• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.100-107
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• 2018

The objective of this study is to assess the strengthening effects of fiber reinforced polymer(FRP) sheets such as Carbon fiber, Glass fiber, and PET(polyethylene terephthalate) on reinforced concrete flexural members. Variables of theoretical analysis are types of strengthening materials, material properties and amount of strengthening materials. A virtual flexural member without FRP sheets was created as a control specimen to understand the structural behavior of the non-strengthened specimen in terms of elastic and ultimate cross section. In total, 11 specimens including one non-strengthened and ten strengthened specimens were investigated. Various variables such as types of strengthening, strengthening properties, and amount of strengthening were studied to compare the behavior of the control specimen with those of strengthened specimens with regard to moment-curvature relationship. Results of theoretical analysis showed that the moment capacity of strengthened specimens was superior to that of the control specimen. However, the control specimen indicated the best ductility among all the specimens. As the amount of strengthening increased, flexural performance was improved. Furthermore, the results indicated that the ductile effect of members was affected by the ultimate strain of FRP sheets. The strengthening effect on the damaged member was similar to that on the non-damaged one since there was less than 10% difference in terms of flexural strength and ductility. Therefore, even if a damaged member is treated as non-damaged for analysis there is probably no noticeable difference.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2016.05a
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• pp.75-77
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• 2016

IMO는 해상에서의 선박 안전 향상을 위해 선박의 복원성능과 조종성능에 관한 국제적 기준을 제시하고 있다. 이러한 기준은 선박 연구자가 수행하는 연구의 방향에도 영향을 미치고 있다. 기존의 수행된 연구는 복원성능과 조종성능의 각각의 분야에서 독립적으로 수행되어 왔으며, 아직 두 분야의 상호 관계에 관한 연구는 미비한 실정이다. 이에 본 논문에서는 선박의 복원성능과 조종성능의 상호 관계를 정량적으로 규명하고자 기초적인 실험 연구를 수행하였다. 이를 위해 복원성능을 나타내는 지표인 GM과 선박의 조종성능을 나타내는 지표인 선회성능을 통해 두 항복 간 상호 관계의 정량적 분석을 시도하였다. 자유항주 모형선을 이용한 선회 시험을 실시하였고, 그 결과 GM 감소에 따른 선회반경 감소 및 초기 횡경사 각도 증가를 확인했으며, 그 변화의 경향은 서로 다르게 나타나는 것을 확인하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6C
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• pp.251-258
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• 2011

Steel pipe piles have been used as various deep foundation materials for a long time. Recent increase in steel material cost has made engineers reluctant in using it even with its good quality and ease of construction. Therefore when constructing with steel pipe pile, the decision to reuse the excessive pile length that is cut off from the designed pile head elevation after pile driving can be cost saving. This has caused many constructors to reuse the pile leftovers with new piles, but the absence of quantitative structural capacity behaviors of steel pipe pile after pile driving or appropriate countermeasures and standards in reusing steel pipe pile has resulted in wrong applications, pile structural integrity problems, inappropriate limitation of reusable pile length, etc. The structural performance analysis between a new pile and a pile that has undergone working state and ultimate state stress level during pile driving was performed in this research by means of comparing the results between the dynamic pile load test, tensile load test, charpy energy test and fatigue test for high strength steel of $440N/mm^2$ yield strength. Test results show that under working load conditions the yield strength variation is less than 2% and for ultimate load conditions the variation is less than 5% for maximum total blow count of 3000. The results have been statistically analyzed to check the sensitivity of each factors involved. From the test results, reusability of steel pipe pile lies not in the main pipe yield strength deviation but in the reduction of absorb energy, strength changes and quality control at the welded section, shape deformation and local buckling during pile driving.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.18-29
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• 2013

A new precast concrete (PC) beam and column connection system using non-prestressed wire strands was recently developed. The system is composed of one unit of two-storied PC-column and PC-beams with U-shaped ends. The connection part of the column and beams is reinforced by deformed bars and non-prestressed wire strands in combination for the improvement of workability. Structural performance of this system was verified by several experimental studies. The purpose of this study is developing a design concept of the beam reinforced by deformed bars and non-prestressed wire strands in combination, in terms of the cross-sectional analysis, based on the preceded experiment. A minimum and maximum reinforcement ratio and the calculation formula for the strength of flexural member reinforced by reinforcements having different yield strengths are derived based on KBC2009. Under consideration existing research results for the application of high strength reinforcement bars, the design yield strength of the non-prestressed wire strand is suggested. An example for the cross section design, satisfying the serviceability requirements, demonstrates the applicability of the design concept developed in the study.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.503-510
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• 2012

High performance, high strength steels were developed and used in steel structures recently. Since the newly developed high strength steels posses different toughness, weldability, yield strength ratio, etc. in compare with conventional structural steels, it is requred to investigate the applicability of the design strength of fillet weld specified in the existing design codes. The comparison of the design strengths of various codes from domestic and overseas shows quite a difference. Test results for fillet weld strengths were collected and statistically analysed. Each of yield strength, tensile strength of parent material and tensile strength of weld metal was selected as a main parameter for each estimation equation respectively. All the estimation equations yield almost same values for each type of steel regardless the type of main parameter selected. Considering the behaviour of fillet welded joints and for practical purposes, it is proposed that the equation with tensile strength of parent material is to be used in design codes. The comparison with the proposed nominal strengths of fillet welds shows that the existing design codes could lead to an uneconomical result for low strength steels and lie on an unsafe side for high strength steels.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.11-20
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• 2013

In this paper, the quantitative damage index for reinforced concrete (RC) columns with non-seismic details were presented. They are necessary to carry out the postearthquake safety evaluation of RC buildings under 5 stories without seismic details. The static cyclic test of the RC frame sub-assemblage that was an one span and actual-sized was first conducted. The specimen collapsed by the shear failure after flexural yielding of a column, lots of cracks on the surfaces of columns and beam-column joints and the cover concrete splitting at the bottom of columns occurred. The damage levels of these kinds of columns with non-seismic details were classified to five based on the load-displacement relationship by the test result. The residual story drift ratios and crack widths were then adapted as the quantitative index to evaluate the damage limit states because those values were comparatively easy to measure right after earthquakes. The highest one among the residual story drift ratios under the similar maximum story drift ratio decided on the residual story drift ratio of each damage limit state. On the other hand, the lowest and average ones among the respective residual shear and flexural widths under the similar maximum story drift ratio decided on the residual shear and flexural widths of each damage limit state, respectively. These values for each damage limit state resulted in being smaller than those by the international damage evaluation guidelines that are for seismically designed members under the same deformations.

• Journal of the Korean GEO-environmental Society
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• v.25 no.8
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• pp.13-19
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• 2024

In this study, to reinforce the surface layer of weathered soil slopes where erosion and collapse of surface layer occur, compression strength tests were conducted by mixing carbon fiber and eco-friendly stabilizer (E.S.B.) To determine the optimal mixing ratio of E.S.B. and carbon fiber, E.S.B. was set at conditions of 10%, 20%, and 30%, and carbon fiber at 0.3%, 0.6%, 0.9%, and 1.2%. Additionally, to analyze the changes in compressive strength according to dry density and curing period, 85% and 95% of the maximum dry unit weight were applied, and curing periods were set to 3 days, 7 days, and 28 days. The standard strength for surface layer reinforcement of slopes is proposed as 4 MPa at 7 days and 6 MPa at 28 days according to ACI 230.1R-09 (2009). The compression test results showed that the unconfined compressive strength of E.S.B. reinforced soil met the standard strength at an E.S.B. mixing ratio of 10% or more for 95% compaction. Moreover, when carbon fiber was mixed with E.S.B. reinforced soil, a ductile fracture pattern was observed after the yield point due to compressive strength, indicating that the mixture could compensate for post-yield failure. It was analyzed that the maximum strength is exhibited at a carbon fiber mixing ratio of 0.6%. The unconfined compressive strength of carbon fiber reinforced soil increases by approximately 54-70% compared to the condition without carbon fiber.

• Journal of Korean Society of Steel Construction
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• v.21 no.1
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• pp.15-26
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• 2009

Push-out tests were performed to evaluate the shear capacity of a composite steel truss deck slab system, called an automatic prefabrication bar-mesh system, using lightweight concrete. The six specimens were classified into three groups: DP, NDP, and Solid, according to the variations between the bar mesh and the zinc plate automatic prefabrications. This paper focused on the failure behaviors, load-displacement characteristics, and a performance comparison based on design codes.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.111-122
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• 2005

The data on the pile load tests performed on 35 large drilled shafts are analyzed to investigate the load-settlement characteristics of large drilled shafts embedded in bed rocks. Generally, the settlement of large drilled shafts embedded in bed rocks is too small to determine the ultimated load with application of the regulation in design code for either the total settlement or the residual settlement. Therefore, to determine the yield load of large drilled shafts embedded in bed rocks, p(load)-logS (settlement) curve method, which has been proposed originally for the driven pile, was applied to the investigation on the data of the pile load tests. This technique shows that the yield load can be determined accurately and easily rather than other conventional techniques such as P-S, logp-logS, S-logt, and P-S curve methods. An empirical equation is proposed to represent the relationship between pile load and settlement before the yield loading condition. And the settlement of piles was related with the depth embedded in rock as well as rock properties. Based on the investigation on the data of pile load tests, the resonable regulations f3r both the total settlement and the residual settlement are proposed to determine the yield load of large drilled shafts embedded in bed rocks.

• Geophysics and Geophysical Exploration
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• v.23 no.1
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• pp.1-12
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• 2020

In the development of geodynamic structures such as subduction and rift zones, a weakening mechanism is essential for localized weak zone formation in the lithosphere. Shear heating, a weakening mechanism, generates short-wavelength temperature elevation in the lithosphere; the increased temperature can reduce lithospheric strength and promote its breakup. A two-dimensional elastoplastic extensional basin model was used to conduct benchmarking based on previous numerical simulation studies to quantitatively analyze shear heating. The amount of shear heating was investigated by controlling the yield strength, extensional velocity, and strain- and temperature-dependent weakening. In the absence of the weakening mechanism, the higher yield strength and extensional velocity led to more vigorous shear heating. The reference model with a 100-MPa yield strength and 2-cm/year extension showed a temperature increase of ~ 50 K when the bulk extension was 20 km (i.e., 0.025 strain). However, in the yield-strength weakening mechanism, depending on the plastic strain and temperature, more efficient weakening induced stronger shear heating, which indicates positive feedback between the weakening mechanism and the shear heating. The rate of shear heating rapidly increased at the initial stage of deformation, and the rate decreased by 80% as the lithosphere weakened. This suggests that shear heating with the weakening mechanism can significantly influence the strength of relatively undamaged lithosphere.