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The Deformation of C–S–H Gel and its Link with Length Change of Cement Pastes on Drying and Resaturation

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SSRN 2023年

作者： Zhang, Xiaoyu Qiao, Jing Feng, Jingjing Xu, Shilang Zhou, Chunsheng Zeng, Qiang Key Lab of Structures Dynamic Behavior and Control Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China College of Water Conservancy and Civil Engineering Shandong Agricultural University Taian271018 China College of Civil Engineering and Architecture Zhejiang University Hangzhou310058 China

Drying shrinkage of cement pastes (CPs) facilitating superficial cracking deserves primary concern when handling durability performance. In order to further clarify shrinkage mechanism, the changes of mass, length and pore water allocation of two mature CPs were monitored principally through non-destructive low-field NMR relaxation technique. Experimental results revealed that, heat treatment under hot water slightly coarsens the pore structure of CPs through modifying the morphology of C-S-H gel, but reduces shrinkage during first drying remarkably. During drying at 80% RH, although both interlayer and gel pores are saturated, they loss their water progressively at reducing rates. At the expense of reducing interlayer space, the contraction of gel pores is partly and even entirely compensated. When drying at lower 43% RH, interlayer pores still saturated are compacted more significantly with reducing size and volume. The compaction of interlayer pores is at the micro-structural origin and dominates drying shrinkage of CPs. © 2023, The Authors. All rights reserved.

关键词： Drying

dynamic Responses and Cumulative Damage of Coastal Bridges Subjected to Extreme Sequential Earthquake-Tsunamis

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SSRN 2024年

作者： Zhu, Deming Dong, You Feng, Ruiwei Li, Yaohan Zhai, Changhai Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Hong Kong Research Institute for Sustainable Urban Development The Hong Kong Polytechnic University Hong Kong Department of Construction and Quality Management Hong Kong Metropolitan University Hong Kong 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 Disaster The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China

Coastal bridges, as vital components of transportation networks, are vulnerable to damage from successive earthquake-tsunami (EQ-TS) events in rapidly developing coastal hazard-prone cities. Understanding how these bridges perform under the combined effects of earthquakes and tsunamis is crucial. Though studies have investigated coastal buildings facing these hazards, there is limited research on bridges experiencing extreme EQ-TS events, especially on the generation of load sequences, dynamic structural responses, and cumulative damage assessment. To overcome these limitations, this study aims to thoroughly examine the dynamic behavior of reinforced concrete coastal bridges subjected to successive EQ-TS hazards. To generate practical sequential EQ-TS loads, records of the 2011 Tohoku earthquake and resulting tsunami heights, which are calculated based on the earthquake magnitude and epicentral distance, are utilized for analyses. The tsunami wave load time series for each earthquake record is created using a high-fidelity computational fluid dynamics model. Nonlinear time-history analyses are then performed for the bridge model in OpenSees under the synthetic EQ-TS sequences, quantifying structural responses and cumulative damage. Moreover, the comparative results of structural performance under single and successive hazard scenarios are presented and discussed. Results indicate that successive EQ-TS hazards not only induce much larger structural responses as compared to a single EQ hazard, but also produce considerable residual displacements for both bearings and decks. The wave height is more appropriate than the peak ground acceleration as an individual intensity measure for predicting the cumulative damage of bridges under cascading EQ-TS hazards. Relying solely on peak responses for assessing the dynamic performance of piers under successive EQ-TS sequences may underestimate the actual damage. © 2024, The Authors. All rights reserved.

关键词： Earthquakes

Compressive sensing of images for automatic crack segmentation based on generative adversarial network 10

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Compressive sensing of images for automatic crack segmentati...

10th International Conference on Structural Health Monitoring of Intelligent Infrastructure, SHMII 2021

作者： Zhang, Haoyu Huang, Yong Wu, Stephen Ministry of Education Key Laboratory of Structural Dynamic Behavior and Control School of Civil Eng. Harbin Institute of Technology Heilongjiang Harbin150090 China Research Organization of Information and Systems The Institute of Statistical Mathematics 10-3 Midori-cho Tachikawa Tokyo190-8562 Japan

In a structural health monitoring (SHM) system that uses digital cameras to monitor cracks of structural surfaces, techniques for reliable and effective data compression are essential to ensure a stable and energy-efficient transmission of crack images in wireless sensing platforms such as drones and wall-climbing robots. Compressive sensing (CS) is a powerful signal processing technique, using the sparsity regularization. It allows accurate recovery of a signal from a sampling rate much smaller than the limitation of the Nyquist sampling theorem. Its hardware implementation allows down sampling of signals during the sensing process. Hence, CS methods can achieve significant energy saving for the wireless sensing devices. However, for the reconstruction of traditional CS methods, the strong assumption of the signals being highly sparse under certain bases is relatively hard to guarantee for many structural crack images. Generative adversarial network (GAN) has powerful capability to learn features of targeted images and is able to effectively capture low-dimensional representations of high-dimensional images. By exploiting the dimensionality reduction effect of GAN, we present a new approach of CS that replaces the sparsity regularization with a GAN model. Based on this new CS method, we developed a recovery framework of compressed crack images for automatic crack segmentation, in which crack images are reconstructed by directly optimizing the low dimension representation learned by GAN. In our experiments, taking advantage of the strong capability of GAN to capture the necessary features required for the crack segmentation task in compressed image data, we demonstrated the remarkable reconstruction precision, calculation speed and robustness toward noise of our recovery framework, even though the backgrounds of images are not well reconstructed. © 2021 International Conference on Structural Health Monitoring of Intelligent Infrastructure: Transferring Research into

关键词： Structural health monitoring

Effects of Various Connectors on the Whole-Life-Cycle Energy Consumption of Sandwich Wall Panels in Five Thermal Zones of China

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SSRN 2022年

作者： Dong, Xianzhang Lu, Yiming Xiao, Huigang Liao, Juan School of Civil Engineering Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control Ministry of Education Harbin Institute of Technology Harbin150090 China China Construction Second Engineering Bureau. Ltd 100160 China

Connectors are not only an important mechanical component of sandwich wall panels (SWPs), but they also contribute to SWP energy loss because they penetrate thermal insulation layers. Reducing the energy consumption (EC) generated by connectors is critical for improving the energy-saving efficiency of SWPs throughout their life cycle. The mechanical and thermal parameters of connectors, structural layers, and insulation layers all have a coupling effect on the EC of connectors in the SWPs studied in this study. First, a connector diameter calculation model and a three-dimensional finite element (3-DFE) model were developed to investigate the mechanism of various connectors' effects on the thermal performance (TP) of SWPs with different structural and insulation layers. It was discovered that increasing the connector shear strength could reduce energy loss by reducing the connector size, and connector energy loss could also be improved by lowering the connector thermal conductivity and increasing the thermal resistance of the structural layers. Then, based on TP, a life cycle assessment (LCA) model was developed. Using five thermal zones in China as research subjects, it was discovered that the effects of connectors on the whole-life-cycle EC of SWPs depend on the value of degree days (DD). The connector manufacturing EC dominated the whole-life-cycle EC in an area with a low DD value. Reduced thermal conductivities of connectors, structural layers, and insulation layers could significantly improve the effects of connectors on the whole-life-cycle EC of SWPs in an area with a high value of DD. These findings are critical for the development of effective SWPs. © 2022, The Authors. All rights reserved.

关键词： Energy utilization

Efficient single-grid and multi-grid solvers for real-space orbital-free density functional theory

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arXiv

arXiv 2022年

作者： Bu, Ling-Ze Wang, Wei School of Civil Engineering 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 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

To improve the computational efficiencies of the real-space orbital-free density functional theory, this work develops a new single-grid solver by directly providing the closed-form solution to the inner iteration and using an improved bisection method to accelerate the line search process in the outer iteration, and extended the single-grid solver to a multi-grid solver. Numerical examples show that the proposed single-grid solver can improve the computational efficiencies by two orders of magnitude comparing with the methods in the literature and the multi-grid solver can improve the computational efficiencies even once for the cases where high-resolution electron densities are needed. © 2022, CC BY-NC-SA.

关键词： Computational efficiency

Reliability Assessment of Offshore structures Using Subset Simulation with Adaptive Standard Deviation for Mmh Algorithm with Two-Stage Delayed Rejection

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SSRN 2023年

作者： Ma, Junming Lan, Chengming Guo, Anxin Li, Hui National Center for Materials Service Safety University of Science & Technology Beijing Beijing100083 China Research Institute of Urbanization and Urban Safety School of Civil and Resource Engineering University of Science & Technology Beijing Beijing100083 China Key Lab of Structures Dynamic Behavior and Control Ministry of Education School of Civil Engineering Harbin Institute of Technology Harbin150090 China

This paper explores modified strategies for MMH in the subset simulation for reliability assessment in ocean engineering. To improve the sampling efficiency in complex distributions comprising correlated or non-normal variables, this study proposes a modified approach involving a two-stage delayed rejection and an adaptive STD for the proposal distribution based on MMH. The acceptance rate of the candidate sample in two-stage delayed rejection approach is derived based on the reversibility condition of Markov chain to reduce the repeated samples. Additionally, the STD for all accepted samples is used as the STD for the proposal, which dominates the sampling scale and increases the acceptance rate. The Neal’s normal distribution, the Banana-shaped bivariate distribution, and the correlated joint distribution for wind and wave are adopted to study the sampling efficiency and ergodicity for MMHDR, AMMHDR, and AMMHDDR. Furthermore, three sampling algorithms are employed to generate conditional samples for estimating the probabilities of base shear failure and system failure in jacket platforms. The results indicate that the AMMHDDR can enhance the sampling efficiency, especially for complex distributions with correlated variables. Also, the AMMHDDR can be used in SS to improve the accuracy and reduce the variation when estimating failure probabilities of offshore structures. © 2023, The Authors. All rights reserved.

关键词： Normal distribution

A coupled model for vortex induced vibration of a circular cylinder with and without passive-jet flow control

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A coupled model for vortex induced vibration of a circular c...

第八届国际振动工程会议

作者： Guanbin Chen Wenli Chen Donglai Gao Xiangwei Min Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of Technology Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology

A coupled dynamic equation model, consisted by two parts: structural dynamic equation and the improved van der Pol equation(IVDPE), is established to predict the vortex induced vibration(VIV) response of circular cylinder dipped in the fluid environment. A classical structural dynamic equation is applied to describe the one degree-of-freedom vibration of a circular cylinder. The improved van der Pol equation is used to model the wake flow dynamics and the fluctuating aerodynamic force derived from the periodic alternating vortex shedding. The complete frequency component of aerodynamic forces, vibration amplitude and lock-in domains can be successfully predicted by the present coupled dynamic equation model. In addition, the passive jet pipes equipped on the circular cylinder to form the jet flow to suppress the VIV through the experimental method. The aerodynamic forces acting on the different sections far away from the passive jet pipes was obtained by the digital pressure measurement system. The aerodynamic force changed by the passive jet flow is consider into the coupled dynamic equation, and then the update coupled model is constructed and can predict the VIV of the circular cylinder with different spacing of adjacent passive jet pipes.

关键词： vortex-induced vibration alternating vortex shedding coupled model passive jet flow

Optimal overlays for preservation of concrete in cold climate: decision-making by the method of fuzzy comprehensive evaluation combined with AHP

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Journal of Infrastructure Preservation and Resilience 2021年第1期2卷 1-16页

作者： Li, Zhipeng Dang, Yudong Tang, Zhen Xie, Ning Lu, Shuang Shi, Xianming Department of Civil & amp Environmental Engineering Washington State University PullmanWA99164-2910 United States Yunnan Key Laboratory of Building Structure and New Materials Yunnan Institute of Building Research Kunming650223 China Key Lab of Structure Dynamic Behavior and Control Ministry of Education Heilongjiang Harbin150090 China School of Civil Engineering Harbin Institute of Technology Heilongjiang Harbin150090 China Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials University of Jinan Shandong Jinan250022 China

Overlays have been extensively employed as an effective preservation or rehabilitation tool to extend the service life of concrete bridges and pavements, especially concrete slabs suffering from salt scaling and abrasion. However, limited attention has been paid to the durability and performance of these overlays which can be jeopardized when they are exposed to freeze/thaw and wet/dry cycles, deicer applications, studded tires, and their coupled effects. Various overlays feature different engineering properties, and they might be only effective in specific service environments but not in others, and research is lacking to examine their ability to adapt to different environments. This study subjected five overlay products on concrete slabs to the combined action of freeze/thaw (F/T) and wet/dry (W/D) cycles with periodical exposure to either 15 wt.% NaCl solution or 15 wt.% MgCl2 solution, to simulate the typical field scenarios in an accelerated manner. The bond strength, splitting tensile strength, and abrasion resistance of the overlaid concrete slabs were tested to evaluate the effectiveness of various overlays against the deicer scaling and the abrasion by studded tires. Based on the experimental data, this study demonstrated a multi-criteria decision-making method, fuzzy comprehensive evaluation (FCE) combined with analytic hierarchy process (AHP), for the selection of optimal overlays in three different service scenarios (e.g., states of Washington and Oregon [USA] and British Columbia [Canada]). The analysis results indicate that one epoxy overlay exhibited the comprehensively best performance and could be a promising candidate in all three given scenarios, another polymer overlay took second place, while the adaptability of the three cement-based overlays varied in different environments. Graphical Abstract: (Figure presented.). © The Author(s) 2021.

关键词： Sodium chloride

Early-Age Hydration Heat Evolution and Kinetics of Portland Cement Containing Nano-Silica at Different Temperatures

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SSRN 2022年

作者： Bai, Shuai Guan, Xinchun Li, Guoyu Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China Harbin Institute of Technology Harbin150090 China State Key Laboratory of Frozen Soil Engineering Northwest Institute of Eco-Environment and Resources Chinese Academy of Sciences Lanzhou730000 China

This study investigated the influence of nano-silica dosages and hydration temperatures on the early-age hydration heat of cement using isothermal calorimetry, and a hydration kinetics model was used to analyze the nucleation and growth rates of hydrates. The calorimetry results show that the addition of nano-silica and the increase of hydration temperature can accelerate the process of hydration reaction. As the dosage of nano-silica increases, the induction period decreases, the acceleration period and exothermic rate peak value increase. The fast pozzolanic effect of nano-silica is responsible for accelerating the hydration reaction. However, the excessive addition (5%) of nano-silica may form many agglomerations, thereby inhibiting the modification effect of nano-silica on the cement hydration. The simulating results of kinetic parameters show that, at three hydration temperatures, the nucleation rate of hydrates increase with the increasing of nano-silica dosages, which indirectly confirms the nucleation effect of nano-silica in the early-age hydration. At 20 °C and 30 °C, the growth rate of hydrates also increases with the increasing of nano-silica dosages. At 40 °C, the growth rate of hydrates is decreased gradually, possibly due to the lack of sufficient Ca2+ and H2SiO42-. In addition, the nucleation rate is more sensitive and the growth rate is less sensitive to the hydration temperature. © 2022, The Authors. All rights reserved.

关键词： Hydration