• Title/Summary/Keyword: Seismic retrofitted

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Seismic Performance Management of Aged Road Facilities Using Deterministic Method vs. Probabilistic Method (확률론적 및 결정론적 방법을 이용한 노후도로시설물 내진성능관리)

  • Kim, Dong Joo;Choi, Ji Hye;Lee, Do Hyung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.40 no.5
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    • pp.455-463
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    • 2020
  • Road facilities with a service life of more than 30 years are expected to triple in the next ten years. The seismic performance of road facilities should be reviewed with consideration of the "Common Application of Seismic Design Standards" issued by Korea's Ministry of Public Administration and Security in 2017. These standards should be applied to all existing road facilities, including retrofitted or seismic-designed facilities, for evaluating seismic performance. In order to manage seismic performance for a large number of facilities, decision-support technology that can provide economic and reliable results is needed. However, the indices method currently used in Korea is a deterministic method, and the seismic performance of individual facilities is evaluated based on qualitative indices so that only retrofitting among road facilities is prioritized. In turn, with the indices method, it is difficult to support decisions other than the decision to prioritize retrofitting. Therefore, it is necessary to use the seismic risk assessment method to overcome such shortcomings and provide useful information such as direct loss, indirect socio-economic loss, and benefit of the investment.

External retrofit of beam-column joints in old fashioned RC structures

  • Adibi, Mahdi;Marefat, Mohammad S.;Arani, Kamyar Karbasi;Zare, Hamid
    • Earthquakes and Structures
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    • v.12 no.2
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    • pp.237-250
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    • 2017
  • 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 0.150${\surd}$($f_c$) and 0.30${\surd}$($f_c$) 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 beam-column 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%.

Displacement Ductility Evaluation of Earthquake Experienced RC Bridge Piers with 2.5 Aspect Ratio (지진을 경험한 형상비 2.5 RC 교각의 내진 변위 연성도 평가)

  • 정영수;박창규;이은희
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.3
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    • pp.79-88
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    • 2003
  • For the construction of PC bridge piers the implementation of 1992 seismic provisions, longitudinal steels were practically lap-spliced in the plastic hinge region. Experimental investigation was conducted ductility of evaluate the seismic earthquake-experienced reinforced concrete columns with 2,5 aspect ratio. Six test specimens were mode with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under a constant axial load, P=0.1f$\_$ck/A$\_$g/. Residual seismic performance of damaged columns was evaluated and compared to that of the corresponding original columns. Test results show that PC bridge piers with lap-spliced longitudinal steels appeared to fail at low ductility. This was due to the debonding of the lap splice, which resulted from insufficient development of the longitudinal steels. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region indicated significant improvement both in flexural strength and displacement ductility.

3-D Configuration Effects of Prestressing Cable Bracing Used for Retrofitting a RC Frame Subjected to Seismic Damage (RC 골조의 내진 보강을 위한 예압 가새의 3-D 배치)

  • Lee, Jin-Ho;Oh, Sang-Gyun;Hisham, El-Ganzori
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.7 no.3
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    • pp.183-191
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    • 2003
  • A four-story reinforced concrete moment resisting frame damaged from an ultimate limit state earthquake is upgraded with prestressing cable bracing. The purpose of this study is to investigate the bracing configuration effects on the 3-D building response using thee different locations of the bracing systems for the retrofitted building. Since the previous work done by the author proved that static incremental loads to collapse analysis as a substitute to dynamic non-linear time history analysis was a valid alternative tool. Thus, static load to collapse analysis is solely applied to evaluate the seismic performance parameters of both the original and upgraded buildings in this study. In results, the exterior bracing system is effective in restraining torsional behavior of the structure under seismic loads, and no sudden failure occurs in this system that enhances the ductility of the building due to the gradual change of building stiffness as the lateral load increases.

Strengthening of Non-ductile Reinforced Concrete (RC) frames with Expansive Joint Mortar and H-beam Frame (팽창형 접합부 모르타르와 H형강 프레임에 의한 비내진 상세를 갖는 철근콘크리트 골조의 내진보강)

  • Kim, Ji-Hyeon;Jang, Seok-Joon;Yun, Da-Ae;Kim, Dae-Young;Yun, Hyun-Do
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.23 no.3
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    • pp.127-135
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    • 2019
  • The seismic performance of non-ductile reinforced concrete (RC) frame retrofitted with H-beam frame and cast expansive mortar into joint between existing RC frame and H-beam frame is investigated experimentally and analytically. RC frames considered in the study contain non-ductile reinforcement details of low-rise school building constructed in Korea before 1988. The tests were conducted on half-scale specimens simulating the lower frame assemblages of a typical school building. Two one-bay, one-story RC frames with and without retrofitting with H-beam frame and expansive joint mortar were tested to failure. Test and analysis results indicated that seismic strengthening using H-beam and expansive joint mortar significantly improved the lateral strength and stiffness of non-ductile RC frame without installing anchor bolts to fit H-beam frame into existing RC frame. The effectiveness of seismic strengthening technology proposed in the study for non-ductile RC frame was verified experimentally and analytically.

Experimental study on identification of stiffness change in a concrete frame experiencing damage and retrofit

  • Zhou, X.T.;Ko, J.M.;Ni, Y.Q.
    • Structural Engineering and Mechanics
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    • v.25 no.1
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    • pp.39-52
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    • 2007
  • This paper describes an experimental study on structural health monitoring of a 1:3-scaled one-story concrete frame subjected to seismic damage and retrofit. The structure is tested on a shaking table by exerting successively enhanced earthquake excitations until severe damage, and then retrofitted using fiber-reinforced polymers (FRP). The modal properties of the tested structure at trifling, moderate, severe damage and strengthening stages are measured by subjecting it to a small-amplitude white-noise excitation after each earthquake attack. Making use of the measured global modal frequencies and a validated finite element model of the tested structure, a neural network method is developed to quantitatively identify the stiffness reduction due to damage and the stiffness enhancement due to strengthening. The identification results are compared with 'true' damage severities that are defined and determined based on visual inspection and local impact testing. It is shown that by the use of FRP retrofit, the stiffness of the severely damaged structure can be recovered to the level as in the trifling damage stage.

Effects of Restrainer upon Bridge Motions with Poundings and frictions under Seismic Excitations (지진시 층돌 및 마찰을 고려한 교량거동에 미치는 Restrainer의 보강효과)

  • 김상효;마호성;이상우;원정훈
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1999.10a
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    • pp.291-300
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    • 1999
  • An idealized analytical model is proposed to estimate the effects of restrainer upon global response behaviors of a bridge system under seismic excitations. Pounding actions between adjacent vibration units and friction at movable supports are introduced in addition to other phenomena such as nonlinear behaviors of pier, motions of the foundation and abutment to achieve the better prediction of the bridge motion. The applied restrainer is assumed to be a dead-band system, which has the force clearance and the linear-elastic force. Using the proposed model, the dynamic characteristics of a bridge system retrofitted by restrainers is examined, and the effects of stiffness and clearance length of restrainer is also investigated. The main effect of the application of restrainers is found to reduce the relative displacements and the trend becomes greater with the shorter clearance length except between pier units. It is found that the relative displacements between abutment and adjacent pier units are decreased as the stiffness of restrainer increases, but almost independent upon the stiffness increments of restrainer. However, the relative displacements between pier units tend to be increased due to the applications of the restrainers.

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Retrofit of a hospital through strength reduction and enhanced damping

  • Viti, Stefania;Cimellaro, Gian Paolo;Reinhorn, Andrei M.
    • Smart Structures and Systems
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    • v.2 no.4
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    • pp.339-355
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    • 2006
  • A procedure to retrofit existing essential facilities subjected to seismic excitation is proposed. The main features of this procedure are to reduce maximum acceleration and associated forces in buildings subjected to seismic excitation by reducing their strength (weakening). The weakening retrofit, which is an opposite strategy to strengthening, is particularly suitable for buildings having overstressed components and foundation supports or having weak brittle components. However, by weakening the structure large deformations are expected. Supplementaldamping devices however can control the deformations within desirable limits. The structure retrofitted with this strategy will have, therefore, a reduction in the acceleration response and a reduction in the deformations, depending on the amount of additional damping introduced in the structure. An illustration of the above strategy is presented here through an evaluation of the inelastic response of the structure through a nonlinear dynamic analysis. The results are compared with different retrofit techniques. A parametric analysis has also been carried out to evaluate the effectiveness of the retrofitting method using different combination of the performance thresholds in accelerations and displacements through fragility analysis.

Retrofitting of squat masonry walls by FRP grids bonded by cement-based mortar

  • Popa, Viorel;Pascu, Radu;Papurcu, Andrei;Albota, Emil
    • Earthquakes and Structures
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    • v.10 no.1
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    • pp.125-139
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    • 2016
  • For seismic retrofitting of masonry walls, the use of fibre reinforced cement-based mortar for bonding the fibre grids can eliminate some of the shortcomings related to the use of resin as bonding material. The results of an experimental testing program on masonry walls retrofitted with fibre reinforced mortar and fibre grids are presented in this paper. Seven squat masonry walls were tested under unidirectional lateral displacement reversals and constant axial load. Steel anchors were used to increase the effectiveness of the bond between the fibre grids and the masonry walls. Application of fibre grids on both lateral faces of the walls effectively improved the hysteretic behaviour and specimens could be loaded until slip occurred in the horizontal joint between the masonry and the bottom concrete stub. Application of the fibre grids on a single face did not effectively improve the hysteretic behaviour. Retrofitting with fibre reinforced mortar only prevented the early damage but did not effectively increase deformation capacity. When the boundaries of the cross sections were not properly confined, midplane splitting of the masonry walls occurred. Steel anchors embedded in the walls in the corners area effectively prevented this type of failure.

Application of three-dimensional modified inclined braces to control soft-story buildings

  • Nodehi, Soroush;Zahrai, Seyed Mehdi
    • Structural Engineering and Mechanics
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    • v.83 no.6
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    • pp.811-824
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    • 2022
  • Despite its disadvantages, soft story can reduce the damage to the upper floors by concentrating drift in that specific story provided that large drifts are avoided. Gapped-Inclined Brace (GIB) with reduced P-delta effects and the control of soft story stiffness makes it possible to take advantage of the soft story in buildings and increase their capacity for energy dissipation. OpenSees software is used in this study to validate and modify the GIB model's shortcomings. Also, the analysis method for this element is changed for design. The modified element is evaluated in 3D analysis. Finally, to retrofit an existing building, this element is used. Based on the Iranian seismic code, a six-story reinforced concrete building is modelled and studied with 3D analysis. In this building, the construction shortcomings and elimination of infills on the ground floor cause the formation of a soft story. Results of nonlinear static analysis, nonlinear dynamic, and incremental dynamic analysis using both components of seismic acceleration applied to the structure at different angles and the fragility curves indicate the improvement of the retrofitted structure's performance using the modified element to reach the required performance level following the retrofit code.