• Earthquakes and Structures
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• 제3권3_4호
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• pp.611-628
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• 2012

The inelastic earthquake response of existing, reinforced concrete buildings with an open ground story, designed according to the old Greek codes, is investigated before and after their seismic strengthening with steel braces restricted to the open ground stories. The seismic performance evaluation is based on Part 3 of Eurocode 8 for assessment and retrofitting of buildings. Three and five-story, symmetric and non-symmetric buildings are subjected to a set of seven pairs of synthetic accelerograms, compatible with the design spectrum, and conclusions are drawn regarding the effectiveness of the strengthening solutions. Seismic behavior of the selected models confirms results of previous work regarding the insufficient capacity of the open ground stories for design level earthquakes. It is also shown that strengthening only the weak ground story, a choice having the substantial advantage of low cost and continued usage of the building during its seismic retrofitting, can remove the inherent weakness without shifting the problem to the stories above and thus making such buildings at least as strong as those without a weak first story. This partial strengthening is possible for symmetric as well as eccentric buildings, in which torsion plays a further detrimental role.

• 한국전산구조공학회논문집
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• 제33권3호
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• pp.193-199
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• 2020

본 논문은 유한요소법과 유전알고리즘을 연동하여 지진하중을 받는 구조물의 강성저하(손상) 및 보강 후 효과를 추정하는 방법을 다루었다. 본 연구의 독창성은 지진하중을 적용하였고, 그 응답으로부터 구조물의 미지 변수를 추정한다는 점이다. 본 연구에서 제안한 방법은 지진하중으로부터 손상된 부위를 추정할 뿐 아니라, 그 위치와 정도를 규명할 수 있다. 제안한 방법을 검증하기 위하여 El Centro 및 포항 지진하중을 적용하여 저층 뼈대구조물와 트러스 교량을 대상으로 알고리즘을 실행하였다. 수치해석 예제는 제안한 방법이 수치해석적인 효율성 뿐 아니라 지진으로부터의 심각한 피해를 예방하는 데 적용할 수 있음을 보여주었다.

• 한국강구조학회 논문집
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• 제21권4호
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• pp.343-350
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• 2009

본 연구에서는, 비내진 설계된 철근콘크리트 교각에 대해 스테인레스강 와이어 메쉬와 고강도 침투성 폴리머 몰탈을 사용한 내진보강 기법을 제안하였다. 본 연구의 목적을 위해, 총 6본의 비내진 설계된 교각 실험체에 대해 반복 가력 실험을 수행하였다. 실험결과, 주철근 겹이음을 갖는 비내진 설계된 교각 실험체에 대한 내진보강이 필요하다는 것을 알 수 있었고, 본 연구에서 제안된 보강 기법은, 비내진 설계된 교각의 강도, 강성 및 에너지 소산능력에 증진 효과가 있음을 알 수 있었다. 또한, 제안된 보강 기법은 비탄성 변위 영역을 경험하는 교각의 강도 저감 완화와 함께 연성도 증진에도 효과가 있을 것으로 기대된다.

• Earthquakes and Structures
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• 제12권6호
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• pp.699-712
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• 2017

This study evaluates the effectiveness of a newly developed retrofitting scheme for masonry-infilled non-ductile RC frames experimentally and by numerical simulation. The technique focuses on modifying the load path and yield mechanism of the infilled frame to enhance the ductility. A vertical gap between the column and the infill panel was strategically introduced so that no shear force is directly transferred to the column. Steel brackets and small vertical steel members were then provided to transfer the interactive forces between the RC frame and the masonry panel. Wire meshes and high-strength mortar were provided in areas with high stress concentration and in the panel to further reduce damage. Cyclic load tests on a large-scale specimen of a single-bay, single-story, masonry-infilled RC frame were carried out. Based on those tests, the retrofitting scheme provided significant improvement, especially in terms of ductility enhancement. All retrofitted specimens clearly exhibited much better performances than those stipulated in building standards for masonry-infilled structures. A macro-scale computer model based on a diagonal-strut concept was also developed for predicting the global behavior of the retrofitted masonry-infilled frames. This proposed model was effectively used to evaluate the global responses of the test specimens with acceptable accuracy, especially in terms of strength, stiffness and damage condition.

• Earthquakes and Structures
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• 제10권1호
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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.

• Advances in concrete construction
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• 제13권4호
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• pp.339-347
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• 2022

Retrofitting in reinforced concrete structures has been one of the most important research topics in recent years. There are several methods for retrofitting RC moment-resisting frames. the most important of which is the use of steel bracing systems with yielding dampers. With a proper design of yielding dampers, the stiffness of RC frame systems can be increased to the required extent so that the ductility of the structure is not significantly reduced. In the present study, two experimental samples of a one-third scale RC moment-resisting frame were loaded in the laboratory. In these experiments, the retrofitting effect of RC frames was investigated using Non-uniform Slit Dampers (NSDs). Based on the experimental results of the samples, seismic parameters, i.e., stiffness, ductility, ultimate strength, strength reduction coefficient, and energy dissipation capacity, were compared. The results demonstrated that the retrofitted frame had very significant growth in terms of stiffness, ultimate strength, and energy dissipation capacity. Although the strength reduction factor and ductility decreased in the retrofitted sample. In general, the behavior of the frame with NSDs was evaluated better than the bare frame.

• 한국지진공학회논문집
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• 제8권3호
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• pp.77-86
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• 2004

본 연구에서는 교량의 내진보강방안을 합리적으로 결정하기 위하여 기존교량 및 보강된 교량의 지진하중에 대한 손상가능성을 이용하여 보강에 따른 내진성능 향상효과를 분석하였다. 교량의 내진보강에 따른 효과는 기존교량 및 보강된 교량에 대해 평가된 보강우선순위의 변화를 통하여 분석하였다. 이를 위하여 본 연구에서는 선행적으로 교량의 사용수명동안에 발생가능한 지진하중에 의한 지진취약부위의 손상확률과 손상으로 인해 예상되는 총 손실비용에 근거한 지진취약부위별 가중치를 이용하여 교량별 내진보강 우선순위를 결정할 수 있는 평가기법을 제안하였다. 제안된 평가기법의 타당성을 검증하기 위하여 다른 형식을 갖는 4개의 PSC 거더교를 대상으로 내진보강 우선순위를 평가하였다. 또한 각 지진취약부위별로 내진 보강된 교량에 대해 재평가된 순위지수를 기존교량에 대해 평가된 결과와 비교함으로써 각 교량별로 적용된 보강기법의 적합성을 검토하였다. 기존교량 및 보강된 교량에 대한 모의분석결과로부터 적용된 보강방안에 따라 해당취약부위의 손상가능성은 상당히 감소될 수 있으나 반면에 인접한 지진취약부위의 손상가능성은 증가되는 경향을 보이는 것으로 나타났다. 그러므로 기존교량에 대한 합리적인 보강방안을 결정하기 위해서는 내진보강에 따른 교량의 전체적인 거동특성변화에 따른 보강효과분석이 필수적으로 요구되며, 이는 본 연구에서 제안한 내진보강 우선순위 평가기법에 따라 기존교량 및 보강된 교량의 보강우선순위를 평가, 비교함으로써 효과적으로 수행될 수 있는 것으로 분석되었다.

• 한국지진공학회논문집
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• 제21권6호
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• pp.311-322
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• 2017

In this study, the seismic performance of concrete-steel composite moment frame structures equipped with seismic retrofitting systems such as seismic reinforcement, base isolators, and bracing members, which are typical earthquake damage mitigation systems, is evaluated through nonlinear dynamic analyses. A total of five frame models were designed and each frame model was developed for numerical analyses. A total of 80 ground acceleration data were used to perform the nonlinear dynamic analysis to measure ground shear force and roof displacement, and to evaluate the behavioral performance of each frame model by measuring inter-story drift ratios. The analysis results indicate that the retrofitting device of the base isolator make a significant contribution to generating relatively larger absolute displacement than other devices due to flexibility provided to interface between ground and column base. However, the occurrence of the inter-story drift ratio, which is a relative displacement that can detect the damage of the structure, is relatively small compared with other models. On the other hand, the seismic reinforced frame model enhanced with the steel plate at the lower part of the column was found to be the least efficient.

• Steel and Composite Structures
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• 제19권2호
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• pp.309-325
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• 2015

A convenient procedure for seismic retrofit of existing buildings is to use passive control methods, like using friction dampers in steel frames with bracing systems. In this method, reduction of seismic demand and increase of ductility generally improve seismic performance of the structures. Some of its advantages are development of a stable rectangular hysteresis loop and independence on environmental conditions such as temperature and loading rate. In addition to friction dampers, masonry-infill panels improve the seismic resistance of steel structures by increasing lateral strength and stiffness and reducing story drifts. In this study, the effect of masonry-infill panels on seismic performance of a three-span four-story steel frame with Pall friction dampers is investigated. The results show that friction dampers in the steel frame increase the ductility and decrease the drift (to less than 1%). The infill panels fulfill their function during the imposed drift and increase structural strength. It can be concluded that infill panels together with friction dampers, reduced structural dynamic response. These infill panels dissipated input earthquake energy from 4% to 10%, depending on their thickness.

• Earthquakes and Structures
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• 제22권2호
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• pp.121-135
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• 2022

Many public buildings such as schools, hospitals, etc., where partial infill walls are present in reinforced concrete (RC) structures, have undergone undesirable damage/failure attributed to captive column effect during a moderate to severe earthquake shaking. Often, the situation gets worsened when these RC frames are non-ductile in nature, thus reducing the deformable capability of the frame. Also, in many parts of the Indian subcontinent, it is mandatory to use fly-ash bricks for construction so as to reduce the burden on the disposal of fly-ash produced at thermal power plants. In some scenario, when the non-ductile RC frame, partially infilled by fly-ash bricks, suffers major structural damage, the challenge remains on how to retrofit and restore it. Thus, in this study, two full-scale one-bay, one-story non-ductile RC frame models, namely, bare frame and RC partially infilled frame with fly-ash bricks in 50% of its opening area are considered. In the previous experiments, these models were subjected to slow-cyclic displacement-controlled loading to replicate damage due to a moderate earthquake. Now, in this study these damaged frames were retrofitted and an experimental investigation was performed on the retrofitted specimens to examine the effectiveness of the proposed retrofitting scheme. A hybrid retrofitting technique combining epoxy injection grouting with an innovative and easy-to-implement steel jacketing technique was proposed. This proposed retrofitting method has ensured proper confinement of damaged concrete. The retrofitted models were subjected to the same slow cyclic displacement-controlled loading which was used to damage the frames. The experimental study concluded that the hybrid retrofitting technique was quite effective in enhancing and regaining various seismic performance parameters such as, lateral strength and lateral stiffness of partially fly-ash brick infilled RC frame. Thus, the steel jacketing retrofitting scheme along with the epoxy injection grouting can be relied on for possible repair of the structural members which are damaged due to the captive column effect during the seismic shaking.