• Structural Engineering and Mechanics
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• 제55권3호
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• pp.461-472
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• 2015

The existence of initial imperfections in manufacturing or assembly of double-layer space structures having hundreds or thousands of members is inevitable. Many of the imperfections, such as the initial curvature of the members and residual stresses in members, are all random in nature. In this paper, the probabilistic effect of initial curvature imperfections in the load bearing capacity of double-layer grid space structures with different types of supports have been investigated. First, for the initial curvature imperfection of each member, a random number is generated from a gamma distribution. Then, by employing the same probabilistic model, the imperfections are randomly distributed amongst the members of the structure. Afterwards, the collapse behavior and the ultimate bearing capacity of the structure are determined by using nonlinear push down analysis and this procedure is frequently repeated. Ultimately, based on the maximum values of bearing capacity acquired from the analysis of different samples, structure's reliability is obtained by using Monte Carlo simulation method. The results show the sensitivity of the collapse behavior of double-layer grid space structures to the random distribution of initial imperfections and supports type.

• Geomechanics and Engineering
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• 제31권6호
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• pp.599-614
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• 2022

One of the methods of stabilizing retaining walls, embankments, and deep excavations is the implementation of plate anchors (like the Geolock wall anchor systems). Back-to-back Mechanically Stabilized Earth (BBMSE) walls are common stabilized earth structures that can be used for bridge ramps. But so far, the analysis of the interactive behavior of two back-to-back anchored walls (BBAW) by double-plates anchors (constructed closely from each other and subjected to the limited-breadth vertical loading) including interference of their failure and sliding surfaces has not been the subject of comprehensive studies. Indeed, in this compound system, the interaction of sliding wedges of these two back-to-back walls considering the shear failure wedge of the foundation, significantly impresses on the foundation bearing capacity, adjacent walls displacements and deformations, and their stability. In this study, the effect of horizontal distance between two walls (W), breadth of loading plate (B), and position of vertical loading was investigated experimentally. In addition, the comparison of using single and equivalent double-plate anchors was evaluated. The loading plate bearing capacity and displacements, and deformations of BBAW were measured and the results are presented. To evaluate the shape, form, and how the critical failure surfaces of the soil behind the walls and beneath the foundation intersect with one another, the Particle Image Velocimetry (PIV) technique was applied. The experimental tests results showed that in this composite system (two adjacent-loaded BBAW) the effective distance of walls is about W = 2.5*H (H: height of walls) and the foundation effective breadth is about B = H, concerning foundation bearing capacity, walls horizontal displacements and their deformations. For more amounts of W and B, the foundation and walls can be designed and analyzed individually. Besides, in this compound system, the foundation bearing capacity is an exponential function of the System Geometry Variable (SGV) whereas walls displacements are a quadratic function of it. Finally, as an important achievement, doubling the plates of anchors can facilitate using concrete walls, which have limitations in tolerating curvature.

• 한국산림과학회지
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• 제102권1호
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• pp.1-6
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• 2013

본 연구는 국내 분포하는 마가목의 집단간 및 집단내 개체간 열매와 종자 형태에 대한 변이를 조사하였다. 6개 천연집단의 42개 개체목에서 열매를 채취하여 열매특성 6가지와 종자특성 4가지를 분석하였다. 모든 특성들에서 집단간 및 집단내 개체간에 유의적인 차이가 인정되었다. 특히, 결실지당 열매수와 열매당 종자수 특성은 전체 분산 가운데 집단이 차지하는 비율이 큰 것으로 나타났다. 변이계수 값은 결실지당 열매수와 종자무게 특성이 다른 특성들(11.9~32.1%)에 비해 높은 42.0~75.3%의 값을 나타냈다. 상관분석결과 결실지당 열매수 특성은 위도와는 정의 상관관계를 보였으며, 경도와는 부의 상관관계를 각각 나타냈다. 군집분석결과 지리적으로 가까운 집단들이 유전적으로 가깝게 묶이는 경향을 나타냈다. 주성분분석결과 집단간의 유연관계에 의미를 갖는 3개 주성분을 도출하였는데 전체 분산에 대한 설명력은 87%였다. 제1주성분은 종자길이와 종자무게, 제2주성분은 열매폭과 종자지수, 제3주성분은 열매길이와 결실지당 열매수 특성이 높은 기여도를 나타냈다.

• Bulletin of the Korean Chemical Society
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• 제33권5호
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• pp.1509-1516
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• 2012

Nano-assisted inclusion separation of alkali metals from basic solutions was reported by inclusion-facilitated emulsion liquid membrane process. The novelty of this study is application of nano-baskets of calixarene in the selective and efficient separation of alkali metals as both the carrier and the surfactant. For this aim, four derivatives of $p-tert-calix$[4]arene bearing different sulfonamide moieties were synthesized and their inclusion-extraction parameters were optimized including the calixarene scaffold $\mathbf{3}$ (4 wt %) as the carrier/demulsifier, the commercial kerosene as diluent in membrane, sulphonic acid (0.2 M) and ammonium carbonate (0.4 M) as the strip and the feed phases, the phase and the treat ratios of 0.8 and 0.3, mixing speed (300 rpm), and initial solute concentration (100 mg/L). The selectivity of membrane over more than ten interfering cations was examined and the results reveled that under the optimized operating condition, the degree of inclusion-extraction of alkali metals was as high as 98-99%.

• Wind and Structures
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• 제19권4호
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• pp.405-420
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• 2014

This paper examines the nonlinear behaviour of corrugated steel plate shear walls under lateral pushover load. One of the innovations in these types of walls which have used in recent years is the use of the corrugated steel shear walls rather un-stiffness plates. In the last decades many experimental studies have been done on the on the corrugated steel shear walls. A finite element analysis that includes both material and geometric nonlinearities is employed for the investigation. A comparison is made between the behaviour of steel shear walls with sinusoidal corrugated plate and trapezoidal corrugated plate. The effects of parameters such as the thickness of the corrugated plate, the corrugation depth in the corrugated plates and the corrugation length of the infill of the corrugated plates, are investigated. The results of this study have demonstrated that in the wall with constant dimensions, the trapezoidal plates have higher energy dissipation, ductility and ultimate bearing than sinusoidal waves, while decreasing the steel material consumption.

• Earthquakes and Structures
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• 제23권6호
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• pp.503-515
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• 2022

Global or partial damage to a structure due to the failure of gravity or lateral load-bearing elements is called progressive collapse. In the present study, the alternate load path (ALP) method introduced by GSA and UFC 4-023-03 guidelines is used to evaluate the progressive collapse in special steel moment-resisting frame (SMRF) buildings. It was assumed that the progressive collapse is due to the earthquake force and its effects after the removal of the elements still remain on the structures. Therefore, nonlinear dynamic time history analysis employing 7 earthquake records is used to investigate this phenomenon. Internal and external column removal scenarios are investigated and the stiffness of the connections is changed from semi-rigid to rigid. The results of the analysis performed in the OpenSees program show that the loss of the bearing capacity of an exterior column due to a seismic event and the occurrence of progressive collapse can increase the inter-story drift of the structure with semi-rigid connections by more than 50% and make the structure unable to satisfy the life safety performance level. Furthermore, connection stiffness severely affects the redistribution of forces and moments in the adjacent elements of the removed column.

• Structural Engineering and Mechanics
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• 제87권4호
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• pp.375-389
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• 2023

In many fiber concrete beams with Carbon Fiber Reinforced Polymer (CFRP), debonding occurs between the carbon sheets and the concrete due to the low strength of the bonding resin. A total of 42 fiber concrete beams with a cross-section of 10×10 cm with a span length of 50 cm are fabricated and retrofitted with CFRP and subjected to a 4-point bending test. Graphene Oxide (GO) at 1, 2, and 3 wt% of the resin is used to improve the mechanical properties of the bonding resins, and the effect of length, width, and the number of layers of CFRP and resin material are investigated. The crack pattern, failure mode, and stress-strain curve are analyzed and compared in each case. The results showed that adding GO to polyamine resin could improve the bonding between the resin and the fiber concrete beam. Furthermore, the optimum amount of nanomaterials is equal to 2% by the weight of the resin. Using 2% nanomaterials showed that by increasing the length, width, and number of layers, the bearing and stiffness of fiber concrete beams increased significantly.

• 한국산림과학회지
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• 제105권1호
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• pp.73-77
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• 2016

다래의 결과지 길이에 따른 다래 과실수와 과실무게를 조사하여 결과지와 과실특성과의 상관관계를 구명하고자 하였다. 다래의 결과지가 15 cm 이하와 30 cm 이상의 경우, 평균 무게와 평균과실수는 각각 11.7 g과 12.3 g 그리고 4.6개와 13.8개였다. 그 결과 15 cm 미만의 결과지는 불량한 과실특성결과를 가져오므로 동계전정시 제거하여야 한다. 전정이 다래 과실등급별 생산량에 미치는 영향을 알아보고자 전정실험을 실시하였다. 결과모지는 80개, 결과모지의 80%를 자르는 강전정 처리구에서는 과실 총 생산량이 본당 평균 $14.3{\pm}1.5kg$이었으며, 이중 대과(15 g 이상)이 $8.2{\pm}0.9kg$, 중과(10~15 g)이 $4.0{\pm}0.7kg$ 그리고 소과(10 g 이하)이 $2.1{\pm}0.3kg$ 생산되었다. 무처리구에서는 과실 총 생산량이 본당 평균 $26.7{\pm}2.1kg$이었으며, 이중 대과는 $2.5{\pm}0.5kg$, 중과 $19.2{\pm}1.4kg$ 그리고 소과 $5.0{\pm}0.6kg$ 생산되었다. 특히, 전정처리구와 무처리구에서 15 g 이상 대과의 무게분포를 보면 무처리구는 대부분 15~16 g의 과실이 분포하였으나, 전정처리구는 15~20 g 이상까지 고르게 분포하는 것으로 나타났다. 전정을 실시하지 않는 경우 15 g 이상의 대과 생산이 쉽지 않을 것으로 판단되며, 생과용 대과 및 특과 생산을 위해서는 적절한 동계전정이 필요하다.

• Steel and Composite Structures
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• 제43권6호
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• pp.773-784
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• 2022

This paper aims to investigate the axial compressive behavior of reinforced concrete (RC) columns strengthened with self-compacting and micro-expanding (SM) concrete-filled steel tubes (SM-CFSTs). Nine specimens were tested in total under the local axial compression. The test parameters included steel tube thickness, filling concrete strength, filling concrete type and initial axial preloading. The test results demonstrated that the initial stiffness, ultimate bearing capacity and ductility of original RC columns were improved after being strengthened by SM-CFSTs. The ultimate bearing capacity of the SM-CFST strengthened RC columns was significantly enhanced with the increase of steel tube thickness. The initial stiffness and ultimate bearing capacity of the SM-CFST strengthened RC columns were slightly enhanced with the increase of filling concrete strength. However, the effect of filling concrete type and initial axial preloading of the SM-CFST strengthened RC columns were negligible. Three equations for predicting the ultimate bearing capacity of the SM-CFST strengthened RC columns were compared, and the modified equation based on Chinese code (GB 50936-2014) was more precise.

• Geomechanics and Engineering
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• 제32권4호
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• pp.453-462
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• 2023

Designing pile foundations subjected to the uplift forces such as buildings, oil platforms, and anchors is becoming increasingly concerned. In this paper, the conceptual design of a new type of driven piles called expanding pile is presented and assessed. Some grooves have been created in the shaft of the novel pile, and some moveable arms have been designed at the pile tip. At first, static analyses using the finite element method were performed to evaluate the effectiveness of the innovative pile on the axial bearing capacity. Then its effect on seismic behavior of moment frame is considered. Results show that the expanding arms were provided an ideal anchorage system because of the soil's noticeable locking-up effect increasing uplift bearing capacity. For example at the end of the static tensile loading procedure, displacement decrement up to 55 percent is observed. In addition, comparing the uplift bearing capacity of the usual and new pile with different lengths in sand and clay layers shows noticeable effect and sharp increase up to about two times especially in longer piles. Besides, a sensible reduction in the seismic response and the stresses in the beam-column connection between 23-36 percent are achieved that ensures better seismic behavior of the structures.