• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.141-155
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• 2018

Recently, the number of ground subsidence resulting from underground cavity has been increased. Accordingly, the importance of restoration of stress release zone around the underground cavity has been emphasized. The stress release zone is composed of low density soils having extremely low stiffness and degree of compaction, which can lead to additional cavity expansion and collapse of overlying ground. Therefore, in this study, the suitability of restoration method of underground cavity using expansive material for reinforcement of stress release zone around the cavity is verified. The basic physical properties and expansion characteristics of the expansive material were examined. The experiment equipment capable simulating of stress release zone was developed and is used to investigate the effect of expanding material on stress release zone. The stress release zone was simulated using the spring in numerical analysis. The factors of the volume ratio of the underground cavity to the expansion material, the degree of stress relaxation, and the shape of the cavity were varied in numerical simulations, and the behavior of stress release zone was analyzed based on the numerical analysis results. Analysis variables are factors that affect each other. Also, filling of underground cavity and capacity of restoration of stress release zone were confirmed when the expansive material was inserted into underground cavity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.84-91
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• 2019

Recently, there has been a tendency to improve seismic performance of building structure by installing a steel hysteretic damping device which is economically efficient and easy to install and maintain. However, for a reinforced concrete building, a set of complicated connecting hardware and braces to fix the steel hysteretic damping device yields deteriorated reliability in damping performance. Therefore, this study presents a method of directly embedding a Kagome damper, which was investigated in previous researches, into a concrete structure without additional connecting hardware. Moreover, in this study, a series of experiments conducted to provide a basis of the Kagome damper by confirming the seismic behavior for various embedded lengths. As a result, in a group of the embedded length of $1.0l_d$, the dampers were pulled out, while concrete breakout occurs. In a group of $2.0l_d$, neither pull-out nor concrete breakout occurred, while the dampers show stable behavior. Moreover, the buried length of $2.0l_d$ has 1.3 times better energy dissipation capacity. The system presented in this study can reduce the cost and period for installing, omitting making additional hardware.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.335-344
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• 2019

Micropiles are widely used for foundation underpinning to enhance bearing capacity and reduce settlement of existing foundation. In this study, the main objective is to evaluate underpinning performance of a newly developed micropile called waveform micropile for foundation underpinning during vertical extension. Finite element method (FEM) was used to evaluate the underpinning performance of waveform micropile in terms of load-settlement response of underpinned foundation and load sharing behavior. For comparison, underpinning effects of three conventional micropiles with different lengths were also discussed in this study. Numerical results of load-settlement response for single pile demonstrated that bearing capacity and axial stiffness of waveform micropiles were higher than those of conventional micropiles because of the effect of shear keys of waveform micropiles. When additional loads 20 %, which is according to design loads of the vertical extension, were applied to the underpinned foundation, load sharing capacity of waveform micropile was 40 % higher than conventional micropile at the same size. The waveform micropile also showed better underpinning performance than the conventional micropile of length 1~1.5 times of waveform micropile.

• Journal of Navigation and Port Research
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• v.43 no.1
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• pp.9-15
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• 2019

Mooring bollards are the mandatory facility in ports for they are the objects used to fasten the ship to its position at the berth. All the mooring bollards were installed following suggested sizes, numbers, materials and shape of installation according to Port and Fishing Design Standards. However, Korea has no management standard for use of mooring bollards to safety in ship berthing. In this research, the installation standard for mooring bollards including the holding power applied to mooring bollards in berthing was studied. Also, the performance of mooring bollards for minimum safety guarantee in berthing based on research of various specification by their sizes was analyzed. The analysis on mooring bollards was examined by each power on mooring bollards from the applied force in berthing divided into horizontal and vertical direction in order to examine the performance of domestic mooring bollards, the limit force is calculated based on detailed specification research result. As a result, the working stress according to the towing force was found to be at least 150Mpa and it was evaluated to be 60% of the limit strength. Also, by comparing each forces, the appropriateness was examined and the specification of maximum capability calculated. This performance evaluation method based on detail specification of mooring bollards will be expected to be useful to examine the appropriateness of mooring bollards for various types of vessel in berthing and to develop maintenance and management standard through the performance change evaluation referring to mooring bollard detailed specification changes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.19-26
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• 2021

The lattice structure is attracting attention from industry because of its excellent strength and stiffness, ultra-lightweight, and energy absorption capability. Despite these advantages, widespread commercialization is limited by the difficult manufacturing processes for complex shapes. Additive manufacturing is attracting attention as an optimal technology for manufacturing lattice structures as a technology capable of fabricating complex geometric shapes. In this study, a unit cell was formed using a three-dimensional coordinate method. The relative density relational equation according to the boundary box size and strut radius of the unit cell was derived. Simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) with a controlled relative density were designed using modeling software. The accuracy of the equations for calculating the relative density proposed in this study secured 98.3%, 98.6%, and 96.2% reliability in SC, BCC, and FCC, respectively. A simulation of the lattice structure revealed an increase in compressive yield load with increasing relative density under the same cell arrangement condition. The compressive yield load decreased in the order of SC, BCC, and FCC under the same arrangement conditions. Finally, structural optimization for the compressive load of a 20 mm × 20 mm × 20 mm structure was possible by configuring the SC unit cells in a 3 × 3 × 3 array.

• Journal of the Korean Geosynthetics Society
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• v.20 no.1
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• pp.9-19
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• 2021

This paper deals with the reinforcement performance of acrylate for reinforcing the settled railway roadbed. Concrete tracks have the advantage of reducing track maintenance costs and high resistance to track destruction. However, roadbed settlement is occurring in some construction sections, and the safety of railways is a serious concern because of difficulties in maintenance. Currently, maintenance through the track restoration method is being carried out in Korea as a way of roadbed settlement in concrete tracks, but continuous re-settlement can occur because the roadbed itself cannot be reinforced, and there are very few cases of reinforcement of railway roadbeds and field application. So the development of reinforcement materials and construction methods to reinforce railway roadbeds is required. Therefore, in this paper, acrylate was selected as reinforcement material for railway roadbed, and the reinforcement performance of acrylate was analyzed through experiment. As a result, it was analyzed that the acrylate can penetrate into a permeability coefficient of 1×10^-4 cm/sec, and secure uniaxial compression strength of 0.5 MPa/30min or more and stiffness of 80 MPa or more.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.9-16
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• 2020

A CFRP sheet has been applied as a structural reinforcement in the field, and various studies are conducted to evaluate the effect of CFRP sheets on reinforced concrete. Although many experiments were performed from previous studies, there are still limitations to analyze structural behaviors with various parameters in experiments directly. This study shows the FEA on structural behaviors of RC beams reinforced with CFRP sheets using ABAQUS software. To simulate debonding failure of CFRP sheets which is a major failure mode of RC beam with CFRP sheets, a cohesive element was applied between the bottom surface of RC beam and CFRP sheets. Both quasi-static method and 2-D symmetric FE model technique were performed to solve nonlinear problems. Results obtained from the FE models show good agreements with experimental results. It was found that reinforcement level of CFRP sheets is closely related to structural behavior of reinforced concrete including maximum strength, initial stiffness and deflection at failure. Also, as over-reinforcement of CFRP sheets could give rise to the brittle failure of RCstructure using CFRP sheets, an appropriate measure should be required when installing CFRP sheets in the structure.

• Journal of the Korean GEO-environmental Society
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• v.23 no.8
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• pp.11-16
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• 2022

The compaction process using vibrating rollers in road construction is essential to increase soil stiffness in earthworks. Currently, there is no clear standard for the operation method of the compaction roller during compaction. Although simple quality inspection techniques have been developed, plate load test (PLT) and field density test (FDT) are the most frequently used test methods to evaluate the degree of compaction during road construction as the most frequently used quality inspection methods. However, both inspection methods are inefficient because they cannot perform quality inspection in all sections due to time and cost reasons. In this study, we analyzed how the operating conditions of vibrating rollers affect the compaction quality. An intelligent quality management system, which is a currently developed and commercialized technology, was used to obtain quality inspection results in all sections. As a result of the test, it was analyzed that the speed and vibration direction of the compaction roller had an effect on the compaction degree, and it was found that the compaction direction had no effect on the compaction degree.

• Journal of the Korean Wood Science and Technology
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• v.32 no.5
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• pp.29-38
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• 2004

In this study, we investigated the thermal properties of corn-starch filled polybutylene succinate-adipate (PBS-AD) bio-composites. Thermal analysis (TA) is used to describe the analytical method for measuring the chemical property and weight loss of composite materials as a function of temperature. The thermal stability of corn-starch was lower than that of pure PBS-AD. As corn-starch loading increased, the thermal stability and degradation temperature of the bio-composites decreased and the ash content increased. It can be seen that the degree of compatibility and interfacial adhesion of the bio-composites decreased because of the increasing mixing ratio of the corn-starch. As the content of corn-starch increased, there was no significant change in the glass transition temperature (T_g) and the melting temperature (T_m) for the bio-composites. The storage modulus (E') and loss modulus (E") of the corn-starch flour filled PBS-AD bio-composites were higher than those of PBS-AD, because of the incorporation of corn-starch increased the stiffness of the bio-composites. At higher temperatures, the decreased storage modulus (E') of bio-composites was due to the increased polymer chain mobility of the matrix polymer. From these results, we can expect that corn-starch has potential as a reinforcing filler for bio-composites. Furthermore, we recommend using a coupling agent to improve the interfacial adhesion between corn-starch and biodegradable polymer.

• Journal of the Korean GEO-environmental Society
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• v.23 no.12
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• pp.5-15
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• 2022

Conventionally, because evaluation methods of the bearing capacity for double steel pipe-concrete composite pile design have not been established, the conventional vertical bearing capacity equations for steel hollow pile are used. However, there are severe differences between the predictions from these equations, and the most conservative one among vertical bearing capacity predictions are conventionally adopted as a design value. Consequently, the current prediction method for vertical bearing capacity of composite pile prediction composite pile causes design reliability and economical feasibility to be low. This paper investigated mechanical behaviors of a new composite pile, with a cross-section composed of double steel pipes filled with concrete (DSCT), vertical bearing capacities were analyzed for several DSCT pile conditions. Axisymmetric finite element models for DSCT pile and surrounding ground were created and they were used to analyze effects on behaviors of DSCT pile pile by embedding depth, stiffness of plugging material at pile tip, height of plugging material at pile tip, and rockbed material. Additionally, results from conventional design prediction equations for vertical bearing capacity at steel hollow pile tip were compared with that from numerical results, and the use of the conventional equations for steel hollow pile was examined to apply to that for DSCT pile.