• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.46-53
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• 2001

Two full scale precast pretensioned dapped ended rectangular beams designed by PCI design handbook for a major domestic live load of market and parking building - 500kgf/㎡ and 1,200kgf/㎡ were investigated experimentally. The bottom length of beams was 60cm which was same to the length of rectangular column in the base of five-story market or parking buildings. The height of dap was web hight plus half of the flange height within the allowable limit of PCI method. Shear tests were performed on four beam ends. Followings were obtained from the experimental study. All of the specimens were fully complied with the PCI design handbook. Two of four specimens which were designed for live load of 1,200kgf/㎡ showed crackings at the re-entrant corner of dap before the full service loadings, and failed by direct shear at the load level much less than their calculated nominal strength. The specimens designed for live load of 1,200kgf/㎡ failed at 772 tonf and 78.36tonf by direct shear crackings. This strength was less than PCI limit of 81.9 tonf and higher than ACI limit of 65.62tonf. Thus, the limit suggested by ACI seems more reasonable in regard of safety in view of this test results. According to load-strain curves, the strain of hanger reinforcement reached almost yield strain. It is recommended to use more inclined hanger reinforcement of improve the strength and serviceability.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2002.05a
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• pp.108-108
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• 2002

고분자전해질들은 제지공정에서 건조지력제, 습윤지력제, 정착제, 보류제 등으로 널리 사 용되어지고 있으며, 이러한 고분자전해질들이 보유하고 있는 관능기의 종류와 분자량에 따라 각각의 다른 특성을 발현하게 된다. 이중 관능기의 종류와 비율에 따라 결정되는 중요한 특성 중 한가지가 전하밀도이며, 이러한 전하밀도는 제지공정에 사용할 때 습부공정에서 매우 중요 한 인자라 할 수 있다. 전하밀도는 고분자전해질의 분자구조와 단량체의 종류에 따라 다르며, 적용 pH의 조건에 따라 변화하게 된다. 3급 아민과 4급 암모늄을 관능기로 가진 고분자전해질 의 경우 pH에 따른 전하밀도의 변화는 이미 잘 알려져 있는 바,3급 아민을 작용기로 가진 양이 온성 고분자전해질은 pH 9에 도달하면 양전하를 완전히 상실하고,4급 암모늄을 작용기로 가진 양이온성 고분자전해질은 pH의 변화에 상관없이 양전하가 변하지 않는다고 보고되어 있다. 본 연구에서는 양이온성과, 양쪽이온성 고분자전해질들 중 Cationic PAM, Amphoteric P PAM, PolyDADMAC, Epoxide polyamide resin, Epi-DMA copolymer 등을 시 료로 사용하였 으며, 양이온성 관능기의 종류가 다른 고분자 전해질을 이용하여 pH 변화에 따른 전하밀도의 변화를 검토하였다. 또한 일반적으로 중성 초지공정의 pH 조건은 7.0 - 8.0이며, 이 pH 조건에 서 고분자전해질의 거동은 매우 중요하다고 할 수 있다. 따라서 양이온 관능기의 종류에 따른 고분자전해질들을 pH 7.8에서 보관시간에 따른 전하밀도의 변화를 조사하였으며, 전하밀도가 변화하는 양상에 따라 양이온성 관능기의 분자구조의 변화를 검토하였다. p pH 변화에 따른 전하밀도의 변화 결과로부터 3급 아민을 포함한 양이온성 고분자전해질 뿐만 아니라,4급 암모늄을 포함한 일부의 양이온성 고분자전해질 또한 알카리 조건에서 전하 밀도가 감소하며, 강한 얄차리 조건에서는 음이온성 고분자전해질로 변화하는 현상을 관찰할 수 있었다. 이상의 결과들로부터 약 알카리(pH 7.5 - 8.0) 조건 하에서도 시간의 변화에 따라 4 급 암모늄을 포함하는 고분자전해질의 전하밀도가 변화할 것이라 예측하였으며, 실험을 통해 그 사실을 확인하였다. 알카리 조건에서 전하밀도가 변하지 않는 4급 암모늄 고분자전해질과, 전하밀도가 변하는 4급 암모늄 고분자전해질의 분자구조를 비교해 볼 때, 그 원인은 4급 암모늄 의 관능기가 고분자 연쇄로부터 가수분해 되어 나타나는 현상으로 판단된다.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.35-43
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• 2017

In this study, the pull-out resistance behavior of the anchor with the bump type resistors at the anchor body was experimentally investigated. In the model tests, the pull-out resistance was measured by pulling out the anchor at a constant speed. Anchor body was installed in the center of the circular sand tank. Pull-out tests were conducted for 10 conditions. The anchor type (existence of the resistor), the friction conditions of the anchor body surface ($1/3{\phi}$, $2/3{\phi}$, ${\phi}$), the bump type resistor set number (1set, 2set, 4set), and the height of resistors (0.05d, 0.10d, 0.20d) were varied. The load-displacement relationship for each conditions was measured during the pull-out tests at a constant speed (1 mm/min). Maximum pull-out length was 80 mm. As a result, the pull-out behavior of the friction type anchor and the expansion type anchor was different. As the number of resistor increased, the maximum pull-out resistance increased and the residual pull-out resistance ratio increased significantly, which were at 171~591 percent larger than that of the friction type anchor.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.2
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• pp.279-299
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• 2019

Recently occurred earthquake Gyeongju and Pohang served as a momentum to remind that Korean peninsular is not a safety zone from earthquake anymore. The importance of seismic design, therefore, have been realized and researches regarding design response spectrum have been actively carried out by many researchers and engineers. Current tunnel seismic design method is conducted to check safety of tunnel structure by dynamic numerical analysis with condition of completed lining installation, so, it is impossible to consider safety of tunnel behavior under construction. In this study, therefore, dynamic numerical analysis considering seismic wave propagations has been performed after back analysis using results from field monitoring of tunnel under construction in fractured zone and 1st reinforcement (shotcrete, rockbolt) behaviour are analyzed. Waves are classified by period characteristic (short and long). As a result, the difference depending on period characteristic is minor, and increasements of displacement are obtained at crown displacement due to seismic wave is 28~31%, 14~16% at left side of tunnel in the fractured zone, 13~27% at right side of tunnel in the bed rock, respectively. In case of shotcrete axial force is increased 113~115% at tunnel crown, 102% at left side, 106~110% at right side, respectively. Displacement and axial force of rockbolts which are selected by type of anchored grounds (only fractured zone, fractured zone and bed rock, only bedrock) are analyzed, as a result, rockbolt which is anchored to fractured zone and bed rock at the same time are weaker than any other case.

• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.651-660
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• 2014

Structural members using ultra high strength concrete which usually used with steel fiber is designed with guidelines based on several investigation of SF-RPC(steel fiber reinforced reactive powder concrete). However, there are not clear design method yet. Especially, SF-RPC member should be casted with steam(90 degree delicious) and members with SF-RPC usually used with precast members. Although the most important design parameter is development method between SF-RPC and steel reinforcement(rebar), there are no clear design method in the SF-RPC member design guidelines. There are many controversial problems on safety and economy. Therefore, in order to make design more optimum safe design, in this study, we investigated bond stress between steel rebar and SF-RPC according to test. Test results were compared with previously suggested analysis method. Test was carried out with direct pull out test using variables of compressive strength of concrete, concrete cover and inclusion ratio of steel fiber. According to test results, bond stress between steel rebar and SF-RPC increased with increase of compressive strength of concrete and concrete cover. Increasing rate of bond stress were decrease with increase of compressive strength of SF-RPC and concrete cover significantly. 1% volume fraction inclusion of steel fiber increase the bond stress between steel rebar and SF-RPC with two times but 2% volume fraction cannot affect the bond stress significantly. There are no exact or empirical equations for evaluation of SF-RPC bond stress. In order to make safe bond design of SF-RPC precast members, previously suggested analysis method for bond stress by Tepfers were evaluated. This method have shown good agreement with test results, especially for steel fiber reinforced RPC.

• Journal of the Korean GEO-environmental Society
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• v.13 no.1
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• pp.53-61
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• 2012

In this study, the research on MC anchor has been developed as composite type has done. MC anchor exerts bearing pressure on pre-bored hole where the end fixing device is expanded. Therefore, the uplift capacity is to be increased and it has the characteristics that the anchor body is not eliminated from the ground even if the grouting is not carried out properly. Furthermore, it reduces the loss of tension and raises the construction availability by inserting the reinforced bar as well as the anchor cable, while it can improve the long-term stability because the nail is expected to play the role when the loss of the anchor cable is occurred in a long-term. However, because the resistance mechanism of the compound anchor such as MC anchor is different from friction anchor, the estimation method of the uplift capacity by the frictional force of the ground and the grout is not proper. Particularly, in domestic cases, the problem to overestimate or underestimate the uplift capacity is expected because the design method considering the soil characteristics about the compound anchor has not been developed. Therefore, in this study, in order to evaluate the characteristics of MC anchor and a kind of compound anchor, we measured the uplift, the tension and the creep by nine anchors tests in shale ground that the fluctuation of the strength is great. In addition, we analyzed the test result comparing to the result of the general friction anchor and evaluated the characteristics of MC anchor movement to gather the results. As a result of the test, we found the effect that the uplift capacity is increased in shale ground comparing to the general friction anchor.

• 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.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1616-1621
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• 2006

하천 지형은 흐름과 유사거동에 의한 세굴 또는 퇴적에 의하여 끊임없이 변한다. 이 연구에서는 최근 하천지형의 변화가 크게 일어나고 있는 한강 신곡수중보 직하류 우안의 고수부지 형성 이력에 대한 조사 및 분석을 실시하였다. 조사결과, 1981년 이전까지 하중도(제주초도)가 안정된 형태로 존재하였으나, 1980년대 중반을 거치면서 하중도는 소멸되었고 1990년대 중반 이후부터 우안에 비슷한 규모의 고수부지가 생성되었음을 알 수 있었다. 이 고수부지의 형성과정을 평가하면 다음과 같다. 1) 초기단계(흐름 변화에 따른 이동사주의 정지): 1995년 이전까지는 하천 내 자연적/인위적 교란에도 불구하고 이열사주 형태의 이동상이 유지되다가 1995년 이후 1988년 준공된 신곡수중보의 직.간접적인 영향을 받는다. 이로 인한 하중도의 소멸이 가중되면서부터 신곡수중보 직하류 우안의 이동사주가 정지하기에 이른다. 2) 성장단계(조석에 따른 부유사 반복 퇴적): 이동상 사주가 정지된 뒤 매일 2회씩 반복되는 조석의 영향을 받은 고농도의 부유사가 정지된 사주 위에 반복되어 퇴적되는 양상이 일어난다. 3) 정착단계(정지사주의 고수부지화): 정지사주에서 부유사가 퇴적하고 갈대와 같은 초본류 식생이 활착하게 되면서 부유사 퇴적은 가중되어 간다. 이러한 과정에서 1999년과 같은 대홍수 때 부유사의 고수부지 내 퇴적이 결정적이었을 것이다. 4) 확장단계(고수부지 확장단계): 대홍수 때 고수부지의 퇴적과 아울러 산재하던 버드나무가 교란을 받아 고수부지에서 새로운 버드나무 군락의 터전을 이루어 밀생하게 된다. 향후 고수부지가 잠기는 규모의 홍수가 빈발할 경우 퇴적층의 유실보다는 부유사 퇴적이 많아져 고수부지는 확장단계에 접어들게 된다.70{\sim}90$ 시간 동안 실험을 수행하였다. 세굴의 측정은 투명한 아크릴로 제작된 수제 내부에 CC카메라를 수제 전 후면 및 측면에 설치하여 월류수제의 세굴 발생을 실시간으로 측정하며 동시에 수제의 각 면에 각각 3개의 압력센서를 설치하여 압력분포를 측정함으로써, 월류수제 주변의 압력변화에 따른 세굴심의 실시간 변화를 비교할 수 있도록 하였다. 수심이 연중 $25{\sim}35m$를 유지하는 H호의 경우 간헐식 폭기장치를 가동하는 기간은 물론 그 외 기간에도 취수구의 심도를 표층 10m 이하로 유지 할 경우 전체 조류 유입량을 60% 이상 저감할 수 있을 것으로 조사되었다.심볼 및 색채 디자인 등의 작업이 수반되어야 하며, 이들을 고려한 인터넷용 GIS기본도를 신규 제작한다. 상습침수지구와 관련된 각종 GIS데이타와 각 기관이 보유하고 있는 공공정보 가운데 공간정보와 연계되어야 하는 자료를 인터넷 GIS를 이용하여 효율적으로 관리하기 위해서는 단계별 구축전략이 필요하다. 따라서 본 논문에서는 인터넷 GIS를 이용하여 상습침수구역관련 정보를 검색, 처리 및 분석할 수 있는 상습침수 구역 종합정보화 시스템을 구축토록 하였다.N, 항목에서 보 상류가 높게 나타났으나, 철거되지 않은 검전보나 안양대교보에 비해 그 차이가 크지 않은 것으로 나타났다.의 기상변화가 자발성 기흉 발생에 영향을 미친다고 추론할 수 있었다. 향후 본 연구에서 추론된 기상변화와 기흉 발생과의 인과관계를 확인하고 좀 더 구체화하기 위한 연구가 필요할 것이다.게 이루어질 수 있을 것으로 기대된다.는 초과수익률이 상승하지만, 이후로는 감소하므로, 반전거래전략을 활용하는 경우 주식투자기간은 24개월이하의 중단기가 적합함을

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.965-975
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• 2014

Pretension PSC (Prestressed Concrete) members are subjected to a certain limit of size as they are generally produced in the off-site plant and transferred to the site due to the large scale of the product on system. In this study, a portable pretensioning production system has been developed, which allow us to apply the pretension method on site. Considering that a 50m span PSC girder using the pretension method requires a pressing device to endure a large jacking force, the portable pretension production system has to ensure safety against such a large pretension jacking force. In this study, the portable pretensioning system to produce a 50m span pretension girder was manufactured by using CFT (Concrete Filled steel Tube) members. In order to understand the stability of the system and the behavior of the elements, a static loading test was conducted and the stability of the proposed portable pretensioning production system was confirmed. The developed portable pretension system was applied to several construction sites and was investigated the problems on site. During the pretension girder and slab members that was producted by this pretension system in construction site, it has be found the several advantages such as simple fabrication processes, reduction of prestress-loss, and a decrease of 15% compared with the fabrcation cost of post-tension girder. After due consideration of the problems, this portable pretension system will be improved.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.1-6
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• 2021

Concrete structures gradually age due to deterioration of materials or excess loads and environmental factors, and their performance decreases, affecting the usability and safety of structures. Although external tension construction methods are widely used among the reinforcement methods of old bridges, it is insufficient to identify the effects and effects of reinforcement depending on the level of aging. Therefore, in this study, a four-point loading experiment was conducted on the subject with the non-reinforced and external tensioning method to confirm the reinforcement effect of the external tensioning method, assuming the aging of the structure as a reduction in the compressive strength and tensile reinforcement of concrete, to analyze the behavior of the reinforcement and confirm the reinforcement effect. As a result of the experiment, it was difficult to identify the amount of reinforcement in the extreme condition due to early elimination of the anchorage. Therefore, compliance with the regulations on anchor bolts is required when applying the external tension reinforcement method. Crack load and yield load increased depending on whether external tension was reinforced, but before the crack, the stiffness before and after reinforcement was similar, making it difficult to confirm the reinforcement effect.