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工程力学
Engineering Mechanics
Since 1984 Monthly
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Chief Editor: Xinzheng LU
Editor & Publisher: 《工程力学》杂志社
ISSN 1000-4750 CN 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. 11, Publish Date: 2023-11-06
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2023, 40(11): 1-10.
doi: 10.6052/j.issn.1000-4750.2022.02.0108
Abstract:
In order to solve the theoretical calculation problem of the internal force of arch structures with non-ideal boundary constraints, this paper simplifies the non-ideal boundary constraints as elastic support, and simplifies the force method equation based on the elastic center method. The elastic compression is considered and the precise curve integral method is adopted. The analytical solutions are derived for rigid arm length, constant displacement, load displacement and internal force of parabolic arch with elastic support and under vertical moving load. The influences of flexural compression stiffness ratio, rise span ratio and horizontal elastic restraint on horizontal thrust at the support are studied. The influence of horizontal elastic restraint on internal force distribution of arch axis is also studied. The results show that the analytical expression proposed in this paper has a clear physical concept, is correct and reliable, and can explicitly show the influence process of elastic support parameters on internal force calculation. The calculation error of horizontal thrust increases with the increase of bending and flexural compression stiffness, ignoring the influence of elastic compression of arch rib. The calculation error of horizontal thrust is the largest when the arch toe support is a rigid constraint, which can reach 27.8%. Horizontal elastic support can significantly change the distribution of horizontal thrust and arch axis internal force at the support. The influence coefficient of horizontal thrust increases nonlinearly with the increase of rise span ratio. The influence coefficient of horizontal thrust corresponding to the common rise span ratio is about 0.15 when the flexural stiffness ratio is 1.93 and the flexibility coefficient of horizontal elastic support is 0.02.
In order to solve the theoretical calculation problem of the internal force of arch structures with non-ideal boundary constraints, this paper simplifies the non-ideal boundary constraints as elastic support, and simplifies the force method equation based on the elastic center method. The elastic compression is considered and the precise curve integral method is adopted. The analytical solutions are derived for rigid arm length, constant displacement, load displacement and internal force of parabolic arch with elastic support and under vertical moving load. The influences of flexural compression stiffness ratio, rise span ratio and horizontal elastic restraint on horizontal thrust at the support are studied. The influence of horizontal elastic restraint on internal force distribution of arch axis is also studied. The results show that the analytical expression proposed in this paper has a clear physical concept, is correct and reliable, and can explicitly show the influence process of elastic support parameters on internal force calculation. The calculation error of horizontal thrust increases with the increase of bending and flexural compression stiffness, ignoring the influence of elastic compression of arch rib. The calculation error of horizontal thrust is the largest when the arch toe support is a rigid constraint, which can reach 27.8%. Horizontal elastic support can significantly change the distribution of horizontal thrust and arch axis internal force at the support. The influence coefficient of horizontal thrust increases nonlinearly with the increase of rise span ratio. The influence coefficient of horizontal thrust corresponding to the common rise span ratio is about 0.15 when the flexural stiffness ratio is 1.93 and the flexibility coefficient of horizontal elastic support is 0.02.
2023, 40(11): 11-20.
doi: 10.6052/j.issn.1000-4750.2022.05.0488
Abstract:
The imposition of boundary conditions is an essential step in solving the definite problem of partial differential equations. When the definite problem of partial differential equations is resolved by neural network, the original problem should be transformed to its corresponding constructive variational problem, and the loss function is a functional consisting of the governing equations and the boundary conditions. If the boundary conditions are imposed by the classical penalty function method and its improvements, the value of the penalty factor will affect the solution accuracy and the computational efficiency. If the boundary conditions are directly imposed by the Lagrange multiplier method, the computational results may deviate from the optimal solution of the original problem. To overcome these limitations, the generalized multiplier method is employed in the imposition of boundary conditions. The predicted solution of the original problem is obtained from the neural network. The generalized multiplier method is used to construct the loss function of the neural network and calculate the loss. The gradient descent method is utilized to perform parameter optimization. Afterwards, the loss function is calculated. The penalty factor and multiplier are updated, and the resolution is repeated till the loss is acceptable. The results of numerical examples verify that the proposed method has better solution accuracy, higher computational efficiency and more stable solution process than those neural networks in which the boundary conditions are applied by the classical penalty function method, L1 exact penalty function method, and Lagrange multiplier method.
The imposition of boundary conditions is an essential step in solving the definite problem of partial differential equations. When the definite problem of partial differential equations is resolved by neural network, the original problem should be transformed to its corresponding constructive variational problem, and the loss function is a functional consisting of the governing equations and the boundary conditions. If the boundary conditions are imposed by the classical penalty function method and its improvements, the value of the penalty factor will affect the solution accuracy and the computational efficiency. If the boundary conditions are directly imposed by the Lagrange multiplier method, the computational results may deviate from the optimal solution of the original problem. To overcome these limitations, the generalized multiplier method is employed in the imposition of boundary conditions. The predicted solution of the original problem is obtained from the neural network. The generalized multiplier method is used to construct the loss function of the neural network and calculate the loss. The gradient descent method is utilized to perform parameter optimization. Afterwards, the loss function is calculated. The penalty factor and multiplier are updated, and the resolution is repeated till the loss is acceptable. The results of numerical examples verify that the proposed method has better solution accuracy, higher computational efficiency and more stable solution process than those neural networks in which the boundary conditions are applied by the classical penalty function method, L1 exact penalty function method, and Lagrange multiplier method.
2023, 40(11): 21-30.
doi: 10.6052/j.issn.1000-4750.2022.01.0100
Abstract:
Determining component damage states according to story drift ratio, the traditional seismic resilience assessment method of buildings is suitable for regular structures. In order to enhance its applicability to space structures without the concept of stories, improve the accuracy of determining component damage states of structures with uneven story deformation or irregular torsion, and make it more flexible for complex buildings, component performance evaluation methods based on material stress and strain or component rotation angle are adopted to determine component damage states. Taking the component damage states as the original samples, a large number of simulation samples of component damage states are generated by expanding the original sample matrix. Monte Carlo method is used to calculate the repair cost, repair time and casualties of the simulated samples, and the resilience assessment index is obtained by probability analysis. In order to consider the influences of the number of ground motions and the dispersion of nonlinear time-history analysis results on seismic resilience assessment index, and to evaluate the reliability of seismic resilience assessment results, a simplified confidence interval algorithm at a given confidence level of resilience assessment index is derived. Through a complex frame-shear wall structure case, the rationality and feasibility of the seismic resilience assessment method are verified.
Determining component damage states according to story drift ratio, the traditional seismic resilience assessment method of buildings is suitable for regular structures. In order to enhance its applicability to space structures without the concept of stories, improve the accuracy of determining component damage states of structures with uneven story deformation or irregular torsion, and make it more flexible for complex buildings, component performance evaluation methods based on material stress and strain or component rotation angle are adopted to determine component damage states. Taking the component damage states as the original samples, a large number of simulation samples of component damage states are generated by expanding the original sample matrix. Monte Carlo method is used to calculate the repair cost, repair time and casualties of the simulated samples, and the resilience assessment index is obtained by probability analysis. In order to consider the influences of the number of ground motions and the dispersion of nonlinear time-history analysis results on seismic resilience assessment index, and to evaluate the reliability of seismic resilience assessment results, a simplified confidence interval algorithm at a given confidence level of resilience assessment index is derived. Through a complex frame-shear wall structure case, the rationality and feasibility of the seismic resilience assessment method are verified.
2023, 40(11): 31-45.
doi: 10.6052/j.issn.1000-4750.2022.01.0101
Abstract:
The seismic behavior of a large-span single-layer spherical reticulated shell with the novel air spring-FPS three-dimensional (3D) isolation bearing is investigated. The influence of long-period ground motions on the vibration control effect of the 3D isolated structure is discussed. The dynamic time-history analysis indicated that 3D isolation bearings can effectively reduce the structural seismic response under various ground motions. With the same peak ground acceleration (PGA), the isolation effect of ordinary ground motions is better than near-fault pulse-like ground motions and much better than far-field long-period ground motions. This phenomenon is related to the quasi-resonance effect between the long-period ground motions and the long-period isolated structures. With the decrease of the bearing stiffness, the isolation effect is improved for ordinary ground motion and near-fault pulse-like ground motion while it is reduced for far-field long-period ground motions. The abundant low-frequency characteristics of far-field long-period ground motion make its response spectra have bimodal characteristics, resulting in the increase of the structural response with the period prolongation. TR is suggested to be larger than 0.2 in order to not only obtain a good isolation effect but also limit the vertical bearing displacement with an allowable value for a three-dimensional isolated structure.
The seismic behavior of a large-span single-layer spherical reticulated shell with the novel air spring-FPS three-dimensional (3D) isolation bearing is investigated. The influence of long-period ground motions on the vibration control effect of the 3D isolated structure is discussed. The dynamic time-history analysis indicated that 3D isolation bearings can effectively reduce the structural seismic response under various ground motions. With the same peak ground acceleration (PGA), the isolation effect of ordinary ground motions is better than near-fault pulse-like ground motions and much better than far-field long-period ground motions. This phenomenon is related to the quasi-resonance effect between the long-period ground motions and the long-period isolated structures. With the decrease of the bearing stiffness, the isolation effect is improved for ordinary ground motion and near-fault pulse-like ground motion while it is reduced for far-field long-period ground motions. The abundant low-frequency characteristics of far-field long-period ground motion make its response spectra have bimodal characteristics, resulting in the increase of the structural response with the period prolongation. TR is suggested to be larger than 0.2 in order to not only obtain a good isolation effect but also limit the vertical bearing displacement with an allowable value for a three-dimensional isolated structure.
2023, 40(11): 46-58.
doi: 10.6052/j.issn.1000-4750.2022.01.0116
Abstract:
An inflated membrane tube is a kind of flexible structure. Its deformation will result in a change in the inner pressure and then affect the stiffness and deformation of the enveloping membrane. This phenomenon reflects the interaction between the pressure of inner air and the deformation of enveloping membrane. The authors, using the finite element method, analyze the effect of air-membrane interaction on the dynamic properties of an inflated membrane tube and its variation with influencing factors. The inner air is treated as a kind of linear potential fluid to consider the effects of air-membrane interaction and added mass of the inner air. Three finite element models of the inflated membrane tube are developed with different methods to treat the inner air, i.e., the inner air is treated respectively as the static boundary conditions of the enveloping membrane, the static boundary conditions plus the added mass, and a kind of linear potential fluid. The numerical results obtained from these three models are compared to study the influences of air-membrane interaction and added mass on dynamic properties of the tube and their variations with the initial inner pressure, slenderness ratio, membrane thickness and constraint type. The comparisons indicate that air-membrane interaction and added mass of the inner air have little influence on the low-order modal shapes; air-membrane interaction plays a significant role in the natural frequencies while the added mass of inner air has a very small effect; with an increase in the initial inner pressure and slenderness ratio, the influence of air-membrane interaction on natural frequencies varies differently for different orders; The influence of air-membrane interaction on natural frequencies decreases with the increasing membrane thickness and is gradually strengthened when the end constraints are weakened. The present research reveals the dynamic effect of air-membrane interaction and is helpful to the understanding of the dynamic behavior of inflated membrane tubes for their rational and reliable design.
An inflated membrane tube is a kind of flexible structure. Its deformation will result in a change in the inner pressure and then affect the stiffness and deformation of the enveloping membrane. This phenomenon reflects the interaction between the pressure of inner air and the deformation of enveloping membrane. The authors, using the finite element method, analyze the effect of air-membrane interaction on the dynamic properties of an inflated membrane tube and its variation with influencing factors. The inner air is treated as a kind of linear potential fluid to consider the effects of air-membrane interaction and added mass of the inner air. Three finite element models of the inflated membrane tube are developed with different methods to treat the inner air, i.e., the inner air is treated respectively as the static boundary conditions of the enveloping membrane, the static boundary conditions plus the added mass, and a kind of linear potential fluid. The numerical results obtained from these three models are compared to study the influences of air-membrane interaction and added mass on dynamic properties of the tube and their variations with the initial inner pressure, slenderness ratio, membrane thickness and constraint type. The comparisons indicate that air-membrane interaction and added mass of the inner air have little influence on the low-order modal shapes; air-membrane interaction plays a significant role in the natural frequencies while the added mass of inner air has a very small effect; with an increase in the initial inner pressure and slenderness ratio, the influence of air-membrane interaction on natural frequencies varies differently for different orders; The influence of air-membrane interaction on natural frequencies decreases with the increasing membrane thickness and is gradually strengthened when the end constraints are weakened. The present research reveals the dynamic effect of air-membrane interaction and is helpful to the understanding of the dynamic behavior of inflated membrane tubes for their rational and reliable design.
2023, 40(11): 59-68.
doi: 10.6052/j.issn.1000-4750.2022.01.0091
Abstract:
Due to the limitations of physical test equipment and conditions, the existing studies on dynamic biaxial compressive strength criteria of concrete only in the range of low strain rate (10−5 s−1~10−2 s−1). To investigate whether these strength criteria are applicable at higher strain rates or not, a mesoscopic random aggregate model was established. The meso-simulation analysis of concrete cubic specimens with side length of 100 mm under dynamic biaxial compressive loads were carried out. The influence of strain rate and lateral stress ratio on dynamic biaxial compressive failure modes and compressive strengths of concrete were analyzed. A dynamic biaxial compressive strength criterion applicable to higher strain rate was established. The conclusions are as follows: Under the same lateral stress ratio, a higher strain rate leads to an increase in the internal damaged area and the dynamic compressive strength of concrete. Under the same strain rate, a higher lateral stress ratio causes the failure mode of concrete changes from cylindrical fracturing to sheet splitting and the dynamic compressive strength first increases and then decreases. The existing dynamic biaxial compressive strength criterion of concrete is inapplicable in 10−5 s−1~1 s−1, while the improved strength criterion proposed can be applied to a larger strain rate range, which has been preliminarily verified by various physical tests.
Due to the limitations of physical test equipment and conditions, the existing studies on dynamic biaxial compressive strength criteria of concrete only in the range of low strain rate (10−5 s−1~10−2 s−1). To investigate whether these strength criteria are applicable at higher strain rates or not, a mesoscopic random aggregate model was established. The meso-simulation analysis of concrete cubic specimens with side length of 100 mm under dynamic biaxial compressive loads were carried out. The influence of strain rate and lateral stress ratio on dynamic biaxial compressive failure modes and compressive strengths of concrete were analyzed. A dynamic biaxial compressive strength criterion applicable to higher strain rate was established. The conclusions are as follows: Under the same lateral stress ratio, a higher strain rate leads to an increase in the internal damaged area and the dynamic compressive strength of concrete. Under the same strain rate, a higher lateral stress ratio causes the failure mode of concrete changes from cylindrical fracturing to sheet splitting and the dynamic compressive strength first increases and then decreases. The existing dynamic biaxial compressive strength criterion of concrete is inapplicable in 10−5 s−1~1 s−1, while the improved strength criterion proposed can be applied to a larger strain rate range, which has been preliminarily verified by various physical tests.
2023, 40(11): 69-80, 109.
doi: 10.6052/j.issn.1000-4750.2022.02.0138
Abstract:
Solving the oblique incident seismic wave field under irregular terrain conditions is challenging, and previous methods are limited in calculation accuracy and application range. A ground motion input method was proposed for irregular terrains based on wave field separation by combining analytical derivation and finite element simulation. Seismic P waves and SV waves are separated under different boundary conditions. When incident vertically, they are decomposed into free wave field and scattered wave field at the side boundary, and incident wave field and boundary outer field at the bottom boundary. For oblique incidence, the seismic wave at the opposite boundary of the input side is separated into incident wave field and outer boundary field. In this paper, the influence of local topographic conditions was fully considered, and the improved wave method was used to input nodal force conveniently. Besides, the vibration responses of regular and irregular terrains under different incidence angles were analyzed. The results show that the method has high computational accuracy and efficiency under multiple topographic conditions and can be applied to complex site conditions. Moreover, the incident angle and local site conditions are found to have significant effects on surface displacement response. The study can provide an effective way for response analysis under irregular terrain conditions.
Solving the oblique incident seismic wave field under irregular terrain conditions is challenging, and previous methods are limited in calculation accuracy and application range. A ground motion input method was proposed for irregular terrains based on wave field separation by combining analytical derivation and finite element simulation. Seismic P waves and SV waves are separated under different boundary conditions. When incident vertically, they are decomposed into free wave field and scattered wave field at the side boundary, and incident wave field and boundary outer field at the bottom boundary. For oblique incidence, the seismic wave at the opposite boundary of the input side is separated into incident wave field and outer boundary field. In this paper, the influence of local topographic conditions was fully considered, and the improved wave method was used to input nodal force conveniently. Besides, the vibration responses of regular and irregular terrains under different incidence angles were analyzed. The results show that the method has high computational accuracy and efficiency under multiple topographic conditions and can be applied to complex site conditions. Moreover, the incident angle and local site conditions are found to have significant effects on surface displacement response. The study can provide an effective way for response analysis under irregular terrain conditions.
2023, 40(11): 81-89.
doi: 10.6052/j.issn.1000-4750.2022.01.0097
Abstract:
How to better simulate the hysteretic performance of separated shock absorber under earthquake is an important part of the seismic design of separated shock absorber. Because theoretical research on describing the mechanical properties of separated shock absorber from material level is relatively insufficient, a calculation method based on the Ramberg-Osgood model to derive the skeleton curve of separated shock absorber is proposed. Based on this method, a simplified algorithm for deriving bilinear model is also proposed. The difference in skeleton curve of separated shock absorber under the bilinear model, Chaboche model and ideal elastoplastic constitutive model is compared using ABAQUS. The applicability of the simplified algorithm in seismic design of bridge engineering is analyzed using an example of a 32 m railway simply-supported beam bridge. The results show that the skeleton curve of separated shock absorber derived based on the Ramberg-Osgood model can better fit that of the Chaboche model. Under near-fault earthquake with velocity-impulse effect, the average errors of bearing displacement and pier bottom bending moment calculated with the bilinear model and Chaboche model are −3.6% and 6.5%, respectively. The proposed simplified algorithm of bilinear model is safe and reasonable for the seismic design in bridge engineering.
How to better simulate the hysteretic performance of separated shock absorber under earthquake is an important part of the seismic design of separated shock absorber. Because theoretical research on describing the mechanical properties of separated shock absorber from material level is relatively insufficient, a calculation method based on the Ramberg-Osgood model to derive the skeleton curve of separated shock absorber is proposed. Based on this method, a simplified algorithm for deriving bilinear model is also proposed. The difference in skeleton curve of separated shock absorber under the bilinear model, Chaboche model and ideal elastoplastic constitutive model is compared using ABAQUS. The applicability of the simplified algorithm in seismic design of bridge engineering is analyzed using an example of a 32 m railway simply-supported beam bridge. The results show that the skeleton curve of separated shock absorber derived based on the Ramberg-Osgood model can better fit that of the Chaboche model. Under near-fault earthquake with velocity-impulse effect, the average errors of bearing displacement and pier bottom bending moment calculated with the bilinear model and Chaboche model are −3.6% and 6.5%, respectively. The proposed simplified algorithm of bilinear model is safe and reasonable for the seismic design in bridge engineering.
2023, 40(11): 90-98.
doi: 10.6052/j.issn.1000-4750.2022.01.0106
Abstract:
The dynamic measurement and identification of structural deformation are of great significance for structural health monitoring and performance assessment. Traditional contact-type displacement monitoring inevitably requires the arrangement of measurement points on physical structures as well as the setting of stable reference systems, limiting the application of dynamic displacement measurement of structures in practice. Computer vision-based structural displacement monitoring has the advantage of non-contact measurement, simple installation, and relatively low cost. However, the existing displacement identification methods are still influenced by lighting conditions, image resolution, and shooting-rate, which restricts its engineering applications. In order to take advantage of the high dynamic sampling rate of the traditional contact acceleration sensor, the concept of 'contact acceleration monitoring and non-contact displacement recognition' was proposed and an accurate estimation method for the critical dynamic deformation state of the structure was constructed. The proposed method is validated through a 1/2 scale reinforced concrete frame structure. The results show that the method can improve the displacement sampling rate and collect high-frequency vibration information compared with a single structural displacement visual measurement technique.
The dynamic measurement and identification of structural deformation are of great significance for structural health monitoring and performance assessment. Traditional contact-type displacement monitoring inevitably requires the arrangement of measurement points on physical structures as well as the setting of stable reference systems, limiting the application of dynamic displacement measurement of structures in practice. Computer vision-based structural displacement monitoring has the advantage of non-contact measurement, simple installation, and relatively low cost. However, the existing displacement identification methods are still influenced by lighting conditions, image resolution, and shooting-rate, which restricts its engineering applications. In order to take advantage of the high dynamic sampling rate of the traditional contact acceleration sensor, the concept of 'contact acceleration monitoring and non-contact displacement recognition' was proposed and an accurate estimation method for the critical dynamic deformation state of the structure was constructed. The proposed method is validated through a 1/2 scale reinforced concrete frame structure. The results show that the method can improve the displacement sampling rate and collect high-frequency vibration information compared with a single structural displacement visual measurement technique.
2023, 40(11): 99-109.
doi: 10.6052/j.issn.1000-4750.2022.01.0112
Abstract:
The monopile supporting structure of offshore wind turbine is composed of monopiles, transitions and conical towers. The large variability of Marine Soil and the characteristic of variable cross-section of wind turbine tower greatly increase the number of divided beam elements in finite element calculation of supporting structures using discrete spring method. In order to achieve efficient simulation of monopile supporting structure, an improved Euler-Bernoulli beam element was proposed in this paper. This element realized the built-in relationship between pile and soil, and could consider the variable section effect of tower section. Compared with traditional beam element, the number of divided elements was reduced greatly by using the improved element. The accuracy and efficiency of the improved element was verified in single-layer and multi-layer soil, and the applicability of the element to the calculation of monopile supporting structure was studied. This paper carried out a parameter analysis of monopile lateral bearing capacity, which analyzed the combined influence of pile length and diameter on lateral deformation characteristics and bearing capacity of large diameter piles. And the research suggested a new critical range of relative stiffness eigenvalues between rigid short pile and medium long pile, which is different from that given in existing standard.
The monopile supporting structure of offshore wind turbine is composed of monopiles, transitions and conical towers. The large variability of Marine Soil and the characteristic of variable cross-section of wind turbine tower greatly increase the number of divided beam elements in finite element calculation of supporting structures using discrete spring method. In order to achieve efficient simulation of monopile supporting structure, an improved Euler-Bernoulli beam element was proposed in this paper. This element realized the built-in relationship between pile and soil, and could consider the variable section effect of tower section. Compared with traditional beam element, the number of divided elements was reduced greatly by using the improved element. The accuracy and efficiency of the improved element was verified in single-layer and multi-layer soil, and the applicability of the element to the calculation of monopile supporting structure was studied. This paper carried out a parameter analysis of monopile lateral bearing capacity, which analyzed the combined influence of pile length and diameter on lateral deformation characteristics and bearing capacity of large diameter piles. And the research suggested a new critical range of relative stiffness eigenvalues between rigid short pile and medium long pile, which is different from that given in existing standard.
2023, 40(11): 110-119.
doi: 10.6052/j.issn.1000-4750.2022.01.0114
Abstract:
In order to study the shear behavior and reinforcement mechanism of brick wall reinforced with basalt textile reinforced concrete (BTRC), the diagonal shear tests have been carried out on BTRC reinforced walls, and the effects of single-side vs. double-side reinforcement, the number of textile layers and the strength of masonry mortar on the improvement of shear resistance have been investigated. The test results show that the BTRC and brick wall work well together, and the shear strength, stiffness and deformation capacity of brick wall are significantly improved; under the same number of textile layers, double-side reinforcement has better effect than single-side reinforcement; with the increase of the number of textile layers, the reinforcement effect of double-side is gradually improved, while the reinforcement effect of single-side changes little; for brick walls built with low strength mortar, the BTRC also transforms the failure mode of slip cracking of mortar joint into diagonal tensile failure with multi-joint cracking characteristics, and the reinforcement effect is remarkable. The mechanical characteristics of BTRC reinforced brick wall were analyzed, and the restraint reinforcement mechanism was put forward. Based on the test results and the reinforcement mechanism, the calculation method of shear capacity of brick wall reinforced with BTRC was studied.
In order to study the shear behavior and reinforcement mechanism of brick wall reinforced with basalt textile reinforced concrete (BTRC), the diagonal shear tests have been carried out on BTRC reinforced walls, and the effects of single-side vs. double-side reinforcement, the number of textile layers and the strength of masonry mortar on the improvement of shear resistance have been investigated. The test results show that the BTRC and brick wall work well together, and the shear strength, stiffness and deformation capacity of brick wall are significantly improved; under the same number of textile layers, double-side reinforcement has better effect than single-side reinforcement; with the increase of the number of textile layers, the reinforcement effect of double-side is gradually improved, while the reinforcement effect of single-side changes little; for brick walls built with low strength mortar, the BTRC also transforms the failure mode of slip cracking of mortar joint into diagonal tensile failure with multi-joint cracking characteristics, and the reinforcement effect is remarkable. The mechanical characteristics of BTRC reinforced brick wall were analyzed, and the restraint reinforcement mechanism was put forward. Based on the test results and the reinforcement mechanism, the calculation method of shear capacity of brick wall reinforced with BTRC was studied.
2023, 40(11): 120-129.
doi: 10.6052/j.issn.1000-4750.2022.01.0117
Abstract:
A compressive composite shear connector with transverse studs is developed for steel-concrete composite structures with high shear resistance. Ten compressive composite shear connectors and one non-compressive composite shear connector were designed, and monotonic push-out tests were carried out. The effects of concrete bearing at the end of rib plate, concrete strength, rib thickness, rib hole diameter and stud diameter on the failure mode and failure process of compressive composite shear connectors were investigated. The finite element models of compressive composite shear connectors were established. Using the simulation model verified by experiments, the shear mechanism of compressive composite shear connector was further revealed. Based on the test variables, 108 finite element models of compressive composite shear connectors were established and analyzed, the linear relationship between the ultimate bearing capacity of compressive composite shear connectors and various parameter variables was deduced, the analysis results of ultimate bearing capacity were regressed, and the calculation model of ultimate bearing capacity of compressive composite shear connectors was proposed. The results show that the failure modes of concrete slabs of compressive composite shear connector are large-area vertical cracks and end cracks, and inclined main cracks extending downward from near the height of welding nails are formed on the inner surface. The concrete slabs with non-compressive composite shear connector have no obvious end cracks, and the ultimate bearing capacity of compressive composite shear connector is about 1.4 times that of the no-compressive type. Compared with the diameter of rib and stud, the ultimate bearing capacity of compressive composite shear connector is more sensitive to concrete strength and rib thickness. The proposed model of ultimate bearing capacity of compressive composite shear connector has clear physical meaning, and the calculated results are in good agreement with the simulation and test results, which can provide a reference for the design and engineering application of composite shear key.
A compressive composite shear connector with transverse studs is developed for steel-concrete composite structures with high shear resistance. Ten compressive composite shear connectors and one non-compressive composite shear connector were designed, and monotonic push-out tests were carried out. The effects of concrete bearing at the end of rib plate, concrete strength, rib thickness, rib hole diameter and stud diameter on the failure mode and failure process of compressive composite shear connectors were investigated. The finite element models of compressive composite shear connectors were established. Using the simulation model verified by experiments, the shear mechanism of compressive composite shear connector was further revealed. Based on the test variables, 108 finite element models of compressive composite shear connectors were established and analyzed, the linear relationship between the ultimate bearing capacity of compressive composite shear connectors and various parameter variables was deduced, the analysis results of ultimate bearing capacity were regressed, and the calculation model of ultimate bearing capacity of compressive composite shear connectors was proposed. The results show that the failure modes of concrete slabs of compressive composite shear connector are large-area vertical cracks and end cracks, and inclined main cracks extending downward from near the height of welding nails are formed on the inner surface. The concrete slabs with non-compressive composite shear connector have no obvious end cracks, and the ultimate bearing capacity of compressive composite shear connector is about 1.4 times that of the no-compressive type. Compared with the diameter of rib and stud, the ultimate bearing capacity of compressive composite shear connector is more sensitive to concrete strength and rib thickness. The proposed model of ultimate bearing capacity of compressive composite shear connector has clear physical meaning, and the calculated results are in good agreement with the simulation and test results, which can provide a reference for the design and engineering application of composite shear key.
RESEARCH ON BEARING DEFORMATION OF SINGLE PILE UNDER VERTICAL FORCE-THERMAL LOAD-TORQUE LOADING PATH
2023, 40(11): 130-139.
doi: 10.6052/j.issn.1000-4750.2022.01.0125
Abstract:
The energy pile exhibits complex mechanical behavior, and there is relatively little research on the bearing deformation characteristics of the energy pile under multi-direction loads. To investigate the bearing characteristics of energy piles under vertical load, thermal load, and torque, the thermal load and torque were applied after preloading the vertical load to the pile top. By considering the effect of thermal load on the shaft resistance and boundary conditions of the pile, the pile displacement control equation is derived based on the load transfer method and boundary element method, and the analysis method of the bearing deformation characteristics of energy pile under vertical force → thermal load → torque loading path is proposed. The proposed method is in good agreement with the existing experiments and ABAQUS finite element results. The results show that thermal loading changes the load transfer characteristics of the monopile and affects the axial force and lateral frictional resistance distribution of the pile. Under the vertical force → thermal load → torque loading path, the additional load caused by the temperature change leads to the reduction of the monopile torsional resistance. Further parametric analysis shows that increasing the vertical load decreases the ultimate circumferential frictional resistance on the pile side, resulting in a 26.2% reduction (75%Pu, where Pu is the ultimate load) in the torsional resistance of the energy pile monopile. With the increase in the length-diameter ratio, the bearing capacity gradually increases, and thus the effect of thermal load can be offset by selecting a suitable length-diameter ratio. With the increase of temperature increment, the deformation increases gradually, and the deformation of the upper 0.6L is more significant, so the engineering pile foundation used as an energy pile needs to be reinforced on the upper part.
The energy pile exhibits complex mechanical behavior, and there is relatively little research on the bearing deformation characteristics of the energy pile under multi-direction loads. To investigate the bearing characteristics of energy piles under vertical load, thermal load, and torque, the thermal load and torque were applied after preloading the vertical load to the pile top. By considering the effect of thermal load on the shaft resistance and boundary conditions of the pile, the pile displacement control equation is derived based on the load transfer method and boundary element method, and the analysis method of the bearing deformation characteristics of energy pile under vertical force → thermal load → torque loading path is proposed. The proposed method is in good agreement with the existing experiments and ABAQUS finite element results. The results show that thermal loading changes the load transfer characteristics of the monopile and affects the axial force and lateral frictional resistance distribution of the pile. Under the vertical force → thermal load → torque loading path, the additional load caused by the temperature change leads to the reduction of the monopile torsional resistance. Further parametric analysis shows that increasing the vertical load decreases the ultimate circumferential frictional resistance on the pile side, resulting in a 26.2% reduction (75%Pu, where Pu is the ultimate load) in the torsional resistance of the energy pile monopile. With the increase in the length-diameter ratio, the bearing capacity gradually increases, and thus the effect of thermal load can be offset by selecting a suitable length-diameter ratio. With the increase of temperature increment, the deformation increases gradually, and the deformation of the upper 0.6L is more significant, so the engineering pile foundation used as an energy pile needs to be reinforced on the upper part.
2023, 40(11): 140-154.
doi: 10.6052/j.issn.1000-4750.2022.02.0128
Abstract:
In order to study the effect of precast filled wall with polystyrene plate horizontal joint on the seismic performance of shear wall, quasi-static tests of 4 pieces of shear wall specimen with the same size were conducted. Three specimens are shear wall specimens with cast-in-place walls at both ends and precast walls with polystyrene board horizontal joint in the middle, and the fourth specimen is cast-in-place shear wall. The test results show that the failure pattern of the four specimens are compression failure of the normal section of the whole wall, but the shear wall specimen with polystyrene plate horizontal joint has vertical cracks through the joint surface of the cast-in-place wall and the precast wall, while the cracks in the middle precast filled wall are significantly less, and the cracks in the middle precast filled wall of the specimen with boundary elements at both ends of the cast-in-place wall are even less. The ultimate drift ratio of the specimens ranges from 1/83 to 1/50. Compared with the cast-in-place shear wall, the yield stiffness of the shear wall specimens with polystyrene plate horizontal joint decreases by 19.4%~61.6%, and the peak stiffness decreases by 37.8%~55.6%, indicating that the precast filled wall with horizontal joint polystyrene plate can effectively reduce the stiffness. The measured peak lateral load of specimens with precast filled wall in the middle is less than that of cast-in-place shear wall, and its eccentric carrying capacity can still be calculated as the whole wall, but the vertically distributed reinforcement of the precast wall is not included. Using the finite element analysis program ABAQUS, the nonlinear numerical simulation and parameter analysis of the specimens were carried out.The simulation results show that the lateral carrying capacity and stiffness decrease, and the deformation capacity increases with the thickness of the polystyrene plate. The lateral carrying capacity and stiffness decrease, and the deformation capacity increases significantly with the decrease of the length of the cast-in-place walls on both sides.
In order to study the effect of precast filled wall with polystyrene plate horizontal joint on the seismic performance of shear wall, quasi-static tests of 4 pieces of shear wall specimen with the same size were conducted. Three specimens are shear wall specimens with cast-in-place walls at both ends and precast walls with polystyrene board horizontal joint in the middle, and the fourth specimen is cast-in-place shear wall. The test results show that the failure pattern of the four specimens are compression failure of the normal section of the whole wall, but the shear wall specimen with polystyrene plate horizontal joint has vertical cracks through the joint surface of the cast-in-place wall and the precast wall, while the cracks in the middle precast filled wall are significantly less, and the cracks in the middle precast filled wall of the specimen with boundary elements at both ends of the cast-in-place wall are even less. The ultimate drift ratio of the specimens ranges from 1/83 to 1/50. Compared with the cast-in-place shear wall, the yield stiffness of the shear wall specimens with polystyrene plate horizontal joint decreases by 19.4%~61.6%, and the peak stiffness decreases by 37.8%~55.6%, indicating that the precast filled wall with horizontal joint polystyrene plate can effectively reduce the stiffness. The measured peak lateral load of specimens with precast filled wall in the middle is less than that of cast-in-place shear wall, and its eccentric carrying capacity can still be calculated as the whole wall, but the vertically distributed reinforcement of the precast wall is not included. Using the finite element analysis program ABAQUS, the nonlinear numerical simulation and parameter analysis of the specimens were carried out.The simulation results show that the lateral carrying capacity and stiffness decrease, and the deformation capacity increases with the thickness of the polystyrene plate. The lateral carrying capacity and stiffness decrease, and the deformation capacity increases significantly with the decrease of the length of the cast-in-place walls on both sides.
2023, 40(11): 155-167.
doi: 10.6052/j.issn.1000-4750.2022.01.0133
Abstract:
In order to reveal the seismic behavior of steel-reinforced concrete (SRC) columns under compression-flexure-shear-torsion combined actions, twelve SRC columns and one reinforced concrete(RC) column were tested by comprehensively considering the cross-sectional dimension of the column, the steel ratio, the reinforcement ratio, the stirrup ratio and, the welded stud location. The failure characteristics of specimens under composite torsional conditions were observed, and the influence of different parameters on the seismic indexes of SRC columns were analyzed, such as hysteric curve, stiffness degradation, energy dissipation and ductility. The test results indicate that the failure patterns of specimens mainly appear as the bending-torsion composite failure occurs. The load - displacement hysteric curves present full spindle shapes, and the torque-torsion angle curves are in “S” shapes with obvious pinching. The torsional and flexural bearing capacity of SRC columns can be effectively improved by increasing the section size or reinforcing ratio. Before the peak load, the degradation rate of torsional stiffness is significantly faster than that of flexural stiffness and, increasing the steel ratio and reinforcement ratio can delay the degradation of SRC column stiffness. The bending energy dissipation capacity of SRC columns is better than the torsional energy dissipation capacity, and the torsional ductility is greater than the bending ductility. SRC columns with rectangular cross-sections have better torsional deformation capacity than those with square cross-sections. Welding studs on I - shaped steel flanges can effectively improve the seismic behavior of SRC columns. According to the current seismic code and test data, some suggestions of structural measures of SRC columns and empirical formula of torsional energy degradation are put forward.
In order to reveal the seismic behavior of steel-reinforced concrete (SRC) columns under compression-flexure-shear-torsion combined actions, twelve SRC columns and one reinforced concrete(RC) column were tested by comprehensively considering the cross-sectional dimension of the column, the steel ratio, the reinforcement ratio, the stirrup ratio and, the welded stud location. The failure characteristics of specimens under composite torsional conditions were observed, and the influence of different parameters on the seismic indexes of SRC columns were analyzed, such as hysteric curve, stiffness degradation, energy dissipation and ductility. The test results indicate that the failure patterns of specimens mainly appear as the bending-torsion composite failure occurs. The load - displacement hysteric curves present full spindle shapes, and the torque-torsion angle curves are in “S” shapes with obvious pinching. The torsional and flexural bearing capacity of SRC columns can be effectively improved by increasing the section size or reinforcing ratio. Before the peak load, the degradation rate of torsional stiffness is significantly faster than that of flexural stiffness and, increasing the steel ratio and reinforcement ratio can delay the degradation of SRC column stiffness. The bending energy dissipation capacity of SRC columns is better than the torsional energy dissipation capacity, and the torsional ductility is greater than the bending ductility. SRC columns with rectangular cross-sections have better torsional deformation capacity than those with square cross-sections. Welding studs on I - shaped steel flanges can effectively improve the seismic behavior of SRC columns. According to the current seismic code and test data, some suggestions of structural measures of SRC columns and empirical formula of torsional energy degradation are put forward.
2023, 40(11): 168-178.
doi: 10.6052/j.issn.1000-4750.2022.02.0136
Abstract:
Crosstie is a promising mean for vibration mitigation of long inclined cables. In order to study the inherent characteristics of the system with crosstie and its variation with key parameters, a model for the sagged-cable-crosstie system composed of N vertical cables and of M crossties was established. The dimensionless equation of motion was obtained and then solved by introducing boundary, continuity, and equilibrium conditions. The general model was reduced to a double-cable-crosstie system, and its dimensionless frequency equation was obtained. The effects of key parameters on the frequencies and modes of the system were studied by numerical analysis, such as Irvine parameter λ2, stiffness and location of crossties, and wave velocity ratio η. The results show that the sag only affects the out-of-phase frequency when the parameters of the two cables are the same, so the ω-λ2 curves of in-phase vibration and out-of-phase vibration show cross-over phenomenon and veering phenomenon, respectively. When λ2 is a certain value, the first order out-of-phase vibration frequency under any crosstie stiffnesses is equal to the first order in-phase frequency, thusly the frequency curves pass through the first cross-over point. If the parameters of the two sagged cables are the same, increasing the stiffness of the crosstie only increases the out-of-phase vibration frequency of the system, but the increase is not more than 1. If the wave velocities of the two sagged cables are different, all the frequencies of the system will be “jumping” to higher orders with the increase of the wave velocity difference, and the higher the frequency order, the more the number of “jumping”.
Crosstie is a promising mean for vibration mitigation of long inclined cables. In order to study the inherent characteristics of the system with crosstie and its variation with key parameters, a model for the sagged-cable-crosstie system composed of N vertical cables and of M crossties was established. The dimensionless equation of motion was obtained and then solved by introducing boundary, continuity, and equilibrium conditions. The general model was reduced to a double-cable-crosstie system, and its dimensionless frequency equation was obtained. The effects of key parameters on the frequencies and modes of the system were studied by numerical analysis, such as Irvine parameter λ2, stiffness and location of crossties, and wave velocity ratio η. The results show that the sag only affects the out-of-phase frequency when the parameters of the two cables are the same, so the ω-λ2 curves of in-phase vibration and out-of-phase vibration show cross-over phenomenon and veering phenomenon, respectively. When λ2 is a certain value, the first order out-of-phase vibration frequency under any crosstie stiffnesses is equal to the first order in-phase frequency, thusly the frequency curves pass through the first cross-over point. If the parameters of the two sagged cables are the same, increasing the stiffness of the crosstie only increases the out-of-phase vibration frequency of the system, but the increase is not more than 1. If the wave velocities of the two sagged cables are different, all the frequencies of the system will be “jumping” to higher orders with the increase of the wave velocity difference, and the higher the frequency order, the more the number of “jumping”.
2023, 40(11): 179-189, 205.
doi: 10.6052/j.issn.1000-4750.2022.02.0144
Abstract:
The steel tubed reinforced concrete (STRC) column joints are strengthened using built-in section steel. To clarify the position of control section and compression-bending capacity of the STRC column with built-in non through section steel in the joint, the quasi-static test and finite element simulation were carried out on the STRC columns with different lengths of built-in section steel and the comparison specimen without section steel. The mechanical mechanism and bearing capacity of the specimens were analyzed, and the effects of the length of section steel and confinement of steel tube were discussed. The results show that with the increase of the length of the built-in section steel, the failure section tends to transfer from the steel-concrete transition section to the column root. Increasing the diameter thickness ratio of steel tube will reduce the compression-bending capacity of steel tube and transition section and then affect the location of failure section. Based on the test and finite element analysis results, the calculation models of compression bending capacity of the column root and transition section are proposed, and the determination method of critical length of section steel is established. The research results provide a theoretical basis for the design of STRC column and joint with built-in non-through section steel.
The steel tubed reinforced concrete (STRC) column joints are strengthened using built-in section steel. To clarify the position of control section and compression-bending capacity of the STRC column with built-in non through section steel in the joint, the quasi-static test and finite element simulation were carried out on the STRC columns with different lengths of built-in section steel and the comparison specimen without section steel. The mechanical mechanism and bearing capacity of the specimens were analyzed, and the effects of the length of section steel and confinement of steel tube were discussed. The results show that with the increase of the length of the built-in section steel, the failure section tends to transfer from the steel-concrete transition section to the column root. Increasing the diameter thickness ratio of steel tube will reduce the compression-bending capacity of steel tube and transition section and then affect the location of failure section. Based on the test and finite element analysis results, the calculation models of compression bending capacity of the column root and transition section are proposed, and the determination method of critical length of section steel is established. The research results provide a theoretical basis for the design of STRC column and joint with built-in non-through section steel.
2023, 40(11): 190-205.
doi: 10.6052/j.issn.1000-4750.2022.02.0152
Abstract:
In order to study the seismic performance and the mechanical behavior of vertical joint of assembled serrate-edges monolithic shear wall, one cast-in-place concrete shear wall and three new type shear walls were conducted by quasi-static tests, whose variable parameters include axial compression ratio and shear span ratio. The results show that: all specimens are flexural failure modes, and the flexural capacity and stiffness of the serrate-edges monolithic shear wall are equivalent to these of cast-in-place concrete shear wall. It can be proved that serrate-edges monolithic shear wall has good seismic performance, which can satisfy the design concept of ‘being equivalent to cast-in-place counterparts’. The vertical joints keep intact when the displacement angle is 1/1000, and the sliding deformation of the vertical joints occurred when the displacement angle is greater than 1/500. The hysteretic curve of assembled serrate-edges monolithic shear wall is full, and the displacement ductility coefficient is greater than 5, which can be proved that the new type shear wall has good deformation performance. Increasing the axial compression ratio and reducing the shear span ratio expedite crack propagation of vertical joints and the development trends of relative deformation between each side of the vertical joints. Changing these parameters, the influence law of flexural and deformation capacity of the serrate-edges monolithic shear wall is the same as that of cast-in-place shear wall. Under high axial compression, the failure region is concentrated in the vicinity of dowel hole, forming vertical cracks, and the collapse area is reduced at the toe of the shear wall. The numerical analysis was carried out by ABAQUS. The skeleton curve and failure morphology are in accordance with the test results. The effect of axial compression ratio and shear span ratio on the wall performance is consistent with the test. Increasing the size of the transverse slot and reducing the inner size of the transverse groove have little effect on the mechanical properties of the walls.
In order to study the seismic performance and the mechanical behavior of vertical joint of assembled serrate-edges monolithic shear wall, one cast-in-place concrete shear wall and three new type shear walls were conducted by quasi-static tests, whose variable parameters include axial compression ratio and shear span ratio. The results show that: all specimens are flexural failure modes, and the flexural capacity and stiffness of the serrate-edges monolithic shear wall are equivalent to these of cast-in-place concrete shear wall. It can be proved that serrate-edges monolithic shear wall has good seismic performance, which can satisfy the design concept of ‘being equivalent to cast-in-place counterparts’. The vertical joints keep intact when the displacement angle is 1/1000, and the sliding deformation of the vertical joints occurred when the displacement angle is greater than 1/500. The hysteretic curve of assembled serrate-edges monolithic shear wall is full, and the displacement ductility coefficient is greater than 5, which can be proved that the new type shear wall has good deformation performance. Increasing the axial compression ratio and reducing the shear span ratio expedite crack propagation of vertical joints and the development trends of relative deformation between each side of the vertical joints. Changing these parameters, the influence law of flexural and deformation capacity of the serrate-edges monolithic shear wall is the same as that of cast-in-place shear wall. Under high axial compression, the failure region is concentrated in the vicinity of dowel hole, forming vertical cracks, and the collapse area is reduced at the toe of the shear wall. The numerical analysis was carried out by ABAQUS. The skeleton curve and failure morphology are in accordance with the test results. The effect of axial compression ratio and shear span ratio on the wall performance is consistent with the test. Increasing the size of the transverse slot and reducing the inner size of the transverse groove have little effect on the mechanical properties of the walls.
2023, 40(11): 206-217, 226.
doi: 10.6052/j.issn.1000-4750.2022.03.0259
Abstract:
In order to study the mechanical performance of UHPC under triaxial compression, the conventional triaxial experiment was carried out to analyse the mechanical properties such as the failure modes, stress-strain curve, peak stress and strain by considering the confining pressure and steel fiber content as experimental parameters. The results show that: the specimens without confining pressure and steel fiber exhibit splitting failure, while the others exhibit shear failure. The elastic modulus and elastic segment curve shape of the stress-strain curves remain unchanged as confining pressure and steel fiber content change. With the increase of confining pressure, the peak stress and strain increase continuously. With the increase of steel fiber content, the peak stress increases firstly and then remains unchanged and the axial peak strain increases firstly and then decreases, while the hoop peak strain increases. Based on the Drucker-Prager two parameter criterion, the octahedron failure criterion calculation method of UHPC was established by analyzing its octahedron normal stress, volume strain relationship and, its octahedron shear stress and shear strain relationship.
In order to study the mechanical performance of UHPC under triaxial compression, the conventional triaxial experiment was carried out to analyse the mechanical properties such as the failure modes, stress-strain curve, peak stress and strain by considering the confining pressure and steel fiber content as experimental parameters. The results show that: the specimens without confining pressure and steel fiber exhibit splitting failure, while the others exhibit shear failure. The elastic modulus and elastic segment curve shape of the stress-strain curves remain unchanged as confining pressure and steel fiber content change. With the increase of confining pressure, the peak stress and strain increase continuously. With the increase of steel fiber content, the peak stress increases firstly and then remains unchanged and the axial peak strain increases firstly and then decreases, while the hoop peak strain increases. Based on the Drucker-Prager two parameter criterion, the octahedron failure criterion calculation method of UHPC was established by analyzing its octahedron normal stress, volume strain relationship and, its octahedron shear stress and shear strain relationship.
2023, 40(11): 218-226.
doi: 10.6052/j.issn.1000-4750.2022.04.0278
Abstract:
In order to study the energy-based seismic design method of RC beam members, it is necessary to establish a reasonable damage index to quantify the structural damage. The research group established the relationship between the energy dissipation capacity of RC beam members and the displacement amplitude, cumulative energy dissipation and design parameters in the early stage, and proposed the damage index of energy dissipation capacity and performance index limits of RC beam members. Referring to existing research, the seismic design method of RC beam members was proposed based on the damage index of energy dissipation capacity. It is found that the seismic design method can establish a quantitative relationship between structural design parameters and seismic parameters, so as to guide the structural design; The increase of stirrup ratio can effectively slow down the damage of RC beam members, but the effect of damage reduction is quick and then slow; The increase of duration can aggravate the damage development of RC beam member, and the increase effect is fast and then slow; The increase of reinforcement ratio can reduce the damage of RC beam members as a whole. This seismic design method can make up for the deficiency of the current building seismic design code that the time lasting effect is not considered.
In order to study the energy-based seismic design method of RC beam members, it is necessary to establish a reasonable damage index to quantify the structural damage. The research group established the relationship between the energy dissipation capacity of RC beam members and the displacement amplitude, cumulative energy dissipation and design parameters in the early stage, and proposed the damage index of energy dissipation capacity and performance index limits of RC beam members. Referring to existing research, the seismic design method of RC beam members was proposed based on the damage index of energy dissipation capacity. It is found that the seismic design method can establish a quantitative relationship between structural design parameters and seismic parameters, so as to guide the structural design; The increase of stirrup ratio can effectively slow down the damage of RC beam members, but the effect of damage reduction is quick and then slow; The increase of duration can aggravate the damage development of RC beam member, and the increase effect is fast and then slow; The increase of reinforcement ratio can reduce the damage of RC beam members as a whole. This seismic design method can make up for the deficiency of the current building seismic design code that the time lasting effect is not considered.
2023, 40(11): 227-235.
doi: 10.6052/j.issn.1000-4750.2022.08.0752
Abstract:
Wire nets refers to the three-dimensional mesh-structure woven by high-strength steel wire, which has been used in the interception of short-range weapons (such as rocket and mortar shells). To understand the mechanical properties of the interaction between the wire nets and the warhead, combined with the intercepted tests and the fracture feature of the wire nets, the rigid warhead device and the static pressure experimental platform of the wire nets were designed, and the static tests had been carried out for the wire nets pressured by the rigid warhead. The results show that: when the wire nets were downing, the wire nets presented the funnel-shaped deformation on a whole and the diamond-shaped mesh at the contact part between the wire nets and the warhead presented the deformation gradually approaching to the profile shape of the warhead; and the fracture was located at the intersection of the steel wires in the diamond-shaped mesh which was belonged to the contact part. Based on the research of experimental phenomena and relevant results, one theoretical calculation method for static pressure critical force by the rigid warhead was deduced and the reasons of the errors were analyzed. Overall, the theoretical calculation method for the static pressure critical force was in a good agreement with that obtained from the tests and the error was within 10%. The research results can provide a reference for the preliminary design of the wire nets used for intercepting the short-range weapons.
Wire nets refers to the three-dimensional mesh-structure woven by high-strength steel wire, which has been used in the interception of short-range weapons (such as rocket and mortar shells). To understand the mechanical properties of the interaction between the wire nets and the warhead, combined with the intercepted tests and the fracture feature of the wire nets, the rigid warhead device and the static pressure experimental platform of the wire nets were designed, and the static tests had been carried out for the wire nets pressured by the rigid warhead. The results show that: when the wire nets were downing, the wire nets presented the funnel-shaped deformation on a whole and the diamond-shaped mesh at the contact part between the wire nets and the warhead presented the deformation gradually approaching to the profile shape of the warhead; and the fracture was located at the intersection of the steel wires in the diamond-shaped mesh which was belonged to the contact part. Based on the research of experimental phenomena and relevant results, one theoretical calculation method for static pressure critical force by the rigid warhead was deduced and the reasons of the errors were analyzed. Overall, the theoretical calculation method for the static pressure critical force was in a good agreement with that obtained from the tests and the error was within 10%. The research results can provide a reference for the preliminary design of the wire nets used for intercepting the short-range weapons.
2023, 40(11): 236-243.
doi: 10.6052/j.issn.1000-4750.2022.02.0139
Abstract:
A method of unequal interval stress spectrum compilation based on fatigue damage was proposed to ensure the stress spectrum compilation from the measured stress-time history to reflect the actual effect characteristics of the load. According to the damage equivalence principle, a mathematical model of the relationship between the stress spectrum classification numbers and fatigue damage were established by adding unequal interval adaptive ratio coefficients. Considering the attribute characteristics of each stress cycle, cluster analysis was used to classify all stress cycles, while the classification accuracy and prediction map under different classification numbers were obtained based on the support vector machine multi-classification. Considering the relative error of damage obtained from the mathematical model and the classification accuracy of support vector machine, the corresponding unequal interval stress spectrum were compiled by means of the optimal number of stress spectrum, which was compared with the equal interval spectrum and unequal interval spectrum of 8 levels. The results show that the stress spectrum of classification based on the damage equivalent principle, cluster analysis and support vector machine considers the overall characteristics of all stress cycle and the local information and properties of the stress, and the results of the fatigue cumulative damage theory are significantly lower than the actual damage, so that the measured data of stress characteristic and the effects of fatigue are accurately reflected. This method can be used for other measured load-time history to unequal interval classification and load spectrum compilation.
A method of unequal interval stress spectrum compilation based on fatigue damage was proposed to ensure the stress spectrum compilation from the measured stress-time history to reflect the actual effect characteristics of the load. According to the damage equivalence principle, a mathematical model of the relationship between the stress spectrum classification numbers and fatigue damage were established by adding unequal interval adaptive ratio coefficients. Considering the attribute characteristics of each stress cycle, cluster analysis was used to classify all stress cycles, while the classification accuracy and prediction map under different classification numbers were obtained based on the support vector machine multi-classification. Considering the relative error of damage obtained from the mathematical model and the classification accuracy of support vector machine, the corresponding unequal interval stress spectrum were compiled by means of the optimal number of stress spectrum, which was compared with the equal interval spectrum and unequal interval spectrum of 8 levels. The results show that the stress spectrum of classification based on the damage equivalent principle, cluster analysis and support vector machine considers the overall characteristics of all stress cycle and the local information and properties of the stress, and the results of the fatigue cumulative damage theory are significantly lower than the actual damage, so that the measured data of stress characteristic and the effects of fatigue are accurately reflected. This method can be used for other measured load-time history to unequal interval classification and load spectrum compilation.
2023, 40(11): 244-256.
doi: 10.6052/j.issn.1000-4750.2022.08.0715
Abstract:
To study the energy absorption capacity of different aluminum foam-filled thin-walled aluminum alloy multi-cell plate (MCP) and single-cell plate (SCP), six kinds of aluminum foam-filled thin-wall aluminum alloy multi-cell plate and one kind of single-cell plate were designed in this study, and the numerical models of MCP and SCP were established upon nonlinear finite element software LS-DYNA. The impact resistance test of the classic aluminum alloy plate and the impact resistance test of the aluminum foam sandwich plate are simulated numerically. The analysis shows that: the numerical model established can better simulate the impact force, the deflection and deformation of the aluminum foam sandwich plate during the impact process. Based on this model, the energy absorption characteristics of aluminum foam-filled thin-walled aluminum alloy MCP and SCP under different factors were compared and studied, and the failure mode and energy absorption mechanism were analyzed. Finally, the energy absorption efficiency under different factors and the selection of optimal section type of multi-cell plate were analyzed by orthogonal tests. The results show that the failure mode of aluminum foam-filled thin-wall aluminum alloy plates is symmetric conical failure under out-of-plane impact. Both structures have two stages: elastic-plastic deformation stage and spring-back stage. Under the same displacement, the total energy (E) and specific energy absorption (SEA) of the MCP with 18 different parameters are increased by more than 400% compared with that of the SCP, which is a plate with more energy absorption characteristics and can be widely used in protection engineering.
To study the energy absorption capacity of different aluminum foam-filled thin-walled aluminum alloy multi-cell plate (MCP) and single-cell plate (SCP), six kinds of aluminum foam-filled thin-wall aluminum alloy multi-cell plate and one kind of single-cell plate were designed in this study, and the numerical models of MCP and SCP were established upon nonlinear finite element software LS-DYNA. The impact resistance test of the classic aluminum alloy plate and the impact resistance test of the aluminum foam sandwich plate are simulated numerically. The analysis shows that: the numerical model established can better simulate the impact force, the deflection and deformation of the aluminum foam sandwich plate during the impact process. Based on this model, the energy absorption characteristics of aluminum foam-filled thin-walled aluminum alloy MCP and SCP under different factors were compared and studied, and the failure mode and energy absorption mechanism were analyzed. Finally, the energy absorption efficiency under different factors and the selection of optimal section type of multi-cell plate were analyzed by orthogonal tests. The results show that the failure mode of aluminum foam-filled thin-wall aluminum alloy plates is symmetric conical failure under out-of-plane impact. Both structures have two stages: elastic-plastic deformation stage and spring-back stage. Under the same displacement, the total energy (E) and specific energy absorption (SEA) of the MCP with 18 different parameters are increased by more than 400% compared with that of the SCP, which is a plate with more energy absorption characteristics and can be widely used in protection engineering.
