• Structural Engineering and Mechanics
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• v.66 no.1
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• pp.15-25
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• 2018

Post-construction subgrade settlement especially differential settlement, has become a key issue in construction and operation of non-ballasted track on high-speed railway soil subgrade, which may also affect the dynamic performance of passing trains. To estimate the effect of differential subgrade settlement on the mechanical behaviors of the vehicle-slab track system, a detailed model considering nonlinear subgrade support and initial track state due to track self-weight is developed. Accordingly, analysis aiming at a typical high-speed vehicle coupled with a deteriorated slab track owing to differential subgrade settlement is carried out, in terms of two aspects: (i) determination of an initial mapping relationship between subgrade settlement and track deflections as well as contact state between track and subgrade based on a semi-analytical method; (ii) simulation of dynamic performance of the coupled system by employing a time integration approach. The investigation indicates that subgrade settlement results in additional track irregularity, and locally, the contact between the concrete track and the soil subgrade is prone to failure. Moreover, wheel-rail interaction is significantly exacerbated by the track degradation and abnormal responses occur as a result of the unsupported areas. Distributions of interlaminar contact forces in track system vary dramatically due to the combined effect of track deterioration and dynamic load. These may not only intensify the dynamic responses of the coupled system, but also have impacts on the long-term behavior of the track components.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.1
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• pp.21-34
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• 2008

An improved optimum design method for reinforced concrete frames using integrated genetic algorithm(GA) with direct search method is presented. First, various sets of initially assumed sections are generated using GA, and then, for each resultant design member force condition optimum solutions are selected by regression analysis and direct search within pre-determined design section database. In advance, global optimum solutions are selected from accumulated results through several generations. Proposed algorithm makes up for the weak point in standard genetic algorithm(GA), that is, low efficiency in convergence causing the deterioration of quality of final solutions and shows fast convergence together with improved results. Moreover, for the purpose of elevating economic efficiency, optimum design based on the nonlinear structural analysis is performed and therefore makes all members resist against given loading condition with the nearest resisting capacity. The investigation for the effectiveness of the introduced design procedure is conducted through correlation study for example structures.

• Journal of the Korean Geosynthetics Society
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• v.19 no.4
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• pp.95-109
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• 2020

In this study, a total of six site cases were reviewed to assess the site applicability of portable dynamic cone penetration test (DCPT) by identifying the cause of damage to the damaged reinforced earth wall using portable dynamic cone penetration test. An improved dynamic concrete penetration tester was used at the site to enable ground surveys of more than 6 meters. The test results were compared with the results of the standard penetration test (SPT) and the correlation was analyzed. Through the analysis of various field application cases, it was found that portable dynamic cone penetration test was very convenient to apply at the site of the damaged reinforced earth wall, and DCPT could play a major role in identifying the cause of damage and verifying stability of the retaining wall by continuously identifying the ground strength. In addition, it was found that the results of the dynamic cone penetration test and the standard penetration test showed a correlation of N≒(1/3~2/3)·Nd in sandy soil.

• Smart Structures and Systems
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• v.31 no.4
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• pp.335-349
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• 2023

Bridges constantly undergo deterioration and damage, the most common ones being concrete damage and exposed rebar. Periodic inspection of bridges to identify damages can aid in their quick remediation. Likewise, identifying components can provide context for damage assessment and help gauge a bridge's state of interaction with its surroundings. Current inspection techniques rely on manual site visits, which can be time-consuming and costly. More recently, robotic inspection assisted by autonomous data analytics based on Computer Vision (CV) and Artificial Intelligence (AI) has been viewed as a suitable alternative to manual inspection because of its efficiency and accuracy. To aid research in this avenue, this study performs a comparative assessment of different architectures, loss functions, and ensembling strategies for the autonomous segmentation of bridge components and damages. The experiments lead to several interesting discoveries. Nested Reg-UNet architecture is found to outperform five other state-of-the-art architectures in both damage and component segmentation tasks. The architecture is built by combining a Nested UNet style dense configuration with a pretrained RegNet encoder. In terms of the mean Intersection over Union (mIoU) metric, the Nested Reg-UNet architecture provides an improvement of 2.86% on the damage segmentation task and 1.66% on the component segmentation task compared to the state-of-the-art UNet architecture. Furthermore, it is demonstrated that incorporating the Lovasz-Softmax loss function to counter class imbalance can boost performance by 3.44% in the component segmentation task over the most employed alternative, weighted Cross Entropy (wCE). Finally, weighted softmax ensembling is found to be quite effective when used synchronously with the Nested Reg-UNet architecture by providing mIoU improvement of 0.74% in the component segmentation task and 1.14% in the damage segmentation task over a single-architecture baseline. Overall, the best mIoU of 92.50% for the component segmentation task and 84.19% for the damage segmentation task validate the feasibility of these techniques for autonomous bridge component and damage segmentation using RGB images.

• Journal of the Korean GEO-environmental Society
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• v.24 no.5
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• pp.5-12
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• 2023

Recently, due to urban development and expansion, construction plans have been increasing adjacent to existing tunnel structures such as subways, roads, and large pipelines. Structural plans adjacent to existing tunnels have different effects on tunnel stability depending on the construction method, degree of proximity, and location of new structures. In particular, the pressure water tunnel shows a very large difference from other road tunnels and railway tunnels in geotechnical characteristics and operation characteristics. Therefore, it is necessary to review the safety zone due to adjacent construction in consideration of the geotechnical characteristics of the water tunnel and the new sturure construction method. In this study, the existing tunnel safety zone standards were investigated. A stability evaluation performed numerical analysis considering the deterioration of concrete lining in operation and the characteristics of water tunnel. In addition, the impact of vibration caused by pile construction and blasting excavation of new structures was reviewed. Based on this, a pressure water tunnel safety zone was proposed in consideration of adjacent construction.

• Journal of the Korea Institute of Building Construction
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• v.23 no.4
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• pp.441-452
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• 2023

Buildings that have been long neglected can suffer severe durability reduction due to factors such as rebar rust and concrete quality deterioration resulting from exposure to outside air. Furthermore, the issues associated with these suspended buildings, including safety accidents, social crimes, and environmental pollution, are becoming increasingly serious. This study investigates the current status of these buildings in the Jeju area, identifies the problems, and examines the durability of the structure in a specific location to assess the possibility of future use. Aesthetic surveys(visual and slope inspections) as well as non-destructive tests(compressive strength tests, neutralization tests, and rebar detection tests) were conducted to assess durability. The analysis revealed that the structure maintained satisfactory durability and the building's condition was good in comparison to the years of neglect.

• Journal of the Korea Institute of Building Construction
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• v.23 no.1
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• pp.45-56
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• 2023

This study was conducted to examine the feasibility of preparing a durability evaluation plan in watertightness for sealant applied to a PC structure. To this end, 5 types of sealant that equally satisfy the quality standards of the relevant KS standard were selected and tested. Through this testing, it was found that 3 of the 5 types of sealant showed deterioration in watertightness and durability, such as falling off and cracking from the substrate. For the remaining two types, a visual observation showed no significant changes, but additional analysis, confirmed that there was a large difference in the stress reduction rate of the material. Therefore, based on the above results, the need for a performance review in durability between sealant was confirmed, and based on this, the validity of the durability evaluation plan that can be used in product selection was quantitatively confirmed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.3
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• pp.223-237
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• 2010

The initial heating rate is well known as one of the most influencing factors on the occurrence of spalling and the loss of strength in concrete after fire initiation. In this study, a series of fire tests were carried out at different initial heating rates to find out its effects on the deterioration of tunnel structural members. Heat transfer analyses combined with an element elimination model were also carried out to verify its applicability in the same conditions as the fire tests. Moreover, the convection heat transfer coefficients compatible with fire test results were derived from parametric studies. In this course, their time-dependent variations were also analyzed at different initial heating rates. Finally, a numerical formula to estimate the heat transfer coefficients at the various initial heating rates was proposed by the interpolation of the results of numerical analyses.

• Journal of the Korea Institute of Building Construction
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• v.16 no.3
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• pp.271-278
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• 2016

In the case of South Korea, steel girder bridge (steel box or H-steel) and PSC (Pre-Stressed Concrete) girder bridge are the representative upper structures of railroad and road bridges. These structures account for 75% of the total bridge constructions and 80% of the total construction cost. Since the form work for concreting bridge slab is difficult, various construction methods developed and applied. However, several problems in those methods did not solve partially, including cost increase by material loss and rise of labor costs, quality deterioration by unskilled workers, increased construction time by complicated method, reduced productivity, safety accident by high place work, difficult transportation by big member, and rise of maintenance cost by material characteristic. Alternative method is needed to solve problems of as-is methods. Therefore, the purpose of this study is development of the purlin hanging system form for the girder bridge slab and its economic analysis. Through the findings of this study, it was verified that the purlin hanging system form is possible 60% reduction in cost and 80% reduction in time as comparison with conventional method.

• International Journal of Highway Engineering
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• v.17 no.2
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• pp.55-62
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• 2015

Cracking is an inevitable fact of asphalt concrete pavements and plays a major role in pavement deterioration. Pavement cracking is one of the main factors determining the frequency and method of repair. Cracks can be treated with a number of preventative maintenance actions, including overlay surface treatments such as slurry sealing, crack sealing, or crack filling. Pavement cracks can show up as one or all of the following types: transverse, longitudinal, fatigue, block, reflective, edge, and slippage. Crack sealing is a frequently used pavement maintenance treatment because it significantly extends the pavement service life. However, crack sealant often fails prematurely due to a loss of adhesion. Because current test methods are mostly empirical and only provide a qualitative measure of the bond strength, they cannot accurately predict the adhesive failure of the sealant. This study introduces a laboratory test aimed at assessing the bonding of hot-poured crack sealant to the walls of pavement cracks. A pneumatic adhesion tensile testing instrument (PATTI) was adopted to measure the bonding strength of the hot-poured crack sealant as a function of the curing time and temperature. Based on a limited number of test results, the hot-poured crack sealants have very different bonding performances. Therefore, this test method can be proposed as part of a newly developed performance-based standard specification for hot-poured crack sealants for use in the future. PURPOSES : The purpose of this study was to evaluate both the adhesion and failure performance of a crack sealant as a function of its curing time and curing temperature. METHODS: A pneumatic adhesion tensile testing instrument (PATTI) was adopted to measure the adhesion performance of a crack sealant as a function of the curing time and curing temperature. RESULTS: With changes in the curing time, curing temperature, and sealant type, the bond strengths were found to be significantly different. Also, higher bond strengths were measured at lower temperatures. Different sealant types produced completely different bond strengths and failure behaviors. CONCLUSIONS: The bonding strength of an evaluated crack sealant was shown to differ depending on various factors. Two sealant types, which were composed of different raw materials, were shown to perform differently. The newly proposed test offers the possibility of evaluating and differentiating between different crack sealants. Based on alimited number of test results, this test method can be proposed as part of a newly developed performance-based standard specification for crack sealants or as part of a guideline for the selection of hot-poured crack sealant in the future.