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2022 Vol. 52, No. 5
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2022, 52(5): 1-8,33.
doi: 10.13204/j.gyjzG22011506
Abstract:
GISE Park is an industrial heritage park located in the center of high-density residential area in Liwan District, Guangzhou. Compared with other industrial heritage parks in sparsely-populated urban suburbs, it faces more incisive urban ecological contradictions and needs. Besides meeting the functional requirements of recreation in general community parks, it should also focus on human, for instance, visual effect, microclimate impact and demand for nature education, etc. In this study, from the perspective of ecological design, based on visual and environmental simulation technology, the layout scheme of water and plants adapted to the humid and hot climate, the scheme of obscured line and guidance of sight, and the patch landscape design and animal habitat creation scheme based on the animal-friendly principle were proposed. The case could provide a reference for ecological design of industrial heritage parks facing high-density communities.
GISE Park is an industrial heritage park located in the center of high-density residential area in Liwan District, Guangzhou. Compared with other industrial heritage parks in sparsely-populated urban suburbs, it faces more incisive urban ecological contradictions and needs. Besides meeting the functional requirements of recreation in general community parks, it should also focus on human, for instance, visual effect, microclimate impact and demand for nature education, etc. In this study, from the perspective of ecological design, based on visual and environmental simulation technology, the layout scheme of water and plants adapted to the humid and hot climate, the scheme of obscured line and guidance of sight, and the patch landscape design and animal habitat creation scheme based on the animal-friendly principle were proposed. The case could provide a reference for ecological design of industrial heritage parks facing high-density communities.
2022, 52(5): 9-15,76.
doi: 10.13204/j.gyjzG22011505
Abstract:
In recent years, with the continuous progress of national urbanization and the deepening of the concept of heritage protection, industrial heritage, as a symbol of the industrialization era and an important part of urban history and culture, has become one of the main contents of urban renewal. Taking the industrial heritage along the Pearl River in Guangzhou, Guangdong Province as the research object, the paper analyzed its distribution characteristics and internal value, introduced the heritage corridor mode of industrial heritage protection and utilization in view of its current characteristics and existing problems, and puts forward that in the protection and utilization of industrial heritage along the river, a diversified development, protection and utilization strategy of the internal space construction of the corridor was proposed by constructing the industrial heritage utilization system, dividing the corridor level, and refining the internal structure. The protection and management was strengthened, as well as the benign interaction with the city, in order to provide a reference for the activation and utilization of the same type of industrial heritage.
In recent years, with the continuous progress of national urbanization and the deepening of the concept of heritage protection, industrial heritage, as a symbol of the industrialization era and an important part of urban history and culture, has become one of the main contents of urban renewal. Taking the industrial heritage along the Pearl River in Guangzhou, Guangdong Province as the research object, the paper analyzed its distribution characteristics and internal value, introduced the heritage corridor mode of industrial heritage protection and utilization in view of its current characteristics and existing problems, and puts forward that in the protection and utilization of industrial heritage along the river, a diversified development, protection and utilization strategy of the internal space construction of the corridor was proposed by constructing the industrial heritage utilization system, dividing the corridor level, and refining the internal structure. The protection and management was strengthened, as well as the benign interaction with the city, in order to provide a reference for the activation and utilization of the same type of industrial heritage.
2022, 52(5): 16-23.
doi: 10.13204/j.gyjzG22011504
Abstract:
In the context of the transformation of ecological civilization and high-quality development, resolving the problems of "Production-living-ecological space" such as mutually exclusive contradictions and efficient allocation of the stock land has become the focus of attention. Shunde District of Foshan City, originated from the village-level industrial park model of traditional collective cooperative production of mulberry-fish-pond, is undergoing renewal and transformation due to problems such as "fragmentation, mixing, inefficiency, and disorder" in land use. Taking the planning and construction of two Wanmu parks in Shunde District as an opportunity, the evaluation methods of landscape connectivity analysis and scenic beauty evaluation were integrated to identify the breakpoints and blockages in the site that affect the integrity of the ecological network structure, and further combining with the breakpoints and blockage patches’ background conditions and resource characteristics of the industrial park where it is located, as well as the overall development goals and strategies of the Wanmu park, three transformation and renewal modes were proposed, such as re-greening demonstration, production and tourism interaction, and site exhibition, to optimize the ecological structure of the site under the guidance of ecological restoration goals and provide a reference for industrial renewal planning and design.
In the context of the transformation of ecological civilization and high-quality development, resolving the problems of "Production-living-ecological space" such as mutually exclusive contradictions and efficient allocation of the stock land has become the focus of attention. Shunde District of Foshan City, originated from the village-level industrial park model of traditional collective cooperative production of mulberry-fish-pond, is undergoing renewal and transformation due to problems such as "fragmentation, mixing, inefficiency, and disorder" in land use. Taking the planning and construction of two Wanmu parks in Shunde District as an opportunity, the evaluation methods of landscape connectivity analysis and scenic beauty evaluation were integrated to identify the breakpoints and blockages in the site that affect the integrity of the ecological network structure, and further combining with the breakpoints and blockage patches’ background conditions and resource characteristics of the industrial park where it is located, as well as the overall development goals and strategies of the Wanmu park, three transformation and renewal modes were proposed, such as re-greening demonstration, production and tourism interaction, and site exhibition, to optimize the ecological structure of the site under the guidance of ecological restoration goals and provide a reference for industrial renewal planning and design.
2022, 52(5): 24-33.
doi: 10.13204/j.gyjzG22011509
Abstract:
Rural landscape is an ecological complex composed of natural environment,cultural landscape and its social structure,it is of great significance to maintain the regional landscape and man-land relationship.Through introducing the theory of "production-living-ecological" function,the spatial analysis of ArcGIS was used to analyze the relationship between the conversion of land use type,the conversion of "production-living-ecological" function of space and the spatial-temporal evolution of rural landscape in the North Seven Rural Area of Xingtan in Shunde from 1988 to 2018 firstly.The results showed that the rural landscape in the study area has experienced three stages from slow change,sharp change to gentle change and experienced the structural transformation from "rural settlement patches, river channel corridor and dike-pond matrix" to "rural settlement and industrial patches, river channel, and road corridor-dike-pond matrix".Finally, the paper proposed the strategies for optimizing rural landscape based on the regional spatial-temporal process of urban and rural areas,total elements of landscape process and reform for promoting ecological progress, which could provide theoretical and practical references for the protection and development of rural traditional regional culture under the rural transformation.
Rural landscape is an ecological complex composed of natural environment,cultural landscape and its social structure,it is of great significance to maintain the regional landscape and man-land relationship.Through introducing the theory of "production-living-ecological" function,the spatial analysis of ArcGIS was used to analyze the relationship between the conversion of land use type,the conversion of "production-living-ecological" function of space and the spatial-temporal evolution of rural landscape in the North Seven Rural Area of Xingtan in Shunde from 1988 to 2018 firstly.The results showed that the rural landscape in the study area has experienced three stages from slow change,sharp change to gentle change and experienced the structural transformation from "rural settlement patches, river channel corridor and dike-pond matrix" to "rural settlement and industrial patches, river channel, and road corridor-dike-pond matrix".Finally, the paper proposed the strategies for optimizing rural landscape based on the regional spatial-temporal process of urban and rural areas,total elements of landscape process and reform for promoting ecological progress, which could provide theoretical and practical references for the protection and development of rural traditional regional culture under the rural transformation.
2022, 52(5): 34-41.
doi: 10.13204/j.gyjzG22011502
Abstract:
CiteSpace software was used to conduct a quantitative analysis of the relevant literatures in the field of conservation and reuse of foreign industrial heritage from 1998 to 2020 in the core collection of Web of Science, and the information of major countries, institutions and authors engaged in the research was summarized, and the international frontier hotspots in the theory and practice of industrial heritage conservation were summarized. The methods of sustainable conservation and development and adaptive reuse were analyzed, and the conservation and reuse of international industrial heritage was divided into four development stages: germination stage, exploration stage, improvement stage and promotion stage. Through the quantitative analysis of keyword clustering, the main research hotspots such as the preventive protection based on risk assessment and prevention, the multidisciplinary restorative protection, the sustainable protection and management and the protection and reuse mode of "industrial heritage+" based on contemporary value realization were proposed. Finally, the research direction suitable for the protection and reuse of industrial heritage in China in the future was pointed out from the aspects of establishing a complete scientific system of industrial heritage, improving the restoration technology, attaching importance to the ecological restoration of brownfield, and innovating the reuse mode.
CiteSpace software was used to conduct a quantitative analysis of the relevant literatures in the field of conservation and reuse of foreign industrial heritage from 1998 to 2020 in the core collection of Web of Science, and the information of major countries, institutions and authors engaged in the research was summarized, and the international frontier hotspots in the theory and practice of industrial heritage conservation were summarized. The methods of sustainable conservation and development and adaptive reuse were analyzed, and the conservation and reuse of international industrial heritage was divided into four development stages: germination stage, exploration stage, improvement stage and promotion stage. Through the quantitative analysis of keyword clustering, the main research hotspots such as the preventive protection based on risk assessment and prevention, the multidisciplinary restorative protection, the sustainable protection and management and the protection and reuse mode of "industrial heritage+" based on contemporary value realization were proposed. Finally, the research direction suitable for the protection and reuse of industrial heritage in China in the future was pointed out from the aspects of establishing a complete scientific system of industrial heritage, improving the restoration technology, attaching importance to the ecological restoration of brownfield, and innovating the reuse mode.
2022, 52(5): 42-50.
doi: 10.13204/j.gyjzG21052409
Abstract:
To master the influence mechanisms of urban spatial form on the thermal environment is essential to improve urban climate adaptability, and to construct a scientific prediction model for the thermal environment effect is an effective way to improve the urban climate environment. Taking Shenyang as an object, a set of parameters to represent the spatial capacity and form characteristics was established, the key parameters were identified through correlation analysis with surface temperatures, and a evaluation model of thermal environment indexes for urban planning was established using the principal element analysis method. The results showed that:in the different form parameters, the leaf area index, the building floor area ratio and the sky view factor were more significant correlated with the urban thermal environment, the spatial distribution map for Shenyang thermal environment was constructed by the evaluation model of the thermal enviroment index could reflect the distribution status of the thermal emironment effect better in the study area, and the spatial units of the thermal environment were divided. According to the parameters of the model and the distribution of the spatial units, the layout optimization of the thermal environment in the scale of the city and the guidance and control strategies for the form quantiation in the site scale were proposed directly, which could provide the planning index of strong operability to improve the urban thermal environment effect.
To master the influence mechanisms of urban spatial form on the thermal environment is essential to improve urban climate adaptability, and to construct a scientific prediction model for the thermal environment effect is an effective way to improve the urban climate environment. Taking Shenyang as an object, a set of parameters to represent the spatial capacity and form characteristics was established, the key parameters were identified through correlation analysis with surface temperatures, and a evaluation model of thermal environment indexes for urban planning was established using the principal element analysis method. The results showed that:in the different form parameters, the leaf area index, the building floor area ratio and the sky view factor were more significant correlated with the urban thermal environment, the spatial distribution map for Shenyang thermal environment was constructed by the evaluation model of the thermal enviroment index could reflect the distribution status of the thermal emironment effect better in the study area, and the spatial units of the thermal environment were divided. According to the parameters of the model and the distribution of the spatial units, the layout optimization of the thermal environment in the scale of the city and the guidance and control strategies for the form quantiation in the site scale were proposed directly, which could provide the planning index of strong operability to improve the urban thermal environment effect.
2022, 52(5): 51-59,23.
doi: 10.13204/j.gyjzG21040601
Abstract:
In order to study the seismic performance of monolithic precast shear wall with partially-connected vertical distributed steel bars, quasi-static tests were performed on one precast wall panel with partically vertical distributed steel bars welded by embedded parts and one precast wall panel with non-connected distributed steel bars. The test results showed that the cracks of the specimen with vertical distributed steel bars welded by embedded parts were evenly distributed, the hysteresis curve was relatively full, the bearing capacity was high, and the seismic performance was good. The failure mode, hysteretic curve and skeleton curve of the two specimens were obtained by finite element analysis with ABAQUS software, and the simulation results were in good agreement with the experimental results. The effects of longitudinal reinforcement ratio, diameter of connecting bars, height-width ratio, axial compression ratio, number and location of embedded welding plates on the seismic performance of specimens were studied. The results showed that the reinforcement ratio, height-width ratio and axial compression ratio of vertical edge members had great influence on the bearing capacity of the wall. The diameter of the connecting steel bars in the precast wall panel had little influence on the bearing capacity of the wall. Reasonable arrangement of embedded parts on both sides of the bottom of the precast wall panel could effectively improve the bearing capacity and ductility of the wall.
In order to study the seismic performance of monolithic precast shear wall with partially-connected vertical distributed steel bars, quasi-static tests were performed on one precast wall panel with partically vertical distributed steel bars welded by embedded parts and one precast wall panel with non-connected distributed steel bars. The test results showed that the cracks of the specimen with vertical distributed steel bars welded by embedded parts were evenly distributed, the hysteresis curve was relatively full, the bearing capacity was high, and the seismic performance was good. The failure mode, hysteretic curve and skeleton curve of the two specimens were obtained by finite element analysis with ABAQUS software, and the simulation results were in good agreement with the experimental results. The effects of longitudinal reinforcement ratio, diameter of connecting bars, height-width ratio, axial compression ratio, number and location of embedded welding plates on the seismic performance of specimens were studied. The results showed that the reinforcement ratio, height-width ratio and axial compression ratio of vertical edge members had great influence on the bearing capacity of the wall. The diameter of the connecting steel bars in the precast wall panel had little influence on the bearing capacity of the wall. Reasonable arrangement of embedded parts on both sides of the bottom of the precast wall panel could effectively improve the bearing capacity and ductility of the wall.
2022, 52(5): 60-69,193.
doi: 10.13204/j.gyjzG21121407
Abstract:
A design method was proposed for the new dry-connection fabricated joints was proposed. This method was based on the traditional self-centering joint design method, combined with the bolted connection design method for joint design. The self-centering ratio was introduced in the joint design, and the iterative method was used to caculate the bearing capacity of the joints, and a design method combining the assembled structure and the self-centering structure was formed. The accuracy of the design results was verified by ABAQUS finite element simulation. The finite element simulation results were basically consistent with the theoretical calculation results, and the error was within 5%.
A design method was proposed for the new dry-connection fabricated joints was proposed. This method was based on the traditional self-centering joint design method, combined with the bolted connection design method for joint design. The self-centering ratio was introduced in the joint design, and the iterative method was used to caculate the bearing capacity of the joints, and a design method combining the assembled structure and the self-centering structure was formed. The accuracy of the design results was verified by ABAQUS finite element simulation. The finite element simulation results were basically consistent with the theoretical calculation results, and the error was within 5%.
2022, 52(5): 70-76.
doi: 10.13204/j.gyjzG22032113
Abstract:
This paper mainly introduced structural design difficulties and treatment measures of an extraordinary irregular TOD project on subway. The influence of adjacent subways on structural design were analyzed. In order to avoid the interaction between the new structure and the subway to the greatest extent, the long cantilevered steel-reinforced concrete underpinning scheme was adopted. For the plane and vertical irregularity of structure, the corresponding calculation and design measures were put forward. The results showed that the long cantilevered steel-reinforced concrete underpinning scheme was feasible and the comfort level of cantilevered floor could meet the requirements; the overturning problem could be solved by rational design of pile foundation, and the settlement of pile foundation should be strictly controlled to reduce the influence on adjacent subways The less-wall frame structure system with local shear walls could obviously increase the stiffness, and improve the torsional effect of the structure.
This paper mainly introduced structural design difficulties and treatment measures of an extraordinary irregular TOD project on subway. The influence of adjacent subways on structural design were analyzed. In order to avoid the interaction between the new structure and the subway to the greatest extent, the long cantilevered steel-reinforced concrete underpinning scheme was adopted. For the plane and vertical irregularity of structure, the corresponding calculation and design measures were put forward. The results showed that the long cantilevered steel-reinforced concrete underpinning scheme was feasible and the comfort level of cantilevered floor could meet the requirements; the overturning problem could be solved by rational design of pile foundation, and the settlement of pile foundation should be strictly controlled to reduce the influence on adjacent subways The less-wall frame structure system with local shear walls could obviously increase the stiffness, and improve the torsional effect of the structure.
2022, 52(5): 77-82.
doi: 10.13204/j.gyjzG20112604
Abstract:
In order to research the minimum plane dimensions of long-span spatial structures that considering traveling wave effect, the time-history analysis method was used to investigate the differences among double-layer cylindrical latticed shells with different plane dimensions under multiple-support excitation and single excitation by discussing the distribution of special members whose peak internal forces under single excitation were greater than 10kN and traveling wave effect coefficient were greater than 1.1. The results showed that changing the structural span or length would lead to the amount or percentage of special members changed, which were concentrated in longitudinal members at the top chord, the percentage of special members was up to 10% when the span of reduce the percentage of special members reached 60 m and the length reached 90 m. Increasing the lergth of structure would increase the proportion of special members, while increastring the span would decrease the proportion. It was concluded that 60 m of the span and 90 m of the length were the minimum plane dimensions of this kind of structure that considering the traveling wave effect of longitudinal members at the top chord.
In order to research the minimum plane dimensions of long-span spatial structures that considering traveling wave effect, the time-history analysis method was used to investigate the differences among double-layer cylindrical latticed shells with different plane dimensions under multiple-support excitation and single excitation by discussing the distribution of special members whose peak internal forces under single excitation were greater than 10kN and traveling wave effect coefficient were greater than 1.1. The results showed that changing the structural span or length would lead to the amount or percentage of special members changed, which were concentrated in longitudinal members at the top chord, the percentage of special members was up to 10% when the span of reduce the percentage of special members reached 60 m and the length reached 90 m. Increasing the lergth of structure would increase the proportion of special members, while increastring the span would decrease the proportion. It was concluded that 60 m of the span and 90 m of the length were the minimum plane dimensions of this kind of structure that considering the traveling wave effect of longitudinal members at the top chord.
2022, 52(5): 83-89,225.
doi: 10.13204/j.gyjzG21070802
Abstract:
To obtain the fatigue crack initiation life of unstiffened CHS X-joints under quasi-static loading, nine groups of unstiffened joints with different geometric parameters were numerically simulated. The hybrid strengthening model of steel and the cyclic hole growth model (CVGM) were used to predict the fatigue crack initiation life of unstiffened X-joints under quasi-static loading and various equal amplitude reciprocating loads. According to the orthogonal design test theory, parametric analysis was carried out on the influencing factors of fatigue crack initiation life (diameter ratio of branch pipe to main pipe β, diameter-thickness ratio of main pipe γ) of unstiffened X-joints. The results showed that the larger the diameter ratio of branch pipe to main pipe, the smaller the crack initiation life of unstiffened X-joints. The larger the diameter-thickness ratio of the main pipe, the longer the crack initiation life of the unstiffened X-joints is. Finally, based on the parametric analysis results of crack initiation life, an empirical formula for predicting the fatigue crack initiation life of unstiffened X-joints under quasi-static loading was proposed.
To obtain the fatigue crack initiation life of unstiffened CHS X-joints under quasi-static loading, nine groups of unstiffened joints with different geometric parameters were numerically simulated. The hybrid strengthening model of steel and the cyclic hole growth model (CVGM) were used to predict the fatigue crack initiation life of unstiffened X-joints under quasi-static loading and various equal amplitude reciprocating loads. According to the orthogonal design test theory, parametric analysis was carried out on the influencing factors of fatigue crack initiation life (diameter ratio of branch pipe to main pipe β, diameter-thickness ratio of main pipe γ) of unstiffened X-joints. The results showed that the larger the diameter ratio of branch pipe to main pipe, the smaller the crack initiation life of unstiffened X-joints. The larger the diameter-thickness ratio of the main pipe, the longer the crack initiation life of the unstiffened X-joints is. Finally, based on the parametric analysis results of crack initiation life, an empirical formula for predicting the fatigue crack initiation life of unstiffened X-joints under quasi-static loading was proposed.
2022, 52(5): 90-97.
doi: 10.13204/j.gyjzG20072206
Abstract:
At present, there is still a lack of vibration testing and comfort evaluation method for the composite floor slabs of the giant steel frame with suspended structure systems at home and abroad. In order to reveal the vibration characteristics and comfort of the composite floor slab of the giant steel frame with suspended structure system under the excitation of human-induced loads, on-site vibration measurement and analysis were carried out based on the research building of the Quantum Academy of the Chinese Academy of Sciences. The frequency distribution of the floor slab was obtained through the dynamic characteristic test; the human-induced load excitation and rhythm jump excitation were applied to the floor slab, focusing on the analysis of the influence of the main factors such as step frequency, pedestrian number, and walking route on the floor vibration comfort of the new suspended structural system. The test results showed that the peak acceleration of the floor slab gradually increased with the increase of the stride frequency and the number of people walking; walking along the width of the floor slab would cause a significant vibration response; rhythmic jump excitation has a great impact on floor comfort, and excessive jump excitation should be avoided when using it. Combining with domestic and foreign codes, this floor was evaluated and analyzed for vibration comfort. The research results showed that the main vibration frequency and vibration intensity could be used to evaluate the vibration comfort of the floor slab of the new structure, which meant that the main vibration frequency should not be less than 3 Hz, and the vibration intensity should not be greater than 0.015 m/s2
At present, there is still a lack of vibration testing and comfort evaluation method for the composite floor slabs of the giant steel frame with suspended structure systems at home and abroad. In order to reveal the vibration characteristics and comfort of the composite floor slab of the giant steel frame with suspended structure system under the excitation of human-induced loads, on-site vibration measurement and analysis were carried out based on the research building of the Quantum Academy of the Chinese Academy of Sciences. The frequency distribution of the floor slab was obtained through the dynamic characteristic test; the human-induced load excitation and rhythm jump excitation were applied to the floor slab, focusing on the analysis of the influence of the main factors such as step frequency, pedestrian number, and walking route on the floor vibration comfort of the new suspended structural system. The test results showed that the peak acceleration of the floor slab gradually increased with the increase of the stride frequency and the number of people walking; walking along the width of the floor slab would cause a significant vibration response; rhythmic jump excitation has a great impact on floor comfort, and excessive jump excitation should be avoided when using it. Combining with domestic and foreign codes, this floor was evaluated and analyzed for vibration comfort. The research results showed that the main vibration frequency and vibration intensity could be used to evaluate the vibration comfort of the floor slab of the new structure, which meant that the main vibration frequency should not be less than 3 Hz, and the vibration intensity should not be greater than 0.015 m/s2
2022, 52(5): 98-105,146.
doi: 10.13204/j.gyjzG22011912
Abstract:
The self-piercing riveting (SPR) connection has the outstanding advantages of good mechanical properties and high connection efficiency, and has a good application prospect in cold-formed steel (CFS) structures. Adopting 8 simplified methods including equivalent area coupling, constraint element and connection element, to establish the simplified finite element model of cold-formed steel self-piercing riveting (CFSSPR) connection under shear; the simplified simulation results and the test results were compared and analyzed, the applicable scope of each simplified model was explored; the parameter analysis of SPR connection with different plate thickness ratios was completed, the simplified nonlinear finite element analysis method for SPR connection of CFS structure was proposed. The research results showed that the main shear failure mode of the SPR were that the rivet leg pulled out the lower steel plate and the rivet head shears off the upper steel plate; the SPR connection between the CFS members in the steel frame could be simplified and simulated by the constraint unit Pin or the fastener unit Fastener, the SPR connection between the steel frame and the panel could be simplified and simulated by the connector unit Cartesian or spring unit Spring2; the Cartesian connector unit could accurately simulate the load-deformation curve and shear performance index of the SPR connection with different plate thickness ratios, and the calculation efficiency was high, it should be preferred in the nonlinear finite element analysis of CFS structure.
The self-piercing riveting (SPR) connection has the outstanding advantages of good mechanical properties and high connection efficiency, and has a good application prospect in cold-formed steel (CFS) structures. Adopting 8 simplified methods including equivalent area coupling, constraint element and connection element, to establish the simplified finite element model of cold-formed steel self-piercing riveting (CFSSPR) connection under shear; the simplified simulation results and the test results were compared and analyzed, the applicable scope of each simplified model was explored; the parameter analysis of SPR connection with different plate thickness ratios was completed, the simplified nonlinear finite element analysis method for SPR connection of CFS structure was proposed. The research results showed that the main shear failure mode of the SPR were that the rivet leg pulled out the lower steel plate and the rivet head shears off the upper steel plate; the SPR connection between the CFS members in the steel frame could be simplified and simulated by the constraint unit Pin or the fastener unit Fastener, the SPR connection between the steel frame and the panel could be simplified and simulated by the connector unit Cartesian or spring unit Spring2; the Cartesian connector unit could accurately simulate the load-deformation curve and shear performance index of the SPR connection with different plate thickness ratios, and the calculation efficiency was high, it should be preferred in the nonlinear finite element analysis of CFS structure.
2022, 52(5): 106-112,139.
doi: 10.13204/j.gyjzG21031004
Abstract:
In order to study the influence of new shear connectors on the mechanical properties of steel reinforced concrete columns under axial compression, six short steel reinforced concrete columns with new shear connectors were tested under axial compression with the form and spacing of shear connectors as variable parameters. The failure mode, load-displacement curve, load-strain curve, ductility coefficient and axial force distribution of the specimens were analyzed. The results showed that the setting of stud, π-type perforated panel and π-type CR shear connector had a great influence on the proportion of concrete bearing load in the strong restraint area, and the ductility of the specimens was improved. The ductility of SRCDC-1 with π-type crestbond shear connector was the best and its ductility coefficient was increased by 8.4% compared with the specimens without shear connector. Finally, the bearing capacity of Steel reinforced concrete columns with new shear connectors under axial compression was calculated on the basis of considering the restraint effect of stirrups and section steel on concrete, and relevant calculation suggestions were given.
In order to study the influence of new shear connectors on the mechanical properties of steel reinforced concrete columns under axial compression, six short steel reinforced concrete columns with new shear connectors were tested under axial compression with the form and spacing of shear connectors as variable parameters. The failure mode, load-displacement curve, load-strain curve, ductility coefficient and axial force distribution of the specimens were analyzed. The results showed that the setting of stud, π-type perforated panel and π-type CR shear connector had a great influence on the proportion of concrete bearing load in the strong restraint area, and the ductility of the specimens was improved. The ductility of SRCDC-1 with π-type crestbond shear connector was the best and its ductility coefficient was increased by 8.4% compared with the specimens without shear connector. Finally, the bearing capacity of Steel reinforced concrete columns with new shear connectors under axial compression was calculated on the basis of considering the restraint effect of stirrups and section steel on concrete, and relevant calculation suggestions were given.
2022, 52(5): 113-119.
doi: 10.13204/j.gyjzG20122411
Abstract:
The mechanical properties of specimens, including the octagonal hollow concrete short columns with inner steel plate and the columns with inner longitudinal steel, were experimentally and numerically investigated under axial compression. The experimental phenomena, the whole test curves, the whole process of stress and the stress contact between each component were emphatically analyzed. The bearing capacity and the stiffness under axial compression obtained from tests were also compared with those calculated by using the revised Code for Design of Concrete Structures (GB 50010—2010). The results showed that the concrete, longitudinal bars and inner steel plates could work together under axial compression. The square high-strength hollow RC short columns showed high load-bearing capacity and stiffness. The sectional dimensions and concrete strength had significant influence on the bearing capacity, stiffness and ductility of the members. However, the thickness of inner steel plate had little influence. The predicted bearing capacity based on the revised GB 50010—2010 was conservative compared to the test results, while the prediction of the stiffness agreed well.
The mechanical properties of specimens, including the octagonal hollow concrete short columns with inner steel plate and the columns with inner longitudinal steel, were experimentally and numerically investigated under axial compression. The experimental phenomena, the whole test curves, the whole process of stress and the stress contact between each component were emphatically analyzed. The bearing capacity and the stiffness under axial compression obtained from tests were also compared with those calculated by using the revised Code for Design of Concrete Structures (GB 50010—2010). The results showed that the concrete, longitudinal bars and inner steel plates could work together under axial compression. The square high-strength hollow RC short columns showed high load-bearing capacity and stiffness. The sectional dimensions and concrete strength had significant influence on the bearing capacity, stiffness and ductility of the members. However, the thickness of inner steel plate had little influence. The predicted bearing capacity based on the revised GB 50010—2010 was conservative compared to the test results, while the prediction of the stiffness agreed well.
2022, 52(5): 120-125.
doi: 10.13204/j.gyjzG21030807
Abstract:
In order to solve the bearing capacity calculation problem of the steel reinforced concrete composite beam in steel support system of foundation excavation, based on the plastic design theory and several assumptions, the calculation formulas for the bending capacity of the steel-concrete composite beam under axial force were derived,which had universal applicability, and the calculated results were in good agreement with the test results, indicating that the calculation formulas given in the paper were reliable. The formulas were summarized and unified, it was found that when axis forces changed,Mu -δ (the distance between the axial force action point and plastic neutral axis) curve ws composed of one or more quadratic parabolas, and the parabolas opened downward. The smaller δ, the larger Mu. When δ was equal to zero, the bending capacity reached the largest, and the corresponding axial force calculation formulas were given. The curvatured of the Mu-N curve was mainly determined by the width and strength of composite beam. The greater the material strength and width, the smaller the curvature, the flatter the curve.
In order to solve the bearing capacity calculation problem of the steel reinforced concrete composite beam in steel support system of foundation excavation, based on the plastic design theory and several assumptions, the calculation formulas for the bending capacity of the steel-concrete composite beam under axial force were derived,which had universal applicability, and the calculated results were in good agreement with the test results, indicating that the calculation formulas given in the paper were reliable. The formulas were summarized and unified, it was found that when axis forces changed,Mu -δ (the distance between the axial force action point and plastic neutral axis) curve ws composed of one or more quadratic parabolas, and the parabolas opened downward. The smaller δ, the larger Mu. When δ was equal to zero, the bending capacity reached the largest, and the corresponding axial force calculation formulas were given. The curvatured of the Mu-N curve was mainly determined by the width and strength of composite beam. The greater the material strength and width, the smaller the curvature, the flatter the curve.
2022, 52(5): 126-139.
doi: 10.13204/j.gyjzG21011504
Abstract:
The shear behavior of crucitorn external diaphragm connection between concrete-filled steel tubular (CFST) column and H-shaped beam was investigated under quasi-static loading. Four joint specimens were designed and tested by weakening the thickness of the steel tube in the panel zone. The studied parameters include the thickness of the steel tube in the panel zone, the width of the external diaphragm, and the axial compression ratio. Deformation phenomena mainly occurred in the panel zone, including the bending of steel tube flange and external diaphragm, the crushing of concrete core, the shear deformation, local buckling and cracking of steel tube web. Local buckling and cracking of steel tube webs were main shear failure modes. Numerically and experimentally parametric studies manifested a positive correlation between the shear bearing capacity and the thickness of the steel tube in the panel zone, whereas the width of the external diaphragm and axial conupression ratio showed an insignificant impact on the shear resistance. Based on the experimental phenomena and the evaluation of three existing calculation methods on frame joints, and considering the effects of steel tube flange and extemal diaphragm on shear behavior, a calculation formula on the shear bearing capacity of external diaphragm connection was proposed. The accuracy and applicability of this calculation formula was verified by the test results, and it could provide a reference for external diaphragm connection design.
The shear behavior of crucitorn external diaphragm connection between concrete-filled steel tubular (CFST) column and H-shaped beam was investigated under quasi-static loading. Four joint specimens were designed and tested by weakening the thickness of the steel tube in the panel zone. The studied parameters include the thickness of the steel tube in the panel zone, the width of the external diaphragm, and the axial compression ratio. Deformation phenomena mainly occurred in the panel zone, including the bending of steel tube flange and external diaphragm, the crushing of concrete core, the shear deformation, local buckling and cracking of steel tube web. Local buckling and cracking of steel tube webs were main shear failure modes. Numerically and experimentally parametric studies manifested a positive correlation between the shear bearing capacity and the thickness of the steel tube in the panel zone, whereas the width of the external diaphragm and axial conupression ratio showed an insignificant impact on the shear resistance. Based on the experimental phenomena and the evaluation of three existing calculation methods on frame joints, and considering the effects of steel tube flange and extemal diaphragm on shear behavior, a calculation formula on the shear bearing capacity of external diaphragm connection was proposed. The accuracy and applicability of this calculation formula was verified by the test results, and it could provide a reference for external diaphragm connection design.
2022, 52(5): 140-146.
doi: 10.13204/j.gyjzG20100803
Abstract:
The finite element model of joint of composite beam and rectangular steel tube was established to investigate the resistance under the progressive collapse scenario through finite element software ABAQUS. The middle-joint above the removed column and the side-joint adjacent to the removed column were considered to investigate the failure mode and resistance mechanism.The results showed the resistance mechanism of middle joint was flexural action, compressive arch action and catenary action, while the resistance mechanism of side joint was flexural action and catenary action. Compressive arch action significantly improved the bearing capality load resistance at flexural stage and delays the catenary action for middle joint. According to the principle of energy, the static responses of two joints were transformed into dynamic responses.With the simplified assessment method,the results indicated that these two joints had enough resistance to withstand progressive collapse.
The finite element model of joint of composite beam and rectangular steel tube was established to investigate the resistance under the progressive collapse scenario through finite element software ABAQUS. The middle-joint above the removed column and the side-joint adjacent to the removed column were considered to investigate the failure mode and resistance mechanism.The results showed the resistance mechanism of middle joint was flexural action, compressive arch action and catenary action, while the resistance mechanism of side joint was flexural action and catenary action. Compressive arch action significantly improved the bearing capality load resistance at flexural stage and delays the catenary action for middle joint. According to the principle of energy, the static responses of two joints were transformed into dynamic responses.With the simplified assessment method,the results indicated that these two joints had enough resistance to withstand progressive collapse.
2022, 52(5): 147-153,82.
doi: 10.13204/j.gyjzG21122206
Abstract:
The fatigue performance of composite beams in bridge structure and crane beam has attracted researchers' attention. The fatigue test of composite beam with laminated slabs under constant amplitude load was carried out. According to the fatigue test results,the data of fatigue life of composite beams with the same fatigue failure mode was fitted according to double logarithmic model. and the S-N curve of composite beams with stud shear failure was obtained. The results were very close to those of ECCS,which could be used to design bridge with the composite beam. Both of the composite beam with laminated plate and with cast-in-site plate showed almost the same fatigue performance.
The fatigue performance of composite beams in bridge structure and crane beam has attracted researchers' attention. The fatigue test of composite beam with laminated slabs under constant amplitude load was carried out. According to the fatigue test results,the data of fatigue life of composite beams with the same fatigue failure mode was fitted according to double logarithmic model. and the S-N curve of composite beams with stud shear failure was obtained. The results were very close to those of ECCS,which could be used to design bridge with the composite beam. Both of the composite beam with laminated plate and with cast-in-site plate showed almost the same fatigue performance.
2022, 52(5): 154-162,168.
doi: 10.13204/j.gyjzG21070117
Abstract:
Based on the City Balcony project of Xiangluwan on conples street of Zhuhai City, the analysis and design of long-span curved steel-concrete composite pedestrian bridge were carried out. The human-induced vibration control method of irregular complex pedestrian bridge using multiple tuned mass dampers (MTMD) was introduced. Firstly, the refined finite element model of the whole bridge was established by using the general finite element software ANSYS. Then the construction process of the whole bridge was reasonably designed and the corresponding construction stage was defined in the finite element program to analyze the mechanical properties of the composite bridge during the whole construction process and the normal operation stage. The comfort of pedestrian bridge was analyzed by avoiding the sensitive frequency and limiting the dynamic response of the structure, and the comfort degree of the structure was evaluated according to the domestic and foreign specifications. Finally, a scheme of installing multiple tuned mass dampers for human-induced vibration control was proposed. The results showed that MTMD could effectively control the vertical vibration response of curved pedestrian bridge structure.
Based on the City Balcony project of Xiangluwan on conples street of Zhuhai City, the analysis and design of long-span curved steel-concrete composite pedestrian bridge were carried out. The human-induced vibration control method of irregular complex pedestrian bridge using multiple tuned mass dampers (MTMD) was introduced. Firstly, the refined finite element model of the whole bridge was established by using the general finite element software ANSYS. Then the construction process of the whole bridge was reasonably designed and the corresponding construction stage was defined in the finite element program to analyze the mechanical properties of the composite bridge during the whole construction process and the normal operation stage. The comfort of pedestrian bridge was analyzed by avoiding the sensitive frequency and limiting the dynamic response of the structure, and the comfort degree of the structure was evaluated according to the domestic and foreign specifications. Finally, a scheme of installing multiple tuned mass dampers for human-induced vibration control was proposed. The results showed that MTMD could effectively control the vertical vibration response of curved pedestrian bridge structure.
2022, 52(5): 163-168.
doi: 10.13204/j.gyjzG20110703
Abstract:
Due to geographical restrictions, Tibetan dwellings mostly adopts traditional stone-wood structure system, which has no seismic design and is easy to be severely damaged by earthquake disasters. In order to understand the weak links of Tibetan-style stone-wood structure dwellings under earthquake action, a typical stone-wood structure dwelling in the suburbs of Lhasa was selected as the research object, and its displacement and acceleration response under three groups of frequent earthquakes were analyzed through ANSYS modeling. As well as the acceleration response, displacement response and stress cloud diagram under the action of the El-Centro rare earthquake wave, the inter-storey drift angle and acceleration magnification factor were calculated; in addition, combined with the distribution of structural shear stress, it was found that under seismic action, the main weak points were the parapet wall, the second-story column joints, the walls near the door and window openings, and the corners; finally, some suggestions for strengthening and improving this type of structure were given based on the analysis results.
Due to geographical restrictions, Tibetan dwellings mostly adopts traditional stone-wood structure system, which has no seismic design and is easy to be severely damaged by earthquake disasters. In order to understand the weak links of Tibetan-style stone-wood structure dwellings under earthquake action, a typical stone-wood structure dwelling in the suburbs of Lhasa was selected as the research object, and its displacement and acceleration response under three groups of frequent earthquakes were analyzed through ANSYS modeling. As well as the acceleration response, displacement response and stress cloud diagram under the action of the El-Centro rare earthquake wave, the inter-storey drift angle and acceleration magnification factor were calculated; in addition, combined with the distribution of structural shear stress, it was found that under seismic action, the main weak points were the parapet wall, the second-story column joints, the walls near the door and window openings, and the corners; finally, some suggestions for strengthening and improving this type of structure were given based on the analysis results.
2022, 52(5): 169-173,218.
doi: 10.13204/j.gyjzG21030818
Abstract:
The dynamic characteristics of nano-SiO2-improved cement-soil and the change of internal micro-pore structure of nano-SiO2-improved cement-soil were studied with the dynamic triaxial test apparatus of GDS and the nuclear magnetic resonance test apparatus PQ001.The dynamic triaxial test results showed that theσd-εd curve of cement-soil first rising and then decline with the increase of the nano-SiO2 content. The curve of the dynamic deformation modulus and dynamic strain, the area surrounding by the hysteresis curve under the same level load, and the curve for damping ratios and dynamic strain of cement-soil first decline and then rising with the increase of the nano-SiO2 content. When the nano-SiO2 content was 2.5%, the dynamic resistance of cement-soil was maximun. Micro structure analysis of cement-soil showed that the pore structure and strength of nano-SiO2-improved cement-soil were increased. The optimal nano-SiO2 content was 2.5%.
The dynamic characteristics of nano-SiO2-improved cement-soil and the change of internal micro-pore structure of nano-SiO2-improved cement-soil were studied with the dynamic triaxial test apparatus of GDS and the nuclear magnetic resonance test apparatus PQ001.The dynamic triaxial test results showed that theσd-εd curve of cement-soil first rising and then decline with the increase of the nano-SiO2 content. The curve of the dynamic deformation modulus and dynamic strain, the area surrounding by the hysteresis curve under the same level load, and the curve for damping ratios and dynamic strain of cement-soil first decline and then rising with the increase of the nano-SiO2 content. When the nano-SiO2 content was 2.5%, the dynamic resistance of cement-soil was maximun. Micro structure analysis of cement-soil showed that the pore structure and strength of nano-SiO2-improved cement-soil were increased. The optimal nano-SiO2 content was 2.5%.
2022, 52(5): 174-178.
doi: 10.13204/j.gyjzG21042505
Abstract:
A model test was conducted to analyze the lateral earth pressure behind a translating retaining structure near an existing composite foundation of long-short piles. The results showed that when the retaining structure was translated outward, the lateral earth pressure behind the retaining structure adjacent to composite foundation of long-short piles was less than that in the natural foundation within the depth of reinforced by short piles. However, the earth pressure below the bottom of reinforcing short piles was significantly larger than that in natureal foundation. It was suggestion that the influence of the additional load transferred from the short piles should be taken into account in calculation of lateral earth pressure behind a retaining structure. It was also found that the lateral earth pressure adjacent to composite foundation with long-short piles could approximately be equivalent to the algebraic sum of the earth pressure caused by additional stress in soil between piles and additional stress from the short and long piles respectively. Based on that, a formula for calculating the lateral earth pressure behind a retaining structure adjacent to composite foundation with long and short piles was proposed.
A model test was conducted to analyze the lateral earth pressure behind a translating retaining structure near an existing composite foundation of long-short piles. The results showed that when the retaining structure was translated outward, the lateral earth pressure behind the retaining structure adjacent to composite foundation of long-short piles was less than that in the natural foundation within the depth of reinforced by short piles. However, the earth pressure below the bottom of reinforcing short piles was significantly larger than that in natureal foundation. It was suggestion that the influence of the additional load transferred from the short piles should be taken into account in calculation of lateral earth pressure behind a retaining structure. It was also found that the lateral earth pressure adjacent to composite foundation with long-short piles could approximately be equivalent to the algebraic sum of the earth pressure caused by additional stress in soil between piles and additional stress from the short and long piles respectively. Based on that, a formula for calculating the lateral earth pressure behind a retaining structure adjacent to composite foundation with long and short piles was proposed.
2022, 52(5): 179-186.
doi: 10.13204/j.gyjzG21012103
Abstract:
To study mechanical characteristics of piled raft under vertical-horizontal combined loads, several indoor model tests were conducted, considering the influence of length to diameter ratios, pile numbers, vertical loads and pile spacing, and the changes of the bending moment and shear forces in pile shafts and earth pressure on piles were analyzed. The test results showed that: The horizontal bearing capacity of piled rafts increased with the increase of vertical loads, pile numbers, length and spacing of piles, on the contrary, the horizontal displacement of piled rafts decreased with their increase. The maximum bending moment was located at 0.3 times length of piles below the earth’s surface,and the maximum bending moment in the front piles was larger than that in the rear,which was about 1.14 times bending moment in the rear piles. The bending moment and shear forces decreased with the increase of vertical loads,and the maximum bending moment of piles increased with the decrease of pile spacing but the bending moment at tops and tips of piles almost kept stable. The location of the maximum negative shear forces could be controlled by adjusting the pile spacing, and the shear forces at the tops of piles decreased with the increase of pile spacing but the shear forces at the tips changed conversely. To increase the pile spacing could mobilize a wider range soil between piles,however the internal forces in piles almost kept steady. The failure mode of piled raftes conformed to the failure laws of rigid piles under the combined loads. The ultimate horizontal bearing capacity of piles was mainly controlled by the compressive strength of soil around piles.
To study mechanical characteristics of piled raft under vertical-horizontal combined loads, several indoor model tests were conducted, considering the influence of length to diameter ratios, pile numbers, vertical loads and pile spacing, and the changes of the bending moment and shear forces in pile shafts and earth pressure on piles were analyzed. The test results showed that: The horizontal bearing capacity of piled rafts increased with the increase of vertical loads, pile numbers, length and spacing of piles, on the contrary, the horizontal displacement of piled rafts decreased with their increase. The maximum bending moment was located at 0.3 times length of piles below the earth’s surface,and the maximum bending moment in the front piles was larger than that in the rear,which was about 1.14 times bending moment in the rear piles. The bending moment and shear forces decreased with the increase of vertical loads,and the maximum bending moment of piles increased with the decrease of pile spacing but the bending moment at tops and tips of piles almost kept stable. The location of the maximum negative shear forces could be controlled by adjusting the pile spacing, and the shear forces at the tops of piles decreased with the increase of pile spacing but the shear forces at the tips changed conversely. To increase the pile spacing could mobilize a wider range soil between piles,however the internal forces in piles almost kept steady. The failure mode of piled raftes conformed to the failure laws of rigid piles under the combined loads. The ultimate horizontal bearing capacity of piles was mainly controlled by the compressive strength of soil around piles.
2022, 52(5): 187-193.
doi: 10.13204/j.gyjzG21022506
Abstract:
It is an important way to evaluate the stability of foundation that establishs the envelope of bearing capacity for foundation in different loading modes by means of numerical analysis and tests. According to the engineering geological conditions, a three-dimensional large-scale numerical model of the suction-caisson and foundation by the finite element method was constructed. The deformation and bearing capacity of the caisson foundation under horizontal loads, vertical loads and bending moment were calculated. The results showed that with the gradual increase of loads, the displacement of the composite caisson foundation increased linearly at the initial stage, increased exponentially at the later stage, and became unstable at last. An appropriate vertical load was beneficial to improve the horizontal and flexural bearing capacity of the composite caisson foundation, while an excessively large vertical load was unfavorable to the stability of the foundation. The failure envelope of the caisson foundation played an important role in structural design, foundation stability judgment and overall safety evaluation.
It is an important way to evaluate the stability of foundation that establishs the envelope of bearing capacity for foundation in different loading modes by means of numerical analysis and tests. According to the engineering geological conditions, a three-dimensional large-scale numerical model of the suction-caisson and foundation by the finite element method was constructed. The deformation and bearing capacity of the caisson foundation under horizontal loads, vertical loads and bending moment were calculated. The results showed that with the gradual increase of loads, the displacement of the composite caisson foundation increased linearly at the initial stage, increased exponentially at the later stage, and became unstable at last. An appropriate vertical load was beneficial to improve the horizontal and flexural bearing capacity of the composite caisson foundation, while an excessively large vertical load was unfavorable to the stability of the foundation. The failure envelope of the caisson foundation played an important role in structural design, foundation stability judgment and overall safety evaluation.
2022, 52(5): 194-198.
doi: 10.13204/j.gyjzG21040602
Abstract:
Pot cover effect refers to the phenomenon that moisture accumulates underneath an airproof cover in the earth's surface. "Pot cover effect" may lead to a high moisture content in soil under the cover and induce engineering disasters. At present, numerical simulations of multi-field coupling are mostly used in the calculation for vapor migration, the processes of calculations are tedious and inconvenient. Accordingto the actual engineering conditions, the calculation formula for temperature at different depth was deduced. Based on the Fick’s law, the formula for calculating the amount of vapor migration was inferred. By combining the above formulas, a simple calculation method of vapor migration on "pot cover effect" was proposed. The calculated values were compared with the measured values. The results showed that the calculation method could reflect the trend of vapor migration in the earth at different depths. The calculation method was effective and feasible.
Pot cover effect refers to the phenomenon that moisture accumulates underneath an airproof cover in the earth's surface. "Pot cover effect" may lead to a high moisture content in soil under the cover and induce engineering disasters. At present, numerical simulations of multi-field coupling are mostly used in the calculation for vapor migration, the processes of calculations are tedious and inconvenient. Accordingto the actual engineering conditions, the calculation formula for temperature at different depth was deduced. Based on the Fick’s law, the formula for calculating the amount of vapor migration was inferred. By combining the above formulas, a simple calculation method of vapor migration on "pot cover effect" was proposed. The calculated values were compared with the measured values. The results showed that the calculation method could reflect the trend of vapor migration in the earth at different depths. The calculation method was effective and feasible.
2022, 52(5): 199-207.
doi: 10.13204/j.gyjzG20091704
Abstract:
In order to study the effects of recycled concrete with 100% replacement rate of coarse aggregate and common concrete on mechanical properties and frost resistance, an experimental study was conducted by changing the number of freeze-thaw cycles. The freeze-thaw damage model was established by analyzed loss rate of compressive strength, mass and dynamic elastic modulus, and also aimed at the anti-freeze durability lives of recycled concrete was predicted for the Inner Mongolia area. The result of research shows that the compressive strength and splitting tensile strength of recycled concrete was inverse to the number of freeze-thaw cycles. For every 50 additional freeze-thaw cycles, the average compressive strength decreased by 33.1%, and the average splitting tensile strength decreased by 33%. In the early stage of the freezing and thawing, the ordinary concrete and recycled concrete anti-freeze performance were similar, but the performance degradation and the recycled concrete degradation are greater than ordinary concrete with the increase of freeze-thaw cycles. The establishment of freeze-thaw damage model can intuitive clearly reflect the mechanical properties of recycled concrete macroscopic changes because of the higher fitting accuracy of dynamic modulus of elasticity loss of freeze-thaw damage model.
In order to study the effects of recycled concrete with 100% replacement rate of coarse aggregate and common concrete on mechanical properties and frost resistance, an experimental study was conducted by changing the number of freeze-thaw cycles. The freeze-thaw damage model was established by analyzed loss rate of compressive strength, mass and dynamic elastic modulus, and also aimed at the anti-freeze durability lives of recycled concrete was predicted for the Inner Mongolia area. The result of research shows that the compressive strength and splitting tensile strength of recycled concrete was inverse to the number of freeze-thaw cycles. For every 50 additional freeze-thaw cycles, the average compressive strength decreased by 33.1%, and the average splitting tensile strength decreased by 33%. In the early stage of the freezing and thawing, the ordinary concrete and recycled concrete anti-freeze performance were similar, but the performance degradation and the recycled concrete degradation are greater than ordinary concrete with the increase of freeze-thaw cycles. The establishment of freeze-thaw damage model can intuitive clearly reflect the mechanical properties of recycled concrete macroscopic changes because of the higher fitting accuracy of dynamic modulus of elasticity loss of freeze-thaw damage model.
2022, 52(5): 208-218.
doi: 10.13204/j.gyjzG21072405
Abstract:
3D printed concrete has significant advantages in moldless and intelligent construction and has huge application potential. It has gradually become a rapidly rising research hotspot all over the world. At present, researchers at home and abroad have carried out research on its working and mechanical properties. The former mainly includes flowability, extrudability and buildability performance, while the latter mainly includes compressive strength, flexural strength and interlayer bond strength. Therefore, based on the current research status of 3D printed concrete at home and abroad, firstly, a specific review of its working properties and mechanical properties was carried out, with a focus on the research methods and research results obtained at this stage. Then, the main problems existing in the performance research and practical application of 3D printed concrete were summarized. At the same time, the current solutions were summarized and analyzed in view of the problems of low tensile strength and insufficient ductility. The future research direction was also pointed out, which could promote the research and application of 3D concrete printing technology.
3D printed concrete has significant advantages in moldless and intelligent construction and has huge application potential. It has gradually become a rapidly rising research hotspot all over the world. At present, researchers at home and abroad have carried out research on its working and mechanical properties. The former mainly includes flowability, extrudability and buildability performance, while the latter mainly includes compressive strength, flexural strength and interlayer bond strength. Therefore, based on the current research status of 3D printed concrete at home and abroad, firstly, a specific review of its working properties and mechanical properties was carried out, with a focus on the research methods and research results obtained at this stage. Then, the main problems existing in the performance research and practical application of 3D printed concrete were summarized. At the same time, the current solutions were summarized and analyzed in view of the problems of low tensile strength and insufficient ductility. The future research direction was also pointed out, which could promote the research and application of 3D concrete printing technology.
2022, 52(5): 219-225.
doi: 10.13204/j.gyjzG21062704
Abstract:
Computerized tomographic technique is a emerging technique for nondestructive bridge inspection. In conventional tomographic inversion, rectangular grid is used to divide the model, and a large number of detection equipment is required to ensure the accuracy. To improve the effect of bridge tomographic inspection, the technique of Fresnel zone was introduced into the inversion to enlarge the coverage range of the inversion ray, which improved the ray sparseness caused by insufficient inspection equipment. By using the time difference method, the accuracy of first arrival data was improved and the influence of the first arrivals pick-up error in small-scale measurement was reduced. In addition, triangular mesh was used to divide the bridge model, which could fit the bridge model with irregular edges better than rectangular mesh. The results of model trial calculation and actual measurement showed that the Fresnel zone method could better deduce the position, shape and size of the velocity anomaly area. After using the time difference method to deal with the data with picking errors, the inversion results were close to the inversion results of accurate data. The algorithm improved the accuracy of inversion and could be effectively applied in bridge inspection projects.
Computerized tomographic technique is a emerging technique for nondestructive bridge inspection. In conventional tomographic inversion, rectangular grid is used to divide the model, and a large number of detection equipment is required to ensure the accuracy. To improve the effect of bridge tomographic inspection, the technique of Fresnel zone was introduced into the inversion to enlarge the coverage range of the inversion ray, which improved the ray sparseness caused by insufficient inspection equipment. By using the time difference method, the accuracy of first arrival data was improved and the influence of the first arrivals pick-up error in small-scale measurement was reduced. In addition, triangular mesh was used to divide the bridge model, which could fit the bridge model with irregular edges better than rectangular mesh. The results of model trial calculation and actual measurement showed that the Fresnel zone method could better deduce the position, shape and size of the velocity anomaly area. After using the time difference method to deal with the data with picking errors, the inversion results were close to the inversion results of accurate data. The algorithm improved the accuracy of inversion and could be effectively applied in bridge inspection projects.
