• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.6
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• pp.124-131
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• 2010

Rock Bolt generally utilizes deformed reinforcing bar welded from structural steel of which strength is higher than required for making advantageous use of the support function of ground. In the condition with highly corrosive underground water, however, problem frequently occurs on tunnel and slope stabilization in terms of repair, rehabilitation and maintenance issues due to the destruction of Rock Bolt by corrosion of steel. A structural performance evaluation for GFRP Rock Bolt was conducted for the purpose of resolving the foregoing problem and at the same time developing a permanently-usable support material. This study intended to evaluate the safety factor of GFRP Rock Bolt by implementing the slope stability interpretation via structural analysis on the basis of its structural characteristics derived from both tensile force function test and shear force function test. It is judged based on the results that GFRP Rock Bolt would secure sufficient ground stability as an alternative material for existing Steel Rock Bolt.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.136-143
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• 2010

There are three parts of tunnel which are influenced by outside temperature, entrance, exit and vent. These parts showed different tendency of deterioration(very rapid deterioration speed, wide range of defects, etc) compared with last parts of tunnel. Therefore, it needs to have different points of view when civil engineers analyze the defects on these parts and apply the retrofit or rehabilitation methods for them. However, when we conduct maintenance works, precise inspection and precise safety diagnosis, these defects had been neglected because those were considered as unimportant defects and caused from temporary weather and temperature change. In this study, two urban tunnels were analyzed to decide the range of tunnel which are influenced by outside temperature using a thermal camera, and to find out the causes of defects on these parts. From the results, the main points of maintenance were presented.

• Fire Science and Engineering
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• v.18 no.1
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• pp.31-36
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• 2004

The purpose of this study is to present data for the reusing, rehabilitation and estimation of safety of RC structure damaged by fire, and for the prevention of explosive spatting by investigation the properties of explosive spalling, compressive strength and ultrasonic pulse velocity according to kinds of fine aggregate, admixture and water-cement ratios. In explosive spalling properties with kinds of aggregate, explosive spalling does not appear or little at surface in the case of used sea sand, but the case of using recycled sand or crushed sand is worse and worse. Property with the kind of admixture does not appear specially. And high strength concrete with W/C 30.5% was taken spalling, but 55% does not appear. It is found that residual compressive strength after exposed at high temperature showed 45％ in W/C 55%, and 64％ in W/C 30.5％ of its original strength averagely. Ultrasonic pulse velocity is different with kinds of aggregate. W/C. and heating time. When 3 month age after heating ultrasonic pulse velocity is recovered abut 1.3％～8.4％ of its 1 month age after heating.

• Journal of the Korean Geotechnical Society
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• v.23 no.12
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• pp.25-32
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• 2007

This study is to evaluate the effect of chemical attack on durability and deterioration of lining concrete in tunnel. Surface examination, nondestructive inspection, uniaxial compressive strength test, carbonation test, chloride diffusion test, micro-structural analysis were performed to analyze the deterioration of lining concrete in tunnel constructed 70 years ago. From surface examination results, the tunnel had been repaired and reinforced in several times. It has many cracks, water-leakage, efflorescence and exploitation. Compressive strengths obtained from nondestructive inspection and uniaxial compressive strength test have measured $17.5{\sim}34.7MPa$, and $12.8{\sim}40.3MPa$, respectively. Carbonation depth specimen cored from concrete lining has ranged from 3mm to 27mm. From chloride diffusion test, most specimens have low permeability. And the XRD analysis was able to detect ettringite and thaumasite, which were confirmed by SEM and EDS results to be the causes for the deterioration of lining concrete.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.109-120
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• 2011

This paper presents an experimental study results on the crack control of flexure-dominant reinforced concrete beams repaired with strain-hardening cement composite (SHCC). Five RC beams were fabricated and tested until failure. One unrepaired RC beam was a control specimen (CBN) and remaining four speciemens were repaired with SHCC materials. The test parameters included two types of SHCC matrix ductility and two types of repair method (patching and layering). Test results demonstrated that RC beams repaired with SHCC showed no concrete crushing or spalling until final failure, but numerous hair cracks were observed. The control specimen CBN failed due to crushing. It is important to note that SHCC matrix can improve crack-damage mitigation and flexural behavior of RC beams such as flexural strength, post peak ductility, and energy dissipation capacity. In the perspective of crack width, crack widths in RC beams repaired with SHCC had far smaller crack width than the control specimen CBN under the same deflection. Especially, the specimens repaired with SHCC of PVA0.75%+PE0.75% showed a high durability and ductility. The crack width indicates the residual capacity of the beam since SHCC matrix can delay residual capacity degradation of the RC beams.

• Journal of the Society of Disaster Information
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• v.15 no.4
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• pp.479-492
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• 2019

Purpose: The purpose of this study is to accurately analyze the damage of bridges in order to determine whether fire bridges can be used continuously or to provide information on maintenance augmentation data. Method: XRD, SEM and EDS analyzes of concrete were carried out to estimate the fire temperature transferred to the structure, and analyzed by depth and area from PSCI beam and bottom plate concrete surface. Results: Test results G_12,11 for the fire zone concrete were confirmed to be affected by heat up to depth of 60mm and the temperature of the hydrothermal heat was above 1000℃. Also, the girder G_10,9,8 was relatively weakly damaged compared to G_12,11, and the degree of damage was confirmed to be affected by heat up to a depth of 40 mm. Conclusion: Based on the analyzed data, it is considered that if the repair / reinforcement and periodic inspection are carried out, the bridge can secure sufficient safety even considering the damage caused by the fire.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.149-160
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• 2015

This study reports the interfacial bond strength between Ultra High Performance Concrete (UHPC) and Normal Strength Concrete (NSC). While previous studies have focused on the interfacial strength between NSC substrate and UHPC overlay, this study use precast UHPC for enhanced constructability and replacement of formwork. The factors affecting the interface strength are comprehensively reviewed. It can be classified into: interface shape, degree of hardening and moisture condition of UHPC before combining with NSC, and curing condition of composite materials. Conducted experiments verify the effects of each factor on the interface strength and, accordingly show different failure modes. In particular, a new failure mode of the failure of a part of UHPC was firstly found in the case of sample with rough interface between UHPC and NSC. The other factors of the degree of hardening and the moisture and curing conditions of UHPC were discussed. This research will provide a valuable foundation to utilize the UHPC as a composite material.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.139-148
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• 2008

The direct inspection of the outward aspects by field engineers is the important and critical part for structural safety assessment according to the related reports. This study presents an improved method of the state assessment for concrete floor slab by separating and evaluating the individual damage types. First, the various types of damage symptoms are separated, which have been included and dealt in a group. Secondly, they are weighted and scored independently based on the present guide and references. Overall procedures other than the above are retained as same as possible to avoid the confusion. The proposed method is applied and tested to a performed assessment project for a bridge for validation. The result shows that it is reasonable and applicable in respect that it is able to make up for the controversial points of the present guide revealed in practices. Careful check of excessively deteriorated parts in addition to the reasonable assessment of system by this method grants the structural repair and reinforcement propriety and economy, and assures of more safety. Twofold appraisal of this approach expands the applicable areas of value engineering to the structural maintenance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.161-170
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• 2022

The maintenance of bridges installed in rivers is carried out through facility safety inspection and repair & reinforcement procedures according to the results. Many studies have been so far conducted on the safety check of the bridge upperstructure because of the ease of access. However as it is impossible to directly investigate whether the pier foundation installed in the river has been scoured. Management of underwater foundations has remained based on theory. In this study, the scour of the bridge foundation installed in such a river was realized in 3D form by using an echo sounder and VRS. This made it possible to predict the scour pattern through comparison and analysis with the ground height of the riverbed at the time of the bridge installation. Based on these results, if the pier foundation is used as an initial data to determine whether or not local scour is present and to predict long-term scouring, bridge collapse due to foundation scour can be prevented.

• Journal of the Korean earth science society
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• v.32 no.1
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• pp.1-11
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• 2011

The impact echo and impulse response methods were applied to the safety inspection of concrete structure, which has the rear cavity. The concrete structure model used in this study was divided into four sections, pure concrete, concrete+cavity, reinforced concrete with iron bar, and reinforced concrete+cavity, respectively. Previous study performed by authors have showed a possibility of success to use these method for detection of the rear cavity of concrete structure. Therefore, we tried to get more enhanced result with IE and IR methods through this study. Especially, IE and IR methods are relatively accurate to map the point of measurement, which makes it possible to interpret the depth of the concrete bed and effect by rear cavity with confidence. Followings were revealed from the results; the IE method shows some small peak zones probably indicating the rear cavity in the frequency lower than the resonance frequency and the changes of mobility and dynamic stiffness in the IR method indicate the weak zones. The proposed methods can be used to delineate the weak zones of the concrete structure.