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The Top 20 Most-Cited Papers from 2022 to 2023
2022 Vol. 37, No. 7
Display Method:
2022, 37(7): 1-19.
doi: 10.13206/j.gjgs22041501
Abstract
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Abstract:
Concrete filled steel tubes(CFST) are easy to fall off the rust layer in the process of transportation and construction, and they are in service under the action of corrosive gas, liquid and soil, which further aggravates the corrosion of steel tube wall, causing section loss and deterioration of steel performance. After corrosion, the overall bearing capacity, plastic deformation capacity, combined elastic modulus and constraint performance of core concrete are reduced, and the risk of overall structure failure is increased.
To fully understand the development status of CFST after corrosion, the static performance, seismic performance and finite element analysis of corroded CFST were compared and summarized from three aspects:microscopic corrosion morphology, mechanical properties of macroscopic components and related theoretical calculation methods, and the research on the mechanical performance of corroded CFST was prospected.
Based on the analysis of the current research, the conclusions and prospects are as follows:the research on the corrosion morphology of CFST can realize the high-precision three-dimensional reconstruction of the corrosion morphology of concrete-filled steel tube through the three-dimensional surface scanner. The influence of the distribution law of corrosion pit size, shape and depth on its mechanical properties can be obtained through the reconstruction of corrosion morphology. The research on the static performance of CFST after corrosion mainly focuses on the axial compression, axial tension and eccentric compression performance of CFST after uniform corrosion. The study of axial compression bearing capacity of corroded CFST shows that the calculation of bearing capacity based on superposition theory is more accurate than that of unified theory. At present, there are few studies on the mechanical properties of c CFST after local corrosion. Although the weight loss rate caused by local corrosion is very small, it will cause stress concentration, buckling in advance and bearing capacity reduction of components, which seriously threatens the safety of structures. It is therefore necessary to increase research in this area. The study on the seismic performance of corroded CFST columns shows that when the axial compression ratio is constant, the higher the corrosion rate is, the greater the decrease in the bearing capacity is, and the energy dissipation capacity of the corroded specimens after yield decreases rapidly. The research on the corrosion test of CFST mainly adopts the methods of electric accelerated corrosion, salt spray corrosion and mechanical groove simulation. The salt spray corrosion can better simulate the actual seawater corrosion through the test, and establish the correlation between the test corrosion and the actual corrosion environment, which can provide more valuable reference for future research. In the study of the finite element simulation method of CFST after corrosion, the wall thickness reduction method, material reduction method, birth and death element method, double shell element method and random pitting method are often used in steel tube corrosion. The study shows that the stress concentration in the corrosion pit area causes the change of failure mode and the strength decreases significantly. The random pitting method realizes the rapid geometric modeling of a large number of pitting examples. The form and distribution of pitting have a significant influence on the fatigue damage of components, and its randomness cannot be ignored when studying fatigue problems such as crack propagation. There are some differences between the random corrosion and the actual corrosion morphology. In the follow-up study, it is the key to consider the correlation between the simulated random pitting method and the actual corrosion morphology of the project. It is suggested to increase this research to realize the refined finite element simulation of the mechanical properties of CFST after corrosion.
This article will introduce the current research situation, discuss and summarize the corrosion morphology, mechanical properties and finite element simulation methods of corroded CFST members, and give relevant suggestions for further research in the future.
Concrete filled steel tubes(CFST) are easy to fall off the rust layer in the process of transportation and construction, and they are in service under the action of corrosive gas, liquid and soil, which further aggravates the corrosion of steel tube wall, causing section loss and deterioration of steel performance. After corrosion, the overall bearing capacity, plastic deformation capacity, combined elastic modulus and constraint performance of core concrete are reduced, and the risk of overall structure failure is increased.
To fully understand the development status of CFST after corrosion, the static performance, seismic performance and finite element analysis of corroded CFST were compared and summarized from three aspects:microscopic corrosion morphology, mechanical properties of macroscopic components and related theoretical calculation methods, and the research on the mechanical performance of corroded CFST was prospected.
Based on the analysis of the current research, the conclusions and prospects are as follows:the research on the corrosion morphology of CFST can realize the high-precision three-dimensional reconstruction of the corrosion morphology of concrete-filled steel tube through the three-dimensional surface scanner. The influence of the distribution law of corrosion pit size, shape and depth on its mechanical properties can be obtained through the reconstruction of corrosion morphology. The research on the static performance of CFST after corrosion mainly focuses on the axial compression, axial tension and eccentric compression performance of CFST after uniform corrosion. The study of axial compression bearing capacity of corroded CFST shows that the calculation of bearing capacity based on superposition theory is more accurate than that of unified theory. At present, there are few studies on the mechanical properties of c CFST after local corrosion. Although the weight loss rate caused by local corrosion is very small, it will cause stress concentration, buckling in advance and bearing capacity reduction of components, which seriously threatens the safety of structures. It is therefore necessary to increase research in this area. The study on the seismic performance of corroded CFST columns shows that when the axial compression ratio is constant, the higher the corrosion rate is, the greater the decrease in the bearing capacity is, and the energy dissipation capacity of the corroded specimens after yield decreases rapidly. The research on the corrosion test of CFST mainly adopts the methods of electric accelerated corrosion, salt spray corrosion and mechanical groove simulation. The salt spray corrosion can better simulate the actual seawater corrosion through the test, and establish the correlation between the test corrosion and the actual corrosion environment, which can provide more valuable reference for future research. In the study of the finite element simulation method of CFST after corrosion, the wall thickness reduction method, material reduction method, birth and death element method, double shell element method and random pitting method are often used in steel tube corrosion. The study shows that the stress concentration in the corrosion pit area causes the change of failure mode and the strength decreases significantly. The random pitting method realizes the rapid geometric modeling of a large number of pitting examples. The form and distribution of pitting have a significant influence on the fatigue damage of components, and its randomness cannot be ignored when studying fatigue problems such as crack propagation. There are some differences between the random corrosion and the actual corrosion morphology. In the follow-up study, it is the key to consider the correlation between the simulated random pitting method and the actual corrosion morphology of the project. It is suggested to increase this research to realize the refined finite element simulation of the mechanical properties of CFST after corrosion.
This article will introduce the current research situation, discuss and summarize the corrosion morphology, mechanical properties and finite element simulation methods of corroded CFST members, and give relevant suggestions for further research in the future.
2022, 37(7): 20-30.
doi: 10.13206/j.gjgS21110501
Abstract:
The concrete-filled steel tube(CFST) combines the structural and mechanical properties of both steel pipe and concrete and are widely used in high-rise buildings as well as bridge structures. Over time, the steel pipe and the core concrete will deform, including elastic deformation, creep, and concrete shrinkage. Due to the material difference of the concrete and steel, the deformation difference between the two materials in steel pipe and concrete eventually leads to debonding, which affects the service performance of the overall structure. In order to investigate the estimation method of debonding of CFST in service life, this paper explored the applicability and accuracy of the calculation model for estimating debonding of CFST by calculating the deformation of core concrete and steel pipe separately and deriving the amount of debonding and comparing it with the measured values of it in Shenzhen Saige Plaza Building.
In CFST, the radial deformation is mainly divided into two parts:the shrinkage, Poisson deformation and creep of the core concrete, and Poisson deformation and creep for the steel tubes. Due to the hermetic condition, a constant temperature and humidity was assumed inside the steel pipe. On this basis, two commonly used concrete code ACI 209 R-92 and CEB-FIP were adopted in this work. And the shrinkage, Poisson's and creep of the concrete were calculated with the calculation time from the completion date of the building to the testing date, and the design load and self-weight as the stress conditions. The steel pipe was analyzed for stress and the corresponding deformation was calculated with the material mechanics. The sum of different deformations was calculated as the amount of debonding in the CFST with the positive direction of debonding growth.
The results show that the calculated values of CEB-FIP are closer to the measured ones compared to the ACI model. In particular, the estimation of shrinkage of core concrete by CEB-FIP model is generally larger than that of ACI model; in terms of creep variation, ACI model is more influenced by size of the concrete and the amount of creep is smaller than that of CEB-FIP model. Both conventional concrete compacted by pounding and self-compacting concrete were used in the CFST of Saige Tower. Compared with the conventional concrete, the self-compacting concrete undergoes larger shrinkage deformation, which is well reflected in the results of both models, and the results of CEB-FIP are closer to its described in the manual. The measured values show a "small-large-small" distribution of core concrete debonding from top to bottom, and the CEB-FIP calculation is consistent with this trend, while the ACI results show a decreasing trend from top to bottom.
The concrete-filled steel tube(CFST) combines the structural and mechanical properties of both steel pipe and concrete and are widely used in high-rise buildings as well as bridge structures. Over time, the steel pipe and the core concrete will deform, including elastic deformation, creep, and concrete shrinkage. Due to the material difference of the concrete and steel, the deformation difference between the two materials in steel pipe and concrete eventually leads to debonding, which affects the service performance of the overall structure. In order to investigate the estimation method of debonding of CFST in service life, this paper explored the applicability and accuracy of the calculation model for estimating debonding of CFST by calculating the deformation of core concrete and steel pipe separately and deriving the amount of debonding and comparing it with the measured values of it in Shenzhen Saige Plaza Building.
In CFST, the radial deformation is mainly divided into two parts:the shrinkage, Poisson deformation and creep of the core concrete, and Poisson deformation and creep for the steel tubes. Due to the hermetic condition, a constant temperature and humidity was assumed inside the steel pipe. On this basis, two commonly used concrete code ACI 209 R-92 and CEB-FIP were adopted in this work. And the shrinkage, Poisson's and creep of the concrete were calculated with the calculation time from the completion date of the building to the testing date, and the design load and self-weight as the stress conditions. The steel pipe was analyzed for stress and the corresponding deformation was calculated with the material mechanics. The sum of different deformations was calculated as the amount of debonding in the CFST with the positive direction of debonding growth.
The results show that the calculated values of CEB-FIP are closer to the measured ones compared to the ACI model. In particular, the estimation of shrinkage of core concrete by CEB-FIP model is generally larger than that of ACI model; in terms of creep variation, ACI model is more influenced by size of the concrete and the amount of creep is smaller than that of CEB-FIP model. Both conventional concrete compacted by pounding and self-compacting concrete were used in the CFST of Saige Tower. Compared with the conventional concrete, the self-compacting concrete undergoes larger shrinkage deformation, which is well reflected in the results of both models, and the results of CEB-FIP are closer to its described in the manual. The measured values show a "small-large-small" distribution of core concrete debonding from top to bottom, and the CEB-FIP calculation is consistent with this trend, while the ACI results show a decreasing trend from top to bottom.
2022, 37(7): 31-40.
doi: 10.13206/j.gjgs21122001
Abstract:
The inner-outer flange(IO flange) is a high-capacity connection for circular hollow section(CHS) tubes, and is mainly implemented in long-span tubular transmission towers for the connection of the high-strength members. The axial tension capacity of IO flanges depends not only on the number and strength of the bolts, but also on the ratio of the tension force of the inner bolt to that of the outer bolt. The out-of-plane stiffness of the flange plate in IO flanges is a crucial parameter in computing this ratio, and has received much attention. However, the analytic solution that is suitable for design is hard to be attained, since many parameters, e.g. the size of the bolt's hole, relationship between the geometrical parameters, and the type of flange, would be involved with regard to the out-of-plane flange stiffness, leading to the complex boundary conditions for the mechanical balance equations. Therefore, it is necessary to perform an in-depth study on the out-of-plane flange stiffness to attain a concise approximating equation for design.
Regarding the inner and the outer flange plates presented in the IO flanges, the mechanical balance equations with the corresponding boundary conditions based on the theory for elastic thin plates were first established in the polar coordinate system. Thereby, the mutual effects of the parameters of the flange plates were analyzed, and the corresponding non-dimensional parameters were derived. In accordance with the ranges of the non-dimensional parameters summarized from practice engineering, a parametric sensitive analysis was performed via 7 144 finite element(FE) models established for outer flange plates and 5 630 FE models for inner outer flange plates. The influences of the non-dimensional parameters on the out-of-plane stiffness of the flange plates were then clarified. Meanwhile the mechanical characteristics of the flange plate was clearly defined. Finally, a concise approximating equation for the out-of-plane stiffness of the flange plate was proposed, which was suitable for the design of IO flanges.
The results show that the out-of-plane stiffness of the flange plate can be characterized by the non-dimensional deflection of the flange plate. It is found that the out-of-plane stiffness of the flange plate increases with the increase of the flange plate thickness, as well as the decrease of the radius of tube. Overall, for common IO flanges, the non-dimensional deflection decreases with the increase of the number of the bolts, as well as the increase of the non-dimensional diameter of the bolts, which means the out-of-plane stiffness of the flanges would increase. In addition, if the ratio of the flange plate's circumferential length to the flange plate's width is relatively big, the flange plate subjected to the bolt force presents a state similar to the cantilever slab, and the loaded flange plate would be similar to the one-way slab if the length to width ratio is sufficiently small. Furthermore, a moderate ratio brings the plate into the triple-side force-bearing state. In terms of the ratio of the FE result to the result obtained via the approximating equation, the statistical results show that the mean value of the ratio is 1.0 and the coefficient of variance is less than 0.7%, which implies that the approximating equation is capable of well estimating the out-of-plane stiffness of the flange plates.
The inner-outer flange(IO flange) is a high-capacity connection for circular hollow section(CHS) tubes, and is mainly implemented in long-span tubular transmission towers for the connection of the high-strength members. The axial tension capacity of IO flanges depends not only on the number and strength of the bolts, but also on the ratio of the tension force of the inner bolt to that of the outer bolt. The out-of-plane stiffness of the flange plate in IO flanges is a crucial parameter in computing this ratio, and has received much attention. However, the analytic solution that is suitable for design is hard to be attained, since many parameters, e.g. the size of the bolt's hole, relationship between the geometrical parameters, and the type of flange, would be involved with regard to the out-of-plane flange stiffness, leading to the complex boundary conditions for the mechanical balance equations. Therefore, it is necessary to perform an in-depth study on the out-of-plane flange stiffness to attain a concise approximating equation for design.
Regarding the inner and the outer flange plates presented in the IO flanges, the mechanical balance equations with the corresponding boundary conditions based on the theory for elastic thin plates were first established in the polar coordinate system. Thereby, the mutual effects of the parameters of the flange plates were analyzed, and the corresponding non-dimensional parameters were derived. In accordance with the ranges of the non-dimensional parameters summarized from practice engineering, a parametric sensitive analysis was performed via 7 144 finite element(FE) models established for outer flange plates and 5 630 FE models for inner outer flange plates. The influences of the non-dimensional parameters on the out-of-plane stiffness of the flange plates were then clarified. Meanwhile the mechanical characteristics of the flange plate was clearly defined. Finally, a concise approximating equation for the out-of-plane stiffness of the flange plate was proposed, which was suitable for the design of IO flanges.
The results show that the out-of-plane stiffness of the flange plate can be characterized by the non-dimensional deflection of the flange plate. It is found that the out-of-plane stiffness of the flange plate increases with the increase of the flange plate thickness, as well as the decrease of the radius of tube. Overall, for common IO flanges, the non-dimensional deflection decreases with the increase of the number of the bolts, as well as the increase of the non-dimensional diameter of the bolts, which means the out-of-plane stiffness of the flanges would increase. In addition, if the ratio of the flange plate's circumferential length to the flange plate's width is relatively big, the flange plate subjected to the bolt force presents a state similar to the cantilever slab, and the loaded flange plate would be similar to the one-way slab if the length to width ratio is sufficiently small. Furthermore, a moderate ratio brings the plate into the triple-side force-bearing state. In terms of the ratio of the FE result to the result obtained via the approximating equation, the statistical results show that the mean value of the ratio is 1.0 and the coefficient of variance is less than 0.7%, which implies that the approximating equation is capable of well estimating the out-of-plane stiffness of the flange plates.
2022, 37(7): 41-51.
doi: 10.13206/j.gjgS22021001
Abstract:
The floating office project of Hunan Radio and Television Station is a large plane multi-layer truss structure supported by multiple tubes. At present, the conventional in-situ construction scheme for the structural system requires a huge amount of measures and a long installation cycle, if the overall lifting construction scheme is adopted, the structure separated from the core tube is separated into several truss units, it is difficult to construct. For the above problems, a ring hoop reinforcing tooling system and a complete set of lifting structure deformation and closing precision control technology were developed, the discrete truss units were converted into integral structural system with sufficient lateral and torsional stiffness, which was satisfied for lifting construction and precise closure, at the same time, the mechanical characteristic of the whole lifting structure system were described and the mechanism in the overall lifting state was revealed.
The research contents and conclusions include:1) Through in-depth analysis of core tube and cantilever truss monomer synergistic effect mechanism, the ring hoop reinforcing tooling system is designed to replace the restraint and force transmission of the original core tube, provides sufficient strength and stiffness in the overall lifting state, the multiple scattered truss monomer can meet the overall lifting construction requirements after reinforcement; 2) Finite element software MIDAS-Gen is used to study the force transfer mode and mechanical characteristics of the ring hoop reinforcement tool system in lifting state, it is further optimized as a mechanical system of carrying pole girder composed of lifting point and bottom beam. The cantilevered trusses at both ends of the carrying pole girder are self-balanced to some extent, although the structure system is simplified, the force transmission path is more direct, the functions of vertical rod force transmission and horizontal rod stiffness control are given full play. According to the comparison analysis of finite element calculation results, compared with the ring hoop reinforcement tooling before optimization, the vertical deformation of the cantilever ends of the lifting structural system is reduced by 10%~12% after optimization, it is more advantageous to control the deformation of the whole structure, and the lifting point is optimized by half, the synchronization of structural lifting is easier to ensure, the measure quantity is optimized by about 30%;3) After lifting the floating office in place, there are 120 seams, its closed precision is the decisive factor for the construction quality control of floating office in the south area. Finite element software MIDAS-Gen is used to calculate and analyze the deformation trend of floating truss structure in lifting state and the regularity of the staggered joints of the closure. It is found that reverse pre-adjustment of the key points of the cantilever end of the lifting unit in the assembly phase can effectively ensure the closing and the overall forming accuracy of the structure; 4) Through the deformation monitoring of floating truss structure from assembling to closing, it is found that the variation trend of the measured relative deformation is basically consistent with that of the result of construction simulation calculation, no excessive structural deformation occurred during lifting and unloading, the reliability of the ring hoop reinforcement system and the complete set of deformation of lifting unit and closing precision control technology are verified.
The floating office project of Hunan Radio and Television Station is a large plane multi-layer truss structure supported by multiple tubes. At present, the conventional in-situ construction scheme for the structural system requires a huge amount of measures and a long installation cycle, if the overall lifting construction scheme is adopted, the structure separated from the core tube is separated into several truss units, it is difficult to construct. For the above problems, a ring hoop reinforcing tooling system and a complete set of lifting structure deformation and closing precision control technology were developed, the discrete truss units were converted into integral structural system with sufficient lateral and torsional stiffness, which was satisfied for lifting construction and precise closure, at the same time, the mechanical characteristic of the whole lifting structure system were described and the mechanism in the overall lifting state was revealed.
The research contents and conclusions include:1) Through in-depth analysis of core tube and cantilever truss monomer synergistic effect mechanism, the ring hoop reinforcing tooling system is designed to replace the restraint and force transmission of the original core tube, provides sufficient strength and stiffness in the overall lifting state, the multiple scattered truss monomer can meet the overall lifting construction requirements after reinforcement; 2) Finite element software MIDAS-Gen is used to study the force transfer mode and mechanical characteristics of the ring hoop reinforcement tool system in lifting state, it is further optimized as a mechanical system of carrying pole girder composed of lifting point and bottom beam. The cantilevered trusses at both ends of the carrying pole girder are self-balanced to some extent, although the structure system is simplified, the force transmission path is more direct, the functions of vertical rod force transmission and horizontal rod stiffness control are given full play. According to the comparison analysis of finite element calculation results, compared with the ring hoop reinforcement tooling before optimization, the vertical deformation of the cantilever ends of the lifting structural system is reduced by 10%~12% after optimization, it is more advantageous to control the deformation of the whole structure, and the lifting point is optimized by half, the synchronization of structural lifting is easier to ensure, the measure quantity is optimized by about 30%;3) After lifting the floating office in place, there are 120 seams, its closed precision is the decisive factor for the construction quality control of floating office in the south area. Finite element software MIDAS-Gen is used to calculate and analyze the deformation trend of floating truss structure in lifting state and the regularity of the staggered joints of the closure. It is found that reverse pre-adjustment of the key points of the cantilever end of the lifting unit in the assembly phase can effectively ensure the closing and the overall forming accuracy of the structure; 4) Through the deformation monitoring of floating truss structure from assembling to closing, it is found that the variation trend of the measured relative deformation is basically consistent with that of the result of construction simulation calculation, no excessive structural deformation occurred during lifting and unloading, the reliability of the ring hoop reinforcement system and the complete set of deformation of lifting unit and closing precision control technology are verified.
2022, 37(7): 52-54.
doi: 10.13206/j.gjgS2022080501
Abstract:
Mechanism of tension development in anchor bolts when they are in shear is described. Three stages of action are detected when the bolts are in shear. A formula for shear capacity used in design and a formula for ultimate shear capacity are proposed.
Mechanism of tension development in anchor bolts when they are in shear is described. Three stages of action are detected when the bolts are in shear. A formula for shear capacity used in design and a formula for ultimate shear capacity are proposed.
