• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.4
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• pp.1-8
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• 2008

RC beam of existing structures often encounter shear problems for various reasons. The shear failure of RC beam is sudden and brittle. Strengthening technique jacketing with external bonding of steel plates(or CFRP and CFS) with epoxy is many use to in practice. This study presents test results on strengthening shear deficient RC beams by external bonding of slit type steel plates. Test parameters are width, interval, length, thickness and angle of slit in steel plates. The purpose was to evaluate the reinforcing effects, failure modes and shear capacities for RC beams of strengthened with various slit type steel plates. The test result confirmed that all slit steel plates improved the stiffness and strength of the specimens significantly. Failure modes of SV series and SD series showed shear fractures and flexure fractures at ultimate state respectively. SD series were ductile rather than SV series.

• Journal of the Earthquake Engineering Society of Korea
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• v.23 no.5
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• pp.239-248
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• 2019

In this study, the out-of-plane seismic resistance of lightly-reinforced existing walls strengthened with thick RC jacket was investigated. The thick RC jacket with a thickness of 500 mm was placed at one side of the thin existing wall with a thickness of 150 mm. At the interface between the wall and RC jacket, a tee-shaped steel section with a number of anchor bolts and dowel bars was used as the shear connector. To investigate the connection performance and strengthening effects, the cyclic loading tests of four jacketed wall specimens were performed. The tests showed that the flexural strength of the jacketed walls under out-of-plane loading was significantly increased. During the initial behavior, the tee shear connector transferred forces successfully at the interface without slip. However, as the cracking, spalling, and crushing of the concrete increased in the exiting walls, the connection performance at the interface was significantly degraded and, consequently, the strength of the jacketed walls was significantly decreased. The flexural strength of the jacketed walls with tee shear connector was estimated considering the full and partial composite actions of the tee shear connector.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.81-88
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• 1999

In order to properly evaluate the shear strength of reinforced concrete circular columns due to the transverse shear reinforcement, the average of fractions of forces generated along the circular transverse hoops across the shear failure plane in the loading direction is calculated. For this, the center-to-center diameter of circular transverse hoops. spacing and the crack angle measured to the column longitudinal axis are considered. Using these variables, an equation representing the effective section area of circular transverse shear steel is proposed. The study result shows that the constant parameter. used for the calculation of the effective section area of circular hoops over the last 10 years, should not universally be applied any more. The use of the constant parameter may not seriously do harm to the evaluation of shear strength for circular columns with non-seismically designed transverse hoop reinforcement, since it gives slightly conservative results. However. for well-confined circular columns with close spacing or circular steel jacketing. it gives about 20% overestimation of the shear capacity contributed by the transverse hoop steel.

• Steel and Composite Structures
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• v.37 no.3
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• pp.371-390
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• 2020

One of the most common strategies for retrofitting as-built reinforced concrete (RC) columns is to enlarge the existing section through the application of a new concrete layer reinforced by both steel transverse and longitudinal reinforcements. The present study was dedicated to developing a comprehensive model to predict the seismic behavior of as-built RC jacketed columns. For this purpose, a new sectional model was developed to perform moment-curvature analysis coupled by the plastic hinge method. In this analysis-oriented model, new methodologies were suggested to address the impacts of axial, flexural and shear mechanisms, variable confining pressure, eccentric loading, longitudinal bar buckling, and varying axial load. To consider the effective interaction between core and jacket, the monolithic factor approach was adopted to extent the response of the monolithic columns to that of a respective RC jacket strengthened column. Next, parametric studies were implemented to examine the effectiveness of the main parameters of the RC jacket strategy in retrofitting as-built RC columns. Ultimately, the reliability of the developed analytical model was validated against a series of experimental results of as-built and retrofitted RC columns.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.451-458
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• 2008

In this study 3- and 6-story flat plate structures designed only for gravity load are retrofitted with steel plates and braces and their seismic performances are evaluated to verify the effect of seismic retrofit. According to the analysis results obtained from nonlinear static and dynamic analyses both the strength and stiffness are significantly enhanced as a result of the seismic retrofit. Especially the effect of column jacketing could be enhanced significantly when slabs were reinforced to prevent premature punching shear failure. When buckling-restrained braces are used instead of conventional braces, the structures showed more ductile behavior, especially in the 3-story structure.

• Structural Engineering and Mechanics
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• v.74 no.2
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• pp.243-254
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• 2020

Devastating RC structural failures in the past have identified that the behavior of beam-column joints is more critical and significantly governs the global structural response under seismic loading. The congestion of reinforcement at the beam-column joints with other constructional difficulties has escalated the attention required for strengthening RC beam-column joints. In this context, numerous studies have been carried out in the past, which mainly focused on jacketing the joints with different materials. However, there is no comparative study of different approaches used to strengthen RC beam-column joints, from efficiency and cost perspective. This paper presents a detailed investigation carried out to study the various strengthening schemes of exterior RC beam-column joints, viz., steel fiber reinforcement, carbon fiber reinforced polymer (CFRP) strengthening, steel haunch strengthening, and confining joint reinforcement. The effectiveness of each scheme was evaluated experimentally. These specimens were tested under horizontal loading that produced opening moments on the joints and their behavior was studied with emphasis on strength, displacement ductility, stiffness, and failure mechanism. Special attention was given to the study of crack-width.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.293-302
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• 2017

This study deals with a numerical investigation of load transfer along interfaces of jacketed columns using finite element models. Appropriate plasticity and constitutive models are used to simulate the response of concrete and steel bars. Experimental data were used to calibrate the simulation of mechanical characteristics. The different compressive strength of core and jacket concrete, the confinement ratio, the dowels' diameter size and the load pattern shapes were considered. The path diagrams along the interfaces elucidate the areas around the dowel bars where due to stress concentration plastic hinges and intense discontinuities are created. The stress flow also depicts the contribution of confinement of the jacketed area to the overall resonant load capacity of the core column. The scope of the research is to identify and quantify the shear transfer along the interfaces of strengthened elements.

• Advances in concrete construction
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• v.8 no.2
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• pp.101-117
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• 2019

Structural strengthening of reinforced concrete (RC) beams is becoming essential to meet the up-gradation of existing structures due to the infrastructure development. Strengthening is also essential for damaged structural element due to the adverse environmental condition and other distressing factors. This article reviews the state of the field on repair, retrofitting and rehabilitation techniques for the strengthening of RC beams. Strengthening of RC beams using various promising techniques such as externally bonded steel plates, concrete jacketing, fibre reinforced laminates or sheets, external prestressing/external bar reinforcement technique and ultra-high performance concrete overlay have been extensively investigated for the past four decades. The primary objective of this article is to discuss investigations on various strengthening techniques over the years. Various parameters that have been discussed include the flexural capacity, shear strength, failure modes of various strengthening techniques and advances in techniques over the years. Firstly, background information on strengthening, including repair, retrofitting, and rehabilitation of RC beams is provided. Secondly, the existing strengthening techniques for reinforced concrete beams are discussed. Finally, the relative comparisons and limitations in the existing techniques are presented.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.2
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• pp.125-133
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• 2007

External confinement by CFS (Carbon Fiber Sheet) is a very effective retrofit method for the reinforced concrete columns subject to either static or seismic loads. For the reliable and cost-effective design of CFS, an accurate stress-strain curve is required for CFS-confined concrete. In this paper, uniaxial compression test on short RC column with circular section was performed. To evaluate the effect of confinement on the stress-strain relationship of CFS-confined concrete, CFS area ratio, spiral area ratio, and concrete compressive strength are considered as the test variables. Experiment results indicate that CFS jacketing significantly enhances strength and ductility of concrete. In addition, the CFS-jacketed specimens with the spiral steel show the lower load increasement ratio than those without the spiral steel.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.1
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• pp.39-46
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• 2017

In this paper, a model updating procedure based on the response surface method combined with the multi-objective optimization was proposed and applied for updating of the FE models representing a low-rise reinforced concrete building before and after the seismic retrofit. The dynamic properties to be matched were obtained from vibration tests using a small shaker system. By varying the structural parameters according to the central composite design, analysis results from the initial FE model using a commercial software were collected and used to produce two regression functions each of which representing the errors in the natural frequencies and mode shapes. The two functions were used as the objective functions for multi-objective optimization. Final solution was determined by examining the Pareto solutions with one iteration. The parameters representing the stiffnesses of existing concrete, masonry, connection stiffness in expansion joint, new concrete, retrofitted members with steel section jacketing were selected and identified.