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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

Experimental investigation on the impingement of synthetic jet vortex rings on a spherical wall

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Physical Review Fluids 2022年第4期7卷 044703-044703页

作者： Changlong Chen Donglai Gao Wen-Li Chen Key Laboratory of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin 150090 China Key Laboratory of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin 150090 China

An experimental study was conducted to investigate the influence of sphere diameter and Reynolds number on synthetic jet vortex rings impinging on a spherical wall. Laser-induced fluorescence and two-dimensional particle image velocimetry techniques were applied to visualize flow and measure flow velocity, respectively. In this experiment, the stroke length was kept constant (L=3.6), and different diameters (d/D=1, 6, and 16) and Reynolds numbers (Resj=227 and 682) were analyzed. In addition to flow visualization images and phase-averaged λci fields, the vortex ring trajectories and circulation are presented to reveal the evolution features of the vortex rings. The results demonstrated that the Reynolds number mainly determined the strength and induced ability of the primary vortex ring (PVR) and the sphere-diameter effect was reflected by the expansion distance of the PVR and its separation from the wall boundary layer. It was found that only a secondary vortex ring (SVR) was induced in the case of a small diameter or a low Reynolds number. As the diameter and Reynolds number increased, the PVR expanded continuously along the wall and induced a SVR and tertiary vortex ring. In particular, driven by the curve, the strength of the induced vortex ring decreased with the increase in the sphere diameter.

关键词： Vortex flows Wakes & jets

Convective meta-thermal concentration for ultrahigh efficient Stirling engine with waste heat and cold utilization

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arXiv

arXiv 2023年

作者： Zhou, Xinchen Xu, Xiang Ouyang, Xiaoping Huang, Jiping Fudan University Shanghai200433 China 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 School of Materials Science and Engineering Xiangtan University Xiangtan411105 China

The Stirling engine, which possesses external combustion characteristics, a simple structure, and high theoretical thermal efficiency, has excellent potential for utilizing finite waste heat and cold resources. However, practical applications of this technology suffered from thermal inefficiency due to the discontinuity and instability of waste resources. Despite advances in energy storage technology, temperature variations in the heat-exchanging fluids at the hot and cold ends of the Stirling engine remained significant obstacles. In this work, convective meta-thermal concentration (CMTC) was introduced between the heating (cooling) fluids and the hot (cold) end of the Stirling engine, employing alternating isotropic materials with high and low thermal conductivities. It was demonstrated that CMTC effectively enhanced the temperature difference between the hot and cold ends, leading to a remarkable improvement in Stirling engine efficiency. Particularly, when the Stirling engine efficiency tended to zero due to the limited availability of waste heat and cold resources, CMTC overcame this limitation, surpassing existing optimization technology. Further analysis under various operating conditions showed that CMTC achieved a significant thermal efficiency improvement of up to 1460%. This work expanded the application of thermal metamaterials to heat engine systems, offering an exciting avenue for sustainable energy utilization. Copyright © 2023, The Authors. All rights reserved.

关键词： Waste heat

Detecting Multiple Change Points in Distributional Sequences Derived from Structural Health Monitoring Data: An Application to Bridge Damage Detection

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arXiv

arXiv 2023年

作者： Lei, Xinyi Chen, Zhicheng Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 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

Detecting damage in critical structures using monitored data is a fundamental task of structural health monitoring, which is extremely important for maintaining structures' safety and life-cycle management. Based on statistical pattern recognition paradigm, damage detection can be conducted by assessing changes in the distribution of properly extracted damage-sensitive features (DSFs). This can be naturally formulated as a distributional change-point detection problem. A good change-point detector for damage detection should be scalable to large DSF datasets, applicable to different types of changes, and capable of controlling for false-positive indications. This study proposes a new distributional change-point detection method for damage detection to address these challenges. We embed the elements of a DSF distributional sequence into the Wasserstein space and construct a moving sum (MOSUM) multiple changepoint detector based on Fréchet statistics and establish theoretical properties. Extensive simulation studies demonstrate the superiority of our proposed approach against other competitors to address the aforementioned practical requirements. We apply our method to the cable-tension measurements monitored from a long-span cable-stayed bridge for cable damage detection. We conduct a comprehensive change-point analysis for the extracted DSF data, and reveal interesting patterns from the detected changes, which provides valuable insights into cable system damage. Copyright © 2023, The Authors. All rights reserved.

关键词： Damage detection

A robust deep learning-based damage identification approach for SHM considering missing data

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arXiv

arXiv 2023年

作者： Deng, Fan Tao, Xiaoming Wei, Pengxiang Wei, Shiyin Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 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

Data-driven method for Structural Health Monitoring (SHM), that mine the hidden structural performance from the correlations among monitored time series data, has received widely concerns recently. However, missing data significantly impacts the conduction of this method. Missing data is a frequently encountered issue in time series data in SHM and many other real-world applications, that harms to the standardized data mining and downstream tasks, such as condition assessment. Imputation approaches based on spatiotemporal relations among monitoring data are developed to handle this issue, however, no additional information is added during imputation. This paper thus develops a robust method for damage identification that considers the missing data occasions, based on long-short term memory (LSTM) model and dropout mechanism in the autoencoder (AE) framework. Inputs channels are randomly dropped to simulate the missing data in training, and reconstruction errors are used as the loss function and the damage indicator. Quasi-static response (cable tension) of a cable-stayed bridge released in 1st IPC-SHM is employed to verify this proposed method, and results show that the missing data imputation and damage identification can be implemented together in a unified way. © 2023, CC BY.

关键词： Structural health monitoring

Experimental and Numerical Studies of Compressive Strength of 3d Printed Concrete Considering Interlayer Bonding Performance

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SSRN 2023年

作者： Tang, Boyang Yan, Jiachuan Han, Xiaoyu Lin, Yini Fan, Feng Key Lab of Structures Dynamic Behavior and Control of 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 School of Civil Engineering Harbin Institute of Technology Harbin150090 China

This paper studied the compressive properties of 3D printed concrete and analyzed their influencing factors, including layer thickness and printing time interval. The investigation also explored the impact of inter-layer and inter-bar bonding properties on concrete's compressive strength by examining key factors. The findings revealed that compressive strength decreases as layer thickness decreases and printing time interval increases. Moreover, interlayer tensile and shear strength decrease with longer printing time intervals, while the anisotropic mechanical properties of 3D printed concrete become more pronounced as the number of printed layers increases. The study employed cohesive elements to numerically simulate the compressive strength of concrete specimens with varying number of layers and interlayer intervals. Parametric analysis was conducted to investigate bonding layer failure under different loading directions, and damage modes were analyzed. Finally, an empirical equation for predicting the compressive strength of 3D printed concrete was proposed and validated using experimental data. © 2023, The Authors. All rights reserved.

关键词： Compressive strength

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

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

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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