• Structural Engineering and Mechanics
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• v.78 no.1
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• pp.77-86
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• 2021

Local school buildings are critical facilities that can provide shelter in disasters such as earthquakes, so they must be more resistant to seismic forces than other structures. In this study, a sensitivity analysis was conducted to determine which columns-as the most critical members in a reinforced concrete building-most urgently require seismic retrofitting. The sensitivity analysis was conducted using an optimization technique with the location of each column as a parameter. A numerical model was developed to simulate a realistic collapse mode through a three-dimensional dynamic analysis. Based on numerical analysis results, it was found that the columns positioned in the lower floors, such as the first floor and in the outer part of a building, urgently require retrofitting. For reinforcement of the RC columns, which has been proven for its performance in previous research, was applied. Through this study, the importance of appropriate retrofitting is demonstrated. Further, a method for determining the appropriate location for retrofitting-when retrofitting is not possible on the entire structure-is presented.

• Structural Engineering and Mechanics
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• v.6 no.7
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• pp.801-815
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• 1998

An overview of an analytical model to predict mortar joint failure in unreinforced masonry (URM) structures is presented. The validity of the model is established by comparison with experimental results at element level as well as structure level. This model is then used to study the behavior of URM walls and two commonly used retrofitting schemes. Finally, effectiveness of the two retrofitting schemes in increasing strength and stiffness of existing URM walls is discussed.

• Earthquakes and Structures
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• v.12 no.3
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• pp.309-319
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• 2017

A new method is suggested for the retrofitting of torsionally sensitive buildings. The main objective is to eliminate the torsional component from the first two natural modes of the structure by properly modifying its stiffness distribution via selective strengthening of its vertical elements. Due to the multi-parameter nature of this problem, state-of-art optimization schemes together with an ad-hoc software implementation were used for quantifying the required stiffness increase, determine the required retrofitting scheme and finally design and analyze the required composite sections for structural rehabilitation. The performance of the suggested method and its positive impact on the earthquake response of such structures is demonstrated through benchmark examples and applications on actual torsionally sensitive buildings.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.04a
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• pp.374-381
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• 2003

In this study, the reduction schemes of ICRS(In-Cabinet Response Spectra), the main part of seismic safety qualification of old nuclear power plant(USI A-46 problem), are studied. To obtain accurate dynamic characteristics of cabinet structure, the cabinet structure modeled by frame model and its eigen analysis is performed. The three types of seismic retrofitting scenarios, such as 1) the installation of bracing, 2) installation of damper, 3) installation of tuned mass damper(TMD), are established and evaluated for the decreasing of ICRS. In the cases of 1) ＆ 2), since, the retrofitted structures show larger ICRS than that of original structure, the careful considerations are need in the application of these methods. Though, the case of TMD show the best retrofitting result, the tuning between the real structure and analysis model is estimated the essential step of retrofitting.

• Earthquakes and Structures
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• v.9 no.3
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• pp.563-576
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• 2015

Over the past few decades, seismic retrofitting of structural systems has been significantly improved by the adoption of various methods such as FRP composite wraps, base isolation systems, and passive/active damper control systems. In parallel with this trend, probabilistic risk assessment (PRA) for structural and nonstructural components has become necessary for risk mitigation and the achievement of reliable designs in performance-based earthquake engineering. The primary objective of the present study was to evaluate the effect on piping fragility at T-joints due to seismic retrofitting of structural systems with passive energy-dissipation devices (i.e., linear viscous dampers). Three mid-rise building types were considered: without any seismic retrofitting; with distributed damper systems; with optimal placement of dampers. The results showed that the probability of piping system failure was considerably reduced in a Multi Degree of Freedom (MDOF) building retrofitted with optimal passive damper systems at lower floor levels. This effect of damper systems on piping fragility became insignificant as the floor level increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.243-254
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• 2002

This study investigates the structural behavior of cracked or uncracked RC columns retrofitted with CFS and evaluates the shear retrofit performance through experiment. Experimental works were conducted for sixth specimens varied in the adhesion method of CFS, the ratio of shear reinforcement bar, and the existence of crack before retrofitting. Throughout cyclic test, the strength, stiffness, failure modes, and ductility are discussed. The test results show that the retrofitting method with CFS improve the shear strength and ductility. The crack width below 2mm, occurred before retrofitting, didn't reduce the shear strengthening effect.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.303-310
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• 2019

Any revision of seismic codes usually demands a higher capacity from structural members, making existing structures unsafe particularly from strength considerations. Retrofitting of capacity deficient members is very suitable for tackling such situations. This paper presents an experimental study on different retrofitting measures adopted for strengthening a series of reinforced concrete (RC) beams. Four identical RC beam specimens were casted, out of which three specimens were strengthened by different schemes (viz., bolted hot rolled flat, bolted cold-formed steel channel, and carbon fibre reinforced polymer (CFRP) laminate, respectively) on their tension face and tested under four-point monotonic loading. This study focuses on the investigation of the flexural behaviour of these retrofitted beams, observed in terms of strength and stiffness. It was concluded that all retrofitting measures improved the structural performance of these beams. However, the cost involved with each strengthening mode was proportional to the improvement in the performance achieved.

• Earthquakes and Structures
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• v.22 no.3
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• pp.319-330
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• 2022

Retrofit of soft-story buildings due to seismic loads using Gap-Inclined-Brace (GIB) system is considered a new retrofit technique that aims to maintain both strength and stiffness of structure. In addition, it provides more ductility and less P-delta effect, and subsequently better performance is observed. In this paper, the effect of the eccentricity between GIB and the retrofitted column due to installation on the efficiency of the retrofitting system is studied. In addition, a modification in the determination method of GIB properties is introduced to reduce the eccentricity effect. Also, the effect of GIB system on the seismic response of mid-rise buildings with different heights considering soft-story at various heights has been studied. A numerical model is developed to study the impact of such system on the response of retrofitted soft-story buildings under the action of seismic loads. To achieve that goal, this model is used to perform a numerical investigation, by considering five case study scenarios represent several locations of soft-story of two mid-rise reinforced concrete buildings. At first, Non-linear static pushover analysis was carried out to develop the capacity curves for case studies. Then, Non-linear time history analyses using ten earthquake records with five peak ground accelerations is performed for each case study scenario before and after retrofitting with GIB. The results show that large GIB eccentricity reduce the ultimate lateral resistance and deformation capacity of the retrofitting system. Moreover, the higher the retrofitted building, the more deformation capacity is observed but without significant increase in ultimate lateral resistance.

• Computers and Concrete
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• v.17 no.1
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• pp.67-86
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• 2016

Strengthening as well as correcting unsightly deflections of reinforced concrete (RC) beam may be accomplished by retrofitting. An innovative way to do this retrofitting that is proposed in this study utilizes turnbuckle to apply external post-tensioning. This Turnbuckle External Post-Tensioning (T-EPT) was experimentally proven to improve the serviceability and load carrying capacity of reinforced concrete beams. The T-EPT system comprises a braced steel frame and a turnbuckle mechanism to provide the prestressing force. To further develop the T-EPT, this research aims to develop a numerical scheme to analyze the structural performance of reinforced concrete beams with this kind of retrofitting. The fiber method analysis was used as the numerical scheme. The fiber method is a simplified finite element method that is used in this study to predict the elastic and inelastic behavior of a reinforced concrete beam. With this, parametric study was conducted so that the effective setup of doing the T-EPT retrofitting may be determined. Different T-EPT configurations were investigated and their effectiveness evaluated. Overall, the T-EPT was effective in improving the serviceability condition and load carrying capacity of reinforced concrete beam.

• Structural Engineering and Mechanics
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• v.27 no.4
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• pp.393-408
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• 2007

This paper presents the findings of an experimental study to evaluate retrofit methods which address particular weaknesses that are often found in reinforced concrete structures, especially older structures, namely the lack of the required flexural and shear reinforcement within the columns and the lack of the required shear reinforcement within the joints. Thus, the use of a high-strength fiber jacket for cases of post-earthquake and pre-earthquake retrofitting of columns and beam-column joints was investigated experimentally. In this paper, the effectiveness of the two jacket styles was also compared.