Seismic Retrofit of Defective RC Beam-Column Joints

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.

Earthquakes and Structures

There has been increasing attention in many countries on seismic retrofit of old fashioned RC structures in recent years. In such buildings, the joints lack transverse reinforcement and suffer inadequate seismic dimensional requirements and the reinforcement is plain bar. The behavior of the joints is governed by sliding of steel bars and diagonal shear failure is less influential. Different methods to retrofit beam-column joints have been proposed in the literature such as wrapping the joint by FRP sheets, enlargement of the beam-column joint, and strengthening the joint by steel sheets. In this study, an enlargement technique that uses external prestressed cross ties with steel angles is examined. The technique has already been used for substructures reinforced by deformed bars and has advantages such as efficient enhancement of seismic capacity and lack of damage to the joint. Three reference specimens and two retrofitted units are tested under increasing lateral cyclic load in combination with two levels of axial load. The reference specimens showed relatively low shear strength of 0.15√(fc) and 0.30√(fc) for the exterior and interior joints, respectively. In addition, relatively brittle behavior was observed and large deformations extended into the panel zone of the joints. The retrofit method has increased ductility ratio of the interior beamcolumn joints by 63%, and energy dissipation capacity by 77%, relative to the control specimen; For external joints, these values were 11%, and 94%. The retrofit method has successfully relocated the plastic joints far from the column face. The retrofit method has improved shear strength of the joints by less than 10%.

Journal of Composites for Construction, 2019

This paper aims to review and critically assess experimental research efforts on the seismic retrofit of existing reinforced concrete (RC) beam-column joints with fibre-reinforced polymer (FRP) sheets of the past 20 years. The review of the literature revealed several promising features of FRP strengthening schemes. FRP retrofits can be used to address a number of different deficiencies in non-seismically designed RC members framing into beam-column joints. A majority of studies concentrate on joint shear strengthening and strengthening in the axis of principle stress is found to be most effective. Other strategies include counteracting the weak-column/strong-beam in nonseismically designed specimens by means of column flexural strengthening, as well as plastic hinge relocation within the beams, away from the joint. Only a limited number of studies look at combining several of these retrofit objectives into a more complete retrofit of the joint sub-assemblage. In most studies it is observed that simple FRP wrapping is used for anchorage, which is not always effective. Instead, it is shown that anchorage by means of FRP anchors or mechanical anchors is required to achieve adequate strengthening in most cases. Next to the detailed discussion of the literature, a database of all tested specimens is compiled and analysed. An assessment of shear strengthening design equations from major design guidelines is made based on the experimental results collected in this database, highlighting the need for their further improvement. Moreover, analysis of the database reveals a lack of tested specimens with realistic test setups , including scaled specimens, testing without axial load, as well lack of slab and transverse beams. It is found that these parameters heavily affect retrofit effectiveness and may lead to non-conservative results. Moreover, on average, the effectiveness of repairing pre-damaged specimens is found to be similar to that of retrofitting specimens without damage. popular, including the use of textile reinforced mortars (Al-Salloum et al. 2011), or fibre reinforced cement composites (Del Vecchio et al. 2018), benefiting from better bond, as well as improved thermal and fire resistance. This paper will instead focus on the use of FRP for joint shear strengthening. FRP can be used to ensure capacity design hierarchy of strengths by providing selective strengthening of members framing into the joint relative to their respective load capacities. FRP upgrades are used to address distinct strengthening objectives: • Joint shear strengthening by means of sheets placed in the horizontal (e.g.: El-Amoury and Ghobarah 2002), vertical (e.g.: Le-Trung et al. 2010) or diagonal axis (e.g.: D'Ayala et al. 2003) across unobstructed joint panels. • Column flexural strengthening to prevent unwanted column hinging failure, using straight FRP sheets along the column axis (Antonopoulos and Triantafillou 2003), L-shapes (Akguzel and Pampanin 2012a; Garcia et al. 2014; Yu et al. 2016), near-surface-mounted (NSM) FRP

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.

2005

The New Madrid Seismic Zone (NMSZ) is the location of several of the largest earthquake events (1811-1812) in the contiguous United States. Due to the infrequent nature of earthquake occurrence in this region, little attention has been paid in the past three decades to its potential threat to regional and national transportation infrastructure. This potential threat is real as inferred from the January 26, 2001, Kutch Earthquake in India, which occurred in a seismic and geological environment similar to the NMSZ and resulted in an estimated 0.45 million deaths and injuries as well as $5 billion in economic losses. This study represents the first systematic investigation in the vicinity of the NMSZ, involving seismologists, geologists, geotechnical and structural engineers, and economists. The objective of this study was to improve earthquake resistance and mitigate earthquake damage to highway transportation networks, including loss of bridges and highways. This is accomplished by d...

2014

The high seismic vulnerability of the existing building stock has led to catastrophic collapses during recent strong earthquakes around the world. This is more evident in developing countries (e.g. Kashmir, 2005; China, 2008; Indonesia, 2009; Haiti, 2010), where many RC buildings were built using inadequate construction practices that result in insufficient lateral load resistance and poor energy dissipation capacity. Many structural failures in these structures have been attributed to the inadequate behaviour of beam-column joints. Joints of RC frame buildings are subjected to a combination of high flexural moments and shear forces during strong earthquakes. Moreover, in comparison to interior joints, exterior joints of substandard RC buildings are more likely to experience damage because fewer beams frame around the joint core, resulting in lower levels of confinement. Since the demolition and replacement of such buildings is uneconomic, the local strengthening of deficient joints...

2011

Most of the experimental studies available in literature on the seismic assessment and retrofit of existing, poorly detailed, reinforced concrete (RC) beam-column joints typical of pre-1970s construction practice have concentrated on the two-dimensional (2D) response, using unidirectional cyclic loading testing protocols and a constant column axial load. Even more limited information is available on the performance of corner three-dimensional (3D) RC beam-column joints with substandard detailing subjected to a bidirectional-loading regime. In addition, little effort has been dedicated to the development of simple but reliable analysis and design procedure for FRPstrengthened joints. This thesis aims to (1) investigate the effects of varying axial and bidirectional loading on the seismic performance of deficient exterior RC beam-column joints before and after retrofit and (2) develop performance-based seismic assessment and FRP-based retrofit procedures for exterior and corner beam-column joints. For this purpose, following a critical review on the seismic vulnerability of both Umut Akguzel Seismic Performance of FRP Retrofitted Exterior RC Beam-Column Joints under Varying Axial and Bi-directional Loading v TABLE OF CONTENTS

ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING …, 2005

This paper reviews the results of some recent works conducted by the author on new methods of retrofitting the RC frames. On the local retrofit of RC members, it includes the work on the application of a new high performance fibre-reinforced cementitious composite material. The composite can be applied either as a wet mix to the desired thickness or attached as precast sheets or strips to the face of the member using a suitable epoxy adhesive. The suitability of this technique of member retrofit to enhance the strength and ductility of the retrofitted member compared with other methods of local retrofit, such as steel plates and FRP laminates, is discussed. Other works reviewed in this paper include those carried out recently on global retrofit of RC frames using direct internal steel bracing. Results of inelastic pushover tests on scaled models of ductile RC frames, directly braced by steel X and knee braces are presented which indicate that such bracings can increase the yield and strength capacities and reduce the global displacements of the frames to the desired levels. Also, the results of direct tensile tests on three full scale models of three different types of brace/RC frame connections are presented. Finally, the values of seismic behaviour factor, R, for this type of brace/frame system, evaluated from inelastic pushover analysis of dual systems of different heights and configurations are presented.

2015

Earthquake resistant structural design and strengthening of buildings are important subjects for many countries that is laying most of its land on earthquake zone. System and component based reinforcements can be performed through the process of retrofitting of reinforced concrete buildings. System based retrofitting type can be categorized into two groups. The first one is the traditional type that aims to fix the ductility, stiffness and the strength of the structures. The second one is the more innovative one that is oriented to reduce the effects of the seismic forces on the structures. Traditional strengthening techniques require heavy demolition and construction work. However, innovative methods that reduce the detrimental effects of earthquakes on buildings are generally expensive to implement, which makes them unsuitable for ordinary buildings. Accordingly, some researchers have focused on the methods that combine the advantages as well as eliminating the disadvantages of th...