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Free Vibration of Axially Moving Functionally Graded Nanoplates Based on the Nonlocal Strain Gradient Theory

INTERNATIONAL JOURNAL OF ACOUSTICS AND VIBRATION 2020年第4期25卷 587-596页

作者： Li, Cheng Wang, P. Y. Luo, Q. Y. Li, S. Soochow Univ Sch Rail Transportat Dept Vehicle Engn Suzhou 215131 Jiangsu Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510632 Guangdong Peoples R China

Using the nonlocal strain gradient theory, we explore vibration behaviours of initially bidirectional tensioned functionally graded nanoplates with axial speed. The governing equation of motion can be obtained based on the differential type of nonlocal strain gradient constitutive relation, which characters the dynamics of nanostructures containing kinematic relation. The simply supported boundary constraints on four sides are considered and subsequently the numerical results are determined. It shows that natural frequencies of axially moving nanoplates decrease when increasing the axial speed and the nonlocal parameter. Hence the nonlocal and kinematic factors cause the natural frequencies to decrease or, weaken the equivalent bending rigidity. On the other hand, natural frequencies increase with an increase in the axial tension and material characteristic scale. Hence the strain gradient and tensile stress factors cause the natural frequencies to increase or, strengthen the equivalent bending rigidity. In addition, the natural frequencies get higher with a larger aspect ratio of the functionally graded nanoplate. The larger one between the nonlocal parameter and the material characteristic scale plays a dominant role in the softening and stiffening mechanisms of the nonlocal strain gradient effect. In case of the same magnitude of the nonlocal parameter and the material characteristic scale, the softening and hardening phenomena disappear. The equivalent bending rigidity neither increases nor decreases in such a situation, and its value degenerates to the classical one.

关键词： Natural frequencies

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Flexural Performance of Layered Macro Fiber Reinforced Concrete Short Beams

SSRN

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SSRN 2022年

作者： Yuan, Hong Fu, Xiao-Hui Fan, Ya-Chen Fu, Bing Zou, Qi-Qi School of Mechanics and Construction Engineering Jinan University Guangzhou510632 China MOE Key Lab of Disaster Forecast and Control in Engineering Jinan University Guangzhou510632 China Department of Ocean Science and Engineering Southern University of Science and Technology Shenzhen518055 China

Fiber-reinforced polymer (FRP) composites have been increasingly used in various sectors, which inevitably results in an increasing amount of FRP waste to be dealt with. A recent study conducted by the author’s group explored a novel mechanical recycling method to process GFRP waste into small slender elements (referred to as "macro fibers") for reinforcing concrete, leading to so called "macro fibre reinforced concrete" (i.e., MFRC). The macro fibres recycled from waste FRP composites bridge the cracks in concrete and mitigate their development, thus enhancing the flexural strength and toughness of MFRC flexural members. However, the macro fibres have a negligible effect on the compressive properties of MFRC, which implies that the macro fibres in the compressive zone cannot be efficiently utilized. As motivated by the concept of the layered structure, this paper presents an experimental investigation on the flexural performance of the layered beams with the MFRC bottom layer and PC (plain concrete) top layer, expecting to improve the utilization of the incorporated macro fibres. The investigated test parameters include the height of the bottom layer as well as the macro fiber content in the bottom layer. The test results show that the application of layer structure effectively enhances the utilization of macro fibers and hence promotes the future technological application of the proposed mechanical recycling method. © 2022, The Authors. All rights reserved.

关键词： Fibers

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R-Function and variation method for bending problem of clamped thin plate with complex shape

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ADVANCES IN MECHANICAL engineering 2021年第7期13卷

作者： Xia, Fengfei Li, Shanqing Jinan Univ Sch Mech & Construct Engn MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510623 Peoples R China

Solving ordinary thin plate bending problem in engineering, only a few analytical solutions with simple boundary shapes have been proposed. When using numerical methods (e.g. the variational method) to solve the problem, the trial functions can be found only it exhibits a simple boundary shape. The R-functions can be applied to solve the problem with complex boundary shapes. In the paper, the R-function theory is combined with the variational method to study the thin plate bending problem with the complex boundary shape. The paper employs the R-function theory to express the complex area as the implicit function, so it is easily to build the trial function of the complex shape thin plate, which satisfies with the complex boundary conditions. The variational principle and the R-function theory are introduced, and the variational equation of thin plate bending problem is derived. The feasibility and correctness of this method are verified by five numerical examples of rectangular, I-shaped, T-shaped, U-shaped, and L-shaped thin plates, and the results of this method are compared with that of other literatures and ANSYS finite element method (FEM). The results of the method show a good agreement with the calculation results of literatures and FEM.

关键词： Complex shape thin plate bending R-function trial function variational method

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Onsite Identification of Moving Vehicle Loads on Multispan Continuous Bridge Using Both Dictionary Expansion and Sparse Regularization

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JOURNAL OF AEROSPACE engineering 2021年第3期34卷 04021018-04021018页

作者： Liu, Huanlin Li, Cheng Yu, Ling Wang, Yafei Zhong, Jiwei Jinan Univ Sch Mech & Construct Engn MOE Key Lab Disaster Forecast & Control Engn 601 West Huangpu Ave Guangzhou 510632 Peoples R China State Key Lab Hlth & Safety Bridge Struct Wuhan 430034 Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn 601 West Huangpu Ave Guangzhou 510632 Peoples R China

Moving force identification (MFI) plays an important role in monitoring moving vehicle loads acting on a bridge, which has attracted great attention in recent years. Although many MFI methods have been proposed, their effectiveness in real bridges has not been carefully investigated. In this study, focusing on how to identify moving forces from structural responses in a real bridge, some important aspects are conducted and discussed in detail. The effectiveness of a MFI method based on dictionary expansion and sparse regularization is evaluated by a five-span continuous bridge in real engineering. First, a finite-element (1-b) model is established to approximately describe the real bridge. Then, the FE model is updated based on the modal information obtained from structural responses, so the transfer matrices between moving forces and structural responses can be calculated. Meanwhile, data preprocessing is conducted and a suitable dictionary is designed to obtain reasonable MFI results. As a result, the MFI equation by adding reweighted l(1)-norm regularization is used for MFI. Finally, two trucks with known gross vehicle weights are adopted to evaluate its effectiveness. The NM results show that this method can reasonably estimate the moving vehicle loads acting on bridge deck, and the identified moving forces are reasonable. (C) 2021 American Society of Civil Engineers.

关键词： Structural health monitoring (SHM) Moving force identification (MFI) Sparse regularization Dictionary expansion

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An analytical method for shallow spherical shell free vibration on two-parameter foundation

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HELIYON 2021年第1期7卷 e05876页

作者： Gan, Jiarong Yuan, Hong Li, Shanqing Peng, Qifeng Zhang, Huanliang Jinan Univ Sch Mech & Construct Engn MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510632 Peoples R China

The free vibration control differential equation of shallow spherical shell on two-parameter foundation is a four order differential equation. Using the intermediate variable, the four order differential equation is reduced to two lower order differential equations. The first lower order differential equation is a Helmholtz equation. A new method of two-dimensional Helmholtz operator is proposed as shown in the paper in which the Bessel function included in Helmholtz equation needs to be treated appropriately to eliminate singularity. The first lower order differential equation is transformed into the integral equation using the proposed method in the paper. The second lower order differential equation which is a Laplace equation is transformed into the integral equation by existing methods. Then the two integral equations are discretized according to the middle rectangle formula, and the corresponding solutions can be obtained by MATlab programming. In this paper, the R-function theory is used to select the appropriate boundary equation to eliminate the singularity. Based on the properties of R-function, the combined method of Helmholtz equation and Laplace equation can solve the free vibration problem of irregular shallow spherical shell on two-parameter foundation. Five examples are given to verify the feasibility of the method.

关键词： Shallow spherical shell Two-parameter foundation Helmholtz equation Laplace equation R-function Green's function

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Indirect Reconstruction of Structural Responses Based on Transmissibility Concept and Matrix Regularization

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SHOCK AND VIBRATION 2021年第1期2021卷

作者： Pan, Chudong Zhang, Liwen Sun, Zhuo Guangzhou Univ Sch Civil Engn Guangzhou Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn Guangzhou Peoples R China

A novel method is proposed based on the transmissibility concept and matrix regularization for indirectly measuring the structural responses. The inputs are some measured responses that are obtained via physical sensors. The outputs are the structural responses corresponding to some critical locations where no physical sensors are installed. Firstly, the transmissibility concept is introduced for expressing the relationship between the measured responses and the indirectly measured ones. Herein, a transmissibility matrix is formulated according to the theory of force identification under unknown initial conditions. Then, in order to reduce the size of the transmissibility matrix, structural responses are reshaped in a form of a matrix by using the concept of moving time windows. According to the matrix form of input-output relationship, indirect reconstruction of responses is boiled down to an optimization equation. Since inverse problem may be ill-conditioned, matrix regularization such as F-norm regularization is then recommended for improving the optimization problem. Herein, the penalty function is defined by using a weighted sum of two F-nonn values, which correspond to the estimated responses of physical sensors and the ones of the concerned critical locations, respectively. Numerical simulations and experimental studies are finally carried out for verifying the effectiveness and feasibility of the proposed method. Some results show that the proposed method can be applied for indirectly measuring the responses with good robustness.

关键词： Matrix algebra

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Moving force identification based on sparse regularization combined with moving average constraint

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JOURNAL OF SOUND AND VIBRATION 2021年 515卷 116496-116496页

作者： Pan, Chudong Huang, Zhenjie You, Junda Li, Yisha Yang, Lihua Guangzhou Univ Sch Civil Engn Guangzhou Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn Guangzhou Peoples R China

An accurate input-output mathematical model is the basis of moving force identification (MFI). However, an absolutely accurate mathematical model between moving forces and structural responses is difficult to be established due to some practical reasons, such as calibration error, modelling error, and so on. An inaccurate input-output relationship may lead to some unreasonable MFI results, for example, an obvious fluctuation of the trend lines in moving forces. To tackle this problem, a constrained sparse regularization-based method is proposed for MFI in this study. Wherein, structural responses obtained from sensors with calibration errors are taken as the inputs. A system matrix reflecting the input-output relationship is formulated in the consideration of unknown moving forces and initial conditions. Sparse regularization is adopted for ensuring that the identified forces are sparse and robust. The constrained condition is expressed as a non-negative function. This function is defined via a strategy named moving average and applied for reflecting the degree of fluctuation of the trend lines for the moving forces. The constrained problem is solved as a standard form of l1-norm regularization via relaxing the constrained condition appropriately. Numerical simulations and experimental studies are conducted for assessing the effectiveness and feasibility of the proposed method. Effects of different calibration errors of sensors are discussed in detail. Illustrated results show that the proposed method can reconstruct the moving forces with a good performance. Some related issues are discussed as well.

关键词： Moving force identification Sparse regularization Moving average constraint Inverse problem Calibration error

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Experimental testing and system identification of the sliding bistable nonlinear energy sink implemented to a four-story structure model subjected to earthquake excitation

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JOURNAL OF BUILDING engineering 2022年 61卷

作者： Chen, Yang-Yang Su, Wei-Te Tesfamariam, Solomon Qian, Zhi-Chao Zhao, Wei Shen, Chao-Yong Zhou, Fu-lin Guangzhou Univ Earthquake Engn Res & Test Ctr Key Lab Earthquake Resistance Earthquake Mitigat & Struct SafetyMOE Guangzhou 510006 Peoples R China Univ British Columbia Sch Engn Okanagan Campus Kelowna BC Canada Jinan Univ Sch Mech & Construction Engn Key Lab Disaster Forecast & Control Engn MOE Guangzhou 510632 Peoples R China

Bistable nonlinear energy sink system has been explored as an efficient vibration absorber in many areas. This paper aims to experimentally validate the seismic mitigation performance of sliding bistable nonlinear energy sink (SBNES) for multi-story building structures. An SBNES device was designed and placed on top of a four-story building structure model. Earthquake ground motions were applied through a shake table as the base excitation input into the structure model. By matching the time history envelope curves between the experiment and numerical simulation, the structural parameters of the primary structure, as well as the constitutive model of the SBNES, were experimentally determined. The comparisons between mitigated and unmitigated structural responses, including inter-story drift, acceleration, base-shear force and baseoverturning moment of the primary structure, show that substantial reduction of structural seismic responses can be achieved by the SBNES device. The 1:1 transient internal resonance is verified as the dominant scheme for highly efficient targeted energy transfer. With respect to variation of peak ground acceleration, a relatively optimal interval distributed near the borderline of intra-well and inter-well regime is proposed for robust SBNES design. The test validates the potential of the SBNES strategy for both acceleration and displacement control of multi-story building structures.

关键词： Sliding bistable nonlinear energy sink Seismic response mitigation Shake table test Parametric identification Targeted energy transfer

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Seismic behavior and design method of seawater sea-sand concrete reinforced with GFRP and five interlocking spirals

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engineering STRUCTURES 2023年第1期291卷

作者： Xiong, Zhe Zheng, Jinhu Chen, Zepeng Huang, Yubiao Wang, Zhimin Chen, Junyu Lin, Lianghao Li, Lijuan Qiao, Sihua Liu, Feng Guangdong Univ Technol Sch Civil & Transportat Engn Guangzhou 510006 Peoples R China Foshan Univ Sch Transportat & Civil Engn & Architecture Foshan Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510632 Peoples R China Guangdong Jialin Construct Co Ltd Maoming 525299 Peoples R China

Seawater sea-sand concrete (SWSSC) columns reinforced with GFRP brings great benefit to island construction but its seismic behavior remains unclear. This paper provides an experimental study on the seismic behavior and design method of SWSSC columns reinforced with GFRP and five interlocking spirals. Seven columns with different stirrup configurations, spirals spacings, outer diameter of conner spirals, axial compression ratios and shear-span ratios were designed and tested under simulated seismic loading. Their failure modes, hysteretic responses, skeleton curves, stiffness degradations, ductility factor and energy dissipations were all attained and discussed in detail. The results show that the SWSSC column confined with interlocking multi spirals has better seismic resistance than that with composite rectangular stirrup. Moreover, the increase of shear-span ratio and outer diameter of conner spirals both improve the ductility and therefore enhance the seismic resistance. In contrast, the increase of axial compression ratio and spiral spacing have inverse impact on seismic resistance enhancement. Based on the testing results, a novel approaching method was also proposed to evaluate the shear bearing capacity of oblique section and the average prediction error was within 1.30% through verification with the test results.

关键词： Seawater sea -sand concrete (SWSSC) columns Interlocking multi spirals Seismic behavior Shear capacity of oblique section

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Finite strain elastoplastic J2-flow model for automatically, accurately simulating pseudo-elastic effects of SMAs 2nd

Finite strain elastoplastic J2-flow model for automatically,...

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2nd International Conference on Material engineering Research, ICMER 2019

作者： Wang, Si-Yu Zhan, Lin Xi, Hui-Feng Xiao, Heng School of Mechanics & Construction Engineering and MOE Lab for Disaster Forecast & Control in Engineering Jinan University West Huangpu Avenue 601 Guangzhou510632 China

ISBN: (纸本)9783035713602

Finite strain elastoplastic J2-flow equations are established toward the purpose of automatically, accurately simulating pseudo-elastic effects of SMAs. The uniaxial responses derived from these equations in each loading-unloading cycle exactly produce a closed stress-strain curve of any given shape. Then, any given test data for pseudo-elastic hysteresis loops of SMAs may be accurately fitted by means of a new technique for combining linear spline functions into a unified, smooth interpolating function, in a sense with no need to identify any unknown parameters. © 2020 Trans Tech Publications Ltd, Switzerland.

关键词： Stress-strain curves

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