• Wind and Structures
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• 제22권1호
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• pp.89-106
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• 2016

With an aim to assess the wind damage to urban trees in more realistic conditions, the nonlinear dynamics of structured trees subjected to strong winds with different levels is investigated in the present paper. For the logical treatment of dynamical behavior of trees, material nonlinearities of green wood associated with tree biomechanics and geometric nonlinearity of tree configuration are included. Applying simulated fluctuating wind velocity to the numerical model, the dynamical behavior of the structured tree is explored. A comparative study against the linear dynamics analysis usually involved in the previous researches is carried out. The failure wind velocity of urban trees is then defined, whereby the failure percentages of the tree components are exposed. Numerical investigations reveal that the nonlinear dynamics analysis of urban trees results in a more accurate solution of wind-induced response than the classical linear dynamics analysis, where the nonlinear effect of the tree behavior gives rise to be strengthened as increasing of the levels of wind velocity, i.e., the amplitude of 10-min mean wind velocity. The study of relationship between the failure percentage and the failure wind velocity provides a new perspective towards the vulnerability assessment of urban trees likely to fail due to wind actions, which is potential to link with the practical engineering.

• 한국수소및신에너지학회논문집
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• 제16권2호
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• pp.159-169
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• 2005

Cellulose, consisted of 45 wt% in wood, is usable as fuels and heavy oil additives if depolymerized to monomer unit, because the chemical structures are similar to high octane materials found in gasoline. In this study, thermochemical degradation by solvolysis reaction of cellulose such as the effect of reaction temperature, reaction time and type of solvent on conversion yield and degradation products were investigated. It was found that the effectiveness of the solvent on the sovolysis reaction was as follows; acetone>n-butanol>tetralin. When acetone was used as a solvent, the highest cellulose conversion was observed to be 91.8% at 500$^{\circ}C$, 40min. Combustion heating value of liquid products from thermochemical conversion processes was in the range of 7,330${\sim}$7,410cal/g. The energy yield and mass yield in acetone-solvolysis of cellulose was as high as 66.8% and 37.0 g oil/100g raw material after 40min of reaction at 400$^{\circ}C$. Various aliphatic and aromatic compounds were detected in the cellulose solvolysis products. The major components of the solvolysis products, that could be used as fuel, were mesityl oxide, mesitylene, isophorone.

• Smart Structures and Systems
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• 제18권4호
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• pp.683-705
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• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

• Earthquakes and Structures
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• 제14권3호
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• pp.241-248
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• 2018

To study the mechanical properties of joints in ancient timber buildings in depth, the force mechanism of the through-tenon joints was analyzed, also the theoretical formulas of the moment-rotation angles of the joints with different loosening degrees were deduced. To validate the rationality of the theoretical calculation formulas, six joint models with 1/3.2 scale ratio, including one intact joint and five loosening joints, were fabricated and tested under cyclic loading. The specimens underwent the elastic stage, the plastic stage and the destructive stage, respectively. At the same time, the moment-rotation backbone curves of the tenon joints with different looseness were obtained, and the theoretical calculation results were validated when compared with the experimental results. The results show that the rotational moment and the initial rotational stiffness of the tenon joints increase gradually with the increase of the friction coefficient. The increase of the tenon section height can effectively improve the bearing capacity of the through-tenon joints. As the friction coefficient of the wood and the insertion length of the tension increase, the embedment length goes up, whereas it decreases with the increase of section height. With the increase of the looseness, the bearing capacity of the joint is reduced gradually.

• 한국실내디자인학회논문집
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• 제22권1호
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• pp.183-193
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• 2013

The study aimed to find the fundamental differences of aesthetics in Korea, China, and Japan by analyzing expressive features and structural meanings of the storage furniture from $17^{th}$ to $19^{th}$ century. The study was performed in four steps; analysis of expressive features, isotopic analysis, semantic structure analysis, and comprehensive interpretation. The results showed that three countries had linear shapes with curvilinear elements, closed forms with open spaces, natural material hues with change of tone or color, and symmetrical forms with asymmetrical patterns and structures in common. Korea comparatively accented on the natural material colors and wood grains. China stressed on the big and wide faces using three-dimensional carving. Japan accented on the linear elements with strong color contrast and decorative metal fixtures. These features were caused by the traditional thoughts and according aesthetic principles. Korea and China were affected by the Confucianism focused on establishing the order of rank. Meanwhile, Japan was more influenced by the Buddhism emphasized on the individuality and communication. Therefore, the differences of the expressive features in furniture among the three countries were inevitable consequences of the different ideologies.

• 한국환경생태학회지
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• 제20권1호
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• pp.1-8
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• 2006

자연식생 재현을 파악하기 위하여 리싸이클링에코녹화공법을 이용한 장흥다목적댐 배면부에 모니터링 시험구를 선정하였다. 모니터링 시험구는 2004년 5월에 설치하였고, 2004년 5월부터 2005년 10월까지 4차례 걸쳐 식물상, 식물군집구조, 자연이입종, 고사율을 모니터링 하였다. 우드칩 멀칭 후 출현 종 수 감소와 함께 출현식물의 도시화지수가 감소하여 자연성은 증진되었으며, 덩굴식물의 세력은 확장되었다. 낙엽활엽수군락에서 자연이 입종 수가 가장 많았고, 식재수목의 고사율도 높았다.

• Wind and Structures
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• 제15권5호
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• pp.423-439
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• 2012

Three common medium- rise building forms were physically tested to study their overall wind induced structural response. Emphasis was placed on the torsional response and its correlation with other peak responses. A higher correlation was found between the peak responses than between the general fluctuating parts of the signals. This suggests a common mechanism causing the peak event, and that this mechanism is potentially different to the mechanism causing the general load fluctuations. The measurements show that about 80% of the peak overall torsion occur simultaneously with the peak overall along wind drag for some generic building shapes. However, the peak torsional response occurs simultaneously with only 30%-40% of the peak overall drag for the rectangular model. These results emphasise the importance of load combinations for building design, which are often neglected in the design of medium sized rigid buildings for which the along-wind drag is dominant. Current design wind loading standards from around the world were evaluated against the results to establish their adequacy for building design incorporating wind-induced torsion effects. Although torsion is frequently neglected, for some structural systems it may become more important.

• Earthquakes and Structures
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• 제7권1호
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• pp.57-82
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• 2014

The heritage value of the mixed wood-masonry 18th century Pombalino buildings of downtown Lisbon is recognized both nationally and internationally. The present paper focuses on the seismic assessment of global response and retrofitting of a typical Pombalino building by nonlinear static analyses, performed by the research software Tremuri, which is able to model 3D configurations. The structure is modelled using nonlinear beams for masonry panels, while in case of the internal walls (frontal walls) an original formulation has been developed in order to take into account their specific seismic behaviour. Floors are modelled as orthotropic membrane finite elements: this feature allows to simulate the presence of both flexible and rigid diaphragms, being the first ones more representative of the original state while the second ones of retrofitted configurations. Seismic assessment has been evaluated by applying nonlinear static procedure and comparing the performance of different configurations (by considering various retrofitting strategies). Finally, assuming a lognormal cumulative distribution, fragility curves are obtained to be representative of Pombalino buildings: the most important application of such curves is for seismic risk and loss estimation analyses.

• 한국조경학회지
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• 제13권2호
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• pp.27-36
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• 1985

^x In Korea, we are entering on a new phase that the use concept of urban park is extending to dynamic activities such as games and sports. This article is to investigate the significance of lawn areas, as a receptive space of such a wide range of recreation activities. As a study process, Green Styles (type of parks) such as Garden Type, Park Type and Forest Type were studied and historical review of lawn areas in park development was performed. In conclusion, the lawn areas ( greensward) are an essential part of park and open space organization. The significance as a conclusion is presented as follows : 1 ) Balance in type of parks The structures of our parks and open spaces are inclined toward the artificial Garden Type and natural Forest Type. Therefore, the intermediate Park Type and sparse wood areas should be a core part of our park and open space development. 2) Psychological effect Park Type areas, thorned by greensward(lawn area), can refresh urban dwellers with natural picturesque landscaps, and Park Type landscape is the most preferred natural landscape. It shows the essence of natural amenity as 3) Accomodation of wide range of recreation activities Lawn areas in urban park are the best place in accomodating the wide range of active and massive recreation activities. Thus, lawn areas can increase the freedom of recreation use in urban park. 4) Enlargement of physical carrying capacity. With expansion of lawn areas of euro- american concept, the structural open space can be transformed into service open space. Thus, the recreation carrying capacity of urban parks can be enlarged.

• 한국가구학회지
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• 제20권5호
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• pp.440-456
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• 2009

Because PBD was started as a design tool for steel construction and concrete construction, it was able to applied to the post and beam method of wooden building constructions. But, it may not suitable to light frame wooden construction that is becoming popular in domestic construction market due to the economical efficiency and the constructive simplification. Owing to the share effects between member and sheathing material or among structural members, light frame wooden construction is different from post and beam construction that use a single structural member. Therefore, consideration on the system analysis and system design are urgently needed to use in actual life and inspect the reliability of structures from the system view. With this in mind, code conversion from ASD to PBD that is pressing issue in domestic wooden building construction was studied, also various countries status about PBD were considered and then approaching methods on the system reliability were referred. Finally, several considerations for the development of PBD were explored. PBD should be considered as, not only a new structural design process that select sizes of structural member, but a industrial tool that can lead a development of more reliable wood products. A strongest point of PBD is independent of various construction materials and construction types.