• Steel and Composite Structures
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• 제50권6호
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• pp.721-734
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• 2024

In this research, the efficiency of a metallic energy dissipation device for seismic retrofit of an existing structure is evaluated by cyclic loading test. The proposed device, which is called multi-slit damper, is made of weak and strong slit dampers connected in series. Its energy dissipation mechanism consists of two stages: (i) yielding of the weak-slit damper under minor earthquakes; (ii) restraint of further deformations of the weak slit damper and activation of the strong slit damper under major earthquakes using a gap mechanism. A reinforced concrete (RC) frame with characteristics similar to soft-first-story structures is tested under cyclic loading before and after retrofit using the proposed device. The details of the experimental study are described and the test is simulated in an available commercial software to validate the analytical model of the damper. To further verify the applicability of the damper, it is applied to an analysis model of a 4-story structure with soft first story and its seismic performance is evaluated before and after retrofit. The experimental and analysis results show that the multi-slit damper is effective in controlling seismic response of structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.81-86
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• 2000

In recent modern protective systems have been introduced to reduce the vulnerability of bridges to seismic events. These protective systems include base isolation devices of different types, damping devices and active control devices. The objective of this study is to analytically evaluate the efficiency of a seismic retrofit scheme using base isolation systems, such as lead rubber bearings and sliding isolators. In this study, a triaxial model was used, which is capable of accurately developing the behavior of sliding isolators including the influence of the changing vertical force and velocity on the friction coefficients. Seismic response analyses of the bridge before and after retrofit were carried out by using a three-dimensional nonlinear seismic analysis program, IDARC-BRIDGE. To evaluate the efficiency of a retrofit scheme using triaxial isolators, a comparative study of performances of above two base isolation systems was conducted, and the numerical results show that the triaxial isolation solution can effectively reduce the sheat forces at the piers for the vertical ground motion.

• 한국공간구조학회논문집
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• 제22권3호
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• pp.73-80
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• 2022

Unlike the CFT retrofit method, The EPFT retrofit method, which fills the steel tube with engineering plastic, does not require a separate concrete forming work and is a lightweight seismic Retrofit Method. In this study, an prototype model of the EPFT was proposed, and to analyze the seismic performance, an independent specimens and a reinforced concrete column were fabricated to conduct a seismic performance test. As a result of loading test of the independent specimens, the strength was increased compared to the steel tube column without internal filling, and the ductility ratio did not significantly increase due to the falling off of the weld. As a result of loading test of the concrete reinforcement specimen, the strength, ductility ratio, and energy dissipation were increased, and the number of cracks by loading step decreased compared to the non-reinforced specimen.

• 교육시설 논문지
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• 제19권4호
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• pp.21-28
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• 2012

This study proposes a procedure for evaluating the seismic performance and retrofit of a typical reinforced building (R/C) school buildings contructed in the 1980s. The procedure is derived from the Japanese Standard for Evaluation of Seismic Capacity of Existing Reinforced Concrete Buildings and Nonlinear Static Procedure (NSP) specified in Federal Emergency Management Agency (FEMA 356). In this study, the Japanese Standard was applied for evaluating the additionally required seismic performance in the existing school building. Cast-in-place (CIP) reinforced concrete infill walls and steel braces were used to seismically retrofit the existing school building located in the region of Hongsung in Chungnam. In the pushover analysis, i.e NSP, the hinge properties of columns, beams, infill walls and steel braces were carefully calibrated based on the existing experiment results in the available literatures. The predicted seismic performance for the retrofitted building was compared to that for the virgin building. Based on the seismic evaluation with the Japanese Standard and the FEMA 356 criteria, the addition of CIP reinforced concrete infill walls and steel braces have superior constructablility and can improve effectively the seismic performance of the existing school buildings constructed in 1980s.

• 한국지진공학회논문집
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• 제8권2호
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• pp.9-17
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• 2004

기존 교량 중 내진 설계가 되어 있지 않은 교량의 내진 성능에 관한 평가는 향후 발생 가능한 지진에 대한 대비로써 중요하다. 성능평가 결과, 소요의 내진 성능을 보유하고 있지 못하다면 그에 대한 보강이 필요하며 보강방법으로는 여러 가지가 있다. 그 중 지진격리증기를 이용한 내진 보강은 교량에서 교각이나 기초 등에 추가적인 시공 없이 기존 받침을 교체함으로써 비교적 간단하게 수행할 수 있다. 본 논문에서는 최근 그 시공사례가 증가하고있는 지진격리증기를 기존 비내진 교량의 보강에 사용할 때 교량의 내진 성능향상을 합리적으로 규명하기 위해 기존상태의 교량 및 지진격리장치로서 내진 보강된 교량의 내진 성능을 비교하였다. 이를 위해 기존 교량 및 내진 보강된 교량에 대해 비선형 정적ㆍ동적 해석을 수행하였으며 목표 수준의 지진에 대하여 각각의 응답을 산정하고 이를 비교하여 내진 성능 향상을 확인하였다.

• Earthquakes and Structures
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• 제3권2호
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• pp.141-168
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• 2012

The Retrofit Yield Spectrum (RYS) is a new spectrum-based device that relates seismic demand of a retrofitted structure with the fundamental design parameters of the retrofit. This is obtained from superposition of Yield Point Spectra with design charts that summarize in pertinent spectrum-compatible coordinates the attributes of a number of alternative retrofit scenarios. Therefore, once the requirements for upgrading a given structure have been determined, the RYS enable direct insight of the sensitivity of the seismic response of the upgraded structure to the preliminary design decisions made while establishing the retrofit plan. By virtue of their spectrum-based origin, RYS are derived with reference to a single mode of structural vibration; a primary objective is to control the contribution of this mode in the retrofit design so as to produce a desirable distribution of damage at the ultimate limit state by removing soft storey formations and engaging the maximum number of structural members in deformation, in response to the input motion. Calculations are performed with reference to the yield-point, where secant stiffness is proportional to the flexural strength of reinforced concrete members. Derivation and use of the Retrofit Yield Spectra (RYS) refers to the seismic demand expressed either in terms of spectral acceleration, spectral displacement or interstory drift, at yield of the first storey. A reinforced concrete building that has been tested in full scale to a sequence of simulated earthquake excitations is used in the paper as a demonstration case study to examine the effectiveness of the proposed methodology.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.15-22
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• 1998

It is needless to say that the computer and/or computational engineering has contributed much to the development of the earthquake engineering such as seismic design of structures in providing good tools to researchers and engineers. However, it has been also pointed out that the proper selection of numerical analysis and/or computer program is very important for engineers in utilizing it in the design of structures, because a numerical analysis method is based upon its own coverage. A rigorous analysis does not always gives a correct solution in a sence of engineering or of structural safety, but, some times, it gives mathematically rigorous but unrealistic solution. Therefore, numerical analysis should be performed with engineering judgement or experiments specially in the field of earthquake engineering because this field has large uncertainties on predicting the effect of earthquake on structures. This paper is based on the presented paper at the Bertero Symposium held in January 31an4 February 1 at Berkeley, California, USA which was entitled "Needs to Evaluate Real Seismic Performance of Buildings-Lessons from 1995 Hyogoken-Nambu Earthquake-". The lessons for buildings from the damage due to the Hyogoken-Nambu Earthquake are necessity to develop more rational seismic design codes based upon a performance-based design concept, and to evaluate seismic performance of existing buildings. In my keynote lecture at the Korean Association for Computational Structural Engineering, the history of seismic design and use of structural analysis in Japan, the lessons for buildings from the Hyogoken-Nambu Earthquake, the building damage due to the earthquake, the reasons why the seismic retrofit has not been implemented much, the responses to the lessons from the earthquake, the Network Committee for promotion of seismic retrofit of buildings, the Law for promotion of seismic retrofit of buildings and the implementation of seismic retrofit in Japan are presented.

• 한국산업융합학회 논문집
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• 제15권1호
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• pp.29-36
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• 2012

Reinforced concrete shear walls and X-type steel braces were applied in seismic retrofit techniques for seismic performance evaluation of school buildings constructed in accordance with standard design announced by the ordinance of the ministry of construction in 1980s. Seismic performance evaluation was based on FEMA 356 using response spectrum as elastic analysis and conducted to pushover analysis with nonlinear static analysis. The maximum displacement ratio between floors in 4th and 3rd floors of the existing school buildings was less than 1.0%, which was functioning level in FEMA 356. However, because plastic hinge occurs somewhat in structural members according to the results of pushover analysis, partial reinforcement will be required. X-direction of the maximum lateral displacement of reinforced concrete shear walls than X-type steel braces was 45% and 32% in 4th and 3rd floors of school buildings, and Y-direction was 18% and 17%, respectively.

• Structural Engineering and Mechanics
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• 제71권4호
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• pp.341-350
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• 2019

Exterior beam-column joint is typically the weakest link in a limited-ductile reinforced concrete (RC) frame structure. The use of diagonal haunch element has been considered as a desirable seismic retrofit option for reducing the seismic demand at the joint. Previous research globally has focused on implementing double haunches, while the use of single haunch element as a less-invasive and more architecturally favorable retrofit option has not been investigated. In this paper, the key formulations and a design procedure for the single haunch system for retrofitting RC exterior beam-column joint are developed. An application of the proposed design procedure is then illustrated through a case study.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.325-330
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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 analysis both the strength and stiffness are significantly enhanced as a result of the seismic retrofit. When buckling-restrained braces are used instead of conventional braces, the structures show more ductile behavior, especially in the 3-story structure.