• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.355-363
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• 2023

In safety assessment of a aged bridge, dynamic characteristics and displacement are directly related to the rigidity of the structural system, especially displacement is the most important factor as the physical quantity that the bridge user can directly detect. However, in order to measure the displacement of the bridge, it is difficult to install displacement sensors at the bottom of the bridge and conduct traffic blocking and loading tests, resulting in increased costs or impossible measurements depending on the bridge's environment. In this study, a method of measuring the displacement of a bridge using only accelerometers without installing displacement sensors and ambient vibration without a loading test was proposed. For the analysis of bridge dynamic characteristics and displacement using ambient vibration, the mode shape and natural frequency of the bridge were extracted using a TDD technique known to enable quick analysis with simple calculations, and the unit load displacement of the bridge was analyzed through flexibility analysis to calculate static displacement. To verify this proposed technology, an on-site test was conducted on C Bridge, and the results were compared with the measured values of the loading test and the structural analysis data. As a result, it was confirmed that the mode shape and natural frequency were 0.42 to 1.13 % error ratio, and the maximum displacement at the main span was 3.58 % error ratio. Therefore, the proposed technology can be used as a basis data for indirectly determine the safety of the bridge by comparing the amount of displacement compared to the design and analysis values by estimating the displacement of the bridge that could not be measured due to the difficulty of installing displacement sensors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.730-736
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• 2016

In a previous study, the impact factor response spectrum and corresponding method for evaluating the load carrying capacity of bridges was suggested to improve the existing evaluation method. To verify the applicability of the suggested method, which is based on the frequency of bridges, the dynamic characteristic test for an actual single span simply-supported bridge was conducted. Through a field test under ambient traffic conditions, the dynamic response of the bridge was obtained using wireless accelometers and its fundamental frequency was identified. The peak impact factor was determined from the identified frequency and the impact factor response spectrum. The load carrying performance variation of the bridge was estimated considering the performance reduction factor, which was calculated using the current and previous natural frequency and impact factor. From the result, the load carrying capacity of the bridge was decreased, but the capacity was still enough because its value is greater than the design live load. Through the overall procedures and technical details presented in this paper, the suggested evaluation method can be applied to actual bridges with the acceleration data measured under ambient traffic conditions and the impact factor response spectrum.

• Tunnel and Underground Space
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• v.10 no.1
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• pp.25-32
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• 2000

This paper presents two new extensions to the DDA method. The extensions consist of sequential loading or unloading and rock reinforcement by rockbolts, shotcrete or concrete lining. Examples of application of the DDA method with the new extensions are presented. Simulations of the underground excavation of the Unju Tunnel of Kyungbu High Speed Railway Project in Korea were carried out to evaluate the influence of excavation sequence and reinforcement on the tunnel stability. The results of the present study indicate that improper selection of excavation sequence could have a destabilizing effect on the tunnel stability. On the other hand, reinforcement by rockbolts and shotcrete can stabilize the tunnel. It is found that, in general, the DDA program with the three new extensions can now be used as d practical tool in the design of underground structures. In particular, phases of construction (excavation, reinforcement) can now be simulated more realistically.

• Korean Journal of Construction Engineering and Management
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• v.5 no.6 s.22
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• pp.212-217
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• 2004

Carbon fiber reinforced plastic(CFRP) plate Is one of the alterative materials for soengthening of reinforced and prestressed connote members due to excellent strength and light weight In this paper, the behavior of beams strengthened with CFRP plate and CFS(Carbon fiber sheet) is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear lone appear in same position. The main failure mode is a peeling-off of the CFRP plate near the loading points due to flexural-shear crack, Because of this failure mode, failure load is not linearly proportional to the thickness of CFRP plates. When beam is wrapped with CFS around oかy loading point it does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When line moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened beam and moment of unstrengthened beam is proposed 1.5-2.0. In order to use the plate of thicker than 6mm, CFS may be extended to the location which moment of strengthened beam is 1.5 times than moment of unstrengthened beam.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.482-493
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• 2003

Flat plate structures subjected to lateral load have less deformability than conventional moment frames, due to the brittle failure of plate-column connection. In the present study, parametric study using nonlinear finite element analysis was performed to investigate the deformability of flat plates. The numerical results show that as number of continuous spans increases, the deformability of flat plates considerably decreases. Therefore, existing experiments using sub-assemblages with 1 or 2 spans may overestimate the deformability of flat plates, and current design provisions based on the experiments may not be accurate in estimating the deformability. A design method estimating the deformability was developed on the basis of numerical results, and verified by comparison with existing experiment. In the proposed method, the effects of primary design parameters such as direct shear force, punching shear capacity, aspect ratio of connection, number of spans, and initial stiffness of plate can be considered.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.73-80
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• 1999

Analytical studies on piles so far have been directed toward prediction of bearing capacity under vertical loads. Various static and dynamic formulas have been used in predicting the ultimate bearing capacity of a pile. Further, the reliability of these formulas has been verified by comparing the predicted values with the pile load test measurements. Accordingly, by means of the ultimate load from the data measured by the actual field load tests of PHC piles, safety factors were compared and analyzed static and dynamic formula methods applying to 4 different sites. As a result, the safety factor by Meyerhof formula method indicates 3.0 and the safety factor by Hiley formula method indicates 5.0.

• International Journal of Highway Engineering
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• v.14 no.2
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• pp.45-53
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• 2012

Hollows are easily made and bearing capacity is lowered near underground structures of concrete pavement because of poor compaction and long term settlement of the ground. Distresses occur and lifespan is shortened because of larger stress induced by external loadings expected than that in the design. In this paper, the distresses of the concrete pavement slab over box culverts were investigated at the Korea Expressway Corporation(KEC) test road. The transverse cracking of the slabs over the culverts was compared between up and down lines with different soil cover depth. The box culvert without soil cover and concrete pavement were modeled and analyzed by the finite element method(FEM) to verify the transverse cracking at the test road. Wheel loading was applied after self weight of the pavement and temperature gradient of the concrete slab at Yeojoo, Gyeonggi where the test road is located were considered. Positions of maximum tensile stress and corresponding positions of the wheel loading were found for each loading combination. Joint position minimizing the maximum tensile stress was found and optimal slab length over the culverts with diverse size were suggested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.245-251
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• 1999

Carbon fibre reinforced plastic(CFRP) plate is one of the alternative materials for strengthening of reinforced and prestressed concrete members due to excellent strength and light weight. In this paper, the behavior of slabs strengthened with CFRP plate is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear force appear in same position. The failure mode is a peeling-off of the CFRP plate due to flexural-shear crack. This is observed near the loading points with thick plates. Because of this failure mode, thickness of CFRP plates does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When large moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened slab and moment of unstrengthened slab is proposed 1.5-2.0.

• Journal of the Korean Geotechnical Society
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• v.38 no.10
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• pp.61-74
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• 2022

Considering that the number of cases in which a structure foundation is located on weathered rock has been increasing recently, for adequate design bearing capacity of a foundation on weathered rock, allowable bearing capacities of such foundations in geotechnical investigation reports were studied. With reference to the study results, the allowable bearing capacity of a foundation on weathered rock was approximately 400-700 kN/m², with a large variation, and was considered a conservative value. Because the allowable bearing capacity of the foundation ground is an important index in determining the foundation type in the early design stage, it can have a significant influence on the construction cost and period according to the initial decision. Thus, in this study, six large-scale plate-bearing tests were conducted on weathered rock, and the bearing capacity and settlement characteristics were analyzed. According to the test results, the bearing capacities from the six tests exceeded 1,500 kN/m², and it shows that the results are similar with the one of bearing capacity formula by Pressuremeter tests when compared with the various bearing capacity formula. In addition, the elastic modulus determined by the inverse calculation of the load-settlement behavior from the large-scale plate-bearing tests was appropriate for applying the elastic modulus of the Pressuremeter tests. With consideration of the large-scale plate-bearing tests in this study and other results of plate-bearing tests on weathered rock in Korea, the allowable bearing capacity of weathered rock is evaluated to be over 1,000 kN/m². However, because the settlement of the foundation increases as the foundation size increases, the allowable bearing capacity should be restrained by the allowable settlement criteria of an upper structure. Therefore, in this study, the anticipated foundation settlements along the foundation size and the thickness of weathered rocks have been evaluated by numerical analysis, and the foundation size and ground conditions, with an allowable bearing capacity of over 1,000 kN/m², have been proposed as a table. These findings are considered useful in determining the foundation type in the early foundation design.

• Journal of the Korean GEO-environmental Society
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• v.11 no.4
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• pp.51-59
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• 2010

This article is a case study for the example of the foundation design, in the project area of the silty sand layer that is spread shallowly with loose status, to make the site for a structure and build it up. The site is located on the dredged and reclaimed land in Gun-San and In-Cheon that is formed the silty sand layer with loose status range around 10 meters underground level, the solid ground for the lower pile is shown around 20 meters underground level. Therefore, this area has to be done by ground improvement when applying for the shallow method of foundation. Dynamic compaction method considering the conditions of the design loads in each zone has to be decided through comparative review on the method of foundations and pilot field test was conducted, and drilling investigation and plate bearing test were achieved as well. The analysis results of the tests prove that stability against bearing capacity was acquired by ground improvement effect.