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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. S, Publish Date: 2023-06-25
Display Method:
2023, 40(S): 1-5.
doi: 10.6052/j.issn.1000-4750.2022.06.S015
Abstract:
A correction method is presented which can effectively improve the spurious oscillation phenomenon in impact problems. Based on the finite element method, the Lagrange multiplier method is introduced to impose contact constraints, and an unconditionally stable implicit combined time integration algorithm is combined to solve the frictionless dynamic contact problem. By introducing additional Lagrange multipliers, the velocity and acceleration obtained by the combined time integration algorithm are modified to meet the persistency conditions of the contact constraints in the form of velocity and acceleration. Numerical example results show that the correction method can effectively improve the spurious oscillation of velocity, contact force, etc. at the time of initial contact, and improve the solution accuracy of impact problems.
A correction method is presented which can effectively improve the spurious oscillation phenomenon in impact problems. Based on the finite element method, the Lagrange multiplier method is introduced to impose contact constraints, and an unconditionally stable implicit combined time integration algorithm is combined to solve the frictionless dynamic contact problem. By introducing additional Lagrange multipliers, the velocity and acceleration obtained by the combined time integration algorithm are modified to meet the persistency conditions of the contact constraints in the form of velocity and acceleration. Numerical example results show that the correction method can effectively improve the spurious oscillation of velocity, contact force, etc. at the time of initial contact, and improve the solution accuracy of impact problems.
2023, 40(S): 6-10.
doi: 10.6052/j.issn.1000-4750.2022.07.S047
Abstract:
Structural modal parameters (frequencies, damping ratios and mode shapes, etc.) play a critical role in structural health monitoring and dynamic test. Knowing their identification uncertainty can significantly enhance the accuracy and robustness of structural damage detection and condition assessment. Focusing on ‘understanding’ rather than ‘computing’ the identification uncertainty, asymptotic uncertainty gives the analytical forms of the coefficient of variation (c.o.v.) of identified modal parameters regardless of the particular dataset and identification algorithm. This paper introduces the asymptotic identification uncertainty of modal parameters in forced vibration test with known single input. Based on the long data and small damping assumptions, asymptotic expressions for the posterior c.o.v. of structural frequency, damping ratio and mode shape are given. A series of field tests are carried out for verification. The asymptotic identification uncertainty can be used to guide the practice of dynamic testing, to resolve the blindness of the dynamic test and the passiveness of the modal identification.
Structural modal parameters (frequencies, damping ratios and mode shapes, etc.) play a critical role in structural health monitoring and dynamic test. Knowing their identification uncertainty can significantly enhance the accuracy and robustness of structural damage detection and condition assessment. Focusing on ‘understanding’ rather than ‘computing’ the identification uncertainty, asymptotic uncertainty gives the analytical forms of the coefficient of variation (c.o.v.) of identified modal parameters regardless of the particular dataset and identification algorithm. This paper introduces the asymptotic identification uncertainty of modal parameters in forced vibration test with known single input. Based on the long data and small damping assumptions, asymptotic expressions for the posterior c.o.v. of structural frequency, damping ratio and mode shape are given. A series of field tests are carried out for verification. The asymptotic identification uncertainty can be used to guide the practice of dynamic testing, to resolve the blindness of the dynamic test and the passiveness of the modal identification.
2023, 40(S): 11-18.
doi: 10.6052/j.issn.1000-4750.2022.06.S016
Abstract:
The influence of mass matrix on dynamic calculation accuracy of Euler-Bernoulli beam theory and two-node bilinear interpolation beam theory is compared and analyzed by displaying uniform mass matrix and concentrated mass matrix. The superiority of two-node bilinear interpolation beam is revealed by numerical simulation using the finite element program Python. The results of theoretical derivation and numerical analysis show that the grid must be divided before the dynamic calculation of beam element. The increase of mesh density does not improve the dynamic accuracy of Euler-Bernoulli beam using concentrated mass matrix, while the convergence of uniform mass matrix is significantly higher than that of concentrated mass matrix.
The influence of mass matrix on dynamic calculation accuracy of Euler-Bernoulli beam theory and two-node bilinear interpolation beam theory is compared and analyzed by displaying uniform mass matrix and concentrated mass matrix. The superiority of two-node bilinear interpolation beam is revealed by numerical simulation using the finite element program Python. The results of theoretical derivation and numerical analysis show that the grid must be divided before the dynamic calculation of beam element. The increase of mesh density does not improve the dynamic accuracy of Euler-Bernoulli beam using concentrated mass matrix, while the convergence of uniform mass matrix is significantly higher than that of concentrated mass matrix.
2023, 40(S): 19-24, 55.
doi: 10.6052/j.issn.1000-4750.2022.06.S018
Abstract:
The state space method is adopted to study the in-plane dynamic behavior of circularly curved beams. By selecting appropriate state variables, the state space formula is properly set up. The frequencies and corresponding modal shapes of circularly curved beams are then obtained on the basis of state-space formulae. By utilizing the conception of symplectic inner product, the mode orthogonality with respect to the mass and rotary inertia properties for curved beams under three common boundary conditions in engineering (simply-supported, clamped and free) is established. Based on the orthogonality relation, the mode superposition method is utilized to obtain the solution of the inhomogeneous equation for forced vibration and dynamic response of curved beams subjected to a vertical moving constant force. The numerical results show that the proposed method is very accurate and reliable.
The state space method is adopted to study the in-plane dynamic behavior of circularly curved beams. By selecting appropriate state variables, the state space formula is properly set up. The frequencies and corresponding modal shapes of circularly curved beams are then obtained on the basis of state-space formulae. By utilizing the conception of symplectic inner product, the mode orthogonality with respect to the mass and rotary inertia properties for curved beams under three common boundary conditions in engineering (simply-supported, clamped and free) is established. Based on the orthogonality relation, the mode superposition method is utilized to obtain the solution of the inhomogeneous equation for forced vibration and dynamic response of curved beams subjected to a vertical moving constant force. The numerical results show that the proposed method is very accurate and reliable.
2023, 40(S): 25-38.
doi: 10.6052/j.issn.1000-4750.2022.05.S020
Abstract:
For the frame-shear wall dual lateral force resistance system, the lateral stiffness of the frame and the shear wall could be reflected comprehensively by the stiffness characteristic values, and investigated its influence on the shear force-sharing ratio and stable bearing capacity of frames. Four analytical models with heights of 48 m, 72 m, 96 m and 120 m were established. The finite element method and the simplified calculation method were used to estimate the stable bearing capacity of the structures and the effective length coefficient of the frame columns respectively. The stiffness characteristic value can comprehensively reflect the relative stiffness of the frame and the shear wall as well as the influence of the structure height. The larger the characteristic stiffness value is, the larger the shear force shared by the frame is. The frame buckling load modified coefficient γ can be used to quantitatively characterize the degree to which the frame is subjected to the lateral support of the shear wall, and γ decreases rapidly with the increase of the structure height. When the height of the frame-shear wall is large, the buckling load of the frame part may be lower than that of the pure frame, indicating that the frame part provides lateral support for the shear wall at this time. The calculation results show that, for the pure frame, the effective length factor of the column obtained by the finite element analysis through segmental loading of the standard stories of the structure remains unchanged within the range of each standard stories, and there is little difference between standard stories. Based on the method of mutual support of the same-story columns in the modified "Steel Structure Design Standard" GB50017, the effective length factor of the column is relatively close to the result of the segmental loading finite element analysis, and the error range is −9.5% to 14.2%. For frame-shear wall structures, the calculated length factor of the column is between the unbraced frame and the braced frame, as the height of the structure increases, its value is gradually close to that of the pure frame. The effective length factor obtained by the method in GB50017 method is close to the result by segmental loading finite element analysis. Since the axial force of the column gradually decreases with the increase of the floor height, the effective length factor of the column is continuously increased according to Euler's formula, which indicates that the finite element model with story-by-story loading has limitations in determining the effective length factor of the column. The method can be used as a reference when determining the effective length coefficient of columns in frame-shear wall dual lateral force resistance structures.
For the frame-shear wall dual lateral force resistance system, the lateral stiffness of the frame and the shear wall could be reflected comprehensively by the stiffness characteristic values, and investigated its influence on the shear force-sharing ratio and stable bearing capacity of frames. Four analytical models with heights of 48 m, 72 m, 96 m and 120 m were established. The finite element method and the simplified calculation method were used to estimate the stable bearing capacity of the structures and the effective length coefficient of the frame columns respectively. The stiffness characteristic value can comprehensively reflect the relative stiffness of the frame and the shear wall as well as the influence of the structure height. The larger the characteristic stiffness value is, the larger the shear force shared by the frame is. The frame buckling load modified coefficient γ can be used to quantitatively characterize the degree to which the frame is subjected to the lateral support of the shear wall, and γ decreases rapidly with the increase of the structure height. When the height of the frame-shear wall is large, the buckling load of the frame part may be lower than that of the pure frame, indicating that the frame part provides lateral support for the shear wall at this time. The calculation results show that, for the pure frame, the effective length factor of the column obtained by the finite element analysis through segmental loading of the standard stories of the structure remains unchanged within the range of each standard stories, and there is little difference between standard stories. Based on the method of mutual support of the same-story columns in the modified "Steel Structure Design Standard" GB50017, the effective length factor of the column is relatively close to the result of the segmental loading finite element analysis, and the error range is −9.5% to 14.2%. For frame-shear wall structures, the calculated length factor of the column is between the unbraced frame and the braced frame, as the height of the structure increases, its value is gradually close to that of the pure frame. The effective length factor obtained by the method in GB50017 method is close to the result by segmental loading finite element analysis. Since the axial force of the column gradually decreases with the increase of the floor height, the effective length factor of the column is continuously increased according to Euler's formula, which indicates that the finite element model with story-by-story loading has limitations in determining the effective length factor of the column. The method can be used as a reference when determining the effective length coefficient of columns in frame-shear wall dual lateral force resistance structures.
2023, 40(S): 39-45.
doi: 10.6052/j.issn.1000-4750.2022.06.S035
Abstract:
The bridge vibration control needs accurate description of the wind field features and dynamic response characteristics of vortex-induced vibration (VIV). The parameter characteristics of wind speed, wind direction, turbulence intensity, gust factor, fluctuating wind power spectrum density, vibration acceleration, and its power spectrum density during ambient vibration and VIV were compared, using the data collected by the structural health monitoring system installed on a large-span suspension bridge. The results show that the wind speed of the typical 6th vertical bending VIV reaches 7.24 m/s-12.24 m/s, with the wind direction being nearly perpendicular to the bridge axis. The turbulence intensity, gust factor in three directions, and fluctuating wind power spectrum in VIV have no discernible differences from those in ambient vibration. Unlike the multi-modal coupling ambient vibration, VIV presents the characteristics of single-mode vibration. This characteristic can be quantified by the difference ratio of peaks in power spectrum to distinguish ambient vibration and VIV.
The bridge vibration control needs accurate description of the wind field features and dynamic response characteristics of vortex-induced vibration (VIV). The parameter characteristics of wind speed, wind direction, turbulence intensity, gust factor, fluctuating wind power spectrum density, vibration acceleration, and its power spectrum density during ambient vibration and VIV were compared, using the data collected by the structural health monitoring system installed on a large-span suspension bridge. The results show that the wind speed of the typical 6th vertical bending VIV reaches 7.24 m/s-12.24 m/s, with the wind direction being nearly perpendicular to the bridge axis. The turbulence intensity, gust factor in three directions, and fluctuating wind power spectrum in VIV have no discernible differences from those in ambient vibration. Unlike the multi-modal coupling ambient vibration, VIV presents the characteristics of single-mode vibration. This characteristic can be quantified by the difference ratio of peaks in power spectrum to distinguish ambient vibration and VIV.
2023, 40(S): 46-55.
doi: 10.6052/j.issn.1000-4750.2022.05.S040
Abstract:
Aluminum alloys have been widely used in structural engineering by virtue of light weight, high strength and good corrosion resistance, while their applications in frames are limited. In order to promote the application and development of aluminum alloy frames, researches are needed on the seismic behavior of aluminum alloy beam-to-column joints and frames. Thusly, engineering applications and researches on aluminum alloy beam-to-column joints and frames are reviewed. Elastoplastic pushover and time-history analyses on an aluminum alloy frame are carried out to evaluate its seismic performance. A reference is thusly provided for the further research, design, and application of aluminum alloy frames.
Aluminum alloys have been widely used in structural engineering by virtue of light weight, high strength and good corrosion resistance, while their applications in frames are limited. In order to promote the application and development of aluminum alloy frames, researches are needed on the seismic behavior of aluminum alloy beam-to-column joints and frames. Thusly, engineering applications and researches on aluminum alloy beam-to-column joints and frames are reviewed. Elastoplastic pushover and time-history analyses on an aluminum alloy frame are carried out to evaluate its seismic performance. A reference is thusly provided for the further research, design, and application of aluminum alloy frames.
2023, 40(S): 56-61.
doi: 10.6052/j.issn.1000-4750.2022.07.S048
Abstract:
To analyze the post-impact mechanical properties of concrete-filled high-strength steel tubes, a numerical model for the residual axial compression resistance of concrete-filled high-strength steel tubes under low-speed lateral impact and axial compression is established in this paper. The model takes into account the material strain rate effects of high-strength steel and concrete, as well as the transfer of results between the dynamic and static analysis procedures. The feasibility of the model is verified using the existing low-speed lateral impact and static loading test results of concrete-filled high-strength steel tubes. The established finite element model is used to compare and analyze the influence of failure mode, local damage and mid-span deflection of post-impact concrete-filled high-strength steel tubes after lateral impact and static lateral loading on its residual axial compressive resistance, elaborating the key factors affecting its residual axial compression resistance. A simplified calculation model for the residual axial compression resistance is established based on the analysis.
To analyze the post-impact mechanical properties of concrete-filled high-strength steel tubes, a numerical model for the residual axial compression resistance of concrete-filled high-strength steel tubes under low-speed lateral impact and axial compression is established in this paper. The model takes into account the material strain rate effects of high-strength steel and concrete, as well as the transfer of results between the dynamic and static analysis procedures. The feasibility of the model is verified using the existing low-speed lateral impact and static loading test results of concrete-filled high-strength steel tubes. The established finite element model is used to compare and analyze the influence of failure mode, local damage and mid-span deflection of post-impact concrete-filled high-strength steel tubes after lateral impact and static lateral loading on its residual axial compressive resistance, elaborating the key factors affecting its residual axial compression resistance. A simplified calculation model for the residual axial compression resistance is established based on the analysis.
2023, 40(S): 62-73, 91.
doi: 10.6052/j.issn.1000-4750.2022.05.S046
Abstract:
According to the actual background of penetration of reinforced ultra-high performance-concrete (UHPC) by drilling weapons, studied by numerical simulation method is the influence of reinforcement on the penetration resistance of ultra-high-performance concrete (UHPC). The reliability of the numerical model and material parameters is verified by the test data of UHPC target of projectile penetration element. Through dimensional analysis, it is determined that steel bar diameter d, steel bar plane spacing sh and layer spacing sv are the main factors affecting the reinforcement. The penetration conditions of UHPC targets with different bar spacing and diameters of 300 m/s and 600 m/s were calculated and analyzed, and the influence of different reinforcement forms on the penetration depth under the same reinforcement ratio was studied. The results show that reinforcement can effectively improve the penetration resistance of ultra-high-performance concrete. The penetration depth and surface pitting diameter are positively correlated with reinforcement spacing, but negatively correlated with reinforcement diameter. Under the same reinforcement ratio, the reinforcement with small spacing and small diameter can improve the penetration resistance of UHPC more effectively than the reinforcement with large spacing and large diameter.
According to the actual background of penetration of reinforced ultra-high performance-concrete (UHPC) by drilling weapons, studied by numerical simulation method is the influence of reinforcement on the penetration resistance of ultra-high-performance concrete (UHPC). The reliability of the numerical model and material parameters is verified by the test data of UHPC target of projectile penetration element. Through dimensional analysis, it is determined that steel bar diameter d, steel bar plane spacing sh and layer spacing sv are the main factors affecting the reinforcement. The penetration conditions of UHPC targets with different bar spacing and diameters of 300 m/s and 600 m/s were calculated and analyzed, and the influence of different reinforcement forms on the penetration depth under the same reinforcement ratio was studied. The results show that reinforcement can effectively improve the penetration resistance of ultra-high-performance concrete. The penetration depth and surface pitting diameter are positively correlated with reinforcement spacing, but negatively correlated with reinforcement diameter. Under the same reinforcement ratio, the reinforcement with small spacing and small diameter can improve the penetration resistance of UHPC more effectively than the reinforcement with large spacing and large diameter.
2023, 40(S): 74-80.
doi: 10.6052/j.issn.1000-4750.2022.06.S045
Abstract:
Since the snowboarding platform is similar to the bridge structure, windbreaks can also make a competition wind environment with low wind speed for the ski jump. The effect of the windbreak porosities on the windproof performance is analyzed by means of numerical calculation. The paper systemically analyzes the laws of vortex structure, dimensionless velocity, influence coefficient of wind environment and turbulence intensity varying with windbreak porosity. The results show that the windbreak can improve the wind field structure on the ski slope effectively, but it can also cause significant vertical velocity component on the jumping height of athlete, which will affect the fairness of the competition. The influence coefficient of wind environment over the ski slope first decrease and then increase with the increase of the porosity of windbreak. Windbreaks with the porosities of 10%~20% have the best effect on preventing crosswind, their windproof efficiency are about 79%~97%, which can also effectively reduce the vertical velocity component on the jumping height of athlete. However, the turbulence intensity will be increased significantly at the same time. The windbreaks with the porosities of 10%~20% are preferred considering that the snowboarding platform is insensitive to the effect of wind loads.
Since the snowboarding platform is similar to the bridge structure, windbreaks can also make a competition wind environment with low wind speed for the ski jump. The effect of the windbreak porosities on the windproof performance is analyzed by means of numerical calculation. The paper systemically analyzes the laws of vortex structure, dimensionless velocity, influence coefficient of wind environment and turbulence intensity varying with windbreak porosity. The results show that the windbreak can improve the wind field structure on the ski slope effectively, but it can also cause significant vertical velocity component on the jumping height of athlete, which will affect the fairness of the competition. The influence coefficient of wind environment over the ski slope first decrease and then increase with the increase of the porosity of windbreak. Windbreaks with the porosities of 10%~20% have the best effect on preventing crosswind, their windproof efficiency are about 79%~97%, which can also effectively reduce the vertical velocity component on the jumping height of athlete. However, the turbulence intensity will be increased significantly at the same time. The windbreaks with the porosities of 10%~20% are preferred considering that the snowboarding platform is insensitive to the effect of wind loads.
2023, 40(S): 81-91.
doi: 10.6052/j.issn.1000-4750.2022.06.S044
Abstract:
A new type of precast RC shear wall with replaceable corner components was proposed and the influence of different parameters on the compressive-flexural behavior were studied based on numerical analysis. These parameters include the strength and height of replaceable corner components, and the thickness of embedded steel plate in non-replaceable zone. The results indicated that the lateral strength of the precast RC shear wall increased as the increase of strength of replaceable corner components. The precast RC shear wall had approximately identical lateral strength with cast-in-situ RC shear wall when the ratio of compressive strength of replaceable corner components to the boundary element of cast-in-situ RC shear wall is 0.85 or the ratio of tensile strength of replaceable corner components to the boundary element of cast-in-situ RC shear wall is 1.35. The height of replaceable corner components had a limited influence on the compressive-flexural lateral strength, on the stiffness and hysteretic behavior of precast RC shear wall; and one-half of sectional height was recommended for the height of replaceable corner comments. The thickness of embedded steel plate in non-replaceable zone also had a limited influence on the compressive-flexural behavior of precast RC shear wall, thus the principle of equal shear resistance between cast-in-situ RC shear wall and precast RC shear wall was recommended to ensure the damage focused on the replaceable zones.
A new type of precast RC shear wall with replaceable corner components was proposed and the influence of different parameters on the compressive-flexural behavior were studied based on numerical analysis. These parameters include the strength and height of replaceable corner components, and the thickness of embedded steel plate in non-replaceable zone. The results indicated that the lateral strength of the precast RC shear wall increased as the increase of strength of replaceable corner components. The precast RC shear wall had approximately identical lateral strength with cast-in-situ RC shear wall when the ratio of compressive strength of replaceable corner components to the boundary element of cast-in-situ RC shear wall is 0.85 or the ratio of tensile strength of replaceable corner components to the boundary element of cast-in-situ RC shear wall is 1.35. The height of replaceable corner components had a limited influence on the compressive-flexural lateral strength, on the stiffness and hysteretic behavior of precast RC shear wall; and one-half of sectional height was recommended for the height of replaceable corner comments. The thickness of embedded steel plate in non-replaceable zone also had a limited influence on the compressive-flexural behavior of precast RC shear wall, thus the principle of equal shear resistance between cast-in-situ RC shear wall and precast RC shear wall was recommended to ensure the damage focused on the replaceable zones.
2023, 40(S): 92-97, 119.
doi: 10.6052/j.issn.1000-4750.2022.06.S043
Abstract:
The inherent dynamic characteristics of different buildings vary a lot. The structural stiffness-flexibility indicator is expressed by the structural height and fundamental period of buildings. The stiffness and flexible properties of the structures will make the seismic displacement response and acceleration response of the buildings different, resulting in different post-earthquake losses. The rigid frame (RF) and the flexible frame (FF) designed according to the current codes are studied. In accordance with the seismic resilience evaluation standard of China, the seismic resilience evaluation of the high-rise steel frame structures is conducted based on the elasto-plastic time history analysis under the action of fortification earthquake and rare earthquake and the component fragility obtained from the building information model. The results show that the response of inter-story drift of RF is smaller and the response of floor acceleration is larger, while the response of FF is the opposite. This shows that the proportion of costs and time of repairmen, as well as personnel losses of various structural and non-structural components, are related to the structural stiffness-flexibility indicator.
The inherent dynamic characteristics of different buildings vary a lot. The structural stiffness-flexibility indicator is expressed by the structural height and fundamental period of buildings. The stiffness and flexible properties of the structures will make the seismic displacement response and acceleration response of the buildings different, resulting in different post-earthquake losses. The rigid frame (RF) and the flexible frame (FF) designed according to the current codes are studied. In accordance with the seismic resilience evaluation standard of China, the seismic resilience evaluation of the high-rise steel frame structures is conducted based on the elasto-plastic time history analysis under the action of fortification earthquake and rare earthquake and the component fragility obtained from the building information model. The results show that the response of inter-story drift of RF is smaller and the response of floor acceleration is larger, while the response of FF is the opposite. This shows that the proportion of costs and time of repairmen, as well as personnel losses of various structural and non-structural components, are related to the structural stiffness-flexibility indicator.
2023, 40(S): 98-107.
doi: 10.6052/j.issn.1000-4750.2022.06.S042
Abstract:
The reinforcement form of ultra-high performance concrete structures significantly impacts the blast resistance characteristics. Numerical methods are thusly utilized to study the effect of different reinforcement forms on the blast resistance of ultra-high performance reinforced concrete. The experimental results are used to verify the reliability of numerical modeling and material parameters, and established are 32 explosive-air-UHPC-rebar numerical models with different steel diameters and spacings. By analyzing the local damage of the structure and the displacement of the back blast surface, presented are the blast resistance characteristics of ultra-high performance concrete structures with different reinforcement forms under explosion. The results show that the dynamic damage laws of steel-UHPC structures are similar under different reinforcement ratios. The diameter of the steel bar is the main factor affecting the blast resistance performance of the structure. Under local loading, the blast resistance performance of the UHPC with thin steel bars is better than that of thick steel bars, and the effect of uniform reinforcement is the best. When the overall load is applied, the difference between UHPC structures with the same reinforcement ratio is small.
The reinforcement form of ultra-high performance concrete structures significantly impacts the blast resistance characteristics. Numerical methods are thusly utilized to study the effect of different reinforcement forms on the blast resistance of ultra-high performance reinforced concrete. The experimental results are used to verify the reliability of numerical modeling and material parameters, and established are 32 explosive-air-UHPC-rebar numerical models with different steel diameters and spacings. By analyzing the local damage of the structure and the displacement of the back blast surface, presented are the blast resistance characteristics of ultra-high performance concrete structures with different reinforcement forms under explosion. The results show that the dynamic damage laws of steel-UHPC structures are similar under different reinforcement ratios. The diameter of the steel bar is the main factor affecting the blast resistance performance of the structure. Under local loading, the blast resistance performance of the UHPC with thin steel bars is better than that of thick steel bars, and the effect of uniform reinforcement is the best. When the overall load is applied, the difference between UHPC structures with the same reinforcement ratio is small.
2023, 40(S): 108-112.
doi: 10.6052/j.issn.1000-4750.2022.06.S037
Abstract:
The vortex-induced vibration (VIV) is a common form of wind-induced vibration of long span streamlined box-girder bridge under low wind speed. It has a great influence on the fatigue life and driving comfort of a bridge structure. In order to reveal the VIV mechanism of a streamlined box girder, it is necessary to study the aerodynamic evolution law of VIV of a streamlined box girder. Taking a streamlined box-girder bridge as an example, a wind tunnel test was conducted to obtain the VIV response and pressure time-history data from pressure measurement points on the experimental model for the angles of attack +5°. The changes of mean values of wind pressure coefficient, of root-mean-square (RMS) values of wind pressure coefficients and, of vortex-induced force (VIF) amplitude spectrum in different vortex-induced stages are analyzed. Those stages include pre-VIV stage, ascent stage, extreme amplitude point, descent stage, and post-VIV stage. It is found that mean values of wind pressure coefficients have little change, however, the distribution of RMS values of wind pressure coefficients has obvious changes. The VIF has obvious predominant frequencies in the ascent stage, at the extreme amplitude point, and in the descent stage. These frequencies are similar to the natural vibration frequency of the structure. However, there is no considerable predominant frequency in pre-VIV stage and post-VIV stage. The amplitude corresponding to the dominant frequency of VIF is positively correlated with the amplitude of VIV and reaches the maximum at the extreme amplitude point.
The vortex-induced vibration (VIV) is a common form of wind-induced vibration of long span streamlined box-girder bridge under low wind speed. It has a great influence on the fatigue life and driving comfort of a bridge structure. In order to reveal the VIV mechanism of a streamlined box girder, it is necessary to study the aerodynamic evolution law of VIV of a streamlined box girder. Taking a streamlined box-girder bridge as an example, a wind tunnel test was conducted to obtain the VIV response and pressure time-history data from pressure measurement points on the experimental model for the angles of attack +5°. The changes of mean values of wind pressure coefficient, of root-mean-square (RMS) values of wind pressure coefficients and, of vortex-induced force (VIF) amplitude spectrum in different vortex-induced stages are analyzed. Those stages include pre-VIV stage, ascent stage, extreme amplitude point, descent stage, and post-VIV stage. It is found that mean values of wind pressure coefficients have little change, however, the distribution of RMS values of wind pressure coefficients has obvious changes. The VIF has obvious predominant frequencies in the ascent stage, at the extreme amplitude point, and in the descent stage. These frequencies are similar to the natural vibration frequency of the structure. However, there is no considerable predominant frequency in pre-VIV stage and post-VIV stage. The amplitude corresponding to the dominant frequency of VIF is positively correlated with the amplitude of VIV and reaches the maximum at the extreme amplitude point.
2023, 40(S): 113-119.
doi: 10.6052/j.issn.1000-4750.2022.05.S036
Abstract:
The slab track damage caused by thermal action will affect the high-speed railway operation safety, therefore, the exact solution about its temperature field is crucial. Based on the concrete random aggregate distribution algorithm and the heat transfer theory, develops a two-dimensional thermal transfer finite element model of the CRTSⅡ track at mesoscale to investigate the mesoscale temperature field. After the model’s reliability is confirmed by comparing the field measurements, the model is analyzed to determine the time-varying rule and spatial distribution rule of the internal temperature characteristics to the track at the mesoscale, and the two influence factors are the coarse aggregate maximum diameter and uneven distribution. The results show that the temperature field changes nonlinearly with depth at different time. The isotherm is generally parallel to the ground at the center of the track but fluctuates locally. The heat flux is preferentially transferred through the coarse aggregate passage, and its direction in the mortar points to the aggregates. The influence of the coarse aggregate maximum diameter and uneven distribution on the precast slab centerline temperature is almost negligible at different depths.
The slab track damage caused by thermal action will affect the high-speed railway operation safety, therefore, the exact solution about its temperature field is crucial. Based on the concrete random aggregate distribution algorithm and the heat transfer theory, develops a two-dimensional thermal transfer finite element model of the CRTSⅡ track at mesoscale to investigate the mesoscale temperature field. After the model’s reliability is confirmed by comparing the field measurements, the model is analyzed to determine the time-varying rule and spatial distribution rule of the internal temperature characteristics to the track at the mesoscale, and the two influence factors are the coarse aggregate maximum diameter and uneven distribution. The results show that the temperature field changes nonlinearly with depth at different time. The isotherm is generally parallel to the ground at the center of the track but fluctuates locally. The heat flux is preferentially transferred through the coarse aggregate passage, and its direction in the mortar points to the aggregates. The influence of the coarse aggregate maximum diameter and uneven distribution on the precast slab centerline temperature is almost negligible at different depths.
2023, 40(S): 120-125.
doi: 10.6052/j.issn.1000-4750.2022.06.S034
Abstract:
The stay cable is one of the main force members of cable-stayed bridges, and the study of its aerodynamic characteristics is the basis for the study of the aerodynamic characteristics of the overall structure. In order to explore the Reynolds number effect of aerodynamic force of stay cable with smooth surface, the wind tunnel pressure measurement test of stay cable section model under different wind speeds was carried out under uniform incoming flow, and the variation law of mean drag coefficient and mean wind pressure coefficient of cable-stay with Reynolds number was obtained. The results show that the mean aerodynamic coefficient of the stay cable with smooth surface has different performance in different Reynolds number regions. The mean drag is stable at 1.2 and 0.6 in the subcritical Reynolds number region and the supercritical Reynolds number region, respectively. The mean lift coefficient is 0. The mean drag coefficient decreases rapidly in the critical Reynolds number region. Correspondingly, the mean lift coefficient increases from 0 to the maximum and then decreases to 0. For the fluctuating aerodynamic force, the value of the fluctuating lift in the subcritical Reynolds number region is much larger than the fluctuating drag, which means that the cross-wind excitation of the stay cable is much larger than the along-wind excitation. The distribution of the mean wind pressure coefficient experienced a symmetric-asymmetric-symmetric variation process with the increase of Reynolds number, which reflected the variation law of laminar separation, unilateral turbulent separation and bilateral turbulent separation, and was a qualitative response to the variation trend of the mean lift coefficient. The variation trend of the absolute value of the mean base pressure coefficient at the back pressure of the stay cable was consistent with the mean drag coefficient.
The stay cable is one of the main force members of cable-stayed bridges, and the study of its aerodynamic characteristics is the basis for the study of the aerodynamic characteristics of the overall structure. In order to explore the Reynolds number effect of aerodynamic force of stay cable with smooth surface, the wind tunnel pressure measurement test of stay cable section model under different wind speeds was carried out under uniform incoming flow, and the variation law of mean drag coefficient and mean wind pressure coefficient of cable-stay with Reynolds number was obtained. The results show that the mean aerodynamic coefficient of the stay cable with smooth surface has different performance in different Reynolds number regions. The mean drag is stable at 1.2 and 0.6 in the subcritical Reynolds number region and the supercritical Reynolds number region, respectively. The mean lift coefficient is 0. The mean drag coefficient decreases rapidly in the critical Reynolds number region. Correspondingly, the mean lift coefficient increases from 0 to the maximum and then decreases to 0. For the fluctuating aerodynamic force, the value of the fluctuating lift in the subcritical Reynolds number region is much larger than the fluctuating drag, which means that the cross-wind excitation of the stay cable is much larger than the along-wind excitation. The distribution of the mean wind pressure coefficient experienced a symmetric-asymmetric-symmetric variation process with the increase of Reynolds number, which reflected the variation law of laminar separation, unilateral turbulent separation and bilateral turbulent separation, and was a qualitative response to the variation trend of the mean lift coefficient. The variation trend of the absolute value of the mean base pressure coefficient at the back pressure of the stay cable was consistent with the mean drag coefficient.
2023, 40(S): 126-135, 157.
doi: 10.6052/j.issn.1000-4750.2022.05.S030
Abstract:
In order to investigate the mechanical properties of steel tie rods under different loading conditions, the monotonic tension and low-cycle reciprocating tension and compression experiment was carried out on ten GLG650 steel tie rod specimens. The load-displacement curves, yield bearing capacity, maximum bearing capacity and ultimate bearing capacity of the steel tie rods and corresponding deformation and failure modes were obtained. The results of experiment and analysis show that the load-displacement curve of the steel tie rod is close to a straight line in the yield strengthening stage, and the load-displacement curves of the steel tie rods with smaller slenderness exhibit cyclic softening phenomenon under reciprocating tension and compression. After yielding in tension, as the axial deformation of the steel tie rod increases, its lateral deflection increases with the reverse compression, and the middle part of the rod enters into yield under compression and bending. The elongation after fracture of the steel tie rods is about 3.4% to 6.8%, which is much smaller than the elongation at breakage of the steel sample. Though the fracture mostly occurs at the loading end or fixed end, the fracture in the middle of the bar increases when the slenderness ratio is small, due to plastic damage accumulation under compression and bending. The load-displacement hysteresis rule of the steel tie rod determined according to the characteristic points can be used for elastic-plastic analysis under reciprocating load.
In order to investigate the mechanical properties of steel tie rods under different loading conditions, the monotonic tension and low-cycle reciprocating tension and compression experiment was carried out on ten GLG650 steel tie rod specimens. The load-displacement curves, yield bearing capacity, maximum bearing capacity and ultimate bearing capacity of the steel tie rods and corresponding deformation and failure modes were obtained. The results of experiment and analysis show that the load-displacement curve of the steel tie rod is close to a straight line in the yield strengthening stage, and the load-displacement curves of the steel tie rods with smaller slenderness exhibit cyclic softening phenomenon under reciprocating tension and compression. After yielding in tension, as the axial deformation of the steel tie rod increases, its lateral deflection increases with the reverse compression, and the middle part of the rod enters into yield under compression and bending. The elongation after fracture of the steel tie rods is about 3.4% to 6.8%, which is much smaller than the elongation at breakage of the steel sample. Though the fracture mostly occurs at the loading end or fixed end, the fracture in the middle of the bar increases when the slenderness ratio is small, due to plastic damage accumulation under compression and bending. The load-displacement hysteresis rule of the steel tie rod determined according to the characteristic points can be used for elastic-plastic analysis under reciprocating load.
2023, 40(S): 136-146.
doi: 10.6052/j.issn.1000-4750.2022.06.S031
Abstract:
Proposes two types of through diaphragm bolted-welded joints (TDBWJs) between narrow concrete-filled steel tube (CFST) column to steel beam. The bolted connection is used in bottom flange and web of the beam, and the welded connection is adopted in the upper flange of the beam. The joints can not only effectively avoid the appearance of exposed corners indoor, but also solve the problems of reserved installation gaps and smaller joint stiffness of full bolted joints. The joints also facilitate assembly and concrete pouring. The structural details, assembly process, design principle of joints were presented. In order to investigate the loading process, failure mode, stiffness and ductility of the joints, monotonic loading tests were carried on the joints, and the finite analysis was conducted based on the tests. The results show good agreement between the tests and finite element analysis. The main failure modes of the joints are the buckling of the flange in compression and the bulge of the adjacent web, with the plastic hinges of the joints far away from the panel zone, which conforms to the design principle of strong joint and weak member. The joints can be classified as rigid connections, which have large stiffness and bearing capacity, as well as preferable ductility.
Proposes two types of through diaphragm bolted-welded joints (TDBWJs) between narrow concrete-filled steel tube (CFST) column to steel beam. The bolted connection is used in bottom flange and web of the beam, and the welded connection is adopted in the upper flange of the beam. The joints can not only effectively avoid the appearance of exposed corners indoor, but also solve the problems of reserved installation gaps and smaller joint stiffness of full bolted joints. The joints also facilitate assembly and concrete pouring. The structural details, assembly process, design principle of joints were presented. In order to investigate the loading process, failure mode, stiffness and ductility of the joints, monotonic loading tests were carried on the joints, and the finite analysis was conducted based on the tests. The results show good agreement between the tests and finite element analysis. The main failure modes of the joints are the buckling of the flange in compression and the bulge of the adjacent web, with the plastic hinges of the joints far away from the panel zone, which conforms to the design principle of strong joint and weak member. The joints can be classified as rigid connections, which have large stiffness and bearing capacity, as well as preferable ductility.
2023, 40(S): 147-157.
doi: 10.6052/j.issn.1000-4750.2022.05.S032
Abstract:
The X-braced structure has been widely used in the design of major support structures in large-scale ocean engineering, the collapse deformation of the structure may be caused by the buckling instability of the support rod if it is not designed properly. Under the ultimate load, the buckling instability of X-braced structure is a typical multi-span stability problem of columns in essence, and its ultimate bearing capacity is closely related to the structural composition, geometric parameters and end restraint of the strut. This paper mainly studies the buckling characteristics of X-braced structures with or without out-of-plane support under arbitrary elastic supports, focusing on the influence of end constraints, force forms and out-of-plane bracing stiffness. Firstly, based on the linear elastic theory framework, the equilibrium equation of double span compression bar was established, and the buckling load was calculated by newton iterative algorithm, so as to obtain the numerical solution of effective length factor for continuous asymmetric cross struts in mid-span, and the sensitivity analysis of the end support stiffness and mid-span support stiffness is also carried out. Combined with engineering practice, the key design parameters, such as buckling length coefficient and stiffness, are given.
The X-braced structure has been widely used in the design of major support structures in large-scale ocean engineering, the collapse deformation of the structure may be caused by the buckling instability of the support rod if it is not designed properly. Under the ultimate load, the buckling instability of X-braced structure is a typical multi-span stability problem of columns in essence, and its ultimate bearing capacity is closely related to the structural composition, geometric parameters and end restraint of the strut. This paper mainly studies the buckling characteristics of X-braced structures with or without out-of-plane support under arbitrary elastic supports, focusing on the influence of end constraints, force forms and out-of-plane bracing stiffness. Firstly, based on the linear elastic theory framework, the equilibrium equation of double span compression bar was established, and the buckling load was calculated by newton iterative algorithm, so as to obtain the numerical solution of effective length factor for continuous asymmetric cross struts in mid-span, and the sensitivity analysis of the end support stiffness and mid-span support stiffness is also carried out. Combined with engineering practice, the key design parameters, such as buckling length coefficient and stiffness, are given.
2023, 40(S): 158-166, 190.
doi: 10.6052/j.issn.1000-4750.2022.06.S027
Abstract:
In order to study the enhancement effect of polypropylene band (PP-band) on the bending performance of brick masonry, the bending tensile test was carried out on 216 brick masonry specimens. Combined with numerical simulation, the influences of masonry mortar strength, coating mortar strength and PP-band mesh with different mesh sizes on the bending performance of brick masonry were studied. The results show that the strength of masonry mortar has the greatest influence on the peak bending load of brick masonry. Compared with M1 strength, when the strength of masonry mortar increases to M2.5, M5, M7.5 and M10, the corresponding peak bending load amplification of continuous section brick masonry is 15.87%, 31.11%, 37.60% and 44.45%, respectively, and that of the dentiform section brick masonry is 28.95%, 46.16%, 55.19% and 56.76%, respectively. The strength of coating mortar has little influence on the peak bending load, and its main function is to enhance the bond between PP-band and brick masonry surface. The joint action of high-strength coating mortar and PP-band can effectively improve the deformation resistance ability of brick masonry. The size of PP-band mesh mainly affects the amplitude of load recovery after the fracture of brick masonry. Compared with the mesh size of 12.5 cm, when the mesh size is reduced to 7.5 cm and 5 cm, the amplification of load recovery peak value of continuous section brick masonry can reach 63.42% and 130.38%, and that of the dentiform section brick masonry can reach 73.29% and 127.66%. The PP-band reinforcement method can provide reference for seismic reinforcement of masonry structures, especially in rural areas.
In order to study the enhancement effect of polypropylene band (PP-band) on the bending performance of brick masonry, the bending tensile test was carried out on 216 brick masonry specimens. Combined with numerical simulation, the influences of masonry mortar strength, coating mortar strength and PP-band mesh with different mesh sizes on the bending performance of brick masonry were studied. The results show that the strength of masonry mortar has the greatest influence on the peak bending load of brick masonry. Compared with M1 strength, when the strength of masonry mortar increases to M2.5, M5, M7.5 and M10, the corresponding peak bending load amplification of continuous section brick masonry is 15.87%, 31.11%, 37.60% and 44.45%, respectively, and that of the dentiform section brick masonry is 28.95%, 46.16%, 55.19% and 56.76%, respectively. The strength of coating mortar has little influence on the peak bending load, and its main function is to enhance the bond between PP-band and brick masonry surface. The joint action of high-strength coating mortar and PP-band can effectively improve the deformation resistance ability of brick masonry. The size of PP-band mesh mainly affects the amplitude of load recovery after the fracture of brick masonry. Compared with the mesh size of 12.5 cm, when the mesh size is reduced to 7.5 cm and 5 cm, the amplification of load recovery peak value of continuous section brick masonry can reach 63.42% and 130.38%, and that of the dentiform section brick masonry can reach 73.29% and 127.66%. The PP-band reinforcement method can provide reference for seismic reinforcement of masonry structures, especially in rural areas.
2023, 40(S): 167-173.
doi: 10.6052/j.issn.1000-4750.2022.06.S028
Abstract:
The shear transmission mechanism of new and old concrete interface with post-installed rebars is summarized, and the influencing factors of the interface shear capacity are divided into four categories: material property and size, interface treatment, reinforcement arrangement, and load action. The research on the interface bending moment and the interface size effect, which are less mentioned in codes, are summarized. An example of anti-floating calculation of a 2 m thick temporary bottom slab of subway station shows that these two factors may have great influence on interface shear capacity. The similarities and differences of shear transmission mechanism, interface roughness and interface bending moment, which are considered in the calculation of shear capacity of new and old concrete interface with post-installed rebars in the codes of China, Europe, America and Canada, are compared. It is suggested that the size effect should be considered when the code is revised.
The shear transmission mechanism of new and old concrete interface with post-installed rebars is summarized, and the influencing factors of the interface shear capacity are divided into four categories: material property and size, interface treatment, reinforcement arrangement, and load action. The research on the interface bending moment and the interface size effect, which are less mentioned in codes, are summarized. An example of anti-floating calculation of a 2 m thick temporary bottom slab of subway station shows that these two factors may have great influence on interface shear capacity. The similarities and differences of shear transmission mechanism, interface roughness and interface bending moment, which are considered in the calculation of shear capacity of new and old concrete interface with post-installed rebars in the codes of China, Europe, America and Canada, are compared. It is suggested that the size effect should be considered when the code is revised.
2023, 40(S): 174-183.
doi: 10.6052/j.issn.1000-4750.2022.06.S029
Abstract:
In order to ensure that the large-span coal shed structure is not damaged by wind load, a series wind tunnel tests was carried out to obtain the wind shape coefficient on the interference effect of coal shed structure. The results show that the structure is mainly subjected to wind pressure in the direction of incoming flow, the roof top is mainly subjected to wind suction, and the wind suction on the top of the roof is the largest. The distribution of wind load on the module shows an obvious gradient along the wind, and the wind load is gradual. The shielding effect of interference coal shed reduces the wind load of the structure as a whole, but we should also pay attention to the phenomenon that the interference causes the local wind load to become larger. When the model to be tested and the interference model are arranged in parallel along the wind direction, the wind load in the middle area of the structure almost does not change with the change of the span direction position, and the wind load in some areas of the structure along the deployment direction changes sharply. The results can provide a reference for the wind resistance design of large-span coal shed structures.
In order to ensure that the large-span coal shed structure is not damaged by wind load, a series wind tunnel tests was carried out to obtain the wind shape coefficient on the interference effect of coal shed structure. The results show that the structure is mainly subjected to wind pressure in the direction of incoming flow, the roof top is mainly subjected to wind suction, and the wind suction on the top of the roof is the largest. The distribution of wind load on the module shows an obvious gradient along the wind, and the wind load is gradual. The shielding effect of interference coal shed reduces the wind load of the structure as a whole, but we should also pay attention to the phenomenon that the interference causes the local wind load to become larger. When the model to be tested and the interference model are arranged in parallel along the wind direction, the wind load in the middle area of the structure almost does not change with the change of the span direction position, and the wind load in some areas of the structure along the deployment direction changes sharply. The results can provide a reference for the wind resistance design of large-span coal shed structures.
2023, 40(S): 184-190.
doi: 10.6052/j.issn.1000-4750.2022.05.S021
Abstract:
Progressive collapse is defined as the localized damage propagating throughout a structural system, which is triggered by the initial failure of critical structural element(s) caused by abnormal loads, eventually resulting in a partial or total collapse of the entire structural system. The progressive collapse resistance of the structural system is significantly affected by its redundant strength. The influences of primary design parameters on the progressive collapse resistance of regular reinforced concrete (RC) frame structures were analyzed and summarized to satisfy the requirement of rapid engineering assessment. Eighteen typical RC frames with regular configurations were designed according to the codes in which the effects of three design parameters, i.e., seismic fortification intensity, total number of structural floors and structural span, on structural redundant strength were considered. The numerical models of the frames were established using fiber beam elements, in which beams were modeled with T-shaped sections considering the contribution of the floor slab within the effective flange width. The nonlinear dynamic alternate path method was utilized to analyze the progressive collapse responses of these frames when initial failure occurred at different locations, and the influences of the primary design parameters on the progressive collapse resistance of the structures were studied.
Progressive collapse is defined as the localized damage propagating throughout a structural system, which is triggered by the initial failure of critical structural element(s) caused by abnormal loads, eventually resulting in a partial or total collapse of the entire structural system. The progressive collapse resistance of the structural system is significantly affected by its redundant strength. The influences of primary design parameters on the progressive collapse resistance of regular reinforced concrete (RC) frame structures were analyzed and summarized to satisfy the requirement of rapid engineering assessment. Eighteen typical RC frames with regular configurations were designed according to the codes in which the effects of three design parameters, i.e., seismic fortification intensity, total number of structural floors and structural span, on structural redundant strength were considered. The numerical models of the frames were established using fiber beam elements, in which beams were modeled with T-shaped sections considering the contribution of the floor slab within the effective flange width. The nonlinear dynamic alternate path method was utilized to analyze the progressive collapse responses of these frames when initial failure occurred at different locations, and the influences of the primary design parameters on the progressive collapse resistance of the structures were studied.
2023, 40(S): 191-199, 206.
doi: 10.6052/j.issn.1000-4750.2022.06.S022
Abstract:
To investigate the mechanical behavior of circular ultra-high performance concrete with coarse aggregate filled steel tube (CA-UHPCFST) slender columns under eccentric compression, 7 specimens were designed and fabricated with the consideration of slenderness ratio and eccentricity. Through eccentric compression tests, the failure modes, load-deformation curves, lateral deflection distributions, load-strain relationships, ductility and ultimate carrying capacity were analyzed. The results show that the CA-UHPCFST slender columns under eccentric compression demonstrate a buckling failure pattern, and the load-deformation curves consist of elastic, elastoplastic and descending stages. The ultimate carrying capacity of specimens is inverse proportional to the slenderness ratio and eccentricity, the ductility coefficient decreases with the slenderness ratio while increases first and then decreases with the eccentricity. The carrying capacity of specimens predicted by GB 50936−2014 is in good agreement with the experimental results. The research outcome can provide reference for further investigation and engineering application of UHPCFST members.
To investigate the mechanical behavior of circular ultra-high performance concrete with coarse aggregate filled steel tube (CA-UHPCFST) slender columns under eccentric compression, 7 specimens were designed and fabricated with the consideration of slenderness ratio and eccentricity. Through eccentric compression tests, the failure modes, load-deformation curves, lateral deflection distributions, load-strain relationships, ductility and ultimate carrying capacity were analyzed. The results show that the CA-UHPCFST slender columns under eccentric compression demonstrate a buckling failure pattern, and the load-deformation curves consist of elastic, elastoplastic and descending stages. The ultimate carrying capacity of specimens is inverse proportional to the slenderness ratio and eccentricity, the ductility coefficient decreases with the slenderness ratio while increases first and then decreases with the eccentricity. The carrying capacity of specimens predicted by GB 50936−2014 is in good agreement with the experimental results. The research outcome can provide reference for further investigation and engineering application of UHPCFST members.
2023, 40(S): 200-206.
doi: 10.6052/j.issn.1000-4750.2022.06.S023
Abstract:
In order to investigate the fracture behavior of steel fiber reinforced concrete materials at low temperatures, 3D numerical models of concrete specimens with different volume fractions of steel fibers (V=0.0%, 0.5% and 1.0%) were developed at the meso-scale by means of finite element analysis, and splitting tensile strength tests as well as three-point bending loading tests were conducted at three temperatures (T=20 ℃, −40 ℃ and −80 ℃). The corresponding damage modes and load-span deflection curves were obtained. The results show that the fracture energy of concrete tends to increase with the decrease of temperature, and the fracture energy increases with the increase of fiber volume fraction. The characteristic length of concrete decreases with decreasing temperature, but the addition of fibers largely increases its characteristic length.
In order to investigate the fracture behavior of steel fiber reinforced concrete materials at low temperatures, 3D numerical models of concrete specimens with different volume fractions of steel fibers (V=0.0%, 0.5% and 1.0%) were developed at the meso-scale by means of finite element analysis, and splitting tensile strength tests as well as three-point bending loading tests were conducted at three temperatures (T=20 ℃, −40 ℃ and −80 ℃). The corresponding damage modes and load-span deflection curves were obtained. The results show that the fracture energy of concrete tends to increase with the decrease of temperature, and the fracture energy increases with the increase of fiber volume fraction. The characteristic length of concrete decreases with decreasing temperature, but the addition of fibers largely increases its characteristic length.
2023, 40(S): 207-212, 247.
doi: 10.6052/j.issn.1000-4750.2022.06.S024
Abstract:
Three sets of corrosion-fatigue coupling bearing tests of reinforced concrete (RC) beams under different stress amplitudes are designed to study the structural mechanical behavior and stiffness degradation of reinforced concrete beams under corrosion-fatigue coupling effect, and the fatigue life and stiffness evolution law of each test beam are analyzed as well. The results indicate that, the coupling effect of corrosion and fatigue reduces the fatigue life of reinforced concrete members, and the deflection development curves of fatigue beams and corrosion-fatigue coupled beams both show a 'sudden increase-stable-sudden increase' change law. And the deflection development rate in the second stage is much larger than that of the fatigue-loaded beam under the same stress amplitude. On the basis of existing codes, the stiffness calculation method of existing fatigue beams and corrosion-fatigue coupled beams is improved. The proposed method systematically considers the effects of fatigue, stress amplitude, concrete elastic modulus degradation and steel corrosion. And a good agreement is observed between theoretical results and experimental values, which verifies the accuracy of the stiffness calculation model.
Three sets of corrosion-fatigue coupling bearing tests of reinforced concrete (RC) beams under different stress amplitudes are designed to study the structural mechanical behavior and stiffness degradation of reinforced concrete beams under corrosion-fatigue coupling effect, and the fatigue life and stiffness evolution law of each test beam are analyzed as well. The results indicate that, the coupling effect of corrosion and fatigue reduces the fatigue life of reinforced concrete members, and the deflection development curves of fatigue beams and corrosion-fatigue coupled beams both show a 'sudden increase-stable-sudden increase' change law. And the deflection development rate in the second stage is much larger than that of the fatigue-loaded beam under the same stress amplitude. On the basis of existing codes, the stiffness calculation method of existing fatigue beams and corrosion-fatigue coupled beams is improved. The proposed method systematically considers the effects of fatigue, stress amplitude, concrete elastic modulus degradation and steel corrosion. And a good agreement is observed between theoretical results and experimental values, which verifies the accuracy of the stiffness calculation model.
2023, 40(S): 213-218.
doi: 10.6052/j.issn.1000-4750.2022.06.S025
Abstract:
The dewatering design of deep excavation with suspended impervious curtain for A station was analyzed by using three-dimensional finite element model and based on the data of geotechnical investigation and pumping test of Metro Green Line Project in Tel Aviv, Israel. According to the simulation results, the original dewatering design could not meet the requirements of water level for construction in the middle of the foundation pit, because the spatial uneven distribution of impervious layer was not fully considered. After further analyzing the influence of several factors on dewatering effect such as discharge of single well, distribution of dewatering wells and depth range of screen, the suggestions for improvement were given, which increase the dewatering effect and reduce the head difference between both ends and the middle of the foundation pit. And it is also conducive to excavation and cost saving. This work can be used as a reference for people related to design and construction in similar projects.
The dewatering design of deep excavation with suspended impervious curtain for A station was analyzed by using three-dimensional finite element model and based on the data of geotechnical investigation and pumping test of Metro Green Line Project in Tel Aviv, Israel. According to the simulation results, the original dewatering design could not meet the requirements of water level for construction in the middle of the foundation pit, because the spatial uneven distribution of impervious layer was not fully considered. After further analyzing the influence of several factors on dewatering effect such as discharge of single well, distribution of dewatering wells and depth range of screen, the suggestions for improvement were given, which increase the dewatering effect and reduce the head difference between both ends and the middle of the foundation pit. And it is also conducive to excavation and cost saving. This work can be used as a reference for people related to design and construction in similar projects.
2023, 40(S): 219-226.
doi: 10.6052/j.issn.1000-4750.2022.06.S001
Abstract:
The computational fluid dynamics (CFD) method is used to analyze the localized fire condition where the brazier is adjacent to a steel column, and the consideration of horizontal flow is taken into account. In order to verify the correctness of the numerical simulation method, the ceiling jet model was thusly taken as an example to conduct a fire analysis under the condition of no wind at first, and the correctness of the numerical model was verified by comparison with the experimental data. In the thermal analysis of steel column near the brazier, it is found that the flame is obviously inclined under the influence of incoming flow. When the incoming flow velocity is greater than the critical value, the fire plume surrounds the steel column from the side surfaces, forming the scene of fire plume around the column, which leads to significant changes in the thermal characteristics of the fluid field and the heating condition of the steel column surfaces. The distribution rules of gas temperature field, of velocity field, of steel column wall temperature field and, of convective heat transfer coefficient are discussed in detail.
The computational fluid dynamics (CFD) method is used to analyze the localized fire condition where the brazier is adjacent to a steel column, and the consideration of horizontal flow is taken into account. In order to verify the correctness of the numerical simulation method, the ceiling jet model was thusly taken as an example to conduct a fire analysis under the condition of no wind at first, and the correctness of the numerical model was verified by comparison with the experimental data. In the thermal analysis of steel column near the brazier, it is found that the flame is obviously inclined under the influence of incoming flow. When the incoming flow velocity is greater than the critical value, the fire plume surrounds the steel column from the side surfaces, forming the scene of fire plume around the column, which leads to significant changes in the thermal characteristics of the fluid field and the heating condition of the steel column surfaces. The distribution rules of gas temperature field, of velocity field, of steel column wall temperature field and, of convective heat transfer coefficient are discussed in detail.
2023, 40(S): 227-233.
doi: 10.6052/j.issn.1000-4750.2022.05.S003
Abstract:
High-rise office buildings mainly adopt frame-shear wall structures. The whole structure may collapse progressively triggered by initial failure of critical structural element(s), eventually resulting in serious economic losses and social impact. Dynamic progressive collapse analysis was conducted on typical reinforced concrete (RC) frame-shear wall structures and the collapse mechanism was summarized, which provided a basis for rapid assessment for the progressive collapse of RC frame-shear wall structures. The research included the following works: Eighteen typical RC frame-shear structures were designed in accordance with different seismic fortification intensities, span lengths and number of stories. The numerical models of the structures were established in which fiber beam elements and multilayer shell elements were used to simulate RC beams and columns and RC shear walls, respectively. The nonlinear dynamic analysis using nonlinear dynamic alternate path method was conducted on the typical RC frame-shear wall structures, and the dynamic responses of the structures triggered by initial local failures were obtained. The dynamic responses of structural progressive collapse varying with different key parameters were compared and analyzed, by which the influence of different structural parameters on the dynamic progressive collapse responses was studied.
High-rise office buildings mainly adopt frame-shear wall structures. The whole structure may collapse progressively triggered by initial failure of critical structural element(s), eventually resulting in serious economic losses and social impact. Dynamic progressive collapse analysis was conducted on typical reinforced concrete (RC) frame-shear wall structures and the collapse mechanism was summarized, which provided a basis for rapid assessment for the progressive collapse of RC frame-shear wall structures. The research included the following works: Eighteen typical RC frame-shear structures were designed in accordance with different seismic fortification intensities, span lengths and number of stories. The numerical models of the structures were established in which fiber beam elements and multilayer shell elements were used to simulate RC beams and columns and RC shear walls, respectively. The nonlinear dynamic analysis using nonlinear dynamic alternate path method was conducted on the typical RC frame-shear wall structures, and the dynamic responses of the structures triggered by initial local failures were obtained. The dynamic responses of structural progressive collapse varying with different key parameters were compared and analyzed, by which the influence of different structural parameters on the dynamic progressive collapse responses was studied.
2023, 40(S): 234-240.
doi: 10.6052/j.issn.1000-4750.2022.05.S004
Abstract:
With the continuous degradation of in-service reinforced concrete (RC) structures, owners are urgently concerned about managing and maintaining a sea of RC members at the proper time with limited funds. Thusly, an optimized approach for the maintenance strategy of corrosion-damaged RC columns is presented upon the gamma process. By analyzing the performance deterioration of the corroded RC columns, proposed are the calculation models for estimating the residual bearing capacity under different damaged levels and various loading conditions. Meanwhile, the gamma process is adopted here to predict the failure probability of corroded columns by considering the uncertainty of structural deterioration. Moreover, the optimal maintenance time of the structure is determined by balancing the maintenance cost and the risk of structural failure. A numerical example is given to demonstrate the effectiveness of the models proposed. The results show that: the residual bearing capacity of RC columns can be significantly affected by the rebar corrosion level and load condition; when the allowable degradation limit of the corroded structure is smaller, the optimal maintenance time of the structure is advanced, and the corresponding expected relative cost increases.
With the continuous degradation of in-service reinforced concrete (RC) structures, owners are urgently concerned about managing and maintaining a sea of RC members at the proper time with limited funds. Thusly, an optimized approach for the maintenance strategy of corrosion-damaged RC columns is presented upon the gamma process. By analyzing the performance deterioration of the corroded RC columns, proposed are the calculation models for estimating the residual bearing capacity under different damaged levels and various loading conditions. Meanwhile, the gamma process is adopted here to predict the failure probability of corroded columns by considering the uncertainty of structural deterioration. Moreover, the optimal maintenance time of the structure is determined by balancing the maintenance cost and the risk of structural failure. A numerical example is given to demonstrate the effectiveness of the models proposed. The results show that: the residual bearing capacity of RC columns can be significantly affected by the rebar corrosion level and load condition; when the allowable degradation limit of the corroded structure is smaller, the optimal maintenance time of the structure is advanced, and the corresponding expected relative cost increases.
2023, 40(S): 241-247.
doi: 10.6052/j.issn.1000-4750.2022.06.S005
Abstract:
In view of the sensitivity of streamlined main girder to wind load, Xiangshangang Bridge with typical streamlined box girder section was taken as the research object, and performed wind tunnel test on a sectional model. The variations of average drag coefficient, average lift coefficient and average moment coefficient with Reynolds number were studied for the construction and completion conditions of bridge girder section. At the same time, the influence of different railings height on the variation of three-component force coefficient of main girder was analyzed. The result shows that the average life coefficient and the average moment coefficient of the bridge at construction condition increase with the increase of wind attack angle; The variation of the three-component coefficients of the bridge in the vortex vibration range (Re=2.92×104-4.05×104) is complicated; with the increase of Reynolds number, the average lift coefficient and the average moment coefficient basically show a trend that the greater the height of the railings, the greater the coefficient.
In view of the sensitivity of streamlined main girder to wind load, Xiangshangang Bridge with typical streamlined box girder section was taken as the research object, and performed wind tunnel test on a sectional model. The variations of average drag coefficient, average lift coefficient and average moment coefficient with Reynolds number were studied for the construction and completion conditions of bridge girder section. At the same time, the influence of different railings height on the variation of three-component force coefficient of main girder was analyzed. The result shows that the average life coefficient and the average moment coefficient of the bridge at construction condition increase with the increase of wind attack angle; The variation of the three-component coefficients of the bridge in the vortex vibration range (Re=2.92×104-4.05×104) is complicated; with the increase of Reynolds number, the average lift coefficient and the average moment coefficient basically show a trend that the greater the height of the railings, the greater the coefficient.
2023, 40(S): 248-258.
doi: 10.6052/j.issn.1000-4750.2022.03.S006
Abstract:
The numerical simulation program of PFC2D (Particle Flow Code in 2 Dimension) particle flow based on the flow-solid coupling principle and, on its built-in FISHTANK function library and FISH language, defines the flow equation and pressure equation of fluid domain respectively, and carries out numerical simulation calculations on the diffusion process and, on the morphology and particle displacement of slurry during the slurry injection process. By adjusting the parameters of hist, n_bond, s_bond and measure in the PFC command flow, the tracking of granular body displacement changes is achieved, and the mesoscopic mechanism such as the diffusion law of soil slurry at different depths and the change of formation porosity is revealed. The numerical calculations show that: the grouting pressure has a significant effect on the alteration and destruction of the formation structure, and the fracturing effect becomes gradually worse with increasing adhesive strength, while the porosity increases significantly with increasing grouting pressure. Based on the elastic-plastic theory of the Mohr-Colomb criterion to theoretically derive the stress field of the soil around the borehole, it is pointed out that the mechanical mechanism of annular tension and radial compression is the fundamental reason for the appearance of fracturing grouting action mode. The increase of slurry viscosity is beneficial to improve the grouting effect of fracturing-compacting grouting, while the increase of friction coefficient has little effect on the grouting effect. The comparative analysis of the laboratory tests shows that the PFC2D simulation of the grouting process is feasible.
The numerical simulation program of PFC2D (Particle Flow Code in 2 Dimension) particle flow based on the flow-solid coupling principle and, on its built-in FISHTANK function library and FISH language, defines the flow equation and pressure equation of fluid domain respectively, and carries out numerical simulation calculations on the diffusion process and, on the morphology and particle displacement of slurry during the slurry injection process. By adjusting the parameters of hist, n_bond, s_bond and measure in the PFC command flow, the tracking of granular body displacement changes is achieved, and the mesoscopic mechanism such as the diffusion law of soil slurry at different depths and the change of formation porosity is revealed. The numerical calculations show that: the grouting pressure has a significant effect on the alteration and destruction of the formation structure, and the fracturing effect becomes gradually worse with increasing adhesive strength, while the porosity increases significantly with increasing grouting pressure. Based on the elastic-plastic theory of the Mohr-Colomb criterion to theoretically derive the stress field of the soil around the borehole, it is pointed out that the mechanical mechanism of annular tension and radial compression is the fundamental reason for the appearance of fracturing grouting action mode. The increase of slurry viscosity is beneficial to improve the grouting effect of fracturing-compacting grouting, while the increase of friction coefficient has little effect on the grouting effect. The comparative analysis of the laboratory tests shows that the PFC2D simulation of the grouting process is feasible.
2023, 40(S): 259-268, 294.
doi: 10.6052/j.issn.1000-4750.2022.06.S007
Abstract:
In order to solve the problem of prefabricated construction between H-shaped steel beams and double-skin composite walls, an assembled endplate joint using slip-critical blind bolts (SCBBs) was proposed in this paper. Two full-scaled specimens were designed and fabricated for low cycle reciprocating loading test and FEM analysis. The deformation mechanism, failure modes, ultimate capacity, ductility, energy dissipation, and stiffness degradation of the joints were studied. The results indicate that the failure modes can be divided into beam buckling and column surface damage according to the different thickness of vertical H-beam flange. The hysteretic curve of the beam buckling joint shows full spindle shape, and the joint shows fine seismic performance with the column surface and infilled concrete approximately remaining undamaged. As for the column surface damaged joint, the circular yield surface formed on the steel plate under tension around the bolt hole and the infilled concrete was crushed. The beam-end rotation of the joint is mainly caused by the rotation of the joint area. This failure mode should be avoided in engineering design due to its low bearing capacity, serious stiffness degradation and poor energy dissipation capacity.
In order to solve the problem of prefabricated construction between H-shaped steel beams and double-skin composite walls, an assembled endplate joint using slip-critical blind bolts (SCBBs) was proposed in this paper. Two full-scaled specimens were designed and fabricated for low cycle reciprocating loading test and FEM analysis. The deformation mechanism, failure modes, ultimate capacity, ductility, energy dissipation, and stiffness degradation of the joints were studied. The results indicate that the failure modes can be divided into beam buckling and column surface damage according to the different thickness of vertical H-beam flange. The hysteretic curve of the beam buckling joint shows full spindle shape, and the joint shows fine seismic performance with the column surface and infilled concrete approximately remaining undamaged. As for the column surface damaged joint, the circular yield surface formed on the steel plate under tension around the bolt hole and the infilled concrete was crushed. The beam-end rotation of the joint is mainly caused by the rotation of the joint area. This failure mode should be avoided in engineering design due to its low bearing capacity, serious stiffness degradation and poor energy dissipation capacity.
2023, 40(S): 269-275.
doi: 10.6052/j.issn.1000-4750.2022.05.S008
Abstract:
In order to study the local buckling behavior of high strength aluminium alloy angle columns under axial compression, 9 different stub angle columns made of 701-T6 and 703-T6 high strength aluminium alloy were tested. The first-order eigenvalue local buckling mode was observed on every specimen before yielding. The finite element models were established for all specimens and the results were compared to the test results to validate these models. The verified models were then used to carry out parametric study to investigate the influence of width-to-thickness ratio on the local buckling behavior. The results show that the local buckling occurs earlier when the width-to-thickness ratio is larger. The experimental and numerical results were compared with the predictions given by the current Chinese standard. The Chinese standard is found to be safe but conservative as it underestimates the loading capacity, which is not conducive to exploit the full strength of the material. Therefore, a modified design method is proposed based on the current standard, which can give more accurate predictions with the same reliability and efficiency.
In order to study the local buckling behavior of high strength aluminium alloy angle columns under axial compression, 9 different stub angle columns made of 701-T6 and 703-T6 high strength aluminium alloy were tested. The first-order eigenvalue local buckling mode was observed on every specimen before yielding. The finite element models were established for all specimens and the results were compared to the test results to validate these models. The verified models were then used to carry out parametric study to investigate the influence of width-to-thickness ratio on the local buckling behavior. The results show that the local buckling occurs earlier when the width-to-thickness ratio is larger. The experimental and numerical results were compared with the predictions given by the current Chinese standard. The Chinese standard is found to be safe but conservative as it underestimates the loading capacity, which is not conducive to exploit the full strength of the material. Therefore, a modified design method is proposed based on the current standard, which can give more accurate predictions with the same reliability and efficiency.
2023, 40(S): 276-282.
doi: 10.6052/j.issn.1000-4750.2022.06.S011
Abstract:
The large aperture space deployable antenna in orbit may encounter high-speed impacts from tiny space debris, which seriously threatens the safe service of the antenna on board. In order to study the dynamic response of the support structure of the space mesh deployable antenna and the parabolic cable-mesh during high speed impact, ANSYS/AUTODYN is selected to build a dynamic impact simulation model of the large aperture space mesh deployable antenna to simulate the dynamic response of the antenna during the impact with space debris of 2.5 mm-7.5 mm when the antenna is deployed and locked. The overall dynamic response of the structure, the damage state of key rods and parabolic cable network as well as the deformation performance of the structure as a whole are considered for impact velocities of 1.0 km/s-15.0 km/s and different impact position conditions. The results show that the structural response of the spatially expandable antenna structure to space debris impact can be divided into three stages: local vibration, cable restraint and overall vibration. A closer distance between the impact point and the centre of the antenna leads to more obvious structural response and larger average deformation of the structure. As the impact velocity increases, the average structural deformation of the spreading antenna tends to increase initially and then decrease. When the impact velocity is greater than 12.5 km/s, the impact area of the antenna is gradually reduced. The overall deformation of the spreading antenna is not negligible when it is impacted by tiny space debris at high velocity, which can provide reference for the subsequent structural protection and vulnerability analysis.
The large aperture space deployable antenna in orbit may encounter high-speed impacts from tiny space debris, which seriously threatens the safe service of the antenna on board. In order to study the dynamic response of the support structure of the space mesh deployable antenna and the parabolic cable-mesh during high speed impact, ANSYS/AUTODYN is selected to build a dynamic impact simulation model of the large aperture space mesh deployable antenna to simulate the dynamic response of the antenna during the impact with space debris of 2.5 mm-7.5 mm when the antenna is deployed and locked. The overall dynamic response of the structure, the damage state of key rods and parabolic cable network as well as the deformation performance of the structure as a whole are considered for impact velocities of 1.0 km/s-15.0 km/s and different impact position conditions. The results show that the structural response of the spatially expandable antenna structure to space debris impact can be divided into three stages: local vibration, cable restraint and overall vibration. A closer distance between the impact point and the centre of the antenna leads to more obvious structural response and larger average deformation of the structure. As the impact velocity increases, the average structural deformation of the spreading antenna tends to increase initially and then decrease. When the impact velocity is greater than 12.5 km/s, the impact area of the antenna is gradually reduced. The overall deformation of the spreading antenna is not negligible when it is impacted by tiny space debris at high velocity, which can provide reference for the subsequent structural protection and vulnerability analysis.
2023, 40(S): 283-288.
doi: 10.6052/j.issn.1000-4750.2022.06.S012
Abstract:
Shape memory alloy (SMA) as joint connection material can limit the plastic deformation and improve the seismic resilience of the assembled steel structure under strong earthquakes. An assembled seismic resilient steel joints using SMA material was investigated. A delicate solid finite element model was established and verified by test data. The influence of bolt preload and SMA tendon pre-stress on the mechanics state and hysteretic performance of assembled steel joints were analyzed. The results show that the hysteretic behavior of assembled beam-column steel joints can be well simulated by the finite element model. The assembled beam-column steel joints connected by SMA tendons have excellent seismic resilience. When subjected to the low cyclic loading, the beam, column and their connectors are basically maintained within the elastic range, with a residual displacement of approximately zero. Increasing the bolt preload can increase the friction between the bolt and steel plate, and can improve the carrying capacity and energy dissipation capacity of the beam-column joint. However, increasing the SMA tendon pre-stress has insignificant effect on the mechanics state and hysteretic performance of the beam-column joint.
Shape memory alloy (SMA) as joint connection material can limit the plastic deformation and improve the seismic resilience of the assembled steel structure under strong earthquakes. An assembled seismic resilient steel joints using SMA material was investigated. A delicate solid finite element model was established and verified by test data. The influence of bolt preload and SMA tendon pre-stress on the mechanics state and hysteretic performance of assembled steel joints were analyzed. The results show that the hysteretic behavior of assembled beam-column steel joints can be well simulated by the finite element model. The assembled beam-column steel joints connected by SMA tendons have excellent seismic resilience. When subjected to the low cyclic loading, the beam, column and their connectors are basically maintained within the elastic range, with a residual displacement of approximately zero. Increasing the bolt preload can increase the friction between the bolt and steel plate, and can improve the carrying capacity and energy dissipation capacity of the beam-column joint. However, increasing the SMA tendon pre-stress has insignificant effect on the mechanics state and hysteretic performance of the beam-column joint.
2023, 40(S): 289-294.
doi: 10.6052/j.issn.1000-4750.2022.06.S013
Abstract:
In order to study the dynamic compressive mechanical properties of ultra-high toughness cementitious composites (UHTCC) in coastal salt spray environment, dynamic compressive mechanical tests of three groups of different strain rates (10−4 s−1, 10−3 s−1, and 10−2 s−1) were carried out on two groups of ultra-high toughness cementitious composites with different corrosion degrees (corrosion period of 0 d and 60 d), and the dynamic compressive stress-strain curves and failure morphology of materials were obtained. The effect of strain rate on elastic modulus, peak strength and peak strain of ultra-high toughness cementitious composites with different corrosion degree was analyzed. The results show that the dynamic compressive strength of ultra-high toughness cementitious composites is 44.5%, 54.4% and 62.4% higher than that of the uncorroded specimen, and the dynamic elastic modulus is 19.4%, 15.3% and 28.4% higher than that of the uncorroded specimen; while the strain rate sensitivity of the compressive strength increases. X-ray computed tomography showed that the porosity of the material decreased and became denser.
In order to study the dynamic compressive mechanical properties of ultra-high toughness cementitious composites (UHTCC) in coastal salt spray environment, dynamic compressive mechanical tests of three groups of different strain rates (10−4 s−1, 10−3 s−1, and 10−2 s−1) were carried out on two groups of ultra-high toughness cementitious composites with different corrosion degrees (corrosion period of 0 d and 60 d), and the dynamic compressive stress-strain curves and failure morphology of materials were obtained. The effect of strain rate on elastic modulus, peak strength and peak strain of ultra-high toughness cementitious composites with different corrosion degree was analyzed. The results show that the dynamic compressive strength of ultra-high toughness cementitious composites is 44.5%, 54.4% and 62.4% higher than that of the uncorroded specimen, and the dynamic elastic modulus is 19.4%, 15.3% and 28.4% higher than that of the uncorroded specimen; while the strain rate sensitivity of the compressive strength increases. X-ray computed tomography showed that the porosity of the material decreased and became denser.
2023, 40(S): 295-302.
doi: 10.6052/j.issn.1000-4750.2022.05.S014
Abstract:
To improve the sensitivity of passive tuned mass damper (TMD) to frequency tuning, overcome the difficulty of frequency changing, and improve its control effect on vertical human-induced vibration of footbridges, an adaptive variable stiffness TMD is studied in this paper. The mass with an internal through hole is placed on the spring, and a cantilever beam is fixed on each side of the mass, to the left and to the right of a stepping push-pull rod. The stepping push-pull rod can adjust the length of the cantilever beam into the tunnel of the mass, which is the length of the free end, to change its stiffness, thereby realizing the tuning of TMD frequency. After TMD is added to the main structure, the spectrum of the main structure will be disturbed, and it is difficult to directly identify the natural frequency of the main structure. Therefore, this paper first introduces the mechanism of adaptive adjustable stiffness TMD, then proposes a frequency identification algorithm of main structure based on undamped two-degrees-of-freedom model, and then conducts model experiments of a footbridge with stiffness adaptive regulation and four kinds of human-induced vibration control; at last, the decoupled structural frequency identification of the footbridge experiment is simulated.
To improve the sensitivity of passive tuned mass damper (TMD) to frequency tuning, overcome the difficulty of frequency changing, and improve its control effect on vertical human-induced vibration of footbridges, an adaptive variable stiffness TMD is studied in this paper. The mass with an internal through hole is placed on the spring, and a cantilever beam is fixed on each side of the mass, to the left and to the right of a stepping push-pull rod. The stepping push-pull rod can adjust the length of the cantilever beam into the tunnel of the mass, which is the length of the free end, to change its stiffness, thereby realizing the tuning of TMD frequency. After TMD is added to the main structure, the spectrum of the main structure will be disturbed, and it is difficult to directly identify the natural frequency of the main structure. Therefore, this paper first introduces the mechanism of adaptive adjustable stiffness TMD, then proposes a frequency identification algorithm of main structure based on undamped two-degrees-of-freedom model, and then conducts model experiments of a footbridge with stiffness adaptive regulation and four kinds of human-induced vibration control; at last, the decoupled structural frequency identification of the footbridge experiment is simulated.
2023, 40(S): 303-306.
doi: 10.6052/j.issn.1000-4750.2022.05.S038
Abstract:
Carbon fabric reinforced cementitious matrix (CFRCM) is often used in the reinforcement of concrete structures and the electrochemical protection of steel bars because of their combination of structural performance improvement and impressed current cathodic protection (ICCP). The effect and mechanism of CFRCM performance are less studied. It is found that the electrical conductivity and mechanical properties of CFRCM are degraded by ICCP through accelerated energization test and tensile test of CFRCM. With the increase of charge density, the damaged occurrence on the surface of carbon fiber is cracking, , peeling, and fracturing. The CFRCM resistance experienced two stages of slow growth and rapid growth, and when the charge density was the same, the resistance change was the same. The larger the charge, the more obvious the fiber fracture phenomenon, and the smaller the ultimate load during the CFRCM tensile process.
Carbon fabric reinforced cementitious matrix (CFRCM) is often used in the reinforcement of concrete structures and the electrochemical protection of steel bars because of their combination of structural performance improvement and impressed current cathodic protection (ICCP). The effect and mechanism of CFRCM performance are less studied. It is found that the electrical conductivity and mechanical properties of CFRCM are degraded by ICCP through accelerated energization test and tensile test of CFRCM. With the increase of charge density, the damaged occurrence on the surface of carbon fiber is cracking, , peeling, and fracturing. The CFRCM resistance experienced two stages of slow growth and rapid growth, and when the charge density was the same, the resistance change was the same. The larger the charge, the more obvious the fiber fracture phenomenon, and the smaller the ultimate load during the CFRCM tensile process.
2023, 40(S): 307-312.
doi: 10.6052/j.issn.1000-4750.2022.06.S041
Abstract:
In order to analyze the effects of turbulence on the aerodynamic performance of a large wind airfoil with low Reynolds number, the aerodynamic performance of a large wind airfoil NREL S810 was systematically studied by wind tunnel test. The lift coefficient, drag coefficient and surface pressure distribution characteristics of the airfoil were obtained. The results show that the existence of turbulence changes the aerodynamic characteristics of S810 airfoil, and the maximum lift coefficient increases first and then decreases. The lift coefficient of S810 airfoil is the highest when the turbulence is 4.6%. With the increase of turbulence, the phenomenon of stall delay occurs, and the stall angle of attack continues to move backward, while the increase of turbulence makes the stall decline curve become flat.
In order to analyze the effects of turbulence on the aerodynamic performance of a large wind airfoil with low Reynolds number, the aerodynamic performance of a large wind airfoil NREL S810 was systematically studied by wind tunnel test. The lift coefficient, drag coefficient and surface pressure distribution characteristics of the airfoil were obtained. The results show that the existence of turbulence changes the aerodynamic characteristics of S810 airfoil, and the maximum lift coefficient increases first and then decreases. The lift coefficient of S810 airfoil is the highest when the turbulence is 4.6%. With the increase of turbulence, the phenomenon of stall delay occurs, and the stall angle of attack continues to move backward, while the increase of turbulence makes the stall decline curve become flat.
2023, 40(S): 313-318.
doi: 10.6052/j.issn.1000-4750.2022.06.S039
Abstract:
How to accurately predict the aerodynamic performance of wind turbine airfoils is a key problem to be solved for well-designed wind turbine blades. The research object is NREL S810 which is a special airfoil for large wind turbine, and pressure measurement method of wind tunnel is adopted. The influences of turbulence intensity on aerodynamic performance of airfoil at different Reynolds numbers are analyzed. The results show that the lift coefficient and drag coefficient of the airfoil increase at first and then decrease with the increase of turbulence intensity. When the turbulence intensity is 4.6%, they increase to the maximum and then begin to decrease. When the turbulence intensity is less than 11%, the lift and drag coefficients increase with the increase of Reynolds number. When the turbulence intensity increases to more than 11%, the lift and drag coefficients decrease with the increase of Reynolds number. With the increase of Reynolds number, the maximum lift-drag ratio increases first and then decreases, and the angle of attack corresponding to the maximum lift-drag ratio moves forward first and then moves back.
How to accurately predict the aerodynamic performance of wind turbine airfoils is a key problem to be solved for well-designed wind turbine blades. The research object is NREL S810 which is a special airfoil for large wind turbine, and pressure measurement method of wind tunnel is adopted. The influences of turbulence intensity on aerodynamic performance of airfoil at different Reynolds numbers are analyzed. The results show that the lift coefficient and drag coefficient of the airfoil increase at first and then decrease with the increase of turbulence intensity. When the turbulence intensity is 4.6%, they increase to the maximum and then begin to decrease. When the turbulence intensity is less than 11%, the lift and drag coefficients increase with the increase of Reynolds number. When the turbulence intensity increases to more than 11%, the lift and drag coefficients decrease with the increase of Reynolds number. With the increase of Reynolds number, the maximum lift-drag ratio increases first and then decreases, and the angle of attack corresponding to the maximum lift-drag ratio moves forward first and then moves back.
