• Steel and Composite Structures
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• 제1권3호
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• pp.283-294
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• 2001

In the present work a constitutive model is developed which permits the assessment of the structural performance through a criterion based on cumulative damage. For it, a damage index is defined and is evaluated through the application of the Miner's rule in low-cycle fatigue. However, the damage index is not considered as a posteriori variable since is incorporated explicitly as an internal variable in the constitutive equations which produces a direct coupling between the damage and the structural mechanical behaviour allowing the possibility of considering as a whole different coupled phenomena. For the elaboration of this damage model, the concepts of the mechanics of continuum medium are applied on lumped dissipative models in order to obtain a coupled simplified model. As a result an elastoplastic model coupled with damage and fatigue damage is obtained.

• Earthquakes and Structures
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• 제25권2호
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• pp.125-134
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• 2023

In the present work, a new global damage index is proposed for the seismic performance and failure analysis of concrete gravity dams. Unlike the existing indices of concrete structures, this index doesn't need scaling with an ultimate or an upper value. For this purpose, the Beni-Haroun dam in north-eastern Algeria, is considered as a case study, for which an average seismic capacity curve is first evaluated by performing several incremental dynamic analyses. The seismic performance point of the dam is then determined using the N2 method, considering multiple modes and taking into account the stiffness degradation. The seismic demand is obtained from the design spectrum of the Algerian seismic regulations. A series of recorded and artificial accelerograms are used as dynamic loads to evaluate the nonlinear responses of the dam. The nonlinear behaviour of the concrete mass is modelled by using continuum damage mechanics, where material damage is represented by a scalar field damage variable. This modelling, which is suitable for cyclic loading, uses only a single damage parameter to describe the stiffness degradation of the concrete. The hydrodynamic and the sediment pressures are included in the analyses. The obtained results show that the proposed damage index faithfully describes the successive brittle failures of the dam which increase with increasing applied ground accelerations. It is found that minor damage can occur for ground accelerations less than 0.3 g, and complete failure can be caused by accelerations greater than 0.45 g.

• 화약ㆍ발파
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• 제28권2호
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• pp.59-68
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• 2010

도심지에서의 건물해체 및 발파공사로 노후된 인접 구조물의 구조적 안정성에 영향을 미칠 가능성이 있다. 본 연구에서는 노후 콘크리트 재료의 물성을 파악하기 위하여 반발경도에 의한 압축강도와 X선 회절 및 상 분석에 의한 성분 함량으로 상관성을 비교하였고, 충격 에너지에 의한 손상도 평가를 위해 측정된 탄성파속도 값으로 손상도를 산출하였다. 결과적으로, 반발경도에 의한 압축강도와 재료의 성분 함량은 상관성이 있음을 확인하였고, 탄성파속도 값으로 산출된 손상도는 압축강도가 큰 재료일수록 작게 나타났고, 충격력이 작을수록 작게 나타났다.

• Smart Structures and Systems
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• 제16권1호
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• pp.1-26
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• 2015

Minimizing construction cost and reducing seismic damage are two conflicting objectives in the design of any new structure. In the present work, we try to develop a framework in order to solve the optimum performance-based design problem considering the construction cost and the seismic damage of steel moment-frame structures. The Park-Ang damage index is selected as the seismic damage measure because it is one of the most realistic measures of structural damage. The non-dominated sorting genetic algorithm (NSGA-II) is employed as the optimization algorithm to search the Pareto optimal solutions. To improve the time efficiency of the proposed framework, three simplifying strategies are adopted: first, simplified nonlinear modeling investigating minimum level of structural modeling sophistication; second, fitness approximation decreasing the number of fitness function evaluations; third, wavelet decomposition of earthquake record decreasing the number of acceleration points involved in time-history loading. The constraints of the optimization problem are considered in accordance with Federal Emergency Management Agency's (FEMA) recommended seismic design specifications. The results from numerical application of the proposed framework demonstrate the efficiency of the framework in solving the present multi-objective optimization problem.

• Smart Structures and Systems
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• 제23권2호
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• pp.195-205
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• 2019

An accurate non-model-based method for delamination identification of laminated composite plates is proposed in this work. A weighted mode shape damage index is formulated using squared weighted difference between a measured mode shape of a composite plate with delamination and one from a polynomial that fits the measured mode shape of the composite plate with a proper order. Weighted mode shape damage indices associated with at least two measured mode shapes of the same mode are synthesized to formulate a synthetic mode shape damage index to exclude some false positive identification results due to measurement noise and error. An auxiliary mode shape damage index is proposed to further assist delamination identification, by which some false negative identification results can be excluded and edges of a delamination area can be accurately and completely identified. Both numerical and experimental examples are presented to investigate effectiveness of the proposed method, and it is shown that edges of a delamination area in composite plates can be accurately and completely identified when measured mode shapes are contaminated by measurement noise and error. In the experimental example, identification results of a composite plate with delamination from the proposed method are validated by its C-scan image.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.557-566
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• 2017

Fiber reinforced polymer (FRP) sheets are the most efficient structural materials in terms of strength to weight ratio and its application in strengthening and retrofitting of a structure or structural elements are inevitable. The performance enhancement of structural elements without increasing the cross sectional area and flexible nature are the major advantages of FRP in retrofitting/strengthening work. This research article presents a detailed study on the inelastic response of conventional and retrofitted Reinforced Concrete (RC) frames using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi-static loading. The hysteretic behaviour, stiffness degradation, energy dissipation and damage index are the parameters employed to analyse the efficacy of FRP strengthening of brick in-filled RC frames. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

• Structural Engineering and Mechanics
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• 제73권4호
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• pp.381-395
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• 2020

Study on the inelastic response of bare and masonry infilled Reinforced Concrete (RC) frames repaired using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi- static loading is presented in the work. The hysteresis behaviour, stiffness retention, energy dissipation and damage index are the parameters employed to analyze the efficacy of FRP strengthening of bare and brick in-filled RC frames. It is observed that there is a significant improvement in load carrying capacity of brick infilled frame over bare RC frame. Also FRP strengthened brick infilled frame performs much better than FRP repaired bare frame under quasi static loading. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

• 대한건축학회논문집:구조계
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• 제34권1호
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• pp.27-32
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• 2018

This work provides the analytical methods to represent the updated form of stiffness or flexibility matrices using the measurements of the first few natural frequencies and the corresponding mode shapes. This study derives the mathematical forms on the variance of stiffness or flexibility matrices to minimize the performance index in the satisfaction of the eigen-function including the residual force depending on the measured data. The proposed methods can be utilized in detecting damage and updating the parameter matrices deviated from the analytical parameter matrices. The validity of the proposed methods is investigated in a numerical experiment of truss structure and the numerical results of stiffness-based and flexibility-based methods are compared. The sensitivity to the external noise is also examined for applying to the practical work.

• 대한건축학회논문집:구조계
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• 제34권3호
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• pp.3-10
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• 2018

It's not practical to collect all information at the entire degrees of freedom of finite element model. The incomplete measurements should be expanded for subsequent analysis and damage detection. This work presents the analytical methods to expand the incomplete static or dynamic response data. Using the expanded data, introducing the concept of residual force, and minimizing the performance index expressed as the stiffness matrix and its difference before and after damage, the variation in stiffness matrix is derived. Based on the difference in the stiffness matrix, the damage detection method of structures is also provided. The validity of the proposed methods is illustrated in a numerical application, the numerical results are analyzed for applications, and the applicability of both methods is investigated.

• 환경정책연구
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• 제5권4호
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• pp.1-18
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• 2006

최근 들어 강원도 및 경상북도 지역에서의 홍수 피해가 증가하고 있다. 우리나라의 강수 패턴이 변화하는 현실에서 적극적인 홍수 대책의 수립이 요구되고 있다. 본 연구는 환경 방재의 정책적 기반이 될 정확하고 정량적인 취약성 산정 근거를 제시하고자 한다. 본 연구는 과거 20년간 한반도에서 발생한 홍수의 피해액에 근거하여 홍수에 대한 취약성을 분석하였다. 1980년대에는 남부지방(경상남도, 전라남도)에서 침수와 범람으로 농경지 유실과 선박 부문에서 가장 큰 피해가 발생하였다. 이후에는 전체 피해액에서 남부지방에서의 피해가 차지하는 비율이 감소하고 중부지방(충청남도)은 점차 피해율이 증가하지만 전체 피해규모는 유지되는 경향을 보인다. 남부지방의 피해가 감소하는 것에 비해 북부지방(강원도, 경기도)과 산간지역(경상북도)의 홍수 피해율은 상대적으로 증가해 왔으며, 피해규모는 20년간 꾸준히 지속되고 있다. 남부지방의 과거 피해 발생요인이 침수인 것에 반해 경상북도와 강원도 지역의 피해는 침수면적과의 상관관계가 적어 침수보다는 다른 요인에 의한 공공시설물의 피해가 크다. 홍수 피해액이 홍수 피해의 영향과 이에 대한 대응조치가 동시에 작용하여 나오는 결과물이라고 할 때, 본 연구의 피해액을 이용한 취약성 평가는 향후 기후환경변화에 따른 간접적인 지표로 사용될 수 있다.