• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.6
• /
• pp.1723-1730
• /
• 2014

The use of strand wire in structure has been increased by the recent development of construction technologies. Until now, in spite of difficult problems in measuring strand stresses within PSC girders, indirect estimation with a load cell or accelerometer has been often used. In this paper, the electrical resistance strand meter for effective measurement of strand stresses is proposed with experiments considering material, location and thickness of sensor. The reliability and feasibility of the strand meter is enhanced through the experiment with 29.9m PSC girder.

• International Journal of Highway Engineering
• /
• v.11 no.1
• /
• pp.247-256
• /
• 2009

This research was conducted to analyze the behavior of PTCP (Post-Tensioned prestressed Concrete Pavement) under tensioning by performing field tests when the experimental PTCP slab was being constructed. The displacements in the slab under the environmental loading and tensioning were measured using temperature measurement sensors and displacement transducers. Tensioning was performed three times and appropriateness of tensioning could be determined by investigating the relationship between temperature and displacement, behavior of transverse crack, and daily change in displacement. The results of this study showed that under the first tensioning at very early age, large displacements were observed only near the joints because of the friction between slab and underlying layer and concrete inelasticity. Under consecutive tensioning, displacements were clearly observed all over the slab, but still affected by the friction. In addition, appropriate tensioning ensured the one-slab behavior of the PTCP slab even though cracks existed.

• Tunnel and Underground Space
• /
• v.19 no.5
• /
• pp.388-396
• /
• 2009

Rock bolt is one of the most important supports for tunnelling to prevent excessive ground relaxation at the primary tunnel excavation stage. It forms a ground arch band by confining the ground around a tunnel. Rock bolt has various effects, such as support or hanging effect, internal pressure effect, arching effect, ground improvement effect etc. Most studies on rock bolt focused on the concept of support, but only a few researches on the ground reinforcing effect by pre-tensioning a rock bolts. In this study, large scale model tests are performed to investigate the ground reinforcing effect of rock bolts for regularly jointed rocks. Simple beam model was built to find out the reinforcing effect of jointed rocks, which was reinforced by pre-tensioned rock bolts. Settlement of model beam was analyzed through measuring its sagging for various installation intervals.

• International Journal of Highway Engineering
• /
• v.12 no.4
• /
• pp.157-164
• /
• 2010

This research was conducted to analyze the behavior of Single-PTAS (Single Post-Tensioned Approach Slab) under tensioning and environmental loads by performing field tests when the demonstration Single-PTAS was being constructed. The temperature measurement sensors were installed at different depths, and the displacements in the approach slab under environmental loads and tensioning were measured using displacement transducers. As an experimental result, an abrupt change in the longitudinal displacement due to tensioning was not observed. The daily temperature change in the approach slab was negligible where the depth is over about 35cm. The temperature gradient in the approach slab adjacent to bridge was smaller than that adjacent to pavement. The patterns and magnitudes of vertical displacements were directly related to the temperature gradient at the measuring location. The behavior of Single-PTAS was very similar to that of concrete pavement. Therefore, a new design methodology for approach slabs is needed to include the pavement concept and to overcome drawback of current design procedures based on the simple beam concept.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.141-142
• /
• 2009

This study discusses attempt of utilizing the natural frequencies to evaluate the effective stress of post-tensioned, external tendon in field. This type of structure has distinct advantage of good accessibility of tendon, which is considered to be one of essential elements in entire bridge. Six tendons in single span of PSC bridge were applied. They were excited using an impact hammer and corresponding vibrations were measured using multiple accelerometers. The stiff string model in idealized conditions was used to evaluate the effective stress in tendons.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.4
• /
• pp.13-25
• /
• 2018

When deformation occurs on slope reinforced with anchor, shear stress and bending stress are applied on the shear surface along the slip surface and increase of the shear deformation causes the tension force variation of the anchor. In this study, shear test was performed by measuring the tension force of the anchor by inducing shear deformation in vertical direction of the anchor using a large-scale direct shear test equipment in order to confirm the tension force variation of the anchor induced by shear deformation. The shear test was performed for 8 conditions which were classified according to the anchor reinforcement, separation distance (1D, 2D, 4D) from the shear surface to bonded part and the lateral-pressure condition (0.1 MPa, 0.2 MPa) of adjacent ground. As a result of the shear test, it was found that the separation distance and the lateral-pressure condition affect the shear force of the ground reinforced by anchor and the tension force of the anchor, and experimentally verified that the shear force variation is related to axial force variation of the anchor head and tip. Therefore, it was confirmed that the behavior of the bonded part induced by the shear deformation can be indirectly predicted by analyzing the tendency of the tension force variation of the anchor head.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.27 no.3
• /
• pp.12-20
• /
• 2023

This study presents basic data on how to secure stability by analyzing the change in tensile force of steel rod and the inclination characteristics of PSC BOX in the "Temporary fixation system using internal prestressing tendon", which is mainly applied to construction of superstructures by FCM. To date, it has been difficult to confirm the changes in tension force of the steel rod and the inclination of the PSC BOX because the steel rod was installed vertically inside the pier and the PSC BOX. Therefore, measurement of the change in length of the steel rod and the displacement of PSC BOX were performed using a micro-measured FBG sensor. Comparisons of the calculated tensile force and the residual tensile force of the steel rod revealed that the safety factor decreased in all bridges. The cause was mainly identified to be the loss of tensile force in fixation~1segment, and countermeasures are suggested. The analysis of the inclination characteristics showed that the inclination increased with the segment progresses even in bridges with sufficient safety factor, and the difference before and after the segment was confirmed. In addition, the increase in inclination was related to the loss of tension force in the steel rod, and the stress on the opposite sides of the inclination was further reduced. It is believed that upward tensile force is generated in the steel rod on the opposite side of the inclined side due to the unbalanced moment, causing the difference in stress of the steel rod between the two sides.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.9
• /
• pp.4098-4106
• /
• 2012

This study aims to investigate the effect of trunk muscle strengthening exercises on balance performance of sitting posture and muscle tone, targeting the children with spastic diplegic cerebral palsy. 16 children with spastic diplegic cerebral palsy in IV phase of GMFCS were sampled at random and the tests were conducted for 6 weeks, 3 times per week. For experimental groups, only trunk muscle strengthening exercises were conducted and for control groups, only basic physical therapy was conducted. The trunk muscle strengthening exercise consisted of 2 exercises to strengthen abdominal muscles and back muscles. BPM(Balance Performance Monitor) was used to measure balance performance and MMAS(Modified Modified Ashworth Scale) was used to measure muscle tone. As a result, the changes of sitting balance performance in experimental groups and control groups show significant difference in the changes of sway path and sway velocity(p<.05), the comparison of changes in sitting balance performance in between experimental groups and control groups show significant difference in the changes of sway path and sway velocity(p<.05). Knee flexor muscles and hip adductor muscles in both groups show no significant difference in changes of the muscle tone(p>.05). Therefore, the balance performance in both experimental groups and control groups was improved. However, the experimental group had more significant improvement in balance performance and no change in muscle tone was detected in both groups. Thus, these findings show trunk muscle strengthening exercises are effective in improving the balance performance of sitting posture for the children with spastic diplegic cerebral palsy without changing muscle tone.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.341-344
• /
• 2008

In this paper, the effect of flame cutting order of tendons on the concrete stress was investigated experimentally. For this, the three slab specimens with 14 tendons were cast and tested. During the detensioning, the longitudinal and transversal strain were measured. Test results showed that the measured strains of transversal stirrups were varied by the cutting order.

• The Journal of the Korea Contents Association
• /
• v.15 no.8
• /
• pp.424-433
• /
• 2015

This study tried to investigate the differences between auditory preferences for a discrimination study of minimal pairs with the different onset and the same nucleus of a syllable on the basis of articulator-distance in case of Korean infants and toddlers. As a result we found a main effect for articulator-distance and age but not an effect according to the types of phonation especially in terms of tense. Former results are line with the previous studies having reported the order of consonants acquisition based on the places of articulation suggesting that more sensitive responses for the contiguous and different phonemes may lead earlier acquisition for the same place of articulation of the speech sounds. Specifically, bilabial soudns are followed by alveolar and palatal sounds in order. The latter results also showed that tense consonants got a high rate of recognition beside lax consonants according to the age and sex.