• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.15-25
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• 2006

The researches on the early-aged concrete hydration process and the techniques for the early-aged concrete crack control mainly have been focused and developed on the massive concretes in both experimental and numerical studies. However, those researches for relatively thin members such as the upper slab of the reinforced concrete rahmen bridge have nearly been attempted. In this study, a designing technique for crack controlling in the thin members of the early-aged reinforced concrete rahmen bridges based on measured temperature history, strength revelation model and sinkage model is proposed. A method of calculating the reinforcing bar area for crack controlling is also proposed and it is found that the distributing bars under the design loads become the main reinforcing bars in the temperature stress analysis of the early-aged reinforced concrete rahmen bridges. It is shown that the proposed analysis technique is able to use the design of crack control for the early-aged reinforced concrete rahmen bridge.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.695-705
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• 2014

Precast concrete (PC) beam-column connections using ductile rods are proposed for earthquake zone. An existing beam-column connection, two PC specimens designed by considering failure modes and a conventional RC specimen were tested under cyclic loading to evaluate the seismic performance. The specimens were designed to satisfy the requirements of current design code. The variables are the yield strength of longitudinal reinforcing bars of PC beams. The test results showed that the proposed system applying smaller yield strength of the longitudinal reinforcing bars at the PC beams than the ductile rods was satisfied with seismic criteria. The deformation capacity and energy dissipation capacity of the proposed PC beam-column connections were greater than those of the existing DDC system.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.55-65
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• 2008

This study introduced a new method to retrofit RC columns with lap splice that do not have enough ductility during an earthquake. The new method used mechanical external pressure and split steel plates around the RC columns. The introduced method does not require grouting the gap between jacket and concrete surface. In this study, 45 concrete cylinders were manufactured with varyingstrengths and part of them was retrofitted with split steel jackets under a lateral confining stress. The effect of the new method was verified by comparing the results from the compressive tests of retrofitted and unretrofitted cylinders. The steel jacket that was built following the new method showed good results of increasing the compressive strength and ductility of concrete cylinders. The thicker steel jackets showed larger compressive strength, however, the ductility at failure depends on their welding quality.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.95-102
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• 2023

This study investigated the structural performance of wire-integrated steel decks with varied lattice end support conditions through finite element analysis. The results indicated that the steel decks with the lattice foots positioned above the supporting structural member have the higher system stiffness compared to the cases with the lattice foots shifted away from the support. It is also observed that the contribution of the end vertical bars on both the system stiffness and the strength is negligible when the lattice foots are located on the support. It is, especially, revealed that the end vertical bars can be eliminated when the lattice foot length is not smaller than 40mm. The ultimate load-carrying capacity of the system is not significantly affected by the lattice end support condition. The failure mode of the system is the top bar buckling at the center of the deck plate, the lattice end buckling, and the combination of both depending of design intention.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.581-590
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• 2008

The panels are used as a composite part of the completed deck. They replace the main bottom transverse deck reinforcement and also serve as a form surface for the cast-in-place concrete upper layer that contains the top of deck reinforcement. In this paper, three types of the detail for joints was selected and their structural performance in terms of strength and crack contral was investigated through static tests on composite beams. Form the results, the validity of loop joints for continuity of half-depth precast deck was observed and especially an overlapping length of loop joint and transverse reinforcement were checked. The results suggest that increasing the loop overlapping length increases the flexural strength of half-depth precast deck with loop joints. In terms of crack contral, the loop joint with transverse reinforcement showed better performance.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.433-445
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• 2009

The panels are used as a composite part of the completed deck. They replace the main bottom transverse deck reinforcement and also serve as a form surface for the cast-in-place concrete upper layer that contains the top of deck reinforcement. Research has also demonstrated that mechanical shear ties on the top of the panels are required. In a composite deck with precast panels, it is required to notice behavior of transverse joints between panels. In this paper, static tests of composite deck with shear ties and loop joints were conducted. From the results, the validity of loop joints for continuity of deck was observed. Also, a composite behavior was abserved between precast panel and slab concrete. Tested composite decks with shear ties have 140~164% ultimate strength than have no shear ties due to the increase of composite action. Therefore, the shear ties between the slabs were sufficient to enforce composite flexural behavior to failure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1A
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• pp.35-43
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• 2010

The panels are used as a composite part of the completed deck. They replace the main bottom transverse deck reinforcement and also serve as a form surface for the cast-in-place concrete upper layer that contains the top of deck reinforcement. However, in order to apply the precast panels to bridges properly, it is necessary to fully understand the structural characteristics of joint in precast panels. Particularly, since the bridge deck is under repeated loads such as traffic loads, fatigue behavior and characteristics of joint should be investigated. In this paper, fatigue tests of composite deck with shear ties and loop joints were conducted. The fatigue tests were conducted with an application of repeated loading and wheel loading. Test results were analyzed to examine the current design code for fatigue of reinforcement bar and serviceability under repeated loading.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.503-514
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• 2011

In this research, the seismic connection details for two concrete-filled U-shape steel beam-to-H columns were proposed and cyclically tested under a full-scale cruciform configuration. The key connecting components included the U-shape steel section (450 and 550 mm deep for specimens A and B, respectively), a concrete floor slab with a ribbed deck (165 mm deep for both specimens), welded couplers and rebars for negative moment transfer, and shear studs for full composite action and strengthening plates. Considering the unique constructional nature of the proposed connection, the critical limit states, such as the weld fracture, anchorage failure of the welded coupler, local buckling, concrete crushing, and rebar buckling, were carefully addressed in the specimen design. The test results showed that the connection details and design methods proposed in this study can well control the critical limit states mentioned above. Especially, the proposed connection according to the strengthening strategy successfully pushed the plastic hinge to the tip of the strengthened zone, as intended in the design, and was very effective in protecting the more vulnerable beam-to-column welded joint. The maximum story drift capacities of 6.0 and 6.8% radians were achieved in specimens A and B, respectively, thus far exceeding the minimumlimit of 4% radians required of special moment frames. Low-cycle fatigue fracture across the beam bottom flange at a 6% drift level was the final failure mode of specimen A. Specimen B failed through the fracture of the top splice plate of the bolted splice at a very high drift ratio of 8.0% radian.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.9-14
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• 2017

In the present work, a mechanical performances under cyclic loading in RC (Reinforced Concrete) beams with normal steel and FRPH (Fiber Reinforced Plastic Hybrid) bar are investigated. For the work, RC beam members with $200{\times}200{\times}2175mm$ of geometry and 24 Mpa of design strength are prepared, and 4-point-bending tests are performed for evaluation of cracking, yielding, and ultimate loads. Through static loading test, 48.9kN and 36.0 kN of yielding loads are measured for normal RC and FRPH beam, respectively. They have almost same ultimate load of 50.0 kN. Typical tension hardening behavior is observed in FRPH beam, which is caused by the behavior of FRPH bar with tension hardening. In cyclic loading conditions, FRPH beam has more smaller crack width and scattered crack pattern, and it shows more elastic recovery than normal RC beam. The energy dissipation ratio in FRPH beam is 0.83, which is greater than 0.62 in normal RC beam and it shows more effective resistance to cyclic loadings.

• Journal of the Korean Society of Physical Medicine
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• v.17 no.4
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• pp.53-63
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• 2022

PURPOSE: This study examined the changes in the thickness of the abdominal muscles, including the transversus abdominis, according to the set pressure applied by a pressure biofeedback unit during contractions of the hip adductor muscles. METHODS: After randomizing 40 healthy adult males in their 20 s and 30 s, the participants were instructed to match the pressure gauge indication of the pressure biofeedback device to continue contracting the hip adductor while maintaining it at 10 mmHg (low), 40 mmHg (medium), or 70 mmHg (high). The measurement was taken over five seconds using an ultrasound device. RESULTS: According to the contractile pressure applied to the hip adductor muscle, there was a significant difference in the muscle thickness change of the transverse abdominis muscle between 10 mmHg and 70 mmHg and between 40 mmHg and 70 mmHg. The muscle thickness ratio of the external oblique/abdominal muscle was significantly different between 10 mmHg and 70 mmHg and between 40 mmHg and 70 mmHg. CONCLUSION: Increased contraction pressure on the hip adductor muscle increases the muscle thickness of the abdominal transverse muscle. Interbody stability exercise with contractions of the hip adductor muscle is expected to help increase in the muscle thickness of the hip adductor muscle.