• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.487-494
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• 2009

Friction coefficients of the prestressing tendon are the basic information required to control the prestressing force introduced to PSC structure during jacking. However, the friction coefficients show considerable differences depending on the specifications, causing much confusion to designers. In this study, the ranges of the friction coefficients presented in domestic and foreign specifications are compared together to clarify the differences. Then, a procedure is proposed that can be used to estimate the wobble and curvature friction coefficients from field data such as elongation and prestressing force and from theory related to the friction. The procedure is applied to various tendon profiles of several PSC bridges constructed by ILM, FCM and MSS. The resulting values are compared with those presented in some specifications and assumed in jacking and a reasonable range of the friction coefficient is discussed. Lift-off tests are also performed in some bridges to further verify the results. The resulting wobble friction coefficients are not as small as those presented in AASHTO specifications but range from the lower limit to mid point of domestic specifications, while the curvature friction coefficients approach or slightly exceed the upper limit.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.1
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• pp.9-20
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• 2023

For highway concrete structures, the deterioration of the structure is accelerated due to the increase in the use of deicing materials, and sectional repair work is being frequently carried out to restore performance. However, after the repair work, re-damage such as cracks, delamination, and poor bond performance is exhibited in the repaired sectional area. In this study, overseas repair material requirements were first analyzed, and present domestic requirements were improved repair material performance through field surveys of common concrete structures, laboratory experiments, and test construction on a disused concrete bridge. In addition, performancebased quality requirements were presented so that all materials that meet the required performance can be applied, and different test methods for each material were unified into concrete test methods for consistent test results analysis. The considered performance requirements were compression strength, bending strength, and bond strength for structural properties, and length change rate, crack resistance, thermal expansion coefficient, and elasticity coefficient were for dimensional behavior. For resistance to chloride penetration resistance and freeze-thaw resistance were presented as durability. The proposed requirements for concrete repair materials are expected to contribute to the improvement of the quality of concrete sectional repair work in Korea.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.555-563
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• 2006

Recently, many bridges become not only functionally obsolete of bridge deck due to inadequate width but also structurally deficient of substructure due to erosion. In these cases, widening is almost always more economical than complete replacement, and therefore there is a need to make available the results of research and field experience pertaining to the widening of bridge substructure. But, an experimental study for the guarantee of unification between existing and new substructure with adhesive anchor is so insufficient that the development of adhesive anchor system for the unification should be settled promptly. The purpose of the present study is to explore pull out and shear characteristics of adhesive anchor system. For this purpose, several series of concrete specimens have been tested. Major test variables were the bonded length, anchor diameter and anchor slope. The pull out strength, bond stress and shear strength of adhesive faces were measured for the specimens. The present study indicates that the pull out strength increased with more bonded length and more anchor diameter, and that the bond stress decreased with more bonded length and more anchor diameter. The pull out strength and the bond stress increases with more anchor slope and it is considered that the slope of $5^{\circ}$ was more efficient. From the shear tests, it is supposed that anchor diameters more than D19 was proper to the adhesive anchor. Finally, it is expected that both experimental data in these tests and further study including mock-up tests will contribute to the establishment of the unification between existing and new substructure with adhesive anchor.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.401-409
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• 2006

This study presents basic information on the mechanical properties and long-term deformations of high-strength steel fiber reinforced concrete(HSFRC). The Influence of steel fiber on modulus of elasticity, compressive, splitting tensile and flexural strength, and drying shrinkage and creep of HSFRC are investigated, and flexural fracture toughness is evaluated. Test results show that Test results show that the effect of steel fibers on the compressive strength is negligible, and the modulus of elasticity of HSFRC increased with the increase of fiber volume fraction. And the effect of fiber volume fraction($V_f$) and aspect ratio($l_f/d_f$) on tensile strength, flexural strength and toughness is extremely prominent. It is observed that the flexural deflection corresponded to ultimate load increased with the increase of $V_f$ and $l_f/d_f$, and due to fiber arresting cracking, the shape of the descending branch of load-deflection tends towards gently. Also, the effect of addition of various amounts of fiber on the creep and shrinkage is obvious. Especially, the effect of adding fibers to high-strength concrete is more pronounced in reducing the drying shrinkage than the creep.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6D
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• pp.969-974
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• 2006

Labor shortages are a serious problem for Korea's construction industry. The problem is both quantitative and qualitative. There is a shortage in supply as due to a decrease in the influx of new labor, and existing workers are less productive as they age. The problem will only get worse as more and more major public projects are being planned. Options for increasing the labor supply are somewhat limited, and thus efforts need to be made to adopt new technologies that can improve the productivity and efficiency of field work and their processes. This paper introduces seven innovation technologies that have the best potential to increase productivity and thus reduce the burden of labor shortage problems. These include 1) Substitution by use of robotics and automation, 2) development and applications of Innovative materials to reduce on site field work, 3) increase in productivity through the implementation of Information Technology, 4) improved productivity through the application of modules, and prefabrication, 5) prevention of rework and redesign, 6) diversification of labor by integrating labor skills, and 7) improved productivity by standardizing site processes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.1-8
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• 2024

The expansion joint is installed to offset the expansion of the superstructure and must ensure sufficient gap during its service life. In detailed guideline of safety inspection and precise safety diagnosis for bridge, damage due to lack or excessive gap is specified, but there are insufficient standards for determining the abnormal behavior of superstructures. In this study, a data-based maintenance was proposed by continuously monitoring the expansion-gap data of the same expansion joint. A total of 2,756 data were collected from 689 expansion joint, taking into account the effects of season. We have developed a method to evaluate changes in the expansion joint-gap that can analyze the thermal movement through four or more data at the same location, and classified the factors that affect the superstructure behavior and analyze the influence of each factor through deep learning and explainable artificial intelligence(AI). Abnormal behavior of the superstructure was classified into narrowing and functional failure through the expansion joint-gap evaluation graph. The influence factor analysis using deep learning and explainable AI is considered to be reliable because the results can be explained by the existing expansion gap calculation formula and bridge design.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.3
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• pp.209-222
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• 2024

The Earth Pressure Balance (EPB) shield Tunnel Boring Machine (TBM) is widely used for underground tunnel construction for its advantages, such as eliminating the need for additional facilities compared to the slurry shield TBM, which requires Slurry Treatment Plant (STP). During EPB shield TBM excavation, a soil conditioning technique is employed to enhance the physical properties of the excavated soil by injecting additives, thus broadening the range of applicable ground conditions to EPB shield TBMs. This study explored the use of xanthan gum, a type of biopolymer, as an alternative to the commonly used polymer additive. Biopolymers, derived from biological sources, are fully biodegradable. In contrast to traditional polymers such as polyacrylic acid, which contain environmentally harmful components, xanthan gum is gaining attention as an eco-friendly material due to its minimal toxicity and environmental impact. Test conditions with similar workability were established through slump tests, and the rheological characteristics were assessed using a laboratory pressurized vane shear test apparatus. The experiments demonstrated that, despite exhibiting similar workability, the peak strength in the flow curve decreased with increasing the content of xanthan gum. Consequently, a correlation between the xanthan gum content and peak strength was established. Replacing the traditional polymers with xanthan gum could enable stable EPB shield TBM operation by reducing equipment load, in addition to offering environmental benefits.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.195-204
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• 2009

Application of steel plates is one of widely used methods for shear strengthening of reinforced concrete beams that are insufficient of shear capacity. While the existing method applying solid steel plates provides good shear rigidity, however, it is concerned by brittle bond failure patterns, inefficient material usage, and low constructability. The use of strap type steel plates has also shortcomings of low strenthening effect due to small interface bonding area and ununified behavior between plates and main body. Therefore, this study aims to introduce the shear strengthening method using slit type steel plate, which can solve out the problems aforementioned, and to verify its strengthening effects on shear capacity. A total of 13 specimens strengthened by slit type steel plates were fabricated with primary test parameters of plate width, slit spacing, and plate thickness. The test results from this study were also compared to those from the existing research on RC beams strengthened by strap type steel plates, and the strengthening effects on shear capacity of specimens having bonded slit type steel plates were quantitatively analyzed. The test results showed that the RC beams strengthened by slit type steel plates had greater shear capacities than those with strap type steel plates, which is considered to be the effects of improved composite behavior and larger interface bonding area in the RC beams strengthened by the slit type steel plates.

• Korean Journal of Construction Engineering and Management
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• v.14 no.1
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• pp.32-42
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• 2013

The Korean Government introduced a cultural heritage supervision system in January 2010 to control quality and to prevent poor construction. However, cultural heritage related constructions that require supervision, a scope of supervision, supervision cost and placement of supervisors have not been standardized yet. For this reason, standards of supervision for repair works of cultural heritage that reflect the characteristics of small-scale repair works and restoration of cultural heritage are required. Accordingly, this study has suggested standards of supervision works and cost by analyzing the average construction period that is suitable for the characteristics of cultural heritage repair works. In other words, this study has suggested standards of full-time supervision costs by applying the fixed amount-added method (adding direct labor cost, direct expenses, overhead expenses, engineering fee, charges for additional works and VAT) which is the same as the method of calculating supervision costs for public construction projects because a supervisor has to work full time at a construction site to perform supervision if the project is a mid/large-scale cultural heritage repair work. Also, this study has suggested standards of part-time supervision costs for a small-scale cultural heritage repair work and the ways of supervising the construction projects by visiting the project site on important occasions. According to the result of the analysis by applying the forgoing standards of supervision costs for cultural heritage, a full-time supervision cost for cultural heritage repair works is approximately 98% compared to the construction supervision of a public construction project, and a part-time supervision is approximately 158% compared to architectural construction supervision. It is expected that the valuable cultural heritage of Korea will be preserved by controlling quality of cultural heritage repair works through the application of this study result - the standards of supervision costs for cultural heritage repair works - to an actual project.

• Korean Journal of Environmental Agriculture
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• v.25 no.3
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• pp.202-210
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• 2006

To develop small-scale sewage treatment apparatus for detached house of agricultural village, a small-scale sewage treatment apparatus by natural purification method that consisted of packaged form of aerobic, anoxic and anaerobic bed was constructed. The efficiency of sewage treatment according to the sewage treatment method, sewage loading, and the injection method of sewage were investigated for small-scale sewage treatment apparatus of packaged form of aerobic, anoxic and anaerobic bed. The removal rate of pollutants according to the sewage treatment method for small-scale sewage treatment apparatus was high in the order of aerobic-anoxic-anoxic bed < aerobic-anoxic-anaerobic bed. The optimum filter media in small-scale sewage treatment apparatus was a broken stone. The removal rate of pollutants according to sewage loading in small-scale sewage treatment apparatus was high in the order of $1,200L/m^2{\cdot}day\fallingdotseq900L/m^2{\cdot}day\fallingdotseq600L/m^2{\cdot}day$. The removal rate of pollutants according to injection method of sewage in small-scale sewage treatment apparatus was high in the order of continuous injection $\fallingdotseq$ intermittent injection. When loaded under the optimum conditions, removal rate of BOD, COD, SS, T-N and T-P were 99, 95, 99, 83 and 96%, respectively, through this 3-stepped small-scale treatment apparatus arrayed with the order of aerobic, anoxic and anaerobic bed.