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2024 Vol. 54, No. 12
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2024, 54(12): 1-9.
doi: 10.3724/j.gyjzG24042402
Abstract:
Two kinds of weathering bridge steels with lath-like bainite (Q470 steel) and granular bainite (Q550 steel) were prepared by controlling the cooling temperature after hot rolling. The effects of tempering treatment on the microstructure and mechanical properties of these two kinds of steels were investigated. Physical-chemical phase analysis method, X ray diffractometer and universal testing machine were used to characterize the evolution of microstructure and mechanical properties during tempering. The results showed that the yield strength and -40 ℃ impact energy of Q470 steel was higher than that of Q550 steel in hot rolling state. After tempering at 500-650 ℃, the yield strength of Q470 steel decreased first and then increased with the increase of tempering temperature (665-705 MPa), and the -40 ℃ impact energy gradually decreased from 300 J to 220 J. Under the same tempering conditions, the yield strength of Q550 steel increased with the increase of tempering temperature (500-650 MPa), and the -40 ℃ impact energy maintained at 210-230 J. The main strengthening mechanisms of these two kinds of steels were dislocation strengthening and fine grain strengthening. In addition, the strengthening of Nb precipitation gradually increases with increasing tempering temperature, compensating for the strength loss caused by the decrease in dislocation density, which was the main reason for the increase in yield strength of experimental steels.
Two kinds of weathering bridge steels with lath-like bainite (Q470 steel) and granular bainite (Q550 steel) were prepared by controlling the cooling temperature after hot rolling. The effects of tempering treatment on the microstructure and mechanical properties of these two kinds of steels were investigated. Physical-chemical phase analysis method, X ray diffractometer and universal testing machine were used to characterize the evolution of microstructure and mechanical properties during tempering. The results showed that the yield strength and -40 ℃ impact energy of Q470 steel was higher than that of Q550 steel in hot rolling state. After tempering at 500-650 ℃, the yield strength of Q470 steel decreased first and then increased with the increase of tempering temperature (665-705 MPa), and the -40 ℃ impact energy gradually decreased from 300 J to 220 J. Under the same tempering conditions, the yield strength of Q550 steel increased with the increase of tempering temperature (500-650 MPa), and the -40 ℃ impact energy maintained at 210-230 J. The main strengthening mechanisms of these two kinds of steels were dislocation strengthening and fine grain strengthening. In addition, the strengthening of Nb precipitation gradually increases with increasing tempering temperature, compensating for the strength loss caused by the decrease in dislocation density, which was the main reason for the increase in yield strength of experimental steels.
2024, 54(12): 10-17.
doi: 10.3724/j.gyjzG24013003
Abstract:
For the bridge construction project in the complex environment of the plateau, the high impact resistance and low tough-brittle transition temperature weathering bridge steel with a yield strength of 500 MPa has been developed. The effects of the final cooling temperature after rolling on the microstructure and mechanical properties of the experimental steels were studied, and the effects of low temperature on the impact toughness of the experimental steels were analyzed in depth. The results showed that the experimental steels after TMCP treatment could meet the mechanical property requirements of Q500 grade bridge steel, and the experimental steels with two different final cooling temperatures (500, 550 ℃) showed good impact properties under the low-temperature environment of -40 to -80 ℃. However, with the increase of final cooling temperature, the grain size of experimental steels increased; the increase of M/A island size and change of morphology and the decrease of the proportion of large-angle grain boundaries were the main reasons for the difference in impact properties of the two experimental steels.
For the bridge construction project in the complex environment of the plateau, the high impact resistance and low tough-brittle transition temperature weathering bridge steel with a yield strength of 500 MPa has been developed. The effects of the final cooling temperature after rolling on the microstructure and mechanical properties of the experimental steels were studied, and the effects of low temperature on the impact toughness of the experimental steels were analyzed in depth. The results showed that the experimental steels after TMCP treatment could meet the mechanical property requirements of Q500 grade bridge steel, and the experimental steels with two different final cooling temperatures (500, 550 ℃) showed good impact properties under the low-temperature environment of -40 to -80 ℃. However, with the increase of final cooling temperature, the grain size of experimental steels increased; the increase of M/A island size and change of morphology and the decrease of the proportion of large-angle grain boundaries were the main reasons for the difference in impact properties of the two experimental steels.
2024, 54(12): 18-25.
doi: 10.3724/j.gyjzG24042401
Abstract:
316L+Q420qENH and 316L+Q500qENH stainless steel clad plates were prepared by Gleeble-1500D to simulate the hot-rolling bonding of Q420qENH/Q500qENH weathering bridge steel and 316L stainless steel. The effects of bridge weathering steel and cooling rate on the interfacial microstructure and shear strength of stainless steel clad plates were investigated. The results showed that 316L+Q500qENH exhibited higher interfacial shear strength (＞420 MPa) than 316L+Q420qENH, which had thinner banded ferrite. For 316L+Q420qENH steel, when the cooling rate increased from 0.25 ℃/s to 1 ℃/s, the degree of element diffusion decreased, leading to a decrease in interfacial shear strength. Within the cooling rate range of 1~10 ℃/s after rolling, the content of ferrite at the interface gradually decreased and the microstructure gradually refined. Therefore the interface shear strength of 316L+Q420qENH steel gradually improved and reached the highest value at 10 ℃/s, which was 422 MPa. In general, the reduction of ferrite content at the interface, the refinement of microstructure and the increase of element diffusion were conducive to improve the interfacial shear strength of the stainless steel clad plates.
316L+Q420qENH and 316L+Q500qENH stainless steel clad plates were prepared by Gleeble-1500D to simulate the hot-rolling bonding of Q420qENH/Q500qENH weathering bridge steel and 316L stainless steel. The effects of bridge weathering steel and cooling rate on the interfacial microstructure and shear strength of stainless steel clad plates were investigated. The results showed that 316L+Q500qENH exhibited higher interfacial shear strength (＞420 MPa) than 316L+Q420qENH, which had thinner banded ferrite. For 316L+Q420qENH steel, when the cooling rate increased from 0.25 ℃/s to 1 ℃/s, the degree of element diffusion decreased, leading to a decrease in interfacial shear strength. Within the cooling rate range of 1~10 ℃/s after rolling, the content of ferrite at the interface gradually decreased and the microstructure gradually refined. Therefore the interface shear strength of 316L+Q420qENH steel gradually improved and reached the highest value at 10 ℃/s, which was 422 MPa. In general, the reduction of ferrite content at the interface, the refinement of microstructure and the increase of element diffusion were conducive to improve the interfacial shear strength of the stainless steel clad plates.
2024, 54(12): 26-34.
doi: 10.3724/j.gyjzG24062601
Abstract:
In response to the demand for high-performance bridge steel in complex high-altitude environments, research and development of matching welding electrode for Q500qENH and Q550qENH bridge steel plates were carried out, and their performance was studied. 6 types of welding electrodes with different compositions were designed. Metallographic analysis and impact fracture morphology analysis were conducted on the weld metals, and the influence of the chemical composition of the deposited metals on the structure and properties was explored. The microstructure inside the weld bead was divided into three parts: columnar grain zone microstructure, reheated coarse grain zone microstructure, and reheated fine grain zone microstructure. The main metallographic structures were Acicular Ferrite, Proeutectoid Ferrite, Carbon Free Bainite, Block Ferrite and a small amount of Granular Bainite. The fiber area of the impact specimen had a relatively uniform dimple shaped structure. The crystalline area of the fracture surface was mostly composed of cleavage river patterns and a small amount of dimples. The research results indicated that Acicular Ferrite had a positive effect on the low-temperature toughness of deposited metals. No.3 had the highest proportion of Acicular Ferrite and the best low-temperature impact toughness. The increase in Mn and Si element content led to an increase in the proportion of Proeutectoid Ferrite and Carbon Free Bainite, while the proportion of Acicular Ferrite decreased. These factors had led to a decrease in low-temperature toughness. Ni element could increase the proportion of Acicular Ferrite tissue, which was beneficial for low-temperature toughness. The developed welding electrode matched well with the weathering steel plate, meeting the task requirements of weather resistance index I≥6.5, -40 ℃ kV2≥60 J, A≥17%.
In response to the demand for high-performance bridge steel in complex high-altitude environments, research and development of matching welding electrode for Q500qENH and Q550qENH bridge steel plates were carried out, and their performance was studied. 6 types of welding electrodes with different compositions were designed. Metallographic analysis and impact fracture morphology analysis were conducted on the weld metals, and the influence of the chemical composition of the deposited metals on the structure and properties was explored. The microstructure inside the weld bead was divided into three parts: columnar grain zone microstructure, reheated coarse grain zone microstructure, and reheated fine grain zone microstructure. The main metallographic structures were Acicular Ferrite, Proeutectoid Ferrite, Carbon Free Bainite, Block Ferrite and a small amount of Granular Bainite. The fiber area of the impact specimen had a relatively uniform dimple shaped structure. The crystalline area of the fracture surface was mostly composed of cleavage river patterns and a small amount of dimples. The research results indicated that Acicular Ferrite had a positive effect on the low-temperature toughness of deposited metals. No.3 had the highest proportion of Acicular Ferrite and the best low-temperature impact toughness. The increase in Mn and Si element content led to an increase in the proportion of Proeutectoid Ferrite and Carbon Free Bainite, while the proportion of Acicular Ferrite decreased. These factors had led to a decrease in low-temperature toughness. Ni element could increase the proportion of Acicular Ferrite tissue, which was beneficial for low-temperature toughness. The developed welding electrode matched well with the weathering steel plate, meeting the task requirements of weather resistance index I≥6.5, -40 ℃ kV2≥60 J, A≥17%.
Research on Corrosion Behavior of 550 MPa Weathering Bridge Steel in Simulated Industrial Atmosphere
2024, 54(12): 35-41.
doi: 10.3724/j.gyjzG24012902
Abstract:
The corrosion behavior of 550 MPa weathering bridge steel in simulated industrial atmosphere was investigated by cyclic immersion corrosion tests. The microscopic morphology, phase composition of corrosion products, cross section morphology and element distribution of rust layer were observed and analyzed by means of scanning electron microscope, X-ray diffraction and electron probe. The mechanism of atmospheric corrosion resistance of high-strength weathering bridge steel was also discussed. The results indicated that the corrosion weight loss rate of Q550qENH-A steel and Q550qENH-B steel decreased rapidly at the initial stage and tended to be stable at the later stage with the extension of corrosion time in the simulated industrial atmosphere, and the corrosion resistance of the two kinds of weathering steels were better than that of Q345B. Cr and Ni were enriched in the rust layer of two kinds of weathering steels, which promoted the formation of α-FeOOH and improved the stability and compactness of the rust layer structure, thus the blocking effect of the rust layer on the corrosion medium was enhanced. Therefore, the weathering steels showed excellent atmospheric corrosion resistance.
The corrosion behavior of 550 MPa weathering bridge steel in simulated industrial atmosphere was investigated by cyclic immersion corrosion tests. The microscopic morphology, phase composition of corrosion products, cross section morphology and element distribution of rust layer were observed and analyzed by means of scanning electron microscope, X-ray diffraction and electron probe. The mechanism of atmospheric corrosion resistance of high-strength weathering bridge steel was also discussed. The results indicated that the corrosion weight loss rate of Q550qENH-A steel and Q550qENH-B steel decreased rapidly at the initial stage and tended to be stable at the later stage with the extension of corrosion time in the simulated industrial atmosphere, and the corrosion resistance of the two kinds of weathering steels were better than that of Q345B. Cr and Ni were enriched in the rust layer of two kinds of weathering steels, which promoted the formation of α-FeOOH and improved the stability and compactness of the rust layer structure, thus the blocking effect of the rust layer on the corrosion medium was enhanced. Therefore, the weathering steels showed excellent atmospheric corrosion resistance.
2024, 54(12): 42-48.
doi: 10.3724/j.gyjzG24030501
Abstract:
The connection structure of metal materials faces serious corrosion failure during long-term service, and the crevice corrosion has a significant impact on the shear bearing capacity of the connection structure. 6 high-strength bolted connectors composed of Q355GNH weathering steel and 6 high-strength bolted connectors composed of Q355B low-carbon steel were tested for accelerated corrosion in acetic acid salt spray. The corroded connectors with the rust outside the gap were used as the control group, and the rust outside the gap of the connecting plate was continuously cleaned during the corrosion process to study the crevice corrosion behavior, as well as the influence of crevice corrosion on the shear bearing capacity of the bolted connectors. The results showed that the anti-slip coefficient μ of the friction surface of the connector increased accordingly with the increase of the proportion of black rust. The rust produced by the weathering steel were dense, which could prevent oxygen to promote the low-oxygen crevice corrosion reaction, after removing the rust outside the gap, the black rust on the friction surface were reduced and the slip load was reduced by 29.2%. Whether the outer rust of the gap was removed or not, the crevice corrosion degree of the low-carbon steel bolted connectors was large, but the low-carbon steel connection that cleaned the outer rust of the gap had greater slip load through changing the roughness of friction surface of bolted connectors, crevice corrosion slowed down the decrease of anti-slip bearing capacity of bolted connectors caused by preload loss.
The connection structure of metal materials faces serious corrosion failure during long-term service, and the crevice corrosion has a significant impact on the shear bearing capacity of the connection structure. 6 high-strength bolted connectors composed of Q355GNH weathering steel and 6 high-strength bolted connectors composed of Q355B low-carbon steel were tested for accelerated corrosion in acetic acid salt spray. The corroded connectors with the rust outside the gap were used as the control group, and the rust outside the gap of the connecting plate was continuously cleaned during the corrosion process to study the crevice corrosion behavior, as well as the influence of crevice corrosion on the shear bearing capacity of the bolted connectors. The results showed that the anti-slip coefficient μ of the friction surface of the connector increased accordingly with the increase of the proportion of black rust. The rust produced by the weathering steel were dense, which could prevent oxygen to promote the low-oxygen crevice corrosion reaction, after removing the rust outside the gap, the black rust on the friction surface were reduced and the slip load was reduced by 29.2%. Whether the outer rust of the gap was removed or not, the crevice corrosion degree of the low-carbon steel bolted connectors was large, but the low-carbon steel connection that cleaned the outer rust of the gap had greater slip load through changing the roughness of friction surface of bolted connectors, crevice corrosion slowed down the decrease of anti-slip bearing capacity of bolted connectors caused by preload loss.
2024, 54(12): 49-57.
doi: 10.3724/j.gyjzG24041801
Abstract:
In this study, acetic acid salt spray test was carried out on Q355GNH weathering steel, and its weathering performance in industrial marine atmospheric corrosion environment was analyzed. After the corrosion tests, the monotonic tensile test was carried out to study the degradation trend of the mechanical properties of pre-corroded Q355GNH with the increase of corrosion rate, and the corrosion damage constitutive model of Q355GNH with 6 mm and 14 mm thickness was established. The results showed that the tensile strength and elongation of the weathering steel decreased after corrosion. The corrosion rate had the greatest influence on the fracture strain, followed by the yield strength and ultimate strength; the yield ratio of weathering steel was always stable after corrosion, and the tensile fracture mode was still ductile fracture; the smaller the thickness of steel was, the more obvious the decrease of mechanical properties of steel after corrosion was; with the increase of corrosion time, the constitutive curve of Q355GNH steel changed, the yield platform and plastic strengthening stage gradually became shorter, and the yield platform of 6 mm material specimen disappeared just after 40 days of corrosion. Based on the constitutive model of Q355GNH weathering steel with smooth surface, the constitutive model of pre-corroded weathering steel was proposed by introducing parameters k1, k2, k3, C, which was in good agreement with the constitutive curve of Q355GNH after corrosion.
In this study, acetic acid salt spray test was carried out on Q355GNH weathering steel, and its weathering performance in industrial marine atmospheric corrosion environment was analyzed. After the corrosion tests, the monotonic tensile test was carried out to study the degradation trend of the mechanical properties of pre-corroded Q355GNH with the increase of corrosion rate, and the corrosion damage constitutive model of Q355GNH with 6 mm and 14 mm thickness was established. The results showed that the tensile strength and elongation of the weathering steel decreased after corrosion. The corrosion rate had the greatest influence on the fracture strain, followed by the yield strength and ultimate strength; the yield ratio of weathering steel was always stable after corrosion, and the tensile fracture mode was still ductile fracture; the smaller the thickness of steel was, the more obvious the decrease of mechanical properties of steel after corrosion was; with the increase of corrosion time, the constitutive curve of Q355GNH steel changed, the yield platform and plastic strengthening stage gradually became shorter, and the yield platform of 6 mm material specimen disappeared just after 40 days of corrosion. Based on the constitutive model of Q355GNH weathering steel with smooth surface, the constitutive model of pre-corroded weathering steel was proposed by introducing parameters k1, k2, k3, C, which was in good agreement with the constitutive curve of Q355GNH after corrosion.
2024, 54(12): 58-70.
doi: 10.3724/j.gyjzG24031201
Abstract:
Weathering bridge steel has the advantage of being applied to bridge steel structures without the need for painting, reducing the initial painting and later maintenance costs of steel structures, and avoiding the negative impact of the painting process on the environment. This type of steel has high strength, excellent corrosion resistance, and environmentally friendly characteristics. Due to significant differences in composition and usage between weathering bridge steel and conventional steel, scholars at home and abroad have conducted extensive research on it. The paper summarized the research results on the research and development, preparation, and welding technique of weathering steel at home and abroad in recent years, including the study of the influence of various elements and environments on the corrosion resistance of weathering steel, the development of weathering steel preparation technique, the study of mechanical properties and corrosion fatigue of weathering steel, the development of weathering steel welding process, and the prediction of the service life of weathering steel structures. On this basis, suggestions were put forward for optimizing the design, manufacturing, and welding technique of weathering steel for practical application scenarios in China, and future research work was discussed.
Weathering bridge steel has the advantage of being applied to bridge steel structures without the need for painting, reducing the initial painting and later maintenance costs of steel structures, and avoiding the negative impact of the painting process on the environment. This type of steel has high strength, excellent corrosion resistance, and environmentally friendly characteristics. Due to significant differences in composition and usage between weathering bridge steel and conventional steel, scholars at home and abroad have conducted extensive research on it. The paper summarized the research results on the research and development, preparation, and welding technique of weathering steel at home and abroad in recent years, including the study of the influence of various elements and environments on the corrosion resistance of weathering steel, the development of weathering steel preparation technique, the study of mechanical properties and corrosion fatigue of weathering steel, the development of weathering steel welding process, and the prediction of the service life of weathering steel structures. On this basis, suggestions were put forward for optimizing the design, manufacturing, and welding technique of weathering steel for practical application scenarios in China, and future research work was discussed.
2024, 54(12): 71-89.
doi: 10.3724/j.gyjzG24013002
Abstract:
The stainless steel clad plates have the advantages of good corrosion resistance, low cost and high strength, compared with the traditional mild steel and stainless steel, the application of stainless steel clad plates extend the design service life of the structure, while reducing the whole life operation and maintenance costs, showing a relatively high comprehensive price in the application of high corrosion-resistant grade structures. At present, stainless steel clad plates have been successfully applied to pressure vessels, railroad highway steel bridge panels and water conservancy and hydropower projects in many fields. The paper analyzed the research status of preparation and welding techniques of stainless steel clad plates, focusing on the vacuum rolling cladding method, explosion cladding method and explosion-rolling cladding method of the three mainstream preparation processes, the welding technique of clad plates were discussed comprehensively from the aspects of welding process, joint non-destructive testing and performance, efficient welding process and welding finite element simulation and so on, as well as the development trend of the preparation and welding technique of stainless steel clad plates.
The stainless steel clad plates have the advantages of good corrosion resistance, low cost and high strength, compared with the traditional mild steel and stainless steel, the application of stainless steel clad plates extend the design service life of the structure, while reducing the whole life operation and maintenance costs, showing a relatively high comprehensive price in the application of high corrosion-resistant grade structures. At present, stainless steel clad plates have been successfully applied to pressure vessels, railroad highway steel bridge panels and water conservancy and hydropower projects in many fields. The paper analyzed the research status of preparation and welding techniques of stainless steel clad plates, focusing on the vacuum rolling cladding method, explosion cladding method and explosion-rolling cladding method of the three mainstream preparation processes, the welding technique of clad plates were discussed comprehensively from the aspects of welding process, joint non-destructive testing and performance, efficient welding process and welding finite element simulation and so on, as well as the development trend of the preparation and welding technique of stainless steel clad plates.
2024, 54(12): 90-98.
doi: 10.13204/j.gyjzG23033114
Abstract:
The epidemic outbreak has made us realize the importance of campus green space in public emergencies: for one, it provides a healing resource of replenishment and relaxation for university students and faculty, in addition to regular exposure to recreational space as an important intervention to alleviate the mental health challenges of the university community. As an independent structure dependent on the urban system, does the campus road network has been discussed for its correlation with the daily leisure behaviors of the audience in its contextual network. To this end, the three types of traversing activities, dynamic stopover activities and static stopover activities were broke down, and the correlation and multiple regression analysis with the environmental characteristic index set composed of road network scale, organizational structure, path interface and facility elements were conducted, and then derives the weight sequences of the relevant influencing factors of the different types of activities were derived, which ultimately could provide certain theoretical bases and references for the generation of public space planning layout and strategies for college campuses.
The epidemic outbreak has made us realize the importance of campus green space in public emergencies: for one, it provides a healing resource of replenishment and relaxation for university students and faculty, in addition to regular exposure to recreational space as an important intervention to alleviate the mental health challenges of the university community. As an independent structure dependent on the urban system, does the campus road network has been discussed for its correlation with the daily leisure behaviors of the audience in its contextual network. To this end, the three types of traversing activities, dynamic stopover activities and static stopover activities were broke down, and the correlation and multiple regression analysis with the environmental characteristic index set composed of road network scale, organizational structure, path interface and facility elements were conducted, and then derives the weight sequences of the relevant influencing factors of the different types of activities were derived, which ultimately could provide certain theoretical bases and references for the generation of public space planning layout and strategies for college campuses.
2024, 54(12): 99-104.
doi: 10.3724/j.gyjzG22060502
Abstract:
The uncertainty and mobility of contemporary cities pose a great challenge to traditional urban planning, yet this challenge has also become an opportunity for the rapid rise of landscape urbanism. The study aimed to explore the approaches of avant-garde landscape architects to the design of contemporary urban open spaces, and to propose open space planning strategies based on the theoretical framework of landscape urbanism. Firstly, the core concepts of landscape urbanism were analysed and interpreted, followed by empirical case studies that revealed how the core elements of landscape urbanism were interpreted in contemporary urban open spaces. A series of urban open space design strategies were analyzed, such as integrating or mimicking natural topography, green infrastructure projects, ecological resilience, adaptability to unplanned events, and analyzing sites at multiple scales, which could provide new guidance and inspiration for the future design of urban landscapes in China.
The uncertainty and mobility of contemporary cities pose a great challenge to traditional urban planning, yet this challenge has also become an opportunity for the rapid rise of landscape urbanism. The study aimed to explore the approaches of avant-garde landscape architects to the design of contemporary urban open spaces, and to propose open space planning strategies based on the theoretical framework of landscape urbanism. Firstly, the core concepts of landscape urbanism were analysed and interpreted, followed by empirical case studies that revealed how the core elements of landscape urbanism were interpreted in contemporary urban open spaces. A series of urban open space design strategies were analyzed, such as integrating or mimicking natural topography, green infrastructure projects, ecological resilience, adaptability to unplanned events, and analyzing sites at multiple scales, which could provide new guidance and inspiration for the future design of urban landscapes in China.
2024, 54(12): 105-113.
doi: 10.3724/j.gyjzG22022507
Abstract:
In the context of rural revitalization strategy, the national traditional villages in Huizhou Cultural Ecological Reserve was taken as the research object, the spatial distribution characteristics and spatial heterogeneity of traditional villages with kernel density and spatial autocorrelation were analyzed, the factors influencing the spatial distribution of traditional villages with the geographically weighted regression model were explored. The results showed that the traditional villages belonged to the same Hui cultural ecosystem and had similar climatic conditions, production, lifestyle and traditional customs, but their distribution showed uneven and significant spatial heterogeneity; the spatial distribution was affected by natural environment, social environment, economic environment, traffic environment and urban environment and other factors; the spatial distribution was discussed from regional perspective so as to provide suggestions for the overall development and differential protection of traditional villages in Huizhou Cultural Ecological Reserve.
In the context of rural revitalization strategy, the national traditional villages in Huizhou Cultural Ecological Reserve was taken as the research object, the spatial distribution characteristics and spatial heterogeneity of traditional villages with kernel density and spatial autocorrelation were analyzed, the factors influencing the spatial distribution of traditional villages with the geographically weighted regression model were explored. The results showed that the traditional villages belonged to the same Hui cultural ecosystem and had similar climatic conditions, production, lifestyle and traditional customs, but their distribution showed uneven and significant spatial heterogeneity; the spatial distribution was affected by natural environment, social environment, economic environment, traffic environment and urban environment and other factors; the spatial distribution was discussed from regional perspective so as to provide suggestions for the overall development and differential protection of traditional villages in Huizhou Cultural Ecological Reserve.
2024, 54(12): 114-120.
doi: 10.3724/j.gyjzG23070418
Abstract:
In order to solve the problems of fire-prone insulation walls and environmentally-unfriendly insulation layer materials at home and abroad, the paper designed a new composite wall made of fiber-reinforced alkali slag cementitious material as the page wall and straw board as the sandwich layer, and tested the mechanical and thermal properties of the new sandwich panel. The test results showed that: in terms of mechanical properties, the sandwich panel split and broke under the action of the axial load, the appropriate amount of connectors could effectively improve the bearing capacity of the sandwich panel, the wire mesh did not significantly improve the bearing capacity of the sandwich panel, and the formula for calculating the bearing capacity of the new sandwich panel was proposed. In terms of thermal performance, the thermal conductivity of the new sandwich panel was 0.21 W/(m·K), which was lower than that of concrete (1.28 W/(m·K)) and building brick (0.69 W/(m·K)). In summary, it can be seen that alkali slag cementitious material is a low-carbon solid waste cementitious material, which is expected to replace traditional cement-based materials. Its sandwich panel has excellent mechanical properties and good thermal insulation performance.
In order to solve the problems of fire-prone insulation walls and environmentally-unfriendly insulation layer materials at home and abroad, the paper designed a new composite wall made of fiber-reinforced alkali slag cementitious material as the page wall and straw board as the sandwich layer, and tested the mechanical and thermal properties of the new sandwich panel. The test results showed that: in terms of mechanical properties, the sandwich panel split and broke under the action of the axial load, the appropriate amount of connectors could effectively improve the bearing capacity of the sandwich panel, the wire mesh did not significantly improve the bearing capacity of the sandwich panel, and the formula for calculating the bearing capacity of the new sandwich panel was proposed. In terms of thermal performance, the thermal conductivity of the new sandwich panel was 0.21 W/(m·K), which was lower than that of concrete (1.28 W/(m·K)) and building brick (0.69 W/(m·K)). In summary, it can be seen that alkali slag cementitious material is a low-carbon solid waste cementitious material, which is expected to replace traditional cement-based materials. Its sandwich panel has excellent mechanical properties and good thermal insulation performance.
2024, 54(12): 121-127.
doi: 10.13204/j.gyjzG23010304
Abstract:
In order to study the calculation method for short-term maximum crack width of HRB400 large diameter reinforced concrete beams under normal service limit states, the short-term maximum crack width of four groups of five beams under various loads was measured, and the effects of the arrangements of large-diameter steel rebars on the inside and outside and the spacing of stirrups on the short-term maximum crack width were analyzed. Based on the measured results, suggestions for revising the short-term maximum crack width formula in the Code for Design of Concrete Structures (GB/T 50010—2010) were proposed. The results showed that when the stirrup spacing was 100 or 200 mm, the average crack spacing was close to the stirrup spacing, and the arrangements of large diameter steel rebars on the outside were more effective in reducing the short-term maximum crack width, which was about 91.5% of that arranged on the inside. The short-term maximum crack width calculated according to the specifications GB 50010—2010 was significantly larger than the experimental values, and the short-term maximum crack width calculation formula considering the effects of stirrup spacing and high stress work of the steel rebars agreed well with the measured values.
In order to study the calculation method for short-term maximum crack width of HRB400 large diameter reinforced concrete beams under normal service limit states, the short-term maximum crack width of four groups of five beams under various loads was measured, and the effects of the arrangements of large-diameter steel rebars on the inside and outside and the spacing of stirrups on the short-term maximum crack width were analyzed. Based on the measured results, suggestions for revising the short-term maximum crack width formula in the Code for Design of Concrete Structures (GB/T 50010—2010) were proposed. The results showed that when the stirrup spacing was 100 or 200 mm, the average crack spacing was close to the stirrup spacing, and the arrangements of large diameter steel rebars on the outside were more effective in reducing the short-term maximum crack width, which was about 91.5% of that arranged on the inside. The short-term maximum crack width calculated according to the specifications GB 50010—2010 was significantly larger than the experimental values, and the short-term maximum crack width calculation formula considering the effects of stirrup spacing and high stress work of the steel rebars agreed well with the measured values.
2024, 54(12): 128-137.
doi: 10.3724/j.gyjzG24012901
Abstract:
To quickly and accurately determine the flexural capacity of corroded reinforced concrete (RC) beams, an ensemble learning-based data-driven bearing capacity prediction model for corroded RC beams was studied. A database of experimental tests on the flexural bearing capacity of corroded RC beams was established based on existing literature. Based on the dataset, five types of ensemble learning algorithms, namely Random Forest (Random Forest), Adaptive Boosting (Adaboost), Gradient Boosting Decision Tree (GBDT), Limit Gradient Boosting Algorithm (XGBoost) and Light Gradient Boosting Algorithm (LightGBM), were used to establish prediction models. Grid search was employed to optimize the hyperparameters of the models to improve their generalization performance. The performance of different ensemble learning algorithms was compared, and the feature importance of input parameters was analyzed through the dataset. The mean absolute error (MAE), determination coefficient (R2) and root mean square error (RMSE) of the prediction models were compared to assess their rationality and accuracy. The analysis results indicated that the prediction model could effectively determine the key influencing factors of the flexural bearing capacity of corroded RC beams, namely the reinforcement ratio and the corrosion rate of the rebar. The model based on RandomForest performed the best, followed by the model based on XGBoost. The fitting degree of the prediction models on the training and test sets could reach over 90%.
To quickly and accurately determine the flexural capacity of corroded reinforced concrete (RC) beams, an ensemble learning-based data-driven bearing capacity prediction model for corroded RC beams was studied. A database of experimental tests on the flexural bearing capacity of corroded RC beams was established based on existing literature. Based on the dataset, five types of ensemble learning algorithms, namely Random Forest (Random Forest), Adaptive Boosting (Adaboost), Gradient Boosting Decision Tree (GBDT), Limit Gradient Boosting Algorithm (XGBoost) and Light Gradient Boosting Algorithm (LightGBM), were used to establish prediction models. Grid search was employed to optimize the hyperparameters of the models to improve their generalization performance. The performance of different ensemble learning algorithms was compared, and the feature importance of input parameters was analyzed through the dataset. The mean absolute error (MAE), determination coefficient (R2) and root mean square error (RMSE) of the prediction models were compared to assess their rationality and accuracy. The analysis results indicated that the prediction model could effectively determine the key influencing factors of the flexural bearing capacity of corroded RC beams, namely the reinforcement ratio and the corrosion rate of the rebar. The model based on RandomForest performed the best, followed by the model based on XGBoost. The fitting degree of the prediction models on the training and test sets could reach over 90%.
2024, 54(12): 138-148.
doi: 10.3724/j.gyjzG24081101
Abstract:
In order to study the bearing capacity relations between circular hollow section (CHS)-to-rectangular hollow section (RHS) T-joints and corresponding RHS joints, the refined finite element analysis models of two kinds of joints were established based on the bearing capacity test data of CHS-to-SHS T-joints, and the parameter analysis of the two types of joints was carried out. The effects of various dimensionless geometric parameters, including the ratio of brace diameter (or side length) to chord width β, the ratio of chord width to its wall thickness γ, the thickness ratio of brace to chord τ, the ratio of chord section height to width ξ, the properties of axial force in the brace, and axial force in the chord on the failure mode, stress distribution and bearing capacity of the joints were considered in the analysis, and the effects of various factors on the bearing capacity ratio of the two types of joints were obtained. The results showed that the dimensionless geometric parameters of the joints and the axial force properties of the brace had great influence on the bearing capacity of the joints, and the bearing capacity relations between the CHS-to-RHS T-joints and corresponding RHS joints were not a simple relations based on the ratio of the diameter of the circular brace to the side length of the square brace (i.e. π/4). Considering the influence of various factors on the bearing capacity ratio of CHS-to-RHS T-joints to RHS joints, a correction coefficient was proposed to calculate the bearing capacity of CHS-to-RHS T-joints based on the formula in Standard for Design of Steel Structure (GB 50017—2017), and its rationality was verified by experimental data.
In order to study the bearing capacity relations between circular hollow section (CHS)-to-rectangular hollow section (RHS) T-joints and corresponding RHS joints, the refined finite element analysis models of two kinds of joints were established based on the bearing capacity test data of CHS-to-SHS T-joints, and the parameter analysis of the two types of joints was carried out. The effects of various dimensionless geometric parameters, including the ratio of brace diameter (or side length) to chord width β, the ratio of chord width to its wall thickness γ, the thickness ratio of brace to chord τ, the ratio of chord section height to width ξ, the properties of axial force in the brace, and axial force in the chord on the failure mode, stress distribution and bearing capacity of the joints were considered in the analysis, and the effects of various factors on the bearing capacity ratio of the two types of joints were obtained. The results showed that the dimensionless geometric parameters of the joints and the axial force properties of the brace had great influence on the bearing capacity of the joints, and the bearing capacity relations between the CHS-to-RHS T-joints and corresponding RHS joints were not a simple relations based on the ratio of the diameter of the circular brace to the side length of the square brace (i.e. π/4). Considering the influence of various factors on the bearing capacity ratio of CHS-to-RHS T-joints to RHS joints, a correction coefficient was proposed to calculate the bearing capacity of CHS-to-RHS T-joints based on the formula in Standard for Design of Steel Structure (GB 50017—2017), and its rationality was verified by experimental data.
2024, 54(12): 149-155.
doi: 10.3724/j.gyjzG22112907
Abstract:
It is generally believed that column transverse stiffeners (also known as continuity plate) will be beneficial to the ductility of the welded beam-to-column connections and the AISC Seismic Provisions for Structural Steel Buildings recommend the use of continuity plates in the column unless tests show that the connection will work without them. The provisions are questionable as many T-shaped connection specimens with continuity plates show little ductility while connections without continuity plates exhibit satisfactory ductility. To further investigate the effects of continuity plates on the ductility of T-shaped connections, nonlinear analysis of welded beam-column connections under both monotonic loading and cyclic loading was performed in the paper. Several mechanical parameters were employed to assess the ductility of the connections. These quantities were sampled at weld-beam flange interface where the stress conditions were more critical at higher plastic rotation. The finite element analysis indicated that the plastic strain at the weld-beam tension flange interface was significantly increased due to the presence of continuity plates, which might cause a great reduction of ductility. Consequently, the analytical results demonstrated that the continuity plate located on both sides of column web was one of mains causes which contributed to brittle failure of T-shaped exterior connections under seismic loading. The conclusion drawn from the paper was verified against experimental data available in the literature.
It is generally believed that column transverse stiffeners (also known as continuity plate) will be beneficial to the ductility of the welded beam-to-column connections and the AISC Seismic Provisions for Structural Steel Buildings recommend the use of continuity plates in the column unless tests show that the connection will work without them. The provisions are questionable as many T-shaped connection specimens with continuity plates show little ductility while connections without continuity plates exhibit satisfactory ductility. To further investigate the effects of continuity plates on the ductility of T-shaped connections, nonlinear analysis of welded beam-column connections under both monotonic loading and cyclic loading was performed in the paper. Several mechanical parameters were employed to assess the ductility of the connections. These quantities were sampled at weld-beam flange interface where the stress conditions were more critical at higher plastic rotation. The finite element analysis indicated that the plastic strain at the weld-beam tension flange interface was significantly increased due to the presence of continuity plates, which might cause a great reduction of ductility. Consequently, the analytical results demonstrated that the continuity plate located on both sides of column web was one of mains causes which contributed to brittle failure of T-shaped exterior connections under seismic loading. The conclusion drawn from the paper was verified against experimental data available in the literature.
2024, 54(12): 156-167.
doi: 10.3724/j.gyjzG23122115
Abstract:
To study the performance of eccentrically-loaded concrete-filled double-skin elliptical steel tubular(CFDEST) short columns, the paper designed and carried out nine eccentric tests on CFDEST short columns, and established a refined numerical analysis model for CFDEST short columns considering elliptical cross-section characteristics. This model incorporated various factors such as eccentricity, hollow ratio, thickness ratio, and aspect ratio, elucidating their influence on the bearing capacity and ductility. Furthermore, it revealed the typical failure modes of CFDEST short columns under eccentric loading. The results showed that the failure modes of CFDEST short columns under eccentric compression include radial bulging of the compression-side outer steel tube, tension yielding of the tension-side outer steel tube, localized inward deformation of the inner steel tube, and concrete crushing failure. Additionally, the eccentric bearing capacity of these columns increased with the decrease of eccentricity, hollow ratio, and thickness ratio, as well as with the increase in steel and concrete strengths.
To study the performance of eccentrically-loaded concrete-filled double-skin elliptical steel tubular(CFDEST) short columns, the paper designed and carried out nine eccentric tests on CFDEST short columns, and established a refined numerical analysis model for CFDEST short columns considering elliptical cross-section characteristics. This model incorporated various factors such as eccentricity, hollow ratio, thickness ratio, and aspect ratio, elucidating their influence on the bearing capacity and ductility. Furthermore, it revealed the typical failure modes of CFDEST short columns under eccentric loading. The results showed that the failure modes of CFDEST short columns under eccentric compression include radial bulging of the compression-side outer steel tube, tension yielding of the tension-side outer steel tube, localized inward deformation of the inner steel tube, and concrete crushing failure. Additionally, the eccentric bearing capacity of these columns increased with the decrease of eccentricity, hollow ratio, and thickness ratio, as well as with the increase in steel and concrete strengths.
2024, 54(12): 168-176.
doi: 10.3724/j.gyjzG24050719
Abstract:
To explore the damage characteristics and dynamic response features of large thin-film tanks under projectile impact, this study designed two prototype cryogenic module target plates according to the BS-7777 standard. Leveraging a large-caliber impact loading device, experiments were conducted on the impact of both flexible and rigid projectiles on the target plates. The research results indicated that, unlike Ni9 tanks, the wooden plywood, foam board, and corrugated board in the insulation structure would be damaged under the impact of concrete conical plugs and scab fragments. In the insulation module, the plywood and foam board showed a greater energy absorption capacity. When the RC structural plate did not undergo perforating damage, the impact energy would be mainly absorbed by the RC plate, plywood, and foam board, while the thin-film corrugated board was less affected.
To explore the damage characteristics and dynamic response features of large thin-film tanks under projectile impact, this study designed two prototype cryogenic module target plates according to the BS-7777 standard. Leveraging a large-caliber impact loading device, experiments were conducted on the impact of both flexible and rigid projectiles on the target plates. The research results indicated that, unlike Ni9 tanks, the wooden plywood, foam board, and corrugated board in the insulation structure would be damaged under the impact of concrete conical plugs and scab fragments. In the insulation module, the plywood and foam board showed a greater energy absorption capacity. When the RC structural plate did not undergo perforating damage, the impact energy would be mainly absorbed by the RC plate, plywood, and foam board, while the thin-film corrugated board was less affected.
2024, 54(12): 177-185.
doi: 10.3724/j.gyjzG22110105
Abstract:
In order to make the parameter prediction equations in engineering applications such as seismic hazard analysis and seismic zoning reflect the time-frequency non-stationarity of ground motion, a new time-frequency parameter prediction model of ground motion is needed. Based on more than 30 earthquake records in the western United States, the complementary ensemble empirical mode decomposition method was used to calculate the time-varying power spectrum, the time-varying power spectrum was used to calculate six time-frequency parameters, and the prediction equation and neural network topology of time-frequency parameters with magnitude, distance and site conditions were established. The nonlinear least squares method was used to fit the coefficient values of the prediction equation, and the neural network prediction model was trained. The results showed that the total energy increased with the increase of magnitude and decreased with the increase of distance. The centroid and standard deviation of the spectrum, the centroid and standard deviation of the time, and the time-frequency correlation coefficients decreased with the increase of the magnitude, but varied with the increase of the distance. The established neural network time-frequency parameter prediction model showed strong generalization ability and could better predict the time-frequency parameters of ground motion.
In order to make the parameter prediction equations in engineering applications such as seismic hazard analysis and seismic zoning reflect the time-frequency non-stationarity of ground motion, a new time-frequency parameter prediction model of ground motion is needed. Based on more than 30 earthquake records in the western United States, the complementary ensemble empirical mode decomposition method was used to calculate the time-varying power spectrum, the time-varying power spectrum was used to calculate six time-frequency parameters, and the prediction equation and neural network topology of time-frequency parameters with magnitude, distance and site conditions were established. The nonlinear least squares method was used to fit the coefficient values of the prediction equation, and the neural network prediction model was trained. The results showed that the total energy increased with the increase of magnitude and decreased with the increase of distance. The centroid and standard deviation of the spectrum, the centroid and standard deviation of the time, and the time-frequency correlation coefficients decreased with the increase of the magnitude, but varied with the increase of the distance. The established neural network time-frequency parameter prediction model showed strong generalization ability and could better predict the time-frequency parameters of ground motion.
2024, 54(12): 186-193.
doi: 10.3724/j.gyjzG23071904
Abstract:
The Hardening Soil Small strain (HSS) model, which can consider the nonlinear performances of soil in the small strain range, has been widely used in the numerical analysis of geotechnical engineering. The HSS model parameters for Taizhou soft clay were elaborately calibrated by series of triaxial shear tests, resonant column tests, and standard consolidation tests. The proportional relations of parameters for soils derived from different layers were established, which was then compared with those of soft soil in other typical areas of China, and the rationality of the relations was verified. The empirical relations between the related perameters and initial void ratios of soil were determined further. The findings could be used to calculate the deformation caused by excavation in soft clay strata. The method could also provide reference to determining parameters of soil for the HSS model in other areas.
The Hardening Soil Small strain (HSS) model, which can consider the nonlinear performances of soil in the small strain range, has been widely used in the numerical analysis of geotechnical engineering. The HSS model parameters for Taizhou soft clay were elaborately calibrated by series of triaxial shear tests, resonant column tests, and standard consolidation tests. The proportional relations of parameters for soils derived from different layers were established, which was then compared with those of soft soil in other typical areas of China, and the rationality of the relations was verified. The empirical relations between the related perameters and initial void ratios of soil were determined further. The findings could be used to calculate the deformation caused by excavation in soft clay strata. The method could also provide reference to determining parameters of soil for the HSS model in other areas.
2024, 54(12): 194-203.
doi: 10.3724/j.gyjzG22101715
Abstract:
Freeze-thaw cycles are one of the important factors causing mechanical damage of soil. To study the strength characteristics of fluidized solidifiable soil integrated by collapsible loess and red sandstone experienced freeze-thaw cycles, mechanical and scanning electron microscope tests were conducted on the fluidized solidifiable soil experienced different rounds of freeze-thaw cycles by indoor tests, and the variable regularities of physical and mechanical parameters and energy dissipation mechanisms of the fluidized solidifiable soil with different mix proportions experienced freeze-thaw cycles were analyzed. The results indicated that the red sandstone content, water content and cement content increased with the rounds of freeze-thaw cycles and had different effects on compressive strength. To mix red sandstone could effectively improve the compressive strength of fluidized solidifiable soil. The relation between compressive strength and the rounds of freeze-thaw cycles complied with a decreasing exponential function relation. The main mechanical indexes, including elastic moduli, masses, cohesion, internal friction angles and strain energy densities, decreased with the increase in the red sandstone content and the rounds of freeze-thaw cycles. Combining with the results by SEM, the variable regularity of microstructure of fluidized solidifiable soil damage by freeze-thaw cycles was analyzed. That freeze-thaw cycles could change the microstructure constructed by red sandstone particles was pointed out, and thus the mechanism of energy dissipation of fluidized solidifiable soil experienced freeze-thaw cycles was clarified.
Freeze-thaw cycles are one of the important factors causing mechanical damage of soil. To study the strength characteristics of fluidized solidifiable soil integrated by collapsible loess and red sandstone experienced freeze-thaw cycles, mechanical and scanning electron microscope tests were conducted on the fluidized solidifiable soil experienced different rounds of freeze-thaw cycles by indoor tests, and the variable regularities of physical and mechanical parameters and energy dissipation mechanisms of the fluidized solidifiable soil with different mix proportions experienced freeze-thaw cycles were analyzed. The results indicated that the red sandstone content, water content and cement content increased with the rounds of freeze-thaw cycles and had different effects on compressive strength. To mix red sandstone could effectively improve the compressive strength of fluidized solidifiable soil. The relation between compressive strength and the rounds of freeze-thaw cycles complied with a decreasing exponential function relation. The main mechanical indexes, including elastic moduli, masses, cohesion, internal friction angles and strain energy densities, decreased with the increase in the red sandstone content and the rounds of freeze-thaw cycles. Combining with the results by SEM, the variable regularity of microstructure of fluidized solidifiable soil damage by freeze-thaw cycles was analyzed. That freeze-thaw cycles could change the microstructure constructed by red sandstone particles was pointed out, and thus the mechanism of energy dissipation of fluidized solidifiable soil experienced freeze-thaw cycles was clarified.
2024, 54(12): 204-213.
doi: 10.3724/j.gyjzG23032203
Abstract:
To demonstrate the interactive mechanical mechanisms between long and short piles in the long-short pile composite support system in the soil-rock composite stratum, according to the force analysis on long and short piles in the soil-rock stratum, the calculation methods for the forces and deformation of long and short piles were proposed respectively:When the rock layer under the soil layer was intact, the forces acting on short piles should meet the stability requirements of the foundation excavation in the soil layer, and the long piles were only used as a safety reserve. Therefore, the long and short piles in the soil layer could be simplified as elastically supported continuous beams. When there was a weak structural plane in the rock stratum, the long pile must meet the stability requirements of the foundation excavation in the rock stratum, and the lateral earth pressure of long piles was obtained according to the force requirements of sliders. Simultaneously, combined with the arrangement form of supports, the long pile was also simplified as the elastically supported continuous beam. Eventually, the calculation methods of long and short piles in two working conditions were given, and based on a real engineering project, the analytical solutions by the proposed methods were compared with numerical solutions by the finite element method to verified the correctness of the proposed. The results indicated that if the long-short pile support system in the soil-rock composite stratum was divided into two types of support system for foundation excavation in the soil layer and rock strata and the long and short piles were simplified into elastically supported continuous beams,the analytical solutions of the support system were basically consistent with the numerical calculation results, and the results were basically reasonable.
To demonstrate the interactive mechanical mechanisms between long and short piles in the long-short pile composite support system in the soil-rock composite stratum, according to the force analysis on long and short piles in the soil-rock stratum, the calculation methods for the forces and deformation of long and short piles were proposed respectively:When the rock layer under the soil layer was intact, the forces acting on short piles should meet the stability requirements of the foundation excavation in the soil layer, and the long piles were only used as a safety reserve. Therefore, the long and short piles in the soil layer could be simplified as elastically supported continuous beams. When there was a weak structural plane in the rock stratum, the long pile must meet the stability requirements of the foundation excavation in the rock stratum, and the lateral earth pressure of long piles was obtained according to the force requirements of sliders. Simultaneously, combined with the arrangement form of supports, the long pile was also simplified as the elastically supported continuous beam. Eventually, the calculation methods of long and short piles in two working conditions were given, and based on a real engineering project, the analytical solutions by the proposed methods were compared with numerical solutions by the finite element method to verified the correctness of the proposed. The results indicated that if the long-short pile support system in the soil-rock composite stratum was divided into two types of support system for foundation excavation in the soil layer and rock strata and the long and short piles were simplified into elastically supported continuous beams,the analytical solutions of the support system were basically consistent with the numerical calculation results, and the results were basically reasonable.
2024, 54(12): 214-220.
doi: 10.3724/j.gyjzG23090403
Abstract:
To quickly evaluate the stability of soil slopes under earthquake action is currently a hot topic in the civil engineering circle. Traditionally, stability charts and the Newmark model were used to quickly evaluate the seismic stability of soil slopes. The safety factor method was used in the most studies on the stability charts to evaluate slope seismic stability. In addition,as the stability charts for permanent displacement on the basis of Newmark Model adopted a hypothesis of infinite plane, the calculations usually were larger than the actual values. Therefore, a new method for quickly calculating the critical acceleration of soil slopes was proposed, which overcome the limitations of stability charts and the Newmark model. Based on the Mohr-Coulomb strength criterion, the numerical model for generalized soil slope was constructed by the finite element limit analysis method. According to the calculation results on 864 cases, a critical acceleration chart for soil slopes was drawn. Through two-step regression analysis, a function expression between critical acceleration of soil slopes and the slope parameters was established, and the method proposed in the paper was compared with the Newmark model and numerical solutions. The results showed that in comparisons with the solutions by the Newmark model, the calculational accuracy of solutions by the proposed method was closer to that by the numerical solutions. The necessity of developing the proposed method was reflected by comparing the quasi-static method with the permanent displacement method. The established evaluation method of permanent displacement for soil slopes was reliable and simple, and could be used for stability evaluation in the initial design stage, providing reference to subsequent seismic design of soil slopes.
To quickly evaluate the stability of soil slopes under earthquake action is currently a hot topic in the civil engineering circle. Traditionally, stability charts and the Newmark model were used to quickly evaluate the seismic stability of soil slopes. The safety factor method was used in the most studies on the stability charts to evaluate slope seismic stability. In addition,as the stability charts for permanent displacement on the basis of Newmark Model adopted a hypothesis of infinite plane, the calculations usually were larger than the actual values. Therefore, a new method for quickly calculating the critical acceleration of soil slopes was proposed, which overcome the limitations of stability charts and the Newmark model. Based on the Mohr-Coulomb strength criterion, the numerical model for generalized soil slope was constructed by the finite element limit analysis method. According to the calculation results on 864 cases, a critical acceleration chart for soil slopes was drawn. Through two-step regression analysis, a function expression between critical acceleration of soil slopes and the slope parameters was established, and the method proposed in the paper was compared with the Newmark model and numerical solutions. The results showed that in comparisons with the solutions by the Newmark model, the calculational accuracy of solutions by the proposed method was closer to that by the numerical solutions. The necessity of developing the proposed method was reflected by comparing the quasi-static method with the permanent displacement method. The established evaluation method of permanent displacement for soil slopes was reliable and simple, and could be used for stability evaluation in the initial design stage, providing reference to subsequent seismic design of soil slopes.
2024, 54(12): 221-228.
doi: 10.3724/j.gyjzG22120208
Abstract:
The traditional vacuum preloading method used to treat waste construction slurry. As there were some problems involving clogging and deformation of drain boards and vacuum attenuation in the traditional vacuum preloading treatment, a method of vacuum preloading with Rib-prefabricated horizontal drains (RPHD) was proposed to treat waste construction slurry. Five groups of indoor vacuum preloading model tests were performed to measure the pore water pressure, water discharge, vacuum degree and surface settlement of soil specimens during the reinforcement processes. Simultaneously, the filter membranes of drainage boards were scanned with electron microscopes to analyze the effect of rib width ratios of RPHD on consolidation of waste construction slurry. The test results indicated that RPHD could improve the vacuum transfer efficiency and weaken the clogging of filter membranes of drainage boards during consolidation of waste construction slurry by the vacuum preloading method. A rib width ratio of 0.5 for ribbed drainage boards achieved the optimal performance of water discharge. The mean moisture content and the vane shear strength of treated soil specimens were respectively 38.51% and 32.38 kPa after reinforcement, which effectively improved the strength of reinforced soil. Analyzing the microstructure of filter membranes of drainage boards, it was found that the rib width ratio directly related the clogging of the ribbed drainage boards in the same width of drainage boards, and rib width ratio of 0.5 could fully play the drainage performance of RPHD.
The traditional vacuum preloading method used to treat waste construction slurry. As there were some problems involving clogging and deformation of drain boards and vacuum attenuation in the traditional vacuum preloading treatment, a method of vacuum preloading with Rib-prefabricated horizontal drains (RPHD) was proposed to treat waste construction slurry. Five groups of indoor vacuum preloading model tests were performed to measure the pore water pressure, water discharge, vacuum degree and surface settlement of soil specimens during the reinforcement processes. Simultaneously, the filter membranes of drainage boards were scanned with electron microscopes to analyze the effect of rib width ratios of RPHD on consolidation of waste construction slurry. The test results indicated that RPHD could improve the vacuum transfer efficiency and weaken the clogging of filter membranes of drainage boards during consolidation of waste construction slurry by the vacuum preloading method. A rib width ratio of 0.5 for ribbed drainage boards achieved the optimal performance of water discharge. The mean moisture content and the vane shear strength of treated soil specimens were respectively 38.51% and 32.38 kPa after reinforcement, which effectively improved the strength of reinforced soil. Analyzing the microstructure of filter membranes of drainage boards, it was found that the rib width ratio directly related the clogging of the ribbed drainage boards in the same width of drainage boards, and rib width ratio of 0.5 could fully play the drainage performance of RPHD.
2024, 54(12): 229-237.
doi: 10.3724/j.gyjzG21122303
Abstract:
Orthotropic steel decks have been widely used in steel bridges due to their small volume weigh, high strength and good applicability of assembly fabrication. The asphalt pavement laying on the orthotropic steel deck can effectively disperse the vehicle wheel loads, and enhance the stiffness of orthotropic steel decks, and release fatigue damage of deck-to-rib welded joints of orthotropic steel decks. However, the effects of asphalt pavement on orthotropic steel decks were affected by the temperature and loading frequency. To determine the coupling effect mechanisms of pavement characteristics, based on the dynamic stress-strain relations, the effects of temperature and dynamic properties on the fatigue damage of deck-to-rib welded joints were firstly analyzed and quantified. The hourly random traffic flow model in a day was established by using the real traffic flow data, then the coupling effects of temperature and dynamic loads on the fatigue damage characteristics of asphalt pavement layers were quantified. The results indicated that when other boundary conditions were the same, the fatigue damage of deck-to-rib welded joints in summer was about 3.7 times as the fatigue damage in winter. The fatigue life assessment without consideration of pavement properties was underestimated. The fatigue life would reduce from 54 years to 47 year after considering the pavement properties.
Orthotropic steel decks have been widely used in steel bridges due to their small volume weigh, high strength and good applicability of assembly fabrication. The asphalt pavement laying on the orthotropic steel deck can effectively disperse the vehicle wheel loads, and enhance the stiffness of orthotropic steel decks, and release fatigue damage of deck-to-rib welded joints of orthotropic steel decks. However, the effects of asphalt pavement on orthotropic steel decks were affected by the temperature and loading frequency. To determine the coupling effect mechanisms of pavement characteristics, based on the dynamic stress-strain relations, the effects of temperature and dynamic properties on the fatigue damage of deck-to-rib welded joints were firstly analyzed and quantified. The hourly random traffic flow model in a day was established by using the real traffic flow data, then the coupling effects of temperature and dynamic loads on the fatigue damage characteristics of asphalt pavement layers were quantified. The results indicated that when other boundary conditions were the same, the fatigue damage of deck-to-rib welded joints in summer was about 3.7 times as the fatigue damage in winter. The fatigue life assessment without consideration of pavement properties was underestimated. The fatigue life would reduce from 54 years to 47 year after considering the pavement properties.
2024, 54(12): 238-245.
doi: 10.3724/j.gyjzG24091101
Abstract:
Carbon fiber reinforced polymer composites (CFRP) are candidates for prestressing tendons due to their advantages over rebars, such as lighter weight, higher strength, and resistance to corrosion, fatigue, and creep. However, the transverse shear and bending properties of pultruded CFRP tendons are insufficient for their widespread application in prestressed structures. Liquid crystal polyarylate (LCP) fibers, known for their excellent mechanical properties and dimensional stability, particularly in shear and cut resistance, are used in various industries including protective clothing, sports equipment, and aerospace. This study aimed to enhance the shear and flexural properties of pultruded CFRP tendons by incorporating braided LCP fibers in the outer layer, thereby improving their suitability for prestressed structures. Shear and three-point bending tests were conducted on CFRP tendons with different fiber volumes (55% and 65%) reinforced with braided LCP fibers. The goal was to assess the impact of the LCP material and the pultrusion-braiding process on the shear and bending characteristics of CFRP tendons. The findings indicate that the braided LCP fibers significantly improved the shear and flexural strength and ductility of pultruded CFRP bars. The shear strengths of the braided CFRP tendons with 55% and 65% fiber content increased by 54.6% and 55.0%, respectively, and the shear peak deformations increased by 10.4% and 38.5%, respectively. Similarly, the flexural strengths increased by 26.6% and 14.9%, and the bending peak deformations increased by 13.1% and 38.8%, respectively. In general, the performance enhancement achieved through braiding with an increase in the volume content of CFRP reinforcement fibers. This research offers valuable insights for the use of LCP-fiber-braided reinforced CFRP tendons in prestressed concrete applications.
Carbon fiber reinforced polymer composites (CFRP) are candidates for prestressing tendons due to their advantages over rebars, such as lighter weight, higher strength, and resistance to corrosion, fatigue, and creep. However, the transverse shear and bending properties of pultruded CFRP tendons are insufficient for their widespread application in prestressed structures. Liquid crystal polyarylate (LCP) fibers, known for their excellent mechanical properties and dimensional stability, particularly in shear and cut resistance, are used in various industries including protective clothing, sports equipment, and aerospace. This study aimed to enhance the shear and flexural properties of pultruded CFRP tendons by incorporating braided LCP fibers in the outer layer, thereby improving their suitability for prestressed structures. Shear and three-point bending tests were conducted on CFRP tendons with different fiber volumes (55% and 65%) reinforced with braided LCP fibers. The goal was to assess the impact of the LCP material and the pultrusion-braiding process on the shear and bending characteristics of CFRP tendons. The findings indicate that the braided LCP fibers significantly improved the shear and flexural strength and ductility of pultruded CFRP bars. The shear strengths of the braided CFRP tendons with 55% and 65% fiber content increased by 54.6% and 55.0%, respectively, and the shear peak deformations increased by 10.4% and 38.5%, respectively. Similarly, the flexural strengths increased by 26.6% and 14.9%, and the bending peak deformations increased by 13.1% and 38.8%, respectively. In general, the performance enhancement achieved through braiding with an increase in the volume content of CFRP reinforcement fibers. This research offers valuable insights for the use of LCP-fiber-braided reinforced CFRP tendons in prestressed concrete applications.
2024, 54(12): 246-253.
doi: 10.3724/j.gyjzG23120709
Abstract:
For investigating the size effects of brick masonry columns and reinforced brick masonry columns with angle steel, axial compression tests were conducted on 12 square cross-section unreinforced and reinforced brick masonry columns with different sizes. The failure characteristics, load-displacement curves, curves of average stress of cross-section versus displacement, axial compressive strength and bearing capacity, nominal peak strain, and other characteristics of the specimens were analyzed. The results showed that, the cross-sectional area of the unreinforced brick masonry column had little effect on the axial compressive strength at height-thickness ratio of 3, but the nominal peak strain increased and then decreased with the increase of the cross-sectional area. The outer angle steel reinforcement could greatly improve the axial compressive load-bearing and deformation capacity of the brick masonry column, but the cross-sectional size had an impact on the reinforcement effect. The reinforcement effect of angle steel on small-sized specimens was better at the same height-thickness ratio, steel content of sections, and volume-reinforcement ratio. The nominal peak strain of the reinforced masonry columns decreased with the increase of cross-sectional area. Finally, the method of calculating the bearing capacity of brick masonry columns reinforced with angle steel was proposed.
For investigating the size effects of brick masonry columns and reinforced brick masonry columns with angle steel, axial compression tests were conducted on 12 square cross-section unreinforced and reinforced brick masonry columns with different sizes. The failure characteristics, load-displacement curves, curves of average stress of cross-section versus displacement, axial compressive strength and bearing capacity, nominal peak strain, and other characteristics of the specimens were analyzed. The results showed that, the cross-sectional area of the unreinforced brick masonry column had little effect on the axial compressive strength at height-thickness ratio of 3, but the nominal peak strain increased and then decreased with the increase of the cross-sectional area. The outer angle steel reinforcement could greatly improve the axial compressive load-bearing and deformation capacity of the brick masonry column, but the cross-sectional size had an impact on the reinforcement effect. The reinforcement effect of angle steel on small-sized specimens was better at the same height-thickness ratio, steel content of sections, and volume-reinforcement ratio. The nominal peak strain of the reinforced masonry columns decreased with the increase of cross-sectional area. Finally, the method of calculating the bearing capacity of brick masonry columns reinforced with angle steel was proposed.
2024, 54(12): 254-260.
doi: 10.3724/j.gyjzG23092603
Abstract:
Based on the experiments of concrete floor slabs strengthened by embedded reinforcement method, combined with numerical simulations and analysis, the study explored the mechanical properties of reinforced concrete floor slabs under bending conditions. The feasibility of reinforcing floor slabs using the embedded reinforcement method was validated. Additionally, the study investigated the influence of different groove widths, embedding materials, original concrete strength grades, and reinforcement configurations on the mechanical properties of reinforced concrete slab elements.The results demonstrated that the combined action of rebars embedded using the embedded reinfocement method and concrete could achieve the same effect as embedded rebars. The size of the groove width, original concrete strength grade and the end configurations had minimal impact on the reinforcement effect of embedded reinforcement method. When high-strength grouting material was used as the embedding material, the bearing performance became closer to that of ordinary components, while offering economic and durable advantages compared to epoxy materials.
Based on the experiments of concrete floor slabs strengthened by embedded reinforcement method, combined with numerical simulations and analysis, the study explored the mechanical properties of reinforced concrete floor slabs under bending conditions. The feasibility of reinforcing floor slabs using the embedded reinforcement method was validated. Additionally, the study investigated the influence of different groove widths, embedding materials, original concrete strength grades, and reinforcement configurations on the mechanical properties of reinforced concrete slab elements.The results demonstrated that the combined action of rebars embedded using the embedded reinfocement method and concrete could achieve the same effect as embedded rebars. The size of the groove width, original concrete strength grade and the end configurations had minimal impact on the reinforcement effect of embedded reinforcement method. When high-strength grouting material was used as the embedding material, the bearing performance became closer to that of ordinary components, while offering economic and durable advantages compared to epoxy materials.
