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  • 25 December 2022 Volume 43 Issue 4
      
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  • Recent Advances in the Mechanical Properties of 3D Printed Fiber-Reinforced Composites
    LI Yan, LONG Yu, HAO Lucen, ZHANG Hanghua, XIAO Jianzhuang
    2022, 43(4): 731-750. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.001
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    3D printed fiber-reinforced composites (3DFRCs) offer the advantages of integrated molding of complex structures, mold-free fabrication and tailored mechanical properties, which can significantly reduce the manufacturing cycle and the cost of fiber-reinforced composites. However, the low molding pressure and layer-by-layer manufacturing characteristics of 3D printing technology bring challenges to the mechanical properties of 3DFRCs. The purpose of this paper is to summarize the recent progress of researches on the mechanical properties of short/continuous fiber-reinforced polymer matrix composites and fiber-reinforced concrete matrix composites in domestic and overseas, in terms of three aspects: printing methods, mechanical properties and their influence factors. In order to show the various 3D printing methods, the level of mechanical properties that can be achieved and the factors influencing the mechanical properties, to provide a reference for achieving the high mechanical performance of 3DFRCs. Finally, the future research directions of the 3D printed fiber-reinforced composites are prospected.
  • Analysis of the Effect of Nominal Electric Field Strength and Axial Constraint on Electric-Field-Induced Bending of Dielectric Liquid Crystal Elastomers
    PU Hongfei, XU Yiwei, HUO Yongzhong
    2022, 43(4): 751-761. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.002
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    Dielectric liquid crystal elastomers (DLCEs) can produce obvious macroscopic deformations under relatively low electric field, which is caused by the rotation of the liquid crystal director. The programming of the electric-field-induced deformation of DLCEs can be realized by designing the directors alignment of the sample. For beam-shaped samples with transversal director orientation gradients, the sample can produce bending deformation accompanied by axial contraction. In this paper, based on the two-dimensional electro-mechanical-director coupling model of the DLCE, the electric-field-induced bending behavior of DLCE beam-shaped sample is studied by finite element simulation. Possible effects of the nominal electric field strength and the axial constraint are mainly concerned. The results show that the deflection of the sample is not simply proportional to the square of the nominal electric field strength at higher electric field strength. Axial constraint will affect the bending shape and degree of the sample: the bending shape is no longer parabolic, but it can still be fitted by a given mathematical expression. Due to the membrane force effect, the bending degree of the axially constrained sample is weaker than that of the unconstrained sample. Our results in this paper could provide some reference for the design and application of the electro bending devices made of DLCEs.
  • Simulation Study on Interfacial Micromechanics of Glass Fiber Reinforced Nylon 6 Composites
    LUO Weiquan, HUANG Zengbin, XUE Ke, LV Dong, CONG Jie, ZHANG Kai
    2022, 43(4): 762-770. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.003
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    Based on the bilinear cohesion model, this paper employed Abaqus to conduct a computer simulation study on the fiber push-out process of glass fiber reinforced nylon 6 composite material. The interface strength between glass fiber and nylon 6 was successfully calculated, and the results were verified using the nanoindentation test. The simulation results were in good agreement with the test results. The initial bending deformation of the sample was the main reason for the difference between the experimental and the theoretical results. The finite element simulation and experiment of the single fiber push-out process test provide effective approaches for understanding the interface properties of composite materials, and also provide a micromechanical model for the study of the trans-scale failure criteria and damage evolution of the composite material.
  • Analysis of Ablation and Strength of CFRP Laminated Structures under Laser Irradiation
    XIONG Liujie, WANG Jiawei, NIE Guohua
    2022, 43(4): 771-781. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.004
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    The damage and strength analysis of Carbon Fiber Reinforced Polymer (CFRP) laminates under combined laser-mechanical loading is carried out in this paper. A laser ablation model is established to determine the temperature fields on the front and rear surfaces and along the direction of thickness of the laminates for different values of intensity of laser irradiation, and the accuracy in computation for the finite element simulation is verified by laser irradiation experiments. Further, according to the ablation model and bridging model, the corresponding UMAT subroutine is compiled into Abaqus code, and the failure time and tensile stress-strain relation of CFRP laminates is thus determined numerically. The effect of laser intensity and irradiation time on the tensile strength of CFRP laminates is predicted. The proposed model and computational method is of great significance to analysis of strength of composite laminated structures and engineering design due to the ablation effect.
  • Effect of Graphene Coating on Friction and Wear Properties of Nanoparticles
    LIU Xiangze, CHEN Yang, HUO Zhanlei, GUO Zhengrong
    2022, 43(4): 782-790. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.005
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    Graphene and nanoparticles are widely used as lubricants in various mechanical systems. Investigating the combined effect of the two on the friction and wear properties of mechanical systems has important scientific research value and realistic meaning. In this paper, based on molecular dynamics simulations, four graphene coating (with or without nanoparticle coating or substrate coating) models are established to study the effect of graphene coating on the sliding friction and wear properties between the nanoparticle and substrate. It is found that graphene coating can greatly change the instantaneous friction between the nanoparticle and substrate, and effectively improve the wear resistance between nanoparticle and substrate. The coating style of graphene will significantly affect the adsorption force between nanoparticle and substrate, and thus affect the friction. For the case of both nanoparticle and substrate coated by graphene, the influence of graphene contact commensurability on the friction is also considered. The results show that the contact commensurability of graphene does not significantly affect the friction properties of the coating structure. Some explanations are also provided.
  • Actuation Coordination of the Earthworm-Like Locomotion Robot Based on Dynamic Model
    ZHANG Gangling, ZHANG Shu
    2022, 43(4): 791-802. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.006
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    Improving the locomotion performance of the robot lies in core of the research on the earthworm-like locomotion robot. In this paper, the dynamic model with multi-degrees of freedom is established for the earthworm-like locomotion robot with multi-segments, and the identical phase difference (IPD) pattern is used to coordinate the deformation of each actuation segment. The numerical results show that the theoretical model can effectively simulate the locomotion of the robot. Based on the dynamic model, the expression of the critical actuated force of the robot is derived for the IPD pattern. Then, an earthworm-like robot with seven segments is taken as an example to study the influence of the actuation coordination mode on the locomotion performance of the robot. The results show that even with fewer actuation segments, the robot can also realize excellent locomotion performance under reasonable selection of the actuation coordination mode. Finally, the relationship between the locomotion performance of the robot and the parameters including the identical phase difference, the anisotropic friction coefficient, and the axial deformation factor is studied, providing theoretical reference for improving the locomotion performance of the earthworm-like robot in practice.
  • Thermal⁃Electrical⁃Mechanical Coupling Behavior of Segmented Thermoelectric Thin Films under Thermal Shock
    LIU Chang, LIU Yue, XIN Shaojie
    2022, 43(4): 803-811. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.007
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    Based on the separation variable method and the singular integral equation, the thermal-electrical-mechanical coupling behavior of the segmented thermoelectric thin film/substrate under thermal shock is studied and the stress concentration at the edge of the thin film is analyzed. The temperature field and interfacial thermal stress distribution are obtained, and the expressions of stress intensity factors are given. The effects of segmented film dimensions, material parameters and interface leakage behavior on the stress intensity factors are analyzed. The results show that a thinner segmented film thickness corresponds to a lower thermal stress concentration. In order to effectively reduce the interfacial thermal stress concentration, a high Seebeck coefficient, a low thermal conductivity and a low electrical conductivity of thermoelectric thin film at hot side should be selected. In addition, the interface leakage can reduce the interfacial thermal stress. These results can provide theoretical guidance for the structural design and application safety of the thermoelectric thin film devices.
  • Design and Control of Bistable Composite Laminates Based on Shape Memory Alloy Sheet Actuator
    WEI Bin, YUAN Guoqing
    2022, 43(4): 812-823. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.008
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    The bistable characteristics of laminates with special laying sequence opened up a broad space for the development of bistable morphing structures. In this paper, a scheme of using SMA sheet actuator to control bistable composite laminates to complete snap through was proposed. Taking the [02/902] asymmetric laminate as an example, the characteristics of four SMA sheet actuator layout schemes to control the bistable composite laminates to complete snap through were simulated. In the analysis, the repeated phase transition effect was considered to modify the one-dimensional Brinson phenomenological constitutive model of SMA and a UMAT subroutine was developed. The experimental results show that the predicted results have sufficient accuracy. An appropriate selection of the bonding position of SMA actuator can not only effectively control the snap through, but also prevent the structure from experiencing a twisted deformation after excitation. The related achievements can lay an important foundation for the further development of bistable morphing composite aircraft structure based on SMA sheet actuators.
  • Identification Method of Human External Nasal Material Parameters Based on Machine Learning
    CAI Zhen, WAN Yongping, ZHANG Hui
    2022, 43(4): 824-834. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.009
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    Nose Augmentation is a rhinoplasty with implanting the prosthesis as the main method, in order to enhance the appearance. For a long time, the determination of prosthesis size in rhinoplasty depends on the surgeon's personal experience and operational skill. Improper size of implants during surgery may lead to various complications after surgery. In this paper, the external nose of human body is considered as a kind of hyperelastic material, and tensile tests are carried out on the nose skin soft tissue of the subjects. Artificial neural network is used to determine the relationship between the material parameters and the tensile test data, and an identification method of nasal material parameters is proposed based on neural networks. The results of this study are helpful for surgeons to quantitatively understand the skin condition of nose and the safety range of nose soft tissue stretching, and then to determine the size of the prosthesis for rhinoplasty, with increased operation success rate and reduced postoperative complications.
  • Study of Nonlinear Creep Model for Rocks Considering Time-Dependent Damage
    LI Zhongjun, SHENG Dongfa, CHENG Xu, WANG Yinan
    2022, 43(4): 835-843. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.010
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    Under the action of high-stress levels, the internal damage of rocks accumulates with time, and the creep behavior shows evident nonlinearity. It is difficult for the traditional linear element combination model to describe the creep characteristics of the rock acceleration stage. In order to better describe the nonlinear creep characterization of rocks, a modified Nishihara model was obtained by introducing a nonlinear damage body based on the traditional Nishihara model, and the three-dimensional creep equations of the model were derived. Based on the Levenberg-Marquardt algorithm of Origin platform, the triaxial compression creep data of mudstone are used to fit the modified Nishihara model and deduce the model's parameters. The fitting results show that the modified Nishihara model can generate a higher degree of fitting with the test data, with the corresponding correlation coefficients above 0.96. These results indicate that the modified model can comprehensively describe the nonlinear creep characteristics of rocks, verifying the rationality and applicability of the modified Nishihara model.
  • Meshfree Stabilized Collocation Method for the Analysis of Heat Conduction Problem
    WU Fanshu, WANG Lihua, HU Minghao
    2022, 43(4): 844-854. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.011
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    In this paper, a new meshfree stabilized collocation method is introduced to solve the heat conduction problem. The reproducing kernel approximation is utilized as the approximation function in the presented method. The integration in the subdomain corresponding to the collocation point can satisfy the higher order consistency conditions in the integration form, which improves the accuracy and stability of the point collocation method. Numerical examples from one-dimensional to three-dimensional show that, compared with the direct collocation method, the stabilized collocation method can significantly improve the accuracy in solving the heat conduction problems, with stable convergence.
  • A Study of Bedrock Ground Motion Simulation Based on a Site Depth-Dependent Coherency Function
    HONG Na, CHEN Qingjun, ZHAO Zhipeng
    2022, 43(4): 855-862. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.012
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    The determination of bedrock ground motion input is one of the key techniques in the seismic analysis of the underground structures and the soil-structure interaction system. In view of difficulties of the equivalent linearization method in treating the inversion problem of vertical ground motion, here we use the site depth-dependent coherency function model established in our earlier work to investigate the bedrock ground motion histories. In this paper, based on the site depth-dependent coherency function model, the non-stationary bedrock ground motion was obtained using the Kriging difference estimation method with the surface ground motion records as the known condition, which satisfy the above depth-dependent coherency requirement. Subsequently, the calculated bedrock ground motion was compared with the recorded data of surface and bedrock motion selected from KiK-net database, in both time domain and frequency domain, to verify the effectiveness of the proposed method. The results show that the established calculation method for bedrock ground motion based on the site depth-dependent coherency function can well simulate the bedrock motion characteristics in both time and frequency domains. The error of the simulation results mainly occurs in the middle and high frequency bands, compared with the measured records.
  • Analysis of Chloride Diffusion Process in Unsaturated Seepage of Concrete Ground Beam
    WANG Deying, DONG Hongjing, PANG Biao, CHEN Xi, DAI Ying
    2022, 43(4): 863-875. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.013
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    Chloride ion is the main corrosion medium for concrete. The transmission of chloride ion in concrete structures is greatly affected by the unsaturated infiltration of pore water. The unsaturated infiltrating process of pore water in concrete is usually quantitatively described by Richards equation. In this paper, the chloride ion concentration as a function of the saturation degree is approximated and the corresponding analytical expression is obtained by introducing the intermediate variables and Bernstein polynomials based on the explicit solution of Richards equation. The analytical solution is applied to investigate the corrosion process of the concrete ground beams under the coupled effects of unsaturated seepage and chloride diffusion. The validity of the analytical expression is verified by comparison with the finite element results.
  • Investigation on Reissner-Sagoci Problem for Functionally Graded Piezoelectric Coating Based on Laminate Model
    MA Zhanzhou, LIU Tiejun
    2022, 43(4): 876-888. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.014
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    In order to study the Reissner-Sagoci problem for the functionally graded piezoelectric coating with arbitrarily varying material properties under a rigid cylindrical indenter, a laminate model is established to analyze the contact behavior on the coating surface. The Hankle integral transform technique and the transfer matrix method are used to convert the torsional contact problem of functionally graded piezoelectric coatings into the integral equation(s) involving Cauchy singular kernels. The Gauss-Jacobi numerical integration method is used to convert this singular integral equation into a system of linear equations. The stress, displacement and electrical displacement on the surface of the gradient piezoelectric coating with arbitrarily varying material parameters can be obtained by solving the linear equations. The results show that the variation of the gradient functionally graded piezoelectric coating parameters has a significantly impact on the electromechanical response of the Reissner-Sagoci problem. The present results provide a foundation for improving the mechanical properties and suppressing the contact damage and failure of piezoelectric components by designing materials parameters of functional graded piezoelectric materials.
  • Interphase Model for Predicting Effective Properties of Nano-Fiber Composites
    CUI Chunli, FU Lei, XU Yaoling
    2022, 43(4): 889-895. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.015
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    Based on the generalized self-consistent method and the average-field theory, the closed-form solution of the effective antiplane shear modulus of fiber reinforced composites with interphase is derived. The interphase model is used to investigate the effective antiplane shear moduli of nano-fiber composites. Letting the interphase shear moduli be the ratio of the interface shear modulus in the interface model to the interphase thickness, the present interphase model can be analytically degraded to the interface model when the interphase thickness tends to zero. In the numerical calculation, the interphase model can generate the results of the interface model with arbitrary precision as long as the interphase thickness is small enough. Taking the aluminium containing nano voids as an example, the results obtained from the interface model and from the interphase model are compared. It is found that a smaller void radius and a higher void volume fraction result in more significant difference between the two models.
  • Spatial-Temporal Evolution Characteristics of Wind Turbine Wake Based on Mode Decomposition Method
    LIU Ming, WANG Bofu
    2022, 43(4): 896-907. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.016
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    The wake of horizontal axis wind turbine has an important influence on the wind power performance and the fatigue load of downstream wind turbine. In this paper, the large-eddy simulation (LES) with actuator line method (ALM) is used to study the temporal and spatial evolution characteristics of the wake of NREL-5MW wind turbine. From the obtained instantaneous field, it can be seen that the tip vortex evolves into a vortex ring after it develops downstream, and then the vortex ring becomes unstable, resulting in a large number of vortex filaments, which are reconnected to form a small-scale vortex ring, and the small-scale vortex ring is further broken into smaller turbulent structures. It can be seen from the average field that after the flow passes through the wind turbine, the speed decreases abruptly, with the W-shaped speed loss section. As the wake develops downstream, the wake speed gradually recovers and the turbulence intensity gradually increases, until the velocity loss profile at the last five rotor diameters of the wind turbine becomes U-shape, at which the peak value of the turbulence intensity begins to decrease. Through the analysis using the proper orthogonal decomposition method (POD) and the dynamic mode decomposition method (DMD), it is found that the related modes of wind blade rotation and the vortex ring mode can be well captured from the evolution process of wind turbine wake.
  • Hopf Bifurcation and First Passage on Conductive Microbeams
    WANG Haoxiang, WANG Ping, ZHUANG Xuhui
    2022, 43(4): 908-922. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.017
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    We studied stochastic Hopf bifurcations and first passage of conductive microbeams under the influence of electromagnetic and mechanical coupling fields. Based on the modified couple stress theory and magneto-elasticity theory, the motion equation of the conductive microbeam under the influence of electromagnetic and mechanical coupling fields was built, and derived the magneto-elastic random vibration equation of the microbeam. The equations were simplified to nonlinear diffrential dynamics equations according to magnetoelasticity theory and Galerkin variational method. We equivalent the equation to a one-dimensional  stochastic differential equation through the stochastic average theory of no-integrable Hamliton system. Then the local stochastic stability of the system was judged by calculating the maximum Lyapunov exponent of the equation. And the global stability of the system was judged by the singular boundary theory which based on stochastic diffusion process. By discussing the graphical changes of these steady-state probability density function graphs of the system, we got the variation law of the stochastic bifurcation of the dynamical system. And then the calculation results were checked by mathematical software, the Hopf bifurcation phenomenon of the model is obtained, and we discussed the conditions for the system to generate Hopf bifurcation. Finally, the numerical simulation method was used to simulate the condition of the system in the first passage, and the influence of the materials intrinsic factor on the reliability function of the system was analyzed. The results show that the initial energy value, bifurcation value, and material intrinsic coefficient all affect the stability of the microbeam.
  • Sparse Identification of Galloping Model of Iced Quad Bundle Conductors
    CHEN Libing, LIU Xiaohui, WU Chuan, YE Zhongfei, ZHANG Bo
    2022, 43(4): 923-933. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.018
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    The galloping of transmission lines seriously threatens the safety and stability of power system. It is particularly important to accurately establish a galloping model of iced conductor. Therefore, a data-driven sparse identification algorithm is adopted, which can effectively identify the control equations of the dynamic system from the data and reduce the calculation cost. In this paper, the galloping equation of the iced quad bundle conductors is identified based on the data-driven sparse recognition algorithm. Firstly, based on Hamilton's principle, the partial differential galloping equation of the iced quad bundle conductors is derived. Then, the partial differential equation is converted into an ordinary differential equation via the Galerkin method. Next, the aerodynamic load model is established, and the aerodynamic force is introduced into the galloping equation, obtaining the final ordinary differential galloping equation of the iced quad bundle conductors. Finally, the equation data are obtained by numerical simulation and the Sparse Identification of Nonlinear Dynamics (SINDy) algorithm is used to conduct the sparse identification. The results show that the SINDy algorithm can accurately identify galloping equation of the iced quad bundle conductors from the noise-free data. When the noise amplitude of the data derivative is below 0.2, the number of terms of the galloping equation can be correctly identified and the mean error of coefficients is within 0.22 %. Additional terms start to be identified when the noise amplitude of data derivative is above 0.3, which leads to a significant increase in the maximum relative error of the coefficients of the identified cubic nonlinear higher-order terms , reaching 58.78 % at a noise amplitude of 0.5. However, the maximum deviation of the final identified galloping amplitude is only 2.1 %. The identification accuracy of the model can be improved by updating the galloping model through adjusting the sparsity promotion parameter and the time step, which proves the strong adaptability of the SINDy algorithm to the data derivative noise. The results of this paper can provide a certain reference for the establishment of the transmission line galloping model.
  • Wind Resistance Test and Analysis of Folded Aluminum Alloy Sheet
    WU Xiufeng, BAI Xiaolong, DU Bingxun, WANG Hui
    2022, 43(4): 934-945. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.019
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    The indoor wind pressure tests of the new open aluminum curtain wall based on the rain curtain, the pressure balance principle and the hanging design are carried out. The mechanical characteristics of the vertical long folded aluminum alloy sheet in the open aluminum curtain wall are studied. In order to fully study the effects of hem width, stiffener layout, stiffener section characteristics and aluminum plate thickness on the wind resistance of vertical long hem aluminum alloy sheet, a finite element model is established via Abaqus software and numerical analysis is carried out. The stiffness is calculated using the sheet calculation formula in JGJ 133-2001 Technical Code for Metal and Stone Curtain Wall Engineering. The results show that: under the load of ±3 kPa wind pressure, the open aluminum curtain wall is in the elastic stage. The arrangement of stiffeners, section characteristics and panel thickness have obvious effects on the bending stiffness and strength of vertical long folded aluminum alloy sheet, while the folding width has no obvious effect. In practical application, the existing calculation formula of large deflection of thin plate can be modified. This research can provide reference for the application in engineering practice.
  • Dynamic Characteristics of Continuous Cracked Beam on Winkler Foundation
    XIAO Wanqi, LIU Xin, YANG Xiao
    2022, 43(4): 946-957. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.020
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    Based on the massless linear torsional spring model of open crack in beam, the dynamic governing differential equation of continuous cracked Euler-Bernoulli beam on Winkler foundation was established, and a simple method for solving its dynamic characteristics was presented. The characteristic equation of natural frequency and the unified explicit analytical expression of vibration mode of continuous Euler-Bernoulli beam with arbitrary number of cracks on Winkler foundation were obtained. Based on this, the dynamic characteristics of simply supported two equi-span continuous crack beams on Winkler foundation were studied numerically, and the influences of beam's length-height ratio, crack depth, crack location and crack number on the dynamic characteristics of continuous cracked beams were revealed. It is revealed that the natural frequencies and the modes of the continuous cracked beam depend on the foundation reaction coefficient, the crack location and depth. When the bending moment is zero at the crack location, the crack has no effect on the natural frequency and mode. Furthermore, the natural frequency increases as the foundation reaction coefficient increases, and decreases as the depth and number of cracks increase. These results can provide guidance for the evaluation of structural safety.
  • Viscoelastic Analysis of Deformation of the Existing Tunnel Due to the Above-Crossing Tunneling
    CHEN Huadong, SHEN Wenming, ZHANG Wenjie
    2022, 43(4): 958-969. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.021
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    To study the deformation of existing tunnel caused by the construction of new tunnel in soft ground, the existing tunnel was considered as an Euler-Bernoulli beam resting on a Pasternak viscoelastic foundation. Considering the viscoelastic properties of the foundation, a viscoelastic solution for the structural deformation of existing tunnel was derived by applying the two-stage method and the Laplace transform. The results were also compared with the results of field measurements and numerical simulations, and the influence of the relevant parameters on the deformation of the existing tunnel was analyzed according to the theoretical solution. The results show that the deformation of the existing tunnel develops with time after the excavation is completed, and takes around 120 d to reach a steady state. The rheological deformation of the tunnel structure accounts for about 23.1 % of the total deformation at the completion of the construction in this case. The increase in excavation width, elastic body (H-body) shear modulus and the decrease in the burial depth of the existing tunnel axis lead to an increase in the rheological deformation. More time is required for the deformation of existing tunnel to reach stable stage for larger viscosity coefficient, but there is no significant difference in the final deformation of the tunnel structure for different viscosity coefficients.
  • Research on Support Deformation and Stress Characteristics of CRD Tunnelling Method in Weakly Sandstone Aquifer
    QU Wenbin
    2022, 43(4): 970-981. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.022
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    The stratum is loose and steady ability is poor in weakly cemented sandstone aquifer tunnels, making tunnel construction difficult. To study the safety of CRD construction and provide reference for similar projects, the field monitoring and numerical simulation are used to study the influence of the proportion of weakly cemented sandstone on the deformation and stress of the initial branch. The safety of CRD construction method in the weakly cemented sandstone formation is also analyzed. The results show that the pressures at the spandrels of the tunnel are large, and the selection of lateral pressure coefficient should be paid special attention to in the design. When the excavation surface is weakly cemented sandstone, the initial support deformation and the stress are increased by 20 %~25 % compared with those of pebble sand case. The horizontal convergences of the tunnel spandrel and arch foot are small, and the settlement of arch crown and the uplift of arch bottom are large. The stress on the inner side of arch frame is slightly greater than that on the outer side, but both are less than the safety limit specified in the regulations. It shows that the tunnel construction in weakly cemented sandstone stratum by CRD method can ensure the safety of lining. The research results can provide reference for the selection, layout and support time of the steel arch frame in similar projects.
  • Application of Reciprocal Theorem of Work in Bending of Rectangular Plates Supported at Four Corners
    CHEN Yingjie, LIU Huanting, CUI Peng
    2022, 43(4): 982-991. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.023
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    In recent years, the collapse accidents of concrete slab beamless floor system occurred frequently in China, causing much attention to the bending problem of the rectangular plate supported by four corners represented by the concrete slab beamless floor system. In this paper, the reciprocal theorem of work is used to solve the bending problem of rectangular plate supported at four corners. The deflection surface equation and the execution equation of rectangular plate supported at four corners under the uniform load, the uniform moment and the linear distribution load are derived respectively. Then, the deflection results obtained under different loads are compared with the Ansys finite element simulation results. It shows that the proposed method is universal and effective in solving the bending problem of rectangular plate supported at four corners, providing a new approach for solving the bending problem of rectangular plate supported at four corners represented by the beamless floor. This work has considerable value of engineering application.
  • Classical Expressions for Bending Solutions of Thick Beams
    WAN Zeqing, LI Shirong
    2022, 43(4): 992-1000. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.024
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    The classical Euler-Bernoulli (E-B) beam theory is simple and easy to use, and has a good accuracy in predicting the deformation of thin beams. However, it will have a significant error in estimating the deformation of thick beams because it neglects the effects of transverse shear deformations on the bending solutions. Based on the refined beam theory, a general shear stress shape function is introduced, and the deflection of the beam is divided into the bending and shearing parts. Using the Levinson beam theory, the governing equations in terms of displacements for static bending of thick beams with rectangular cross sections are established. Then, by using the reciprocal relation of loads, the general solutions for the Levinson beams expressed by the deflections of the related E-B beams with the same loadings and end constraints are derived. As a result, the classical expression of solutions based on the higher-order shear deformation beam theories is realized, which simplifies the solution of complex bending-shearing coupling problem into the calculations of two dimensionless coefficients together with the determination of the integrating constants under the specified boundary conditions, since the solutions of E-B beam for different loadings and end constraints can be easily found in the text books of Strength of Materials. Two examples are given to quantitatively analyze the influence of the slenderness ratio and the shear stress shape function on the deflection. The results show that the deflection values corresponding to different shear stress shape functions have little difference from each other. Solutions presented in this paper can be conveniently applied to the static bending analysis of thick beams.
  • Comparative Study of Concrete Constitutive Models in the Ultimate Behavior Analysis of RC Shell Structures Based on Layered Elements
    ZHANG Junfeng, JIA Jilong, XU Shiyao, ZHU Bing, LIU Qingshuai
    2022, 43(4): 1001-1010. https://doi.org/10.15959/j.cnki.0254-0053.2022.04.025
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    This study was initiated for identifying the applicability and the parameter determination of applying concrete constitutive models in the analysis of the static ultimate behaviors of Reinforced Concrete (RC) shell structures based on layered elements in Abaqus. The smeared crack model (SCCM) and concrete damaged plasticity model (CDPM) were employed in the simulations of two RC plates and a RC cooling tower respectively, and the main features and parameters of the two constitutive models were identified. The results show that both concrete constitutive models are applicable to the analysis of the static ultimate behaviors of RC shell structures based on the layered elements in Abaqus. The tension stiffening parameter TS in SCCM has no influence on the cracking load, but plays a crucial role for the load and displacement results under the yielding or ultimate conditions. The corresponding loads and displacements generally increase with the TS value, and are also influenced by the structure type and the reinforcement ratio. The discrepancy between the two models is mainly reflected in the post-cracking stage. SCCM with TS=10 gives the load-displacement curve close to that of the damage plasticity model. However, CDPM endows the structures with larger ductility due to its larger ultimate strain, thus can better simulate the complete ultimate behaviors of RC structures. On the other hand, SCCM with TS=10 may be unable to capture the complete structure failure process after reinforcement yielding unless a bigger TS is employed.