• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.17-24
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• 2018

The pullout test, a nondestructive testing(NDT), for pre-installed inserts is perhaps the most widely used technique to estimate the in-situ compressive strength of concrete. It measures the force needed to pullout a standardized metal insert embedded into concrete members. The pullout test was certified by the American Society for Testing and Materials(ASTM) and Canadian Standards Association(CSA) as a reliable method for determining the strength of concrete in concrete structures under construction. To easily estimate the strength of ultra-high-strength concrete, a simplified pullout tester, primarily composed of a standard 12mm bolt with a groove on the shaft as a break-off bolt, an insert nut, and a hydraulic oil pump without a load cell, was proposed. Four wall and two slab specimens were tested for two levels of concrete strength, 80MPa and 100MPa, using a simplified pullout tester with a load cell to verify the advantages of the pullout test and simplified pullout test. The compressive strength of concrete, pullout load, and the rupture of the break-off bolt were measured 11 times, day 1 to 7, 14, 21, 28, and 90. The correlation of the pullout load and the compressive strength of each specimen show a higher degree of reliability. Therefore, a simplified pullout test can be used to evaluate the in-place strength of ultra-high-strength concrete in structures. The prediction equation for the groove diameter of the break-off bolt(y) with the concrete strength(x) was proposed as y=0.0184x+5.4. The results described in this research confirm the simplified pullout's utility and potential for low cost, simplicity, and convenience.

• Tunnel and Underground Space
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• v.21 no.5
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• pp.377-385
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• 2011

In order to prove the applicability of rock bolts with compressible spacers, laboratory model tests and large scale model tests were conducted. Laboratory model tests were performed in various distance of compressible spacers to determine the optimal distance of compressible spacers. The optimal distance of compressible spacers was found that is 1/4 of rock bolts unit length. Large scale model tests that the size was 0.6 m (diameter) ${\times}$ 4.45 m (length) were conducted. Test results showed that pull out resistance could be increased up to 15% larger than that of unused case by using compressible spacers.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.49-55
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• 2017

In the seventies, a number of researchers carried out experiments on pullout tests with prototype equipment, and the pullout test was certified as a reliable nondestructive testing(NDT) method for determining the strength of concrete. To estimate the strength of high-strength concrete, we propose a simplified pullout test that uses as a break-off bolt a standard 10mm bolt with a groove on the shaft, an insert nut, and a pullout instrument that includes a hydraulic oil pump without a load cell. To verify the advantages of the simplified pullout test(low cost, simplicity, and convenience), four wall specimens were tested with two levels of concrete strength, 30 MPa and 50 MPa, using a simplified pullout tester with a load cell. The pullout load and concrete compressive strength were measured every day until day 7, day 14, day 21 and day 28. It was found that the pullout load was very similar to the compressive strength. Therefore, we have verified that a simplified pullout test can be used to evaluate the in-place strength of high-strength concrete in structures. The prediction equation of the groove diameter of the break-off bolt(y) with the concrete strength(x) was derived as y=0.05x+3.79, with a coefficient of determination of 0.88 found through regression analysis.

• Journal of the Korean Geotechnical Society
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• v.17 no.3
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• pp.77-82
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• 2001

반복하중을 받는 현장타설말뚝에 대한 두 가지의 주요 관심사항은: (a) 지지력의 변화 가능성 그리고 (b) 누적변형량에 의한 기초의 가능성 저하이다. 이러한 인자들에 대한 평가를 위하여, 모형점토지반에 설치된 24개의 모형현장타설말뚝에 대한 정적 및 동적경사재하시험(12개의 압축 및 12개의 인발)을 수행하였다. 경사반복압축재하시험에서는 반복하중에 의한 지지력의 변화가 무시할 정도였으며, 누적변형량은 송전철탑의 기능성에 영향을 줄수도 있을 것으로 사료된다. 그러나, 경사반복인발시험에서는 과도한 누적변형이 발생하게 되어 결과적으로 현장타설말뚝주변과 점토사이의 접촉면적이 감소하는 것으로 나타났다. 접촉면적의 감소 결과, 반복경사인발하중에 의해서 경사인발지지력의 현저한 감소가 일어난다는 사실을 알 수 있었다. 정적경사인발지지력의 50에서 70퍼센트에 해당되는 반복하중을 받는 대부분의 현장타설말뚝들은 인발되었다.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.63-78
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• 1999

For the design of compression anchor, three things should be considered. The first is a resistance force by skin friction, the second is a tension strength of tendon, and the third is a compressive strength of grout. Especially, compressive strength of grout is the most important design parameter of compression anchor. When compression anchor is pulled out from the ground, the compressive strength of grout increases by confining pressure of ground($\sigma_{tg$). Here, $\sigma_{tg$ is the confining pressure which is produced by earth pressure at rest and by lateral expansion of grout. We call this phenomenon of increase of confining pressure "poisson effect". In this paper, the design method of compression anchor called SSC anchor and the computer program for the design are developed through compression tests of anchor body grout.ody grout.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.143-155
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• 2008

Ground anchors are classified depending on the kind of stress the grout is subjected to. If the grout material is subjected to tension then it is classified as tension anchor while when the grout material is subjected to compression it is classified as compression anchor. In this study a composite type anchor that possesses both the tension and compression mechanism was developed. For field tests, strain gauges were installed inside the anchor body in soft: soil. From the strain monitoring results, pull-out resistance mechanism that possesses both tension and compression strain was seen.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1095-1102
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• 2010

본 연구에서는 펄스 방전 기술에 의해 확공된 앵커의 인발 거동에 대한 수치해석을 수행하였다. 펄스 방전 현상을 등가의 폭발 현상으로 모델링하여 점성토와 사질토 지반에 대한 확공해석을 수행하였으며 이를 통해 펄스 방전에 의해 개량된 지반 조건을 구현하였다. 확공된 지반에 대해 설치된 압축형 그라우트 앵커의 인발 거동을 시뮬레이션하여 인발력-인발변위 곡선을 산정하였다. 해석 결과, 점성토의 경우에는 확공 정도가 인발 거동과 밀접한 관련을 갖는 반면, 사질토의 경우에는 확공 정도 이외의 추가적인 증가 요인이 확인되는 것으로 나타났으며 펄스 방전 기술이 사질토 지반의 다짐을 통해 앵커의 인발력을 증가시키는 것으로 판단되었다.

• Geotechnical Engineering
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• v.12 no.2
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• pp.71-84
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• 1996

In order to investigate the influence of slanting angle of reticulated root piles(RRP) on their bearing capacities, model tests of compressive and uplift loads on RRP with different slanting angles, which were installed in sandy soils with a relative density of 47%, were carried out. Each pile which is made of a steel bar of 5mm in diameter and 300mm in length, is coated with sand to be 6.5mm in diameter. One set of RRP consists of 8 piles which are installed in circular patterns forming two concentric circles, each of which has 4 piles. Slanting angles of RRP for load tests are 0$^{\circ}$, 5$^{\circ}$, 10$^{\circ}$, 15$^{\circ}$, 20$^{\circ}$, and 25$^{\circ}$. In addition, compressive load tests on circular footing whose diameter is the same as the outer circle of RRP were carried out. Test results show that maximum load bearing capacities of RRP by regression analysis are obtained at about 12$^{\circ}$ and 13$^{\circ}$ of slanting angles for compressive and uplift load tests, respectively. Maximum compressive bearing capacity is estimated to be 13oA bigger than that of the vertical RRP and 95% bigger than that of surface footing. Maximum uplift capacity is estimated to be 21% bigger than that of the vertical RRP. And it can be appreciated that increasing the slanting angle makes the load -Settlement behavior more ductile.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.231-239
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• 2001

건설 현장에서 널리 사용되고 있는 그라운드 앵커의 거동 특성을 연구하기 위하여 계측기를 부착한 일곱 개의 그라운드 앵커를 국내에 널리 분포되어 있는 화강 풍화토 지반인 $\bigcirc$$\bigcirc$$\bigcirc$대학교 지반 시험장에 설치하여 인발 시험을 수행하였다. 저압 그라우트 인장형 앵커 3개와 압축형 앵커 4개를 시험하였고, 시험은 AASHTO 규정에 의거한 인발시험, 크리프시험, 장기거동시험을 수행하였다. 시험 결과로부터 화강 풍화토 지반에 설치된 저압그라우트 직선형 앵커의 지반과의 마찰계수, 크리프 변형율, 하중감소 특성을 평가하였다.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.615-624
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• 2006

In the present paper, an extended composite beam theory that has no restriction on the lay-up and can account for Poisson effect which is significant for composite materials is proposed. Buckling equations for composite thin-walled members which are subjected to axial compression are derived based on the composite beam theory. In order to check the validity of the derived buckling equations, the results of experiments on the flexural-torsional buckling of vinylester/E-glass and polyester/E-glass pultruded T-section members and the flexural buckling of vinylester/E-glass pultruded H-section members are used as numerical examples. The comparison of the analytical results to the experimental and FE analysis results reveals that the proposed buckling equations predict the buckling loads of pultruded members conservatively by about 7%.