• Journal of Mechanical Science and Technology
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• v.19 no.7
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• pp.1469-1477
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• 2005

Vibrations related to ride comfort should be considered at the beginning of design stage. In general, ride comfort of human is mainly affected by vibration transmitted from the floor and seat. Also, vibration level is very important regarding with running safety on freight wagon. To ensure ride comfort for passenger coach and vibration level for freight wagon, tests had been repeated by different test procedures with several equipments. With different measuring and evaluations for these results, it took much time to evaluate test results. In this paper, a new evaluation procedure was developed combining several software for ride comfort and vibration level test on railway vehicles. In addition, this developed system is capable of ride comfort test and vibration test by a single integrated system that is capable of immediate reporting the test result. With this developed system, the comfort in a passenger coach and the vibration in a freight car were evaluated. And the simulation results from the proposed system are verified by a field test.

• Wind and Structures
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• v.16 no.2
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• pp.157-178
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• 2013

Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

• International Journal of High-Rise Buildings
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• v.8 no.2
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• pp.117-123
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• 2019

Tall buildings are prone to wind-induced vibrations due to their slenderness whereby peak structural accelerations may be higher than the recommended maximum value. The common countermeasure is the installation of a tuned mass damper (TMD) near the highest occupied floor. Due to the extremely large modal mass of tall buildings and because of the narrow to broad band type of wind excitation the TMD mass may become inacceptable large - in extreme cases up to 2000 metric tons. It is therefore a need to develop more efficient TMD concepts which provide the same damping to the building but with reduced mass. The adaptive TMD concept described in this paper represents a solution to this problem. Frequency and damping of the adaptive TMD are controlled in real-time by semi-active oil dampers according to the actual structural acceleration. The resulting enhanced TMD efficiency allows reducing its mass by up to 20% compared to the classical passive TMD. The adaptive TMD system is fully fail-safe thanks to a smart valve system of the semi-active oil dampers. In contrast to active TMD solutions the adaptive TMD is unconditionally stable and its power consumption on the order of 1 kW is negligible small as controllable oil dampers are semi-active devices. The adaptive TMD with reduced mass, stable behavior and lowest power consumption is therefore a preferable and cost saving damping tool for tall buildings.

• Explosives and Blasting
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• v.21 no.4
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• pp.11-21
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• 2003

An experimental study was carried out in order to reduce the period and cost of construction of Missiryung tunnel, which is a relatively long one 3.6 km long. An allowable vibration level for curing concrete was established based on the extensive case studies done over the world. and assessment was performed on the possibility of constructing concrete structures like lining during tunnel blasting. Attenuation relationships were obtained by processing more than 130 measurement data from a series of tunnel blasting in the site. A Guideline for safe construction work was suggested. To verification, low small concrete blocks with a constant standoff distance were installed in the floor of the tunnel After the blocks were exposed to blast vibrations for 28 days, compressive strength tests were performed on 20 specimens taken from the blocks. It was shown that the suggested guideline was appropriate for the safe construction work at the site.

• Fire Science and Engineering
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• v.34 no.1
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• pp.79-88
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• 2020

This study analyzes the issue of the supply of force of fire in the high-rise buildings, and proposes an efficient method to do so. The results are as follows. First, in terms of Detect fire, it is necessary to shorten force of fire supply time by diversifying fire alarms such as alarms, vibrations, and voices from outside, clarification of fire occurrence points, and marking of fire. Second, with regard to communication signals, strengthening the installation target of wireless communication auxiliary facilities, supplementing the installation of repeaters, and constructing a multicommunications network were proposed. Third, in terms of Decide action, it is necessary to supply firefighter and firefighting equipment with the method of crossing of a river in adjacent buildings. Fourth, in terms of Respond to site, helicopters and emergency elevators are used to assist in the supply of firefighting equipment using drones. Easy-to-break glass windows and identification marks are required in every floor. Finally, in terms of applying fire suppressants, water can be supplied by means of a helicopter adjacent to the structure.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4146-4158
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• 2022

Ultra-high performance concrete (UHPC) has been widely utilized in military and civil protective structures to resist intensive loadings attributed to its excellent properties, e.g., high tensile/compressive strength, high dynamic toughness and impact resistance. At present, aiming to improve the defects of the traditional vertical concrete cask (VCC), i.e., the external storage facility of spent fuel, with normal strength concrete (NSC) shield, e.g., heavy weight and difficult to fabricate/transform, the feasibility of UHPC applied in the shield of VCC is numerically examined considering its high radiation and corrosion resistance. Firstly, the finite element (FE) analyses approach and material model parameters of NSC and UHPC are verified based on the 1/3 scaled VCC tip-over test and drop hammer test on UHPC members, respectively. Then, the refined FE model of prototypical VCC is established and utilized to examine its dynamic behaviors and damage distribution in accidental tip-over and end-drop events, in which the various influential factors, e.g., UHPC shield thickness, concrete ground thickness, and sealing methods of steel container are considered. In conclusion, by quantitatively evaluating the safety of VCC in terms of the shield damage and vibrations, it is found that adopting the 300 mm-thick UHPC shield instead of the conventional 650 mm-thick NSC shield can reduce about 1/3 of the total weight of VCC, i.e., about 50 t, and 37% floor space, as well as guarantee the structural integrity of VCC during the accidental drop simultaneously. Besides, based on the parametric analyses, the thickness of concrete ground in the VCC storage site is recommended as less than 500 mm, and the welded connection is recommended for the sealing method of steel containers.

• Explosives and Blasting
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• v.41 no.4
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• pp.17-28
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• 2023

Recently, the utilization of underground space for research facilities and resource development has been on the rise, expanding development from shallow to deep underground. The establishment of deep underground spaces necessitates a thorough examination of rock stability under conditions of elevated stress and temperature. In instances of greater depth, the stability is influenced not only by the geological structure and discontinuity of rock but also by the propagation of ground vibrations resulting from earthquakes and rock blasting during excavation, causing stress changes in the underground cavity and impacting rock stability. In terms of blasting engineering, empirical regression models and numerical analysis methods are used to predict ground vibration through statistical regression analysis based on measured data. In this study, single-hole blasting was conducted, and the pressure of the blast hole and observation hole and ground vibration were measured. Based on the experimental results, the blast pressure blasting vibration at a distance, and the response characteristics of the tunnel floor, side walls, and ceiling were analyzed.

• Geotechnical Engineering
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• v.11 no.2
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• pp.139-156
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• 1995

A set of field investigations was performed to estimate accurately the predominant periods of seismic 8round motions and the attenuation characteristics of the seismic ground vibration. Predominant periods of ground motions were estimated from the measurement of the continuous microseismic vibratins of certain periods, inherent in the ground and in the buildings, utilizing the high sensitivity digital velocity seismometer consisting of 3-component geophones and a digital seismograph. Estimated predominant periods of microseismic vibraion of the ground(measured on'the ground surface) and the building (measured on the second floor) were in the range of 0.18~0.235 sec. and 0.26~0.31 sec. respectively. The subsurface structure of the site ground was surveyed by the seismic refraction method utilizing the digital seismicwave probing system. The ground structure was found to be a two-layered system : an upper top soil layer of 7m in thickness with the P-wave velocity of 662m1sec and a lower layer of silty-clayey soils with the P -wave velocity of 2210m1 sec. The attenuation characteristics of the seismic ground vibrations were determined by the amplitude decay measurement method us;ng the Seisgun, which produces strong artificial seismic energy. Measured spatial attenuation coefficients of the ground vibration in vertical(Z) longitudinal(X), transverse(Y) direction were 0.1137, 0.0025, and 0.0290 respectively. Estimated Spartial QP's (inverse of the specific dissipation constant w.r.t. shear waved of X, Y, and Z directions were in the range of 5.913~7.575, 32.371~41.452, 2.794~3.579 re spectively. This indicates that aseimic design of the structures on the site should take stronger consideration regarding the earthquake resistance characteristics of the structures against longitudinal ground motion.

• Journal of Bio-Environment Control
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• v.24 no.2
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• pp.85-92
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• 2015

This study examined the settlement of a 1-2W type greenhouse using a timber pile, which was recently established on Gyehwa-do reclaimed land, in order to obtain base data for the construction of a greenhouse on reclaimed land. The results of this study are as follows. foundation and timber pile increased over time, irrespective of the interior and exterior of the upon investigation of the ground, it was confirmed that there was no soft rock stratum (bedrock), and that a sedimentary stratum existed under the fill deposit, which is estimated to have been reclaimed during the site renovation. It was also found that a weathered zone was located under the fill deposit and sedimentary stratum, and that the soil texture of the entire ground floor consisted of clay mixed with sand, silty clay, and granite gneiss, in that order, regardless of boreholes. In addition, the underground water level was 0.3m below ground, regardless of boreholes. Despite a slight difference, the settlement of the greenhouse or measurement sites (channels). With regard to the pillar inside the greenhouse, except in the case of CH-2, the data at a site located on the side wall of the greenhouse (wind barrier side) indicated vibrations of relatively larger amplitude. Moreover, the settlement showed a significant increase during a certain period, which was subsequently somewhat reversed. Based on these phenomena, it was verified that the settlement range of each site in the interior and exterior of the greenhouse was between 1.0 and 7.5mm at this time, except in the case of CH-1. The results of the regression analysis indicated good correlation, with the coefficient of determination by site ranging between 0.6362 and 0.9340. Furthermore, the coefficient of determination ranged between 0.6046 and 0.8822 on the exterior of the greenhouse, which is lower than inside the greenhouse, but still indicates significant correlation.