• Smart Structures and Systems
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• 제4권2호
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• pp.233-245
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• 2008

For historical masonry structures existing in the Mediterranean area, structural strengthening is of primary importance due to the continuous earthquake threat that is posed on them. Proper retrofitting of historical structures involves a thorough understanding of their structural pathology, before proceeding with any intervention measures. In this paper, a methodology is presented for the evaluation of the actual state of historical masonry structures, which can provide a useful tool for the seismic response assessment before and after the retrofitting. The methodology is mainly focused on the failure and vulnerability analysis of masonry structures using the finite element method. Using this methodology the retrofitting of historical structures with innovative techniques is investigated. The innovative technique presented here involves the exploitation of Shape Memory Alloy prestressed bars. This type of intervention is proposed because it ensures increased reversibility and minimization of interventions, in comparison with conventional retrofitting methods. In this paper, a case study is investigated for the demonstration of the proposed methodologies and techniques, which comprises a masonry Byzantine church and a masonry Cistern. Prestressed SMA alloy bars are placed into the load-bearing system of the structure. The seismic response of the non-retrofitted and the retrofitted finite element models are compared in terms of seismic energy dissipation and displacements diminution.

• 한국구조물진단유지관리공학회 논문집
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• 제27권6호
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• pp.162-171
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• 2023

본 연구에서는 기존 구조물의 면내 보강을 위해 콘크리트 구조물과 보강재를 쉽게 연결할 수 있는 내진 어댑터의 세부 설계 방안을 제안하였다. 제안된 내진 어댑터는 실제 크기의 절반으로 축소된 2층짜리 기둥-보 구조물에서 동적 시뮬레이션을 통해 성능을 테스트하였다. 실험 결과, 내진 어댑터를 사용하여 보강된 시험체는 보강되지 않은 시험체에 비해 에너지 소산 능력이 3.5배 향상되었음을 보여주어, 일반적인 사용 범위 내에서 내진 어댑터가 손상되지 않았음이 확인되어 그 효과를 입증하였다. 이어서 변형 한계(변형 각도 3.3%)까지 하중을 가했을 때, 1층 하부에서 어댑터와 보강재를 연결하는 M10 볼트 중 하나가 파손된 것을 관찰하였다. 이러한 발견을 고려할 때, 실제 상황에서 내진 보강을 적용할 때는 내진 어댑터를 연결하는 볼트와 앵커의 설계에 중점을 둬야 할 것으로 판단되었다.

• 콘크리트학회논문집
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• 제25권6호
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• pp.667-674
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• 2013

기존 강재 브레이싱 내진보강법은 정착부의 안정성 문제와 브레이싱의 국부좌굴이 발생할 문제가 있으며, 이를 방지하기 위한 추가보강으로 인해 불필요한 자중증가 등으로 경제적인 내진보강성능 확보에 어려움이 있다. 이 연구에서는 지진피해를 받은 건물에 지진피해로 인한 기존 기둥의 연성확보를 위해서 유리섬유시트(glass fiber sheet)로 래핑을 함과 동시에 기존 철골 X-브레이싱 내진보강법에 비교해서 경량의 고강도 재료로 보강 후 추가적인 중량증가가 거의 없으며, 브레이싱 압축 좌굴거동에 자유로운 탄소섬유 앵커 X-브레이싱공법(carbon fiber X-brace)을 조합한 경제적이며 효과적인 새로운 내진보강법(GFS-CFXB)을 제안하였다. 이 연구에서 제안한 GFS-CFXB공법의 유용성을 검증할 목적으로 지진피해를 받은 골조를 대상으로 반복가력에 의한 구조실험을 실시하여 내진성능 및 내진보강 효과를 검증하였다.

• Earthquakes and Structures
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• 제26권5호
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• pp.383-400
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• 2024

For a conventionally repaired frame-supported-transfer-slab (FSTS) reinforced concrete (RC) structure, both the transfer slab and the beam-to-column and transfer slab-to-column joints remain vulnerable to secondary earthquakes. Aimed at improving the seismic performance of a damaged FSTS RC structure, an innovative retrofitting scheme is proposed, which adopts the sector lead rubber dampers (SLRDs) at joints after the damaged FSTS RC structure is repaired by conventional approaches. In this paper, a series of quasi-static cyclic tests was conducted on a large-scale retrofitted FSTS RC structure. The seismic performance was evaluated and the key test results, including deformation characteristics, damage pattern, hysteretic behaviour, bearing capacity and strains on key components, were reported in detail. The test results indicated that the SLRDs started to dissipate energy under the service level earthquake, and thus prevented damages on the beam-to-column and transfer slab-to-column joints during the secondary earthquakes and shifted the plastic hinges away from the beam ends. The retrofitting scheme of using SLRDs also achieved the seismic design concept of 'strong joint, weak component'. The FSTS RC structure retrofitted by the SLRDs could recover more than 85% bearing capacity of its undamaged counterpart. The hysteresis curves were featured by the inverse "S" shape, indicating good bearing capacity and hysteresis performance. The deformation capacity of the damaged FSTS RC structure retrofitted by the SLRDs met the corresponding codified requirements for the case of the maximum considered earthquake, as set out in the Chinese seismic design code. The stability of the FSTS RC structure retrofitted by the SLRDs, which was revealed by the developed stains of the RC frame and transfer slab, was improved compared with the undamaged FSTS RC structure.

• Steel and Composite Structures
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• 제29권3호
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• pp.287-299
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• 2018

The purpose of this study is to investigate the effectiveness of damped cable systems (DCS) to mitigate the earthquake-induced responses of a building frame structure. The seismic performance of the DCS is investigated using the fragility analysis and life cycle cost evaluation of an existing building retrofitted with the DCS, and the results are compared with the structure retrofitted with conventional fluid viscous dampers. The comparison of the analysis results reveals that, due to the self-centering capability of the DCS, residual displacement approximately reaches to zero for the structure retrofitted with the DCS. The fragility analysis shows that the structure retrofitted with the DCS has the least probability of reaching the specific limit states compared to the bare structure and the structure with the conventional fluid viscous damper (VD), especially under the severe ground motions. It is also observed that both the initial and the life cycle costs of the DCS seismic retrofitting technique is lesser compare to the structure retrofitted with the VD.

• Smart Structures and Systems
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• 제4권5호
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• pp.685-696
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• 2008

This paper deals with the numerical model of a bracing-friction damper system and its deployment using the optimal slip load distribution for the seismic retrofitting of a damaged building. The Slotted Bolted Connection (SBC) type friction damper system was tested to investigate its energy dissipation characteristic. Test results coincided with the numerical ones using the conventional model of a bracing-friction damper system. The placement of this device was numerically explored to apply it to the assumed damaged-building and to evaluate its efficiency. It was found by distributing the slip load that minimizes the given performance indicies based on structural response. Numerical results for the damaged building retrofitted with this slip load distribution showed that the seismic design of the bracing-friction damper system under consideration is effective for the structural response reduction.

• Structural Engineering and Mechanics
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• 제59권2호
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• pp.209-226
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• 2016

Integral bridges are typically designed with flexible foundations that include one row of piles. The construction of integral bridges solves difficulties due to the maintenance of expansion joints and bearings during serviceability. It causes integral bridges to become more economic comparing with conventional bridges. Research has been focused not only to enhance the seismic performance of newly designed bridges, but also to develop retrofit strategies for existing ones. The local performance of the pile to abutment connection will have a major effect on the performance of the structure and the embedment length of pile inside the abutment has a key role to provide shear and flexural resistance of pile-abutment connections. In this paper, a simple method was developed to estimate the initial value of embedment length of the pile for retrofitting of specimens. Four specimens of pile-abutment connections were constructed with different embedment lengths of pile inside the abutment to evaluate their performances. The results of the experimentation in conjunction with numerical and analytical studies showed that retrofitting pile-abutment connections with CFRP wraps increased the strength of the connection up to 86%. Also, designed connections with the proposed method had sufficient resistance against lateral load.

• 한국공간구조학회논문집
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• 제24권1호
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• pp.29-36
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• 2024

The paper presents the experimental investigation of RC beams retrofitted with Textile Reinforced Mortar (TRM), featuring enhanced bond capacity. Anchoring systems, including an extension of retrofitting length and the use of chemical anchors, are newly employed to improve the structural performance of the RC beam retrofitted with TRM. For the experimental investigation, a total of seven shear-critical RC beams, with and without stirrups, were designed and constructed. The structural behaviors of specimens retrofitted with the proposed TRM methods were compared to those of non-retrofitted specimens or specimens strengthened with conventional TRM methods. Crack pattern, force-displacement relationship, and absorbed energy were evaluated for each specimen. The experimental results indicate a significant improvement in the shear capacity of the RC beam with the proposed retrofitting method. Therefore, it is concluded that the application of an extended retrofitting length and chemical anchors to the TRM retrofitting method can effectively enhance the bond capacity of TRM, thereby improving the shear performance of RC beams.

• Earthquakes and Structures
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• 제10권3호
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• pp.589-611
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• 2016

This paper presents an analytical study aimed at evaluating the seismic performance of steel moment resisting frames (MRFs) retrofitted with different approaches. For this, 3, 6 and 12 storey MRFs having four equal bays of 5 m were selected as the case study models. The models were designed with lateral stiffness insufficient to satisfy code drift and hinge limitations in zones with high seismic hazard. Three different retrofit strategies including traditional diagonal bracing system and energy dissipation devices such as buckling restrained braces and viscoelastic dampers were used for seismic upgrading of the existing structures. In the nonlinear time history analysis, a set of ground motions representative of the design earthquake with 10% exceedance probability in fifty years was taken into consideration. Considering the local and global deformations, the results in terms of inter-storey drift index, global damage index, plastic hinge formations, base shear demand and roof drift time history were compared. It was observed that both buckling-restrained braces and viscoelastic dampers allowed for an efficient reduction in the demands of the upgraded frames as compared to traditional braces.

• 한국공간구조학회논문집
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• 제15권1호
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• pp.85-94
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• 2015

SAFE damper is a hybrid damper which is comprised of a friction damper and a metallic damper. These two dampers combine to resist external energy in stages. Under minor earthquake loads, the friction damper operates alone. However, the friction damper and metallic damper dissipate the energy together when a severe earthquake occurs. In comparison with other methods for seismic retrofitting, the SAFE damper has many advantages. The SAFE damper doesn't cause damage to façade of the building, and the construction period can be reduced when retrofitting. This paper describes experiments evaluating the structural performance of the SAFE damper. From the results, it was found that the structural performance of a conventional RC bare frame can be significantly improved by the installation of the SAFE damper.