• Steel and Composite Structures
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• 제43권2호
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• pp.201-219
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• 2022

This paper firstly proposed high performance composite columns for cold-region infrastructures using ultra-high performance concrete (UHPC) and ultra-high strength steel (UHSS) Q960E. Then, 24 square UHPC-filled UHSS tubes (UHSTCs) at low temperatures of -80, -60, -30, and 30℃ were performed under axial loads. The key influencing parameters on axial compression performance of UHSS were studied, i.e., temperature level and UHSS-tube wall thickness (t). In addition, mechanical properties of Q960E at low temperatures were also studied. Test results revealed low temperatures improved the yield/ultimate strength of Q960E. Axial compression tests on UHSTCs revealed that the dropping environmental temperature increased the compression strength and stiffness, but compromised the ductility of UHSTCs; increasing t significantly increased the strength, stiffness, and ductility of UHSTCs. This study developed numerical and theoretical models to reproduce axial compression performances of UHSTCs at low temperatures. Validations against 24 tests proved that both two methods provided reasonable simulations on axial compression performance of UHSTCs. Finally, simplified theoretical models (STMs) and modified prediction equations in AISC 360, ACI 318, and Eurocode 4 were developed to estimate the axial load capacity of UHSTCs at low temperatures.

• Advances in nano research
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• 제15권2호
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• pp.155-163
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• 2023

Exercise is beneficial to the body in some ways. It is vital for people who have heart problems to perform exercise according to their condition. This paper describes how an Android platform can provide early warnings of fatigue during wushu exercise using Photoplethysmography (PPG) signals. Using the data from a micro-electro-mechanical system (MEMS) gyroscope to detect heart rate, this study contributes an algorithm to determine a user's fatigue during wushu exercise. It sends vibration messages to the user's smartphone device when the heart rate exceeds the limit or is too fast during exercise. The heart rate monitoring system in the app records heart rate data in real-time while exercising. A simple pulse sensor and Android app can be used to monitor heart rate. This plug-in sensor measures heart rate based on photoplethysmography (PPG) signals during exercise. Pulse sensors can be easily inserted into the fingertip of the user. An embedded microcontroller detects the heart rate by connecting a pulse sensor transmitted via Bluetooth to the smartphone. In order to measure the impact of physical activity on heart rate, Wushu System tests are conducted using various factors, such as age, exercise speed, and duration. During testing, the Android app was found to detect heart rate with an accuracy of 95.3% and to warn the user when their heart rate rises to an abnormal level.

• 한국지진공학회논문집
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• 제27권2호
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• pp.91-99
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• 2023

Structural vibration induced by earthquake hazards is one of the most significant concerns in structure performance-based design. Structural hazards evoked from seismic events must be properly identified to make buildings resilient enough to withstand extreme earthquake loadings. To investigate the effects of combined earthquake-resistant systems, shear walls and five types of dampers are incorporated in nineteen structural models by altering their arrangements. All the building models were developed as per ACI 318-14 and ASCE 7-16. Seismic fragility curves were developed from the incremental dynamic analyses (IDA) performed by using seven sets of ground motions, and eventually, by following FEMA P695 provisions, the collapse margin ratio (CMR) was computed from the collapse curves. It is evident from the results that the seismic performance of the proposed combined shear wall-damper system is significantly better than the models equipped with shear walls only. The scrutinized dual seismic resisting system is expected to be applied practically to ensure a multi-level shield for tall structures in high seismic risk zones.

• Smart Structures and Systems
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• 제31권5호
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• pp.501-516
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• 2023

Dynamic irregularity and acceleration of bridges subjected to high-speed trains provide crucial information for comprehensive evaluation of the health state of under-track structures. This paper proposes a novel approach for real-time estimation of vertical track dynamic irregularity and bridge acceleration using deep generative adversarial network (GAN) and vibration data from in-service train. The vehicle-body and bogie acceleration responses are correlated with the two target variables by modeling train-bridge interaction (TBI) through least squares generative adversarial network (LSGAN). To realize supervised learning required in the present task, the conventional LSGAN is modified by implementing new loss function and linear activation function. The proposed approach can offer pointwise and accurate estimates of track dynamic irregularity and bridge acceleration, allowing frequent inspection of high-speed railway (HSR) bridges in an economical way. Thanks to its applicability in scenarios of high noise level and critical resonance condition, the proposed approach has a promising prospect in engineering applications.

• Structural Engineering and Mechanics
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• 제86권4호
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• pp.573-587
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• 2023

A conventional tuned mass damper (TMD) provides a passive control option to suppress the structures' wind- or earthquake-induced vibrations. However, excessive displacements of the TMD raise concerns in the practical implementation. Therefore, this study proposes a novel TMD designed for and deployed on a high-rise sightseeing tower. The device consists of an integrated two-way slide rail mount and an eddy current damper (ECD) with a stroke control mechanism. This stroke control mechanism allows the damping coefficient to automatically increase when the stroke reaches a predetermined value, preventing excessive damper displacements during large earthquakes. The corresponding two-stage damping parameters are designed with a variable-thickness copper plate to enable the TMD stroke within a specified range. Thus, this study discusses the detailed design schemes of the device components in TMD. The designed two-stage damping parameters are also numerically verified, and the structural responses with/without the TMD are compared. As seen in the results, the proposed TMD yields effective control authority to limit the acceleration response within a comfort level. In addition, this TMD resolves the spatial availability for the damper movement in high-rise buildings by the controllable damping mechanism.

• Wind and Structures
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• 제38권2호
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• pp.119-128
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• 2024

The aerodynamic damping is an essential factor that can considerably affect the dynamic response of the cable-stayed bridge induced by crosswind load. However, developing an accurate and efficient aerodynamic damping model is crucial for evaluating the crosswind load-induced response on cable-stayed bridges. Therefore, this study proposes a new method for identifying aerodynamic damping of the bridge structures under crosswind load using an extended Kalman filter (EKF) and the particle filter (PF) algorithm. The EKF algorithm is introduced to capture the aerodynamic damping ratio. PF technique is used to select the optimal spectral representation of the noise. The effectiveness and accuracy of the proposed solution were investigated through full-scale vibration measurement data of the crosswind-induced on the bridge's girder. The results show that the proposed solution can generate an efficient and robust estimation. The errors between the target and extracted values are around 0.01mm and 0.003^o, respectively, for the vertical and torsional motion. The relationship between the amplitude and the aerodynamic damping ratio is linear for small reduced wind velocity and nonlinear with the increasing value of the reduced wind velocity. Finally, the results show the influence of the level of noise.

• Annals of Clinical Neurophysiology
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• 제12권1호
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• pp.21-26
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• 2010

Background: Although quantitative sensory test (QST) is being used with increasing frequency for measuring sensory thresholds in clinical practice and epidemiologic studies, there has been no age-matched normative data in Korean adults. The objective of this study is to evaluate the value of QST in diabetic polyneuropathy with normal range in Korean adults. Methods: The Computer Aided Sensory Examination IV 4,2 (WR Medical Electronics Co., Stillwater, Minnesota, U.S.A.), with 4,2,1 stepping algorithm was used to determine vibration and cold perception threshold in 70 normal controls and 19 patients with diabetic polyneuropathy aged from 21 to 79 years. The data were used to define age-matched upper and lower normal limits and normal range of side to side difference. We also evaluated the duration of diabetes, serum HbA1C level, and findings of nerve conduction study (NCS) and QST in patients with diabetic polyneuropathy. Results: In normal adults, sensory thresholds slightly increased with age, and a slight side-to-side difference was observed. The diagnostic sensitivity of QST was not higher than NCS in patients with diabetic polyneuropathy (36.8% vs. 42.1%, p=0.716), especially among elderly patients. Conclusions: QST might be used as a complementary test for NCS in the diagnosis of diabetic polyneuropathy. Although the QST is a simple method for the evaluation of peripheral nerve function, there are some limitations. Most of all, because the QST measuring is dependent on the subjective response of patients, the degree of concentration and cooperation of the patients can significantly affect the result. And thus, attention should be paid during the interpretation of QST results in patients with peripheral neuropathy.

• 터널과지하공간
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• 제18권6호
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• pp.418-426
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• 2008

인도네시아 파시르탄광에서 적용되고 있는 전형적인 발파방법은 지표면을 유일한 자유면으로 하는 일자유면 노천발파 공법이다. 일반적으로 일자유면 발파방법은 자유면이 하나뿐이므로 구속이 커서 큰 지반진동을 일으키게 된다. 큰 지반진동은 다시 채광장의 경계를 이루는 사면의 안정성에 나쁜 영향을 미칠 수 있다. 이런 측면에서 발파로 인한 지반진동으로부터 파시르탄광의 채광장 사면과 폐석장의 안전을 확보할 수 있는 발파지침을 마련하기로 하였다 먼저, 파시르탄광에서 발파로 발생될 수 있는 지반진동 수준을 예측할 수 있는 예측식을 유도하였다. 다음으로, 채광장 사면과 폐석장의 폐석더미를 관리하기 위한 지반진동 허용수준을 PPV 측정치로 각각 120mm/s 및 60mm/s로 설정하였다. 도출된 예측식과 설정된 허용수준으로부터 현장에서 사용할 수 있는 안전발파를 위한 환산거리 조건식을 설정하였다. 설정된 환산거리 조건식은 채광장 사면과 폐석더미에 대해 각각 $D_s{geq}5$ 및 $D_s{geq}10$이다. 또한, 환산거리 조건식을 만족시킬 수 있도록 천공장 $3.3{sim}8.8m$에 대하여 몇 가지 표준발파패턴을 제안하였다.

• 한국수산과학회지
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• 제28권4호
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• pp.492-502
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• 1995

공사 소음이 공사장 주변의 양식 가물치 (체장 44cm)의 유영행동에 어떠한 영향을 미치는지 조사하기 위하여 1993년 9월 12일 경기도 평택시 신대리의 아산호 부근에 위치한 육상 양어장에서 파일작업전과 파일작업중의 소음 레벨과 진동을 측정하고, 바이오 텔레메트리 기법을 사용하여 유영행동을 측정하였으며, 그 결과는 다음과 같다. 1) 파일작업중 소음원으로 부터 약 90m의 거리에서 측정한 수중 소음 레벨, 공중 소음 레벨 및 진동 변위는 파일 작업전에 비하여 각각 36.5dB$(re\;l{\mu}Pa)$, 23dB$(re\;0.0002{\mu}bar)$ 및 $5.9{\mu}m$로 증가하였다. 2) 유영속도의 변화 폭은 자극을 가한 초기에 크고, 자극이 계속되면 그 변동폭은 감소하는 경향을 보였다. 활동량은 야간 보다 주간이 많고, 심한 자극을 받으면 상하운동을 많이 하며 양어장 바닥의 진흙 속으로 도피하는 경우도 있음을 알 수 있었다. 3) 파일작업중의 평균 유영속도는 0.50m/sec (체장대비 1.1배), 파일작업이 없을 때의 평균 유영속도는 0.36m/sec (체장대비 0.8배)이었으며, 파일작업중의 가물치의 평균 속도가 파일작업이 없을 때에 비하여 약 1.4배 빠른 것으로 나타났다. 이러한 소음이나 진동으로 인한 자극은 가물치의 생태에 상당한 영향을 미칠 것으로 사료된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.835-841
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• 2013

Modern solid-state gyroscopes (HRG) with hemispherical resonators from high-purity quartz glass and special surface superfinishing and ultrathin gold coating become the best instruments for precise-grade inertial reference units (IRU) targeting long-term space missions. Designing of these sensors could be a notable contribution into development of Korea as a space nation. In participial, 40mm diameter thin-shell resonator from high-purity fused quartz, fabricated as a single-piece with its supporting stem has been designed, machined, etched, tuned, tested, and delivered by STM Co. (ATS of Ukraine) several years ago; an extremely-high Q-factor (upto 10~20 millions) has been shown. Understanding of the best way how to match such a unique sensor with inner glass assembly of the gyro means how to use the high potential in a maximal extent; and this has become the urgent task. Inner quartz glass assembly has a very thin indium (In) layer soldered the resonator and its silica base (case), but effects of internal resonances between operational modal pair of the shell-cup and its side (parasitic) modes can notable degrade the potential of the sensor as a whole, instead of so low level of resonator's intrinsic losses. Unfortunately, there are special combinations of dimensions of the parts (so-called, "resonant sizes"), when intensive losses of energy occurs. The authors proposed to use the length of stem's fixture as an additional design parameter to avoid such cases. So-called, a cyclic scheme of finite element method (FEM) and ANSYS software were employed to estimate different combinations of gyro assembly parameters. This variant has no mismatches of numerical origin due to FEM's discrete mesh. The optimum length and dangerous "resonant lengths" have been found. The special attention has been paid to analyses of 3D effects in a cup-stem transient zone, including determination of a difference between the positions of geometrical Pole of the resonant hemisphere and of its "dynamical Pole", i.e., its real zone of oscillation node. Boundary effects between the shell (cup) and 3D short "beams" (inner and outer stems) have been ranged. The results of the numerical experiments have been compared with the classic model of a quasi-hemispherical shell band with inextensional midsurface, and the solution using Rayleigh's functions of the $1^{st}$ and $2^{nd}$ kinds. To guarantee the truth of the recommended sizes to a designer of the real device, the analytical and FEM results have been compared with experimental data for a party of real resonators. The consistency of the results obtained by different means has been shown with errors less than 5%. The results notably differ from the data published earlier by different researchers.