• Earthquakes and Structures
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• 제8권6호
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• pp.1499-1528
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• 2015

The yielding mechanisms of reinforced concrete (RC) structures are the main cause of the collapse of RC buildings during earthquake excitation. Nowadays, the application of earthquake energy dissipation devices, such as viscous dampers (VDs), is being widely considered to protect RC structures which are designed to withstand severe seismic loads. However, the effect of VDs on the formation of plastic hinges and the yielding criteria of RC members has not been investigated extensively, due to the lack of an analytical model and a numerical means to evaluate the seismic response of structures. Therefore, this paper offers a comprehensive investigation of how damper devices influence the yielding mechanisms of RC buildings subjected to seismic excitation. For this purpose, adapting the Newmark method, a finite element algorithm was developed for the nonlinear dynamic analysis of reinforced concrete buildings equipped with VDs that are subjected to earthquake. A special finite element computer program was codified based on the developed algorithm. Finally, a parametric study was conducted for a three-story RC building equipped with supplementary VD devices, performing a nonlinear analysis in order to evaluate its effect on seismic damage and on the response of the structure. The results of this study showed that implementing VDs substantially changes the mechanism and formation of plastic hinges in RC buildings.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.137-140
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• 2005

This paper focuses on the premature failure of RC beams bonded with FRP. A number of failure modes for RC beams bonded with FRP have been observed in numerous experimental studies during past decade. Particularly, Rip-off failure and Debonding failure were majority failure modes in RC beams bonded with FRP. Rip-off failure occurred at the plate end due to high interfacial shear and normal stresses however Debonding failure was caused by the yielding of reinforcing bar and the increasing of shear deformation in shear span. On the basis of premature failure mechanism in RC beams bonded with FRP, Basic strengthening length and Premature failure criteria were derived

• Smart Structures and Systems
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• 제23권4호
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• pp.329-335
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• 2019

Structural fuses are made up from oriented steel plates to be used to resist seismic force with shear loading resistance capabilities. The damage and excessive inelastic deformations are concentrated in structural fuses to avoid any issues for the rest of the surrounding elements. Recently developed fuse plates are designed with engineered cutouts leaving flexural or shear links with controlled yielding features. A promising type of link is proposed to align better bending strength along the length of the link with the demand moment diagram is a butterfly-shaped link. Previously, the design methodologies are purely based on the flexural stresses, or shear stresses only, which overestimate the dampers capability for resisting against the applied loadings. This study is specifically focused on the optimized design methodologies for commonly used butterfly-shaped dampers. Numerous studies have shown that the stresses are not uniformly distributed along the length of the dampers; hence, the design methodology and the effective implementation of the steel need revisions and improvements. In this study, the effect of shear and flexural stresses on the behavior of butterfly-shaped links are computationally investigated. The mathematical models based on von-Mises yielding criteria are initially developed and the optimized design methodology is proposed based on the yielding criterion. The optimized design is refined and investigated with the aid of computational investigations in the next step. The proposed design methodology meets the needs of optimized design concepts for butterfly-shaped dampers considering the uniform stress distribution and efficient use of steel.

• Steel and Composite Structures
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• 제23권3호
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• pp.285-302
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• 2017

Buckling-restrained braced frames (BRBFs) are commonly used as the lateral force-resisting systems in building structures in the seismic regions. The nearly-symmetric hysteretic response and the delayed brace core fracture of buckling-restrained braces (BRBs) under the axial cyclic loading provide the adequate lateral force and deformation capacity to BRBFs under the earthquake excitation. However, the smaller axial stiffness of BRBs result in the undesirable higher residual drift response of BRBFs in the post-earthquake scenario. Two alternative approaches are investigated in this study to improve the elastic axial stiffness of BRBs, namely, (i) by shortening the yielding cores of BRBs; and (ii) by reducing the BRB assemblies and adding the elastic brace segments in series. In order to obtain the limiting yielding core lengths of BRBs, a modified approach based on Coffin-Manson relationship and the higher mode compression buckling criteria has been proposed in this study. Both non-linear static and dynamic analyses are carried out to analytically evaluate the seismic response of BRBFs fitted with short-core BRBs of two medium-rise building frames. Analysis results showed that the proposed brace systems are effective in reducing the inter-story and residual drift response of braced frames without any significant change in the story shear and the displacement ductility demands.

• Structural Engineering and Mechanics
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• 제67권6호
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• pp.587-601
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• 2018

Elevated water tanks are inverted pendulum type structures where drift limit is an important criterion for seismic design and performance evaluation. Explicit drift criteria for elevated water tanks are not available in the literature. In this study, probabilistic approach is used to determine maximum drift limit for damage state of yielding and damage state of collapse for the elevated water tanks supported on RC frame staging. The two damage states are defined using results of incremental dynamic analysis wherein a total of 2160 nonlinear time history analyses are performed using twelve artificial spectrum compatible ground motions. Analytical fragility curves are developed using two-parameter lognormal distribution. The maximum allowable drifts corresponding to yield and collapse level requirements are estimated for different tank capacities. Finally, a single fragility curve is developed which provides maximum drift values for the different probability of damage. Further, for rational consideration of the uncertainties in design, three confidence levels are selected and corresponding drift limits for damage states of yielding and collapse are proposed. These values of maximum drift can be used in performance-based seismic design for a particular damage state depending on the level of confidence.

• 대한조선학회지
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• 제24권3호
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• pp.43-51
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• 1987

In this paper, dynamic elastic, plastic response of beam-columns is analysed using discrete models. composed of rigid bars and springs. The equation of motion is formulated including the shear deformation effect, and the stress change of yielding points is calculated with various yielding criteria. The effect of initial axial force is considered by two ways: (1) including the effect in interaction curve only. (2) including the effect directly in the equation of motion in terms of initial stiffness method is also used in nonlinear interaction procedure. It is found that this model is very effective in analysing not only the plastic response but the elastic response, and present method is more efficient than Finite Element Method from the viewpoint of calculation time and accuracy.

• Advances in concrete construction
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• 제6권2호
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• pp.123-143
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• 2018

Self compacting concrete (SCC) has good flowability, passability and segregation resistance because of voluminous cementitious material & high coarse aggregate to fine aggregate ratio, and high free water availability. But these factors make it highly susceptible to shrinkage. Fibers are known to reduce shrinkage in concrete mixes. Until now for conserving cement, only pozzolanic materials are admixed in concrete to yield a SCC. Hence, this study compares the use of wollastonite micro fiber (WMF), a cheap pozzolanic easily processed raw mineral fiber, and flyash in yielding economical SCC for rigid pavement. Microsilica was used as a complimentary material with both admixtures. Since WMF has large surface area ($827m^2/kg$), is acicular in nature; therefore its use in yielding SCC was dubious. Binary and ternary mixes were constituted for WMF and flyash, respectively. Paste mixes were tested for compatibility with superplasticizer and trials were performed on a normal concrete mix of flexural strength 4.5 MPa to yield SCC. Flexural strength test and restrained shrinkage test were performed on those mixes, which qualified self compacting criteria. Results revealed that WMF admixed pastes have high water demand, and comparable setting times to flyash mixes. Workability tests showed that 20% WMF with microsilica (5-7.5%) is efficient enough in achieving SCC and higher flexural strength than normal concrete at 90 days. Also, stress rate due to shrinkage was lesser and time duration for final strain was higher in WMF admixed SCC which encourages its use in yielding a SCC than pozzolanic materials.

• 대한산업공학회지
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• 제37권4호
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• pp.358-366
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• 2011

Multi-criteria ABC inventory classification, which aims to classify inventory items by considering more than one criterion, is one of the most widely employed techniques for inventory control. The weighted linear optimization (WLO) model proposed by Ramanathan (2006) solves the problem of multi-criteria ABC inventory classification by generating a set of criterion weights for each inventory item and assigning a normalized score to the item for ABC analysis. However, the WLO model has some limitations. First, many inventory items can share the same optimal score, which can hinder a precise classification of inventory items. Second, the model allows too much flexibility in weighting multiple criteria; each item is allowed to choose its own weights so that it can maximize its score. As a result, if an item dominates the others in terms of a certain criterion, it may be classified into a higher class regardless of other criteria by assigning an overwhelming weight to the criterion. Consequently, an item with a high value in an unimportant criterion and low values in others may be inappropriately classified as class A, leading to an inaccurate classification of inventory items. To overcome these shortcomings, we extend the WLO model by using the cross-efficiency method in data envelopment analysis. We claim that the proposed model can provide a more reasonable and accurate classification of inventory items by mitigating the adverse effect of flexibility in the choice of weights and yielding a unique ordering of inventory items.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.781-790
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• 2022

The present paper describes a general procedure of the structural safety assessment for the independent type C tank of LNG bunkering ship. This strength assessment procedure consists of two main scheme, global Finite Element Analysis (FEA) model primarily for hull structure assessment and detailed LNG Tank structures FEA model including the cylindrical tank itself and saddle-support structures. Two kinds of mechanism are used, fixed and slides constraints in fore and rear of the saddle-support structures that result in a variation of the reaction forces. Finite Element (FE) analyses have been performed and verified by the strength acceptance criteria to evaluate the safety adequacy of yielding and buckling of the hull and supporting structures. The detail of FE model for an LNG type C tank and its saddle supports was made, which includes the structural members such as cylindrical tank shell, ring stiffeners, swash bulkhead, and saddle supports. Subsequently, the FE buckling analysis of the Type C tank has been performed under external pressure following International Gas Containment (IGC) code requirements. Meanwhile, the assessment is also performed for yielding and buckling strength evaluation of the cylindrical LNG tank according to the PD 5500 unfired fusion welded pressure vessels code. Finally, a complete procedure for assessing the structural strength of 500 CBM LNG cargo tank, saddle support and hull structures have been provided.

• 한국강구조학회 논문집
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• 제25권2호
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• pp.131-139
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• 2013

본 연구의 목적은 H-형강 압축재의 온도상승에 따른 파괴거동을 중심으로 압축력과 파괴온도의 상관관계를 파악하기 위한 실험을 수행하는 것이다. SS400 강재로 제작된 H-형강의 시험체를 선정하여, ISO 834의 재하가열 시험방법에 따라 온도 상승에 대한 실험을 한국방재시험연구원(FILK)에서 수행하였다. 고온상태의 강재에 대한 항복강도 및 탄성계수의 감소계수는 EC3 (Eurocode3) Part 1.2 (1993) 관계식을 근거로 하여 파괴온도시 국부 및 전체좌굴 응력도와 항복응력도를 실험결과와 비교 검토하였다. 실험조건은 세장비 45.4이고 상온에서의 항복내력에 대한 50%, 70%, 80%를 재하압축력으로 설정하여 파괴온도를 측정하였다. 파괴온도와 재하압축력에 대한 실험결과로 부터 온도상승에 따른 내력은 탄성 좌굴강도보다는 항복내력에 근접함을 파악할 수 있었다.