2020 Vol. 37 No. 2
2020, 37(2): 1-15.
DOI: 10.6052/j.issn.1000-4750.2019.05.ST07
Abstract：
Strength theory deals with the failure of materials under complex stress states. Summarizing the classical strength theories and two kinds of modern strength theories of concrete and isotropic rock. Isotropic strength theories include shear stress strength theory, octahedral strength theory, and principal stress strength theory. Various major strength theories were discussed, compared, and evaluated through collecting relevant domestic and foreign triaxial experimental data. Based on previous researches, the principal stress-space strength theories of concrete and isotropic rock were prospected.
Strength theory deals with the failure of materials under complex stress states. Summarizing the classical strength theories and two kinds of modern strength theories of concrete and isotropic rock. Isotropic strength theories include shear stress strength theory, octahedral strength theory, and principal stress strength theory. Various major strength theories were discussed, compared, and evaluated through collecting relevant domestic and foreign triaxial experimental data. Based on previous researches, the principal stress-space strength theories of concrete and isotropic rock were prospected.
2020, 37(2): 16-22,80.
DOI: 10.6052/j.issn.1000-4750.2019.01.0096
Abstract：
Based on the exact geometric beam element model, the nonlinear stiffness characteristic of helix spring with circular cross-sections was investigated. The way to choose descriptive variables of spring model was combined with deformation characteristics of slender helix spring, and the spring radius, height, helix polar angle and torsion angle of the cross-section of spring wire were selected as the descriptive variables of helix spring. According to the Bernoulli beam theory, the cross-section coordinate system was established by the centroid curve tangent vector and torsion angle of the cross-section. Spring deformation virtual power equation was built using curvature vector of helix spring which was based on the deformation virtual power of large rotating beam. The deformation virtual power equation of spring was built by using the method of removing high-frequency vibrations in flexible body systems. As validated by numerical examples, the results conformed to the deformation law of spring stiffness. In addition, compared with the classical theory algorithm and the traditional finite element method, the results proved the validity and rationality of the analytical procedure.
Based on the exact geometric beam element model, the nonlinear stiffness characteristic of helix spring with circular cross-sections was investigated. The way to choose descriptive variables of spring model was combined with deformation characteristics of slender helix spring, and the spring radius, height, helix polar angle and torsion angle of the cross-section of spring wire were selected as the descriptive variables of helix spring. According to the Bernoulli beam theory, the cross-section coordinate system was established by the centroid curve tangent vector and torsion angle of the cross-section. Spring deformation virtual power equation was built using curvature vector of helix spring which was based on the deformation virtual power of large rotating beam. The deformation virtual power equation of spring was built by using the method of removing high-frequency vibrations in flexible body systems. As validated by numerical examples, the results conformed to the deformation law of spring stiffness. In addition, compared with the classical theory algorithm and the traditional finite element method, the results proved the validity and rationality of the analytical procedure.
Abstract：
A new numerical algorithm is presented to solve viscoelastic problems by combining a temporally piecewise adaptive technique with the isogeometric analysis. By expanding variables at a discretized time interval, a series of recursive scaled boundary finite element method equations in spatial domain is established with non-uniform rational B-spline discretization in the circumferential direction. The proposed algorithm not only takes advantages of conventional scaled boundary finite element method in dealing with singularity and unbounded domains, but also provides a more accurate geometric description of the boundary, resulting in more accurate special solutions. A piecewise adaptive process is utilized to fully maintain a steady accuracy in the time domain for different sizes of time step. Numerical examples are presented to demonstrate the effectiveness of the proposed model in term of computational accuracy and convergence.
A new numerical algorithm is presented to solve viscoelastic problems by combining a temporally piecewise adaptive technique with the isogeometric analysis. By expanding variables at a discretized time interval, a series of recursive scaled boundary finite element method equations in spatial domain is established with non-uniform rational B-spline discretization in the circumferential direction. The proposed algorithm not only takes advantages of conventional scaled boundary finite element method in dealing with singularity and unbounded domains, but also provides a more accurate geometric description of the boundary, resulting in more accurate special solutions. A piecewise adaptive process is utilized to fully maintain a steady accuracy in the time domain for different sizes of time step. Numerical examples are presented to demonstrate the effectiveness of the proposed model in term of computational accuracy and convergence.
Abstract：
It discusses the static performance deterioration of corroded concrete-filled steel tubular members by simulating acid rain solution, including:the mechanical properties of corroded steel materials; the axial compressive behavior of corroded concrete-filled steel tubular members; the pure bending mechanical properties of corroded concrete-filled steel tubular members; the eccentric compressive mechanical properties of corroded concrete-filled steel tubular members. The impact of corrosion ratio on the yield strength, elastic modulus, ultimate tensile strength, and ultimate elongation of corroded steel are analyzed. By using wall thickness reduction and wall thickness coupling with material property reduction method to simulate corrosion damage in conjunction with finite element commercial software ABAQUS and design code formulas, the relationships between load and displacement as well as the bearing capacity of corroded concrete-filled steel tubular members are computated. The computational solutions are compared with the test results, implying that the wall thickness reduction method is superior to the wall thickness coupling with material property reduction method, and that the local design code is stricter to the state code.
It discusses the static performance deterioration of corroded concrete-filled steel tubular members by simulating acid rain solution, including:the mechanical properties of corroded steel materials; the axial compressive behavior of corroded concrete-filled steel tubular members; the pure bending mechanical properties of corroded concrete-filled steel tubular members; the eccentric compressive mechanical properties of corroded concrete-filled steel tubular members. The impact of corrosion ratio on the yield strength, elastic modulus, ultimate tensile strength, and ultimate elongation of corroded steel are analyzed. By using wall thickness reduction and wall thickness coupling with material property reduction method to simulate corrosion damage in conjunction with finite element commercial software ABAQUS and design code formulas, the relationships between load and displacement as well as the bearing capacity of corroded concrete-filled steel tubular members are computated. The computational solutions are compared with the test results, implying that the wall thickness reduction method is superior to the wall thickness coupling with material property reduction method, and that the local design code is stricter to the state code.
Abstract：
The high-rise frame-diagrid structure is a new dual system. It is composed of a high-rise diagrid structure and a frame structure. The horizontal shear-force distributions under elastic and plastic states are studied by theoretical derivation and numerical simulation. According to the characteristics of cooperative deformation of the diagrid structure and the frame structure, a simplified 2D elastic analysis model is proposed. Formulas for calculating the lateral deformation and the shear force of structures are derived. The shear distribution characteristics of the structure in the elastic state are also studied. The non-linear static Pushover method is used to calculate the structural system. The deformation characteristics, stiffness degradation and shear-force distribution in plastic stage are studied. The results show that the high-rise diagrid structure and the frame structure have good cooperative behaviors. In the elastic state, the eigenvalues of structural stiffness and the load distribution have a great influence on the shear-force distribution of the structure. In the plastic state, the stiffness of diagonal columns will degrade and the shear force will be redistributed.
The high-rise frame-diagrid structure is a new dual system. It is composed of a high-rise diagrid structure and a frame structure. The horizontal shear-force distributions under elastic and plastic states are studied by theoretical derivation and numerical simulation. According to the characteristics of cooperative deformation of the diagrid structure and the frame structure, a simplified 2D elastic analysis model is proposed. Formulas for calculating the lateral deformation and the shear force of structures are derived. The shear distribution characteristics of the structure in the elastic state are also studied. The non-linear static Pushover method is used to calculate the structural system. The deformation characteristics, stiffness degradation and shear-force distribution in plastic stage are studied. The results show that the high-rise diagrid structure and the frame structure have good cooperative behaviors. In the elastic state, the eigenvalues of structural stiffness and the load distribution have a great influence on the shear-force distribution of the structure. In the plastic state, the stiffness of diagonal columns will degrade and the shear force will be redistributed.
Abstract：
The rigid-structure method, Morison method and a method based on approximation of fundamental frequency are applicable simplified methods for the hydrodynamic force of incompressible non-viscous water. To investigate the differences of the above methods, the responsesof elastic cantilever circular piers were compared in the form of frequency domain transfer function, with the exact solutions which based on the radiation theory of incompressible non-viscous water considering structural deformation. Two kinds of size parameters were selected and 84 different sizes of piers were designed. By inputting impulse excitation, the transfer functions of displacement at the bottom, the transfer function of shear force and bending moment at the top were obtained. Then the first two order resonance-peak amplitude and resonance frequency were extracted for error analysis. Through the analysis of the range and variation trend of errors, it is found that:the resonance peak amplitude obtained by the rigid-structure method is more accurate, the resonance period obtained by the method based on approximation of fundamental-frequency is more accurate, and the error of the Morison method is significantly affected by the parameters. In addition, the amplitude of formant obtained by the fundamental frequency approximation is mostly smaller, while the amplitude and period obtained by the Morrison method are mostly larger.
The rigid-structure method, Morison method and a method based on approximation of fundamental frequency are applicable simplified methods for the hydrodynamic force of incompressible non-viscous water. To investigate the differences of the above methods, the responsesof elastic cantilever circular piers were compared in the form of frequency domain transfer function, with the exact solutions which based on the radiation theory of incompressible non-viscous water considering structural deformation. Two kinds of size parameters were selected and 84 different sizes of piers were designed. By inputting impulse excitation, the transfer functions of displacement at the bottom, the transfer function of shear force and bending moment at the top were obtained. Then the first two order resonance-peak amplitude and resonance frequency were extracted for error analysis. Through the analysis of the range and variation trend of errors, it is found that:the resonance peak amplitude obtained by the rigid-structure method is more accurate, the resonance period obtained by the method based on approximation of fundamental-frequency is more accurate, and the error of the Morison method is significantly affected by the parameters. In addition, the amplitude of formant obtained by the fundamental frequency approximation is mostly smaller, while the amplitude and period obtained by the Morrison method are mostly larger.
2020, 37(2): 62-69.
DOI: 10.6052/j.issn.1000-4750.2019.01.0091
Abstract：
To study the damage equivalent factors of urban rail transit steel bridge, the factors of Chinese urban rail transit steel bridge are analyzed based on the S-N curve and damage equivalent factor method in Eurocode. Six traffic types of urban rail transit applied to Chinese urban rail transit steel bridge are proposed, and three load diagrams, ZC, ZK and LM71, are selected as fatigue load models. According to the actual traffic volume of Chinese urban rail transit, a simplified calculation method using bi-linear S-N curve is proposed, which is compared with the methods using single slope S-N curve. Thus, damage equivalent factors of urban rail transit steel bridge are analyzed. To consider the characteristics of Chinese urban rail transit, an equivalent factor λv considering the maximum permitted vehicle speed is proposed. The results demonstrate that by taking diagram ZC as fatigue load model and considering influence of the maximum permitted vehicle speed, the damage equivalent factors based on the simplified bi-linear S-N calculation method can be reasonably applied to fatigue verification of Chinese urban rail transit steel bridge.
To study the damage equivalent factors of urban rail transit steel bridge, the factors of Chinese urban rail transit steel bridge are analyzed based on the S-N curve and damage equivalent factor method in Eurocode. Six traffic types of urban rail transit applied to Chinese urban rail transit steel bridge are proposed, and three load diagrams, ZC, ZK and LM71, are selected as fatigue load models. According to the actual traffic volume of Chinese urban rail transit, a simplified calculation method using bi-linear S-N curve is proposed, which is compared with the methods using single slope S-N curve. Thus, damage equivalent factors of urban rail transit steel bridge are analyzed. To consider the characteristics of Chinese urban rail transit, an equivalent factor λv considering the maximum permitted vehicle speed is proposed. The results demonstrate that by taking diagram ZC as fatigue load model and considering influence of the maximum permitted vehicle speed, the damage equivalent factors based on the simplified bi-linear S-N calculation method can be reasonably applied to fatigue verification of Chinese urban rail transit steel bridge.
2020, 37(2): 70-80.
DOI: 10.6052/j.issn.1000-4750.2019.02.0063
Abstract：
This study evaluated the seismic performance of RC shear walls under freezing and thawing environment. The results of the quasi-static tests of eight freeze-thaw damage squat RC shear walls were analyzed by using theoretical analysis and experimental regression. A shear hysteresis model of a squat RC shear wall was proposed considering the degree of freeze-thaw damage and the axial load ratio. Subsequently, a numerical simulation method of the squat RC shear wall was put forward considering the combined shear effect and uneven freeze-thaw damage. Comparing the simulation results with the experimental results, it is found that the hysteresis curve, the skeleton curve, and the cumulative energy dissipation were in good agreement with the experimental results, which indicated that the numerical simulation method proposed in this paper can accurately reflect the mechanical properties and seismic performance of squat RC shear walls with freeze-thaw damage, and can be used for seismic performance evaluation of in-service RC shear walls in frost action regions.
This study evaluated the seismic performance of RC shear walls under freezing and thawing environment. The results of the quasi-static tests of eight freeze-thaw damage squat RC shear walls were analyzed by using theoretical analysis and experimental regression. A shear hysteresis model of a squat RC shear wall was proposed considering the degree of freeze-thaw damage and the axial load ratio. Subsequently, a numerical simulation method of the squat RC shear wall was put forward considering the combined shear effect and uneven freeze-thaw damage. Comparing the simulation results with the experimental results, it is found that the hysteresis curve, the skeleton curve, and the cumulative energy dissipation were in good agreement with the experimental results, which indicated that the numerical simulation method proposed in this paper can accurately reflect the mechanical properties and seismic performance of squat RC shear walls with freeze-thaw damage, and can be used for seismic performance evaluation of in-service RC shear walls in frost action regions.
2020, 37(2): 81-89,144.
DOI: 10.6052/j.issn.1000-4750.2019.01.0092
Abstract：
The nodes in single-layer gridshells transmit axial forces and moments along two axes simultaneously. Therefore, the nodes in single-layer gridshells, which bear a complex combination of forces and moments, should have reasonable configurations and excellent mechanical performances as rigid connections. Moreover, because of the difficulty of assembling of the gridshell high above the ground and the complexity of the gridshell's configuration, the connections between nodes and members should be reliable, convenient and applicable to any situation. This paper proposes a design optimization method of rigid nodes in single-layer gridshells. The end piece of the node is firstly configured so that a bar can be connected to the node easily. Subsequently, topology optimization is carried out upon the node core to explore highly-efficient configurations. In the optimization model, the rotational stiffness of the node is represented by a set of self-equilibrium moments which are irrelevant to loads, and thus the optimal nodes can transmit moments from any direction. Applying the force directly upon the design domain will cause some problems, such as the stress singularity and limitations for the topology optimization to explore other potential configurations. To solve this key problem, an inertia action, which is generated by applying an acceleration field, is applied to be equivalent to the concentrated force. With this equivalence, reliable and stable optimal results are obtained which are insensitive to the boundary conditions. Finally, a real-life node is designed and optimized as an example. The analysis of the connection of the optimal node to tube members and the analysis of mechanical performances of the optimal nodes are conducted. And the optimal node is compared with the traditional node. The analyses and comparison verify the proposed design optimization method, which combines the design of connection and topology optimization.
The nodes in single-layer gridshells transmit axial forces and moments along two axes simultaneously. Therefore, the nodes in single-layer gridshells, which bear a complex combination of forces and moments, should have reasonable configurations and excellent mechanical performances as rigid connections. Moreover, because of the difficulty of assembling of the gridshell high above the ground and the complexity of the gridshell's configuration, the connections between nodes and members should be reliable, convenient and applicable to any situation. This paper proposes a design optimization method of rigid nodes in single-layer gridshells. The end piece of the node is firstly configured so that a bar can be connected to the node easily. Subsequently, topology optimization is carried out upon the node core to explore highly-efficient configurations. In the optimization model, the rotational stiffness of the node is represented by a set of self-equilibrium moments which are irrelevant to loads, and thus the optimal nodes can transmit moments from any direction. Applying the force directly upon the design domain will cause some problems, such as the stress singularity and limitations for the topology optimization to explore other potential configurations. To solve this key problem, an inertia action, which is generated by applying an acceleration field, is applied to be equivalent to the concentrated force. With this equivalence, reliable and stable optimal results are obtained which are insensitive to the boundary conditions. Finally, a real-life node is designed and optimized as an example. The analysis of the connection of the optimal node to tube members and the analysis of mechanical performances of the optimal nodes are conducted. And the optimal node is compared with the traditional node. The analyses and comparison verify the proposed design optimization method, which combines the design of connection and topology optimization.
Abstract：
A mechanical model is proposed accurately describe the hysteretic behavior of pre-pressed spring self-centering energy dissipation (PS-SCED) brace. The state variables are introduced to distinguish different stages of PS-SCED brace and then its mechanical responses are determined. The secondary development of the mechanical model is carried out based on ABAQUS. The simulation results of the developed PS-SCED brace element are compared with the test results of the brace, and the seismic performances of a 3-story reinforced concrete frame structure with PS-SCED braces are analyzed. The results indicate that the hysteretic curves obtained from the brace element simulation agree well with the test results, and the brace element is accurate enough to describe the mechanical performance of the brace under dynamic loads. The seismic energy dissipates sufficiently and the plastic deformation of the structure is controlled effectively by PS-SCED braces subjected to strong earthquake. Additionally, the residual deformations of frame structure with PS-SCED braces are reduced by 72.1%~92.1% compared with the original frame structure. The PS-SCED brace exhibits full hysteretic performances with good energy dissipation capacity and self-centering behavior, which significantly improves the seismic performances of reinforced concrete frame structures.
A mechanical model is proposed accurately describe the hysteretic behavior of pre-pressed spring self-centering energy dissipation (PS-SCED) brace. The state variables are introduced to distinguish different stages of PS-SCED brace and then its mechanical responses are determined. The secondary development of the mechanical model is carried out based on ABAQUS. The simulation results of the developed PS-SCED brace element are compared with the test results of the brace, and the seismic performances of a 3-story reinforced concrete frame structure with PS-SCED braces are analyzed. The results indicate that the hysteretic curves obtained from the brace element simulation agree well with the test results, and the brace element is accurate enough to describe the mechanical performance of the brace under dynamic loads. The seismic energy dissipates sufficiently and the plastic deformation of the structure is controlled effectively by PS-SCED braces subjected to strong earthquake. Additionally, the residual deformations of frame structure with PS-SCED braces are reduced by 72.1%~92.1% compared with the original frame structure. The PS-SCED brace exhibits full hysteretic performances with good energy dissipation capacity and self-centering behavior, which significantly improves the seismic performances of reinforced concrete frame structures.
Abstract：
Based on the experimental study of the partially encased composite frame-thin steel plate shear walls, it is found that the failure stages of the infilled steel plate include initial diagonal yielding, uniformed yielding, and strain hardening. By introducing the partially encased composite column, the bending-torsion failure modes of traditional steel columns are effectively improved. The failure mode of the partially encased composite column is the strength failure of plastic hinges formed at the top and bottom of the column. Based on the design concept of "strong frame and weak wall panel", it determines the calculation principle of the internal force of the partially encased composite column in the uniformed yielding stage and the strain hardening stage according to the superposition principle, and proposes a design method suitable for frame column of the partially encased composite frame-thin steel plate shear walls. The finite element simulation shows that the design method can effectively predict the failure modes and the locations of the plastic hinges of the bottom compressed column, which can provide theoretical basis for reasonable design of boundary frame column in steel plate shear walls.
Based on the experimental study of the partially encased composite frame-thin steel plate shear walls, it is found that the failure stages of the infilled steel plate include initial diagonal yielding, uniformed yielding, and strain hardening. By introducing the partially encased composite column, the bending-torsion failure modes of traditional steel columns are effectively improved. The failure mode of the partially encased composite column is the strength failure of plastic hinges formed at the top and bottom of the column. Based on the design concept of "strong frame and weak wall panel", it determines the calculation principle of the internal force of the partially encased composite column in the uniformed yielding stage and the strain hardening stage according to the superposition principle, and proposes a design method suitable for frame column of the partially encased composite frame-thin steel plate shear walls. The finite element simulation shows that the design method can effectively predict the failure modes and the locations of the plastic hinges of the bottom compressed column, which can provide theoretical basis for reasonable design of boundary frame column in steel plate shear walls.
Abstract：
Aimed at the problem that there is serious fatigue cracking in the steel box girder of a suspension bridge, the vehicle type, wheelbase, axle load, total weight and overload of the bridge are statistically analyzed, and the traffic load characteristics of the bridge and the difference of random traffic flow in each lane are clarified by the base of the data collected by a WIM dynamic weighing system. According to the dynamic strain monitoring data of a real bridge, the fatigue stress spectrum of each lane under operating condition was obtained by using the rain-flow counting method and the Palmgren-Miner linear damage accumulation theory. Based on the UD-RBF-IMC algorithm, the fatigue reliability of U-rib butt weld was evaluated by linear elastic fracture mechanics. The influence of traffic volume and the shaft weight on fatigue reliability were studied. The result show that:the type of a fatigue vehicle can be simplified to V2-V10, a total of 9 categories, the total weights of V2 vehicles are a unimodal skewed distribution, overload rate of less than 4%, the total weights of V3-V10 vehicles are multi-peak distribution, overload rate greater than 30%, up to 69%. The proportion of V2-V10 vehicles of a heavy lane is obviously higher than that of other lanes. The daily variation of temperature has little effect on the fatigue stress spectrum, and the influence of sampling frequency on the stress spectrum is significant, which should not be less than 50 Hz. Combining the respective advantages of UD, RBF and IMC, the accuracy and efficiency of the fatigue reliability index of steel box girders based on monitoring data are effectively improved. The effect of axle weight growth coefficients on fatigue reliability is obviously greater than that of traffic volume growth. In addition to controlling the traffic volume during operation, it is also necessary to focus on controlling the proportion of heavy vehicles and overloading rate. When the growth coefficient of traffic volume is 3% and the growth coefficient of axle load is 0.6%, the fatigue life of measuring point 1# is only 74 years. The number of overloaded heavy-duty trucks of passing lane is less, the high-level stress cycles are less, and the fatigue life is longer, while the number of heavy-haul trucks of a fast lane and a heavy lane is more, the high-level stress cycles are more, there is a risk of fatigue cracking, which should be paid more attention to.
Aimed at the problem that there is serious fatigue cracking in the steel box girder of a suspension bridge, the vehicle type, wheelbase, axle load, total weight and overload of the bridge are statistically analyzed, and the traffic load characteristics of the bridge and the difference of random traffic flow in each lane are clarified by the base of the data collected by a WIM dynamic weighing system. According to the dynamic strain monitoring data of a real bridge, the fatigue stress spectrum of each lane under operating condition was obtained by using the rain-flow counting method and the Palmgren-Miner linear damage accumulation theory. Based on the UD-RBF-IMC algorithm, the fatigue reliability of U-rib butt weld was evaluated by linear elastic fracture mechanics. The influence of traffic volume and the shaft weight on fatigue reliability were studied. The result show that:the type of a fatigue vehicle can be simplified to V2-V10, a total of 9 categories, the total weights of V2 vehicles are a unimodal skewed distribution, overload rate of less than 4%, the total weights of V3-V10 vehicles are multi-peak distribution, overload rate greater than 30%, up to 69%. The proportion of V2-V10 vehicles of a heavy lane is obviously higher than that of other lanes. The daily variation of temperature has little effect on the fatigue stress spectrum, and the influence of sampling frequency on the stress spectrum is significant, which should not be less than 50 Hz. Combining the respective advantages of UD, RBF and IMC, the accuracy and efficiency of the fatigue reliability index of steel box girders based on monitoring data are effectively improved. The effect of axle weight growth coefficients on fatigue reliability is obviously greater than that of traffic volume growth. In addition to controlling the traffic volume during operation, it is also necessary to focus on controlling the proportion of heavy vehicles and overloading rate. When the growth coefficient of traffic volume is 3% and the growth coefficient of axle load is 0.6%, the fatigue life of measuring point 1# is only 74 years. The number of overloaded heavy-duty trucks of passing lane is less, the high-level stress cycles are less, and the fatigue life is longer, while the number of heavy-haul trucks of a fast lane and a heavy lane is more, the high-level stress cycles are more, there is a risk of fatigue cracking, which should be paid more attention to.
Abstract：
Under the action of mainshock-aftershock sequences, the aftershock can cause additional damage to a damaged structure by the mainshock, or even cause it to collapse, especially for a low ductility structure. Currently, the analysis and evaluation of aseismic performance of low-ductile structures under the mainshock-aftershock sequences are not sufficient. According to the failure characteristics of a low-ductile reinforced concrete (RC) frame, the shear failure of beam-column joints, the flexure-shear failure of column, the strength and stiffness degradation, and the bond-slip failure of longitudinal reinforcement at the end of beam were taken into consideration for the numerical simulation of a low-ductile RC frame. The refined analytical model of a 6-story 3-span low-ductile RC frame structure was established via OpenSees finite element software. The real mainshock-aftershock sequences and the mainshock-aftershock sequences based on repeated method were selected. The effects of aftershock directionality and the number of aftershocks were also considered. Taking different mainshock-aftershock sequences as input, the dynamic analysis of the low-ductile RC frame model was carried out and the seismic fragility curves corresponding to different damage states were obtained. Then the effect of different mainshock-aftershock sequences on its aseismic performance was analyzed. The results show that the refined analytical model of a low-ductile RC frame presented can simulate the degradation of stiffness and strength of beam-column joints due to shearing actions. Comparing with the mainshock input only, the exceedance probability of the damage state of the low-ductile RC frame under the influence of the mainshock-aftershock sequences is higher, and with the increase of the damage extent under the mainshock, the increase is much more obvious. The exceedance probability of the corresponding damage state under the influence of the mainshock-aftershock sequences based on the repeated method is higher than that under the influence of the real mainshock-aftershock sequences. The different direction of aftershock has certain influence on the exceedance probability of corresponding damage states. Increasing the number of aftershocks will also increase the exceedance probability of corresponding damage states.
Under the action of mainshock-aftershock sequences, the aftershock can cause additional damage to a damaged structure by the mainshock, or even cause it to collapse, especially for a low ductility structure. Currently, the analysis and evaluation of aseismic performance of low-ductile structures under the mainshock-aftershock sequences are not sufficient. According to the failure characteristics of a low-ductile reinforced concrete (RC) frame, the shear failure of beam-column joints, the flexure-shear failure of column, the strength and stiffness degradation, and the bond-slip failure of longitudinal reinforcement at the end of beam were taken into consideration for the numerical simulation of a low-ductile RC frame. The refined analytical model of a 6-story 3-span low-ductile RC frame structure was established via OpenSees finite element software. The real mainshock-aftershock sequences and the mainshock-aftershock sequences based on repeated method were selected. The effects of aftershock directionality and the number of aftershocks were also considered. Taking different mainshock-aftershock sequences as input, the dynamic analysis of the low-ductile RC frame model was carried out and the seismic fragility curves corresponding to different damage states were obtained. Then the effect of different mainshock-aftershock sequences on its aseismic performance was analyzed. The results show that the refined analytical model of a low-ductile RC frame presented can simulate the degradation of stiffness and strength of beam-column joints due to shearing actions. Comparing with the mainshock input only, the exceedance probability of the damage state of the low-ductile RC frame under the influence of the mainshock-aftershock sequences is higher, and with the increase of the damage extent under the mainshock, the increase is much more obvious. The exceedance probability of the corresponding damage state under the influence of the mainshock-aftershock sequences based on the repeated method is higher than that under the influence of the real mainshock-aftershock sequences. The different direction of aftershock has certain influence on the exceedance probability of corresponding damage states. Increasing the number of aftershocks will also increase the exceedance probability of corresponding damage states.
Abstract：
Using the semi-analytical finite element method and MATLAB, a mechanical analysis program CP-SAFEM (cement pavement semi-analytical finite element method) for cement concrete pavements was developed. Based on various engineering cases, the analysis results from CP-SAFEM were compared with the current standards and ABAQUS. The results indicate that the calculation error between the CP-SAFEM and the standards was less than 1% for single-layer pavements, and approximately 6% for double-layer pavements. In addition, the error between CP-SAFEM and ABAQUS was less than 5%. With the same meshing scheme in the pavement cross section, the computation time of CP-SAFEM was only 1/6 of that of ABAQUS. Furthermore, the critical loading position was determined by the tensile stress of the panel. As a result, the CP-SAFEM was proven to have adequate computational accuracy and efficiency.
Using the semi-analytical finite element method and MATLAB, a mechanical analysis program CP-SAFEM (cement pavement semi-analytical finite element method) for cement concrete pavements was developed. Based on various engineering cases, the analysis results from CP-SAFEM were compared with the current standards and ABAQUS. The results indicate that the calculation error between the CP-SAFEM and the standards was less than 1% for single-layer pavements, and approximately 6% for double-layer pavements. In addition, the error between CP-SAFEM and ABAQUS was less than 5%. With the same meshing scheme in the pavement cross section, the computation time of CP-SAFEM was only 1/6 of that of ABAQUS. Furthermore, the critical loading position was determined by the tensile stress of the panel. As a result, the CP-SAFEM was proven to have adequate computational accuracy and efficiency.
Abstract：
High strength steel fabricated framed-tube structure with replaceable shear links (HSS-SFT) was proposed to improve the poor energy dissipation capacity and replicability after earthquakes. To investigate the response modification factor of HSS-SFTs, eight HSS-SFTs with ideal yield mechanism were established. The capacity curves of HSS-SFTs were obtained by stepwise lateral force adjustment method considering the effects of high-order vibration mode. The response modification factor R and displacement amplification factor Cd were obtained based on the improved capability spectrum method. Subsequently, the effects of parameters influencing R and Cd, including the building total story number and the shear link length, were investigated. According to the analysis results, HSS-SFTs have great overstrength and good ductility due to internal force redistribution of inelastic state. The R decreased, and Cd had no significant change as the total story number increased. The R and Cd slightly increased by an increase in the shear link length. Based on the analysis results, the R, RΩ and the Cd equalled 3.65, 2.92 and 7.45 respectively and 30% elastic design earthquake action of HSS-SFTs can be approximately reduced though national seismic code. HSS-SFTs can characterize an ideal failure mode during rare earthquakes and effectively improve the poor energy dissipation and post-earthquakes repairable abilities of traditional steel frame-tube structure.
High strength steel fabricated framed-tube structure with replaceable shear links (HSS-SFT) was proposed to improve the poor energy dissipation capacity and replicability after earthquakes. To investigate the response modification factor of HSS-SFTs, eight HSS-SFTs with ideal yield mechanism were established. The capacity curves of HSS-SFTs were obtained by stepwise lateral force adjustment method considering the effects of high-order vibration mode. The response modification factor R and displacement amplification factor Cd were obtained based on the improved capability spectrum method. Subsequently, the effects of parameters influencing R and Cd, including the building total story number and the shear link length, were investigated. According to the analysis results, HSS-SFTs have great overstrength and good ductility due to internal force redistribution of inelastic state. The R decreased, and Cd had no significant change as the total story number increased. The R and Cd slightly increased by an increase in the shear link length. Based on the analysis results, the R, RΩ and the Cd equalled 3.65, 2.92 and 7.45 respectively and 30% elastic design earthquake action of HSS-SFTs can be approximately reduced though national seismic code. HSS-SFTs can characterize an ideal failure mode during rare earthquakes and effectively improve the poor energy dissipation and post-earthquakes repairable abilities of traditional steel frame-tube structure.
Abstract：
Reinforced concrete (RC) beams tend to elongate after flexural cracking and yielding. The elongation is restrained by the surrounding structural components in the RC frame and therefore axial comprehensive force is formed. The seismic performance and failure modes of RC frame joints are affected by the unexpected axial compressive force. The influence of axial restraint force on the shear transfer mechanism of the joints was analyzed. Six 1/2-scale RC beam-column subassemblies, four of which were restrained by an equivalent device, were tested under cyclic loading to study the impacts of the beam elongation on the seismic shear demand, strength and failure modes. The results show that the beam elongation effects on the seismic shear demand were more obvious than those on the strength. The beam elongation caused large compressive axial force in beams with the increase of the beam bending deformation. Compared with the unrestrained specimens, the shear demand of the joints due to the axial restraint force was increased by 1.14~2.22 times. The widths of the inclined cracks in the joint area were larger, and the damage to the joints were relatively more serious in the axially restrained specimens.
Reinforced concrete (RC) beams tend to elongate after flexural cracking and yielding. The elongation is restrained by the surrounding structural components in the RC frame and therefore axial comprehensive force is formed. The seismic performance and failure modes of RC frame joints are affected by the unexpected axial compressive force. The influence of axial restraint force on the shear transfer mechanism of the joints was analyzed. Six 1/2-scale RC beam-column subassemblies, four of which were restrained by an equivalent device, were tested under cyclic loading to study the impacts of the beam elongation on the seismic shear demand, strength and failure modes. The results show that the beam elongation effects on the seismic shear demand were more obvious than those on the strength. The beam elongation caused large compressive axial force in beams with the increase of the beam bending deformation. Compared with the unrestrained specimens, the shear demand of the joints due to the axial restraint force was increased by 1.14~2.22 times. The widths of the inclined cracks in the joint area were larger, and the damage to the joints were relatively more serious in the axially restrained specimens.
Abstract：
Low yield point steel with low yield strength, high ductility and high energy dissipation capacity is used for steel frame joints. It dissipates seismic energy, is replaceable after earthquakes and provides a high-quality solution for structures with resilience requirement. To propose a design for a steel frame connection with low yield point steel "ductile fuses", a nonlinear numerical model was established by using ABAQUS. The model was verified by typical static tests of steel frame joints with bolted connections. The influence of different impact factors on the performance of this kind of joints was explored, and how these impact factors influenced the "structural fuse" was investigated. Subsequently, the design method was proposed and verified by using an example of practical engineering design. The results indicated that the width of the joint gap, the thickness of the web cover plate and the beam width had little influence on the actual bearing capacity coefficient of the joint and the function of "structural" fuse effect. The position of splicing, the height of the beam and the thickness of the flange cover plate were the key factors of the actual bearing capacity coefficient of the joints. The "structural fuse" will be prematurely ineffective if the design is nonviable. The relationship between the critical value of the design bearing capacity coefficient and the position of the joint and the height of the beam was established by data fitting. When the design bearing capacity coefficient is less than the critical value, the "structural fuse" works normally. When the design bearing capacity coefficient is larger than the critical value, the effect of ‘structural fuse’ gradually decreases.
Low yield point steel with low yield strength, high ductility and high energy dissipation capacity is used for steel frame joints. It dissipates seismic energy, is replaceable after earthquakes and provides a high-quality solution for structures with resilience requirement. To propose a design for a steel frame connection with low yield point steel "ductile fuses", a nonlinear numerical model was established by using ABAQUS. The model was verified by typical static tests of steel frame joints with bolted connections. The influence of different impact factors on the performance of this kind of joints was explored, and how these impact factors influenced the "structural fuse" was investigated. Subsequently, the design method was proposed and verified by using an example of practical engineering design. The results indicated that the width of the joint gap, the thickness of the web cover plate and the beam width had little influence on the actual bearing capacity coefficient of the joint and the function of "structural" fuse effect. The position of splicing, the height of the beam and the thickness of the flange cover plate were the key factors of the actual bearing capacity coefficient of the joints. The "structural fuse" will be prematurely ineffective if the design is nonviable. The relationship between the critical value of the design bearing capacity coefficient and the position of the joint and the height of the beam was established by data fitting. When the design bearing capacity coefficient is less than the critical value, the "structural fuse" works normally. When the design bearing capacity coefficient is larger than the critical value, the effect of ‘structural fuse’ gradually decreases.
Abstract：
At present, the standing seam roof system with anti-wind clips is adopted in many largespan buildings to resist the action of strong wind. However, few further studies have been conducted on the changes in the deformation, stress and other characteristic responses of the standing seam roof system with anti-wind clips under wind loading. By means of experiment and numerical simulation, the influence of plate width, plate thickness, spacing between wind clips and other parameters on the characteristic response and bearing capacity of the roof system is studied. The failure criterion of the roof system is proposed and the formula for calculating the bearing capacity of the roof system is obtained by fitting. The research shows that the bearing capacity increases by about 10% for every 0.1 mm increase in plate thickness. The bearing capacity increases by 25% for every 100 mm reduction in plate width. When the anti-wind clips spacing is less than 1100 mm, the bearing capacity increases by about 20% for each reduction of 100 mm. When the anti-wind clips spacing is more than 1100 mm, the bearing capacity increases by about 10% for each reduction of 100 mm. Changing the structure of an anti-wind clip has little effect on the bearing capacity.
At present, the standing seam roof system with anti-wind clips is adopted in many largespan buildings to resist the action of strong wind. However, few further studies have been conducted on the changes in the deformation, stress and other characteristic responses of the standing seam roof system with anti-wind clips under wind loading. By means of experiment and numerical simulation, the influence of plate width, plate thickness, spacing between wind clips and other parameters on the characteristic response and bearing capacity of the roof system is studied. The failure criterion of the roof system is proposed and the formula for calculating the bearing capacity of the roof system is obtained by fitting. The research shows that the bearing capacity increases by about 10% for every 0.1 mm increase in plate thickness. The bearing capacity increases by 25% for every 100 mm reduction in plate width. When the anti-wind clips spacing is less than 1100 mm, the bearing capacity increases by about 20% for each reduction of 100 mm. When the anti-wind clips spacing is more than 1100 mm, the bearing capacity increases by about 10% for each reduction of 100 mm. Changing the structure of an anti-wind clip has little effect on the bearing capacity.
Abstract：
Based on the coupled free vibration records of bridge deck sectional model testing, a flutter derivatives identification method based on the artificial bee colony (ABC) algorithm is proposed. The objective function is constructed as the ensemble residual quadratic sum of the vertical and torsional vibration time histories in the sense of least squares. The ABC algorithm is used to search the optimal parameters so that the value of the objective function is minimized. Compared with other iteration methods, the ABC algorithm can facilitate the identification process with no need for initial values. In order to investigate the effectiveness of the ABC algorithm in the flutter derivatives identification, an ideal thin-plate model simulation and a real bridge sectional model testing are carried out. The results show that the ABC algorithm for the flutter derivatives identification of bridge decks is robust and reliable.
Based on the coupled free vibration records of bridge deck sectional model testing, a flutter derivatives identification method based on the artificial bee colony (ABC) algorithm is proposed. The objective function is constructed as the ensemble residual quadratic sum of the vertical and torsional vibration time histories in the sense of least squares. The ABC algorithm is used to search the optimal parameters so that the value of the objective function is minimized. Compared with other iteration methods, the ABC algorithm can facilitate the identification process with no need for initial values. In order to investigate the effectiveness of the ABC algorithm in the flutter derivatives identification, an ideal thin-plate model simulation and a real bridge sectional model testing are carried out. The results show that the ABC algorithm for the flutter derivatives identification of bridge decks is robust and reliable.
Abstract：
This paper proposes a new type of connector in fully assembled steel-concrete composite beams, through which the precast floor slab and steel beam are integrated. The load transfer along the interface of the precast concrete slab and the steel beam is primarily achieved through the friction between the connectors and the channels. To achieve a better understanding of the behavior of the connectors and the channels, push-out tests were conducted on 3 specimens. The effects of different channel types, repeated loading, and number of connectors were investigated. The test results show that all the connectors exhibited satisfactory performance, and the load slip curve can be divided into three segments. When the section height of channel is small, the restraining effect is more remarkable. The shear strength and shear stiffness of the connectors can be improved by reloading. The formulas to calculate the shear strength proposed in this paper agree well with the experimental results.
This paper proposes a new type of connector in fully assembled steel-concrete composite beams, through which the precast floor slab and steel beam are integrated. The load transfer along the interface of the precast concrete slab and the steel beam is primarily achieved through the friction between the connectors and the channels. To achieve a better understanding of the behavior of the connectors and the channels, push-out tests were conducted on 3 specimens. The effects of different channel types, repeated loading, and number of connectors were investigated. The test results show that all the connectors exhibited satisfactory performance, and the load slip curve can be divided into three segments. When the section height of channel is small, the restraining effect is more remarkable. The shear strength and shear stiffness of the connectors can be improved by reloading. The formulas to calculate the shear strength proposed in this paper agree well with the experimental results.
Abstract：
Through experiments of concrete of different strength grades such as C40, C50 and C60 that experiences 0, 16 and 30 cycles of ultralow temperature freeze-thaw cycle action from 15℃ to -120℃ and -190℃, the effects of the strength grades on the concrete compressive strength are discussed. The test results show that the failure modes of the specimens with different concrete strength grades are similar and generally cone-shaped regardless of the loading at the lower or upper limit temperature, but the failure surface characteristics and so on are different. After experiencing ultralow temperature freeze-thaw cycle action, the relative concrete compressive strengths at the lower and upper limit temperatures decrease with the increase in the concrete water content. With an increase in the concrete strength grade, the relative concrete compressive strengths increase at the upper limit temperature, while the relative concrete compressive strength of every strength grade decreases with the increase in the number of freeze-thaw cycles. Although the relative concrete compressive strength in different ultralow temperature ranges increases at the lower limit temperature, there is obvious difference in the reasons for its increase. The variation trend of the relative concrete compressive strength with the increase in the number of freeze-thaw cycles is similar in a given ultralow temperature range regardless of the concrete strength grade, but there exists a difference between different ultralow temperature ranges. The influence of ultralow temperature freeze-thaw action on the concrete mechanical performance is different from that of natural ambient temperature freeze-thaw action, from which the degradation of the concrete compressive strength is much more serious. In practical engineering, the results from natural ambient temperature freeze-thaw action should not be directly applied to the design of concrete structures that undergo ultralow temperature freeze-thaw action.
Through experiments of concrete of different strength grades such as C40, C50 and C60 that experiences 0, 16 and 30 cycles of ultralow temperature freeze-thaw cycle action from 15℃ to -120℃ and -190℃, the effects of the strength grades on the concrete compressive strength are discussed. The test results show that the failure modes of the specimens with different concrete strength grades are similar and generally cone-shaped regardless of the loading at the lower or upper limit temperature, but the failure surface characteristics and so on are different. After experiencing ultralow temperature freeze-thaw cycle action, the relative concrete compressive strengths at the lower and upper limit temperatures decrease with the increase in the concrete water content. With an increase in the concrete strength grade, the relative concrete compressive strengths increase at the upper limit temperature, while the relative concrete compressive strength of every strength grade decreases with the increase in the number of freeze-thaw cycles. Although the relative concrete compressive strength in different ultralow temperature ranges increases at the lower limit temperature, there is obvious difference in the reasons for its increase. The variation trend of the relative concrete compressive strength with the increase in the number of freeze-thaw cycles is similar in a given ultralow temperature range regardless of the concrete strength grade, but there exists a difference between different ultralow temperature ranges. The influence of ultralow temperature freeze-thaw action on the concrete mechanical performance is different from that of natural ambient temperature freeze-thaw action, from which the degradation of the concrete compressive strength is much more serious. In practical engineering, the results from natural ambient temperature freeze-thaw action should not be directly applied to the design of concrete structures that undergo ultralow temperature freeze-thaw action.
2020, 37(2): 221-229.
DOI: 10.6052/j.issn.1000-4750.2019.04.0158
Abstract：
To investigate the shear performance of Tibetan stone masonry, double-shear experiments along horizontal bed joints of 13 specimens (four groups in different compressing load) made of granites and earthen mortar were carried out. Through the test, the shear strength along horizonal bed joints of Tibetan stone masonry was obtained. Meanwhile the failure mechanism of bed joints was analyzed, and methods to estimate shear strength of Tibetan stone masonry through shear strength of bed joints were studies. The results showed that the shear failure mode of bed joints in Tibetan stone masonry was a ductile failure process in which the deformation of earthen mortar and interface separation were developing at the same time, and the ultimate mode was pure slip along the separating interface. A computational model of shear strength for Tibetan stone masonry was proposed based on statistical analysis of the test results and the results showed good agreement with the test data. Compared to hydraulic mortar, earthen mortar has a lower cohesion and friction coefficient. Through two theoretical models, the relationship between the bed mortar's shear strength parameters and the masonry's was analyzed, and experimental data of other researchers was used to verify the results. A calculation formula to estimate shear strength of Tibetan stone masonry based on data obtained by the double-shear test was proposed, and it can be referred to for studies on Tibetan stone masonry's shear performance.
To investigate the shear performance of Tibetan stone masonry, double-shear experiments along horizontal bed joints of 13 specimens (four groups in different compressing load) made of granites and earthen mortar were carried out. Through the test, the shear strength along horizonal bed joints of Tibetan stone masonry was obtained. Meanwhile the failure mechanism of bed joints was analyzed, and methods to estimate shear strength of Tibetan stone masonry through shear strength of bed joints were studies. The results showed that the shear failure mode of bed joints in Tibetan stone masonry was a ductile failure process in which the deformation of earthen mortar and interface separation were developing at the same time, and the ultimate mode was pure slip along the separating interface. A computational model of shear strength for Tibetan stone masonry was proposed based on statistical analysis of the test results and the results showed good agreement with the test data. Compared to hydraulic mortar, earthen mortar has a lower cohesion and friction coefficient. Through two theoretical models, the relationship between the bed mortar's shear strength parameters and the masonry's was analyzed, and experimental data of other researchers was used to verify the results. A calculation formula to estimate shear strength of Tibetan stone masonry based on data obtained by the double-shear test was proposed, and it can be referred to for studies on Tibetan stone masonry's shear performance.
Abstract：
High strength steel has been gradually applied in the steel structure constructions in recent years. Q690D high strength steel specimens were tested under monotonic loading and extremely low cyclic loading in the paper. The crack initiation locations of specimens were investigated and the effect of loading history on strength and deformation of notched specimens was analyzed. Scanning electron microscope revealed that the fracture morphology of specimens was a dimple pattern with the features of ductile fracture. Based on monotonic tensile test results of notched specimens and finite element analyses, the continuum damage model parameters of Q690D steel were calibrated. Finally, the continuum damage model was applied to predict fracture failure of notched coupon specimens and the specimens with initial gap under different loading conditions. It shows that the cracking location, load-displacement curves, fracture displacement and fatigue life obtained from the numerical simulation are in good agreement with the experimental results.
High strength steel has been gradually applied in the steel structure constructions in recent years. Q690D high strength steel specimens were tested under monotonic loading and extremely low cyclic loading in the paper. The crack initiation locations of specimens were investigated and the effect of loading history on strength and deformation of notched specimens was analyzed. Scanning electron microscope revealed that the fracture morphology of specimens was a dimple pattern with the features of ductile fracture. Based on monotonic tensile test results of notched specimens and finite element analyses, the continuum damage model parameters of Q690D steel were calibrated. Finally, the continuum damage model was applied to predict fracture failure of notched coupon specimens and the specimens with initial gap under different loading conditions. It shows that the cracking location, load-displacement curves, fracture displacement and fatigue life obtained from the numerical simulation are in good agreement with the experimental results.
Abstract：
A dynamic model for iced conductor describing the coupling of the first four in-plane and torsional modes has been established by applying the Galerkin method. Subsequently, the Bifurcation theory was employed to study the critical unstable condition of every mode. Galloping laws of iced conductor were analyzed under different parameters including wind velocity, torsional ratio, cable length and initial tension. Numerical procedures were finally used to verify the theoretical results. The results indicate that with the consideration of the first four torsional modes, the real parts of the eigenvalues for the first four in-plane modes experienced two Hopf bifurcations as the wind velocity increased, performing limited vibration. The increase in the torsional damping ratio could enlarge the instable region of in-plane modes. The longer cable length made a left shift of Hopf bifurcations for both in-plane and torsional modes, denoting that in-plane galloping would be substituted by the torsional ones in longer cable length. Initial tension had a remarkable impact on in-plane modes, but no obvious influence on the torsional ones. The conclusion can provide theoretical basis for conductor optimization.
A dynamic model for iced conductor describing the coupling of the first four in-plane and torsional modes has been established by applying the Galerkin method. Subsequently, the Bifurcation theory was employed to study the critical unstable condition of every mode. Galloping laws of iced conductor were analyzed under different parameters including wind velocity, torsional ratio, cable length and initial tension. Numerical procedures were finally used to verify the theoretical results. The results indicate that with the consideration of the first four torsional modes, the real parts of the eigenvalues for the first four in-plane modes experienced two Hopf bifurcations as the wind velocity increased, performing limited vibration. The increase in the torsional damping ratio could enlarge the instable region of in-plane modes. The longer cable length made a left shift of Hopf bifurcations for both in-plane and torsional modes, denoting that in-plane galloping would be substituted by the torsional ones in longer cable length. Initial tension had a remarkable impact on in-plane modes, but no obvious influence on the torsional ones. The conclusion can provide theoretical basis for conductor optimization.
Abstract：
The study on full-scale wind field characteristics is one of the fundamental works in the structural wind-resistance design. Being one of the main parameters among them, the wind speed spectrum describes the distribution of turbulence energy with the frequency. Van der Hoven first proposed the wind speed spectrum in the wide frequency range, including the macro-meteorological and micro-meteorological peaks, which made a pioneering contribution in wind engineering. Considering that the data acquisition equipment and computing ability in early years were relatively poor and the urbanization is accelerating recently, the full-scale wind speed spectrum should be further examined in urban areas. The paper obtains the wind speed spectrum in a wide frequency range including the macro-meteorological and micro-meteorological peaks based on the wind speed data collected by the sonic anemometers at the heights of 47 m, 80 m and 140 m of the Beijing Meteorological Tower in 2013. The wind speed spectrum is compared with the Van der Hoven spectrum and other previous spectra. The results show that for the macro-meteorological spectrum, besides around the 4-day cycle, the periodic deterministic component with a period of 24 hours is also detectable and prominent. However, the spectrum does not show significant peaks at a period of 12 hours. The micro-meteorological peak is relatively weak compared with the macro-meteorological peak. The macro-meteorological peak increases with the height, while the micro-meteorological peak shows little change for different heights. Considering that the wind spectrum in the high frequency range is the main focus of the structural wind-resistance design, the micro-meteorological spectrum is recalculated based on the strong wind speed samples whose mean wind speeds are larger than 8 m/s. The comparisons with typical power spectrum are performed. It is shown that the micro-meteorological spectrum for different heights generally correspond with each other, and they are shown to be close to the Kaimal spectrum.
The study on full-scale wind field characteristics is one of the fundamental works in the structural wind-resistance design. Being one of the main parameters among them, the wind speed spectrum describes the distribution of turbulence energy with the frequency. Van der Hoven first proposed the wind speed spectrum in the wide frequency range, including the macro-meteorological and micro-meteorological peaks, which made a pioneering contribution in wind engineering. Considering that the data acquisition equipment and computing ability in early years were relatively poor and the urbanization is accelerating recently, the full-scale wind speed spectrum should be further examined in urban areas. The paper obtains the wind speed spectrum in a wide frequency range including the macro-meteorological and micro-meteorological peaks based on the wind speed data collected by the sonic anemometers at the heights of 47 m, 80 m and 140 m of the Beijing Meteorological Tower in 2013. The wind speed spectrum is compared with the Van der Hoven spectrum and other previous spectra. The results show that for the macro-meteorological spectrum, besides around the 4-day cycle, the periodic deterministic component with a period of 24 hours is also detectable and prominent. However, the spectrum does not show significant peaks at a period of 12 hours. The micro-meteorological peak is relatively weak compared with the macro-meteorological peak. The macro-meteorological peak increases with the height, while the micro-meteorological peak shows little change for different heights. Considering that the wind spectrum in the high frequency range is the main focus of the structural wind-resistance design, the micro-meteorological spectrum is recalculated based on the strong wind speed samples whose mean wind speeds are larger than 8 m/s. The comparisons with typical power spectrum are performed. It is shown that the micro-meteorological spectrum for different heights generally correspond with each other, and they are shown to be close to the Kaimal spectrum.
