• Ocean Systems Engineering
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• 제8권1호
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• pp.21-32
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• 2018

Due to the escalation in hydrocarbon consumption, the offshore industry is now looking for advanced technology to be employed for deep sea exploration. Riser system is an integral part of floating structure used for such oil and gas extraction from deep water offering a system of drill twines and production tubing to spread the exploration well towards the ocean bed. Thus, the marine risers need to be precisely employed. The incorporation of the strengthening material, fiber reinforced polymer (FRP) for deep and ultra-deep water riser has drawn extensive curiosity in offshore engineering as it might offer potential weight savings and improved durability. The design for FRP strengthening involves the local design for critical loads along with the global analysis under all possible nonlinearities and imposed loadings such as platform motion, gravity, buoyancy, wave force, hydrostatic pressure, current etc. for computing and evaluating critical situations. Finite element package, ABAQUS/AQUA is the competent tool to analyze the static and dynamic responses under the offshore hydrodynamic loads. The necessities in design and operating conditions are studied. The study includes describing the methodology, procedure of analysis and the local design of composite riser. The responses and fatigue damage characteristics of the risers are explored for the effects of FRP strengthening. A detail assessment on the technical expansion of strengthening riser has been outlined comprising the inquiry on its behavior. The enquiry exemplifies the strengthening of riser as very potential idea and suitable in marine structures to explore oil and gas in deep sea.

• Steel and Composite Structures
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• 제31권6호
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• pp.617-628
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• 2019

As an extremely destructive accident, progressive collapse is defined as the spread of an initial local failure from element to element, resulting eventually in the collapse of an entire structure or disproportionately large of it. To prevent the occurrence of it and evaluate the ability of structure resisting progressive collapse, the nonlinear static procedure is usually adopted in the whole structure design process, which considered dynamic effect by utilizing Dynamic Increase Factor (DIF). In current researches, the determining of DIF is performed in full-rigid frame, however, the performance of beam-column connection in the majority of existing frame structures is not full-rigid. In this study, based on the component method proposed by EC3 guideline, the expression of extended endplate connection performance is further derived, and the connection performance is taken into consideration when evaluated the performance of structure resisting progressive collapse by applying the revised plastic P-M hinge. The DIF for structures with extended endplate beam-column connection have been determined and compared with the DIF permitted in current GSA guideline, the necessity of considering connection stiffness in determining the DIF have been proved.

• 한국지진공학회논문집
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• 제25권6호
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• pp.293-303
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• 2021

Seismic fragility functions for unreinforced masonry buildings were derived based on the incremental dynamic analysis of eight representative inelastic numerical models for application to Korea's earthquake damage estimation system. The effects of panel zones formed between piers and spandrels around openings were taken into account explicitly or implicitly regarding stiffness and inelastic deformation capacity. The site response of ground motion records measured at the rock site was used as input ground motion. Limit states were proposed based on the fraction of structural components that do not meet the required performance from the nonlinear static analysis of each model. In addition to the randomness of ground motion considered in the incremental dynamic analysis explicitly, supplementary standard deviation due to uncertainty that was not reflected in the fragility assessment procedure was added. The proposed seismic fragility functions were verified by applying them to the damage estimation of masonry buildings located around the epicenter of the 2017 Pohang earthquake and comparing the result with actual damage statistics.

• Steel and Composite Structures
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• 제49권1호
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• pp.47-64
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• 2023

Due to their efficient use of materials, hybrid reinforced concrete-steel (RCS) systems provide more practical and economic advantages than traditional steel and concrete moment frames. This study evaluated the seismic design factors and response modification factor 'R' of RCS composite moment frames composed of reinforced concrete (RC) columns and steel (S) beams. The current International Building Code (IBC) and ASCE/SEI 7-05 classify RCS systems as special moment frames and provide an R factor of 8 for these systems. In this study, seismic design parameters were initially quantified for this structural system using an R factor of 8 based on the global methodology provided in FEMA P695. For analyses, multi-story (3, 5, 10, and 15) and multi-span (3 and 5) archetypes were used to conduct nonlinear static pushover analysis and incremental dynamic analysis (IDA) under near-field and far-field ground motions. The analyses were performed using the OpenSees software. The procedure was reiterated with a larger R factor of 9. Results of the performance evaluation of the investigated archetypes demonstrated that an R factor of 9 achieved the safety margin against collapse outlined by FEMA P695 and can be used for the design of RCS systems.

• 한국지반공학회논문집
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• 제21권6호
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• pp.67-79
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• 2005

현장 평판재하시험은 평판에 작용하는 하중과 변위를 동시에 측정하기 때문에 역학적인 특성치 결정의 가능성이 높은 시험방법이다. 그러나 지금까지 평판재하시험으로부터 추정한 탄성계수는 일정 변위를 유발한 하중강도하에서의 지지력계수로부터 구한 하나의 상수값으로서, 이는 포장구조에서 노상이 경험하는 사용하중 단계에서의 대표적인 변형특성치로 결정하기에는 어려움이 있다. 포장설계시 사용되는 회복탄성계수 개념의 변형계수는 중간변형률$(0.01\%\sim0.1\%)$ 영역에서의 값으로서, 현장 노상토의 경우에도 이와 같은 변형률 범위에서의 변형계수를 평가하는 것이 중요하다. 본 논문에서는 노상 현장에서 반복평판재하시험을 이용하여 중간변형률 영역에서의 변형계수를 산정하는 방법을 제안하였다. 이의 신뢰성을 검토하기 위하여 현장에서 크로스홀 시험과 실내에서 공진주시험을 수행하여 전체변형률 영역에서의 현장의 변형특성을 평가하여 평판재하시험 결과와 비교하였다. 두 시험결과 사이의 응력상태를 고려하면 변형률에 따른 변형계수의 값과 경향이 비교적 일치하였고, 제안된 반복식 평판재하시험을통해 현장변형계수의 평가가 가능함을 알 수 있었다.

• 한국지진공학회논문집
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• 제18권1호
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• pp.37-43
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• 2014

In current seismic design code, steel moment frames are classified into ordinary, intermediate, and special moment frames. In the case of special moment frames which have large R-factor, economic design is possible by reducing the design lateral force. However, there is difficulty for practical application due to constraints such as strong column-weak beam requirement. This study evaluated if steel intermediate moment frame could maintain enough seismic capacity when the R-factor is increased from 4.5 to 6. As for the analytical models, steel moment frames of 3 and 5 stories were categorized into four performance groups according to seismic design category. Seismic performances of the frames were evaluated through the procedure based on FEMA P695. FEMA P695 utilizes nonlinear static analysis(pushover analysis) and nonlinear dynamic analysis(incremental dynamic analysis, IDA). In order to reflect the characteristics of Korean steel moment frames on the analytical model, the beam-column connection was modeled as weak panel zone where the collapse of panel zone was indirectly considered by checking its ultimate rotational angle after an analysis is done. The analysis result showed that the performance criteria required by FEMA P695 was satisfied when R-factor increased in all the soil conditions except $S_E$.

• 대한토목학회논문집
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• 제8권2호
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• pp.13-24
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• 1988

본(本) 논문(論文)은 평면(平面)뼈대 구조물(構造物)의 동적(動的) 후좌굴(後座屈) 거동(擧動)을 파악(把握)하기 위하여 기하적(幾何的)인 비선형(非線型) 유한요소법(有限要素法)을 제시(提示)한다. 이를 위하여 3차원(次元) 연속체(連續體)에 대한 가상(假想)일의 원리(原理)에 배루누이-오일러 가정을 도입하므로서, 평면(平面)뼈대에 대한 탄성강도(彈性剛度)매트릭스, 기하적(幾何的)인 강도(剛度)매트릭스 그리고 질량(質量)매트릭스들을 유도한다. circulatory force를 받는 경우에는 circulatory discrete joint load와 circulatory distributed load에 대한 load correction stiffness matrix를 유도하므로써 이러한 하중을 받는 구조물(構造物)의 접선강도(接線剛度)매트릭스는 비대칭 행렬임을 보인다. 유도된 비선형(非線型) 운동방정식(運動方程式)의 해(解)는 Newton-Raphson 방법(方法) 및 Newmark 방법(方法)을 사용(便用)하여 구한다.

• 한국농공학회지
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• 제40권5호
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• pp.91-99
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• 1998

The widespread use of thin shell structures has created a need for a systematic method of analysis which can adequately account for arbitrary geometric form and boundary conditions as well as arbitrary general type of loading. Therefore, the stress and analysis of thin shell has been one of the more challenging areas of structural mechanics. A wide variety of numerical methods have been applied to the governing differential equations for spherical and cylindrical structures with a few results applicable to practice. The analysis of axisymmetric spherical shell is almost an every day occurrence in many industrial applications. A reliable and accurate finite element analysis procedure for such structures was needed. Dynamic loading of structures often causes excursions of stresses well into the inelastic range and the influence of geometry changes on the response is also significant in many cases. Therefore both material and geometric nonlinear effects should be considered. In general, the shell structures designed according to quasi-static analysis may fail under conditions of dynamic loading. For a more realistic prediction on the load carrying capacity of these shell, in addition to the dynamic effect, consideration should also include other factors such as nonlinearities in both material and geometry since these factors, in different manner, may also affect the magnitude of this capacity. The objective of this paper is to demonstrate the dynamic characteristics of spherical shell. For these purposes, the spherical shell subjected to uniformly distributed step load was analyzed for its large displacements elasto-viscoplastic static and dynamic response. Geometrically nonlinear behaviour is taken into account using a Total Lagrangian formulation and the material behaviour is assumed to elasto-viscoplastic model highly corresponding to the real behaviour of the material. The results for the dynamic characteristics of spherical shell in the cases under various conditions of base-radius/central height(a/H) and thickness/shell radius(t/R) were summarized as follows : The dynamic characteristics with a/H. 1) AS the a/H increases, the amplitude of displacement in creased. 2) The values of displacement dynamic magnification factor (DMF) were ranges from 2.9 to 6.3 in the crown of shell and the values of factor in the mid-point of shell were ranged from 1.8 to 2.6. 3) As the a/H increases, the values of DMF in the crown of shell is decreased rapidly but the values of DMF in mid-point shell is increased gradually. 4) The values of DMF of hoop-stresses were range from 3.6 to 6.8 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.3 to 2.6, and the values of DMF of stress were larger than that of displacement. The dynamic characteristics with t/R. 5) With the thickness of shell decreases, the amplitude of the displacement and the period increased. 6) The values of DMF of the displacement were ranged from 2.8 to 3.6 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.1 to 2.2.

• 한국지진공학회논문집
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• 제8권1호
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• pp.67-76
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• 2004

본 연구는 콘크리트 교량의 지진취약도 곡선을 개발함에 있어 성능 스펙트럼 기법(Capacity Spectrum Method)에 대한 고찰을 통해 가장 적절한 해석방법을 제시하는데 그 목적이 있다. 원래 성능 스펙트럼 기법은 빌딩 구조물을 위한 간략화된 정적 비선형 해석의 일환으로 개발되었는 바, 본 연구에서는 이 기법을 교량의 지진취약도 곡선을 개발하는데 응용하였다. 서로 다른 네가지의 방법으로 성능 스펙트럼 기법을 통해 구해진 취약도 곡선들을 비선형 시간이력해석 방법에 의해 구해진 취약도 곡선과 비교하였다. 취약도 곡선은 두 개의 변수를 가진 lognormal 분포를 따르는 것으로 가정하였으며 PGA(Peak Ground Acceleration)의 함수로 나타내어졌다. FEMA(Federal Emergency Management Agency) SAC(SEAOC-ATC-CUREe) steel 프로젝트에 의해 개발된 로스앤젤레스 지역 60개의 지진이 교량해석을 위해 사용되었다. 성능 스펙트럼 기법과 시간이력해석에 따라 만들어진 교량의 지진취약도 곡선들을 비교 검토한 바, 이 중 하나의 방법이 부합되는 결과를 보여주었다. 요구 스펙트럼 작성시 본 논문에서 제시된 지침을 따르면 비선형 시간이력 해석시와 유사한 결과를 얻을 수 있을 것으로 사료된다. 다만 지진과 교량이 지닌 특수성으로 인해 본 연구의 결과가 항상 적용되는지는 더 심도있는 연구를 통해 검증되어야 할 것이다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권4호
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• pp.65-72
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• 2022

최근 국내 지진으로 인한 건축물의 피해는 주로 학교건물과 필로티형 다가구 주택에서 발생함으로써 동일한 형식의 건물에 대한 내진보강 필요성을 부각시켰다. 학교시설 내진보강사업은 초기에 연성보강방법으로서 댐퍼를 활용한 다양한 특허공법들이 충분한 검증 절차 없이 적용되었다. 그러나 「학교시설 내진성능평가 및 보강 매뉴얼, 2021」에서는 특허공법 적용시 별도의 엄격한 검증절차를 통하여 적용토록 하고 대신 일반공법으로서 강도/강성보강공법의 활성화를 유도하였다. 학교건물의 강도/강성 보강공법으로서 활발히 적용되고 있는 철골 끼움가새골조보강을 위한 내진선능평가 시 실무에서는 일부 제한된 조건에서 안전측의 내진성능평가 결과를 도출할 것으로 판단하여 기존 RC 부재에 철골가새만을 직접연결하여 해석모델을 구성하고 있다. 그러나 철골 끼움가새골조의 해석모델에서 프레임을 제거할 경우 강성감소로 인한 보강 부근의 기존 RC부재에 발생하는 하중감소는 매우 클 것으로 사료되며 이는 보강부위 기초보강 유무 검토에도 영향을 미칠 것으로 판단된다. 따라서 본 연구에서는 철골 끼움가새골조를 이용하여 저층 RC 학교건물 내진보강 시 성능평가를 위한 해석모델에 대하여 철골 프레임 고려 유무, 프레임 링크방식 등을 변수로 한 예비해석과 실제 3층 학교 건물에 대한 비선형 정적해석에 따른 내진성능평가 를 수행하였으며, 변수별 예비해석 및 푸쉬오버 해석결과를 비교함으로써 합리적인 해석모델 설정을 위한 기초자료를 제시하였다.