• Structural Engineering and Mechanics
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• v.77 no.4
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• pp.509-521
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• 2021

The neighbouring gaps at the mortise-tenon joint in traditional timber structure, which leads to the complexity of the joint, are considered to impair the mechanical performance of the joint. In this paper, numerical simulation of loose joint was conducted to examine the deformation states, stress distributions, and bearing capacities, which was verified by full-scale test. On the basis of the experimental and numerical results, a simplified mechanics model with gaps has been proposed to present the bending capacity of the loose joint. Besides, the gap effects and parameter studies on the influences of tenon height, friction coefficient, elastic modulus and axial load were also investigated. As a result, the estimated relationship between moment and rotation angle of loose joint showed the agreement with the numerical results, demonstrating validity of the proposed model; The bending bearing capacity and rotational stiffness of loose joint had a certain drop with the increasing of gaps; and the tenon height may be the most important factor affecting the mechanical behaviors of the joint when it is subjected to repeated load; Research results can provide important references on the condition assessments of the existing mortise-tenon joint.

• Advances in nano research
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• v.10 no.3
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• pp.271-280
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• 2021

The present work deals with an investigation on longitudinal wave propagation in nanobeams made of graphene sheets, for the first time. The nanobeam is modelled via a higher-order shear deformation theory accounts for both higher-order and thickness stretching terms. The general nonlocal strain gradient theory including nonlocality and strain gradient characteristics of size-dependency in order is used to examine the small-scale effects. This model has three-small scale coefficients in which two of them are for nonlocality and one of them applied for gradient effects. Hamilton supposition is applied to obtain the governing motion equation which is solved using a harmonic solution procedure. It is indicated that the longitudinal wave characteristics of the nanobeams are significantly influenced by the nonlocal parameters and strain gradient parameter. It is shown that higher nonlocal parameter is more efficient than lower nonlocal parameter to change longitudinal phase velocities, while the strain gradient parameter is the determining factor for their efficiency on the results.

• Earthquakes and Structures
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• v.22 no.6
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• pp.585-595
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• 2022

Using the nonlinear static procedures has become very common in seismic codes to achieve the nonlinear response of the structure during an earthquake. The capacity spectrum method (CSM) adopted in ATC-40 is considered as one of the most known and useful procedures. For this procedure the seismic demand can be approximated from the maximum deformation of an equivalent linear elastic Single-Degree-of-Freedom system (SDOF) that has an equivalent damping ratio and period by using an iterative procedure. Data from the results of this procedure are plotted in acceleration- displacement response spectrum (ADRS) format. Different improvements have been made in order to have more accurate results compared to the Non Linear Time History Analysis (NL-THA). A new procedure is presented in this paper where the iteration process shall not be required. This will be done by estimation the ductility demand response spectrum (DDRS) and the corresponding effective damping of the bilinear system based on a new parameter of control, called normalized yield strength coefficient (η), while retaining the attraction of graphical implementation of the improved procedure of the FEMA-440. The proposed procedure accuracy should be verified with the NL-THA analysis results as a first implementation. The comparison shows that the new procedure provided a good estimation of the nonlinear response of the structure compared with those obtained when using the NL-THA analysis.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.5
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• pp.121-127
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• 2021

Reverse offset printing is considering as an emerging technology for printed electronics owing to its environmentally friendliness and cost-effectiveness. In reverse offset printing, selecting the materials for cliché and blanket is critical because of its minimum resolution, registration errors, aspect ratio of reliefs, pattern area, and reusability. Various materials such as silicon, quartz, glass, electroplated nickel plates, and imprinted polymers on rigid substrates can be used for the reverse offset printing of cliché. However, when new structures are designed for specific applications, new clichés need to re-fabricated each time employing multiple time-consuming and costly processes. Therefore, by modifying the blanket materials containing the printing ink, several new structures can be easily created using the same cliché. In this study, we investigated various elastomeric materials and evaluated their applicability for designing a highly stretchable blanket with controlled elastic deformation to implement tunable reverse offset printing.

• Geomechanics and Engineering
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• v.29 no.6
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• pp.615-626
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• 2022

The soft clays are widely distributed, and one of the prominent engineering problems is the creep behavior. In order to predict the creep deformation of soft clays in an easier and more acceptable way, a simple creep constitutive model has been proposed in this paper. Firstly, the triaxial creep test data indicated that, the strain-time (𝜀-t) curve showing in the 𝜀-lgt space can be divided into two lines with different slopes, and the time referring to the demarcation point is named as t_EOP. Thereafter, the strain increments occurred after the time t_EOP are totally assumed to be the creep components, and the elastic and plastic strains had occurred before t_EOP. A hyperbolic equation expressing the relationship between creep volumetric strain, stress and time is proposed, with several triaxial creep test data of soft clays verifying the applicability. Additionally, the creep flow law is suggested to be similar with the plastic flow law of the modified Cam-Clay model, and the proposed volumetric strain equation is used to deduced the scaling factor for creep strains. Therefore, a creep constitutive model is thereby established, and verified by successfully predicting the creep principal strains of triaxial specimens.

• Steel and Composite Structures
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• v.41 no.5
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• pp.713-730
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• 2021

The seismic performance of rigid steel frames is widely investigated, but that of semi-rigid (SR) steel frames are not studied extensively, especially for near-field earthquakes. In this paper, the performances of five and ten-story steel SR frames having different degrees of semi-rigidity are evaluated at four performance points in the four different deformation states, namely, the elastic, elasto-plastic, plastic, and near collapse states. The performances of the SR frames are measured by the response parameters including the maximum values of the top floor displacement, base shear, inter-story drift ratio, number of plastic hinges, and SRSS of plastic hinge rotations. These response parameters are obtained by the capacity spectrum method (CSM) using pushover analysis. The validity of the response parameters determined by the CSM is evaluated by the results of the nonlinear time history analysis (NLTHA) for both near and far-field earthquakes at different PGA levels, which are consistent with the performance points. Results of the study show that the plastic hinges of SR frame significantly increase in the range of plastic to near-collapse states for both near and far-field earthquakes. The effect of the degree of semi-rigidity is pronounced only at higher degrees of semi-rigidity. The predictions of the CSM are fairly well in comparison to the NLTHA.

• Journal of Korea Multimedia Society
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• v.25 no.2
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• pp.206-214
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• 2022

The way to measure the extent of damage from floods and droughts is to identify changes in the extent of water systems. In order to effectively grasp this at a glance, satellite images are used. KOMPSAT-5 uses Synthetic Aperture Radar (SAR) to capture images regardless of weather conditions such as clouds and rain. In this paper, various deep learning models are applied to perform semantic segmentation of the water system in this SAR image and the performance is compared. The models used are U-net, V-Net, U2-Net, UNet 3+, PSPNet, Deeplab-V3, Deeplab-V3+ and PAN. In addition, performance comparison was performed when the data was augmented by applying elastic deformation to the existing SAR image dataset. As a result, without data augmentation, U-Net was the best with IoU of 97.25% and pixel accuracy of 98.53%. In case of data augmentation, Deeplab-V3 showed IoU of 95.15% and V-Net showed the best pixel accuracy of 96.86%.

• Design & Manufacturing
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• v.16 no.4
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• pp.40-45
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• 2022

The EV electric vehicle market is growing rapidly worldwide. An electric vehicle means a vehicle that uses energy charged through an electricity source as power. The precision of the press is important to mass-produce the drive motor, which is a key component of the electric vehicle. The size of the driving motor is increasing, and The size of the mold is also growing. In this study, the precision of large high-speed presses for mass production of driving motors was measured. A study was conducted on the measurement method of press and the analysis of measurement data. A drive motor is a component that transmits power by converting electrical energy into kinetic energy. EV driven motors have key material properties to improve efficiency. The material properties are the thickness of the material. As a method for improving performance, use a 0.2mm thin steel sheet. Mold is also becoming larger. As the mold grows, the size of the high-speed press for mass production of the driving motor is also increasing. Also, the precision of the press is the most important because it uses a thin iron plate material. So the importance of large press precision is being emphasized. In this study, the effect of large high-speed press structure on precision was verified

• Journal of the Korean Society for Precision Engineering
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• v.14 no.11
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• pp.34-41
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• 1997

This paper presents a technique to control a very flexible robot moving in a vertical plane. The flexible robot is modeled as an Euler-Bernoulli beam. Elastic deformation is approximated using the assmed modes method. A comparison function which satisfies all geometric and natural boundary conditions of a cantilever beam with an end mass is used as an assumed mode shape. Lagrange's equation is utilized for the development of a discretized model. A control algorithm is developed using a simple PID cnotrol tech- nique. The proportional, integral and deivative control gains are determined based on the dominant pole placement method and tuned to show no overshoot and no steady state error, and short settling time. The effectiveness of the developed control scheme is showed in the hub angular diaplacement control experiment. Three different end masses are uned in the experiment. The experimental results show that developed control algorithm is very effective showing little overshoot, no steady state error, and less than 2.5 second settl- ing time in case of having an end mass which is equivalent to 45% of the manipulator mass. Also the experimental results show that the residual vibration fo the end point is effectively controlled.

• Earthquakes and Structures
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• v.23 no.4
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• pp.339-352
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• 2022

Due to the large volume and generally as a public building, the damage of large-span space structures under various non-conventional loads will cause greater economic losses, casualties, and social impacts, etc. Therefore, it is particularly important to evaluate the seismic performance of large-span space structures. This paper taked a multipurpose sports center as an example and considered its synergistic deformation based on the method of equivalent damping ratio. Furthermore, The ABAQUS software was used to analyze the time-history and energy response of the multipurpose sports center under the action of rare earthquakes, and proposed a quantitative damage index to assess the overall damage of the structure. Finally, the research results indicated that the maximum inter-story drift ratio of the multipurpose sports center under the action of rare earthquakes was less than its limit value. The frame beams presented different degrees of damage, but the key members were basically in an elastic state. The bearing capacity did not reach the limit value, which satisfied the intended seismic performance target. This study taked an actual case as an example and proposed a relevant damage evaluation system, which provided some reference for the analysis of the seismic performance of large-span space structures.