Code-compliant seismic design should be essentially applied to realize the so-called emulative performance of precast concrete (PC) lateral force-resisting systems, and this study developed simple procedures to design precast industrial buildings with intermediate precast bearing wall systems considering both the effect of seismic and blast loads. Seismic design provisions specified in ACI 318 and ASCE 7 can be directly adopted, for which the so-called 1.5S y condition is addressed in PC wall-to-wall and wall-to-base connections. Various coupling options were considered and addressed in the seismic design of wall-to-wall connections for the longitudinal and transverse design directions to secure optimized performance and better economic feasibility. On the other hand, two possible methods were adopted in blast analysis: 1) Equivalent static analysis (ESA) based on the simplified graphic method and 2) Incremental dynamic time-history analysis (IDTHA). The ESA is physically austere to use in practice for a typical industrial PC-bearing wall system. Still, it showed an overestimating trend in terms of the lateral deformation. The coupling action between precast wall segments appears to be inevitably required due to substantially large blast loads compared to seismic loads with increasing blast risk levels. Even with the coupled-precast shear walls, the design outcome obtained from the ESA method might not be entirely satisfactory to the drift criteria presented by the ASCE Blast Design Manual. This drawback can be overcome by addressing the IDTHA method, where all the design criteria were fully satisfied with precast shear walls’ non-coupling and group-coupling strength, where each individual or grouped shear fence was designed to possess 1.5S y for the seismic design.

By developing molds and facilities to horizontally mold the functional part of the dry-cast concrete block, We intend to develop molds and a series of facilities to horizontally mold the functional part of the dry-cast concrete block to increase production per cycle while maintaining existing production methods and major facilities. In order to do so, CAE analysis is first required to develop molds and facilities for horizontally molding the functional part of the drycast concrete block in the horizontal direction. The procedure will be carried out by reviewing the validity of boundary conditions and physical properties, 3D modeling, grid generation, construction of analysis models, model validity, analysis according to frequency changes, and analysis according to physical properties. First, through the comparison of two-point support, three-point support, and two-point and three-point support in the constraint conditions, We would like to compare it with the actual molded product in the horizontal direction. But first of all, it is considered two-point support in the constraint conditions in this paper.

전 세계 대부분의 국가들은 탄소배출량을 줄이기 위한 노력을 지속하고 있다. RC구조물의 탄소배출량을 줄이기 위해 수십 년간 건설 분야의 많은 연구자들이 철근콘크리트 구조물에서 철근을 FRP보강근으로 대체하기 위한 연구를 수행하여 왔다. 북미지역을 비롯한 일부 지역에서는 해양구조물이나 도로 등에 CFRP보강근을 사용한 바 있다. 그러나 건축물에는 철근을 CFRP보강근으로 대체한 사례와 적용을 위한 연구는 거의 진행되지 않았다. 따라서 본 연구에서는 예제건물을 선정하여 철근콘 크리트구조로 설계한 후, 철근을 CFRP보강근으로 대체하여 설계함으로써, 철근콘크리트건물에서 철근을 CFRP보강근으로 대체 하였을 때 철근량을 비교하였다. 그 결과 슬래브의 철근비가 0.005미만으로서 CFRP의 사용량을 줄일 수 있을 뿐만 아니라 안전 율 측에서도 우수한 것으로 나타났다.

A new clamped mechanical splice system was proposed to develop structural performance and constructability for precast concrete connections. The proposed mechanical splice resists external loading immediately after the engagement. The mechanical splices applicable for both large-scale rebars for plants and small-scale rebars for buildings were developed with the same design concept. Quasi-static lateral cyclic loading tests were conducted with reinforced and precast concrete members to verify the seismic performance. Also, shaking table tests with three types of seismic wave excitation, 1) random wave with white noise, 2) the 2016 Gyeongju earthquake, and 3) the 1999 Chi-Chi earthquake, were conducted to confirm the dynamic performance. All tests were performed with real-scale concrete specimens. Sensors measured the lateral load, acceleration, displacement, crack pattern, and secant system stiffness, and energy dissipation was determined by lateral load-displacement relation. As a result, the precast specimen provided the emulative performance with RC. In the shaking table tests, PC frames’ maximum acceleration and displacement response were amplified 1.57 - 2.85 and 2.20 - 2.92 times compared to the ground motions. The precast specimens utilizing clamped mechanical splice showed ductile behavior with energy dissipation capacity against strong motion earthquakes.

Wolsong unit 1 (W1), which is a CANDU-6 type PHWRs that had been operated for 30 years since 1983, was shutdown in 2019. In this study, the radioactive waste levels of calandria and concrete structures were calculated to establish a decommissioning plan for W1. The specific systems within the scope of this study were grouped into 6 major categories as follows: Calandria, End Shield, Fuel Channel Assembly, Reactivity Control Device, End Shield Support, Vault. The main operating history of W1 is that the re-tubing project was performed. These characteristics and operation history were reflected in the evaluation. The neutron flux and energy spectrum of each structure were calculated by using MCNP code, and ORIGEN code is implemented to the calculation of radioactivity for each nuclide using the results from MCNP and the material information of the structure. As for the impurity information, ASTM B350, B351, B353 standard was used for zircaloy alloy. For other alloy, impurity information provided by NUREG/CR-3474 was applied. Since W1 is expected to be decommissioned immediately, the waste level was evaluated under cooling conditions for 5 years after permanent shutdown. Through the level evaluation of each component obtained as a result of the study, it can be used as basic data for the radioactive waste management of the decommissioning plan.

최근 현장작업을 최소화할 수 있는 PC(Precast Concrete) 건축공법의 적용이 급속하게 활성화되고 있다. 그러나 PC 공법은 시공 중, 특히 부재간 일체화 이전에 구조적 성능을 발휘하기 어렵고 완공 후에도 접합부의 일체성을 확보하기 어려워 연쇄붕괴에 취약하다. PC 건축물에서는 다양한 PC 부재간 접합 상세가 존재하며, 국내외 구조/시공 상세가 현격히 다르다. 그러나 국내 PC 시스템의 시스템 과 상세 특성을 반영한 연쇄붕괴에 대한 연구는 매우 미비하다. 따라서, 본 연구에서는 국내에서 주로 사용하는 PC 구조시스템과 접 합부 구조/시공 상세를 조사 분석하였다. 이를 기반으로 국내에서 사용되는 전형적인 PC 시스템의 유형을 설정하고 상기 PC 시스템 의 연쇄붕괴방지성능을 평가하기 위하여 비선형 유한요소해석을 수행하였다. 해석결과를 바탕으로 국내에서 주로 사용된 PC 구조시 스템의 연쇄붕괴방지 성능을 평가하고 구조설계시 고려사항을 제안하였다.

본 연구는 이러한 단점을 보완하기 위해 철근을 대체하여 내산화성과 전기저항이 높은 GFRP 보강근을 적용한 도상슬래브의 최적 변수해석을 수행하였다. 철도 궤도슬래브에 적용되는 철근은 열차 운행 중 신호전류의 손실을 일으켜 열차의 안정성을 저해하며, 철 근의 부식으로 내구성이 저하될 수 있다. GFRP 보강근의 직경 및 배근 개수 변화가 전체 콘크리트 도상슬래브의 휨강도 및 균열제어 에 미치는 영향을 유한요소 변수해석을 통하여 상세분석하였다. 해석 결과, GFRP 보강근의 직경 및 배근을 합리화하여 제안하였으며 이러한 경우 기존 배근보다 더욱 경제적인 단면을 도출할 수 있음을 알 수 있었다. 본 연구로부터 도출된 결과는 향후 GFRP 보강근을 적용하여 도상슬래브를 설계하는 경우 보다 합리적이고 경제적인 단면을 산정할 수 있는 가이드라인이 될 수 있을 것으로 기대된다.

본 연구는 Mori-Tanaka 방법 및 멀티스케일 접근 방법을 적용하여 CNT의 굴곡성을 고려한 CNT-복합재 보강 콘크리트 보에 대한 균열해석을 수행하였다. Ad-hoc Eshelby 텐서에 기반하여 CNT의 굴곡성을 기하학적으로 고려하여 폴리머와 합성 하는 방법을 적용하였다. 멀티스케일 방법이 기반하여 CNT 함유량 및 굴곡성 변화에 따른 복합재의 탄성계수 및 강도변화를 추정하였다. 본 해석모델은 기존 문헌과 비교검증하였다. 본 연구에서 도출한 결과는 CNT 함유량과 CNT 굴곡성의 상호관계를 도시하였다. CNT 보강 복합재 구조물의 해석에 있어서 CNT 굴곡성의 중요성을 입증하였다.

PURPOSES : Nitrogen oxides (NOx) are the main precursors to generate fine particulate matter, which significantly contribute to air pollution. NOx gases are transmitted into the atmosphere in large quantities, especially in areas with a high volume of traffic. Titanium dioxide (TiO2), which is a photocatalytic reaction material, is very efficient for removing NOx. The application of TiO2 to concrete road structures is a good alternative to remove NOx. Generally, TiO2 concrete is produced by mixing concrete with TiO2 . However, a significant amount of TiO2 in concrete cannot be exposed to air pollutants or UV. Therefore, an alternative method of penetrating TiO2 into horizontal concrete structures using a surface penetration agent was proposed in a previous study. This method may not only be economical but also applicable to various types of horizontal concrete structures. However, the TiO2 penetration method may not be applied to vertical structures because it has a mechanism for the penetration of TiO2-containing penetration agents via gravity and capillary forces. Therefore, this study aimed to evaluate the applicability of the pressurized TiO2 fixation method for existing vertical road structures. METHODS : For the application of vertical concrete structures — such as retaining walls, side ditches, and barriers — the applicability of a static and dynamic pressurized TiO2 fixation method was evaluated according to the experimental conditions, considering the amount of pressure and time. The penetration depth and distribution of TiO2 particles in the concrete specimen were measured using SEM/EDAX. In addition, the NOx removal efficiencies of TiO2 concrete were evaluated using the NOx analysis system. RESULTS : As a result of measuring the penetration depth and distribution of TiO2 in the concrete, it was found that the surface-predicted mass ratio increased with increasing pressure and time. In the case of the static pressurized fixation method, it was confirmed that a pressure time of at least 10 s at a pressure of 0.2 MPa and 5 s at a pressure higher than 0.3 MPa were required to achieve a NOx removal efficiency higher than 40 %. Conversely, for the dynamic pressurized fixation method applying a hitting energy of 16.95 J, NOx removal efficiencies higher than 50 % were secured in a pressure time of more than 3 s. CONCLUSIONS : The results of this study showed that the static and dynamic pressurized TiO2 fixation method was advantageous in penetrating and distributing TiO2 particles into the concrete surface to effectively remove NOx. It was confirmed that the proposed method to remove NOx was sufficiently applicable to existing vertical concrete road structures.

한본 연구에서는, 철근콘크리트 보 구조물의 동결융해에 따른 장기거동특성 및 최종 파괴형태를 비교 분석하고자 하였다. 철근콘크리트 보 시험체와 재료 시험체를 제작하여, 동결융해 챔버를 이용하여 동결과 융해를 반복적으로 수행하였다. 동결융해를 위하여 기존의 시험법을 참고하여 철근콘크리트 구조물에 대한 시험을 수행 하였다. 동결융해에 따른 콘크리트의 재 료특성 변화와 철근콘크리트 보 구조물의 거동특성 변화를 통하여 동결융해에 대한 영향을 평가하였다. 제안된 동결융해 시험법을 통하여 콘크리트 공시체의 압축강도가 약 19%감소하였다. 철근콘크리트 보 시험체의 경우, 콘크리트의 표면 강도가 동결 융해에 의하여 감소되어 사인장 균열이 발생하여, 재료적 강도 감소에 의한 구조물의 성능이 감소함을 확인하였다. 또한, 사인장 균열이 발생한 동결융해 시험체의 에너지 소산능력이 동결융해를 거치지 않은 시험체와 비교하여 적게 발생하였다.

PURPOSES: Nitrogen oxide (NOx) is a particulate matter precursor, which is a harmful gas contributing to air pollution and causes acid rain. The approaching methods for NOx removal from the air are the focus of numerous researchers worldwide. Titanium dioxide (TiO2) and activated carbon are particularly useful materials for NOx removal. The mechanism of NOx elimination by using TiO2 requires sunlight for a photocatalytic reaction, while activated carbon absorbs the NOx particle into the pore itself after contact with the atmosphere. The mixing method of these two materials with concrete, coating, and penetration methods on the surface is an alternative method for NOx removal. However, this mixing method is not as efficient as the coating and penetration methods because the TiO2 and the activated carbon inside the concrete cannot come in contact with sunlight and air, respectively. Hence, the coating and penetration methods may be effective solutions for directly exposing these materials to the environment. However, the coating method requires surface pretreatment, such as milling, prior to securing contact, and this may not satisfy economic considerations. Therefore, this study aims to apply TiO2 and activated carbon on the concrete surface by using the penetration method. METHODS : Surface penetrants, namely silane siloxane and silicate, were used in this study. Photocatalyst TiO2 and adsorbent activated carbons were selected. TiO2 was formed by the crystal structures of anatase and rutile, while the activated carbons were plant- and coal-type materials. Each penetrant was mixed with each particulate matter reductant. The mixtures were sprayed on the concrete surface using concentration ratios of 8:2 and 9:1. A scanning electron microscopy with energy dispersive X-ray equipment was employed to measure the penetration depth of each specimen. The optimum concentration ratio was selected based on the penetration depth. RESULTS: TiO2 and activated carbon were penetrated within 1 mm from the concrete surface. This TiO2 distribution was acceptable because TiO2 and activated carbon locate to where they can directly come in contact with sunlight and air pollutant, respectively. Infiltration to the concrete surface was easily achieved because the concrete voids were bigger than the nanosized TiO2 and microsized activated carbon. The amount of penetration for each particulate matter reductant was measured from the concrete surface to a certain depth. CONCLUSIONS : The mass ratio on the surface can be predicted from the mass ratio of the particulate matter reductant measurement distributed through the penetration depth. The optimum mass ratio was also presented. Moreover, the mixtures of TiO2 with silane siloxane and activated carbon with silicate were recommended with an 8:2 concentration ratio.