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2024 Vol. 54, No. 9
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2024, 54(9): 1-9.
doi: 10.3724/j.gyjzG24031816
Abstract:
The Microbially Induced Calcite Precipitation (MICP) grouting technique was conducted to cement strongly weathered granular granite, and the influence on physical and mechanical properties and disintegration characteristics of specimens after being cemented with different cementing solvents, cementitious concentrations, and rounds of grouting cycles in the seawater environment was analyzed. The results showed the physical and mechanical properties and disintegration resistance of the strongly weathered granular granite were distinctly improved after being cured by MICP; meanwhile, when seawater was used as cementing solvents, the cementitious effect for specimens was better than that in freshwater, and its unconfined compressive strength, calcium carbonate content, dry density and disintegration resistance were higher than those in freshwater. In addition, with the increase in the cementitions concentration, unconfined compressive strength, calcium carbonate content and dry density of specimens tended to first increasing and then decreasing, simultaneously, the final disintegration ratios of specimens tended to first decreasing and then increasing. The optimum cementitious concentration was 0.75 mol/L. The calcium carbonate content and unconfined compressive strength of cured specimens increased with the increase in rounds of grouting cycles and the final disintegration ratios were gradually decreased in the optimum cementitious concentration solution; the maximum value of unconfined compressive strength of specimens after 4 rounds of grouting cycles was up to 9.38 MPa, and the disintegration ratio was only 1.5%.
The Microbially Induced Calcite Precipitation (MICP) grouting technique was conducted to cement strongly weathered granular granite, and the influence on physical and mechanical properties and disintegration characteristics of specimens after being cemented with different cementing solvents, cementitious concentrations, and rounds of grouting cycles in the seawater environment was analyzed. The results showed the physical and mechanical properties and disintegration resistance of the strongly weathered granular granite were distinctly improved after being cured by MICP; meanwhile, when seawater was used as cementing solvents, the cementitious effect for specimens was better than that in freshwater, and its unconfined compressive strength, calcium carbonate content, dry density and disintegration resistance were higher than those in freshwater. In addition, with the increase in the cementitions concentration, unconfined compressive strength, calcium carbonate content and dry density of specimens tended to first increasing and then decreasing, simultaneously, the final disintegration ratios of specimens tended to first decreasing and then increasing. The optimum cementitious concentration was 0.75 mol/L. The calcium carbonate content and unconfined compressive strength of cured specimens increased with the increase in rounds of grouting cycles and the final disintegration ratios were gradually decreased in the optimum cementitious concentration solution; the maximum value of unconfined compressive strength of specimens after 4 rounds of grouting cycles was up to 9.38 MPa, and the disintegration ratio was only 1.5%.
2024, 54(9): 10-18.
doi: 10.3724/j.gyjzG22112006
Abstract:
Severe soil erosion in arsenic sandstone areas not only reduces the local vegetation and deteriorates the ecological environment, but also the debris formed by weathered arsenic sandstone constantly migrates into the Yellow River and other rivers, becoming the main source of coarse sediment in the middle and upper reaches of the Yellow River. Therefore, the microbial-induced calcium precipitation technique was applied to arsenic sandstone and its weathered soil to cure and improve their water disintegration. On the basis of the mineralization and cementation for weathered soil of arsenic sandstone, macroscopic mechanical properties tests combined with microstructural tests of pore sizes were conducted to study the property changes and deteriorative mechanisms of the weathered soil after freeze-thaw cycles in the salt corrosion environment. The test results indicated that the strength of the soil-mineralized specimens decreased after freeze-thaw cycles in the salt corrosion environment, and the internal pores changed continuously with different sizes of pores developing or transforming into each other. The attenuation in the intensity properties of soil-mineralized specimens in the salt corrosion environment was greater than that in the deionized water environment, and the attenuation in the intensity properties of soil-mineralized specimens in the composite salt environment was greater than that in the single salt environment. After five rounds of freeze-thaw cycles in the mixed salt environment, the soil-mineralized specimens were damaged and the freeze-thaw resistance was reduced to 0.125 6, and simultaneously, the freeze-thaw resistance of the soil-mineralized specimens in the deionized water environment was reduced to 0.416 7 in the same period, a difference was nearly three times; the porosity of the soil-mineralized specimens increased as a result of the frost heave action, wet-dry action and the destruction of inter-particle connections, and the cumulative ratio of change in different types of pores increased with the round of freeze-thaw cycles. The reduction in strength of the soil-mineralized specimens was actually a macroscopic reflection of the reduction in the mechanical properties of the internal skeleton. The macroscopic strength dropped constantly reducing with the resistance to frost heaving of pore skeleton of the soil-mineralized specimens. As the potential deformation resistance of soil-mineralized specimens was released, the volume expansion coefficient and pore shrinkage coefficient of ice continued to increase. Due to the frequent internal bonding damage and weak deformation ability of the pore skeleton, the mixed salt had the highest expansion coefficient and the lowest shrinkage coefficient.
Severe soil erosion in arsenic sandstone areas not only reduces the local vegetation and deteriorates the ecological environment, but also the debris formed by weathered arsenic sandstone constantly migrates into the Yellow River and other rivers, becoming the main source of coarse sediment in the middle and upper reaches of the Yellow River. Therefore, the microbial-induced calcium precipitation technique was applied to arsenic sandstone and its weathered soil to cure and improve their water disintegration. On the basis of the mineralization and cementation for weathered soil of arsenic sandstone, macroscopic mechanical properties tests combined with microstructural tests of pore sizes were conducted to study the property changes and deteriorative mechanisms of the weathered soil after freeze-thaw cycles in the salt corrosion environment. The test results indicated that the strength of the soil-mineralized specimens decreased after freeze-thaw cycles in the salt corrosion environment, and the internal pores changed continuously with different sizes of pores developing or transforming into each other. The attenuation in the intensity properties of soil-mineralized specimens in the salt corrosion environment was greater than that in the deionized water environment, and the attenuation in the intensity properties of soil-mineralized specimens in the composite salt environment was greater than that in the single salt environment. After five rounds of freeze-thaw cycles in the mixed salt environment, the soil-mineralized specimens were damaged and the freeze-thaw resistance was reduced to 0.125 6, and simultaneously, the freeze-thaw resistance of the soil-mineralized specimens in the deionized water environment was reduced to 0.416 7 in the same period, a difference was nearly three times; the porosity of the soil-mineralized specimens increased as a result of the frost heave action, wet-dry action and the destruction of inter-particle connections, and the cumulative ratio of change in different types of pores increased with the round of freeze-thaw cycles. The reduction in strength of the soil-mineralized specimens was actually a macroscopic reflection of the reduction in the mechanical properties of the internal skeleton. The macroscopic strength dropped constantly reducing with the resistance to frost heaving of pore skeleton of the soil-mineralized specimens. As the potential deformation resistance of soil-mineralized specimens was released, the volume expansion coefficient and pore shrinkage coefficient of ice continued to increase. Due to the frequent internal bonding damage and weak deformation ability of the pore skeleton, the mixed salt had the highest expansion coefficient and the lowest shrinkage coefficient.
2024, 54(9): 19-25.
doi: 10.3724/j.gyjzG23031311
Abstract:
Microbial-induced calcium carbonate precipitation (MICP) is a new reinforcement and remediation method for contaminated soil, which also provides a new direction to cement drill cuttings. Based on the analysis of the cemented body of highly active magnesium oxide gel material, an in-depth study on synergistic cementation for drill cuttings by microorganisms and magnesium oxide was conducted, and a new treatment methods for drill cuttings was presented. The speciemens cemented by microorganisms combined with magenesium oxide were tested with FTIRs, XRDs and SEMs, and the results indicated that rosette hydro-magnesite (4MgCO3·Mg(OH)2·4H2O) and acicular nesquehonite (MgCO3·3H2O) were yielded in synergy of microorganism and magnesium oxide. The loose particles were cemented into the well-structured cemented body by the dense carbonate network which was the cementitious mechanism of the synergistic effect of microorganism and magnesium oxide. The analysis of the factors affecting the strength of the cured body showed that the development trend of the strength of the cured body was positively correlated with microbial concentrations, active magnesium oxide concentrations, and curing times, and negatively correlated with the water content and the urea concentration.
Microbial-induced calcium carbonate precipitation (MICP) is a new reinforcement and remediation method for contaminated soil, which also provides a new direction to cement drill cuttings. Based on the analysis of the cemented body of highly active magnesium oxide gel material, an in-depth study on synergistic cementation for drill cuttings by microorganisms and magnesium oxide was conducted, and a new treatment methods for drill cuttings was presented. The speciemens cemented by microorganisms combined with magenesium oxide were tested with FTIRs, XRDs and SEMs, and the results indicated that rosette hydro-magnesite (4MgCO3·Mg(OH)2·4H2O) and acicular nesquehonite (MgCO3·3H2O) were yielded in synergy of microorganism and magnesium oxide. The loose particles were cemented into the well-structured cemented body by the dense carbonate network which was the cementitious mechanism of the synergistic effect of microorganism and magnesium oxide. The analysis of the factors affecting the strength of the cured body showed that the development trend of the strength of the cured body was positively correlated with microbial concentrations, active magnesium oxide concentrations, and curing times, and negatively correlated with the water content and the urea concentration.
Experimental Research on Microbial Grouting Effect on Strength of Granite Residual Soil in Guangdong
2024, 54(9): 26-31.
doi: 10.3724/j.gyjzG23082602
Abstract:
Be aimed at the issue that granite residual soil slopes are prone to landslide in heavy rainfall in Guangdong, the use of microbial induced calcium carbonate precipitation technique to improve the mechanical properties of granite residual soil was performed. The specimens of granite residual soil with a average particle diameter of 0.179 mm and 1.547 mm respectively, taken from Zhaoqing and Qingyuan in Guangdong, were grounted by MICP and tested their mechanisal properties before and after being grouted. The results showed that both types of granite residual soil had been successfully cemented, and the particle sizes and composition of soil influenced the cemented effect by MICP. Their uniaxial unconfined compressive strength reached 2.74 MPa and 3.36 MPa respectively. Triaxial compression tests were also conducted, and the test result indicated that the cohesion of specimens from both sites were improved.
Be aimed at the issue that granite residual soil slopes are prone to landslide in heavy rainfall in Guangdong, the use of microbial induced calcium carbonate precipitation technique to improve the mechanical properties of granite residual soil was performed. The specimens of granite residual soil with a average particle diameter of 0.179 mm and 1.547 mm respectively, taken from Zhaoqing and Qingyuan in Guangdong, were grounted by MICP and tested their mechanisal properties before and after being grouted. The results showed that both types of granite residual soil had been successfully cemented, and the particle sizes and composition of soil influenced the cemented effect by MICP. Their uniaxial unconfined compressive strength reached 2.74 MPa and 3.36 MPa respectively. Triaxial compression tests were also conducted, and the test result indicated that the cohesion of specimens from both sites were improved.
2024, 54(9): 32-42.
doi: 10.3724/j.gyjzG23031904
Abstract:
With the rapid development of industry, the problem of soil contaminated by heavy metals, represented by Zn, has been becoming more and more prominent, and it is important to study the treatment methods and cured effects on Zn-contaminated silt. Based on the microbial induced calcium carbonate precipitation (MICP) technique, a series of indoor experiments on microbial-cemented Zn-contaminated soil were conducted to reveal the mechanism of microbial cementation of Zn-contaminated soil from the perspective of microstructural evolution. The results showed that microbial mineralization significantly improved the mechanical properties of Zn-contaminated soil, and reduced the permeability coefficient of Zn-contaminated soil by an order of magnitude, significantly reduced the leaching concentration of Zn ions and the percentage of the exchangeable Zn content. It mainly might produce calcite crystals with colloidal properties during the microbial mineralization process, and zinc ions were fixed and tranfered to zinc carbonate, which made the microbial-cemented Zn-contaminated soil achieve the dual objectives of contaminant control and strength enhancement simultaneously. The microbial cure and stabilization of Zn-contaminated silt were most effective when the cementitious solution concentration was 1 mol/L, the cementitious solution ratio (CaCl2∶Urea) was 1∶2, and the curing age was 28 d.
With the rapid development of industry, the problem of soil contaminated by heavy metals, represented by Zn, has been becoming more and more prominent, and it is important to study the treatment methods and cured effects on Zn-contaminated silt. Based on the microbial induced calcium carbonate precipitation (MICP) technique, a series of indoor experiments on microbial-cemented Zn-contaminated soil were conducted to reveal the mechanism of microbial cementation of Zn-contaminated soil from the perspective of microstructural evolution. The results showed that microbial mineralization significantly improved the mechanical properties of Zn-contaminated soil, and reduced the permeability coefficient of Zn-contaminated soil by an order of magnitude, significantly reduced the leaching concentration of Zn ions and the percentage of the exchangeable Zn content. It mainly might produce calcite crystals with colloidal properties during the microbial mineralization process, and zinc ions were fixed and tranfered to zinc carbonate, which made the microbial-cemented Zn-contaminated soil achieve the dual objectives of contaminant control and strength enhancement simultaneously. The microbial cure and stabilization of Zn-contaminated silt were most effective when the cementitious solution concentration was 1 mol/L, the cementitious solution ratio (CaCl2∶Urea) was 1∶2, and the curing age was 28 d.
2024, 54(9): 43-50.
doi: 10.3724/j.gyjzG23080412
Abstract:
It is of direct significance to carry out quantitative research on the morphology of microbial cemented constructional waste soil for analyzing the effect of soil improvement. The morphological indexes such as rectangularity, shape indexes, angularity and overall contour coefficients could directly and quantitatively characterize the soil structure, which are important parameters to reflect the stability and cured effect of soil. The apparent scan of the microbial cemented soil by CT was conducted, and the geometric shape parameters (the length, perimeter, area, external rectangular area, and equivalent elliptical perimeter) of cemented soil particles were obtained by the digital image processing technique. The geometric shape coefficient,namely morphological index, was calculated statistically, so as to quantitatively characterize the microbial cemented soil structure and analyze the correlation between geometric shape coefficient and gradation. The results showed: with the increase in the scale of the structure, the shape index and the angularity of the microbial cemented constructional waste soil increased as a whole, the rectangularity and the overall contour coefficient decreased, the structure shape was more irregular. The geometric shape coefficient had a good correlation with the particle gradation of cemented construction waste soil. It was because that the calcium carbonate induced by microbial precipitates covered and accumulated on the surface of the soil particles, increasing the particle size of the waste soil and making the particle surface rougher, and then changing the primary characteristic parameters, affecting the morphological indexes.
It is of direct significance to carry out quantitative research on the morphology of microbial cemented constructional waste soil for analyzing the effect of soil improvement. The morphological indexes such as rectangularity, shape indexes, angularity and overall contour coefficients could directly and quantitatively characterize the soil structure, which are important parameters to reflect the stability and cured effect of soil. The apparent scan of the microbial cemented soil by CT was conducted, and the geometric shape parameters (the length, perimeter, area, external rectangular area, and equivalent elliptical perimeter) of cemented soil particles were obtained by the digital image processing technique. The geometric shape coefficient,namely morphological index, was calculated statistically, so as to quantitatively characterize the microbial cemented soil structure and analyze the correlation between geometric shape coefficient and gradation. The results showed: with the increase in the scale of the structure, the shape index and the angularity of the microbial cemented constructional waste soil increased as a whole, the rectangularity and the overall contour coefficient decreased, the structure shape was more irregular. The geometric shape coefficient had a good correlation with the particle gradation of cemented construction waste soil. It was because that the calcium carbonate induced by microbial precipitates covered and accumulated on the surface of the soil particles, increasing the particle size of the waste soil and making the particle surface rougher, and then changing the primary characteristic parameters, affecting the morphological indexes.
2024, 54(9): 51-56.
doi: 10.3724/j.gyjzG22101309
Abstract:
The improving effect of liquefiable sand strengthened by microbes was influenced by bacterial volumes and transfer rates of slurry in the grouting, redistribution of pores, and etc. Due to differences of internal qualities, densities and other factors caused by preparation for specimens in actual application, it was difficult to scientifically judge the mineralization effect in specimens, thereby, the application of the microbial induced carbonate precipitation (MICP) technique in sites was restricted. The existing experimental study on microbial induced carbonate precipitation was in unit scales, rarely in sand column scales. Therefore, multi-point and real-time monitoring was conducted on sand columns (in a length of 0.5 m) in the process of microbial grouting with the self-developed multi-point and multi-channel measurement device of bender elements for shear wave velocity, and the mineralization effect of microorganisms in specimens was expressed in stages. It was verified that the multi-point shear wave velocity measurement device could be explored the real-time MICP mineralization situation in specimens.
The improving effect of liquefiable sand strengthened by microbes was influenced by bacterial volumes and transfer rates of slurry in the grouting, redistribution of pores, and etc. Due to differences of internal qualities, densities and other factors caused by preparation for specimens in actual application, it was difficult to scientifically judge the mineralization effect in specimens, thereby, the application of the microbial induced carbonate precipitation (MICP) technique in sites was restricted. The existing experimental study on microbial induced carbonate precipitation was in unit scales, rarely in sand column scales. Therefore, multi-point and real-time monitoring was conducted on sand columns (in a length of 0.5 m) in the process of microbial grouting with the self-developed multi-point and multi-channel measurement device of bender elements for shear wave velocity, and the mineralization effect of microorganisms in specimens was expressed in stages. It was verified that the multi-point shear wave velocity measurement device could be explored the real-time MICP mineralization situation in specimens.
2024, 54(9): 57-65.
doi: 10.13204/j.gyjzG22102514
Abstract:
Innovating with history and winning through symbiosis. Taking "urban acupuncture" as the starting point, it was proposed that the mainstream of organic renewal of urban blocks should be cell metabolism and acupuncture rather than surgery. Through sorting out and analyzing the problems existing in Pangcun Avenue, Yibin District, Luoyang, looking for key problems, the problems were regarded as important "acupoints" points of urban acupuncture, and through precise intervention measures targeting these problem points, the city's "meridians" were dredged, and micro-renewal design was carried out. At the same time, regional cultural elements were implanted to integrate traditional culture with modern cities, awaken the vitality of streets, and activate the entire urban space.
Innovating with history and winning through symbiosis. Taking "urban acupuncture" as the starting point, it was proposed that the mainstream of organic renewal of urban blocks should be cell metabolism and acupuncture rather than surgery. Through sorting out and analyzing the problems existing in Pangcun Avenue, Yibin District, Luoyang, looking for key problems, the problems were regarded as important "acupoints" points of urban acupuncture, and through precise intervention measures targeting these problem points, the city's "meridians" were dredged, and micro-renewal design was carried out. At the same time, regional cultural elements were implanted to integrate traditional culture with modern cities, awaken the vitality of streets, and activate the entire urban space.
2024, 54(9): 66-74.
doi: 10.13204/j.gyjzG22081810
Abstract:
As a typical representative of Chinese landscape culture and a well-known tourist destination at home and abroad, West Lake Scenic Area has achieved remarkable results after nearly three decades of night scene construction. Timely retrospective research has positive significance for the sustainable and healthy development of West Lake Night Scene spatial intention. This study analyzed tourists’ night behavior preference with the help of big data of hot spot distribution in tourists’ behavior space, evaluated the night scene spatial intention of the West Lake loop trail in the eyes of tourists through image analysis and tourists’ perception evaluation, and put forward the promotion strategy of night scene spatial intention.
As a typical representative of Chinese landscape culture and a well-known tourist destination at home and abroad, West Lake Scenic Area has achieved remarkable results after nearly three decades of night scene construction. Timely retrospective research has positive significance for the sustainable and healthy development of West Lake Night Scene spatial intention. This study analyzed tourists’ night behavior preference with the help of big data of hot spot distribution in tourists’ behavior space, evaluated the night scene spatial intention of the West Lake loop trail in the eyes of tourists through image analysis and tourists’ perception evaluation, and put forward the promotion strategy of night scene spatial intention.
2024, 54(9): 75-80.
doi: 10.3724/j.gyjzG23110115
Abstract:
In recent years, the number of depression patients in China has sharply increased, posing a serious threat to the lives and health of the people. However, there is a lack of environmental design methods targeting the psychological characteristics and behavioral patterns of depression patients. Behavioral observation method was used to record the patient behavior types, frequency, and location information of five typical mental health centers in east China. Combined with relevant literature and theories, environmental factors and pathways that affect the psychological healing of depression patients were put forward. On this basis, the paper combined relevant case studies to propose interior design strategies that promote the rehabilitation efficiency from five aspects: reducing stimulation levels, avoiding negative intentions, providing natural landscapes, meeting sunlight needs and supporting diverse activities. The research may contribute to the theoretical system of healing environment, and provide some guidances for healthcare building designers and managers.
In recent years, the number of depression patients in China has sharply increased, posing a serious threat to the lives and health of the people. However, there is a lack of environmental design methods targeting the psychological characteristics and behavioral patterns of depression patients. Behavioral observation method was used to record the patient behavior types, frequency, and location information of five typical mental health centers in east China. Combined with relevant literature and theories, environmental factors and pathways that affect the psychological healing of depression patients were put forward. On this basis, the paper combined relevant case studies to propose interior design strategies that promote the rehabilitation efficiency from five aspects: reducing stimulation levels, avoiding negative intentions, providing natural landscapes, meeting sunlight needs and supporting diverse activities. The research may contribute to the theoretical system of healing environment, and provide some guidances for healthcare building designers and managers.
2024, 54(9): 81-89.
doi: 10.3724/j.gyjzG23090720
Abstract:
At present, prefabricated concrete shear walls are mostly connected by grouting sleeves, which can lead to defects such as loose grouting during construction. To avoid potential grouting defects, a prefabricated shear wall with vertical steel bars connected by prestressed cone-sleeve in reserved post cast area is proposed, and seismic performance research was carried out. Quasi-static tests were conducted on two concrete shear walls with an axial compression ratio of 0.1. One shear wall was cast-in-place, and the other was a prefabricated shear wall with prestressed cone-sleeve connections. The experiment found that when the drift ratio of the cast-in-place shear wall and the prefabricated shear wall were 1/40 and 1/50, respectively, the load of the specimens decreased to less than 85% of the peak load. The concrete on the lower corner wall of the cast-in-place shear wall was crushed, and the vertical steel bars in the left post-cast area of the prefabricated shear wall were pulled off. The ductility of the former was 22% higher than that of the latter, and the initial stiffness of the latter was 20% higher than that of the former. In addition, the failure modes of the two shear walls were basically the same, both of which underwent bending and shear failure, and the hysteresis performance and energy dissipation capacity were basically the same.
At present, prefabricated concrete shear walls are mostly connected by grouting sleeves, which can lead to defects such as loose grouting during construction. To avoid potential grouting defects, a prefabricated shear wall with vertical steel bars connected by prestressed cone-sleeve in reserved post cast area is proposed, and seismic performance research was carried out. Quasi-static tests were conducted on two concrete shear walls with an axial compression ratio of 0.1. One shear wall was cast-in-place, and the other was a prefabricated shear wall with prestressed cone-sleeve connections. The experiment found that when the drift ratio of the cast-in-place shear wall and the prefabricated shear wall were 1/40 and 1/50, respectively, the load of the specimens decreased to less than 85% of the peak load. The concrete on the lower corner wall of the cast-in-place shear wall was crushed, and the vertical steel bars in the left post-cast area of the prefabricated shear wall were pulled off. The ductility of the former was 22% higher than that of the latter, and the initial stiffness of the latter was 20% higher than that of the former. In addition, the failure modes of the two shear walls were basically the same, both of which underwent bending and shear failure, and the hysteresis performance and energy dissipation capacity were basically the same.
2024, 54(9): 90-99.
doi: 10.3724/j.gyjzG23092702
Abstract:
The structural deformation and failure of reinforced concrete (RC) walls during cooling after one-sided fire was studied by numerical simulations. Heat conduction analysis was carried out by finite element approximation to obtain the temperature distribution inside the wall,and the nonlinear shooting method was used to iteratively solve the structural model. The model took into account the thermal strain of reinforced concrete at high temperatures, compressive strain softening, tensile hardening, cracking and steel yielding, and geometric nonlinearity. The effects of transient creep of concrete were explicitly considered. After verifying the validity of the model, the structural deformation and failure mechanism of RC walls during the cooling after fire was revealed by a numerical example, followed by parametric studies. The results showed that RC wall may buckle in the post-fire cooling stage and its failure time could be earlier than that of the wall subjected to continuous fire. The loss of the strength of materials, the shifting of the neutral axis and the transient creep of concrete were the key factors leading to the post-fire buckling failure. In addition, the wall height, wall thickness and load eccentricity had a significant effect on the structural deformation and failure of RC walls during cooling after fire. The fire resistance of RC walls considering post-fire failure was significantly lower than that of RC walls subjected to continuous fire. The fire resistance of RC shear walls considering post-fire failure is significantly lower than that subjected to continuous fire, failure of RC shear wall during the cooling after fire could occur when the fire lasts for more than 15 minutes. Increasing the reinforcement ratio has a certain preventive effect on the failure of RC shear wall during the cooling after fire.
The structural deformation and failure of reinforced concrete (RC) walls during cooling after one-sided fire was studied by numerical simulations. Heat conduction analysis was carried out by finite element approximation to obtain the temperature distribution inside the wall,and the nonlinear shooting method was used to iteratively solve the structural model. The model took into account the thermal strain of reinforced concrete at high temperatures, compressive strain softening, tensile hardening, cracking and steel yielding, and geometric nonlinearity. The effects of transient creep of concrete were explicitly considered. After verifying the validity of the model, the structural deformation and failure mechanism of RC walls during the cooling after fire was revealed by a numerical example, followed by parametric studies. The results showed that RC wall may buckle in the post-fire cooling stage and its failure time could be earlier than that of the wall subjected to continuous fire. The loss of the strength of materials, the shifting of the neutral axis and the transient creep of concrete were the key factors leading to the post-fire buckling failure. In addition, the wall height, wall thickness and load eccentricity had a significant effect on the structural deformation and failure of RC walls during cooling after fire. The fire resistance of RC walls considering post-fire failure was significantly lower than that of RC walls subjected to continuous fire. The fire resistance of RC shear walls considering post-fire failure is significantly lower than that subjected to continuous fire, failure of RC shear wall during the cooling after fire could occur when the fire lasts for more than 15 minutes. Increasing the reinforcement ratio has a certain preventive effect on the failure of RC shear wall during the cooling after fire.
2024, 54(9): 100-107.
doi: 10.3724/j.gyjzG23101115
Abstract:
The experiments were designed for the characterizing the damage progress in the stirrup confined concrete. Through the uniaxial compression test, the parametric study was conducted to investigate the effects of loading rate, concrete strength, stirrup diameter, volume stirrup ratio on the mechanical properties and damage behaviors of the confined concrete. The experimental results were analyzed and demonstrated that: 1) with the increase of loading rate, the elastic deformation stage of concrete is shortened; and the plasticity of the whole damage process is weakened; moreover, the damage shows more brittle patterns. At low loading rate, the local failure and shear failure were mainly observed. When the loading rate is reaching at a high level, the longitudinally splitting mainly occurs. 2) Increasing the yield strength of stirrups is equivalent to the enhancement of the lateral confining pressure during the damage process of concrete, which plays an essential role in restraining the damage of the sample; 3) With the increase of stirrup ratio, the confinement effect of stirrups on the damage process is becoming more obvious, which effectively constrains the damage evolution process. 4) The samples with higher strength concrete show more brittle behavior and faster crack development during axial compression. Appropriate increase of concrete strength is beneficial to cooperative work with stirrups to restrain the evolution of damage.
The experiments were designed for the characterizing the damage progress in the stirrup confined concrete. Through the uniaxial compression test, the parametric study was conducted to investigate the effects of loading rate, concrete strength, stirrup diameter, volume stirrup ratio on the mechanical properties and damage behaviors of the confined concrete. The experimental results were analyzed and demonstrated that: 1) with the increase of loading rate, the elastic deformation stage of concrete is shortened; and the plasticity of the whole damage process is weakened; moreover, the damage shows more brittle patterns. At low loading rate, the local failure and shear failure were mainly observed. When the loading rate is reaching at a high level, the longitudinally splitting mainly occurs. 2) Increasing the yield strength of stirrups is equivalent to the enhancement of the lateral confining pressure during the damage process of concrete, which plays an essential role in restraining the damage of the sample; 3) With the increase of stirrup ratio, the confinement effect of stirrups on the damage process is becoming more obvious, which effectively constrains the damage evolution process. 4) The samples with higher strength concrete show more brittle behavior and faster crack development during axial compression. Appropriate increase of concrete strength is beneficial to cooperative work with stirrups to restrain the evolution of damage.
2024, 54(9): 108-114.
doi: 10.3724/j.gyjzG21112303
Abstract:
A double angle steel-shear web joint frame suitable for high intensity area was proposed. A multi-story prefabricated steel structure housing in Xuzhou was selected as the design and test prototype. The seismic performance of the double angle-steel shear webs joint frame and the original joint frame model were studied under quasi-static. The damage of the two frame specimens first appeared on the external wall panels, and then on the angle steel stiffeners at the beam-column joints and the column roots. The results showed that the bearing capacity of the double angle-steel shear web joint frame was slightly lower than that of the original joint frame, but the yield displacement of the double angle-steel shear web joint frame was larger. The hysteresis loop at the early stage was slightly thinner. In the later stage of loading, due to the shear web and avoidances angle formed three supporting points toward constraint hysteresis loop more full. The ductility of the two frames could meet the design requirements. The energy dissipation capacity of the double-angle steel-shear web joint frame was slightly lower than that of the original joint frame but had a large space to rise in the process of late failure, which could meet the requirements of seismic area for structural design.
A double angle steel-shear web joint frame suitable for high intensity area was proposed. A multi-story prefabricated steel structure housing in Xuzhou was selected as the design and test prototype. The seismic performance of the double angle-steel shear webs joint frame and the original joint frame model were studied under quasi-static. The damage of the two frame specimens first appeared on the external wall panels, and then on the angle steel stiffeners at the beam-column joints and the column roots. The results showed that the bearing capacity of the double angle-steel shear web joint frame was slightly lower than that of the original joint frame, but the yield displacement of the double angle-steel shear web joint frame was larger. The hysteresis loop at the early stage was slightly thinner. In the later stage of loading, due to the shear web and avoidances angle formed three supporting points toward constraint hysteresis loop more full. The ductility of the two frames could meet the design requirements. The energy dissipation capacity of the double-angle steel-shear web joint frame was slightly lower than that of the original joint frame but had a large space to rise in the process of late failure, which could meet the requirements of seismic area for structural design.
2024, 54(9): 115-124.
doi: 10.3724/j.gyjzG21122011
Abstract:
According to the architectural shape and structural characteristics of an actual project, a structural system of sightseeing tower consisting of three twisted columns and one spiral beam was proposed, and the influence laws of column twisting angle θ, spiral beam rotation direction, structural diameter D and number of spiral beam turns n on the period, displacement (lateral stiffness), member force and structural stability of the structural system were analyzed in detail. The analysis results showed that the increase of column twisting angle θ in the range of the studied parameters was unfavorable to the structural force, and the structural diameter D and the number of spiral beam turns n had some influence on the structural force, but the degree of influence of number of spiral beam turns n was smaller than that of column twisting angle θ. The torsion direction of the bending-torsion column was more favorable to the overall stability of the structure when the torsion direction was opposite to that of the spiral beam. The lateral stiffness of the structure decreased when the column twisting angle increased within the studied parameters (θ=0°-360°), and the lateral stiffness of the structure decreased when the structural diameter increased within the studied parameters (D=5-8 m). The lateral stiffness of the structure increased when the number of spiral beam turns increased within the studied parameters (n=7-11). The lateral stiffness of the structure increased when the bent and twisted column was rotated in the opposite direction to the spiral beam. Based on the coil spring transverse static stiffness theory, the lateral stiffness calculation formula of the bending-torsion column and spiral beam structure was established, and the formula calculation results were in good agreement with the software calculation results.
According to the architectural shape and structural characteristics of an actual project, a structural system of sightseeing tower consisting of three twisted columns and one spiral beam was proposed, and the influence laws of column twisting angle θ, spiral beam rotation direction, structural diameter D and number of spiral beam turns n on the period, displacement (lateral stiffness), member force and structural stability of the structural system were analyzed in detail. The analysis results showed that the increase of column twisting angle θ in the range of the studied parameters was unfavorable to the structural force, and the structural diameter D and the number of spiral beam turns n had some influence on the structural force, but the degree of influence of number of spiral beam turns n was smaller than that of column twisting angle θ. The torsion direction of the bending-torsion column was more favorable to the overall stability of the structure when the torsion direction was opposite to that of the spiral beam. The lateral stiffness of the structure decreased when the column twisting angle increased within the studied parameters (θ=0°-360°), and the lateral stiffness of the structure decreased when the structural diameter increased within the studied parameters (D=5-8 m). The lateral stiffness of the structure increased when the number of spiral beam turns increased within the studied parameters (n=7-11). The lateral stiffness of the structure increased when the bent and twisted column was rotated in the opposite direction to the spiral beam. Based on the coil spring transverse static stiffness theory, the lateral stiffness calculation formula of the bending-torsion column and spiral beam structure was established, and the formula calculation results were in good agreement with the software calculation results.
2024, 54(9): 125-132.
doi: 10.3724/j.gyjzG22010405
Abstract:
As a part of the research on the countermeasures of prefabricated steel structure residences under rarely occurred earthquakes, the concept of realizing rapid replaceable resilient function of peripheral wall panel system under rarely occurred earthquakes was put forward, based on the traditional connection technique between wallboard and main structure was optimized and improved, and an L-shaped joint with angle steel perpendicular to light wall panel was proposed, six specimens of autoclaved aerated concrete wall panels (ALC) were designed. Through the quasi-static load test, the deformation behavior of the new connection and the failure mode of ALC were studied. The effects of thickness of angle steels at connections and restraint at the lower end of wall panels on the hysteretic characteristics, deformation capacity, stiffness degradation, angle steel strain and energy dissipation capacity of peripheral wall panels were discussed. The test results showed that the smaller thickness of angle steel of L-shaped joints, the greater the deformation, the better the energy consumption and the less the damage of wall panels;the lower end restraint of the wall panels was strengthened, the overall stiffness and bearing capacity of the peripheral wall panels were increased, small residual deformation;when the drift reached 2%, the L-shaped node had sufficient stability and the wall panel had no obvious damage; when the drift exceeded 2%, the L-shaped joint showed a good deformation performance, which could make the peripheral wall plate adapt to large structural deformation.
As a part of the research on the countermeasures of prefabricated steel structure residences under rarely occurred earthquakes, the concept of realizing rapid replaceable resilient function of peripheral wall panel system under rarely occurred earthquakes was put forward, based on the traditional connection technique between wallboard and main structure was optimized and improved, and an L-shaped joint with angle steel perpendicular to light wall panel was proposed, six specimens of autoclaved aerated concrete wall panels (ALC) were designed. Through the quasi-static load test, the deformation behavior of the new connection and the failure mode of ALC were studied. The effects of thickness of angle steels at connections and restraint at the lower end of wall panels on the hysteretic characteristics, deformation capacity, stiffness degradation, angle steel strain and energy dissipation capacity of peripheral wall panels were discussed. The test results showed that the smaller thickness of angle steel of L-shaped joints, the greater the deformation, the better the energy consumption and the less the damage of wall panels;the lower end restraint of the wall panels was strengthened, the overall stiffness and bearing capacity of the peripheral wall panels were increased, small residual deformation;when the drift reached 2%, the L-shaped node had sufficient stability and the wall panel had no obvious damage; when the drift exceeded 2%, the L-shaped joint showed a good deformation performance, which could make the peripheral wall plate adapt to large structural deformation.
2024, 54(9): 133-140.
doi: 10.3724/j.gyjzG23082308
Abstract:
In order to study the seismic performance of prefabricated joints in underground space structures, a new type of prefabricated CFST composite column-reinforced concrete beam joint was designed and fabricated and compared with the cast-in-place CFST composite column-reinforced concrete beam joint. Quasi-static load tests were conducted on two types of joints. The hysteresis curves, skeleton scurves, stiffness degradation curves, energy dissipation capacity, ductility, and other indicators of the two types of joints were compared and analyzed. The results showed that both types of joints were subjected to bending failure in the plastic hinge area of the beam end and the ultimate displacement of the assembled joint was 47.6% higher than that of the cast-in-place joint, but the difference in ultimate bearing capacity between the two joints was not significant. The stiffness of the final joints was reached failure by about 10% of the initial stiffness, and the joints underwent significant nonlinear deformation and damage. The final cumulative total energy consumption of cast-in-place and prefabricated joints reached 35.69 kN·m and 58.77 kN·m, respectively. The prefabricated joint was greater than that of the cast-in-place joint, which was 1.65 times the cast-in-place joint. The yield and ultimate displacement of the prefabricated joint had increased by 30.68% and 32.47% respectively compared with the cast-in-place joint. The difference in yield and ultimate load between the two types of joints was not significant, and the ductility coefficients of prefabricated joints was slightly higher than cast-in-place joints. The ductility of the prefabricated joint was better than the cast-in-place joint.
In order to study the seismic performance of prefabricated joints in underground space structures, a new type of prefabricated CFST composite column-reinforced concrete beam joint was designed and fabricated and compared with the cast-in-place CFST composite column-reinforced concrete beam joint. Quasi-static load tests were conducted on two types of joints. The hysteresis curves, skeleton scurves, stiffness degradation curves, energy dissipation capacity, ductility, and other indicators of the two types of joints were compared and analyzed. The results showed that both types of joints were subjected to bending failure in the plastic hinge area of the beam end and the ultimate displacement of the assembled joint was 47.6% higher than that of the cast-in-place joint, but the difference in ultimate bearing capacity between the two joints was not significant. The stiffness of the final joints was reached failure by about 10% of the initial stiffness, and the joints underwent significant nonlinear deformation and damage. The final cumulative total energy consumption of cast-in-place and prefabricated joints reached 35.69 kN·m and 58.77 kN·m, respectively. The prefabricated joint was greater than that of the cast-in-place joint, which was 1.65 times the cast-in-place joint. The yield and ultimate displacement of the prefabricated joint had increased by 30.68% and 32.47% respectively compared with the cast-in-place joint. The difference in yield and ultimate load between the two types of joints was not significant, and the ductility coefficients of prefabricated joints was slightly higher than cast-in-place joints. The ductility of the prefabricated joint was better than the cast-in-place joint.
2024, 54(9): 141-148.
doi: 10.3724/j.gyjzG23121108
Abstract:
The traditional back propagation (BP) neural network has some defects in predicting the axial compressive capacity of concrete-filled rectangular steel tube (CFRST), such as system instability, slow convergence speed and difficult selection of hyperparameters, which will affect the stability of the prediction model and the accuracy of the prediction results. In order to improve the traditional BP model to achieve better prediction effect, particle swarm optimization algorithm (PSO) was applied to BP prediction model, and a CFRST axial compressive capacity prediction model PB7-7-1 based on PSO-BP neural network was proposed. The results showed that the fluctuation range of the predicted values of the PB7-7-1 model was substantially reduced compared with that of the traditional BP model, in which the absolute relative error (ARE) of the predicted values of 45% of the components was within 5%, and the ARE of 80% of the components was within 10%; prediction accuracy of the PB7-7-1 model had been improved by 30.79%, and the average ARE of its predictive values was only 6%. This showed that the PB7-7-1 model based on PSO-BP neural network had a significant improvement in the stability and accuracy of prediction results of CFRST axial compressive capacity compared with traditional BP network. In addition, according to the weight and bias of the hidden layer and output layer of PB7-7-1 model, the prediction formula of CFRST axial compressive capacity was constructed. Finally, SHAP machine learning interpretation algorithm was used to analyze the importance and contribution of each input parameter to the axial compressive capacity.
The traditional back propagation (BP) neural network has some defects in predicting the axial compressive capacity of concrete-filled rectangular steel tube (CFRST), such as system instability, slow convergence speed and difficult selection of hyperparameters, which will affect the stability of the prediction model and the accuracy of the prediction results. In order to improve the traditional BP model to achieve better prediction effect, particle swarm optimization algorithm (PSO) was applied to BP prediction model, and a CFRST axial compressive capacity prediction model PB7-7-1 based on PSO-BP neural network was proposed. The results showed that the fluctuation range of the predicted values of the PB7-7-1 model was substantially reduced compared with that of the traditional BP model, in which the absolute relative error (ARE) of the predicted values of 45% of the components was within 5%, and the ARE of 80% of the components was within 10%; prediction accuracy of the PB7-7-1 model had been improved by 30.79%, and the average ARE of its predictive values was only 6%. This showed that the PB7-7-1 model based on PSO-BP neural network had a significant improvement in the stability and accuracy of prediction results of CFRST axial compressive capacity compared with traditional BP network. In addition, according to the weight and bias of the hidden layer and output layer of PB7-7-1 model, the prediction formula of CFRST axial compressive capacity was constructed. Finally, SHAP machine learning interpretation algorithm was used to analyze the importance and contribution of each input parameter to the axial compressive capacity.
2024, 54(9): 149-155.
doi: 10.3724/j.gyjzG24050615
Abstract:
Concrete-filled double-skin circular aluminum tube short columns consisting of PVC tube inside and aluminum alloy tube outside was taken as the research object, considering two variables of PVC tube diameter and aluminum tube wall thickness, axial compression test research and corresponding finite element simulation analysis on the concrete-filled double-skin circular aluminum tube short columns were carried out. The failure modes, ultimate bearing capacities and load-strain relation of the concrete-filled double-skin circular aluminum tube short column specimens were obtained. The feasibility of using existing calculation methods for the bearing capacity of steel tube concrete short columns under axial compression to predict the bearing capacity of concrete-filled double-skin circular aluminum tube short columns were compared and analyzed. The research results indicated that the failure mode of concrete-filled double-skin circular aluminum tube short columns exhibited bulging failure. When the diameter of the PVC tube remained constant, the ultimate bearing capacity of the specimen increased by 46.6%-96.6% with the increase of the wall thickness of the aluminum tube. When the thickness of the aluminum tube remained unchanged, the bearing capacity of the specimen decreased by 8.3%-28.4% with the increase of the diameter of the PVC tube. The accuracy of the projected results of the existing European EC 4 code and the United States AISC code for CFST column bearing capacity was affected by the wall thickness of the aluminum tube and the result were too conservative. The predicted data stability of CCES standard for specimens with different wall thicknesses was insufficient. The method proposed by scholar Tao Zhong showed the best predicted results and data stability.Finally, a suggestion was put forward for the calculation of the bearing capacity of concrete-filled double-skin circular aluminum tube short columns under axial compression.
Concrete-filled double-skin circular aluminum tube short columns consisting of PVC tube inside and aluminum alloy tube outside was taken as the research object, considering two variables of PVC tube diameter and aluminum tube wall thickness, axial compression test research and corresponding finite element simulation analysis on the concrete-filled double-skin circular aluminum tube short columns were carried out. The failure modes, ultimate bearing capacities and load-strain relation of the concrete-filled double-skin circular aluminum tube short column specimens were obtained. The feasibility of using existing calculation methods for the bearing capacity of steel tube concrete short columns under axial compression to predict the bearing capacity of concrete-filled double-skin circular aluminum tube short columns were compared and analyzed. The research results indicated that the failure mode of concrete-filled double-skin circular aluminum tube short columns exhibited bulging failure. When the diameter of the PVC tube remained constant, the ultimate bearing capacity of the specimen increased by 46.6%-96.6% with the increase of the wall thickness of the aluminum tube. When the thickness of the aluminum tube remained unchanged, the bearing capacity of the specimen decreased by 8.3%-28.4% with the increase of the diameter of the PVC tube. The accuracy of the projected results of the existing European EC 4 code and the United States AISC code for CFST column bearing capacity was affected by the wall thickness of the aluminum tube and the result were too conservative. The predicted data stability of CCES standard for specimens with different wall thicknesses was insufficient. The method proposed by scholar Tao Zhong showed the best predicted results and data stability.Finally, a suggestion was put forward for the calculation of the bearing capacity of concrete-filled double-skin circular aluminum tube short columns under axial compression.
2024, 54(9): 156-162.
doi: 10.3724/j.gyjzG22011706
Abstract:
In order to study the failure mode and the bending capacity of fluxural acrylic beams, a series of tests were conducted on the acrylic and flexural members, so as to obtain the material properties, failure modes and bending capacity. Besides, the DIC technology was used to obtain the full-field strain distribution. Test results indicated that PMMA had asymmetric material properties, and compression strength was higher than tensile strength. The combination of the fracture in tension zone and burst in compression zone was the major failure mode, and the failure would happen when the tensile strain reached the ultimate strain in tension. The strain distribution in the mid-span met the plan-section assumption, and the neutral axis was slightly above the centroid of the cross-section. Elastic model, elastic-plastic model and simplified model were used to calculate the bending capacity and deflection. Analysis showed that the predictions of elastic model were lower than the test results, while the predictions of elastic-plastic model and the simplified model matched the test result well. It was recommended to use the simplified model to predict the bending capacity and deflections of flexural acrylic beams due to convenient in calculation.
In order to study the failure mode and the bending capacity of fluxural acrylic beams, a series of tests were conducted on the acrylic and flexural members, so as to obtain the material properties, failure modes and bending capacity. Besides, the DIC technology was used to obtain the full-field strain distribution. Test results indicated that PMMA had asymmetric material properties, and compression strength was higher than tensile strength. The combination of the fracture in tension zone and burst in compression zone was the major failure mode, and the failure would happen when the tensile strain reached the ultimate strain in tension. The strain distribution in the mid-span met the plan-section assumption, and the neutral axis was slightly above the centroid of the cross-section. Elastic model, elastic-plastic model and simplified model were used to calculate the bending capacity and deflection. Analysis showed that the predictions of elastic model were lower than the test results, while the predictions of elastic-plastic model and the simplified model matched the test result well. It was recommended to use the simplified model to predict the bending capacity and deflections of flexural acrylic beams due to convenient in calculation.
2024, 54(9): 163-169.
doi: 10.3724/j.gyjzG23102312
Abstract:
In recent years, beam-arch combination system bridges in China has been developing rapidly, the V-shaped continuous rigid frame system beam-arch combination bridge is a new type of structural system. The Fuzhou WanBian Bridge was taken as the engineering background, using the large-scale universal finite element software to establish a bridge structure model, mechanical analysis of key joints in the construction stage of the V-shaped continuous rigid frame system beam-arch composite bridge was carried out, including stress analysis of the V-braced position in the cantilever state of the box girder, internal force analysis of arch ribs during the stage of pouring concrete into the arch rib tube, stability analysis of steel pipe arch ribs, and dynamic characteristic analysis. Finally, the study of key joints during the construction stage of the bridge revealed that the calculated stress of the bridge during the construction stage met the requirements of the specifications, various materials would not exhibit stress yielding phenomenon during the pouring process.
In recent years, beam-arch combination system bridges in China has been developing rapidly, the V-shaped continuous rigid frame system beam-arch combination bridge is a new type of structural system. The Fuzhou WanBian Bridge was taken as the engineering background, using the large-scale universal finite element software to establish a bridge structure model, mechanical analysis of key joints in the construction stage of the V-shaped continuous rigid frame system beam-arch composite bridge was carried out, including stress analysis of the V-braced position in the cantilever state of the box girder, internal force analysis of arch ribs during the stage of pouring concrete into the arch rib tube, stability analysis of steel pipe arch ribs, and dynamic characteristic analysis. Finally, the study of key joints during the construction stage of the bridge revealed that the calculated stress of the bridge during the construction stage met the requirements of the specifications, various materials would not exhibit stress yielding phenomenon during the pouring process.
2024, 54(9): 170-176.
doi: 10.3724/j.gyjzG23120806
Abstract:
Modeling by micromechanics is an effective means to study the macroscopic mechanical properties of concrete. By using the ABAQUS finite element software and cohesive element, a three-dimensional mesoscopic model of concrete specimen with random aggregate distribution was established to simulate the failure state of concrete specimens under static and dynamic compression, and the crack growth state of each stage was compared with that obtained by experimental loading. Based on the effective numerical model, the differences of peak intensity and crack propagation under different loading rates were studied, and the damage evolution value was calculated. The results showed that the stress variation characteristics of the models at different stages were obvious, which were basically consistent with the macroscopic strength of concrete. The failure modes of different components were obviously different, and the compressive strength of internal aggregate was the highest at the beginning of failure. The failure state obtained by numerical simulation was basically consistent with the test results. The damage variables were calculated by the exponential evolution method based on energy parameters, and it was verified that the constitutive model based on brittle fracture could effectively predict the failure process of concrete specimens.
Modeling by micromechanics is an effective means to study the macroscopic mechanical properties of concrete. By using the ABAQUS finite element software and cohesive element, a three-dimensional mesoscopic model of concrete specimen with random aggregate distribution was established to simulate the failure state of concrete specimens under static and dynamic compression, and the crack growth state of each stage was compared with that obtained by experimental loading. Based on the effective numerical model, the differences of peak intensity and crack propagation under different loading rates were studied, and the damage evolution value was calculated. The results showed that the stress variation characteristics of the models at different stages were obvious, which were basically consistent with the macroscopic strength of concrete. The failure modes of different components were obviously different, and the compressive strength of internal aggregate was the highest at the beginning of failure. The failure state obtained by numerical simulation was basically consistent with the test results. The damage variables were calculated by the exponential evolution method based on energy parameters, and it was verified that the constitutive model based on brittle fracture could effectively predict the failure process of concrete specimens.
2024, 54(9): 177-184.
doi: 10.3724/j.gyjzG23042807
Abstract:
Sulfate attack is one of the main factors leading to the damage and deterioration of concrete. The prediction of the temporal and spatial distribution of sulfate ions in concrete is the basis of studying the damage and deterioration of concrete. Compared with the macroscopic model, the mesoscopic model can better reflect the actual migration law of sulfate ion in concrete, but there are some problems such as complex modeling and long calculation time. In this paper, concrete was regarded as four composite materials composed of cement mortar, interfacial layer, coarse aggregate and macro defects, and a two-dimensional mesoscopic model of concrete was constructed. Then, the effects of macro and mesoscopic models on numerical simulation were studied and compared, and mesoscopic parameters were defined to make the macroscopic model achieve the simulation effect of the mesoscopic model. The results showed that: 1) the influence of mesoscopic model randomness on sulfate ion diffusion could be eliminated by taking the average value of multiple models; 2) the increase of stone content was accompanied by the deepening of erosion depth and the decrease of sulfate ion concentration at the same location, and this phenomenon was more obvious with the increase of depth; 3) the mesoscopic parameters increased with the increase of stone content.
Sulfate attack is one of the main factors leading to the damage and deterioration of concrete. The prediction of the temporal and spatial distribution of sulfate ions in concrete is the basis of studying the damage and deterioration of concrete. Compared with the macroscopic model, the mesoscopic model can better reflect the actual migration law of sulfate ion in concrete, but there are some problems such as complex modeling and long calculation time. In this paper, concrete was regarded as four composite materials composed of cement mortar, interfacial layer, coarse aggregate and macro defects, and a two-dimensional mesoscopic model of concrete was constructed. Then, the effects of macro and mesoscopic models on numerical simulation were studied and compared, and mesoscopic parameters were defined to make the macroscopic model achieve the simulation effect of the mesoscopic model. The results showed that: 1) the influence of mesoscopic model randomness on sulfate ion diffusion could be eliminated by taking the average value of multiple models; 2) the increase of stone content was accompanied by the deepening of erosion depth and the decrease of sulfate ion concentration at the same location, and this phenomenon was more obvious with the increase of depth; 3) the mesoscopic parameters increased with the increase of stone content.
2024, 54(9): 185-190.
doi: 10.3724/j.gyjzG24012606
Abstract:
Magnesium phosphate cement, recognized for its environmental sustainability, boasts attributes such as rapid setting, high early strength, low shrinkage, exceptional bond performance, robust corrosion resistance, and resilience against wear and freezing. These distinctive properties position it as a promising material for diverse applications in civil engineering. This study aims to explore the influence of various factors, including phosphate type, fly ash content, water-to-binder ratio, and curing age, on the compressive strength of magnesium phosphate cement mortar (MPCM). Experimental findings revealed that in the absence of fly ash, the utilization of a 1∶1 mass ratio blend of two phosphate salts led to a notable enhancement in the early compressive strength of MPCM compared to the individual application of either ammonium dihydrogen phosphate or potassium dihydrogen phosphate. Moreover, the addition of 20% fly ash by mass of cementitious material enhanced the 1-day compressive strength of MPCM formulated with potassium dihydrogen phosphate or a combination of phosphate salts, although it might potentially compromise the strength at 28 days. Generally, the reduction in the water-to-binder ratio from 0.25 to 0.20 and the extension of curing age from 1 day to 28 days exhibited favorable impacts on the compressive strength of MPCM.
Magnesium phosphate cement, recognized for its environmental sustainability, boasts attributes such as rapid setting, high early strength, low shrinkage, exceptional bond performance, robust corrosion resistance, and resilience against wear and freezing. These distinctive properties position it as a promising material for diverse applications in civil engineering. This study aims to explore the influence of various factors, including phosphate type, fly ash content, water-to-binder ratio, and curing age, on the compressive strength of magnesium phosphate cement mortar (MPCM). Experimental findings revealed that in the absence of fly ash, the utilization of a 1∶1 mass ratio blend of two phosphate salts led to a notable enhancement in the early compressive strength of MPCM compared to the individual application of either ammonium dihydrogen phosphate or potassium dihydrogen phosphate. Moreover, the addition of 20% fly ash by mass of cementitious material enhanced the 1-day compressive strength of MPCM formulated with potassium dihydrogen phosphate or a combination of phosphate salts, although it might potentially compromise the strength at 28 days. Generally, the reduction in the water-to-binder ratio from 0.25 to 0.20 and the extension of curing age from 1 day to 28 days exhibited favorable impacts on the compressive strength of MPCM.
2024, 54(9): 191-197.
doi: 10.3724/j.gyjzG22102404
Abstract:
Microbial Induced Calcium Carbonate Precipitation (MICP) technique is a new method to improve wind erosion and dust resistance of bare soil and protect the ecological environment. The reinforcing mechanisms and curing methods for bare soil cemented by MICP to improve its properties of wind erosion and dust resistance were summarized. The effects of cured conditions and environmental factors on wind erosion and dust resistance of bare soil cemented by MICP were systematically analyzed. The existing findings indicated that freeze-thaw action influenced on the structural stability and physical and mechanical properties of bare soil cemented by MICP, which deteriorated the wind erosion and dust resistance of soil. Therefore, the necessity to study the effects of freeze-thaw action on wind erosion and dust resistance of bare soil cemented by MICP were presented. Finally, it was pointed out that durability study on freeze-thaw resistance of bare soil cemented by MICP was the theoretical base of stabilizing soil and improving wind erosion and dust resistance.
Microbial Induced Calcium Carbonate Precipitation (MICP) technique is a new method to improve wind erosion and dust resistance of bare soil and protect the ecological environment. The reinforcing mechanisms and curing methods for bare soil cemented by MICP to improve its properties of wind erosion and dust resistance were summarized. The effects of cured conditions and environmental factors on wind erosion and dust resistance of bare soil cemented by MICP were systematically analyzed. The existing findings indicated that freeze-thaw action influenced on the structural stability and physical and mechanical properties of bare soil cemented by MICP, which deteriorated the wind erosion and dust resistance of soil. Therefore, the necessity to study the effects of freeze-thaw action on wind erosion and dust resistance of bare soil cemented by MICP were presented. Finally, it was pointed out that durability study on freeze-thaw resistance of bare soil cemented by MICP was the theoretical base of stabilizing soil and improving wind erosion and dust resistance.
2024, 54(9): 198-208.
doi: 10.3724/j.gyjzG23112502
Abstract:
With the rapid development of prefabricated steel structures in our country, a higher request has been put forward for the connection performance and economic index of exterior wallboard system. Based on a large number of literature retrieval at home and abroad, the research and application progress of exterior wallboards in the types, mechanical properties and connection structure were summarized, the advantages and disadvantages of various types of exterior wallboards and main structure connection joints were analyzed, and the main problems existing in the connection joints of exterior wallboards and fabricated steel structures were summarized.It was found that the exterior wallboards materials mainly showed poor durability, high energy consumption, poor environmental benefits, low comprehensive performance problems, the connection joints between exterior wallboards and the main structure also remained some problems,such as poor standardization in design, poor industrialization and automation in production, complex joint form, and poor operability.Finally, the key bottleneck existing in the current application was pointed out, and some reasonable suggestions for the future development direction were put foward.
With the rapid development of prefabricated steel structures in our country, a higher request has been put forward for the connection performance and economic index of exterior wallboard system. Based on a large number of literature retrieval at home and abroad, the research and application progress of exterior wallboards in the types, mechanical properties and connection structure were summarized, the advantages and disadvantages of various types of exterior wallboards and main structure connection joints were analyzed, and the main problems existing in the connection joints of exterior wallboards and fabricated steel structures were summarized.It was found that the exterior wallboards materials mainly showed poor durability, high energy consumption, poor environmental benefits, low comprehensive performance problems, the connection joints between exterior wallboards and the main structure also remained some problems,such as poor standardization in design, poor industrialization and automation in production, complex joint form, and poor operability.Finally, the key bottleneck existing in the current application was pointed out, and some reasonable suggestions for the future development direction were put foward.
2024, 54(9): 209-218.
doi: 10.3724/j.gyjzG23051209
Abstract:
Bridge and tunnel engineering is an important branch in the field of civil engineering. With the increasing digitization of construction and upgrades in hardware equipment, computer vision has become a key technology supporting the digital development of bridge and tunnel engineering. To comprehensively reveal the research hotspots and trends of computer vision in the field of bridge and tunnel engineering, the paper focused on the application of computer vision in bridge and tunnel engineering, used knowledge graph tools to conduct visualized analysis of relevant literature, and systematically summarized the theoretical and applied technologies of computer vision tasks, including image processing and feature extraction, object detection and tracking, object classification and recognition, 3D reconstruction and SLAM, and intelligent analysis and decision-making. Based on this, the paper also summarized the current research difficulties from four aspects: dataset defects, image accuracy, detection real-time performance, and algorithm applicability. The paper also identified and discussed solutions to application difficulties and provided prospects for future development, so as to provide theoretical support for further research and technological application.
Bridge and tunnel engineering is an important branch in the field of civil engineering. With the increasing digitization of construction and upgrades in hardware equipment, computer vision has become a key technology supporting the digital development of bridge and tunnel engineering. To comprehensively reveal the research hotspots and trends of computer vision in the field of bridge and tunnel engineering, the paper focused on the application of computer vision in bridge and tunnel engineering, used knowledge graph tools to conduct visualized analysis of relevant literature, and systematically summarized the theoretical and applied technologies of computer vision tasks, including image processing and feature extraction, object detection and tracking, object classification and recognition, 3D reconstruction and SLAM, and intelligent analysis and decision-making. Based on this, the paper also summarized the current research difficulties from four aspects: dataset defects, image accuracy, detection real-time performance, and algorithm applicability. The paper also identified and discussed solutions to application difficulties and provided prospects for future development, so as to provide theoretical support for further research and technological application.
Research on Construction and Optimization of Lattice-Based Printing Based on Finite Element Analysis
2024, 54(9): 219-226.
doi: 10.3724/j.gyjzG23100912
Abstract:
In recent years, there has been rapid progress in the use of robotic arms for 3D printing construction, and it has also made significant advancements in the field of architecture. However, the system of lattice-based printing using robotic arm platforms still faces the practical need to print large-scale building components and achieve the overall printing of buildings. The paper first utilized Rhino Vault tools and Karamba3D finite element optimization software to construct shell components. Secondly, through the optimization of variable cross-sections of shell components and the application of lattice segmented printing methods, a complete process from design to construction for large-scale shell morphological components was provided. Finally, this process was validated through printing and construction experiments. The goal is to enhance the structural feasibility of large-scale shell lattice printing, aiming to offer references for architects exploring the integration of digital design and construction.
In recent years, there has been rapid progress in the use of robotic arms for 3D printing construction, and it has also made significant advancements in the field of architecture. However, the system of lattice-based printing using robotic arm platforms still faces the practical need to print large-scale building components and achieve the overall printing of buildings. The paper first utilized Rhino Vault tools and Karamba3D finite element optimization software to construct shell components. Secondly, through the optimization of variable cross-sections of shell components and the application of lattice segmented printing methods, a complete process from design to construction for large-scale shell morphological components was provided. Finally, this process was validated through printing and construction experiments. The goal is to enhance the structural feasibility of large-scale shell lattice printing, aiming to offer references for architects exploring the integration of digital design and construction.
2024, 54(9): 227-235.
doi: 10.3724/j.gyjzG23091709
Abstract:
In order to achieve the circumferential discontinuous stepped shaped of the roof canopy of the Chengdu Sport University Stadium, while ensuring the continuity of the structure, a pipe truss with built-up top chord section was proposed. The section properties were assigned to the geometric model generated by using a self-developed program Grasshopper, conducting modal, stress, deformation, and buckling analysis of the canopy in SAP 2000, and performing finite element analysis on the key joints by using ABAQUS. The analysis results showed that the arrangement of the canopy structure adopting pipe truss with built-up top chord section was reasonable; the force transmission was clear; the overall integrity was good; the joint design was safe and reliable, and it could perfectly present the architectural stepped shape, providing a reference for similar structural designs.
In order to achieve the circumferential discontinuous stepped shaped of the roof canopy of the Chengdu Sport University Stadium, while ensuring the continuity of the structure, a pipe truss with built-up top chord section was proposed. The section properties were assigned to the geometric model generated by using a self-developed program Grasshopper, conducting modal, stress, deformation, and buckling analysis of the canopy in SAP 2000, and performing finite element analysis on the key joints by using ABAQUS. The analysis results showed that the arrangement of the canopy structure adopting pipe truss with built-up top chord section was reasonable; the force transmission was clear; the overall integrity was good; the joint design was safe and reliable, and it could perfectly present the architectural stepped shape, providing a reference for similar structural designs.
