초대형 매트기초 매스 콘크리트의 응결시간조정에 의한 온도균열저감 공법적용의 기초적 실험

한천구,이재삼,노상균 한국건축시공학회 2009 한국건축시공학회지 Vol.9 No.3

Constructing large-scale mat foundation mass concrete is increasing for the stability of building structure, because a lot of high rise building are being built in order to make full use of limited space. However, It is of increasing concerns that because limited placing equipments, available job-site and systems for mass concete placement in construction field do not allow to place great quantity of concrete at the same time in large scale mat foundation, consistency between placement lift can not be secured. And also, it is likely to crack due to stress caused by the difference of hydration heat generation time. To find out the solution against above problems, this study is to reconfirm the performance of normal concrete designed by mix proportion and super retarding concrete. The Fundamental test shows what happens if low heat proportioning and control method of setting time are applied at the job-site of newly constructed high rise building. The test result show that slump flow of concrete has been somewhat increased as the target retarding time gets longer, while the air content has been slightly decreased but this is no great difference from normal concrete. The setting time shows to be retarded as target retarding time gets longer, the range of retarding time increases. It is necessary to increase the amount of mix of super retarding agent in the proportion ration by setting curing temperature high since outdoor curing is about 6 hours faster than standard curing, which means the temperature of the concrete will be higher than the temperature of the surrounding environment, due to its high hydration heat when applying in a construction site. The compressive strength of super retarding concrete appears to be lower than normal concrete due to the retarding action in the early stage. However, as the time goes by, the compressive strength gets higher, and by the 28th day the strength becomes the same or higher than normal concrete.

응결시간조정에 의한 매트기초 매스 콘크리트의 온도균열저감 공법적용의 Mock-up Test

한천구,이재삼,노상균 한국건축시공학회 2009 한국건축시공학회지 Vol.9 No.4

Recently, the number of high-rise buildings being built in Korea by major construction companies for residential and commercial use has been increasing. When constructing a high-rise building, it is necessary to apply massive amounts of concrete to form a mat foundation that can withstand the huge load of the upper structure. However, it is of increasing concern that due to limitations in terms of the amount ofplacing equipment, available job-sites and systems for mass concrete placement in the construction field, it is not always possible to place a great quantity of concrete simultaneously in a large-scale mat foundation, and for this reason consistency between placement lift cannot be secured. In addition, a mat foundation is likely to crack due to the stress caused by differences inhydration heat generation time. To derive a solution for these problems, this study provides test results of a hydration heat crack reduction method by applying placement lift change and setting time control with a super retarding agent for mass concrete in a large-scale mat foundation. Mock-up specimens with different mixtures and placement liftswere prepared at the job-site of a newly-constructed high-rise building. The test results show that slump flow of concrete before and after adding the super retarding agent somewhat increases as the target retarding time gets longer, while the air content shows no great difference. The setting time was observed to be retarded as the target retarding time gets longer. As the target retarding time gets longer, compressive strength appears to be decreased at an early stage, but as time goes by, compressive strength gets higher, and the compressive strength at 28 days becomes equal or higher to that of plain concrete without a super retarding agent. For the effect of placement lift change and super retarding agent on the reduction of hydration heat, the application of 2 and 4 placement lifts and a super retarding agent makes it possible to secure consistency and reduce temperature difference between placement lifts, while also extending the time to reach peak temperature. This implies that the possibility of thermal crack induced by hydration heat is reduced. The best results are shown in the case of applying 4 placement lifts. 현재 국내의 건설공사현장에서는 도심부에 대형 건설사를 중심으로 초고층 건축물의 시공이 진행 중에 있다. 그런데 이러한 초고층 건축물의 기초는 상부의 큰 하중을 지지하기 위해 매우 두꺼운 매트 콘크리트가 필수적이다. 그러나 이와 같은 매스 콘크 리트는 현장여건상 다량의 콘크리트를 동시에 타설할 수 없기 때문에 일체성에 의문이 제기되는 것은 물론이고 수화발열시간의 서로 다름에 따른 내응력에 의한 균열발생 가능성이 증가한다. 따라서 본 연구에서는 상기의 문제점을 해소시키고자 국내 모처에 건설되고 있는 초고층 건축물을 대상으로 초지연제의 응결시간차를 활용한 수평분할타설 건축 매스 콘크리트의 수화열 조정공법 을 실제 건축현장에 적용하고자 Mock-up test를 통하여 그 효율성을 확인하였다. 실험결과 초지연제 투입 전·후 슬럼프 플로 우는 목표 지연시간이 길어질수록 다소 증가하였고, 공기량은 큰 차이는 없는 것으로 나타났으며, 응결시간은 목표 지연시간이 길어질수록 지연되었다. 목표 지연시간이 길어질수록 초기재령에서는 압축강도가 작게 나타났으나, 재령이 경과할수록 강도증진 폭이 크게 되어 재령 28일에서는 보통 콘크리트보다 동등 혹은 그 이상을 나타내었다. 또한 2단 및 4단으로 초지연제에 의한 응 결시간차공법을 활용한 경우 하부와 상부간 콘크리트의 일체화 및 온도차를 낮추고, 수화열 피크시점이 후기로 늦어짐에 따라 균 열발생가능성을 저하시키는 효과를 확인할 수 있었는데, 특히 4단 타설에서 가장 양호한 효과가 나타남을 확인할 수 있었다.

Structural Responses of Reinforced Concrete Pile Foundations Subjected to Pressures from Compressed Air for Renewable Energy Storage

Dichuan Zhang,Jong Kim,Saule Tulebekova,Dilmurat Saliyev,Deuckhang Lee 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.7

A renewable energy storage system is being proposed through a multi-disciplinary research project. This system utilizes reinforced concrete pile foundations to store renewable energy generated from solar panels attached to building structures. The renewable energy can be stored in the form of compressed air inside the pile foundation with a hollowed section. The pile foundation should resist complex combined actions including structural loads, soil effects, and pressures induced from the compressed air, and thus it requires a careful analysis and design considerations to secure a sufficient structural safety. This paper presents analytical investigation results on the structural responses of the energy piles under these combined loadings. The pile foundations were designed based on the current design practices for various building geometries including the number of stories and column spacing. The magnitude of air pressure was determined from the thermodynamic cycles for the available renewable energy for storage considering building and pile foundation geometries. Finite element analyses were conducted using an elastic 3D model to determine critical tensile stresses of the pile foundation. These critical tensile stresses were used to identify required reinforcement in the pile section. On this basis, several nonlinear finite element analyses were then conducted using inelastic constitutive models of materials to investigate the crack patterns of the hollowed concrete section. Recommendations were finally presented for proper practical designs of the pile foundation serving as the renewable energy storage medium.

Seismic analysis in pad concrete foundation reinforced by nanoparticles covered by smart layer utilizing plate higher order theory

Reza Taherifar,Seyed Alireza Zareei,Mahmood Rabani Bidgoli,Reza Kolahchi 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.1

This article deals with the dynamic analysis in pad concrete foundation containing Silica nanoparticles (SiO2) subject to seismic load. In order to control the foundation smartly, a piezoelectric layer covered the foundation. The weight of the building by a column on the foundation is assumed with an external force in the middle of the structure. The foundation is located in soil medium which is modeled by spring elements. The Mori-Tanaka law is utilized for calculating the equivalent mechanical characteristics of the concrete foundation. The Kevin-Voigt model is adopted to take into account the structural damping. The concrete structure is modeled by a thick plate and the governing equations are deduced using Hamilton’s principle under the assumption of higher-order shear deformation theory (HSDT). The differential quadrature method (DQM) and the Newmark method are applied to obtain the seismic response. The effects of the applied voltage to the smart layer, agglomeration and volume percent of SiO2 nanoparticles, damping of the structure, geometrical parameters and soil medium of the structure are assessed on the dynamic response. It has been demonstrated by the numerical results that by applying a negative voltage, the dynamic deflection is reduced significantly. Moreover, silica nanoparticles reduce the dynamic deflection of the concrete foundation.

Seismic Analysis of Concrete Gravity Dams Considering Foundation Mass Effect

Erfan Asghari,Reza Taghipour,Mohsen Bozorgnasab,Mojtaba Moosavi 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.12

Incorporating the dam-reservoir-foundation interaction effects into the seismic analysis of a dam can lead to a more accurate evaluation of its behavior. This study proposes a method for modeling the dam-reservoir-foundation system by considering mass of the foundation. In order to validate the proposed numerical modeling approach, its results are compared with those of previous studies. The Koyna concrete gravity dam is used as the case study and to consider the nonlinear material behavior, the Concrete Damage Plasticity (CDP) model is applied. Four models are established and their results are compared and discussed through displacement, principal stresses, crack propagation, damage dissipation energy curves and damage indices. The results show that considering massed foundation trigger a profound impact on the seismic response of the gravity dams. The results of this study could be used as an approach for conducting nonlinear seismic evaluation of concrete gravity dams by considering mass of the foundation.

Nonlinear responses of energy storage pile foundations with fiber reinforced concrete

Saule Tulebekova,Dichuan Zhang,Deuck Hang Lee,Jong R. Kim,Temirlan Barissov,Viktoriya Tsoy 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.4

A renewable energy storage pile foundation system is being developed through a multi-disciplinary research project. This system intends to use reinforced concrete pile foundations configured with hollowed sections to store renewable energy generated from solar panels attached to building structures in the form of compressed air. However previous research indicates that the compressed air will generate considerable high circumferential tensile stresses in the concrete pile, which requires unrealistic high hoop reinforcement ratio to avoid leakage of the compressed air. One possible solution is to utilize fiber reinforced concrete instead of placing the hoop reinforcement to resist the tensile stress. This paper investigates nonlinear structural responses and post-cracking behavior of the fiber reinforced concrete pile subjected to high air pressure through nonlinear finite element simulations. Concrete damage plasticity models were used in the simulation. Several parameters were considered in the study including concrete grade, fiber content, and thickness of the pile section. The air pressures which the pile can resist at different crack depths along the pile section were identified. Design recommendations were provided for the energy storage pile foundation using the fiber reinforced concrete.

케미컬 앵커 기초시스템의 인발성능

홍기남 ( Ki Nam Hong ),한상훈 ( Sang Hun Han ),박재규 ( Jae Kyu Park ),정규산 ( Kyu San Jung ),김성보 ( Sung Bo Kim ) 충북대학교 건설기술연구소 2014 建設技術論文集 Vol.33 No.1

본 논문은 개발된 케미컬 앵커 기초 시스템(CAFS)의 인발 성능을 제시한다. CAFS의 내력을 조사하기 위하여 10개의 케미컬 앵커 실험체들에 대해 인발실험들이 수행되어졌다. 실험변수로서 케미컬 앵커의 직경과 매립깊이가 선택되어졌다. 추가적으로 콘크리트 기초의 내력이 CAFS의 내력과 비교하기 위하여 마찬가지로 조사되었다. 콘크리트 기초와 CAFS의 최대인발하중은 각각 3.5 kN과 5.6에서 47.1 kN까지 이었다. CAFS의 내력은 콘크리트 기초의 내력보다 적어도 1.7배 이었다. 실험결과로부터 CAFS가 콘크리트 기초보다 높은 인발내력을 가질 수 있음을 확인할 수 있었다. This paper presents pullout performance of chemical anchor foundation system (CAFS) which was invented in this study. In order to investigate the capacity of CAFS, pullout tests were performed 10 CAFS specimens. As test variable, diameter and embedment length of chemical anchor were selected. In addition, the capacity of concrete foundation was also investigated to compare with that of CAFS. The maximum pullout loads of concrete foundation and CAFS were a 32 kN and from 5.6 to 47.1 kN, respectively. The capacity of CAFS was at least 1.7 times of that of concrete foundation. From the test results, it should be mentioned that CAFS have higher pullout capacity than concrete foundation.\

재활용 소재를 이용한 지하매설관 기초 성능 개선

김성겸(Kim, Seongkyum),이관호(Lee, Kwanho) 한국방재학회 2022 한국방재학회논문집 Vol.22 No.2

서울시 조사에 의하면 도심지 지반침하 발생은 약 84%가 하수관로 손상이 주요 원인인 것으로 조사되었고, 하수관 기초 및 하수관 자체의 노화 등이 연관되어 있다. 이러한 하수관로의 손상을 저감시키기 위하여 현장조립식 재활용 플라스틱 기초와 유동성 뒤채움재 조합을 기초 및 뒤채움재로 적용하였다. 기존의 쇄석기초 및 콘크리트 기초와 비교를 위해 지지력, 침하량 및 관의 안전율 등을 평가하였다. 해석에 사용된 뒤채움재의 종류에 따른 침하량의 변화는 상대적으로 작은 것으로 나타났다. 강성관용 하수관로의 기초 선정 시 사용하는 지지방식은 자유단식보다는 고정식을 적용하는 것이 관의 안전성을 향상시키는 것으로 나타났다. 현장조립식 재활용 플라스틱 기초는 콘크리트 기초에 비해 재료적 강성은 작으나, 이를 보완하기 위하여 시멘트를 2-4% 이용한 유동성 뒤채움재를 이용하여 부착력 증대 및 뒤채움재의 강도를 증진시키는 효과가 있어서 전체적으로 부설된 관의 안전성을 증가시키는 것으로 나타났다. According to the Seoul City survey, about 84% of the occurrence of ground subsidence was the main cause of damage to the sewer pipe, and it was related to the aging of the sewage pipe foundation and the sewage pipe itself. To reduce the damage, a combination of field-assembled recycled plastic foundation and a fluid backfill material was applied. The bearing capacity, settlement, and pipe safety factor were evaluated for comparison with the existing crushed stone foundation and concrete foundation. The change in settlement was relatively small, according to the type of backfill used in the analysis. As for the support method used when selecting the foundation for the sewage pipe for a rigid pipe, it was found that applying a fixed type rather than a free type improved the safety of the pipe. The field-fabricated recycled plastic foundation has less material rigidity than the concrete foundation, but to compensate for this, applying the fluid backfill using 2% to 4% cement had the effect of increasing adhesion and enhancing the strength of the backfilling material, thus increasing the safety of the installed pipe.

지연제를 혼입한 고강도콘크리트의 매트기초 적용을 위한 최적배합 산정에 관한 실험적 연구

이동하,임남기 대한건축학회지회연합회 2016 대한건축학회연합논문집 Vol.18 No.2

본 연구에서는 플라이애쉬와 지연제를 사용한 고강도 콘크리트의 매트기초 최적 배합설계를 제시하고자 하는 연구이다. 본 연구는 40MPa이상의 고강도 콘크리트에서 결합재량(385∼415kg/㎥), 플라이애시 치환율(0∼25%), 지연제 첨가율(0∼1.2%)에 따른 콘크리트의 역학적 특성을 평가하였다. 그리고 결과는 다음과 같다. 매트기초 하부에 적용할 콘크리트는 수화열 발생을 억제하고 응결지연을 통한 일체 타설을 위해 결합재량 385kg/㎥에 FA를 25% 치환하고 지연제를 1% 사용한 배합을 적용적용하는 것이 바람직한 것으로 판단된다. 단열온도상승 실험 결과, 단열온도상승 계수 K값과 α값은 콘크리트 초기온도 약 19℃ 조건에서 지연형 콘크리트는 40.68과 1.08, 표준형 콘크리트는 42.8과 1.13로 나타났다. 동일 온도조건에서 지연제 사용에 따른 단열온도 상승속도 차이는 크지 않으며, 지연형 콘크리트의 최대 단열온도상승값이 표준형 콘크리트 대비 낮게 나타났다. This study is to be suggest the optimal mat foundation mixing design of high strength concrete by using fly ash and retarding admixture. This study applied retarding admixture to high strength concrete over 40MPa, and tested the mechanical properties of concrete according to binder content(385∼415kg/㎥), fly ash substitution rate(0~25%), and adding rate of retarding admixture(0~1.2%) As a results, For the concrete to be applied to lower part of mat foundation, it is suitable to substitute FA 25% with binder contents 385kg/㎥ and to apply the mixing with adding retarding admixture 1% in order to repress hydration heat and to cast concrete at once through congelation delay. As a result of experiments of adiabatic temperature rising, coefficients of adiabatic temperature rising K and α were 40.68 and 1.08 for retarding-type concrete and 42.8 and 1.13 for standard concrete, respectively, under the condition of initial concrete temperature about 19℃. In the identical temperature condition, differences of adiabatic temperature rising speed according to use of retarding admixture were not different, and maximum value of adiabatic temperature rising of retarding-type concrete was lower than standard concrete.

Feasibility of concrete-filled fiber-reinforced plastic piles for deep foundation: a comprehensive review on geotechnical and structural characteristics

이학성,최만권,김병주 한국탄소학회 2024 Carbon Letters Vol.34 No.1

Traditional piles used for deep foundation, such as steel, concrete, and timber, are susceptible to corrosion and a reduction in structural capacity over time. This has led to the development of new materials like concrete-filled FRP piles (CFFP). CFFP is a composite pile filled with concrete and covered with a fiber-reinforced plastic (FRP) shell, providing non-corrosive reinforcement and protection to the concrete. As a result, CFFP is a highly promising candidate for implementation in various fields due to its structural advantages and necessity. Compared to traditional concrete piles, CFFP can be installed with less damage and a lower blow range due to its elastic modulus, damping ratio, and specific weight. The bearing capacity of a pile is influenced by various factors, including its stiffness, residual stress, and axial load resistance. Due to competitive pricing, glass fiber has been widely utilized, and there is a growing interest regarding carbon-fiber-reinforced concrete piles due to the excellent mechanical properties of carbon fiber. The remarkable stiffness and strength attributes of carbon fibers are evident in CFRP-confined piles, which present a notably wide range of load-bearing capacities, boasting an ultimate axial load capacity ranging from 500 to 4000 kN. Furthermore, CFFPs have been confirmed to have superior lateral load resistance compared to conventional piles, attributed to the reinforcement provided by FRP materials. Conventional piles face a challenge in that their structural characteristics deteriorate in the corrosive marine environment, with a projected lifespan of less than 20 years. In contrast, the service life of CFFPs is estimated to range from 50 to 75 years.