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Engineering Mechanics
Since 1984 Monthly
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Chief Editor:Xinzheng LU
Editor & Publisher:《 》杂志社
ISSN 1000-4750CN 11-2595/O3
Articles online first have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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2023 No. 12, Publish Date: 2023-12-07
Display Method:
2023, 40(12): 1-12.
doi:10.6052/j.issn.1000-4750.2022.02.0156
Abstract:
A semi-analytical solution for the dynamic response of a flexible pavement structure on an anisotropic layered foundation under a moving load is proposed. Based on the theory of soil-structure interaction, a road-foundation coupling model for the flexible pavement and layered foundation is established. A wavenumber finite element model is established for the near-field road structure. Based on the precise integration and spectral element method, a novel spectral element model is established for the far-field foundation. According to the substructure method, the boundary conditions at near-far field coupling interface are determined, and the near-field and far-field structures are coupled together. Using fast Fourier transform, the dynamic response of the flexible pavement in the time and space domain can be obtained. The proposed method can consider the geometric characteristics of the road structure and take the stratification and anisotropy of foundation into account. The dimension of the near-field wavenumber finite element model is not affected by the number and thickness of foundation layers, and the computational result is stable. Both the validity and rationality of the proposed method are verified by comparing with the analytical solutions. Numerical examples are presented to reflect the difference between the dynamic responses obtained by using the road-foundation coupling model and previous overall layered model, and the effect of elastic modulus of road layer is also discussed.
A semi-analytical solution for the dynamic response of a flexible pavement structure on an anisotropic layered foundation under a moving load is proposed. Based on the theory of soil-structure interaction, a road-foundation coupling model for the flexible pavement and layered foundation is established. A wavenumber finite element model is established for the near-field road structure. Based on the precise integration and spectral element method, a novel spectral element model is established for the far-field foundation. According to the substructure method, the boundary conditions at near-far field coupling interface are determined, and the near-field and far-field structures are coupled together. Using fast Fourier transform, the dynamic response of the flexible pavement in the time and space domain can be obtained. The proposed method can consider the geometric characteristics of the road structure and take the stratification and anisotropy of foundation into account. The dimension of the near-field wavenumber finite element model is not affected by the number and thickness of foundation layers, and the computational result is stable. Both the validity and rationality of the proposed method are verified by comparing with the analytical solutions. Numerical examples are presented to reflect the difference between the dynamic responses obtained by using the road-foundation coupling model and previous overall layered model, and the effect of elastic modulus of road layer is also discussed.
2023, 40(12): 13-27.
doi:10.6052/j.issn.1000-4750.2022.02.0179
Abstract:
Aiming at the problem of velocity and displacement distortion after integration caused by error trend term in acceleration signal tested in explosion test, the velocity and displacement after integration were reconstructed by removing the trend term of explosion acceleration based on least square fitting, wavelet decomposition and EEMD (Ensemble Empirical Mode Decomposition). The research shows that: The fitting order of the least square method, the number of decomposition layers of the wavelet decomposition method and, the standard deviation of the white noise of EEMD method have great influence on the reconstruction speed and displacement amplitude. A new method is proposed to evaluate the trend term correction results by using the spectral deviation indexs2and the mean deviation indexS2, and the appropriate order, decomposition level and white noise standard deviation can be selected through the joint analysis of the frequency distribution and integral time history characteristics of the deviationS2to accurately remove the trend term in the signal. Compared with the explosion test results, it is proved that the three methods can restore the motion trend and residual displacement characteristics under the impact of explosion, and the wavelet decomposition method has some advantages.
Aiming at the problem of velocity and displacement distortion after integration caused by error trend term in acceleration signal tested in explosion test, the velocity and displacement after integration were reconstructed by removing the trend term of explosion acceleration based on least square fitting, wavelet decomposition and EEMD (Ensemble Empirical Mode Decomposition). The research shows that: The fitting order of the least square method, the number of decomposition layers of the wavelet decomposition method and, the standard deviation of the white noise of EEMD method have great influence on the reconstruction speed and displacement amplitude. A new method is proposed to evaluate the trend term correction results by using the spectral deviation indexs2and the mean deviation indexS2, and the appropriate order, decomposition level and white noise standard deviation can be selected through the joint analysis of the frequency distribution and integral time history characteristics of the deviationS2to accurately remove the trend term in the signal. Compared with the explosion test results, it is proved that the three methods can restore the motion trend and residual displacement characteristics under the impact of explosion, and the wavelet decomposition method has some advantages.
2023, 40(12): 28-40.
doi:10.6052/j.issn.1000-4750.2022.02.0129
Abstract:
To promote the development of cold-formed thin-walled steel structures from low-rise system to multi-storey system, a new form of cold-formed thin-walled steel tube end studs shear wall covered steel plate was proposed. Technical problems such as insufficient shear capacity of traditional shear wall, easy buckling and local bearing failure of end studs were solved, so as to achieve the design principle of "strong end studs, weak wall sheathings". The shear performance of shear wall was studied by horizontal low-cycle cyclic loading test. The test results show that the failure mode of steel tube end studs shear wall covered steel plate is sheet diaphragm effect invalidation caused by screw connection failure around the steel plate. And there is no buckling occurring on the steel tube end studs. The shear bearing capacity, lateral stiffness, ductility and energy dissipation capacity of shear wall can be improved as well as the steel plate tension strip is fully developed by reducing the spacing of self-tapping screws around the shear wall. The shear performance of steel tube steel plate self-tapping screw connection specimens was studied. The results show that the failure characteristics of the screw connection specimens are pore wall bearing failure of steel plate. The shear capacity of self-tapping screw group connection have group reduction effect. Based on shear test results of shear walls and self-tapping screw connection specimens, the calculation methods of shear capacity and lateral stiffness of steel tube end studs shear wall covered steel plate were proposed. The research results provide reliable bases for theoretical research and engineering application of multi-storey cold-formed thin-walled steel structural system.
To promote the development of cold-formed thin-walled steel structures from low-rise system to multi-storey system, a new form of cold-formed thin-walled steel tube end studs shear wall covered steel plate was proposed. Technical problems such as insufficient shear capacity of traditional shear wall, easy buckling and local bearing failure of end studs were solved, so as to achieve the design principle of "strong end studs, weak wall sheathings". The shear performance of shear wall was studied by horizontal low-cycle cyclic loading test. The test results show that the failure mode of steel tube end studs shear wall covered steel plate is sheet diaphragm effect invalidation caused by screw connection failure around the steel plate. And there is no buckling occurring on the steel tube end studs. The shear bearing capacity, lateral stiffness, ductility and energy dissipation capacity of shear wall can be improved as well as the steel plate tension strip is fully developed by reducing the spacing of self-tapping screws around the shear wall. The shear performance of steel tube steel plate self-tapping screw connection specimens was studied. The results show that the failure characteristics of the screw connection specimens are pore wall bearing failure of steel plate. The shear capacity of self-tapping screw group connection have group reduction effect. Based on shear test results of shear walls and self-tapping screw connection specimens, the calculation methods of shear capacity and lateral stiffness of steel tube end studs shear wall covered steel plate were proposed. The research results provide reliable bases for theoretical research and engineering application of multi-storey cold-formed thin-walled steel structural system.
2023, 40(12): 41-54.
doi:10.6052/j.issn.1000-4750.2022.02.0171
Abstract:
Study of seismic behavior of Zhutou Puzuo with “Ang” lays critical foundations for insight into the seismic performance of Yingxian Wood Pagoda. To explore deforming behavior and seismic performance of Zhutou Puzuo with “Ang”, two scaled models derived from Yingxian Wood Pagoda at 1∶3.7 were designed and manufactured. Low cyclic-reversed loading experiments under different vertical loads were carried out. Based on the analysis of hysteretic curve, of skeleton curve, and of equivalent viscous damping coefficient, the effects of different loads on the above relevant seismic behavior indexes were clarified as following: Increasing vertical load hardly to change deformation features of this kind of Puzuo, but it would result in much more asymmetric performance in hysteretic curve and remarkable improvement on all Puzuo's relative properties. The vertical load increased 3.7 times, the horizontal bearing capacity increased 2.2 times and 2.9 times in positive and negative directions, the initial stiffness increased 2.4 times, and the dissipated energy increased 3.0 times. In addition, raising vertical load changed the position where the initial slip occurred at early stage of test. But it changed neither mode of accumulating slip nor the weaken positions. However, the Puzuo's finial slip pattern remained similar, which mainly performed as slipping between two Huagongs. A simplified model for the displacement-bearing capacity of the Puzuo was proposed. The influence coefficientsβkandβFof different vertical loads were obtained according to fit the data of these two tests, and the coefficients were able to modify the initial stiffnesskof the simplified skeleton curve model under different loads.
Study of seismic behavior of Zhutou Puzuo with “Ang” lays critical foundations for insight into the seismic performance of Yingxian Wood Pagoda. To explore deforming behavior and seismic performance of Zhutou Puzuo with “Ang”, two scaled models derived from Yingxian Wood Pagoda at 1∶3.7 were designed and manufactured. Low cyclic-reversed loading experiments under different vertical loads were carried out. Based on the analysis of hysteretic curve, of skeleton curve, and of equivalent viscous damping coefficient, the effects of different loads on the above relevant seismic behavior indexes were clarified as following: Increasing vertical load hardly to change deformation features of this kind of Puzuo, but it would result in much more asymmetric performance in hysteretic curve and remarkable improvement on all Puzuo's relative properties. The vertical load increased 3.7 times, the horizontal bearing capacity increased 2.2 times and 2.9 times in positive and negative directions, the initial stiffness increased 2.4 times, and the dissipated energy increased 3.0 times. In addition, raising vertical load changed the position where the initial slip occurred at early stage of test. But it changed neither mode of accumulating slip nor the weaken positions. However, the Puzuo's finial slip pattern remained similar, which mainly performed as slipping between two Huagongs. A simplified model for the displacement-bearing capacity of the Puzuo was proposed. The influence coefficientsβkandβFof different vertical loads were obtained according to fit the data of these two tests, and the coefficients were able to modify the initial stiffnesskof the simplified skeleton curve model under different loads.
2023, 40(12): 55-64.
doi:10.6052/j.issn.1000-4750.2022.02.0142
Abstract:
Data and features are the foundation of intelligent technologies, but the existing literature on structural intelligent computation rarely covers data-side related studies. Therefore, the research on feature engineering of intelligent computation in civil engineering was carried out, which automatically nondimensionalize the raw data of structural problems and transform them into effective features, thus improving the performance of the model. A feature engineering architecture independent of the downstream intelligent computation models was established. The input structural features were automatically nondimensionalized by introducing a dimensionless preprocessing net based on dimensional analysis and using logarithmic activation functions. On this basis, an algorithm was proposed to interpret the physical meaning of the dimensionless parameters obtained by model training, which could perform the factor analysis on the input data and enhance the physical interpretability of the model. In order to validate the proposed model and algorithm, numerical experiments regarding the biaxial bending of reinforced concrete columns were conducted. Compared with the control model without feature engineering, this architecture could speed up the model convergence rate by 4~5 times and improve the prediction accuracy rate by 20%~50%. At the same time, the dimensionless parameters reproduced by the physical meaning interpretation algorithm were highly consistent with the classical theoretical analysis conclusions, which proved that the feature engineering architecture successfully captured the influencing factors closely related to the target problem.
Data and features are the foundation of intelligent technologies, but the existing literature on structural intelligent computation rarely covers data-side related studies. Therefore, the research on feature engineering of intelligent computation in civil engineering was carried out, which automatically nondimensionalize the raw data of structural problems and transform them into effective features, thus improving the performance of the model. A feature engineering architecture independent of the downstream intelligent computation models was established. The input structural features were automatically nondimensionalized by introducing a dimensionless preprocessing net based on dimensional analysis and using logarithmic activation functions. On this basis, an algorithm was proposed to interpret the physical meaning of the dimensionless parameters obtained by model training, which could perform the factor analysis on the input data and enhance the physical interpretability of the model. In order to validate the proposed model and algorithm, numerical experiments regarding the biaxial bending of reinforced concrete columns were conducted. Compared with the control model without feature engineering, this architecture could speed up the model convergence rate by 4~5 times and improve the prediction accuracy rate by 20%~50%. At the same time, the dimensionless parameters reproduced by the physical meaning interpretation algorithm were highly consistent with the classical theoretical analysis conclusions, which proved that the feature engineering architecture successfully captured the influencing factors closely related to the target problem.
2023, 40(12): 65-75.
doi:10.6052/j.issn.1000-4750.2022.02.0145
Abstract:
The water dynamics and their effects on the different direction vibrations of facility are complicated and difficult to compensate during underwater shaking table tests. As a result, before conducting the tests, it is necessary to confirm the capacity and accuracy of facility. This paper investigated the effect of several factors on the coupling control performance of a hydrodynamic-shaking table, such as water depth, excitation frequency, and movement directions. The transfer function model for the water-shaking table system is firstly identified using measured data, and then a data-driven hybrid control strategy is proposed, combining model-based feedforward compensation and reinforcement learning (RL). The Actor-Critic networks in RL are trained offline using the error data of displacement commands according to the DDPG algorithm, and they are utilized to compensate the model-based commands in real-time. By comparing with the feedforward compensation, 50 test cases were conducted, considering different water depths, excitation frequency and shaking directions, to validate the method and to evaluate its performance. The results reveal that: the control performance decreases with the increase of water depth and excitation frequency; the water depth has a greater impact on the vertical motion of a shaking table. Under the most unfavorable condition of the vertical motion with a water depth of 2m, the proposed method enhanced the performance with 6.54% and 7.52% for indicatorsJ1andJ2, respectively. The proposed method has an optimized time-delay compensation effect when considering the nonlinear dynamics of the water-shaking table interaction system, and it is also a broadband compensation technique.
The water dynamics and their effects on the different direction vibrations of facility are complicated and difficult to compensate during underwater shaking table tests. As a result, before conducting the tests, it is necessary to confirm the capacity and accuracy of facility. This paper investigated the effect of several factors on the coupling control performance of a hydrodynamic-shaking table, such as water depth, excitation frequency, and movement directions. The transfer function model for the water-shaking table system is firstly identified using measured data, and then a data-driven hybrid control strategy is proposed, combining model-based feedforward compensation and reinforcement learning (RL). The Actor-Critic networks in RL are trained offline using the error data of displacement commands according to the DDPG algorithm, and they are utilized to compensate the model-based commands in real-time. By comparing with the feedforward compensation, 50 test cases were conducted, considering different water depths, excitation frequency and shaking directions, to validate the method and to evaluate its performance. The results reveal that: the control performance decreases with the increase of water depth and excitation frequency; the water depth has a greater impact on the vertical motion of a shaking table. Under the most unfavorable condition of the vertical motion with a water depth of 2m, the proposed method enhanced the performance with 6.54% and 7.52% for indicatorsJ1andJ2, respectively. The proposed method has an optimized time-delay compensation effect when considering the nonlinear dynamics of the water-shaking table interaction system, and it is also a broadband compensation technique.
2023, 40(12): 76-88.
doi:10.6052/j.issn.1000-4750.2022.02.0146
Abstract:
An experimental research was conducted on seismic behavior of stiffened thin steel plate shear walls (SPSWs) considering the effect of vertical load on frame column. Two full-scale rectangular concrete-filled steel tube columns-stiffened thin steel plate shear specimens were tested under low-cycle reverse load. The design of specimens considers two cases of vertical stiffeners with equal spacing and variable spacing. The test results show that the specimens have good ductility and energy consumption capacity when the frame columns are subjected to high axial pressure. The ultimate drift angle of the specimens reaches 1/30. The plastic deformation of the specimens is mainly manifested as the out-of-plane buckling, which satisfies the design concept of “strong column and weak beam”. The arrangement of the stiffeners has no obvious influence on the seismic performance of the specimens. The nonlinear finite element method is further used to study the influence of initial defects and axial compression ratio on the lateral resistance performance of the specimen. The analysis results show that the initial defect distribution mode of the wall and the out-of-plane deflection amplitude have little effect on the pushover curve of the specimens. When the axial compression ratio of the frame column is greater than 0.7, the bearing capacity and deformation capacity of the specimens are reduced. Based on the shear control failure characteristics of the specimens, the calculation method of the specimen’s shear capacity is given. The calculated value is in good agreement with the finite element simulation value, and it is conservative than the experimental value.
An experimental research was conducted on seismic behavior of stiffened thin steel plate shear walls (SPSWs) considering the effect of vertical load on frame column. Two full-scale rectangular concrete-filled steel tube columns-stiffened thin steel plate shear specimens were tested under low-cycle reverse load. The design of specimens considers two cases of vertical stiffeners with equal spacing and variable spacing. The test results show that the specimens have good ductility and energy consumption capacity when the frame columns are subjected to high axial pressure. The ultimate drift angle of the specimens reaches 1/30. The plastic deformation of the specimens is mainly manifested as the out-of-plane buckling, which satisfies the design concept of “strong column and weak beam”. The arrangement of the stiffeners has no obvious influence on the seismic performance of the specimens. The nonlinear finite element method is further used to study the influence of initial defects and axial compression ratio on the lateral resistance performance of the specimen. The analysis results show that the initial defect distribution mode of the wall and the out-of-plane deflection amplitude have little effect on the pushover curve of the specimens. When the axial compression ratio of the frame column is greater than 0.7, the bearing capacity and deformation capacity of the specimens are reduced. Based on the shear control failure characteristics of the specimens, the calculation method of the specimen’s shear capacity is given. The calculated value is in good agreement with the finite element simulation value, and it is conservative than the experimental value.
SEISMIC BEHAVIOR OF ECCENTRIC GRAVITY COLUMN-CORE WALL SYSTEM SUBJECTED TO PULSE-LIKE GROUND MOTIONS
2023, 40(12): 89-98, 132.
doi:10.6052/j.issn.1000-4750.2022.02.0153
Abstract:
The effects of the pulse-like ground motion and structural eccentricity on the seismic response of a new gravity column-core wall structural system are investigated. Based on the earthquake shaking table test, the rationality of parameter setting is verified using CANNY software. Gravity column-core wall structures with mass eccentricity and different height are designed, and 10 pulse-like and 10 corresponding non-pulse-like ground motion records are selected as the input. The dynamic time-history analysis is conducted to these eccentric systems upon employing CANNY. The effects of the velocity pulse and the eccentricity on the structural seismic response are systematically studied. The results show that: the elastic and elastic-plastic inter-story drift, shear force, and torsional and rotational angles of each eccentric system for pulse-like cases are significantly higher than those for non-pulse cases. The increasing effect of the elastic-plastic cases is more obvious than that of the elastic cases, and the increasing effect of the deformation is more significant than that of the force. With the increase of eccentricity, the elastic and elastic-plastic inter-story drift, and torsional and rotational angles increase, while the inter-story shear decreases. The results of incremental dynamic analysis also show that the eccentricity and velocity pulse effects will significantly increase the inter-story drift. It is suggested that the coupling effect of pulse-like ground motion and eccentricity on the seismic response should be fully considered in the seismic design of the new gravity column-core wall structure.
The effects of the pulse-like ground motion and structural eccentricity on the seismic response of a new gravity column-core wall structural system are investigated. Based on the earthquake shaking table test, the rationality of parameter setting is verified using CANNY software. Gravity column-core wall structures with mass eccentricity and different height are designed, and 10 pulse-like and 10 corresponding non-pulse-like ground motion records are selected as the input. The dynamic time-history analysis is conducted to these eccentric systems upon employing CANNY. The effects of the velocity pulse and the eccentricity on the structural seismic response are systematically studied. The results show that: the elastic and elastic-plastic inter-story drift, shear force, and torsional and rotational angles of each eccentric system for pulse-like cases are significantly higher than those for non-pulse cases. The increasing effect of the elastic-plastic cases is more obvious than that of the elastic cases, and the increasing effect of the deformation is more significant than that of the force. With the increase of eccentricity, the elastic and elastic-plastic inter-story drift, and torsional and rotational angles increase, while the inter-story shear decreases. The results of incremental dynamic analysis also show that the eccentricity and velocity pulse effects will significantly increase the inter-story drift. It is suggested that the coupling effect of pulse-like ground motion and eccentricity on the seismic response should be fully considered in the seismic design of the new gravity column-core wall structure.
2023, 40(12): 99-112.
doi:10.6052/j.issn.1000-4750.2022.02.0154
Abstract:
Urban water distribution network is an important part of lifeline engineering. With the development of the research and construction of resilient cities, it becomes a practical need to re-examine the comprehensive disaster prevention and mitigation capability of water distribution networks from the perspective of resilient cities and to establish a quantitative resilience assessment method that can effectively reflect the post-earthquake recovery process of water distribution networks. A characterization of the four-stage recovery process of water distribution networks after an earthquake was proposed based on the investigation of the typical post-earthquake recovery process of water distribution networks. Then, a dynamic seismic resilience assessment method for water distribution networks at the emergency and relief stages was proposed based on system dynamics theory. This method can not only effectively reflect the changing characteristics of water demand requirements from crowd and fire after an earthquake disaster, but also effectively assess the impact of rescue resources on the functional recovery of the network, and finally realize the dynamic seismic resilience assessment of the water distribution network.
Urban water distribution network is an important part of lifeline engineering. With the development of the research and construction of resilient cities, it becomes a practical need to re-examine the comprehensive disaster prevention and mitigation capability of water distribution networks from the perspective of resilient cities and to establish a quantitative resilience assessment method that can effectively reflect the post-earthquake recovery process of water distribution networks. A characterization of the four-stage recovery process of water distribution networks after an earthquake was proposed based on the investigation of the typical post-earthquake recovery process of water distribution networks. Then, a dynamic seismic resilience assessment method for water distribution networks at the emergency and relief stages was proposed based on system dynamics theory. This method can not only effectively reflect the changing characteristics of water demand requirements from crowd and fire after an earthquake disaster, but also effectively assess the impact of rescue resources on the functional recovery of the network, and finally realize the dynamic seismic resilience assessment of the water distribution network.
2023, 40(12): 113-123.
doi:10.6052/j.issn.1000-4750.2022.02.0157
Abstract:
To study the fire response of stay cable in open space, a heat transfer calculation method of cable cavity near open-air fire is established, considering the spatial radiation theory of fire source and environmental heat transfer boundary of cable surface, combined with three basic heat transfer theories of internal cavity radiation, contact conduction and interstitial heat conduction. And the accuracy of the numerical analysis model is verified through experimental results. The time-space distribution characteristics of temperature field and stress field, together with the time-varying characteristics of axial force and bending moment, of cross-section in prestressed cable are analysed under different internal heat transfer modes, different wrapping conditions and different wind conditions. The analysis results show that the transient temperature distribution of cable cross-section near open-air fire can be calculated accurately taking into account the complete cavity heat transfer model when analysing fire response of the cable. The temperature and stress distributions of cross-section in cable present anti-symmetric state and exhibit an approximation from quadratic distribution characteristics to linear distribution characteristics with the increase of fire exposure time, and axial force loss and bending moment effect can occur in the cable cross-section. Compared with the complete cavity heat transfer model, the round steel heat transfer model has a uniform cross-section stress distribution, larger axial force loss and much smaller bending moment effect. The cavity radiation model has an overly concentrated cross-section stress distribution, larger bending moment effect and smaller axial force loss. The smoke-wrapped condition can exacerbate loss of axial force and weaken bending moment effect in the cable cross-section. The windward condition can seriously aggravate loss of axial force and bending moment effect in the cable cross-section. The research results can provide a theoretical basis for the fire-resistant design and protection of cable structures.
To study the fire response of stay cable in open space, a heat transfer calculation method of cable cavity near open-air fire is established, considering the spatial radiation theory of fire source and environmental heat transfer boundary of cable surface, combined with three basic heat transfer theories of internal cavity radiation, contact conduction and interstitial heat conduction. And the accuracy of the numerical analysis model is verified through experimental results. The time-space distribution characteristics of temperature field and stress field, together with the time-varying characteristics of axial force and bending moment, of cross-section in prestressed cable are analysed under different internal heat transfer modes, different wrapping conditions and different wind conditions. The analysis results show that the transient temperature distribution of cable cross-section near open-air fire can be calculated accurately taking into account the complete cavity heat transfer model when analysing fire response of the cable. The temperature and stress distributions of cross-section in cable present anti-symmetric state and exhibit an approximation from quadratic distribution characteristics to linear distribution characteristics with the increase of fire exposure time, and axial force loss and bending moment effect can occur in the cable cross-section. Compared with the complete cavity heat transfer model, the round steel heat transfer model has a uniform cross-section stress distribution, larger axial force loss and much smaller bending moment effect. The cavity radiation model has an overly concentrated cross-section stress distribution, larger bending moment effect and smaller axial force loss. The smoke-wrapped condition can exacerbate loss of axial force and weaken bending moment effect in the cable cross-section. The windward condition can seriously aggravate loss of axial force and bending moment effect in the cable cross-section. The research results can provide a theoretical basis for the fire-resistant design and protection of cable structures.
2023, 40(12): 124-132.
doi:10.6052/j.issn.1000-4750.2022.02.0160
Abstract:
Under time-varying conditions, the key points of risk decision-making are important for structural performance assessment and lifetime estimation when considering structural accumulation damage. However, the calculation of structural cumulative damage is usually involved in complex mathematical operations. Based on this, the main purpose of this paper is to propose a simplified model for estimating the structural lifetime distribution in the seismic high-incidence region. The model assumes that the cumulative damage of an existing structure is only caused by a series of earthquake actions that may occur during the design reference period. And the advantage of this method is that the structural life can be estimated by simple mathematical operation. An example application is performed on the proposed simplified structural lifetime model to verify the feasibility of the method.
Under time-varying conditions, the key points of risk decision-making are important for structural performance assessment and lifetime estimation when considering structural accumulation damage. However, the calculation of structural cumulative damage is usually involved in complex mathematical operations. Based on this, the main purpose of this paper is to propose a simplified model for estimating the structural lifetime distribution in the seismic high-incidence region. The model assumes that the cumulative damage of an existing structure is only caused by a series of earthquake actions that may occur during the design reference period. And the advantage of this method is that the structural life can be estimated by simple mathematical operation. An example application is performed on the proposed simplified structural lifetime model to verify the feasibility of the method.
2023, 40(12): 133-147.
doi:10.6052/j.issn.1000-4750.2022.02.0166
Abstract:
The fracture of steel components may result in progressive collapse of a steel structure in fire events. Understanding the temperature-dependent fracture behavior of steel materials is the basis for investigating fire resistance of steel structures and for assessing their post-fire safety. Tensile fracture tests were thusly carried out on smooth and notched round specimens made of Q355 steel under different stages of fire including a heating stage, a cooling stage, and a post-fire stage. The influence of stress state (stress triaxiality) and temperature experience (peak experienced temperature and target temperature) on the engineering/true stress-strain behavior and fracture strain are studied. The micro fracture mechanism is investigated by scanning electron microscope. A fracture model is calibrated upon the test and numerical results. It is found that Q355 steel exhibit ductile fracture behavior in fire, which is greatly affected by the stress triaxiality and temperature experience. The higher the peak and target temperatures, the greater the fracture strain and the better the ductility. The post-fire fracture behavior is similar to that at ambient temperature. The stress triaxiality may affect the sensitivity of fracture behavior of materials to the temperature, while the temperature experience has an influence on the plastic stage of the true stress-strain curve. The SMCS fracture model can accurately predict the fracture behavior of Q355 steel during the whole process of a fire accident, where different parameters should be used to model the fracture behavior for the heating and cooling stages.
The fracture of steel components may result in progressive collapse of a steel structure in fire events. Understanding the temperature-dependent fracture behavior of steel materials is the basis for investigating fire resistance of steel structures and for assessing their post-fire safety. Tensile fracture tests were thusly carried out on smooth and notched round specimens made of Q355 steel under different stages of fire including a heating stage, a cooling stage, and a post-fire stage. The influence of stress state (stress triaxiality) and temperature experience (peak experienced temperature and target temperature) on the engineering/true stress-strain behavior and fracture strain are studied. The micro fracture mechanism is investigated by scanning electron microscope. A fracture model is calibrated upon the test and numerical results. It is found that Q355 steel exhibit ductile fracture behavior in fire, which is greatly affected by the stress triaxiality and temperature experience. The higher the peak and target temperatures, the greater the fracture strain and the better the ductility. The post-fire fracture behavior is similar to that at ambient temperature. The stress triaxiality may affect the sensitivity of fracture behavior of materials to the temperature, while the temperature experience has an influence on the plastic stage of the true stress-strain curve. The SMCS fracture model can accurately predict the fracture behavior of Q355 steel during the whole process of a fire accident, where different parameters should be used to model the fracture behavior for the heating and cooling stages.
2023, 40(12): 148-159.
doi:10.6052/j.issn.1000-4750.2023.05.0360
Abstract:
Efficient methods for incorporating engineering experience into the intelligent generation and optimization of shear wall structures are lacking, hindering intelligent design performance assessment and enhancement. This study introduces an assessment method used in the intelligent design and optimization of shear wall structures that effectively combines mechanical analysis and formulaic encoding of empirical rules. First, the critical information about the structure was extracted through data structuring. Second, an empirical rule assessment method was developed based on the engineer's experience and design standards to complete a preliminary assessment and screening of the structure. Subsequently, an assessment method based on mechanical performance and material consumption was used to compare different structural schemes comprehensively. Finally, the assessment effectiveness was demonstrated using a typical case. Compared to traditional assessment methods, the proposed method is more comprehensive and significantly more efficient, promoting the intelligent transformation of structural design.
Efficient methods for incorporating engineering experience into the intelligent generation and optimization of shear wall structures are lacking, hindering intelligent design performance assessment and enhancement. This study introduces an assessment method used in the intelligent design and optimization of shear wall structures that effectively combines mechanical analysis and formulaic encoding of empirical rules. First, the critical information about the structure was extracted through data structuring. Second, an empirical rule assessment method was developed based on the engineer's experience and design standards to complete a preliminary assessment and screening of the structure. Subsequently, an assessment method based on mechanical performance and material consumption was used to compare different structural schemes comprehensively. Finally, the assessment effectiveness was demonstrated using a typical case. Compared to traditional assessment methods, the proposed method is more comprehensive and significantly more efficient, promoting the intelligent transformation of structural design.
2023, 40(12): 160-174.
doi:10.6052/j.issn.1000-4750.2022.02.0167
Abstract:
In residential steel building structures, the identical depth design among joints and, the boundary element of steel plate shear wall and I-beam can lead to a required interior space, but it makes the joint design more difficult. A combination type of the joint connecting the boundary element with the I-beam was proposed, with an external-diaphragm connection on the upper flange and with a flitch plate connection on the lower flange of I-beam. The hysteretic tests of two specimens with different axial compression ratios were carried out to study their load-bearing performance, failure mode, hysteretic performance, skeleton curve and, strength and stiffness degradation. The test results indicated that: The average yield displacement angle of 1/136 and limit displacement angle of 1/42 both could meet the specified requirements in Chinese Code for the seismic design of buildings GB 50011−2010; The deformability of the flitch plate connection on the lower flange is weaker than that of the external-diaphragm connection on the upper flange; The cracking is prone to occur in the weld seam of the flitch plate connection, resulting in the strength and stiffness degrade rapidly. A refined finite element model including all details of connecting joints was established and the tests are simulated numerically. A good agreement between the test and finite element results was reached, and the investigation of the validated finite element model could provide fundamentals for establishing the design methods of the flitch plate connection.
In residential steel building structures, the identical depth design among joints and, the boundary element of steel plate shear wall and I-beam can lead to a required interior space, but it makes the joint design more difficult. A combination type of the joint connecting the boundary element with the I-beam was proposed, with an external-diaphragm connection on the upper flange and with a flitch plate connection on the lower flange of I-beam. The hysteretic tests of two specimens with different axial compression ratios were carried out to study their load-bearing performance, failure mode, hysteretic performance, skeleton curve and, strength and stiffness degradation. The test results indicated that: The average yield displacement angle of 1/136 and limit displacement angle of 1/42 both could meet the specified requirements in Chinese Code for the seismic design of buildings GB 50011−2010; The deformability of the flitch plate connection on the lower flange is weaker than that of the external-diaphragm connection on the upper flange; The cracking is prone to occur in the weld seam of the flitch plate connection, resulting in the strength and stiffness degrade rapidly. A refined finite element model including all details of connecting joints was established and the tests are simulated numerically. A good agreement between the test and finite element results was reached, and the investigation of the validated finite element model could provide fundamentals for establishing the design methods of the flitch plate connection.
2023, 40(12): 175-184.
doi:10.6052/j.issn.1000-4750.2022.02.0168
Abstract:
Focused is on the theoretical analysis of a new type of self-resetting prestressed steel frame system, upon analyzing and expounding the various states of the change process of the wire force of the steel strand and the force of the self-centering joint, to deduce the theoretical calculation formula of the initial rotation center position, of the changing length of the steel strand, of the wire force of the steel strand and, of the external load under different states. By analyzing the theoretical hysteresis curve of the self-centering joint and the load-displacement curve of the self-centering frame, it is further deduced for the theoretical calculation formula of the ratio of the energy dissipation coefficient of the self-centering joint to the stiffness of the frame before and after the opening of the joint, and each process in the load-displacement curve is analyzed and explained. The opening load, energy dissipation coefficient, and stiffness ratio of frame before and after opening of self-centering joints in the self-centering frame test were compared with the theoretical calculation value. The results show that: the experimental value is basically equal to the theoretical value, thusly the theoretical analysis is reasonable, which can predict and explain the experimental phenomena and results well, and the theoretical formula has high accuracy, providing a theoretical basis for subsequent engineering applications.
Focused is on the theoretical analysis of a new type of self-resetting prestressed steel frame system, upon analyzing and expounding the various states of the change process of the wire force of the steel strand and the force of the self-centering joint, to deduce the theoretical calculation formula of the initial rotation center position, of the changing length of the steel strand, of the wire force of the steel strand and, of the external load under different states. By analyzing the theoretical hysteresis curve of the self-centering joint and the load-displacement curve of the self-centering frame, it is further deduced for the theoretical calculation formula of the ratio of the energy dissipation coefficient of the self-centering joint to the stiffness of the frame before and after the opening of the joint, and each process in the load-displacement curve is analyzed and explained. The opening load, energy dissipation coefficient, and stiffness ratio of frame before and after opening of self-centering joints in the self-centering frame test were compared with the theoretical calculation value. The results show that: the experimental value is basically equal to the theoretical value, thusly the theoretical analysis is reasonable, which can predict and explain the experimental phenomena and results well, and the theoretical formula has high accuracy, providing a theoretical basis for subsequent engineering applications.
2023, 40(12): 185-193.
doi:10.6052/j.issn.1000-4750.2022.02.0180
Abstract:
Based on the assumptions such as plane section assumption, the mechanical model of flange bolt group is established upon local bolt loosening. By introducing the concept of influence line, a method is proposed for detecting local bolt loosening in the main wind direction of wind turbine tower flange based on the influence line of flexibility coefficient. The location identification and degree evaluation of local bolt loosening in main wind direction can be realized by drawing the curve of nose azimuth-flexibility coefficient. The finite element analysis model of wind turbine tower flange bolt group is established to verify the validity of the detection method. The strain gauges are arranged in the orthogonal directions at the joint of the connecting flange of the tower cylinder of the wind turbine and connected to the SCADA system of the wind turbine, which is collected synchronously with the upper unit parameters such as wind direction, angle and hub speed. The on-line analysis program is developed, and the on-line monitoring and evaluation method of wind turbine tower flange bolt looseness identification based on influence line is put forward, which can be used in practical projects.
Based on the assumptions such as plane section assumption, the mechanical model of flange bolt group is established upon local bolt loosening. By introducing the concept of influence line, a method is proposed for detecting local bolt loosening in the main wind direction of wind turbine tower flange based on the influence line of flexibility coefficient. The location identification and degree evaluation of local bolt loosening in main wind direction can be realized by drawing the curve of nose azimuth-flexibility coefficient. The finite element analysis model of wind turbine tower flange bolt group is established to verify the validity of the detection method. The strain gauges are arranged in the orthogonal directions at the joint of the connecting flange of the tower cylinder of the wind turbine and connected to the SCADA system of the wind turbine, which is collected synchronously with the upper unit parameters such as wind direction, angle and hub speed. The on-line analysis program is developed, and the on-line monitoring and evaluation method of wind turbine tower flange bolt looseness identification based on influence line is put forward, which can be used in practical projects.
2023, 40(12): 194-202.
doi:10.6052/j.issn.1000-4750.2022.02.0182
Abstract:
Aerodynamic instability is one of the significant concerns in the design of long-span suspension bridges. To provide reference for the determination of decks and spans length in the preliminary design stage of suspension bridges, the aerodynamic stability analysis of suspension bridges with spans from 1000 m to 5000 m was carried out. Based on dynamic characteristics of existing suspension bridges with spans from 888 m (Humen Bridge) to 1991 m (Akashi-Kaikyo Bridge), the developing trends of natural frequencies were discussed. Following developing tendency, finite element models (FEMs) of suspension bridges with spans from 1000 m to 5000 m were established, and the sag to span ratio was 1/11. Four commonly used forms of bridge decks were selected, i.e., single box section (SBS), latticed truss section (LTS), narrow slotted section (NSS) and wide slotted section (WSS). All the widths of decks were adjusted to 36 m with influence on aerodynamic stability excluded. 3-D nonlinear aerostatic instability analysis considering structural geometric nonlinearity and aerodynamic load nonlinearity and 3-D frequency domain flutter analysis were carried out, in which the aerodynamic parameters such as static aerodynamic coefficients and flutter derivatives were obtained from wind tunnel tests. Aerostatic instability wind speeds and flutter critical wind speeds of suspension bridges at 0° and ±3° angle of attack were calculated. The results show that aerostatic instability wind speeds have a decrement with spans from 1000 m to 3000 m. However, aerostatic instability wind speeds rise up with spans increasing between 3000 m and 5000 m. Flutter critical wind speeds continuously decrease with spans growth, similar to the decrement of torsional natural frequencies of main girder. Moreover, a comparison of aerodynamic stability by sections were studied. It shows that the minimum aerostatic instability wind speeds of suspension bridges with SBS and LTS decks are lower than the maximum gust wind speed of 80 m/s in measurement. It is also found that bridges with all four forms of sections have flutter critical wind speeds less than 70 m/s when spans are longer than 2000 m. The study indicates that the aerostatic instability is possible for SBS or LTS suspension bridges modeled in this paper with spans about 3500 m. Flutter will always be the control factor in wind-resistant design of super long-span suspension bridges, and it will be more severe with spans extending.
Aerodynamic instability is one of the significant concerns in the design of long-span suspension bridges. To provide reference for the determination of decks and spans length in the preliminary design stage of suspension bridges, the aerodynamic stability analysis of suspension bridges with spans from 1000 m to 5000 m was carried out. Based on dynamic characteristics of existing suspension bridges with spans from 888 m (Humen Bridge) to 1991 m (Akashi-Kaikyo Bridge), the developing trends of natural frequencies were discussed. Following developing tendency, finite element models (FEMs) of suspension bridges with spans from 1000 m to 5000 m were established, and the sag to span ratio was 1/11. Four commonly used forms of bridge decks were selected, i.e., single box section (SBS), latticed truss section (LTS), narrow slotted section (NSS) and wide slotted section (WSS). All the widths of decks were adjusted to 36 m with influence on aerodynamic stability excluded. 3-D nonlinear aerostatic instability analysis considering structural geometric nonlinearity and aerodynamic load nonlinearity and 3-D frequency domain flutter analysis were carried out, in which the aerodynamic parameters such as static aerodynamic coefficients and flutter derivatives were obtained from wind tunnel tests. Aerostatic instability wind speeds and flutter critical wind speeds of suspension bridges at 0° and ±3° angle of attack were calculated. The results show that aerostatic instability wind speeds have a decrement with spans from 1000 m to 3000 m. However, aerostatic instability wind speeds rise up with spans increasing between 3000 m and 5000 m. Flutter critical wind speeds continuously decrease with spans growth, similar to the decrement of torsional natural frequencies of main girder. Moreover, a comparison of aerodynamic stability by sections were studied. It shows that the minimum aerostatic instability wind speeds of suspension bridges with SBS and LTS decks are lower than the maximum gust wind speed of 80 m/s in measurement. It is also found that bridges with all four forms of sections have flutter critical wind speeds less than 70 m/s when spans are longer than 2000 m. The study indicates that the aerostatic instability is possible for SBS or LTS suspension bridges modeled in this paper with spans about 3500 m. Flutter will always be the control factor in wind-resistant design of super long-span suspension bridges, and it will be more severe with spans extending.
2023, 40(12): 203-211.
doi:10.6052/j.issn.1000-4750.2022.02.0194
Abstract:
Aftershocks occurring in a short time after a strong earthquake have an important impact on the structure damaged by the mainshock. Existing researches on seismic performance of underground structures are mainly based on the action of a single earthquake, and the understanding of the damage caused by aftershocks needs to be further improved. A soil-underground structure interaction model was established based on a typical two-story and three-span subway station to reveal the incremental damage and performance deterioration of the subway station subjected to mainshock-aftershock earthquakes. A set of 85 real mainshock records and mainshock-aftershock sequences from 14 real earthquakes were selected as inputs. Then, the seismic responses of underground structures were studied. The damage degree of the underground structure during the mainshock-aftershock earthquakes is obviously more serious than that when only the mainshock is applied. The increment amplitude and extension range of the structure damage are related to such factors as the peak acceleration ratioξ, the characteristics of ground motion and the polarity of the main aftershock. Due to the cumulative effect of structural damage, the interlayer displacement of subway stations caused by aftershock excitation is greater than that of the mainshock when the seismic intensity of the mainshock is similar to that of the aftershock (ξ≈1.0). When the intensity of the mainshock is much greater than that of the aftershock (ξ≥1.4), the additional damage caused by aftershock to the underground structure is limited.
Aftershocks occurring in a short time after a strong earthquake have an important impact on the structure damaged by the mainshock. Existing researches on seismic performance of underground structures are mainly based on the action of a single earthquake, and the understanding of the damage caused by aftershocks needs to be further improved. A soil-underground structure interaction model was established based on a typical two-story and three-span subway station to reveal the incremental damage and performance deterioration of the subway station subjected to mainshock-aftershock earthquakes. A set of 85 real mainshock records and mainshock-aftershock sequences from 14 real earthquakes were selected as inputs. Then, the seismic responses of underground structures were studied. The damage degree of the underground structure during the mainshock-aftershock earthquakes is obviously more serious than that when only the mainshock is applied. The increment amplitude and extension range of the structure damage are related to such factors as the peak acceleration ratioξ, the characteristics of ground motion and the polarity of the main aftershock. Due to the cumulative effect of structural damage, the interlayer displacement of subway stations caused by aftershock excitation is greater than that of the mainshock when the seismic intensity of the mainshock is similar to that of the aftershock (ξ≈1.0). When the intensity of the mainshock is much greater than that of the aftershock (ξ≥1.4), the additional damage caused by aftershock to the underground structure is limited.
2023, 40(12): 212-221.
doi:10.6052/j.issn.1000-4750.2022.02.0195
Abstract:
In order to investigate the seismic performance of circular timber columns strengthened with near surface mounted steel bars and wrapped CFRP (carbon fiber reinforced polymer) strips, and to propose the calculation method for the lateral performance of strengthened timber columns, 5 timber columns with composite reinforcement were tested under lateral cyclic loading, with the number of mounted steel bars and wrapped CFRP strips as variables. The test results indicated that the composite reinforcement method could delay the damage process of timber columns, and the specimens showed tensile rupture of timber grain near the bottom section, indicating significant brittle failure. The bearing capacity and deformation performance of strengthened timber columns were improved obviously. Furthermore, with the increase of wrapped CFRP strips, the peak load and ductility of specimens showed trend of improvement, and the position of the mounted steel bars could influence the bearing capacity of timber columns. The distributions of strain-displacement hysteretic curves of steel bars and CFRP strips were almost consistent with the corresponding curves of timber, which denoted that the strengthening materials could deform and work together with timber, and improve the hysteretic performance of timber columns. The strip method was adopted for the force analysis of the specimen’s cross section, and the reliability of the internal force analysis was verified through the comparison between theoretical calculation and test results. Based on the materials mechanics, the calculation method for the lateral performance of composite strengthened timber column was proposed, and the theoretical results were in good agreement with the experimental data.
In order to investigate the seismic performance of circular timber columns strengthened with near surface mounted steel bars and wrapped CFRP (carbon fiber reinforced polymer) strips, and to propose the calculation method for the lateral performance of strengthened timber columns, 5 timber columns with composite reinforcement were tested under lateral cyclic loading, with the number of mounted steel bars and wrapped CFRP strips as variables. The test results indicated that the composite reinforcement method could delay the damage process of timber columns, and the specimens showed tensile rupture of timber grain near the bottom section, indicating significant brittle failure. The bearing capacity and deformation performance of strengthened timber columns were improved obviously. Furthermore, with the increase of wrapped CFRP strips, the peak load and ductility of specimens showed trend of improvement, and the position of the mounted steel bars could influence the bearing capacity of timber columns. The distributions of strain-displacement hysteretic curves of steel bars and CFRP strips were almost consistent with the corresponding curves of timber, which denoted that the strengthening materials could deform and work together with timber, and improve the hysteretic performance of timber columns. The strip method was adopted for the force analysis of the specimen’s cross section, and the reliability of the internal force analysis was verified through the comparison between theoretical calculation and test results. Based on the materials mechanics, the calculation method for the lateral performance of composite strengthened timber column was proposed, and the theoretical results were in good agreement with the experimental data.
2023, 40(12): 222-233.
doi:10.6052/j.issn.1000-4750.2022.07.0633
Abstract:
In order to investigate the bearing performance of tapered end bearing friction piles under the combined effect of torqueTand vertical loadV, the paper obtained separately the differential governing equations of pile vertical displacement and torsion angle under the action of vertical load and torque on pile top based on the energy method and the variational principle, in which the subsoil shear modulus was assumed to be non-zero at the ground surface and have a distribution form of power function with depth. The ultimate vertical load and torque of tapered end bearing friction pile were solved by MATLAB programming, and then the corresponding bearing capacity envelope diagram was obtained. UnderT→Vloading sequence, the influence of initial torque on the vertical bearing characteristics of tapered end bearing friction pile was analyzed by changing the initial torque value. The influence of parameters on tapered end bearing friction pile under combinedT-Vloads was analyzed. The results show that, compared with equal section pile, the ultimate vertical load and ultimate torque of tapered end bearing friction pile under pure compression and pure torsion are increased. UnderT→Vloading sequence, the bearing capacity envelope of tapered end bearing friction pile is expanded compared with the equal section pile. With the increase of the change rate of pile diameter, the bearing capacity envelope of tapered end bearing friction piles also expands outward. When the ratio of initial torque to ultimate torque exceeds a certain value, the ultimate vertical load of tapered end bearing friction pile begins to decrease significantly, and attention should be paid toT-Vcombination effect. For large-diameter long piles, it is necessary to pay attention to the effect of initial torque on the vertical bearing capacity of foundation piles. The vertical bearing capacity of single pile underT→Vloading mode can’t be greatly improved simply by increasing the concrete grade.
In order to investigate the bearing performance of tapered end bearing friction piles under the combined effect of torqueTand vertical loadV, the paper obtained separately the differential governing equations of pile vertical displacement and torsion angle under the action of vertical load and torque on pile top based on the energy method and the variational principle, in which the subsoil shear modulus was assumed to be non-zero at the ground surface and have a distribution form of power function with depth. The ultimate vertical load and torque of tapered end bearing friction pile were solved by MATLAB programming, and then the corresponding bearing capacity envelope diagram was obtained. UnderT→Vloading sequence, the influence of initial torque on the vertical bearing characteristics of tapered end bearing friction pile was analyzed by changing the initial torque value. The influence of parameters on tapered end bearing friction pile under combinedT-Vloads was analyzed. The results show that, compared with equal section pile, the ultimate vertical load and ultimate torque of tapered end bearing friction pile under pure compression and pure torsion are increased. UnderT→Vloading sequence, the bearing capacity envelope of tapered end bearing friction pile is expanded compared with the equal section pile. With the increase of the change rate of pile diameter, the bearing capacity envelope of tapered end bearing friction piles also expands outward. When the ratio of initial torque to ultimate torque exceeds a certain value, the ultimate vertical load of tapered end bearing friction pile begins to decrease significantly, and attention should be paid toT-Vcombination effect. For large-diameter long piles, it is necessary to pay attention to the effect of initial torque on the vertical bearing capacity of foundation piles. The vertical bearing capacity of single pile underT→Vloading mode can’t be greatly improved simply by increasing the concrete grade.
2023, 40(12): 234-244.
doi:10.6052/j.issn.1000-4750.2022.02.0186
Abstract:
Composite sandwich structure is widely used in lightweight design of rail vehicles. Traditional composite sandwich structure with a single aluminum honeycomb core has poor impact resistance, which is difficult to meet the application requirements. A rectangular aluminum grid structure is added into the core of the traditional carbon fiber/aluminum honeycomb sandwich structure to form the carbon fiber/grid reinforced honeycomb sandwich structure, and the drop hammer impact test and post-impact compression test are carried out at three typical positions, the intersection of the grid, the center of the single rib plate and the center of the grid. The carbon fiber/grid reinforced honeycomb sandwich structure is applied to vehicle roof. The simulation models of vehicle roofs of three different materials are established under the rockfall impact condition to analyze the mechanical properties such as specific peak load and specific stiffness. The results show that the carbon fiber/grid reinforced honeycomb sandwich structure has stronger impact resistance than traditional carbon fiber/aluminum honeycomb sandwich structure, with compression of approximately 34% higher and compressive stiffness of 52% higher after impact strength; The peak contact force, delamination critical load and dent depth at the intersection of the grid and the center of the single ribbed plate are significantly better than those at the center of the grid; Compared with the carbon fiber/aluminum honeycomb vehicle roof, the deformation of the carbon fiber/grid reinforced honeycomb vehicle roof under rockfall impact is reduced by 71.73%, and the specific peak load and specific stiffness are increased by 133.33% and 146.72% respectively. The carbon fiber/grid reinforced honeycomb sandwich structure has the advantages of both lightweight and strong performance, which is suitable as large-scale bearing structure and can provide a reference for the structural design of high-speed train body.
Composite sandwich structure is widely used in lightweight design of rail vehicles. Traditional composite sandwich structure with a single aluminum honeycomb core has poor impact resistance, which is difficult to meet the application requirements. A rectangular aluminum grid structure is added into the core of the traditional carbon fiber/aluminum honeycomb sandwich structure to form the carbon fiber/grid reinforced honeycomb sandwich structure, and the drop hammer impact test and post-impact compression test are carried out at three typical positions, the intersection of the grid, the center of the single rib plate and the center of the grid. The carbon fiber/grid reinforced honeycomb sandwich structure is applied to vehicle roof. The simulation models of vehicle roofs of three different materials are established under the rockfall impact condition to analyze the mechanical properties such as specific peak load and specific stiffness. The results show that the carbon fiber/grid reinforced honeycomb sandwich structure has stronger impact resistance than traditional carbon fiber/aluminum honeycomb sandwich structure, with compression of approximately 34% higher and compressive stiffness of 52% higher after impact strength; The peak contact force, delamination critical load and dent depth at the intersection of the grid and the center of the single ribbed plate are significantly better than those at the center of the grid; Compared with the carbon fiber/aluminum honeycomb vehicle roof, the deformation of the carbon fiber/grid reinforced honeycomb vehicle roof under rockfall impact is reduced by 71.73%, and the specific peak load and specific stiffness are increased by 133.33% and 146.72% respectively. The carbon fiber/grid reinforced honeycomb sandwich structure has the advantages of both lightweight and strong performance, which is suitable as large-scale bearing structure and can provide a reference for the structural design of high-speed train body.
2023, 40(12): 245-256.
doi:10.6052/j.issn.1000-4750.2022.02.0189
Abstract:
The viscoelastic materials have many applications in the fields of noise reduction, of vibration control for precision instrument, and of earthquake prevention and, of disaster reduction for building structures. Filling systems such as carbon black and silicon are important components of viscoelastic materials. Thusly, the random sequence absorption method is used to establish representative volume element (RVE) models of carbon black-filled viscoelastic materials with different volume fractions, and the finite element model is modified upon the effective volume fraction. The mechanical behavior and dynamic energy dissipation index of the carbon black-filled viscoelastic material with different volume fractions is calculated and analyzed at mesoscale, and it is also compared with empirical values and test data. It shows that the stress-strain curve and dynamic energy dissipation index of the carbon black-filled viscoelastic material with different volume fractions calculated by the RVE method are in a good agreement with the experimental and theoretical results when utilizing effective volume fraction to build the models.
The viscoelastic materials have many applications in the fields of noise reduction, of vibration control for precision instrument, and of earthquake prevention and, of disaster reduction for building structures. Filling systems such as carbon black and silicon are important components of viscoelastic materials. Thusly, the random sequence absorption method is used to establish representative volume element (RVE) models of carbon black-filled viscoelastic materials with different volume fractions, and the finite element model is modified upon the effective volume fraction. The mechanical behavior and dynamic energy dissipation index of the carbon black-filled viscoelastic material with different volume fractions is calculated and analyzed at mesoscale, and it is also compared with empirical values and test data. It shows that the stress-strain curve and dynamic energy dissipation index of the carbon black-filled viscoelastic material with different volume fractions calculated by the RVE method are in a good agreement with the experimental and theoretical results when utilizing effective volume fraction to build the models.
