• Earthquakes and Structures
• /
• v.23 no.4
• /
• pp.373-384
• /
• 2022

To improve the seismic performance of suspended ceiling structures, various vibration-damping devices have been developed. However, the devices made of metals have a limit in that they cause large deformation and seriously damages the exterior of the suspended ceiling structure from the wall. As a results, their strengthening effect of the suspended ceiling structure was minimal. Thus, this study employed a spring and vibration-proof rubber effectively controlled vibrations without increasing horizontal seismic loads on the ceiling to enhance the seismic resistance of suspended ceiling structures. The objective of the study is to examine the dynamic properties of a seismic damping-isolation unit (SDI) with various details developed. The developed SDI was composed of a spring, embossed rubbers, and prestressed bolts, which were the main factors enhancing the damping effect. The shaking table tests were performed on eight SDI specimens produced with the number of layers of embossed rubber (n_s), presence or absence of a spring, prestressed force magnitude introduced in bolts (f_ps), and mass weight (W_m) as the main parameters. To identify the enhancement effect of the SDI, the dynamic properties of the control specimen with a conventional hanger bolt were compared to those of the SDI specimens. The SDI specimens were effective in reducing the maximum acceleration (A_{c max}), acceleration amplification factor (α_p), relative displacement (δ_R), and increasing the damping ratio (ξ) when compared to the control specimen. The A_{c max}, α_p, and δ_R of the SDI specimens with two rubbers, spring, and f_ps of 0.1f_by, where f_by is the yielding strength of the screw bolt were 57.8%, 58.0%, and 61.9% lower than those of the conventional hanger bolt specimens, respectively, resulting in the highest ξ (=0.127). In addition, the α_p of the SDI specimens was 50.8% lower than those specified in ASCE 7 and FEMA 356. Consequently, to accurately estimate the α_p of the SDI specimens, a simple model was proposed based on the functions of f_ps, stiffness constant of the spring (K), W_m, and n_s.

• Journal of the Microelectronics and Packaging Society
• /
• v.31 no.1
• /
• pp.29-34
• /
• 2024

The heating element utilizing the Joule heating generated when current flows through a conductor is widely researched and developed for various industrial applications such as moisture removal in automotive windshield, high-speed train windows, and solar panels. Recently, research utilizing heating elements with various nanostructures has been actively conducted to develop flexible heating elements capable of maintaining stable heating even under mechanical deformation conditions. In this study, flexible polyurethane possessing excellent flexibility was selected as the substrate, and silver (Ag) thin films with low electrical resistivity (1.6 μΩ-cm) were fabricated as the heating layer using magnetron sputtering. The 2D heating structure of the Ag thin films demonstrated excellent heating reproducibility, reaching 95% of the target temperature within 20 seconds. Furthermore, excellent heating characteristics were maintained even under mechanically deforming environments, exhibiting outstanding flexibility with less than a 3% increase in electrical resistance observed in repetitive bending tests (10,000 cycles, based on a curvature radius of 5 mm). This demonstrates that polyurethane/Ag planar heating structure bears promising potential as a flexible/wearable heating element for curved-shaped appliances and objects subjected to diverse stresses such as human body parts.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.36 no.4
• /
• pp.129-137
• /
• 2024

An analytic solution for the interaction between an array of circular piles made by joining trapezoid steel pipes (TSP) and waves was obtained using an eigenfunction expansion method. First, an analytic model for the wave scattering of multiple piles fixed at arbitrary positions was derived, and then a simplified model was obtained assuming that an infinite array of identical piles were deployed perpendicular to the propagating direc- tion of incident waves. A regular wave experiment was conducted using an experimental model with a scale ratio of 1/100 in a two-dimensional wave tank to verify the analytic solutions. The analytic results and experimental results were qualitatively consistent with each other. Using a developed analytic model, we examined the wave force on the multiple piles and the wave deformation in front of the arrayed piles. The period for the installation is greatly reduced as the TSP pile can be prefabricated in a factory. In particular, it is possible to install at the soft seabed. A seawall structure using arrayed TSP piles will be an ideal complement for a concrete seawall in future.

• The Journal of Engineering Geology
• /
• v.7 no.3
• /
• pp.191-205
• /
• 1997

Measurements on subsurface movement of the Songsanri tomb site including the Muryong royal tomb was conducted using a tiltmeter system for the period of 15 months form July 7, 1996 to September 30, 1997. Two coordinate tilt monitoring data shows the biggest movement rate of 2.3mm/m/yr toward south in the frontal wall(N-S tilt) of the Muryong royal tomb. Southward tilting of bricks above the southern fire place in the western wall of the Muryong royal tomb is a proof of southward tilting of the royal tomb since its excavation in 1971. The eastern wall of the Muryong royal tomb is also tilting toward inside the tomb with the rate of 1.523mm/m/yr. Furthermore, tilting rate of wall increases twice in rainy season. It is interpreted tbat infiltration of water into the tomb and nearby ground in rainy season results in dangerous status for the safety of tomb structure. On the whole, normal component tilting of the walls of the 5th tomb is large than its shear component. It shows a small displacement toward one direction without no abrupt change in its direction and amount of tilting. The tilting rate of walls of the 6th tomb is about 8.8mm/m/yr in the dry season which is much bigger than those of other tombs in rainy season. Deformation events of walls of the tombs are closely related to amount of precipitation and variation of temperature. In comparison with different weather conditions, tilting is much bigger during the period of rainy weather than sunny weather. It is interpreted that rainwater flew into the turm through faults and nearby ground. High water content in nearby ground resulted strength of ground. The tilting event of walls shows a hysterisis phenomenon in analysis of temperature effect on tilting event. The walls tilt rapidly with steep rising of temperature, but the tilted walls do not come back to original position with temperature falling. Therefore, a factor of steep increase of the temperature must be removed. It means the tomb have to be kept with constant temperature. The observation of groundwater level using three boreholes located in construction site and original ground represented that groundwater level in construction site is higher than that of original ground during the rainy season from the end of June to August. It means that the drainage system of the Muryong royal tomb is worse than original ground, and it is interpreted that the poor drainage system is related to safety of tomb structure. As above mentioned, it is interpreted that artificial changes of the tomb environment since the excavation, infiltration of rainwater and groundwater into the tomb site and poor drainage system had resulted in dangerous situation for the tomb structure. According to the result of the long period observation for the tomb site, it is interpreted that protection of the tomb site from high water content should be carried out at first, and the rise of temperature by means of the dehumidifier inside the tomb must be removed.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.41 no.4
• /
• pp.347-355
• /
• 2021

During the earthquake, for multi-story structure, if the first floor is soft, the deformation will concentrate on that floor causing a serious damage to the column members which might leads to the collapse of the whole structure like Piloti structure during the Pohang earthquake in Korea. According to the 2016 National Disaster Management Research Institute's "Investigation of Seismic Reinforcement and Cost Analysis of Domestic Non-seismic Buildings", the rate of seismic resistance of private reinforced concrete buildings was 38.3 %. Among them, it was reported that the seismic-resistance ratio of the two to five-story structures was less than 50 %. Accordingly, the government is trying to improve the seismic rate through support projects, but the conventional seismic reinforcement methods are still expensive, and emergency construction is difficult. Therefore, in this study, the field applicability was evaluated by improving the reinforcement method using Velcro, which was developed through the research project of the Ministry of Land, Transport and Maritime Affairs in 2014. In order to improve the performance of the Velcro reinforcement method, introducing the initial tension of Velcro using high foaming rigid urethane filling between the Velcro and concrete of the columns was applied. Additionally, an experiment was conducted to evaluate the ductility of Velcro specimen from the concrete confinement effect. As a result, the ductility of the Velcro specimen was improved compare to Normal specimen. However, the energy dissipation capacity of VELCRO2 is better than VELCRO1, yet the maximum ductility of those two specimens did not show a significant difference. Therefore, the improvement of the internal filler material is still needed to have a better maximum ductility.

• Journal of the Korean Wood Science and Technology
• /
• v.36 no.6
• /
• pp.77-87
• /
• 2008

Wooden model erosion control dam was made with pitch pine, of which the strength properties was evaluated. Wooden model erosion control dam was made with diameter 90 mm of pitch pine round posts treated with CUAZ-2 (Copper Azole), changing joint in three different types. In each type, erosion control dam was made in nine floor (cross-bar of five floors and vertical-bar of four floors), of which the hight was 790 mm. And then strength properties were investigated through horizontal loading test and impact strength test, and the deformation of structure through image processing (AICON 3D DPA-PRO system). In horizontal loading test of wooden model erosion control dam using round post of diameter 90 mm, whether there was stone or not did not affect strength much when using self drill screw, but strength was decreased by 23%. In monolithic type of erosion control dam using screw bar, strength was increased by 1.5 times and deformation was decreased when filling with stone. When reinforcing with screw bar that ring is connected to self drill screw, strength was increased by 4.8 times. In impact strength test of wooden model erosion control dam made with round post of diameter 90 mm, the erosion control dam connected with self drilling screw not filling with stone was totally destroyed by the 1st impact, and the erosion control dam using screw bar was ruptured at cross-bar at which 779 kgf of impact was loaded in the 1st impact. In the 2nd impact, the base parts were ruptured, and reaction force was decreased to 545 kgf. In the 3rd impact, whole base parts were destroyed, and reaction force was decreased to 263 kgf.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.24 no.2
• /
• pp.55-64
• /
• 1988

Stow nets have widely been used in the western sea of Korea from the olden age. The original structure of a stow net is a large square-sectional bag net made of 4 netting panels, and the front fringes of top and bottom panels are connected to the top and bottom beams respectively. Wire ropes, which is originated from the holding anchor are gradually forked and biforked, and finally 4 pieces of wire rope (biforked pendants) are jointed to each beam. Much convenience caused by long and heavy beams were problemed, then some studies have been carried out to improve the net since 1930's. The most effective improvement were achieved in 1980 by Mr. Han and his colleagues. The key point of improvement was that the beams were removed and the belt shaped shearing device made by canvas was attached to the side panels, the head rope and ground rope to the front fringe of top and bottom panel, and biforked pendants are joined to the shearing device. Even though this is the epoch-making improvement of a stow net, the further study should be required to find out more effective method. The authors carried out a model experiment on the stow net to determine the vertical and horizontal opening of a net mouth, and also examine the front, top and side-view configuration of the net. The model net was constructed depending on the Similarity Law of Fishing Gear in 1/10 and 1/20 scale and set against to the current at shallow and speedy flowing channel. The vertical and horizontal openings were determined by using scaled bamboo poles, and the configuration was observed by using specially prepared observation platform and underwater observation glass, and also photographed by using specially prepared underwater photographic equipment. The results obtained can be summarized as follows: 1. The opening height and width of the shearing device varied in accordance with the relative length of the biforked pendants. Considering the height and width of shearing device in 6 cases of the arrangement system of biforked pendants, the best result was obtained in the case that the 2nd, 3rd and 4th pendents from the bottom-most was 5%, 9% and 4% longer than that. 2. On the top-view configuration the excessive deformation of head rope and ground rope were observed. In the actual net, 54m long head rope and ground rope were attached to the front fringe of top and bottom panels so that the head rope may be lifted to make the net mouth open highly. But actually the head rope and the ground rope are streamed backward without any lift, and also the netting followed the ropes were deformed until the 2/5 in the whole length of the net. This deformation may be guessed to disturb the entrance of fish school into the net and also caused the net to get caught by obstacles in the sea bed and to be broken largely. 3. Hydrodynamic resistance R of the actual net may be deduced as R(kg)=29.2$\times$103 v1.65. It is also expressed as R(kg)=5.9$\times$d/l$\times$ab v1.65. depending on the formula deduced by Koyama to estimate the resistance of trawl nets, where d/l denote the ratio between diameter of netting twine and length of mesh leg in every part of side panel, a and b, the stretched circumference of the mouth and the stretched length of the net, respectively.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.5 s.78
• /
• pp.569-580
• /
• 2005

The postbeam joint connection of the existing steel structure moment flexible frame system did not produce sufficient seismic resistance during the earthquakes in Northridge and Kobe, and it sustained brittle fracturing on the joint connection. This study was performed to execute the high-tensile bolt share connection of H-beams web and the full-scale experiment as a parameter of the existing reinforcement of H-flange rib, by making the shape of the existing joint connection. This experiment was performed to determine the extent of the decrease of the number of high-tensile bolts and how to improve workability of the two-phase shear connection of web beam. In addition, this study was performed to enhance the seismic resistant capacity through the enforcement of rib plates. As a result of the experiment of two-phase shear connection of H-beam web and of joint connection to be reinforced by rib plates, the results of this study showed that the initial stiffness, energy-dissipation capacity, and rotational capacity of plasticity was higher than the existing joint connection. As to the rate of increasing the strength and deformation capacity, there were differences between the tension side and compression side because of the position of shear tap. However, as a whole, they have shown excellent seismic resistant capacity. Also, all the test subjects exceeded 4% (rate of delamination), about 0.029 rad (total plastic capacity), and about 130% (maximum strength of joint connection) of fully plastic moment for the original section. Accordingly, this study was considered as it would be available in the design more than the intermediate-level of moment flexible frame.

• Journal of the Korea Concrete Institute
• /
• v.21 no.3
• /
• pp.319-326
• /
• 2009

Two parallel wide flange built-up beams are widely used as struts in resisting lateral earth pressure because of the effectiveness in structure and construction. In a certain structural system, the reinforced concrete columns are to be placed at the intersection where two perpendicular beams cross each other, the square part of the joint being filled with concrete. In the punching shear mechanism of the beam-column joint, the radial deformation caused due to shear cracking will be constrained by the spring action of the squarely encompassed beam flanges. As a result, the punching shear strength of the joint concrete can be expected to be increased. To verify this phenomenon experiments have been performed for various constraining elements and distances between columns and constraints. Test results are compared with the approximation analysis formula which has been proposed in this study, based on the code formula. The results calculated by the proposed equation show comparatively close agreement with the punching shear strength detected from the test.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.4
• /
• pp.371-382
• /
• 2008

The objective of this study is to develop the laboratory testing method for evaluating the loading capacity of lattice girder used for support in tunnel structure. 3-point flexible strength test and 4-point flexible strength test were performed on three types of lattice girder, such as $LG-50{\times}20{\times}30$, $LG-70{\times}20{\times}30$, and $LG-95{\times}22{\times}32$, mainly used in Korea. Two types of loading position for each flexible strength test were used to analyze the behavior of load-deformation. The loading distribution in the lattice girder was analyzed by means of strains measured by strain gauges attached on chords and diagonal bars. In 3-point flexible strength test, the difference of the average of maximum flexible strength according to loading position had the range from 10% to 33%. In 4-point flexible strength test, the average of maximum flexible strength according to loading position was almost no difference. The difference between the average of maximum flexible strengths obtained from 3-point and 4-point flexible strength tests was from 13.56 to 31.55%. The load applied on the lattice girder was concentrated to the main chord in 3-point flexible strength test. The load applied on the lattice girder in 4-point flexible strength test was distributed to three chords and diagonal bars.