• Wind and Structures
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• v.38 no.1
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• pp.75-91
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• 2024

Reliable wind signal reconstruction can be beneficial to the operational safety of long-span bridges. Non-Gaussian characteristics of wind signals make the reconstruction process challenging. In this paper, non-Gaussian wind signals are converted into a combined prediction of two kinds of features, actual wind speeds and wind angles of attack. First, two decomposition techniques, empirical mode decomposition (EMD) and variational mode decomposition (VMD), are introduced to decompose wind signals into intrinsic mode functions (IMFs) to reduce the randomness of wind signals. Their principles and applicability are also discussed. Then, four artificial intelligence (AI) algorithms are utilized for wind signal reconstruction by combining the particle swarm optimization (PSO) algorithm with back propagation neural network (BPNN), support vector regression (SVR), long short-term memory (LSTM) and bidirectional long short-term memory (Bi-LSTM), respectively. Measured wind signals from a bridge site in a deep-cutting gorge are taken as experimental subjects. The results showed that the reconstruction error of high-frequency components of EMD is too large. On the contrary, VMD fully extracts the multiscale rules of the signal, reduces the component complexity. The combination of VMD-PSO-Bi-LSTM is demonstrated to be the most effective among all hybrid models.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.949-952
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• 2006

An understanding of rheological property on cement paste is one of the important factor to design concrete such as High-fluidity Concrete (HFC) for a specific application. The HFC is a specially proportioned hydraulic cement concrete that enables the fresh concrete to flow easily into the forms and around the reinforcement and prestressing steel without vibration and segregation. Use of this type of concrete for the concrete building construction, manufacture of precast, prestressed bridge elements provides the benefits of increased rate of production and safety, reduced labor needs, and lower noise levels. This paper presents the performance of rheological properties of cement paste incorporating domestic high-water-reduced-admixture (HWRA) for an Ultra-high-fluidity concrete (UHFC). Investigation was carried out on cement pastes with combinations of various dosages of HWRA and water/cement ratios.

• Journal of Navigation and Port Research
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• v.33 no.5
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• pp.295-301
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• 2009

Recently, considerable number of bridges crossing over navigable waterways are under construction for the connection of coastal islands with mainland and the optimization of logistic system However, the most planned bridges have been initiated without paying much attention to ships safety aspects but with great emphasis on the economic factors, it has often been confronted with difficult social issues arising from opposing views and conflicts between building bodies and affected port users. The main reason for the conflicts is the lack of standards or specifications on the bridge design The proper location and scale of sea bridges are suggested in this paper considering fairway design criteria of both domestic and foreign countries, status analysis on the designs of existing and planned bridges, investigation findings of bridge-related marine accidents, the views of pilots and navigators collected through questionnaire. Since there is no general domestic or international design rules on bridge's scale, the design standards proposed in this paper may be useful at initial design stage of bridge.

• Steel and Composite Structures
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• v.49 no.1
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• pp.81-89
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• 2023

A simplified calculation method of natural vibration characteristics of high-speed railway multi-span bridge-longitudinal ballastless track system is proposed. The rail, track slab, base slab, main beam, bearing, pier, cap and pile foundation are taken into account, and the multi-span longitudinal ballastless track-beam-bearing-pier-cap-pile foundation integrated model (MBTIM) is established. The energy equation of each component of the MBTIM based on Timoshenko beam theory is constructed. Using the improved Fourier series, and the Rayleigh-Ritz method and Hamilton principle are combined to obtain the extremum of the total energy function. The simplified calculation formula of the natural vibration frequency of the MBTIM under the influence of vertical and longitudinal vibration is derived and verified by numerical methods. The influence law of the natural vibration frequency of the MBTIM is analyzed considering and not considering the participation of each component of the MBTIM, the damage of the track interlayer component and the stiffness change of each layer component. The results show that the error between the calculation results of the formula and the numerical method in this paper is less than 3%, which verifies the correctness of the method in this paper. The high-order frequency of the MBTIM is significantly affected considering the track, bridge pier, pile soil and pile cap, while considering the influence of pile cap on the low-order and high-order frequency of the MBTIM is large. The influence of component damage such as void beneath slab, mortar debonding and fastener failure on each order frequency of the MBTIM is basically the same, and the influence of component damage less than 10m on the first fourteen order frequency of the MBTIM is small. The bending stiffness of track slab and rail has no obvious influence on the natural frequency of the MBTIM, and the bending stiffness of main beam has influence on the natural frequency of the MBTIM. The bending stiffness of pier and base slab only has obvious influence on the high-order frequency of the MBTIM. The natural vibration characteristics of the MBTIM play an important guiding role in the safety analysis of high-speed train running, the damage detection of track-bridge structure and the seismic design of railway bridge.

• Proceedings of KOSOMES biannual meeting
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• 2002.10a
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• pp.111-124
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• 2002

Ship manoeuvring simulator has been widely utilized for training mariners, for assessing safety, for developing harbour and port, and for designing ships. We discuss a ship manoeuvring simulator which has been newly developed by Korea Maritime University. The simulator consists of simulator bridge and control console. All the computers used in the simulator are connected with one another by UDP or TCP network system. All the instruments are connected with interface computer by signal line which is controlled by RS232 communication protocol, or by voltage controlled A/D board. Next the mathematical model of ship manoeuvring motion in harbour areas, and ship and terrain modeling technique are also briefly discussed. Finally using the simulator an experiment of distance cognition and a simulation example of berthing/deberthing manoeuvre are shown.

• Geomechanics and Engineering
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• v.32 no.1
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• pp.111-123
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• 2023

The slope of an open cut tunnel is located above the exit of the Leijia tunnel on the Changgan high-speed railway. During the excavation of the open cut tunnel foundation pit, the slope slipped twice, a large landslide of 92500 m³ formed. The landslide body and unstable slope body not only caused the foundation pit of the open cut tunnel to be buried and the anchor piles to be damaged but also directly threatened the operational safety of the later high-speed railway. Therefore, to study the stability change in the slope of the open cut tunnel under heavy rain and excavation conditions, a 3D numerical calculation model of the slope is carried out by Midas GTS software, the deformation mechanism is analyzed, anti-sliding measures are proposed, and the effectiveness of the anti-sliding measures is analyzed according to the field monitoring results. The results show that when rainfall occurs, rainwater collects in the open cut tunnel area, resulting in a transient saturation zone on the slope on the right side of the open cut tunnel, which reduces the shear strength of the slope soil; the excavation at the slope toe reduces the anti-sliding capacity of the slope toe. Under the combined action of excavation and rainfall, when the soil above the top of the anchor pile is excavated, two potential sliding surfaces are bounded by the top of the excavation area, and the shear outlet is located at the top of the anchor pile. After the excavation of the open cut tunnel, the potential sliding surface is mainly concentrated at the lower part of the downhill area, and the shear outlet moves down to the bottom of the open cut tunnel. Based on the deformation characteristics and the failure mechanism of the landslides, comprehensive control measures, including interim emergency mitigation measures and long-term mitigation measures, are proposed. The field monitoring results further verify the accuracy of the anti-sliding mechanism analysis and the effectiveness of anti-sliding measures.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.166-171
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• 2012

This study aims to analyze the hydrological characteristics of downstream areas by the dam discharge of Soyanggang dam by using HEC-RAS Model. As a result of analyzing the data of dam discharge divided into hydropeaking discharge and total discharge, it as found that the maximum hydro-peaking discharge and the maximum total discharge have been 254.4 CMS and 1567.7 CMS respectively for the past 11 years. When the hydro-peaking discharge was applied to HEC-RAS Model, there occurred some sections where the water level rapidly changed, but the velocity of moving water was quite stable in the range between 0.23 m/sec and 1.16m/sec. Besides, when the total discharge was applied to this model, the submersible bridge along the dam downstream was flooded, and in some sections, the water level increased over the flood plain. Accordingly, this study judged that it is required to necessarily consider all the influence made by an increase of Soyanggang Dam's discharge when waterfronts are installed or used at dam downstream areas.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.32 no.2
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• pp.68-81
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• 2014

This study was conducted to identify the spacialty, to illuminate the existence and values of Myeongwoldae(明月臺) and Forest Myeongwol, and to suggest the sustainable usage, preservation and management plans with the purpose of ecological and cultural landscaping characteristic and value identification. The result of the study is as follows. Castle Myeongwol and Port Myeongwol shows the status of Hallim-eup Myeongwol District which is the administrative center of western Jeju as well as is the fortress. Building Wolgyejeongsa and School Woohakdang, the head temple of education and culture, located in Myeongwol District represents the spaciality of Myeonwol-ri which was the center of education. Stand Myeongwol is one of the most representative Confucian cultural landscapes in Jeju Island and the field of communion with nature where scholars enjoy poetries, nature, changgi(Korean chess), and go in the Joseon Dynasty period. It was found that the current relics of Myeongwoldae was recovered through the maintenance project conducted by Youth Group Myeongwol composed with Hongjong-si(洪鍾時) as the center during the Japanese colonial era in 1931. It seems that the stonework of Myeongwoldae composed of three levels in the order of square, octagon, and circle based on the heaven-man unity theory of Confucianism and the octagon in the middle is the messenger of Cheonwonjibang(天圓地方), in other words, between the square-shaped earth and the circle-shaped sky. It is assumed that both Grand Bridge Myeongwol and Bridge Myeongwol were constructed as arched bridges in early days. Bridge Myeongwol is the only arched bridge remaining in Jeju Island now, which has the modern cultural heritage value. In Forest Myeongwol, 97 taxa of plants were confirmed and in accordance with 'Taxonomic Group and Class Criteria of Floristic Specific Plants', eight taxa were found; Arachniodes aristata of FD IV and Ilex cornuta, Piper kadsura, Litsea japonica, Melia azedarach, Xylosma congestum, Richosanthes kirilowii var. japonica, Dichondra repens, Viburnum odoratissimum var. awabuki of FD III. Otherwise, 14 taxa of naturalized plants including Apium leptophylihum which is imported to Jeju Island only were confirmed. In Forest Myeongwol, 77 trees including 41 Celtis sinensis, 30 Aphananthe aspera, two Wylosma congestum, a Pinus densiflora, a Camellia japonica, a Melia azedarach, and an Ilex cornuta form a colony. Based on the researched data, the preservation and plans of Myeongwoldae and Forest Myeongwol is suggested as follows. Myeongwoldae, Bridge Myeongwol, and Forest Myeongwol should be managed as one integrated division. Bridge Myeongwol, an arched bridge which is hard to be found in Jeju Island is a high-standard stonework requiring long-term preservation plans. Otherwise, Grand Bridge Myeongwol that is exposed to accident risks because of deterioration and needs safety diagnosis requires measures according to the result of precise safety diagnosis. It is desirable to restore it to a two-sluice arched bridge as its initial shape and to preserve and use it as a representative local landmark with Stand Myeongwol. In addition, considering the topophsis based on the analysis result, the current name of Jeju Special Self-Governing Province Monument No. 19 'Myoengwol Hackberry Colony' should change to 'Myeongwol Hackberry-Muku Tree Colony'. In addition, the serial number system which is composed without distinction of hackberry and muku tree should be improved and the regular monitoring of big and old trees, specific plants, and naturalized species is required.

• Smart Structures and Systems
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• v.33 no.3
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• pp.189-199
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• 2024

To properly extract the strain components under varying operational conditions is very important in bridge health monitoring. The abnormal sensor readings can be correctly identified and the expected operational performance of the bridge can be better understood if each strain components can be accurately quantified. In this study, strain components under varying load conditions, i.e., temperature variation and live-load variation are evaluated based on field strain measurements collected from a real concrete box-girder bridge. Temperature-induced strain is mainly regarded as the trend variation along with the ambient temperature, thus a smoothing technique based on the wavelet packet decomposition method is proposed to estimate the temperature-induced strain. However, how to effectively extract the vehicle-induced strain is always troublesome because conventional threshold setting-based methods cease to function: if the threshold is set too large, the minor response will be ignored, and if too small, noise will be introduced. Therefore, an autoencoder framework is proposed to evaluate the vehicle-induced strain. After the elimination of temperature and vehicle-induced strain, the left of which, defined as the model error, is used to assess the operational performance of the bridge. As empirical techniques fail to detect the degraded state of the structure, a clustering technique based on Gaussian Mixture Model is employed to identify the damage occurrence and the validity is verified in a simulation study.