• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.81-92
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• 2018

For a marine bridge foundation construction, a large-circular-steel-pipe has been proposed for supporting vertical load and preventing water infiltration. However, a ship collision can adversely affect the structural stability. This paper presents a fundamental study on dynamic responses of the large-circular-steel-pipe by an impact load. In laboratory experiments, small-scaled steel pipe is installed in a soil tank. The soil height and water level are set to 23 cm and 25~70 cm, respectively. The upper part of the steel pipe is impacted using a hammer to simulate the ship collision. The dynamic responses are measured using accelerometers and strain gauges. Experimental results show that the strain decreases as the measured location is lowered. The higher frequency components appear in the impact load condition compared to the microtremor condition. However, the higher frequency components measured at the strain gauge located below the water level do not appear. For the accelerometer signal, the maximum frequency under the impact load is higher than that of the microtremor. The maximum frequency decreases as water level increases but it is larger than the maximum frequency of the microtremor. This study shows that strain gauge and accelerometer can be useful for evaluating the dynamic responses of large-circular-steel-pipes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.638-644
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• 2019

In this study, the fluid flow and heat transfer characteristics within sandwich panels are investigated using computational fluid dynamics. Within the sandwich panels having periodic cellular cores, air can freely move inside the core section so that the structure is able to perform multi-functional roles such as simultaneous load bearing and heat dissipation. Thus, there needs to examine the thermal and flow analysis with respect to design variables and various conditions. In this regard, ANSYS Fluent was utilized to explore the flow and heat transfer within the pyramidal truss sandwich structures by varying the truss angle and inlet velocity. Without the entry effect in the first unitcell, the constant rate of pressure and the constant rate of Nusselt number was observed. As a result, it was demonstrated that Nusselt number increases and friction factor decreases as the inlet velocity increases. Moreover, the rate of Nusselt number and friction factor was appreciable in the range of V=1-5m/s due to the transition from laminar to turbulent flow. Regarding the effect of design variable, the variation of truss angle did not significantly influence the characteristics.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.1-8
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• 2019

Steel elevator pit was developed for the purpose of minimizing the excavation, simplifying the construction of the frame and economical efficiency by improving the problems that occurred in the existing reinforced concrete. It is common to apply conventional RC method through excavation to underground structures such as underground floor collector well and elevator pit. In recent years, the use of steel collector well and steel elevator pits to reduce construction costs by minimizing the materials of steel and concrete has been continuously increasing. The steel elevator pit is an underground structure and then the performance of the welding part and the structure system is important. Specimen with only steel plate and concrete without studs could support the load more than 3 times than the specimen with deck only. Therefore, even if there is no stud, the deck (steel plate) rib is formed and the effect of restraining the steel plate and the concrete during the bending action can be expected. However, since sudden fracture in the elevator pit may occur, stud bolt arrangement is necessary for the composite effect of steel plate and concrete. It is expected that the bending strength can be expected to increase by about 15% or more depending with and without stud bolts.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.84-95
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• 2019

This paper reports the process of seismic fragility analysis for the rahman-type continuous bridge system. The target structure was the five span highway bridge with maximum pier hight of 72m. OpenSees software was used for the nonlinear time history analysis. In this study, 50 ground motions are considered for nonlinear time history analysis. For each ground motion, PGA was scaled from 0.1g to 2.0g with intervals of 0.1g in order to consider a wide range of the seismic intensity measure. In addition, yield displacement and ultimate displacement of each pier were calculated through section analysis. Based on the result of non linear time history analysis and section analysis, damage condition of target bridge was classified according to the definition of damage condition proposed by Barbat et al. As a result, it was predicted that Extensive Damage occurred at P1 when 0.731 g earthquake occurred in the longitudinal direction. Based on the seismic fragility analysis results, it is found that the probability of occurrence of Extensive Damage in the 4,800 - year period earthquake was about 4.2%. Therefore the target bridge has enough safety for earthquake.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.71-77
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• 2019

Recently, most of the pile foundations have been applied as a method to transfer the heavy load of the structure to the ground with high bearing capacity. In this study, the pile-cap behavior between foundation and hollow-head precast reinforced concrete(HPC) pile reinforced with longitudinal rebar and filling concrete was experimentally evaluated depending on the cyclic load and reinforcement ratio. As the drift ratio increases, it was found that the cracks pattern and fracture behavior of two types of pile-cap specimens according to the reinforcement ratio were evaluated to be similar. As the reinforcement ratio increases by 1.77 times, the BS-H25 specimen increases the maximum load by 1.47 times compared to the BS-H19 specimen. However, the ductility ratio of positive and negative was decreased by 76% and 70% respectively. After the yielding of the pile-cap reinforcing rebars, the positive and negative stiffness of the all specimens were decreased by a range from 66% to 71% and a range from 54% to 57% respectively, and the average stiffness of BS-H25 specimen is 13% higher than that of BS-H19 specimen. The cumulative dissipated energy capacity of BS-H19 and BS-H25 specimen under ultimate load state is 5.5 times and 6.6 times higher than that of service load state.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.569-576
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• 2019

PSC-Edge Rahmen Bridge makes low thickness and long span by introducing prestressed force to the edge girder and reducing positive moment. In the bridge, diagonal tension cracks occurred in the direction of $45^{\circ}$ to outer side of the girder after the temporary bent supported on the lower part of the upper slab and the secondary strand is tensioned on the girder. Researches on stress distribution and burst crack behavior of pre-stress anchorage has been conducted, it is difficult to analyze an obvious cause due to difference between actual shape and boundary condition. This study performed 3D frame analysis with additional boundary condition of temporary bent, the maximum compression stress occurred in the girder and there was a limit to identify the cause. It performed 3D Solid analysis with LUSAS 16.1 and the maximum principal tensile stress occurred at the boundary between the girder and the slab. As analyzing required reinforcement quantity at obtuse angle of the girder with the maximum principal tensile stress and directional cosine, reinforcement quantity was insufficient. Additional bridges have increased reinforcement quantity and extended area and crack was not occurred. It is expected that cracks on the girder during construction could be controlled by applying the proposed method to PSC-Edge Rahmen Bridge.

• Journal of the Korean Geosynthetics Society
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• v.18 no.1
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• pp.67-77
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• 2019

The grouting method is utilized to reinforce and waterproof poor grounds, enhance the bearing capacity of structures damaged resulting from settlement due to elevation and vibration or differential settlement, and for cutoff. The purpose of this research is to enhance the compressive strength of grout materials by using aramid fiber and develop a high-strength ground improvement method by using blast furnace slag powder. In this regard, this study has conducted a uniaxial compression test after checking the high charge (higher than 50%) of the ratio of blast furnace slag powder and cement at 100:0, 70:30 and 40:60%, adding the aramid mixture based on 0, 0.5 and 1.0% of the cement and furnace slag powder weight and creating sand gels based on surface oiling rate of 0.7 and 1.2%. For the environmental review evaluation, a heavy metal exudation test and a pH test measurement have been conducted. The experiment results showed that 1% increase of aramid fiber led to 1.3 times greater uniaxial compression intensity. As for the hexavalent chrome, a 30% increase in blast furnace slag powder led to approximately 50% decrease in heavy metal exudation. However, the pH test revealed that a 30% increase in blast furnace slag powder resulted in approximately 0.5 increase in pH. Further research on the pH part is needed in the future.

• Journal of the Korean Geotechnical Society
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• v.35 no.7
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• pp.15-27
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• 2019

The purpose of this study is to investigate the mechanism about damages occurring at quay wall and backfill in Youngilman Port during Pohang earthquake (M5.4) on November 15, 2017. In the field investigation, the horizontal displacement of the caisson occurred between 5 cm and 15 cm, and the settlement at backfill occurred higher than 10 cm. 2D-effective Stress Analysis was performed to clarify the mechanism for the damage. The input earthquake motion used acceleration ($3.25m/s^2$) measured at bedrock of Pohang habor. Based on a numerical analysis, it was found that the effective stress decreased due to the increase of excess pore pressure in the backfill ground and the horizontal displacement of the caisson occurred by about 14 cm, and the settlement occurred by about 3 cm. In backfill, the settlements occurred between 6 cm and 9 cm. This is similar to field investigation results. Also, it was found that the backfill soil was close to the Mohr-Coulomb failure line due to the cyclic loading from the effective stress path and the stress-strain behavior. It may be related to decreasing of bearing capacity induced by the reduction of effective stress caused by the increase of the excess pore water pressure.

• Journal of the Korean Geotechnical Society
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• v.37 no.8
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• pp.25-35
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• 2021

Recently, the ground anchor method is commonly applied with nail and rock bolt to secure the stability of slopes and structures in Korea. Among them, permanent anchor which is used for long-term stability should secure bearing capacity and durability during the period of use. However, according to recent studies, phenomenon such as deformation to slope and the reduction of residual tensile load over time have been reported along the long-term behavior of the anchors. These problems of reducing residual tensile load are expected to increase in the future, which will inevitably lead to problems such as increasing maintenance costs. In this study, we identified the factors that affect the tensile load of permanent anchor from a literature study on the domestic and foreign, and investigated the prior studies that analyzed previously conducted load cell monitoring data. Afterwards, using this as basic data, the load cell measurement data collected at the actual site were analyzed to identify the tensile load reduction status of anchors, and the long-term load reduction characteristics were analyzed. Finally, by aggregating the preceding results, proposed a technique to predict the long-term load reduction characteristics of permanent anchors through short-term data to around 100 days after installation.

• Journal of the Korean GEO-environmental Society
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• v.12 no.3
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• pp.55-61
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• 2011

Song-Do international city is the area developed in large-scale land reclamation. Song-Do area consists of reclamation layer, sedimentary layer(loose silt, soft clay and sand alternating) and residual layer from the ground surface. Therefore, using pile foundation is inevitable to build structures safely. In this area, driven PHC piles have been generally constructed in terms of environmental and economic conditions. As a result of analyzing 4 sites in Song-Do district 5 and 7 recently, the method of driving pile has many problems because of existence of rigid soil in sedimentary layer and installation of more than 30m piles. In this case, when installing piles by drive after pre-boring up to appropriate depth, the results of constructability analysis were very good. And in the economic efficiency, although 4% of construction cost rose, it was a very slight increase in comparison with improvement of workability. In the case of the stability, more than 70% compared to the allowable stress of piles was satisfied through the load test. As a result, when PHC piles is installed in Song-Do district, the proper construction method is that piles are located at bearing layer after boring rigid sand layer.