarcity of available land. In general, tall structures are quite sensitive to lateral stresses induced by earthquakes. Because it is expensive to construct structures to endure these lateral pressures on occasion, it is not always desirable. Retrofit procedures are the exact methods utilised to carry out the retrofit plan in its entirety. Numerous retrofit strategies are possible for a particular refit scheme. Many structural failures during earthquakes are a result of insufficient shear strength and inappropriate confinement spacing in concrete columns. Thus, to enhance the cross section of the column, column strengthening operations such as jacketing the column are performed. Nonetheless, concrete jacketing of concrete columns has been shown to be quite successful at increasing strength and ductility and transforming strongbeam weak-column structures into strong-column weakbeam structures.

2013

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Engineering Structures, 2014

Reinforced concrete (RC) structures that were built prior to the 1970s generally do not meet current seismic design requirements, especially in terms of reinforcement details. An innovative and practical seismic retrofit method is proposed for non-seismically detailed external beam–column joints of existing concrete structures, based on a two-dimensional enlargement of the beam–column joint using steel angles that are mounted using prestressed cross-ties. Seven half-scale external RC beam–column joints were subjected to lateral cyclic loading of increasing amplitudes. The tested specimens comprised of three control units and four retrofitted units. The test results confirmed that the proposed retrofit method not only resulted in relocation of beam plastic hinges to outside the joint panel zone but also improved the bond between the longitudinal beam and column tension reinforcement and concrete in the joint panel zone. The proposed method was shown to significantly enhance the seismic capacity of the joints, in terms of strength, stiffness, energy dissipation and ductility capacity.

2010

In this paper an innovative method for seismic retrofitting of poorly detailed reinforced concrete beam-column joints and structures using haunch type elements connected with post-installed anchors is discussed. During an earthquake, the global behaviour of the structure significantly depends on behaviour of the beam-column connections, but no special emphasis was given to that till the eighty's. Therefore, it is recognized that the joints of old and non-seismically detailed structures are more vulnerable and behave poorly under the earthquakes compared to the joints of new and seismically detailed structures. Thus, often the joints of such old structures require retrofitting in order to deliver better response during earthquakes. A relatively new technique for retrofitting the beam-column connections using steel diagonal elements to prevent a brittle failure of the joint core was investigated by mean of experiments on beam-column joints under quasi-cyclic loads and numerical simulations. Highly encouraging results were obtained that proved the efficacy of the system in improving the seismic behaviour of poorly detailed joints. In order to prove their usefulness at the structural level under dynamic loads, shake table tests on 2-D frames are planned. This paper presents the main results of the quasi-static cyclic tests carried out for seismic retrofitting of RC beam-column joints using haunch elements and the further research planned at the structural level. The strengths, limitations and the open issues of the proposed method are discussed in brief.