• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.148-160
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• 2012

This study proposed more reasonable prediction models on compressive strength and carbonation of concrete structure and developed a more effective tunnel safety diagnosis and maintenance method through field application of the proposed prediction models. For this study, the Seoul Metro's Line 1 through Line 4 were selected as target structures because they were built more than 30 years ago and have accumulated numerous diagnosis and maintenance data for about 15 years. As a result of the analysis of compressive strength and carbonation, we were able to draw prediction models with accuracy of more than 80% and confirmed the prediction model's reliability by comparing it with the existing models. We've also confirmed field suitability of the prediction models by applying field, the average error of an estimate on compressive strength and carbonation depth was about 20%, which showed an accuracy of more than 80%. We developed a more effective maintenance method using durability prediction Map before field inspection. With the durability prediction Map, diagnostic engineers and structure managers can easily detect the vulnerable points, which might have failed to reach the standard of designed strength or have a high probability of corrosion due to carbonation, therefore, it is expected to make it possible for them to diagnose and maintain tunnels more effectively and efficiently.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.93-101
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• 2022

RC Slab bridges in Korea account for more than 70% of the total bridges for more than 20 years of service. As the number of aging structures increases, the importance of safety diagnosis and maintenance of structures increases. For highway bridges, cracks are a main cause of deck deterioration, which is very closely related to the decrease in bridge durability and service life. In addition, the damage rate of expansion joints and bearings accounts for approximately 73% higher than that of major members. Therefore, this study defined damage scenarios combined with devices damages and deck deterioration. The stress distribution and maximum stress on the deck were then evaluated using design vehicle load and daily temperature gradient for single and combined damage scenarios. Furthermore, this study performed damage-spread analysis and predicted condition ratings according to a deck deterioration model generated from the inspection and diagnosis history data of cracks. The heterogeneous damages combined with the member damages of expansion joints and bearings increased the rate of crack area and damage spread, which accelerated the time to reach the condition rating of C. Therefore, damage to bridge members requires proper and prompt repair and replacement, and otherwise it can cause the damage to bridge deck and the spread of the damage.

• Economic and Environmental Geology
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• v.35 no.4
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• pp.355-368
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• 2002

The multi-storied Daewonsa stone pagoda (Treasure No. 1112) in the Sancheong, Korea was studied on the basis of deterioration and geological safety diagnosis. The stone pagoda is composed mainly of granitic gneiss, partly fine-grained granitic gneiss, leucocratic gneiss, biotite granite and ceramics. Each rock of the pagoda is highly exfoliated and fractured along the edges. Some fractures in the main body and roof stones are treated by cement mortar. This pagoda is strongly covered with yellowish to reddish brown tarnish due to the amorphous precipitates of iron hydroxides. Dark grey crust by manganese hydroxides occur Partly, and some Part coated with white grey gypsum and calcite aggregates from the reaction of cement mortar and rain. As the main body, roof and upper part of the pagoda, the rocks are developed into the radial and linear cracks. Surface of this pagoda shows partly yellowish brown, blue and green patchs because of contamination by algae, lichen, moss and bracken. Besides, wall-rocks of the Daewonsa temple and rock aggregates in the Daewonsa valley are changed reddish brown color with the same as those of the pagoda color. It suggests that the rocks around the Daewonsa temple are highly in iron and manganese concentrations compared with the normal granitic gneiss which color change is natural phenomena owing to the oxidation reaction by rain or surface water with rocks. Therefore, for the attenuation of secondary contamination, whitening and reddishness, the possible conservation treatments are needed. Consisting rocks of the pagoda would be epoxy to reinforce the fracture systems for the structural stability on the basements.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.3
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• pp.30-37
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• 2023

The PSCB girder bridge is a closed cross-section in which the top and bottom flanges and the web are integrated, and the structural characteristics are generally different from the bridges in which the girder and the floor plate are separated, so a maintenance plan that reflects the characteristics of the PSCB girder bridge is required. As a result of analyzing damage types by collecting detailed safety diagnosis reports of highway PSCB girder bridges, most of the deterioration and damage occurring during use is concentrated on the top flange. In particular, cracks in the bridge direction on the underside of the top flange occurred in about 70 % of the PSCB girder bridges to be analyzed, and these cracks were judged to be caused by indirect loads such as heat of hydration and drying shrinkage rather than structural cracks caused by external loads. In order to improve durability and reduce maintenance costs of PSCB girder bridges in use, it is necessary to control restraint drying shrinkage cracks from the design stage. Therefore, in this paper, the cracks caused by drying shrinkage under restraint, which is the main cause of cracks under the flanges of the top part of the PSCB girder bridge, were directly calculated using the Gilbert Model, and the influencing factors such as the amount of reinforcing bars, diameter and spacing of reinforcing bars were analyzed. As a result of the analysis, it was found that the crack width caused by restraint drying shrinkage exceeded the allowable crack width of 0.2 mm for reinforcing bars with a reinforcing bar ratio of 0.01 or less based on the H16 reinforcing bar and a reinforcing bar with a diameter greater than H19 based on the reinforcing bar ratio of 0.01. Finally, based on the results of the crack width review, a method for controlling the crack width of the top flange of the PSCB girder bridge was proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.37-44
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• 2018

This study proposed the modified weighting values for jointed rock slopes. The studies on deduction of evaluation index and calculation of weighting, development of criteria for evaluation and evaluation models have been conducted through decision making techniques such as the Delphi method and the AHP method by many researchers. Because these decisions making techniques may be less objective, it is necessary to calculate reasonable weighting considering both an objective weighting and a subjective weighting simultaneously. In this study, utilizing the inspection data of jointed rock slopes, an objective weighting that the concept of entropy is applied was calculated. And the subjective weighting values by AHP technique was calculated based on the opinion of experts. And a modified weighting was suggested by combining the two. As a result, it was found that jointed rock slopes have higher weighting in artificial factors and the damage status items. In addition based on the finally suggested weighting (mixed weighting), the revised evaluation criteria could be presented by converting it into the evaluation score (76 points). And it is expected that it could be usefully utilized upon inspections on cutting slopes and safety diagnosis since objective and highly reliable criteria compared to the condition evaluation criteria that are currently used could be presented through the results of the study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.148-156
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• 2022

Although most domestic concrete structures are simultaneously exposed to freeze-thaw and chloride environments, concrete durability in the field is evaluated by each single action, and the evaluation of chloride-caused damage of concrete requires additional indoor experimental analysis of chloride contents by coring samples from structures in the field. However, in Korea, policies to strengthen facility maintenance, such as 「Special Act on the Safety Control and Maintenance of Establishments」 and 「Framework Act on Sustainable Infrastructure Management」, have been established and implemented since 2018 and facilities subject to safety inspection management by the government and local governments increases, the effective simplification technology for the inspection and diagnosis of concrete structure is needed. Therefore, this study attempted to evaluate the possibility of determining the acceleration chloride penetration of freeze-thaw damaged concrete by using the surface rebound value. For this purpose, concrete specimens already having freeze-thaw damage by exposure to the freeze-thaw acceleration environment were immersed in chloride water. After that, the acceleration relationship of chloride penetration according to freeze-thaw damage was analyzed using the amount of chloride contents in concrete.

• 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 the Korean Institute of Gas
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• v.22 no.6
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• pp.44-51
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• 2018

As the LNG storage tank is aged, if there is a crack in the outer wall concrete or corrosion of the reinforcing steel, there is a risk of a major accident such as collapse of the structure depending on the type and degree of damage. Since 2014, LNG storage tanks have undergone precise safety diagnosis and safety inspection has been carried out. The condition evaluation criteria for each component have been revised and applied in January 2016. The condition evaluation standard is to evaluate the status of storage tanks based on the appearance survey and material test results of LNG storage tanks and it is important for maintenance. In addition, the representative condition evaluation standard that shows the comprehensive state of each LNG storage tank is important in maintenance, but the related standard for LNG storage tank outer concrete is not available in Korea and abroad, and development of the condition evaluation standard is necessary. In this paper, we examined the structural characteristics of LNG storage tanks, analyzed the status of the condition evaluation criteria for each member, and developed a comprehensive status rating system by weighting the members. We used the AHP(Analytic Hierarchy Process) technique and developed a representative conditon evaluation criteria through surveys of professional organizations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.102-110
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• 2023

PSC-I girder bridges constitute the largest proportion among highway bridges in Korea. According to the precision safety diagnosis data for the past 10 years, approximately 41.3% of the PSC-I bridges have been graded as C. Furthermore, with the increase in the aging of bridges, preemptive management is becoming more important. Damage and deterioration to the deck and girder with a long replacement cylce can have considerable impacts on the service and deterioration of a bridge. In addition, the high rate of device damages, including expansion joints and bearings, necessitates an investigation into the influence of the device damage in the structural members of the bridge. Therefore, this study defined representative PSC-I girder bridges with single and multiple spans to evaluate heterogeneous damages that incorporate the damage of the bridge member and device with the deterioration of the deck. The heterogeneous damages increased a crack area ratio compared to the individual single damage. For the single-span bridge, the occurrence of bearing damage leads to the spread of crack distribution in the girder, and in the case of multi-span bridges, expansion joint damage leads to the spread of crack distribution in the deck. The research underscores that bridge devices, when damaged, can cause subsequent secondary damage due to improper repair and replacement, which emphasizes the need for continuous observation and responsive action to the damages of the main devices.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.595-603
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• 2012

This study applied elastic supports in order to evaluate load carrying capacity using measurement data obtained from load tests actively and utilizing various evaluation methods. In order to confirm the adequacy of structural analysis based on elastic supports and to improve the reliability of experiment results, we conducted a deflection test with flexural beams prepared as overhanging beams and, based on the results, performed precision safety diagnosis for real bridges under public service for improving the load carrying capacity evaluation method for bridges under public service. In the results of the bending test, compared to deflection calculated by the existing method, deflection obtained by applying elastic supports was closer to the actually measured deflection. In the results of evaluating load carrying capacity for a 3 span continuous steel box girder bridge just after its completion, load carrying capacity by elastic supports was smaller by up to 39% than that by the existing method. When the load carrying capacity of bridges is evaluated by the existing method the results vary among engineers due to lack of guidelines for evaluation such as the application of stress modification factor. This study was conducted as an effort to solve this problem through active research.