• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.463-473
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• 2000

This paper presents the results of the experimental and analytical investigation for the fatigue strength of welded details frequently used in steel bridges, especially for the details with relatively lower fatigue strength. The welded details included four kinds of welded details corresponding to the categories C, D, E and E' which represent the flange attachment details, web attachment details, transverse stiffeners and cover-plate details. Tensile fatigue tests were performed. The test results were compared with other available test results and the fatigue criteria of AASHTO, JSSC and Eurocode specifications. Generally, our test results were well agreed with other test results and satisfied with above-mentioned fatigue design provisions. However, it was found that transversely loaded weld-details showed lower fatigue strength than longitudinally loaded weld-details in transverse stiffener detail, and the test results of those details were not satisfied with AASHTO fatigue provisions. Examining the effect of length of gusset plate attachment details, welded details with longer attachment showed relatively lower fatigue strength, especially for the out-of-plane gusset plate details. It is recommended to perform additional fatigue tests with various loading and detail parameters and to establish the more detailed fatigue categories such as Eurocode or JSSC

• Journal of Korean Society of Steel Construction
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• v.18 no.1
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• pp.33-45
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• 2006

Cable-stayed bridges are more inherently vulnerable to wind during the erection stages than when they are already being used. Even if a bridge that is already being used is aerodynamically stable, it is prone to having aerodynamic instabilities within the design wind speed during construction. Therefore, when the bridge's designers deliberate on the method they will use in constructing the bridge, they must likewise come up with a suitable plan to ensure the stability of the bridge during its erection (e.g., conducting a wind-tunnel investigation). This paper describes the aeroelastic full-bridge model tests that were conducted to investigate the aerodynamic behavior of the bridge during erection, with emphasis on aerodynamic stability and the mitigation of the buffeting response through temporary stabilization. The aerodynamic performance of a cable -stayed bridge with a main span of 50 m was studied in its completed stage and in two erection stages, corresponding 50% and 90% completion, respectively. In the 50% erection stage tests, a balanced cantilever configuration, with wind cable and temporary support at the tower, was conducted. The system that was determined to be most effective in reducing wind action on the bridge during construction was proposed in the paper, based on the results of the comparative study that was conducted.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.6
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• pp.53-60
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• 2008

The cross-sections of continuous multi-span beams sometimes suddenly increase, or become stepped, at the interior supports of continuous beams to resist high negative moments. The three-dimensional finite-element program ABAQUS (2007) was used to analytically investigate the inelastic lateral-torsional buckling behavior of stepped beams subjected to linear moment gradient and resulted in the development of design equations. The ratios of the flange thickness, flange width, and stepped length of beam are considered for the analytical parameters. Two groups of 27 cases and 36 cases, respectively, were analyzed for doubly and singly stepped beams in the inelastic buckling range. The combined effects of residual stresses and geometrical imperfection on inelastic lateral-torsional buckling of beams are considered. First, the distributions of residual stress of the cross-section is same as shown in Pi and Trahair (1995), and the initial geometric imperfection of the beam is set by central displacement equal to 0.1% of the unbraced length of beam. The new proposed equations definitely improve current design methods for the inelastic lateral-torsional buckling problem and increase efficiency in building and bridge design.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.6 s.52
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• pp.79-91
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• 2006

A new methodology of guided wave based nondestructive testing (NDT) is developed to detect crack damage in civil infrastructures such as steel bridges without using prior baseline data. In conventional guided wave based techniques, damage is often identified by comparing the "current" data obtained from a potentially damaged condition of a structure with the "past" baseline data collected at the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. To develop a more robust damage diagnosis technique, a new concept of NDT is conceived so that cracks can be detected without direct comparison with previously obtained baseline data. The proposed NDT technique utilizes the polarization characteristics of the piezoelectric wafers attached on the both sides of the thin metal structure. Crack formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the crack by extracting this mode conversion from the measured Lamb waves even at the presence of changing operational and environmental conditions. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to crack detection.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.10-19
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• 2013

Recently, researches related to precast modular construction have been actively conducted for nuclear power plant, LNG gas tank, and small-medium PCCV as well as bridges and buildings. In this study, the precast panel cast with steel mesh reinforced mortar (SRM) which is similar reinforced ferrocement was developed for efficient precast construction, construction time reduction, and easy transportation. Mortar mixture with high strength and flowability was obtained from various case studies using silica fume and GGBS. Also, $1,200{\times}600{\times}150mm$ SRM and reinforced concrete (RC) panels were manufactured with reinforcing ratio of 2% and 4%. To verify structural performance of the SRM specimen, the basic material tests, free shrinkage test, and 3-point flexural test with a line loading were carried out. From the test results, it was determined that SRM specimens showed outstanding flexural capacity and ductility. However, the 4% reinforced SRM specimens must consider shear reinforcing to be used as a precast modular member.

• Journal of the Korean Association of Geographic Information Studies
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• v.13 no.2
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• pp.64-73
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• 2010

This research collected some multi-image information of Nakdong River Estuary Eulsukdo area in last 30 years, which are used as the basis information in running the qualitative analysis of the topography relief's deformation. First, to obtain the data, this research carried out a field survey and GCP measurement, then classified and collected the image information by analog and digital image. The acquired images which have passed a high-precise scan process and geometric correction is manufactured by Ortho Mosaic image, then divided them into 9 sections time period classification before we run a qualitative analysis. In late of 1980's there are many changes of environmental topography deformation of the Eulsukdo area which caused by large scale building constructions, appeared to be known through this research. And then in late of 1990's, we organized the wild cultivated lands, started the wetland restoration of the artificial ecology, in 2000's we are able to know the existence of topograph relief change which caused by big scale of bridge construction. Hereafter, in this quick process of the environmental and topographical change of this area caused by the 4 major rivers restoration project, the analysis results of this experiment are expected to be something applicable as important basic data.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.671-678
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• 1997

Water surface velocity meters with microwave were applied to stream discharge measurements and its practical aspects were evaluted. The rating of the surface velocity meters was performed through a carriage and a water tank for the ship model test. It gave5.5% or less errors of average measured velocities under the vertical tilt ang1e of 20$^{\circ}$, 35$^{\circ}$, or 45$^{\circ}$ . A surface velocity meter was used to measure flood velocities at Yoju bridge from 8:00 a.m. to 10:00 a.m. on August 26, 1995. The results showed that surface velocities ranged from 2 to 4 m/s. With the measured surface velocities multiplied by 0.85, the discharge was computed as 10,500 m$^3$/s. It differed $\pm$2% or less from the value of a stage-discharge curve and that of an unsteady flow simulation. Although the measured data are used sparsely per 40 or 60 meters, the computed discharges do not give large variation. Stream discharge measurements were also performed under the normal condition without floods. With the known values of Taechong Dam releases. the depth averaging factors of velocity were calculated by 0.83~0.87. Although there are errors from wind action and inherent ones in the velocity meters, the research showed that surface velocity meters could be an simple and practical alternative for flood discharge measurements.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.542-550
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• 2020

The use of high-strength aluminum alloys for ships and of shore structures has many benefits compared to carbon steels. Recently, high-strength aluminum alloys have been widely used in onshore and of shore industries, and they are widely used for the side shell structures of special-purpose ships. Their use in box girders of bridge structures and in the topside of fixed platforms is also becoming more widespread. Use of aluminum material can reduce fuel consumption by reducing the weight of the composite material through a weight composition ratio of 1/3 compared to carbon steel. The characteristics of the stress strain relationship of an aluminum structure are quite different from those of a steel structure, because of the influence of the welding[process heat affected zone (HAZ). The HAZ of aluminum is much wider than that of steel owing to its higher heat conductivity. In this study, by considering the HAZ generated by metal insert gas (MIG) welding, the buckling and final strength characteristics of an aluminum reinforcing plate against longitudinal compression loads were analyzed. MIG welding reduces both the buckling and ultimate strength, and the energy dissipation rate after initial yielding is high in the range of the HAZ being 15 mm, and then the difference is small when HAZ being 25 mm or more. Therefore, it is important to review and analyze the influence of the HAZ to estimate the structural behavior of the stiffened plate to which the aluminum alloy material is applied.

• Journal of the Korean Association of Geographic Information Studies
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• v.6 no.1
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• pp.132-142
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• 2003

A significant deficiency of most computer models used for stream floodplain analysis, is that the locations of structures impacted by flood waters, such as roads, buildings, and bridges, cannot be effectively compared to the floodplain location. The purpose of this study is the integration of the HEC River Analysis System(HEC-RAS) with ArcView geographic information system to develop a regional model for floodplain determination and representation. Also this study presents to enable two- and three-dimensional floodplain mapping and analysis in the ArcView. The methodology is applied to a Yeoju of Kyunggi-do, located in South Han River Basin. A digital terrain model is synthesized from HEC-RAS cross-sectional data and a digital elevation model of the study area. The flood plain data developed in ArcView was imported into HEC-RAS where it was combined with the field surveyed channel data in order to construct full floodplain cross sections that reflected accurate channel and overbank data for the HEC-RAS model. The flood plain limits could be expressed more accurately on ArcView by using water level data to be computed in HEC-RAS program. The computed water surface elevations and information of cross-section must be manually plotted in order to delineate floodplains. The resulting of this study provided a good representation of the general landscape and contained additional detail within the stream channel. Overall, the results of the study indicate that GIS combined with HEC-RAS is proven to be very useful and efficient for the automatic generation of flood maps, and an effective environment for floodplain mapping and analysis.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.197-208
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• 2003

This paper is to determine the possibility of re-using waste concrete from Incheon city area. The strength test was conducted with five aggregate compounds which was replaced a natural aggregate with recycled aggregate. After checking the physical characteristics of recycled aggregate compounds, the mix design of recycled concrete was conducted. For the relatively comparison between natural and recycled compounds, while the unit aggregate weight was changed, other conditions were fixed. The freezing and thawing test which included fly-ash and super-plastezer were performed to check the durability and workability when recycling waste concrete. In the physical characteristics of recycled aggregate, it was found that the specific gravity of recycled coarse aggregate and recycled fine aggregate satisfied the first grade of recycle specification(KS), and all compounds of recycled aggregate also satisfied the second grade of absorption specification, Especially up to the 50% substitution of recycled aggregate is equal to or a bit lower than that of convention aggregate. In comparison with conventional concrete, the recycled concrete is lower than maximum by 7% in compressive strength decreasing rate after freezing-thawing test. From now, although most of recycled concrete was used to the building lot, subgrade, asphalt admixture, through the result. It was proved that possibility of re-using recycled aggregate as the substructure of bridge, retaining wall, tunnel lining and concrete structure which is not attacked the drying shrinkage severely.