• Structural Engineering and Mechanics
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• v.74 no.6
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• pp.747-756
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• 2020

High-strength concrete (HSC) generally is made with high amount of cement which may release large amount of hydration heat at early age. The hydration heat will increase the internal temperature of slab and may cause potential cracking. In this study, slab specimens with a dimension of 600 × 600 × 100 mm were cast with concrete incorporating silica fume for test. The thermistors were embedded in the slabs therein to investigate the interior temperature development. The test variables include water-to-binder ratio (0.25, 0.35, 0.40), the cement replacement ratio of silica fume (RSF; 5 %, 10 %, 15 %) and fly ash (RFA; 10 %, 20 %, 30 %). Test results show that reducing the W/B ratio of HSC will enhance the temperature of first heat peak by hydration. The increase of W/B decrease the appearance time of second heat peak, but increase the corresponding maximum temperature. Increase the RSF or decrease the RFA may decrease the appearance time of second heat peak and increase the maximum central temperature of slab. HSC slab with the range of W/B ratio of 0.25 to 0.40 may occur cracking within 4 hours after casting. Reducing W/B may lead to intensive cracking damage, such as more crack number, and larger crack width and length.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.51-56
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• 2000

Demand for new nondestructive evaluations is growing to detect tensile crack growth behavior to predict long term performance of materials and structure in aggressive environments, especially when they are in non-visible area. Acoustic emission technique is well suited to these problems and has drawn a keen interests because of its dynamic detection ability, extreme sensitivity and location of growing defects. In this study, we analysed acoustic emission signals obtained in tensile test of high strength fire resistance steel for frame structure with time frequency analysis methods. The results obtained are summaries as follows ; In the T and TN specimen consisting of ferrite and pearlite grains, most of acoustic emission events were produced near yield point, mainly due to the dislocation activities during the deformation. However, B specimen under $600^{\circ}C$ - 10min had a two peak which was attribute to the presence of martensite phase. The first peak is before yield point the second is after yield point. The sources of second acoustic emission peak were the debonding of martensite-martensite interface and the micro-cracking of brittle martensite phase. In $600^{\circ}C$-30min to $700^{\circ}C$-60min specimens, many signals were observed from area before yield point and counts were decreased after yield point.

• The Journal of Korean Physical Therapy
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• v.11 no.1
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• pp.103-110
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• 1999

The purpose of this study was to analyze the correlation coefficients between delayed muscle soreness after eccentric exercise, muscle strength, CPK, and ALD. Subjects of this study were 9 male students. CPK, ALD that known as the indicators of muscle damage and eccentric strength of the Lt elbow flexors were measured prior to exercise. After measurements Hey Perform an isokinetic eccentric exercise of flexor group of 1 elbow(10 repetitions 3 bouts) by make use of KIN-COM isokinetic device. After exercise, CPK, ALD, and peak torque of elbow flexor group was measured at the just after exercise, 24hr after, 72hr after. Also muscle soreness level was evaluated at same intervals by make use of VAS(visual analog scale). The results were as follows : 1 . There was significant differencess or muscle soreness, CPK, ALD, peak torque with the passage or recovery time (p<0.001). 2. There was negative correlation coefficients between CPK and peak torque at 24hr after(p<0.05). 3. There was positive correlation coefficients between ALD and CPK at 24hr after(p<0.05). 4. There was no correlation coefficients between other variables but ALD was the most important factors that can be explains the muscle sur eness very well.

• Journal of Korea Multimedia Society
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• v.21 no.7
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• pp.772-778
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• 2018

We have previously proposed a preliminary cut-off indoor positioning scheme considering the reference point with the same signal similarity. This scheme estimates the position using the relative rank of the peak of received signal strength from the beacons around user. However, this scheme has a weak point with lower accuracy when there are more than one nearest reference points having the same signal similarity. In order to tackle this, we propose a weighted preliminary cut-off indoor positioning scheme. Firstly, if the above problem occurs, the similarity to the peak of signal strength is considered as well as the relative rank. Next, weights are assigned to the nearest reference points using the similarity to the peak of the received signal strength. Finally, the user's position is estimated by applying the weights. As a result, the weighted preliminary cut-off scheme improves the positioning accuracy by about 7.9% compared to the previous scheme.

• Physical Therapy Korea
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• v.1 no.1
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• pp.47-54
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• 1994

This study was designed to develop an objective method of strength measurement of muscles controlling the wrist joint in normal subjects. Forty subjects (20 male, 20 female) with a mean age of 22 years, were tested isokinetically at $60^{\circ}/sec$ and $120^{\circ}/sec$. Results were as follows, 1) Peak torque for wrist flexors, extensors were significantly different for both speeds, but wrist ulnar deviator, radial deviator peak torques were not, 2) Mean values for all muscle groups controlling the wrist were not significantly different for both speeds in the female group, 3) All mean values at both $60^{\circ}/sec$ and $120^{\circ}/sec$ were significantly different between males and females, 4) Means and standard deviations of wrist joint angle of movement at peak torque were determined.

• Geomechanics and Engineering
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• v.24 no.1
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• pp.81-89
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• 2021

Uniaxial compression tests were conducted on sandstone-CGFB composite samples with different interface angles, and their strength, acoustic emission (AE), and failure characteristics were investigated. Three macro-failure patterns were identified: the splitting failure accompanied by local spalling failure in CGFB (Type-I), the mixed failure with small sliding failure along with the interface and Type-I failure (Type-II), and the sliding failure along with the interface (Type-III). With an increase of interface angle β measured horizontally, the macro-failure pattern changed from Type-I to Type-II, and then to Type-III, and the uniaxial compressive strength and elastic modulus generally decreased. Due to the small sliding failure along with the interface in the composite sample with β of 45°, AE events underwent fluctuations in peak values at the later post-peak failure stage. The composite samples with β of 60° occurred Type-III failure before the completion of initial compaction stage, and the post-peak stress-time curve initially exhibited a slow decrease, followed by a steep linear drop with peaks in AE events.

• Steel and Composite Structures
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• v.31 no.6
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• pp.559-573
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• 2019

Spiral spacing effect on axial compressive behavior of reinforced concrete filled steel tube (RCFST) stub column is experimentally investigated in this paper. A total of twenty specimens including sixteen square RCFST columns and four benchmarked conventional square concrete filled steel tube (CFST) columns are fabricated and tested. Test variables include spiral spacing (spiral ratio) and concrete strength. The failure modes, load versus displacement curves, compressive rigidity, axial compressive strength, and ductility of the specimens are obtained and analyzed. Especially, the effect of spiral spacing on axial compressive strength and ductility is investigated and discussed in detail. Test results show that heavily arranged spirals considerably increase the ultimate compressive strength but lightly arranged spirals have no obvious effect on the ultimate strength. In practical design, the effect of spirals on RCFST column strength should be considered only when spirals are heavily arranged. Spiral spacing has a considerable effect on increasing the post-peak ductility of RCFST columns. Decreasing of the spiral spacing considerably increases the post-peak ductility of the RCFSTs. When the concrete strength increases, ultimate strength increases but the ductility decreases, due to the brittleness of the higher strength concrete. Arranging spirals, even with a rather small amount of spirals, is an economical and easy solution for improving the ductility of RCFST columns with high-strength concrete. Ultimate compressive strengths of the columns are calculated according to the codes EC4 (2004), GB 50936 (2014), AIJ (2008), and ACI 318 (2014). The ultimate strength of RCFST stub columns can be most precisely evaluated using standard GB 50936 (2014) considering the effect of spiral confinement on core concrete.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.345-346
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• 1996

The contrasting values of the oscillator strengths for the (0,0) band of SiH+ molecules for the $A\;^1II-X\;^1{\sum}+$ transition reported in literature, motivated us to reinvestigate the same with the help of a new set of well accepted solar photospheric models, elemental abundances and dissociation energy.

• Tunnel and Underground Space
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• v.7 no.1
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• pp.31-38
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• 1997

Residual shear strength should be taken into consideration as well as peak one when analysing stability of slopes constituted by weathered rock or overconsolidated soils since such materials could be subjected to progressive failure mechanism. When landslide of a slope is related to progressive failure phenomenon, the failure might occur even though shear strength of the slope materials does not reach their residual shear strength over the whole slip surface. Therefore, stability of the slope concerned may be overstimated or underestimated when using only its peak or residual shear srength parameters. Mechanical description for progressive failure phenomenon is given by Bjerrum(1967). In parameters. Mechanical description for progressive failure phenomenon is given by Bjerrum(1967). In this study, his theory has been extended to estimate the distance of failed zone for a plane slope and the results calculated by this extended equatio has been compared with that obtained by numerical modelling using FLAC. In addition, stress state on the slip surface has been, in detail, analysed to understand failure mechanism when a limited progressive failure occurs. Effects of mechanical and hydraulic factors on progressive failure have also been analysed.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.659-664
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• 2001

Concrete has a different fracture mechanism from the other materials, with the existing of FPZ at the ahead of its cracks, and represents the softening curves at the post-peak load in the load-displacement diagrams. So, it can transmit the stress at the post-peak load. This can not be understood with the traditional concept of strength, but with the theory based energy approach. For the purpose of this study is mainly used RILEM(1990 TC89-FMT) and TPM, and the concrete fracture properties have been evaluated according to the its compressive strength. The evaluated fracture properties is $G_{F}$, $a_{c}$, $K_{IC}$ , CTODc, Q etc.c.c.