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2023 Vol. 53, No. 2
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2023, 53(2): 1-7.
doi: 10.13204/j.gyjzG22073106
Abstract:
The cultural venues has the characteristics of complex space and system, high requirements for reliability and comfort of operation and maintenance. The traditional passive operation and maintenance mode of "problem-solving" is difficult to meet the requiements of operation, so there is a strong demand for intelligent operation and maintenance system. The practical experience of intelligent operation and maintenance system based on digital twins after the opening of Shanghai Astronomy Museum was snmmarized, including implementation methods, application values, existing problems and countermeasures, so as to provide a reference for the implementation of intelligent operation and maintenance system in subsequent science and technology exhibition halls and other buildings. The application practice showed that although it was difficult to review and improve the BIM model, repair the building intelligent systems and merge their data after the opening, with the strong support of the owner, the construction of building intelligent operation and maintenance system could still be completed within the building maintenance time, and effectively improve the level and efficiency of building intelligent operation and maintenance, as well as the reliability.
The cultural venues has the characteristics of complex space and system, high requirements for reliability and comfort of operation and maintenance. The traditional passive operation and maintenance mode of "problem-solving" is difficult to meet the requiements of operation, so there is a strong demand for intelligent operation and maintenance system. The practical experience of intelligent operation and maintenance system based on digital twins after the opening of Shanghai Astronomy Museum was snmmarized, including implementation methods, application values, existing problems and countermeasures, so as to provide a reference for the implementation of intelligent operation and maintenance system in subsequent science and technology exhibition halls and other buildings. The application practice showed that although it was difficult to review and improve the BIM model, repair the building intelligent systems and merge their data after the opening, with the strong support of the owner, the construction of building intelligent operation and maintenance system could still be completed within the building maintenance time, and effectively improve the level and efficiency of building intelligent operation and maintenance, as well as the reliability.
2023, 53(2): 8-11,63.
doi: 10.13204/j.gyjzG20111210
Abstract:
Evaluating the damage state of masonry structures based on the characteristics of acoustic emission (AE) signal parameters is an innovative method for health monitoring. The axial compression test of the brick masonry specimen and the in-situ axial compression test of the in-service masonry brick wall were performed. The characteristics of the AE ring counts, energy, and peak frequencies during the test were analyzed. The results showed that the AE parameters presented different characteristics, and the variation characteristics were in good agreement with the evolution process of masonry damage. In the failure stage of the specimen, the AE signals were marked as high energy and low frequencies. These characteristics could provide support and guidance for assessing the state of masonry structures and early warning of structural safety.
Evaluating the damage state of masonry structures based on the characteristics of acoustic emission (AE) signal parameters is an innovative method for health monitoring. The axial compression test of the brick masonry specimen and the in-situ axial compression test of the in-service masonry brick wall were performed. The characteristics of the AE ring counts, energy, and peak frequencies during the test were analyzed. The results showed that the AE parameters presented different characteristics, and the variation characteristics were in good agreement with the evolution process of masonry damage. In the failure stage of the specimen, the AE signals were marked as high energy and low frequencies. These characteristics could provide support and guidance for assessing the state of masonry structures and early warning of structural safety.
2023, 53(2): 12-21.
doi: 10.13204/j.gyjzG22012601
Abstract:
To enhance the informatization of building demolition and improve the utilization of construction waste, the paper proposed a framework of intelligent demolition based on BIM and 3D scanning. Firstly, the point cloud of existing structures is obtained and registered by using a 3D scanner and the triangular target proposed in this paper. Then the geometric parameters of the structures are extracted used for the reconstruction of the BIM model based on the point cloud processing extraction algorithm. Afterwards, the demolition plan, safety simulation and economic evaluation are carried out based on the BIM model. The practical application showed that the point cloud registration method based on the triangular target was applicable to the point cloud registration of large point cloud, and the geometric measurement algorithm could accurately extract the dimensions of the building components; the demolition scheme, numerical simulation and cost measurement model developed based on this BIM model could accurately evaluate the safety and economy of the demolition method in advance. The framework constructed an intelligent building demolition system from four aspects:site investigation, scheme development, safety assessment, and cost analysis, which could provide a new way to realize information-based and sustainable building demolition.
To enhance the informatization of building demolition and improve the utilization of construction waste, the paper proposed a framework of intelligent demolition based on BIM and 3D scanning. Firstly, the point cloud of existing structures is obtained and registered by using a 3D scanner and the triangular target proposed in this paper. Then the geometric parameters of the structures are extracted used for the reconstruction of the BIM model based on the point cloud processing extraction algorithm. Afterwards, the demolition plan, safety simulation and economic evaluation are carried out based on the BIM model. The practical application showed that the point cloud registration method based on the triangular target was applicable to the point cloud registration of large point cloud, and the geometric measurement algorithm could accurately extract the dimensions of the building components; the demolition scheme, numerical simulation and cost measurement model developed based on this BIM model could accurately evaluate the safety and economy of the demolition method in advance. The framework constructed an intelligent building demolition system from four aspects:site investigation, scheme development, safety assessment, and cost analysis, which could provide a new way to realize information-based and sustainable building demolition.
2023, 53(2): 22-28,21.
doi: 10.13204/j.gyjzG21032003
Abstract:
To investigate the mechanical properties of RC columns confined with self-compacting and micro-expanding concrete filled circular steel tube (SMCFCST) under axial compression, 8 confined RC columns and 1 unconfined RC column were designed and fabricated, and an axial compressive test was conducted. The test parameters including the thickness of the steel tube, the strength of self-compacting and micro-expanding filling concrete, the type of the filling concrete and the magnitude of the initial axial pressure were considered. The failure modes of specimens and the loading data were recorded, while the load versus vertical deformation curves and the load-strain curves were depicted accordingly. The results showed that the peak loads and ductility of the RC columns were significantly improved after being confined by SMCFCST. The peak loads of the confined columns were apparently increased with the increase of the thickness of steel tube. The peak loads of the confined columns were slightly increased with the increase of the strength of self-compacting and micro-expanding filling concrete. However, the effects of the type of filling concrete and the magnitude of the initial axial pressure on the peak loads of the confined columns were negligible. The formula from Technical Code for Concrete Filled Steel Tubular Structures (GB 50936-2014) was modified to obtain the predictive formula of the bearing capacity of the SMCFCST confined columns under axial compression. The average value of the ratio of the predicted value to the test value was 0.956, and the standard deviation was 0.064.
To investigate the mechanical properties of RC columns confined with self-compacting and micro-expanding concrete filled circular steel tube (SMCFCST) under axial compression, 8 confined RC columns and 1 unconfined RC column were designed and fabricated, and an axial compressive test was conducted. The test parameters including the thickness of the steel tube, the strength of self-compacting and micro-expanding filling concrete, the type of the filling concrete and the magnitude of the initial axial pressure were considered. The failure modes of specimens and the loading data were recorded, while the load versus vertical deformation curves and the load-strain curves were depicted accordingly. The results showed that the peak loads and ductility of the RC columns were significantly improved after being confined by SMCFCST. The peak loads of the confined columns were apparently increased with the increase of the thickness of steel tube. The peak loads of the confined columns were slightly increased with the increase of the strength of self-compacting and micro-expanding filling concrete. However, the effects of the type of filling concrete and the magnitude of the initial axial pressure on the peak loads of the confined columns were negligible. The formula from Technical Code for Concrete Filled Steel Tubular Structures (GB 50936-2014) was modified to obtain the predictive formula of the bearing capacity of the SMCFCST confined columns under axial compression. The average value of the ratio of the predicted value to the test value was 0.956, and the standard deviation was 0.064.
2023, 53(2): 29-36.
doi: 10.13204/j.gyjzG22113007
Abstract:
In order to analyze the effects of concrete strength and interface roughness on the crack propagation and fracture properties of mixed mode Ⅰ-Ⅱ concrete-epoxy mortar interface, four-point shear tests were conducted on 15 specimens, and the displacement and strain fields of the specimens were obtained by digital image correlation (DIC) technology. The fracture energy, ductility index and the stress intensity factors of mode Ⅰ and mode Ⅱ at the crack tip were calculated based on the linear-elastic fracture mechanics theory and fracture initiation toughness of mode Ⅰ measured by tests. The test results showed that the crack propagated along the interface, which belonged typical quasi-brittle failure. The fracture performance of the interface could be significantly enhanced through increasing the concrete strength, however, there was little effect of the concrete strength on the ratio of the stress intensity factors of mode Ⅰ and mode Ⅱ. The fracture performance, stress field at the crack tip, and failure angle of the specimen was relevant to the interface roughness. As increased from 0 mm to 0.31 mm, 0.97 mm, fracture energy Gu increased by 16.1% and 66.9%, ductility index Gu increased by 5.4% and 27.6% respectively, the ratio of the stress intensity factors of mode Ⅰ and mode Ⅱ decreased by 11.96% and 39.7%, and the failure angle increased by 11.9% and 37.8%, respectively.
In order to analyze the effects of concrete strength and interface roughness on the crack propagation and fracture properties of mixed mode Ⅰ-Ⅱ concrete-epoxy mortar interface, four-point shear tests were conducted on 15 specimens, and the displacement and strain fields of the specimens were obtained by digital image correlation (DIC) technology. The fracture energy, ductility index and the stress intensity factors of mode Ⅰ and mode Ⅱ at the crack tip were calculated based on the linear-elastic fracture mechanics theory and fracture initiation toughness of mode Ⅰ measured by tests. The test results showed that the crack propagated along the interface, which belonged typical quasi-brittle failure. The fracture performance of the interface could be significantly enhanced through increasing the concrete strength, however, there was little effect of the concrete strength on the ratio of the stress intensity factors of mode Ⅰ and mode Ⅱ. The fracture performance, stress field at the crack tip, and failure angle of the specimen was relevant to the interface roughness. As increased from 0 mm to 0.31 mm, 0.97 mm, fracture energy Gu increased by 16.1% and 66.9%, ductility index Gu increased by 5.4% and 27.6% respectively, the ratio of the stress intensity factors of mode Ⅰ and mode Ⅱ decreased by 11.96% and 39.7%, and the failure angle increased by 11.9% and 37.8%, respectively.
2023, 53(2): 37-41.
doi: 10.13204/j.gyjzG23010503
Abstract:
Due to abnormal equipment or environmental noise, cusp anomaly data usually occurs in structural monitoring data. Manual handing is time-consuming, and cusp anomaly data disturbs the accuracy of alarm. Based on moving average filter and 3σ criterion, dual-window sliding filter was used for jump value anomaly recognition in structural monitoring. Abnormal data was translated to reasonable data by reasonable representative value of abnormal data based on 3σ criterion. The phenomenon of the jump of construction data was considered in moving average filter. Thus, misjudgment was solved. The proposed method was verified by real monitoring data in Hangzhouxi Railway Station. The results indicated that dual-window sliding filter could identify the abnormal jump point efficiently and avoid misjudgment by the phenomenon of the jump of construction data.
Due to abnormal equipment or environmental noise, cusp anomaly data usually occurs in structural monitoring data. Manual handing is time-consuming, and cusp anomaly data disturbs the accuracy of alarm. Based on moving average filter and 3σ criterion, dual-window sliding filter was used for jump value anomaly recognition in structural monitoring. Abnormal data was translated to reasonable data by reasonable representative value of abnormal data based on 3σ criterion. The phenomenon of the jump of construction data was considered in moving average filter. Thus, misjudgment was solved. The proposed method was verified by real monitoring data in Hangzhouxi Railway Station. The results indicated that dual-window sliding filter could identify the abnormal jump point efficiently and avoid misjudgment by the phenomenon of the jump of construction data.
2023, 53(2): 42-50.
doi: 10.13204/j.gyjzG22030401
Abstract:
To overcome the tendenly of fragmentization, setting, and hollowing of traditional landscape resources caused by the existing protection methods of traditional settlements and to achieve the purpose of overall protection, Taxia Village in Fujian was taken as the research object to explore the tradition. The cognitive approach to the overall value of the settlement was discussed, context of the role of the traditional settlement "culture-activity-landscape" and the cultural mechanism of the overall style generation were explored, and the delineation method of the protection zone under the concept of historical landscape was proposed, aiming to preserve the characteristics and completeness of the traditional settlement style.
To overcome the tendenly of fragmentization, setting, and hollowing of traditional landscape resources caused by the existing protection methods of traditional settlements and to achieve the purpose of overall protection, Taxia Village in Fujian was taken as the research object to explore the tradition. The cognitive approach to the overall value of the settlement was discussed, context of the role of the traditional settlement "culture-activity-landscape" and the cultural mechanism of the overall style generation were explored, and the delineation method of the protection zone under the concept of historical landscape was proposed, aiming to preserve the characteristics and completeness of the traditional settlement style.
2023, 53(2): 51-57.
doi: 10.13204/j.gyjzG22101206
Abstract:
Adequate outdoor activities are of great significance to the healthy development of children. However, with the continuous increase of urban population and building density under the background of rapid urbanization, the outdoor space for urban children urgently needs to be expanded. Although rooftop space of public buildings is a huge stock of urban resources, currently the consideration of children's benefits is very limited. By analyzing the carrier and expansion path of today's urban children's outdoor activity space, this study point out the advantages and significances of using public building rooftops as children's outdoor playground. From the Child-friendly perspective, combined with prototype extraction and case analysis, this paper discussed the environmental characteristics of public building rooftop outdoor activity space from four aspects:spatial form, spatial interface, traffic connection and landscape theme. Finally, some suggestions were put forward such as attaching importance to children's rights and interests, supplying a diversified supplements to the outdoor activity space of urban children, and improving the quality of rooftop spaces, so as to provide useful ideas for expanding urban outdoor space for children and promoting the construction of child-friendly cities.
Adequate outdoor activities are of great significance to the healthy development of children. However, with the continuous increase of urban population and building density under the background of rapid urbanization, the outdoor space for urban children urgently needs to be expanded. Although rooftop space of public buildings is a huge stock of urban resources, currently the consideration of children's benefits is very limited. By analyzing the carrier and expansion path of today's urban children's outdoor activity space, this study point out the advantages and significances of using public building rooftops as children's outdoor playground. From the Child-friendly perspective, combined with prototype extraction and case analysis, this paper discussed the environmental characteristics of public building rooftop outdoor activity space from four aspects:spatial form, spatial interface, traffic connection and landscape theme. Finally, some suggestions were put forward such as attaching importance to children's rights and interests, supplying a diversified supplements to the outdoor activity space of urban children, and improving the quality of rooftop spaces, so as to provide useful ideas for expanding urban outdoor space for children and promoting the construction of child-friendly cities.
2023, 53(2): 58-63.
doi: 10.13204/j.gyjzG22081804
Abstract:
In the promotion process of many industrialized and low-energy rural house systems in Guanzhong area of Shaanxi in recent years, courtyard layout, the most prominent architectural regional characteristic, is often overlooked; its practical and artistic advantages such as microclimate mediation, continuation of village texture, inhertance of cultural characteristics and so on, can be in herited by retaining and renovating the gatehouse or interiorizing the inner courtyard. The paper focused on the introduction of a standardized courtyard house design with glass skylights, so as to inherit regional characteristics and adapt to modern life. At the same time, in order to improve the individual requirements, site adaptability, customer participation and design efficiency of the standardized house design, based on the data-driven characteristics of parametric software, combined with the generation logic of the courtyard house and the construction characteristics of EPS modular house, the parametric derivative development of standardized house design was carried out. The research could provide a reference for the parametric design of rural houses, so as to inherit the regional characteristics and avoid the homogenization of appearances.
In the promotion process of many industrialized and low-energy rural house systems in Guanzhong area of Shaanxi in recent years, courtyard layout, the most prominent architectural regional characteristic, is often overlooked; its practical and artistic advantages such as microclimate mediation, continuation of village texture, inhertance of cultural characteristics and so on, can be in herited by retaining and renovating the gatehouse or interiorizing the inner courtyard. The paper focused on the introduction of a standardized courtyard house design with glass skylights, so as to inherit regional characteristics and adapt to modern life. At the same time, in order to improve the individual requirements, site adaptability, customer participation and design efficiency of the standardized house design, based on the data-driven characteristics of parametric software, combined with the generation logic of the courtyard house and the construction characteristics of EPS modular house, the parametric derivative development of standardized house design was carried out. The research could provide a reference for the parametric design of rural houses, so as to inherit the regional characteristics and avoid the homogenization of appearances.
2023, 53(2): 64-71.
doi: 10.13204/j.gyjzG21062102
Abstract:
The environmental services and quality of high-speed railway station affects the travel experience and satisfaction of passengers, which is also the basic guarantee for the overall coordination and service integrity of the station. In order to find out the key facts that affect the environmental service qualities and improve the space environment and the integrated services as well, taking the typical railway station in China as the research object, the development demands of its environmental qualities and the connotation characteristics were combed. Based on the post-occupancy evaluation results, taking the importance of environmental characteristics such as evaluation level and high frequency as the potential basis, the key contents closely related to the user experience were extracted, and five core elements of environmental quality were reconstructed based on space, facilities, services, nature and landscape. Meanwhile, the paper discussed its related influence and modes of action, and put forward the design inspiration and optimization strategies from the aspects of space efficiency, environmental quality, comprehensive services, etc., which could provide some references for the guarantee of the environmental services and quality of high-speed railway stations as well as the scientificity and rationality of planning and design.
The environmental services and quality of high-speed railway station affects the travel experience and satisfaction of passengers, which is also the basic guarantee for the overall coordination and service integrity of the station. In order to find out the key facts that affect the environmental service qualities and improve the space environment and the integrated services as well, taking the typical railway station in China as the research object, the development demands of its environmental qualities and the connotation characteristics were combed. Based on the post-occupancy evaluation results, taking the importance of environmental characteristics such as evaluation level and high frequency as the potential basis, the key contents closely related to the user experience were extracted, and five core elements of environmental quality were reconstructed based on space, facilities, services, nature and landscape. Meanwhile, the paper discussed its related influence and modes of action, and put forward the design inspiration and optimization strategies from the aspects of space efficiency, environmental quality, comprehensive services, etc., which could provide some references for the guarantee of the environmental services and quality of high-speed railway stations as well as the scientificity and rationality of planning and design.
2023, 53(2): 72-78,41.
doi: 10.13204/j.gyjzG21070907
Abstract:
With the acceleration of urbanization, a variety of ecological and environmental problems began to appear, especially in recent years. Under this background, LID (low impact development) has become a hot issue in landscape architecture industry.China is the most widely distributed loess country in the world, so the loess landscape has become an indispensable part of the landscape in China.Loess geology is prone to mutation, discontinuity and irreversibility, which makes it difficult to control flood peak discharge, runoff pollution and rainwater regulation.Aiming at the above special challenges,according to the site environment, through a series of analysis such as GIS, this paper selected LID measures to integrate the environment. In addition, aiming at the special geological condition of loess, artificial transformation was carried out according to local conditions to create ecological green landscape with unique northern landscape artistic conception. Based on the data model of GIS and MIKE, the rain flood of LID scheme of the project was evaluated and analyzed. After the transformation, the flood peak control, runoff pollution and rainwater regulation and storage capacity in the design site could meet the design expectations, which proved that it was feasible to integrate the scientific LID technology into the loess condition.
With the acceleration of urbanization, a variety of ecological and environmental problems began to appear, especially in recent years. Under this background, LID (low impact development) has become a hot issue in landscape architecture industry.China is the most widely distributed loess country in the world, so the loess landscape has become an indispensable part of the landscape in China.Loess geology is prone to mutation, discontinuity and irreversibility, which makes it difficult to control flood peak discharge, runoff pollution and rainwater regulation.Aiming at the above special challenges,according to the site environment, through a series of analysis such as GIS, this paper selected LID measures to integrate the environment. In addition, aiming at the special geological condition of loess, artificial transformation was carried out according to local conditions to create ecological green landscape with unique northern landscape artistic conception. Based on the data model of GIS and MIKE, the rain flood of LID scheme of the project was evaluated and analyzed. After the transformation, the flood peak control, runoff pollution and rainwater regulation and storage capacity in the design site could meet the design expectations, which proved that it was feasible to integrate the scientific LID technology into the loess condition.
2023, 53(2): 79-86.
doi: 10.13204/j.gyjzG22080917
Abstract:
The ontological value evaluation of industrial heritage is the basis of protection and reuse. The ontological value evaluation of the industrial heritage elements of The Great Harbour of Qingdao should focus on the context of city-shipping-port development, and make scientific evaluation according to the characteristics of nearly construction, large number and unique industrial types. Based on comprehensive evaluation method and supplemented by empirical judgment method and expert scoring method, the index system of historical, technological and artistic value was constructed by classification and stratification, and the index standard was refined as the basis of scoring. The value of various heritage elements was quantified, and 121 elements were finally divided into 4 levels. The purpose was to provide a reasonable basis for the preservation and demolition of each heritage element and provide support for protection and reuse.
The ontological value evaluation of industrial heritage is the basis of protection and reuse. The ontological value evaluation of the industrial heritage elements of The Great Harbour of Qingdao should focus on the context of city-shipping-port development, and make scientific evaluation according to the characteristics of nearly construction, large number and unique industrial types. Based on comprehensive evaluation method and supplemented by empirical judgment method and expert scoring method, the index system of historical, technological and artistic value was constructed by classification and stratification, and the index standard was refined as the basis of scoring. The value of various heritage elements was quantified, and 121 elements were finally divided into 4 levels. The purpose was to provide a reasonable basis for the preservation and demolition of each heritage element and provide support for protection and reuse.
2023, 53(2): 87-91.
doi: 10.13204/j.gyjzG21081809
Abstract:
As an important type of Qiuci Grottoes, the central pillar grottoes not only inherited the basically architectural style and function from the Indian grottoes, but also was influenced by the local environment and culture of Xinjiang, forming a style of grotto carving with obvious regional characteristics. On the basis of field investigation, combined with the architectural form characteristics and construction background of the central pillar grottoes in Qiuci, the influence of the natural climate, geographical environment, economic culture and other factors on the constructional characteristics of the grottoes were discussed, and the regional techniques in the constructional characteristics were analyzed and summarized.
As an important type of Qiuci Grottoes, the central pillar grottoes not only inherited the basically architectural style and function from the Indian grottoes, but also was influenced by the local environment and culture of Xinjiang, forming a style of grotto carving with obvious regional characteristics. On the basis of field investigation, combined with the architectural form characteristics and construction background of the central pillar grottoes in Qiuci, the influence of the natural climate, geographical environment, economic culture and other factors on the constructional characteristics of the grottoes were discussed, and the regional techniques in the constructional characteristics were analyzed and summarized.
2023, 53(2): 92-98,91.
doi: 10.13204/j.gyjzG22031203
Abstract:
Through similarity analysis, the 1:4 scale model of CFRP (carbon fiber reinforced plastics) reinforced concrete frame structure was designed and manufactured, and the dynamic test of simulated seismic shaking table was carried out. Unidirectional, bidirectional and tridirectional seismic excitation was applied to test the dynamic characteristics of the structural model. The seismic performance of the CFRP reinforced concrete frame structure was investigated by analyzing the dynamic response and hysteretic performance of the structure under different levels of earthquake, such as acceleration, displacement and internal force. The results showed that with the enhancement of seismic excitation, the natural vibration period of the structure kept getting longer increasing 54% in the X direction and 60% in the Y direction from seven-degree to eight-degree earthquake action, indicating that the structural model had been damaged to varying degrees, resulting in continuous degradation of structural stiffness, increasing deformation and partial concrete crushing failure. However, the structure model still did not collapse after experiencing the rarely accurred earthquake with the peak acceleration of 0.788 g, and the maximum inter-storey displacement angle was less than 1/50, indicating that the structure model had good seismic performance and could meet the seismic fortifying level requirements of "not bad in small earthquakes, repairable in medium earthquakes, and not falling in large earthquakes".
Through similarity analysis, the 1:4 scale model of CFRP (carbon fiber reinforced plastics) reinforced concrete frame structure was designed and manufactured, and the dynamic test of simulated seismic shaking table was carried out. Unidirectional, bidirectional and tridirectional seismic excitation was applied to test the dynamic characteristics of the structural model. The seismic performance of the CFRP reinforced concrete frame structure was investigated by analyzing the dynamic response and hysteretic performance of the structure under different levels of earthquake, such as acceleration, displacement and internal force. The results showed that with the enhancement of seismic excitation, the natural vibration period of the structure kept getting longer increasing 54% in the X direction and 60% in the Y direction from seven-degree to eight-degree earthquake action, indicating that the structural model had been damaged to varying degrees, resulting in continuous degradation of structural stiffness, increasing deformation and partial concrete crushing failure. However, the structure model still did not collapse after experiencing the rarely accurred earthquake with the peak acceleration of 0.788 g, and the maximum inter-storey displacement angle was less than 1/50, indicating that the structure model had good seismic performance and could meet the seismic fortifying level requirements of "not bad in small earthquakes, repairable in medium earthquakes, and not falling in large earthquakes".
2023, 53(2): 99-108,57.
doi: 10.13204/j.gyjzG22040211
Abstract:
The "three levels and two stages" seismic design method currently adopted in China allows structures to undergo plastic deformation under the action of earthquake. However, due to the complexity and uncertainty of earthquakes, structures and components have large residual deformation, which makes it difficult or impossible to repair after the earthquake. Therefore, the displacement-based seismic design method was adopted to calculate the earthquake force and design the self-centering frame, and the dynamic elastic-plastic time-history analysis of the structure was carried out. The results showed that when the self-centering frame joint design was completed, the self-centering ratio and the base shear VBase of the whole structure were recalculated, which was less than 1% from the design base shear force, indicating that the design method had a good fit; according to the results of dynamic time-history analysis, it could be seen that the overall seismic performance of the structure was good, and there was no collapse damage, which could meet the seismic fortification requirements under rarely occurred earthquakes, and the seismic performance of the structure was better than that of cast-in-place joints.
The "three levels and two stages" seismic design method currently adopted in China allows structures to undergo plastic deformation under the action of earthquake. However, due to the complexity and uncertainty of earthquakes, structures and components have large residual deformation, which makes it difficult or impossible to repair after the earthquake. Therefore, the displacement-based seismic design method was adopted to calculate the earthquake force and design the self-centering frame, and the dynamic elastic-plastic time-history analysis of the structure was carried out. The results showed that when the self-centering frame joint design was completed, the self-centering ratio and the base shear VBase of the whole structure were recalculated, which was less than 1% from the design base shear force, indicating that the design method had a good fit; according to the results of dynamic time-history analysis, it could be seen that the overall seismic performance of the structure was good, and there was no collapse damage, which could meet the seismic fortification requirements under rarely occurred earthquakes, and the seismic performance of the structure was better than that of cast-in-place joints.
2023, 53(2): 109-115,182.
doi: 10.13204/j.gyjzG20110507
Abstract:
The response of cathead-type transmission towers under the coupling loading of ice and broken wire were studied by using arc length method. The correlative development of bearing capacity, the development and distribution of inner forces, the stress and out-of-plane deformation of braces were analyzed. The effect of ice thickness on the bearing capacities and failure modes of various types of cathead-type transmission towers were investigated. The results indicated that when the transmission towers were under the coupling load of broken wire and icing, the yielding of the column on the compression side and the members at stiffness mutation part were induced by the bending of towers; The internal force between the tower head and top diaphragm was relatively large when the tower body was subjected to torsion, resulting in yielding to the lower diagonal materials. the column yielding on the compression side of the tower botton combining with the brace buckling on the tower body were triggered by the torsion-bending of towers. The increase of self weight of the tower after being covered with ice would exacerbate the bucking of main materials on the compression side and the yielding of braces, reducing the lateral resistance of towers under broken wire load. The coupling of ice and broken wire loads should be taken into account in the design of transmission towers.
The response of cathead-type transmission towers under the coupling loading of ice and broken wire were studied by using arc length method. The correlative development of bearing capacity, the development and distribution of inner forces, the stress and out-of-plane deformation of braces were analyzed. The effect of ice thickness on the bearing capacities and failure modes of various types of cathead-type transmission towers were investigated. The results indicated that when the transmission towers were under the coupling load of broken wire and icing, the yielding of the column on the compression side and the members at stiffness mutation part were induced by the bending of towers; The internal force between the tower head and top diaphragm was relatively large when the tower body was subjected to torsion, resulting in yielding to the lower diagonal materials. the column yielding on the compression side of the tower botton combining with the brace buckling on the tower body were triggered by the torsion-bending of towers. The increase of self weight of the tower after being covered with ice would exacerbate the bucking of main materials on the compression side and the yielding of braces, reducing the lateral resistance of towers under broken wire load. The coupling of ice and broken wire loads should be taken into account in the design of transmission towers.
2023, 53(2): 116-121.
doi: 10.13204/j.gyjzG20102301
Abstract:
Stainless steel is more and more widely used in civil engineering because of its superior material properties. However, its frame design often refers to steel structure, ignoring the plastic strain before the nominal yield strength of stainless steel, which may cause hidden dangers in stainless steel frame design. In order to reveal the influence of the plastic effect on stainless steel frame, the accurate second-order elastoplastic analysis of three typical frames was carried out and compared with the simplified design method of the national standard Standard for Design of Steel Structures (GB 50017-2017). The results showed that the plastic effect had a great effect on the bending moment and side shift of the stainless steel frame in most cases. The design of the stainless steel frame with reference to the steel structure tended to be unsafe, and the plastic effect coefficient could better reflect the influence of the plastic effect on the frame. Based on the analysis results, the design proposal of stainless steel frame structures was proposed.
Stainless steel is more and more widely used in civil engineering because of its superior material properties. However, its frame design often refers to steel structure, ignoring the plastic strain before the nominal yield strength of stainless steel, which may cause hidden dangers in stainless steel frame design. In order to reveal the influence of the plastic effect on stainless steel frame, the accurate second-order elastoplastic analysis of three typical frames was carried out and compared with the simplified design method of the national standard Standard for Design of Steel Structures (GB 50017-2017). The results showed that the plastic effect had a great effect on the bending moment and side shift of the stainless steel frame in most cases. The design of the stainless steel frame with reference to the steel structure tended to be unsafe, and the plastic effect coefficient could better reflect the influence of the plastic effect on the frame. Based on the analysis results, the design proposal of stainless steel frame structures was proposed.
Quasi-Static Test Study on Eccentrically Braced Steel Frames with Replaceable Links After Earthquake
2023, 53(2): 122-128.
doi: 10.13204/j.gyjzG20101907
Abstract:
In recent years, the goal of seismic fortification has gradually shifted from protecting life safety to quickly returning to normal after an earthquake. The semi-rigid connection eccentrically braced steel frame system with replaceable links can be quickly restored to use by replacing the new link after an earthquake.In order to study the seismic performance of the eccentrically braced steel frame repaired after earthquake and demonstrate the feasibility of replacing links after earthquake, a 1:2 scaled eccentrically braced steel frame was first subjected to quasi-static load, then it was repaired with a new links after the earthquake, and perform quasi-static loading tests again. The test results showed that compared with the original specimen, the hysteresis performance, bearing capacity, ductility coefficient, lateral stiffness and energy dissipation performance of the repaired and specimen with replaceable link were not as good as the original specimen, but still retained a certain bearing capacity and generally good energy-dissipating capacity. Through the analysis of inter-storey displacement angle and the rotation angle of the link, it was shown that the overall deformation capacity of the repaired model and the rotation capacity of the link were still very good.The failure mode and strain of key parts of the frame were analyzed to verify the feasibility of replacing the link repair method.
In recent years, the goal of seismic fortification has gradually shifted from protecting life safety to quickly returning to normal after an earthquake. The semi-rigid connection eccentrically braced steel frame system with replaceable links can be quickly restored to use by replacing the new link after an earthquake.In order to study the seismic performance of the eccentrically braced steel frame repaired after earthquake and demonstrate the feasibility of replacing links after earthquake, a 1:2 scaled eccentrically braced steel frame was first subjected to quasi-static load, then it was repaired with a new links after the earthquake, and perform quasi-static loading tests again. The test results showed that compared with the original specimen, the hysteresis performance, bearing capacity, ductility coefficient, lateral stiffness and energy dissipation performance of the repaired and specimen with replaceable link were not as good as the original specimen, but still retained a certain bearing capacity and generally good energy-dissipating capacity. Through the analysis of inter-storey displacement angle and the rotation angle of the link, it was shown that the overall deformation capacity of the repaired model and the rotation capacity of the link were still very good.The failure mode and strain of key parts of the frame were analyzed to verify the feasibility of replacing the link repair method.
2023, 53(2): 129-132,50.
doi: 10.13204/j.gyjzG22011302
Abstract:
In order to research the critical apparent wave velocity of long-span spatial structures considering traveling wave effect, the time-history method was used to investigate the seismic response of double-layer cylindrical latticed shells with different structural styles and geometric sizes under multiple-support excitation with kinds of apparent wave velocities and single excitation. The results showed that the traveling wave effect with any apparent wave velocity had no obviously disadvantaged effect on transverse and web members, but had a great disadvantaged effect on longitudinal members, in which the internal force was small at the bottom chord and large at the top chord. Changing the spacing of supports had little effect on the traveling wave effect, while the effect of apparent wave velocity on the traveling wave effect was related to the structural style and geometric sizes and so on. It was concluded that only the longitudinal members at the top chord were needed for the research of the traveling wave effect, and the critical apparent wave velocity of any structure considering traveling wave effect should be analyzed separately.
In order to research the critical apparent wave velocity of long-span spatial structures considering traveling wave effect, the time-history method was used to investigate the seismic response of double-layer cylindrical latticed shells with different structural styles and geometric sizes under multiple-support excitation with kinds of apparent wave velocities and single excitation. The results showed that the traveling wave effect with any apparent wave velocity had no obviously disadvantaged effect on transverse and web members, but had a great disadvantaged effect on longitudinal members, in which the internal force was small at the bottom chord and large at the top chord. Changing the spacing of supports had little effect on the traveling wave effect, while the effect of apparent wave velocity on the traveling wave effect was related to the structural style and geometric sizes and so on. It was concluded that only the longitudinal members at the top chord were needed for the research of the traveling wave effect, and the critical apparent wave velocity of any structure considering traveling wave effect should be analyzed separately.
2023, 53(2): 133-137,196.
doi: 10.13204/j.gyjz2018121501
Abstract:
Bosed on the design concept of reinforced concrete special-shaped column, a composite cross-shaped concrete filled steel tubular column formed by the welding of square steel tube and channel steel was put forward. Taking the length and cross-section form as the main parameters, 5 specimens were designed and fabricated. Through the axial compression test, the failure modes and load-strain curves of the specimens were investigated, and the effects of various parameters on the bearing capacity and ductility of the new section concrete filled steel tubular columns under axial compression were analyzed. The final faiure mode of composite cross-shaped concrete filled steel tube specimens was a number of small bulge distributed along the specimen length. The results showed that steel tube had good restraint to the concrete, this combination was effective to improve the bearing capacity of cross-shaped column and improve its ductility. The ultimate bearing capacity of specimens with the same cross-seotion form slightly decreased with the increase of column height while the specimens with the same column height and different cross-section forms significantly increased with the increase of column leg length, on the basis of current norms, the calculation formula for the bearing capacity of composite cross-shaped concrete filled steel tube columns under axial compression was proposed, the calculated results agreed well with the experimental results.
Bosed on the design concept of reinforced concrete special-shaped column, a composite cross-shaped concrete filled steel tubular column formed by the welding of square steel tube and channel steel was put forward. Taking the length and cross-section form as the main parameters, 5 specimens were designed and fabricated. Through the axial compression test, the failure modes and load-strain curves of the specimens were investigated, and the effects of various parameters on the bearing capacity and ductility of the new section concrete filled steel tubular columns under axial compression were analyzed. The final faiure mode of composite cross-shaped concrete filled steel tube specimens was a number of small bulge distributed along the specimen length. The results showed that steel tube had good restraint to the concrete, this combination was effective to improve the bearing capacity of cross-shaped column and improve its ductility. The ultimate bearing capacity of specimens with the same cross-seotion form slightly decreased with the increase of column height while the specimens with the same column height and different cross-section forms significantly increased with the increase of column leg length, on the basis of current norms, the calculation formula for the bearing capacity of composite cross-shaped concrete filled steel tube columns under axial compression was proposed, the calculated results agreed well with the experimental results.
2023, 53(2): 138-143,121.
doi: 10.13204/j.gyjzG21073103
Abstract:
Based on the time history of wind loads at each structural story obtained from wind tunnel tests, the wind-induced vibration responses of uncontrolled and controlled landscape towers by return period winds for 10 years, 50 years and 100 years were analyzed by the ABAQUS software, and the vibration reduction effect of TMD under wind loads in different return periods were obtained. The calculation results showed that the two-stage variable damping from TMDs could effectively reduce structural responses excited by wind loads, and the vibration-reduction efficiency increased with the increase of stories; TMDs did not exceed the longest stroke length under wind loads. It was in primary damping that excited by the return period wind for 10 years and in secondary damping excited by return period winds for 50 and 100 years; TMDs could effectively improve the structural comfort, and the efficiency of acceleration control was higher than that of displacement control; vibration reduction measures by TMDs were suitable for wind vibration control design of high-rise structures.
Based on the time history of wind loads at each structural story obtained from wind tunnel tests, the wind-induced vibration responses of uncontrolled and controlled landscape towers by return period winds for 10 years, 50 years and 100 years were analyzed by the ABAQUS software, and the vibration reduction effect of TMD under wind loads in different return periods were obtained. The calculation results showed that the two-stage variable damping from TMDs could effectively reduce structural responses excited by wind loads, and the vibration-reduction efficiency increased with the increase of stories; TMDs did not exceed the longest stroke length under wind loads. It was in primary damping that excited by the return period wind for 10 years and in secondary damping excited by return period winds for 50 and 100 years; TMDs could effectively improve the structural comfort, and the efficiency of acceleration control was higher than that of displacement control; vibration reduction measures by TMDs were suitable for wind vibration control design of high-rise structures.
2023, 53(2): 144-150.
doi: 10.13204/j.gyjzG20082506
Abstract:
In order to establish the calculation method for the critical moment of simply-supported steel beams with lateral restraints equally distributed along the span, the segments between two lateral restraints were treated as simply-supported steel beams firstly. Then, the characteristic of the end moment ratio for these segments were revealed for variable number of lateral restraints and end moment ratio of lateral restrained steel beams. A segment with the maximum end moment of the lateral restrained steel beam, which named as the calculated segment, was selected for determining the critical moment. The interaction between the calculated segment and other segments were analyzed and revealed for pure bending and impure bending theoretically and numerically. Values of the coefficient C1 and the expressions of the interaction coefficient α were proposed, by which the calculation of the critical moment for lateral restrained steel beams was transformed to the calculation of the critical moment for the calculated segment. Finally, comparisons were carried ont between the critical moments obtained from the proposed method, the method in current design standards and the numerical results. The results showed that the values of the coefficient C1 and the expressions of the interaction coefficient α were accurate enough for determining the critical moment of lateral restrained steel beams subjected to end moments, while the βb coefficient provided in Standard for Design of Steel Structures (GB 50017-2017) and the C1 provided in Technical Code of Cold-Formed Thin-Wall Steel Structures (GB 50018-2002) were accurate for pure bending, but for impure bending, unsafe or too safe predictions were generated.
In order to establish the calculation method for the critical moment of simply-supported steel beams with lateral restraints equally distributed along the span, the segments between two lateral restraints were treated as simply-supported steel beams firstly. Then, the characteristic of the end moment ratio for these segments were revealed for variable number of lateral restraints and end moment ratio of lateral restrained steel beams. A segment with the maximum end moment of the lateral restrained steel beam, which named as the calculated segment, was selected for determining the critical moment. The interaction between the calculated segment and other segments were analyzed and revealed for pure bending and impure bending theoretically and numerically. Values of the coefficient C1 and the expressions of the interaction coefficient α were proposed, by which the calculation of the critical moment for lateral restrained steel beams was transformed to the calculation of the critical moment for the calculated segment. Finally, comparisons were carried ont between the critical moments obtained from the proposed method, the method in current design standards and the numerical results. The results showed that the values of the coefficient C1 and the expressions of the interaction coefficient α were accurate enough for determining the critical moment of lateral restrained steel beams subjected to end moments, while the βb coefficient provided in Standard for Design of Steel Structures (GB 50017-2017) and the C1 provided in Technical Code of Cold-Formed Thin-Wall Steel Structures (GB 50018-2002) were accurate for pure bending, but for impure bending, unsafe or too safe predictions were generated.
2023, 53(2): 151-156,223.
doi: 10.13204/j.gyjzG22050702
Abstract:
Based on the steel trestle of Pingtan Straits Rail-cum-Road Bridge, the corrosion status of the steel pipe piles in the deep water-bare rock area was investigated. Firstly, the steel plates under corrosion were sampled on site, and the surface morphology of the steel plates was measured, and then the steel pipe piles were simplified into the stepped columns for analysis according to the depth distribution of steel pit corrosion. Finally, the refined finite element model considering the pit corrosion was established based on the field test results, and the stability bearing capacity of the corroded steel pipe piles was analyzed. The results showed that a non-uniform corrosion distribution along the column height could be observed on the corroded steel pipe piles in the marine environment, and the maximum corrosion depth in the splash zone could be 5 times of that in the full immersion zone. The steel pipe piles could be simplified as the stepped columns with variable cross-section, and the formula for calculating the effective length of stepped columns was proposed. The finite element model of stepped columns could be used as the simplified model to analyze the stability bearing capacity of corroded steel pipe piles, which could provide a reference for the future research on the working performance of corroded steel trestles.
Based on the steel trestle of Pingtan Straits Rail-cum-Road Bridge, the corrosion status of the steel pipe piles in the deep water-bare rock area was investigated. Firstly, the steel plates under corrosion were sampled on site, and the surface morphology of the steel plates was measured, and then the steel pipe piles were simplified into the stepped columns for analysis according to the depth distribution of steel pit corrosion. Finally, the refined finite element model considering the pit corrosion was established based on the field test results, and the stability bearing capacity of the corroded steel pipe piles was analyzed. The results showed that a non-uniform corrosion distribution along the column height could be observed on the corroded steel pipe piles in the marine environment, and the maximum corrosion depth in the splash zone could be 5 times of that in the full immersion zone. The steel pipe piles could be simplified as the stepped columns with variable cross-section, and the formula for calculating the effective length of stepped columns was proposed. The finite element model of stepped columns could be used as the simplified model to analyze the stability bearing capacity of corroded steel pipe piles, which could provide a reference for the future research on the working performance of corroded steel trestles.
2023, 53(2): 157-162.
doi: 10.13204/j.gyjzG21121703
Abstract:
Triaxially consolidated drained shear tests by the GDS standard stress path were conducted on the Qinzhou Port sea sand under the different effective confining pressures and clay content, which was be analyzed the effect of effective confining pressure and clay content on the strength and deformation characteristics of sea sand in Qinzhou Port. The results showed:under the same effective confining pressure, as the clay content increased, the stress-strain curves of clay-contained sea sand converted from a strain-softening curve to a strain-hardening curve. The peak strength, relative stress softening coefficient, and volumetric strain decreased steadily; the peak strain increased simultaneously. In the same clay content, the peak strength of the specimens increased gradually with the increase of the effective confining pressure. When the effective confining pressure for specimens of pure sand was 300 kPa, the peak strength of specimens was 1.517 times higher than that whose confining pressure was 100 kPa. There was a good linear relation between the effective confining pressure and the peak strength. Simultaneously, the relative softening coefficient of stress and volumetric strain decreased with the increase of the effective confining pressure. Finally, in the range of 0% to 20% of the clay content, and the relation between the relative stress softening coefficient and the effective confining pressure and clay content was established.
Triaxially consolidated drained shear tests by the GDS standard stress path were conducted on the Qinzhou Port sea sand under the different effective confining pressures and clay content, which was be analyzed the effect of effective confining pressure and clay content on the strength and deformation characteristics of sea sand in Qinzhou Port. The results showed:under the same effective confining pressure, as the clay content increased, the stress-strain curves of clay-contained sea sand converted from a strain-softening curve to a strain-hardening curve. The peak strength, relative stress softening coefficient, and volumetric strain decreased steadily; the peak strain increased simultaneously. In the same clay content, the peak strength of the specimens increased gradually with the increase of the effective confining pressure. When the effective confining pressure for specimens of pure sand was 300 kPa, the peak strength of specimens was 1.517 times higher than that whose confining pressure was 100 kPa. There was a good linear relation between the effective confining pressure and the peak strength. Simultaneously, the relative softening coefficient of stress and volumetric strain decreased with the increase of the effective confining pressure. Finally, in the range of 0% to 20% of the clay content, and the relation between the relative stress softening coefficient and the effective confining pressure and clay content was established.
2023, 53(2): 163-168.
doi: 10.13204/j.gyjzG21120802
Abstract:
The threshold value of rock is an important parameter to predict whether deformation failure occurs. To study the changing law of threshold value and its influence on rock deformation characteristics, using the CSS-1950 biaxially rheological testing machine for rock to conduct the cyclic loading and unloading test for cement mortar blocks with different roughness of Barton curve discontinuities, by analyzing the deformation characteristics of different rock discontinuities specimens under various normal stresses, the solution method of threshold value was summarized. Based on the calculation results of threshold values, the relation between the threshold value, the joint roughness coefficient (JRC) and the normal stress was analyzed. The effects of the JRC and the normal stress on the deformation characteristics of rock discontinuities were discussed. Research showed that with the increase of the shear load level, the displacement of the rock discontinuity subjected to cyclic loading first grew in a linear trend, and then grew in a nonlinear development state. The horizontal stress values corresponding to the two turning points were the threshold values of the rock discontinuity. With the increase of the JRC or normal stress, the threshold values of the rock discontinuity increased, however the threshold value ratio decreased.
The threshold value of rock is an important parameter to predict whether deformation failure occurs. To study the changing law of threshold value and its influence on rock deformation characteristics, using the CSS-1950 biaxially rheological testing machine for rock to conduct the cyclic loading and unloading test for cement mortar blocks with different roughness of Barton curve discontinuities, by analyzing the deformation characteristics of different rock discontinuities specimens under various normal stresses, the solution method of threshold value was summarized. Based on the calculation results of threshold values, the relation between the threshold value, the joint roughness coefficient (JRC) and the normal stress was analyzed. The effects of the JRC and the normal stress on the deformation characteristics of rock discontinuities were discussed. Research showed that with the increase of the shear load level, the displacement of the rock discontinuity subjected to cyclic loading first grew in a linear trend, and then grew in a nonlinear development state. The horizontal stress values corresponding to the two turning points were the threshold values of the rock discontinuity. With the increase of the JRC or normal stress, the threshold values of the rock discontinuity increased, however the threshold value ratio decreased.
2023, 53(2): 177-182.
doi: 10.13204/j.gyjzG22011009
Abstract:
With the increasing development of unmanned aerial vehicle technology, unmanned aerial vehicle remote sensing (UAVRS) has been widely used in the risk analysis of geological hazards. However, the quantitative risk analysis method of landslide hazards based on that technique has still being developed up to now. A three-dimensional geometric model of slopes based on the laser point cloud data collected by UAVRS was built, the failure probability of the slope was appraised by the first-order reliability method, the safety factors of the slope were calculated by the numerical simulation software of FLAC3D, the failure consequences of the slope were determined based on the secondary development of FLAC3D, and the quantitative risk analysis on a single landslide hazard was conducted. The proposed analysis method was simple and straightforward, which provided a new idea for assessment risks of landslide hazards.
With the increasing development of unmanned aerial vehicle technology, unmanned aerial vehicle remote sensing (UAVRS) has been widely used in the risk analysis of geological hazards. However, the quantitative risk analysis method of landslide hazards based on that technique has still being developed up to now. A three-dimensional geometric model of slopes based on the laser point cloud data collected by UAVRS was built, the failure probability of the slope was appraised by the first-order reliability method, the safety factors of the slope were calculated by the numerical simulation software of FLAC3D, the failure consequences of the slope were determined based on the secondary development of FLAC3D, and the quantitative risk analysis on a single landslide hazard was conducted. The proposed analysis method was simple and straightforward, which provided a new idea for assessment risks of landslide hazards.
2023, 53(2): 183-189,150.
doi: 10.13204/j.gyjzG22081709
Abstract:
The hydration exothermic characteristics of fly ash micro beads and superfine slag powder when they are mixed alone or in combination at a water-binder ratio of 0.16 were studied by isothermal calorimeter. The influence on the compressive strength of paste were discussed, and two low-heat cementitious systems were proposed. The results showed that the 56 d compressive strength could still reach 157.3-176.5 MPa when the total dosage of micro beads and super slag powder was 50%-65%, which was not lower than that of pure cement system; compared with superfine slag powder, micro beads had more prominent peak shaving and heat reduction capacity. When the two were mixed together, the exothermic rate and total hydration heat in the early induction period and acceleration period could be further reduced as a whole. The second exothermic peak could be as low as 48.0% of the straight cement. When the content of micro beads was more than 35%, the superposed effect of superfine powder made the exothermic rate in the acceleration period before 8.9 h higher than that of straight cement. The X-ray diffraction and thermogravimetry analysis showed that the superposed effect did not accelerate the formation of early ettringite, but it promoted the early activation of pozzolanic activity to a certain extent after 3 days, and generated more low alkaline hydrated calcium silicate and gismondine; the fiber-free ultra-high performance concrete with 56 d compressive strength of 150-160 MPa was prepared by using the proposed low-heat cementitious system. Their adiabatic temperature rise ΔT was 37.4-41.2℃, and the minimum cement dosage was 35%, which could provide a reference for the preparation of low-heat ultra-high performance concrete above 150 MPa.
The hydration exothermic characteristics of fly ash micro beads and superfine slag powder when they are mixed alone or in combination at a water-binder ratio of 0.16 were studied by isothermal calorimeter. The influence on the compressive strength of paste were discussed, and two low-heat cementitious systems were proposed. The results showed that the 56 d compressive strength could still reach 157.3-176.5 MPa when the total dosage of micro beads and super slag powder was 50%-65%, which was not lower than that of pure cement system; compared with superfine slag powder, micro beads had more prominent peak shaving and heat reduction capacity. When the two were mixed together, the exothermic rate and total hydration heat in the early induction period and acceleration period could be further reduced as a whole. The second exothermic peak could be as low as 48.0% of the straight cement. When the content of micro beads was more than 35%, the superposed effect of superfine powder made the exothermic rate in the acceleration period before 8.9 h higher than that of straight cement. The X-ray diffraction and thermogravimetry analysis showed that the superposed effect did not accelerate the formation of early ettringite, but it promoted the early activation of pozzolanic activity to a certain extent after 3 days, and generated more low alkaline hydrated calcium silicate and gismondine; the fiber-free ultra-high performance concrete with 56 d compressive strength of 150-160 MPa was prepared by using the proposed low-heat cementitious system. Their adiabatic temperature rise ΔT was 37.4-41.2℃, and the minimum cement dosage was 35%, which could provide a reference for the preparation of low-heat ultra-high performance concrete above 150 MPa.
2023, 53(2): 190-196.
doi: 10.13204/j.gyjzG21061106
Abstract:
In order to overcome the defects of Portland cement with its high energy consumption, high pollution and high CO2 emission, it has reached a consensus on the development of new low-carbon cementing materials that can replace Portland cement. In this paper, composite geopolymer cement (CGC) was prepared by using alkaline solution to activate multi-componental aluminum silicates under normal conditions. Based on the molar ratio of key oxides and geopolymeric reaction mechanism, the mixture proportions of CGC were designed. The effects of key parameters including precursor, alkali activator, water-solid ratio, curing medium on compressive strength of CGC were discussed. The results showed that the prepared CGC under normal conditions met the usage requirements well. When the contents of slag and metakaolin in the precursor were higher, the strength of CGC was greater. When the content of fly ash was higher, the strength of CGC was lower. The relation between CGC's strength and the contents of water glass and NaOH was non-monotonic. The strength of CGC specimens immersed in artificial seawater was nearly 7% lower than the one stored in standard conditions.
In order to overcome the defects of Portland cement with its high energy consumption, high pollution and high CO2 emission, it has reached a consensus on the development of new low-carbon cementing materials that can replace Portland cement. In this paper, composite geopolymer cement (CGC) was prepared by using alkaline solution to activate multi-componental aluminum silicates under normal conditions. Based on the molar ratio of key oxides and geopolymeric reaction mechanism, the mixture proportions of CGC were designed. The effects of key parameters including precursor, alkali activator, water-solid ratio, curing medium on compressive strength of CGC were discussed. The results showed that the prepared CGC under normal conditions met the usage requirements well. When the contents of slag and metakaolin in the precursor were higher, the strength of CGC was greater. When the content of fly ash was higher, the strength of CGC was lower. The relation between CGC's strength and the contents of water glass and NaOH was non-monotonic. The strength of CGC specimens immersed in artificial seawater was nearly 7% lower than the one stored in standard conditions.
2023, 53(2): 197-203.
doi: 10.13204/j.gyjzG22071819
Abstract:
Memetics is a theory that explains the laws of cultural transmission and evolution from the view of Darwin's theory of evolution, and the architectural meme theory is the latest cross achievement of memetics in architecture. From the perspective of memetics, the connotation and concept of architectural memes were analyzed and defined, and the homologous research context of architectural memes between China and the West was studied. Firstly, based on the memetics representation theory, the core information of the concept and connotation of architectural memes were analyzed. Secondly, the concept of architectural memes was defined based on the connotation information of unique architectural information, the representational capability and defined transmission evolution capability. Finally, the research tendency on the homology of architectural memes was divided into two types:the research on the order, structure and evolution characteristics of the architectural complex system, and the exploration on the minimal characteristic factor of architecture. Thereby, the development contexts of architectural memes at home and abroad were obtained.
Memetics is a theory that explains the laws of cultural transmission and evolution from the view of Darwin's theory of evolution, and the architectural meme theory is the latest cross achievement of memetics in architecture. From the perspective of memetics, the connotation and concept of architectural memes were analyzed and defined, and the homologous research context of architectural memes between China and the West was studied. Firstly, based on the memetics representation theory, the core information of the concept and connotation of architectural memes were analyzed. Secondly, the concept of architectural memes was defined based on the connotation information of unique architectural information, the representational capability and defined transmission evolution capability. Finally, the research tendency on the homology of architectural memes was divided into two types:the research on the order, structure and evolution characteristics of the architectural complex system, and the exploration on the minimal characteristic factor of architecture. Thereby, the development contexts of architectural memes at home and abroad were obtained.
2023, 53(2): 204-210,168.
doi: 10.13204/j.gyjzG22041004
Abstract:
As a kind of lightweight and high-strength member, autoclaved aerated concrete slabs have been widely used in multi-high-level building envelope structures, and the mechanical properties of such slabs can effectively ensure the structure safety. The codes of autoclaved aerated concrete in China and Europe were comparatively analyzed from the four aspects of the positive section bearing capacity, oblique cross-section bearing capacity, and the cracked load. The results showed that compared with the experimental values, the design valves of the bearing capacity of normal sechen and obliqhe section in JGJ/T 17-2020 had smaller error than those in EN 12602:2016, and the oblique section bearing capacity was mainly related to the strength of the concrete; under the limit state of normal use, the deflection and crack load has a safety reserve of 1.5 to 2 times the design value. The EN 12602:2016 considered the bonding properties of steel bars, autoclaved aerated concrete creep and contraction, and this kind of theoretical value ratio and test value ratio between 0.71 to 1.02 and 0.78 to 1.06, respectively, the degree of fit could be used as a basis for structure.
As a kind of lightweight and high-strength member, autoclaved aerated concrete slabs have been widely used in multi-high-level building envelope structures, and the mechanical properties of such slabs can effectively ensure the structure safety. The codes of autoclaved aerated concrete in China and Europe were comparatively analyzed from the four aspects of the positive section bearing capacity, oblique cross-section bearing capacity, and the cracked load. The results showed that compared with the experimental values, the design valves of the bearing capacity of normal sechen and obliqhe section in JGJ/T 17-2020 had smaller error than those in EN 12602:2016, and the oblique section bearing capacity was mainly related to the strength of the concrete; under the limit state of normal use, the deflection and crack load has a safety reserve of 1.5 to 2 times the design value. The EN 12602:2016 considered the bonding properties of steel bars, autoclaved aerated concrete creep and contraction, and this kind of theoretical value ratio and test value ratio between 0.71 to 1.02 and 0.78 to 1.06, respectively, the degree of fit could be used as a basis for structure.
2023, 53(2): 211-217,71.
doi: 10.13204/j.gyjzG22042524
Abstract:
The modified polypropylene fiber reinforced cement-based materials prepared by two kinds of mixing processes (pre-fiber mixing method and post-fiber mixing method) were tested to study the fiber dispersion and working performance of fresh mortar under different mixing times and mixing rates, and the compression test and flexural test of its castables at different ages were carried out. Based on the above test results, a reliable mixing process was established, and the flat plate specimens were poured. The effects of the length and content of modified polypropylene fibers on the bending properties were studied by four-point-bending test. The results showed that the mixing processes of post-fiber mixing method and slow mixing method were reliable.When the fiber length was 12 mm, the strength was the largest, and when the fiber length was 20 mm, the ductility, toughness and residual strength were the best. When the fiber length was the same, the bending properties would increase with the increase of fiber content. This study can provide an experimental basis for the preparing fiber-reinforced cement-based materials by modified polypropylene fibers.
The modified polypropylene fiber reinforced cement-based materials prepared by two kinds of mixing processes (pre-fiber mixing method and post-fiber mixing method) were tested to study the fiber dispersion and working performance of fresh mortar under different mixing times and mixing rates, and the compression test and flexural test of its castables at different ages were carried out. Based on the above test results, a reliable mixing process was established, and the flat plate specimens were poured. The effects of the length and content of modified polypropylene fibers on the bending properties were studied by four-point-bending test. The results showed that the mixing processes of post-fiber mixing method and slow mixing method were reliable.When the fiber length was 12 mm, the strength was the largest, and when the fiber length was 20 mm, the ductility, toughness and residual strength were the best. When the fiber length was the same, the bending properties would increase with the increase of fiber content. This study can provide an experimental basis for the preparing fiber-reinforced cement-based materials by modified polypropylene fibers.
2023, 53(2): 218-223.
doi: 10.13204/j.gyjzG21100402
Abstract:
To ensure the safe operation of a certain flood control wall in Shanghai and sustainable development of social production, life and economy,based on the on-site investigation into the surface cracks of the flood control wall project, the method combining mechanical analysis and finite element numerical simulations was adopted and analyzed the selected most unfavorable section of flood control walls subjected to concentrated tension of sunken ships in floods. The finite element software PLAXIS was used to analyze the safety of the flood control wall. The research results showed that although obvious horizontal displacement had occurred in the wall,the calculation values of horizontal displacement at the top of the wall and internal force in the control section at both the actual ground elevation and design ground elevation were all smaller than those of theoretical allowable values of displacement and internal force. In other words,the flood control wall was still integrated and kept in good operation.
To ensure the safe operation of a certain flood control wall in Shanghai and sustainable development of social production, life and economy,based on the on-site investigation into the surface cracks of the flood control wall project, the method combining mechanical analysis and finite element numerical simulations was adopted and analyzed the selected most unfavorable section of flood control walls subjected to concentrated tension of sunken ships in floods. The finite element software PLAXIS was used to analyze the safety of the flood control wall. The research results showed that although obvious horizontal displacement had occurred in the wall,the calculation values of horizontal displacement at the top of the wall and internal force in the control section at both the actual ground elevation and design ground elevation were all smaller than those of theoretical allowable values of displacement and internal force. In other words,the flood control wall was still integrated and kept in good operation.
