• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.555-567
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• 2013

Slim floor system using deep decks has been developed and employed in Europe to reduce the floor height of steel structures. Although long span buildings involving the issue of reducing floor height are being increasingly built in Korea, employing deep decks in more than 7m long span structures is likely to cause problems associated with excessive deflection. This study is applied to the long-span concrete casting of the deep deck plate usability of deflection due to bending and torsional instability of open cross-section, as a way to improve the problem of cap plates are suggested, and the optimum length of reinforcement and location are derived from theoretic estimation. The cap plates are placed on the deep decks with regular intervals to overcome the instability of open sections, improve the stiffness of the sections and control the deflection at the centers. The improvement in flexural capacity associated with the location of the cap plates and the length of reinforcement are verified through analysis and test.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.9-12
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• 2008

The semi-rigid joint is the shape of middle that can supplement the defect of pin joints and accept the good point of rigid joints. Recently, a study on the pin joints is activated in the country, but because the study on semi-rigid joints is not many, this study tried to prove with producing test model of three shape. The test models are rigid joint HI-R, semi-rigid joint HI-S, pin joint HI-P. As a result of the test, respectively HI-R, HI-S, HI-P appeared shear failure of joint, flexure failure of the top fixing, flexure failure of the lower part slipping stair slab, and the maximum strength is measured to 51.74, 51.4, 24.63kN, the stiffness is appeared 1.58, 1.19, 0.37 respectively, The yield strength is respectively kept 44.5, 47.3, 24kN, and ductility ratio is appeared to 3.31, 2.32, 1.54, when is based on KBC code, sag of the acting service load is appeared that HI-P model is over the standard. When is based on distribution of bars strain ratio, HI-S seems similar behavior incipiently, but after the yield, the semi-rigid joint was able to be judged better than pin joint because of the stress allotment of joint internal elements.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.10-18
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• 2014

Mechanically fastening FRP (MF-FRP) strips using nails and anchors, has been shown to provide a more ductile behavior to the strengthened structural element than using bonded FRP. To further advance the state of the knowledge on this strengthening method, the current study examined environmental effects for six months on MF-FRP beams. Reinforced concrete beams strengthened with mechanically fastened FRP strips and subjected to sustained loads for six months were exposed to outdoor weather and constant high temperatures ($40^{\circ}C$). For comparison, the behavior of RC beam with and without sustained loads was evaluated. Results from flexural tests did not show any significant degradation or change of failure mode as a result of sustained load and of environmental effects such as high temperatures and outdoor weather over a period of six months. Failure of the beams was governed by FRP delamination followed by concrete crushing as not much load applied to the nail and anchors because of slip effects.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.1-8
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• 2017

Three small scale hollow circular reinforced concrete columns with aspect ratio 4.5 were tested under cyclic lateral load with constant axial load. Diameter of section is 400 mm, hollow diameter is 200 mm. The selected test variable is transverse steel ratio. Volumetric ratios of spirals of all the columns are 0.302~0.604% in the plastic hinge region. It corresponds to 45.9~91.8% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The longitudinal steel ratio is 2.017%. The axial load ratio is 7%. This paper describes mainly crack behavior, load-displacement hysteresis loop, seismic performance such as equivalent damping ratio, residual displacement and effective stiffness and flexural over-strength of circular reinforced concrete bridge columns with respect to test variable. The regulation of flexural over-strength is adopted by Korea Bridge Design Specifications (Limited state design, 2012). The test results are compared with nominal strength, result of nonlinear moment-curvature analysis and the design specifications such as AASHTO LRFD and Korea Bridge Design Specifications(Limited state design).

• Polymer(Korea)
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• v.36 no.5
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• pp.555-563
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• 2012

Warpage of injection molded product is caused by non-uniform shrinkage during shaping operation and relaxation of residual stress. Robust part design and glass fiber reinforced reins have been adopted to prevent warpage of part. Warpages for part designs have been investigated in this study according to the injection molding conditions. Part design contains flat specimen and two different rib designs in the flat part. Resins used in this study were glass fiber reinforced amorphous plastics, PC and ABS. Different rib designs showed significant differences of warpages in the parts. Various warpages have been observed in the three regions of the part, near gate region, opposite region to the gate, and flow direction region. Results of computer simulation revealed that the warpages were strongly related to glass fiber orientation. Flat specimen showed the smallest warpage and the specimen with ribs to the flow direction showed a high resistance to warpage. Warpage highly depended upon part design rather than molding condition. It was concluded that the rib design and selection of gate location in injection molding would be the most important factors for the control of warpage since those are directly related to the fiber orientation during molding.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.125-135
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• 2015

The tendency of more longer span length being required economical in railway bridges is studying about PSC I shaped girder. In this case, it is important to analyze and choose the effective girder section for stiffness of bridge. This study investigates the dynamic properties and safety of PSC I shaped girder being used wide upper flange whose selection based on radii and efficiency factor of flexure for railway bridge in different span type. In addition, 40m PSC Box girder bridge adopted in Honam high speed railway is further analyzed to compare dynamic performance of PSC I shaped girder railway bridge with same span length. Time history response is acquired based on the mode superposition method. Static analysis is also analyzed using standard train load combined with the impact factor. Consequently, the result met limit values in every case including vertical displacement, acceleration and distort.

• Journal of the Korean Society for Railway
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• v.20 no.5
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• pp.649-657
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• 2017

In this study, fatigue testing was carried out for long-term use of rail according to track type. From S-N curves for 50%~0.01% failure probability, the fatigue life of the long-term use rail for each track type was derived using the weight probability analysis technique on the experimental data. Because the rails used in the fatigue test have different cumulative tonnages, the number of repetitions was modified by averaging the cumulative tonnage. In addition, the bending stresses of rail bottoms, considering rail surface irregularities, track support stiffnesses and train speeds, were evaluated using the predicted rail bending stresses derived from existing studies. As a result, for rail fatigue life evaluation, the fatigue life of rail on the ballast track was found to be more than 200 million tons higher than the standard value for rail replacement. Also, the fatigue life of rail on concrete track is more than 300 million tons higher than that on ballast track. The Haibach rule is adaptable for the fatigue life evaluation of rail for stress range under fatigue limit.

• Journal of the Korean Geotechnical Society
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• v.24 no.7
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• pp.61-73
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• 2008

Piles of a bridge pier are connected with the column through the pile cap (footing). Behavior of the pile foundation can be different according to the connection method between piles and the pile cap. Connection methods between pile heads and the pile cap are divided into two groups : rigid connections and hinge connections. Domestic design code has been specified to use rigid connection method for the highway bridge. In the rigid connection method, maximum bending moment of a pile occurs at the pile head and this helps the pile to prevent the excessive displacement. Rigid methods are also good to improve the seismic performance. However, some specifications prescribe that conservative results through investigations of both the fixed-head condition and the free-head condition should be reflected in the design. This statement may induce an over-estimated design for the bridge which has high-quality structures with casing covered drilled shafts and the PC-house contained pile cap. Because the assumption of free-head conditions (hinge connections) is unreal for the elevated pile cap system with multiple piles of the long span sea-crossing bridges. On the other hand, elastic displacement method to evaluate the pile reactions under the pile cap is not suitable for this type of bridges due to impractical assumptions. So, full modeling techniques which analyze the superstructure and the substructure simultaneously should be performed. Loads and stress state of the large diameter drilled shaft and the pile cap for Incheon Bridge which will be the longest bridge of Korea were investigated through the full modeling for rigid connection conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.301-310
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• 2006

Carbon fiber reinforced polymer (CRFP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength to weight ratio and high stiffness to weight ratio. Their application in the field of the rehabilitation of concrete structures is increased due to the vast number of bridges and buildings in need of strengthening. However, RC members, strengthened with externally bonded CFRP plates, happened to collapse before reaching the expected design failure load. Therefore, it is necessary to develop the new strengthening method to overcome the problems of previous bonded strengthening method. This problems can be solved by prestressing the CFRP plate before bonding to the concrete. In this study, a total of 21 specimens of 3.3 m length were tested by the four point bending method after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with various prestress levels ranging from 0.4% to 0.8% of CFRP plate strain. All specimen with end anchorage failed by a plate fracture regardless of the prestress levels while the specimen without end anchorage failed by the separation of the plate from the beam due to premature debonding. The cracking loads was proportionally related to the prestress levels, but the maximum loads of specimens strengthened with prestressed CFRP plates were insignificantly affected by the prestress levels.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.169-176
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• 2010

Generally, poly-urea is widely used as waterproof coating material due to its superior adhesiveness, elongation capacity, and permeability resistance. In addition, it can be quickly and easily applied on structure surfaces using spray application. Since it hardens in about 30 seconds after application, its construction efficiency is very high and its usage as a special functional material is also excellent. However, currently, poly-urea is mostly used as waterproof coating material and the researches on its usage as a retrofitting material is lacking at best. Therefore, basic studies on the use of poly-urea as a general structural retrofitting material are needed urgently. The objective of this study is to develop most optimum poly-urea composition for structure retrofitting purpose. Moreover, the structural strengthening capacity of the developed poly-urea is evaluated through flexural capacity experiments on RC beams and RC slabs. From the results of the flexural test of poly-urea strengthened RC beam and slab specimens, the poly-urea and concrete specimen showed monolithic behavior where ductility and ultimate strength of the poly-urea strengthened specimen showed slight increase. However, the doubly reinforced specimens with FRP sheet and poly-urea showed lower capacity than that of the specimen reinforced only with FRP sheet.