• 콘크리트학회논문집
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• 제22권1호
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• pp.29-39
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• 2010

이 연구에서는 고강도 콘크리트의 전열특성 및 화재거동을 구명하기 위해 실증실험과 수치해석을 병행하였으며, 화재실험조건 및 제약 상황으로 인해 실험을 통해 도출할 수 없는 고강도 콘크리트의 화재성상은 수치해석을 통해 예측하였다. 이를 위해 수치해석결과와 실험 결과를 비교 검증하여 해석기법의 신뢰성을 확보하였으며, 80 MPa 및 100 MPa의 고강도 콘크리트의 전열특성 및 화재거동을 상용 소프트웨어인 아바쿠스(V.6.8)를 사용하여 수치해석을 수행하였다. 실증실험결과 폭렬저감재를 혼입한 콘크리트의 경우 무 혼입 콘크리트에 비해 표준화재조건에서 약 25~55% 정도의 기둥 수축량이 제어되어 내화성능이 향상되었으며, 이는 섬유혼입으로 인해 콘크리트의 전열특성이 제어되어 기둥부재의 내화성능을 향상시키기 때문이다.

• 한국건설순환자원학회논문집
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• 제3권1호
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• pp.54-64
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• 2007

This study is a fundamental research in order to establish the design code of recycled aggregate concrete structure. The structural properties of recycled aggregate concrete such as flexure, shear, fatigue, compression, and bond development are experimentally investigated and confirmed. In this study, laboratory-scale reinforced concrete beam, column, and pull-out test specimens using recycled coarse aggregate are manufactured. Then, the structural performances of recycled aggregate concrete according to replacement ratios of recycled coarse aggregate are evaluated. Also, finite element analysis using commercial code DIANA is carried out to predict the test results and the analysis results are compared with test results in this study. Structural test results showed that the structural performances of recycled aggregate concrete specimens with 60% replacement ratio are reduced by approximately 15-20%. These results indicated that the replacement ratio of recycled coarse aggregate within 30% is a suitable to use for structural members. The results of finite element analysis showed that the specimens with 30% replacement ratio possessed similar or more excellent structural performance than normal concrete specimens. However, recycled aggregate concrete with 60% replacement ratio of recycled coarse aggregate must be carefully considered for structural applications due to significant decrease of the failure loads.

• Interaction and multiscale mechanics
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• 제3권1호
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• pp.55-79
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• 2010

The effect of soil-structure interaction on a single-storey, two-bay space frame resting on a pile group embedded in the cohesive soil (clay) with flexible cap is examined in this paper. For this purpose, a more rational approach is resorted to using the finite element analysis with realistic assumptions. Initially, a 3-D FEA is carried out independently for the frame on the premise of fixed column bases in which members of the superstructure are discretized using the 20-node isoparametric continuum elements. Later, a model is worked out separately for the pile foundation, by using the beam elements, plate elements and spring elements to model the pile, pile cap and soil, respectively. The stiffness obtained for the foundation is used in the interaction analysis of the frame to quantify the effect of soil-structure interaction on the response of the superstructure. In the parametric study using the substructure approach (uncoupled analysis), the effects of pile spacing, pile configuration, and pile diameter of the pile group on the response of superstructure are evaluated. The responses of the superstructure considered include the displacement at top of the frame and moments in the columns. The effect of soil-structure interaction is found to be quite significant for the type of foundation considered in the study. Fair agreement is observed between the results obtained herein using the simplified models for the pile foundation and those existing in the literature based on a complete three dimensional analysis of the building frame - pile foundation - soil system.

• Steel and Composite Structures
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• 제18권5호
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• pp.1083-1101
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• 2015

Previous theoretical equations for the shear capacity of steel beam to concrete filled steel tube (CFT) column connections vary in the assumptions for the shear deformation mechanisms and adopt different equations for calculating shear strength of each component (steel tube webs, steel tube flanges, diaphragms, and concrete etc.); thus result in different equations for calculating shear strength of the joint. Besides, shear force-deformation relations of the joint, needed for estimating building drift, are not well developed at the present. This paper compares previously proposed equations for joint shear capacity, discusses the shear deformation mechanism of the joint, and suggests recommendations for obtaining more accurate predictions. Finite element analyses of internal diaphragm connections to CFT columns were carried out in ABAQUS. ABAQUS results and theoretical estimations of the shear capacities were then used to calibrate rotational springs in joint elements in OpenSEES simulating the shear deformation behavior of the joint. The ABAQUS and OpenSEES results were validated with experimental results available. Results show that: (1) shear deformation of the steel tube dominates the deformation of the joint; while the thickness of the diaphragms has a negligible effect; (2) in OpenSEES simulation, the joint behavior is highly dependent on the yielding strength given to the rotational spring; and (3) axial force ratio has a significant effect on the joint deformation of the specimen analyzed. Finally, modified joint shear force-deformation relations are proposed based on previous theory.

• Structural Engineering and Mechanics
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• 제39권2호
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• pp.241-266
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• 2011

The Self Compacting Concrete, SCC is the new generation type of concrete which is not needed to be compacted by vibrator and it will be compacted by its own weight. Since SCC is a new innovation and also the high strength self compacting concrete, HSSCC behavior is like a brittle material, therefore, understanding the strength effect on the serviceability performance of reinforced self compacting concretes is critical. For this aim, first the normal and high strength self compacting concrete, NSSCC and HSSCC was designed. Then, the serviceability performance of reinforced connections consisting of NSSCC and HSSCC were investigated. Twelve reinforced concrete connections (L = 3 m, b = 0.15 m, h = 0.3 m) were simulated, by this concretes, the maximum and minimum reinforcement ratios ${\rho}$ and ${\rho}^{\prime}$ (percentage of tensile and compressive steel reinforcement) are in accordance with the provision of the ACI-05 for conventional RC structures. This study was limited to the case of bending without axial load, utilizing simple connections loaded at mid span through a stub (b = 0.15 m, h = 0.3 m, L = 0.3 m) to simulate a beam-column connection. During the test, concrete and steel strains, deflections and crack widths were measured at different locations along each member. Based on the experimental readings and observations, the cracked moment of inertia ($I_{cr}$) of members was determined and the results were compared with some selective theoretical methods. Also, the flexural crack widths of the members were measured and the applicability for conventional vibrated concrete, as for ACI, BS and CSA code, was verified for SCCs members tested. A comparison between two Codes (ACI and CSA) for the theoretical values cracking moment is indicate that, irrespective of the concrete strength, for the specimens reported, the prediction values of two codes are almost equale. The experimental cracked moment of inertia $(I_{cr})_{\exp}$ is lower than its theoretical $(I_{cr})_{th}$ values, and therefore theoretically it is overestimated. Also, a general conclusion is that, by increasing the percentage of ${\rho}$, the value of $I_{cr}$ is increased.

• Structural Engineering and Mechanics
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• 제31권2호
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• pp.163-180
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• 2009

In the design of tall reinforced concrete (R/C) buildings, the serviceability stiffness criteria in terms of maximum lateral displacement and inter-story drift must be satisfied to prevent large second-order P-delta effects. To accurately assess the lateral deflection and stiffness of tall R/C structures, cracked members in these structures need to be identified and their effective member flexural stiffness determined. In addition, the implementation of the geometric nonlinearity in the analysis can be significant for an accurate prediction of lateral deflection of the structure, particularly in the case of tall R/C building under lateral loading. It can therefore be important to consider the cracking effect together with the geometric nonlinearity in the analysis in order to obtain more accurate results. In the present study, a computer program based on the iterative procedure has been developed for the three dimensional analysis of reinforced concrete frames with cracked beam and column elements. Probability-based effective stiffness model is used for the effective flexural stiffness of a cracked member. In the analysis, the geometric nonlinearity due to the interaction of axial force and bending moment and the displacements of joints are also taken into account. The analytical procedure has been demonstrated through the application of R/C frame examples in which its accuracy and efficiency in comparison with experimental and other analytical results are verified. The effectiveness of the analytical procedure is also illustrated through a practical four story R/C frame example. The iterative procedure provides equally good and consistent prediction of lateral deflection and effective flexural member stiffness. The proposed analytical procedure is efficient from the viewpoints of computational effort and convergence rate.

• Steel and Composite Structures
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• 제10권3호
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• pp.207-222
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• 2010

Fire incident in buildings is common, so the fire safety design of the framed structure is imperative, especially for the unprotected or partly protected bare steel frames. However, software for structural fire analysis is not widely available. As a result, the performance-based structural fire design is urged on the basis of using user-friendly and conventional nonlinear computer analysis programs so that engineers do not need to acquire new structural analysis software for structural fire analysis and design. The tool is desired to have the capacity of simulating the different fire scenarios and associated detrimental effects efficiently, which includes second-order P-D and P-d effects and material yielding. Also the nonlinear behaviour of large-scale structure becomes complicated when under fire, and thus its simulation relies on an efficient and effective numerical analysis to cope with intricate nonlinear effects due to fire. To this end, the present fire study utilizes a second-order elastic/plastic analysis software NIDA to predict structural behaviour of bare steel framed structures at elevated temperatures. This fire study considers thermal expansion and material degradation due to heating. Degradation of material strength with increasing temperature is included by a set of temperature-stress-strain curves according to BS5950 Part 8 mainly, which implicitly allows for creep deformation. This finite element stiffness formulation of beam-column elements is derived from the fifth-order PEP element which facilitates the computer modeling by one member per element. The Newton-Raphson method is used in the nonlinear solution procedure in order to trace the nonlinear equilibrium path at specified elevated temperatures. Several numerical and experimental verifications of framed structures are presented and compared against solutions in literature. The proposed method permits engineers to adopt the performance-based structural fire analysis and design using typical second-order nonlinear structural analysis software.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.675-684
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• 2020

An innovative retrofit method using pre-stressed steel strips and externally-bonded steel plates was presented in this paper. With the aim of exploring the seismic performance of the retrofitted RC interior joints, four 1/2-scale retrofitted joint specimens together with one control specimen were designed and subjected to constant axial compression and cyclic loading, with the main test parameters being the volume of steel strips and the existence of externally-bonded steel plates. The damage mechanism, force-displacement hysteretic response, force-displacement envelop curve, energy dissipation and displacement ductility ratio were analyzed to investigate the cyclic behavior of the retrofitted joints. The test results indicated that all the test specimens suffered a typical shear failure at the joint core, and the application of externally-bonded steel plates and that of pre-stressed steel strips could effectively increase the lateral capacity and deformability of the deficient RC interior joints, respectively. The best cyclic behavior could be found in the deficient RC interior joint retrofitted using both externally-bonded steel plates and pre-stressed steel strips due to the increased lateral capacity, displacement ductility and energy dissipation. Finally, based on the test results and the softened strut and tie model, a theoretical model for determining the shear capacity of the retrofitted specimens was proposed and validated.

• 한국전산구조공학회논문집
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• 제25권4호
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• pp.363-372
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• 2012

본 논문에서는 수학적 구조 모델과 인공신경망 기법을 상호 유기적으로 결합하여 구조물의 거동 데이터로부터 부재모델 또는 재료모델의 정확도를 높이는 정보기반 하이브리드 모델 업데이트 기법을 개발하였다. 유한요소와 같은 수학적 모델을 사용하여 구조물의 거동을 모사하기 위해서는 재료, 부재, 그리고 시스템의 정확한 모델링이 우선하여야 한다. 그러나 재료, 부재의 각 레벨에서의 수학적인 모델은 이상화과정을 거치면서 중요한 특성을 생략하거나, 시스템 구성시 부재간의 상호작용이나 경계조건의 단순화로 인해 유한요소 모델은 실제 구조물의 거동과 차이를 보이게 된다. 본 논문에서 제시된 하이브리드 모델 업데이트 기법은 구조물의 거동과 수학적 모델의 해석결과 차이를 인공신경망 기법을 사용하여 보완함으로써 시스템 모델의 정확도를 높일 수 있다. 이때 시스템의 거동 데이터로부터 부재 또는 재료모델을 개선할 수 있는 데이터를 추출하여 부재 또는 재료모델을 개선한다. 제시된 기법은 보-기둥 접합부의 이력모델을 개선하는 것으로 검증하였으며, 복잡한 거동을 보이는 시스템 모델링에 광범위하게 사용될 수 있다.

• 한국전산구조공학회논문집
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• 제23권1호
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• pp.111-119
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• 2010

여러 연구자들에 의해 최적화 알고리즘을 이용한 최적내진설계에 관한 연구가 컴퓨터의 발달과 더불어 활발히 이루어져 왔다. 하지만 지금까지의 최적내진설계에 관한 연구는 대부분 모멘트저항골조를 대상구조물로 한 연구였다. 가새골조는 모멘트저항골조와 더불어 대표적인 횡력저항시스템이기 때문에 가새골조의 최적내진설계기법 개발을 통해 경제적이며 효율적인 설계가이드라인을 제시할 수 있다면 실무에 미치는 파급효과는 클 것이라 판단된다. 본 논문에서는 가새의 좌굴을 고려한 역V형 특수중심가새골조의 최적내진설계 알고리즘을 제안하고자 한다. 제안된 알고리즘은 구조물의 물량과 에너지 소산량을 목적함수로 설정하고, 강도조건 및 층간변위 조건등의 제약조건으로 설정한다. 알고리즘의 검증을 위해 2D 3층, 9층 역V형 특수중심가새골조 예제를 적용한다.