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One type of massive concrete structure is the foundation of high-rise buildings due to the need for larger foundations to provide more stability to the buildings. This paper describes the development of a case study applied to a piled raft foundation of a high-rise building in Fortaleza/CE, in northeastern Brazil. For this purpose, it aimed to deve...
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... In a separate study, B4Cast software was employed to determine the temperature distribution and temperature history at different sections of the concrete, considering various pouring conditions [158]. Additionally, a thermal analysis of the raft foundation was carried out using B4Cast, and the findings were presented in [159]. Examples of the application of ANSYS for the determination of thermal fields in concrete structures can be referred to, e.g., [151]. ...
... In a separate study, B4Cast software was employed to determine the temperature distribution and temperature history at different sections of the concrete, considering various pouring conditions [158]. Additionally, a thermal analysis of the raft foundation was carried out using B4Cast, and the findings were presented in [159]. ...
Cement-based materials encompass a broad spectrum of construction materials that utilize cement as the primary binding agent. Among these materials, concrete stands out as the most commonly employed. The cement, which is the principal constituent of these materials, undergoes a hydration reaction with water, playing a crucial role in the formation of the hardened composite. However, the exothermic nature of this reaction leads to significant temperature rise within the concrete elements, particularly during the early stages of hardening and in structures of substantial thickness. This temperature rise underscores the critical importance of predictive modeling in this domain. This paper presents a review of modeling approaches designed to predict temperature and accompanying moisture fields during concrete hardening, examining different levels of modeling accuracy and essential input parameters. While modern commercial finite element method (FEM) software programs are available for simulating thermal and moisture fields in concrete, they are accompanied by inherent limitations that engineers must know. The authors further evaluate effective commercial software tools tailored for predicting these effects, intending to provide construction engineers and stakeholders with guidance on managing temperature and moisture impacts in early-age concrete.
... A significant portion of this research is dedicated to understanding the formation of cracks in early-age concrete, typically induced by shrinkage and temperature differences. These factors are most impactful during the initial stages of the concrete's life [4][5][6][7]. Many studies have analyzed crack formation to reduce its occurrence in this phase [8][9][10][11][12][13][14][15]. ...
... This occurrence is observable in Fig. 1 and has been reported in various research studies [19][20][21][22][23][24][25][26][27][28][29][30]. The phenomenon has garnered significant attention globally, with the cause of cracking believed to be attributed to the effects of concrete shrinkage and temperature differences, particularly during the early stages when these effects are most pronounced [4][5][6][7][8][9][10][11][12][13][14][15]. ...
... As depicted in Fig. 2, this quantity can be computed by determining the ratio between the area of a single steel bar (A s ) and 2.5 times the area from the center of the steel bar to the concrete edge (a+ s /2) within the distance between two steel bars (d), as per Eqn. (6). ...
This research investigates cracking in Reinforced Concrete Structures (RCS), particularly in bridge abutments, box girders, and culverts. Cracks often appear even after the concrete has reached its full strength. The current American Bridge Design Standard (AASHTO) permits cracks but doesn’t specify quantitative limits on crack widths. This study uses the fib MODEL CODE 2010 (fib) to analyze RCS under shrinkage and temperature loading. It was found that cracks often exceed fib’s allowable limits, primarily due to significant temperature differences between concrete and steel reinforcement. This is especially prevalent in larger structures with high hydration heat. The use of smaller diameter reinforcement can significantly reduce crack width compared to larger ones, given the same steel ratio. However, a high steel ratio, while reducing crack width, increases susceptibility to cracking. Cracks typically occur after several weeks to months, with widths ranging from 0.30 to 0.70 millimeters due to shrinkage and temperature differences. These findings underscore the importance of considering both shrinkage and temperature differences in the design and maintenance of RCS. By understanding the impact of these factors, as well as the role of reinforcement diameter and steel ratio, engineers can develop more effective strategies for managing and mitigating cracking.
... Nếu thiết kế đáp ứng được yêu cầu nêu trên, kết cấu bê tông cốt thép được coi như không bị nứt dưới tác dụng của các yếu tố kết hợp gồm nhiệt độ thay đổi, co ngót của bê tông. Tuy vậy, trên thực tế, hiện tượng nứt vẫn xảy ra phổ biến như Hình 1 và ở các công trình nghiên cứu khác [7,8] cho dù kết cấu được coi là đáp ứng được yêu cầu chống nứt theo tiêu chuẩn thiết kế. Trên thế giới, hiện tượng này được quan tâm nhiều gần đây và nguyên nhân nứt được cho rằng do tác động của co ngót bê tông và nhiệt độ chênh lệch, đặc biệt là lúc bê tông còn non tuổi khi các hiệu ứng nói trên phát triển mạnh nhất [9-18]. ...
... Giai đoạn 2 là co ngót khô, kết thúc quá trình bảo dưỡng và nước trong bê tông bắt đầu thoát ra ngoài và làm bê tông co lại, cds(t,ts). Tổng biến dạng do co ngót tại thời gian ts (ngày) bất kỳ sau thời gian t bảo dưỡng được xác định theo công thức (8). ...
Hiện tượng nứt trong kết cấu bê tông cốt thép ở các bộ phận công trình cầu cống xảy ra phổ biến. Trong khi tiêu chuẩn thiết kế cầu Việt Nam hiện nay tuy cho phép vết nứt xuất hiện nhưng lại không định lượng về bề rộng vết nứt cho phép. Nội dung nghiên cứu này phân tích cơ cấu hình thành vết nứt theo mô hình thanh chịu kéo trong kết cấu bê tông cốt thép dưới tác động của tải trọng co ngót và nhiệt độ. Kết quả nghiên cứu cho thấy, mặc dù bố trí thép đảm bảo theo yêu cầu chống co ngót và nhiệt độ theo tiêu chuẩn thiết kế cầu hiện tại, hiện tượng nứt có thể dễ dàng xảy ra với kết cấu bê tông và bề rộng vết nứt lớn hơn bề rộng ở quy định hiện hành cho phép. Lý do chính là nếu việc kiểm soát nhiệt độ thi công bê tông không tốt. Việc bố trí thép có đường kính nhỏ sẽ làm giảm độ mở rộng vết nứt đáng kể hơn là thép đường kính lớn hơn mà có cùng hàm lượng thép. Việc bố trí nhiều thép có thể làm vết nứt có bề rộng nhỏ nhưng kết cấu lại dễ nứt hơn. Thời điểm vết nứt thường không xuất hiện ngay sau khi kết thúc bảo dưỡng mà sau đó khoảng từ vài ngày đến vài tháng
... Consequently, the risk of cracking is further exacerbated. Therefore, for high-strength large-volume marine concrete structures [25][26][27][28][29][30] above C50 where it is not possible to install cooling water pipes, further research is required to develop novel methods for controlling cracks. ...
High-strength large-volume marine concrete is a critical material required for the construction of large-span sea-crossing bridges. However, the widespread issue of cracking in this concrete type significantly impacts the durability and load-bearing capacity of concrete structures. Dealing with these cracks not only delays construction schedules but also increases project costs. Addressing these pressing technical issues, this project proposes the use of newly developed high-modulus heat-shrinkable fibers (polyethylene terephthalate fiber, also known as PET fiber) from the textile industry. These fibers utilize the heat generated during the hydration of large-volume concrete to trigger its contraction, applying three-dimensional micro-prestressing stress to enhance its crack resistance, while simultaneously incorporating prewetted aggregates with high-performance micro-porous structures and utilizing their internal curing effect to reduce concrete shrinkage. This helps to minimize the loss of micro-prestressing stress caused by concrete shrinkage and creep. This synergistic approach aims to improve the crack resistance of high-strength large-volume marine concrete. By employing modern testing and simulation analysis techniques, this study aims to uncover the mechanism by which the heat-shrinkable fibers exert micro-prestressing stress on concrete and the water release mechanism of internal curing aggregates during the temperature rise and fall stages of large-volume concrete. It seeks to elucidate the cooperative regulation of the microstructure and performance enhancement mechanisms of high-strength large-volume marine concrete by the heat-shrinkable fibers and internal curing aggregates. This research will lead to the development of novel methods for the design and crack control of high-strength large-volume marine concrete, which will be validated through engineering demonstrations. The outcomes of this study will provide theoretical foundations and technical support for the preparation of the crack-resistant large-volume marine concrete used in large-span bridges.
