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Experimental Study on Flexural Performance of Ultra-High-Performance Concrete with Recycled Aggregate Co-Modified by Nano-Silica and Steel Fiber

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SSRN 2023年

作者： Luo, Liang Shi, Jun Wang, Jianan Qu, Yiwen Dai, Bin School of Civil Engineering Central South University Changsha410075 China Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

Expanding the application of defective recycled aggregates (RA) to ultra-high performance concrete (UHPC), it is necessary to modify them with nano-silica (NS) in conjunction with steel fibers (SF), and it is worthwhile to investigate the bending behavior under the typical characteristics of this new *** study investigates the flexural performance of recycled aggregate ultra-high-performance concrete (RA-UHPC) using a four-point bending test and analyzes the influence of RA substitution rates (0%, 50%, and 100%), SF content (0%, 1%, and 2%), and NS content (0%, 1%, 3%, and 5%) on its flexural toughness and microstructure. Additionally, digital image correlation (DIC) technology was employed to capture crack evolution during the test, and SEM microstructural analysis was used to elucidate the flexural mechanism of this fiber-nano composite concrete. The results show that the load-deflection curves of specimens without SF exhibit initial linear-elastic growth, followed by a sharp decrease in load after the peak without a distinct descending stage. In contrast, specimens with SF display three typical stages, with a smoother and flatter descending stage. The cross-distributed SF enhances post-peak ductility, transforming the failure behavior from quasi-brittle to ductile. Increasing SF content significantly enhances the flexural strength and toughness of the specimens, while an increase in RA substitution rate and NS content results in a slight reduction in flexural strength (fp). The changes in residual strength observed through both methods are consistent, with almost no residual strength in the brittle failure specimens. Moreover, DIC technology, relying on precise image capture, can predict crack positions before the peak load is reached. Finally, the microstructural analysis in SEM is combined to illustrate the flexural mechanism of this fiber-nanocomposite concrete. © 2023, The Authors. All rights reserved.

关键词： Image correlation

考虑非线性相关性影响的结构整体可靠度评估——增强型高阶矩方法

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Acta Mechanica Sinica 2023年第4期39卷 3-13页

作者：宋鹏彦王涛吕大刚 College of Civil Engineering and Architecture Hebei UniversityBaoding071002China School of Transportation Science and Engineering Harbin Institute of TechnologyHarbin150040China Chongqing Research Institute of Harbin Institute of Technology Harbin Institute of TechnologyChongqing401151China Key Lab of Structure Dynamic Behavior and Control of China Ministry of Education Harbin Institute of TechnologyHarbin150090China

考虑随机变量间相关性的复杂工程结构整体可靠性分析仍然是一个挑战,特别是对于非线性相关问题.该文考虑到随机变量之间非线性相关的影响,提出了一种用于结构整体可靠性分析的增强型高阶矩方法.该文首先回顾了传统的Nataf变换,进而通过... 详细信息

考虑随机变量间相关性的复杂工程结构整体可靠性分析仍然是一个挑战,特别是对于非线性相关问题.该文考虑到随机变量之间非线性相关的影响,提出了一种用于结构整体可靠性分析的增强型高阶矩方法.该文首先回顾了传统的Nataf变换,进而通过引入Copula理论提出了广义Nataf变换;其次,采用状态变量描述法统一描述整体可靠性问题对应的功能函数,并发展了基于GL_(2)-偏差点集的状态变量高阶矩估计和灵敏度分析方法;再次,通过改进的最大熵法准确估计了结构整体可靠度;最后,通过两个算例验证了所提方法的准确性和有效性以及考虑随机变量间的非线性相关性对结构整体可靠度影响的必要性.算例结果与蒙特卡洛模拟方法比较表明,随机变量间的非线性相关性对结构的整体可靠度有显著影响,所提方法对结构高阶矩估计和全局可靠度分析具有较高的精度和效率.

关键词：最大熵法非线性相关整体可靠性随机变量状态变量可靠度评估蒙特卡洛模拟方法功能函数

Tensile behavior of Uhpfrc Made by a Fiber Orientation Device with Adjustable Vibrational Frequency

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SSRN 2023年

作者： Li, Zhihao Zhou, Wei School of Civil Engineering Key Lab of Structures Dynamic Behavior and Control Ministry of Education Key Lab of Smart Prevention and Mitigation of Civil Engineering Disaster Ministry of Industry and Information Technology Harbin Institute of Technology 73 Huanghe Road Nangang District Harbin150090 China

Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) not only has high compressive and tensile strength, but also exhibits strain-hardening characteristics in tension due to the addition of steel fibers. In this study, a new-style fiber orientation device equipped with a vibration motor of adjustable vibrational frequency was used to prepare UHPFRC. The wall effect and fiber length were considered in the manufacturing process of the device. Uniaxial tensile tests were conducted on fiber-oriented UHPFRC to explore the effects of vibrational frequency and corresponding vibrational force on the tensile behaviors. The test results showed that the elastic ultimate tensile strength, elastic ultimate tensile strain, tensile strength, peak tensile strain, and tensile elastic modulus of UHPFRC specimens cast by fiber orientation process at various vibrational frequencies were different. The fiber orientation parameters were quantitatively evaluated by the image analysis technique to explain the differences in tensile properties of the specimens. The effect of different vibrational frequencies on the tensile strength of UHPFRC matrix and its porosity was also considered. Therefore, this study provides a reference for how to adjust the vibrational frequency of the vibrating platform under the directional channel when pouring relevant components. © 2023, The Authors. All rights reserved.

关键词： Steel fibers

Experimental and Analytical Investigations on Impact Responses of Scs Panel with Dual Energy Absorbers

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SSRN 2024年

作者： Lu, Jingyi Wang, Yonghui Zhou, Hongyuan Ma, Jialu Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China Key Lab of Urban Security and Disaster Engineering The Ministry of Education Beijing University of Technology Beijing100124 China Institute of Engineering Mechanics China Earthquake Administration Harbin150080 China

A new steel-concrete-steel panel with front aluminum foam layer and rear energy absorbing connector (SCS-FL-EAC) was firstly developed. The dynamic behavior of SCS-FL-EAC was studied through conducting drop-weight impact tests. Three stages of impact process of SCS-FL-EAC were identified. The aluminum foam layer and energy absorbing connector were crushed under impact loading. The aluminum foam layer reached densification, and a local indention was observed beneath the projectile. Plastic hinges were also found at the corners of the pleated steel plate of the energy absorbing connector. The SCS panel exhibited the combination of bi-linear global flexural deformation and local deformation. Furthermore, the effects of aluminum foam layer on the impact resistant performances of SCS-FL-EAC were investigated. The results indicated that the inclusion of the aluminum foam layer effectively mitigated inertial effects and reduced the maximum impact force. Additionally, the SCS-FL-EAC demonstrated improved impact-resistant performances with an increased thickness of the aluminum foam layer. Furthermore, an analytical model was proposed to predict the force and displacement responses of SCS-FL-EAC subjected to impact load, and the predicted impact responses showed good agreement with experimental results. © 2024, The Authors. All rights reserved.

关键词： Energy absorption

Mechanical Properties and Microstructure of Ultra-High-Performance Concrete Containing Recycled Aggregates Co-Modified with Steel Fibres and Nanosilica after Exposure to Elevated Temperatures

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SSRN 2023年

作者： Sun, Hang Luo, Liang Yuan, Huan Li, Xi Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Transportation and Science Engineering Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

This study explores the mechanical properties and microstructure of ultra-high-performance concrete with recycled aggregates (UHPC-RA) enhanced by nanosilica (NS) and steel fibers (SF) at elevated temperatures. Thirty-six mixtures, varying in RA replacement rates, SF, and NS content, were prepared and tested for compressive strength, splitting tensile strength, and elastic modulus. Microstructural analyses included SEM morphology, XRD composition, pore size distribution, thermal conductivity, and elemental distribution studies. Results show temperature-induced changes, including SF oxidation and spalling, causing brittle failures due to weakened cementitious matrix and ITZ bonding. Moisture evaporation and hydration product decomposition lead to mass loss. Compressive strength initially increases and then decreases with rising temperatures, while overall splitting tensile strength decreases. Deterioration in UHPC-RA's microstructure is main reason for macroscopic mechanical property degradation. Linear relationships between compressive and splitting tensile strength were established. SEM and XRD confirmed that NS particles contribute to the conversion of CH to C-S-H gels. © 2023, The Authors. All rights reserved.

关键词： Steel fibers

Experiment and Analysis on Flexural behavior of Uhpc Encased Steel Beams

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SSRN 2024年

作者： Wang, Kun Wang, Jiahui Omar, Ahmed Ahmad Luo, Huihui Yang, Yang Chen, Zaixian Tao, Qiyu College of Civil Science and Engineering Yangzhou University Yangzhou225127 China Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Heilongjiang Harbin150090 China Guangling College Yangzhou University Yangzhou225127 China Key Lab of Civil Engineering Structure and Disaster Prevention in Universities of Shandong Harbin Institute of Technology at Weihai Shandong Weihai264209 China

To improve the normal section design approach for ultra-high-performance concrete (UHPC) encased steel beams, this paper first conducted a flexural experiment on eight simply supported UHPC encased steel beams, where the test parameters included the longitudinal reinforcement ratio in tension, the width and thickness of H-shaped steel flanges, the strength grade of H-shaped steel, and the location of H-shaped steel. Then, the calculation method of the flexural capacity of the UHPC encased steel beams was proposed based on the position of the neutralization axis. The short-term stiffness before and after cracking, as well as the average crack width, were established by considering the effect of the steel fibers. Finally, a finite element model of the UHPC encased steel beam was constructed using reasonable material relations and compared with the test results for validation. The results showed that the longitudinal steel bars and the lower flanges of the UHPC encased steel beams first reached a yielding state, and then the upper UHPC was crushed, exhibiting an under-reinforced damage pattern. Increasing the longitudinal reinforcement ratio, the width and thickness of the H-shaped steel flange, the strength grade of the steel, and offsetting the H-shaped steel downward can effectively increase the vertical load-carrying capacity. Due to the high compression strength of the UHPC and the small depth of the compression zone, the upper flanges of the H-shaped steels for some UHPC encased steel beams did not reach yield. Concerning the presence of the H-shaped steel, after the upper UHPC in the span was crushed, the falling branches of the vertical load-deflection curves flattened, showing good ductility. The equivalent stress coefficient k in tension is suggested to be 0.7 when calculating the flexural capacity. For predicting the post-crack stiffness and the average crack width, the fiber influence coefficients B and w are recommended to be 0.2 and 0.3, respectively. The

关键词： Stiffness

An experimental study on early age compression and shear strength properties of mixed clay soil

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Arabian Journal of Geosciences 2024年第2期17卷 1-14页

作者： Abbas, Azhar Akbar, Muhammad Huali, Pan Zar, Ali Ramzan, Samar Hussain, Zahoor Department of Geotechnical Engineering Tongji University Shanghai China Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu China Sir Syed University of Engineering & Technology Karachi Pakistan Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin China Department of Civil Engineering University of Engineering and Technology Lahore Lahore Pakistan Zhengzhou University Zhengzhou China

Clay mixed soil is a combination of clay and soil components that may be used as the core of earth dams and the foundation for building and road construction. Up until now, significant research work has been carried out to design cement-based clay materials; however, only a couple of studies have been reported in the literature on earth-based materials. The methodology portion provides an overview of the different materials, tools, and protocols used during work to develop ways to earth-based materials and study their early age compression strength along with their shear strength. Finally, it summarizes all the results and the outcome of the experimental work done. The probability of producing an object using earth-based material was examined. Improvement in the compressive strength in the early age of strength by adding additives like bentonite and rice husk was assessed in this study. Three clayey soil samples were investigated. The undrained shear strength based on an unconfined compression test (UCT) over those samples was measured by varying the moisture content (MC). After performing all these tests, a relationship was developed between the UCT and vane shear test (VST) undrained shear strengths of the selected soil samples. Clay samples with different mix designs were investigated, and building components were printed out to check the early age shear strength development and printable properties of different mix designs. This study will lay the foundation for further research on different aspects relating to the emerging technology of 3D clay printing in Pakistan.

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Defect-Mediated Work Function Regulation in Graphene Film for High-Performing Triboelectric Nanogenerators

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SSRN 2022年

作者： Zhou, Jian Zhang, Jianing Deng, Yuanpeng Zhao, Han Zhang, Pengyu Fu, Shubing Xu, Xiang Li, Hui Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China

Triboelectric nanogenerators (TENGs) demonstrate an attractive pathway to directly convert broadband mechanical energy into electrical energy for a green and clean energy source. Triboelectric material design with tailored work function has played a critical role in enhancing the output performance of TENGs. However, regulating the work function of triboelectric materials still remains challenging due to the limited particle/group/ion doping rate. Here, we reported a simple defect-mediated strategy (DMS) to regulate the work function in graphene film as the positive triboelectric material by different contents of oxygen and carbon defects derived at annealing temperatures from 500 ºC to 3000 ºC. Our DMS features a continuous and wide-range tunable work function from 4.680 eV to 4.479 eV, and the as-assembled TENGs produce output voltages and currents up to 190 V and 14 μA, respectively. The efficient work function regulation of this type establishes a set of fundamental considerations in triboelectric material design, especially the two-dimensional materials, to enhance the energy harvesting and sensing performances of TENGs. © 2022, The Authors. All rights reserved.

关键词： Nanogenerators

The Micro–Mechanical Mechanism of Multiple Cracking behavior Induced by Interface Strengthening for Ultra–High–Performance Concrete

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SSRN 2023年

作者： Du, Junjie Xiao, Huigang Zhang, Fengling Liu, Min Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China School of Civil Engineering Shandong University 17923 Jingshi Road Jinan250061 China

The multiple cracking behavior of ultra–high–performance concrete （UHPC） is strongly dependent on the bridging of cracks by fibers and the spatial strength distribution of matrix. A good match between fiber bridging properties and matrix tensile strength can significantly improve the utilization of fibers and matrix. In this study, a micromechanics based theoretical model is proposed, which can match the matrix tensile strength with the fiber–matrix interface bonding strength. The spatial strength distribution of the matrix and the stress transfer between the fiber and the matrix is considered in the model. Bridge stresses, additional stresses, stress transfer distances, and pulley forces at the crack face for various crack openings are derived. Dense multiple cracks were observed in the UHPC tensile samples at a common condition ( ) designing based on the calculation results. The applicability of the model is validated by comparing the simulation results and the experimental results in previous investigations at the same paraments ( ). With the proposed model, the mechanism of fiber–matrix interface enhancement contributing to the multiple cracking behavior can be understood. The results of this study could provide fundamental insights for the design of UHPC for various ductility and strength requirements. © 2023, The Authors. All rights reserved.

关键词： Fibers