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2021 Vol. 51, No. 8
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2021, 51(8): 1-10,27.
doi: 10.13204/j.gyjzG20111404
Abstract:
There are many serious challenges for the environment and energy in China, energy efficiency in residential districts has attracted much attention. Optimizing the layout of residential districts to improve urban microclimate is an effective mean to reduce building energy consumption. Based on the Grasshopper parametric platform, combined with the Ladybug Tools,a simulation plug-in of sunshine, microclimate, and energy consumption, and using the single-objective genetic algorithm operator Galapagos, the paper proposed an energy-efficiency-oriented method for automatically optimizing the layout of residential districts. This paper took the planning of a high-rise residential district in Nanjing city as an example, selected the building location, building orientation, and building height as the form variables, and took the total energy use intensity of the annual building cooling and heating load as the optimization objective to develop the form layout and its automatic optimization, and explained its use steps and application effects in detail. The results showed that a better energy-saving effect could be achieved in the early scheme stage by optimizing the layout of residential districts. This method could provide technical reference for designers to design energy saving in the early stage.
There are many serious challenges for the environment and energy in China, energy efficiency in residential districts has attracted much attention. Optimizing the layout of residential districts to improve urban microclimate is an effective mean to reduce building energy consumption. Based on the Grasshopper parametric platform, combined with the Ladybug Tools,a simulation plug-in of sunshine, microclimate, and energy consumption, and using the single-objective genetic algorithm operator Galapagos, the paper proposed an energy-efficiency-oriented method for automatically optimizing the layout of residential districts. This paper took the planning of a high-rise residential district in Nanjing city as an example, selected the building location, building orientation, and building height as the form variables, and took the total energy use intensity of the annual building cooling and heating load as the optimization objective to develop the form layout and its automatic optimization, and explained its use steps and application effects in detail. The results showed that a better energy-saving effect could be achieved in the early scheme stage by optimizing the layout of residential districts. This method could provide technical reference for designers to design energy saving in the early stage.
2021, 51(8): 11-18.
doi: 10.13204/j.gyjzG20040907
Abstract:
Urban rail transit has brought a series of social problems about energy consumption and environment with its rapid development. With the gradual advancement of green development in various industries, the green development of urban rail transit has gradually attracted people's attention. Combined with the development status and problems of urban rail transit development process and the results of on-site testing and research, the paper proposed five key points of green development of urban rail transit, such as appropriate design and construction, healthy environment protection, efficient energy system, intelligent operation and maintenance, and humanized supporting facilities. The key points provide direction and ideas to the further development of green development of urban rail transit.
Urban rail transit has brought a series of social problems about energy consumption and environment with its rapid development. With the gradual advancement of green development in various industries, the green development of urban rail transit has gradually attracted people's attention. Combined with the development status and problems of urban rail transit development process and the results of on-site testing and research, the paper proposed five key points of green development of urban rail transit, such as appropriate design and construction, healthy environment protection, efficient energy system, intelligent operation and maintenance, and humanized supporting facilities. The key points provide direction and ideas to the further development of green development of urban rail transit.
RESEARCH ON DIAGNOSIS AND TREATMENT FOR THERMAL ENVIRONMENT FROM THE PERSPECTIVE OF HEALTHY DWELLING
2021, 51(8): 19-27.
doi: 10.13204/j.gyjzG20103004
Abstract:
With the increasing concern about healthy human dwellings, how to diagnose and treat the healthy levels of newly built and existing buildings in our country has become a key problem. Healthy settlements are closely related to healthy buildings, and its thermal environment has become an indispensable part of healthy buildings. By sorting out the relevant requirements of the thermal environment in the domestic and foreign healthy building standards, a case study of the residential area of Yuedao in Lingnan was carried out. At the same time, as the on-site measurement, numerical simulation was also performed for verification and comparative analysis. Based on the diagnosis results, a reasonable optimization direction was proposed, and the true effectiveness and complementarity of the two methods were discussed, hoping to contribute theoretical connotations and construct a reasonable method process for the diagnosis and treatment for the thermal environment of healthy buildings.
With the increasing concern about healthy human dwellings, how to diagnose and treat the healthy levels of newly built and existing buildings in our country has become a key problem. Healthy settlements are closely related to healthy buildings, and its thermal environment has become an indispensable part of healthy buildings. By sorting out the relevant requirements of the thermal environment in the domestic and foreign healthy building standards, a case study of the residential area of Yuedao in Lingnan was carried out. At the same time, as the on-site measurement, numerical simulation was also performed for verification and comparative analysis. Based on the diagnosis results, a reasonable optimization direction was proposed, and the true effectiveness and complementarity of the two methods were discussed, hoping to contribute theoretical connotations and construct a reasonable method process for the diagnosis and treatment for the thermal environment of healthy buildings.
2021, 51(8): 28-33.
doi: 10.13204/j.gyjzG20111203
Abstract:
Based on the theory of microclimate, architectural space form is closely related to microclimate, village spatial form planning and design has high energy-saving potential. The paper took village in Guanzhong region of Shaanxi Province as the research object, performance-based design methods and parameterized platforms were used to integrate building environment information and to realize the optimal layout of ideal village models. Combined with statistical analysis methods, quantitative research method was used to propose a dense agglomeration form with stable staggered boundary, which had well-controlled development scale, small linear open space, increasing inhabitation units, so as to form a hierarchical and centripetal village space organization system. The performance-based quantitative design method for the village spatial form under the influence of microclimate was discussed, which could provide a reference for the village green planning and design.
Based on the theory of microclimate, architectural space form is closely related to microclimate, village spatial form planning and design has high energy-saving potential. The paper took village in Guanzhong region of Shaanxi Province as the research object, performance-based design methods and parameterized platforms were used to integrate building environment information and to realize the optimal layout of ideal village models. Combined with statistical analysis methods, quantitative research method was used to propose a dense agglomeration form with stable staggered boundary, which had well-controlled development scale, small linear open space, increasing inhabitation units, so as to form a hierarchical and centripetal village space organization system. The performance-based quantitative design method for the village spatial form under the influence of microclimate was discussed, which could provide a reference for the village green planning and design.
2021, 51(8): 34-38.
doi: 10.13204/j.gyjzG20020705
Abstract:
As an important part of low-carbon economy, low-carbon housing has become a trend in the development of real estate industry. It will also become the future choice of urban development in China. Taking the field construction of the first prize of the "2011 Taida Cup International Solar Energy Architectural Design Competition" as an example, the paper expounded a green housing design system with architectural design and low-carbon technology, including the application of passive energy-saving technology, renewable energy technology, and ecological sustainable technology. Comfortable and convenient indoor living experience that can be provided on the basis of realizing low-carbon energy-saving building.
As an important part of low-carbon economy, low-carbon housing has become a trend in the development of real estate industry. It will also become the future choice of urban development in China. Taking the field construction of the first prize of the "2011 Taida Cup International Solar Energy Architectural Design Competition" as an example, the paper expounded a green housing design system with architectural design and low-carbon technology, including the application of passive energy-saving technology, renewable energy technology, and ecological sustainable technology. Comfortable and convenient indoor living experience that can be provided on the basis of realizing low-carbon energy-saving building.
2021, 51(8): 39-44.
doi: 10.13204/j.gyjzG21022002
Abstract:
Providing public open space that can satisfy people's life needs with higher quality in high-density urban blocks is an important task and challenge for urban construction and management in the new era. The establishment of a method for evaluating the publicness of open space is an important way to quickly and scientifically identify the quality and influencing factors of open space. The core area of Guangzhou Pearl River New Town and Manhattan's Yorkville, New York were taken as the research objects, and the analytic hierarchy process was used to establish the publicity evaluation system of the building attached open space (AOS), the index weight was calculated, and the evaluation standard was established. The results showed that: 1)the importance of the six evaluation indicators should be ranked as: access time> recreational facilities> degree of openness> visual perception> spatial scale> monitoring impact; 2)in general, Manhattan’s Yorkville showed more public than the core area of Guangzhou Pearl River New Town slightly; and each had its own advantages and disadvantages in individual indicators. This research has supplemented and developed the existing AOS publicness evaluation method, which is suitable for the comparison of the publicity quality of various urban blocks. At the same time, it can also scientifically and quickly identify the individual factors that affect AOS, and provide information for planning, design and construction management of urban block.
Providing public open space that can satisfy people's life needs with higher quality in high-density urban blocks is an important task and challenge for urban construction and management in the new era. The establishment of a method for evaluating the publicness of open space is an important way to quickly and scientifically identify the quality and influencing factors of open space. The core area of Guangzhou Pearl River New Town and Manhattan's Yorkville, New York were taken as the research objects, and the analytic hierarchy process was used to establish the publicity evaluation system of the building attached open space (AOS), the index weight was calculated, and the evaluation standard was established. The results showed that: 1)the importance of the six evaluation indicators should be ranked as: access time> recreational facilities> degree of openness> visual perception> spatial scale> monitoring impact; 2)in general, Manhattan’s Yorkville showed more public than the core area of Guangzhou Pearl River New Town slightly; and each had its own advantages and disadvantages in individual indicators. This research has supplemented and developed the existing AOS publicness evaluation method, which is suitable for the comparison of the publicity quality of various urban blocks. At the same time, it can also scientifically and quickly identify the individual factors that affect AOS, and provide information for planning, design and construction management of urban block.
2021, 51(8): 45-52,105.
doi: 10.13204/j.gyjzG20071008
Abstract:
Based on the design method of "three-line defenses seismic fortification", two pieces of first aseismic grade frames with PSRC vierendeel truss transfer story and different numbers of the upper stories were designed under eight degree (0.2g) of seismic fortification level, and a series of elastic-plastic time-history analysis had been completed under rare intensity level of different intensity aftershocks (ΔPGA=0, 0.5, 0.8, 1.0). After that, the seismic performance and damage of components, defenses, and structures were studied with inter-story drift ratios, ratios of demand to capacity of plastic hinge rotation, damage indexes and others. The results showed that the structures could avoid overall damage under the main-after shocks, and the damage indexes of a few upper beams appeared local damage when the aftershocks were strong; a "beam-column mixed hinge mechanism" could be formed to dissipate energy mainly with the beam hinges in the first line defense, and the damage indexes of the last two defenses were obviously smaller than the first one, so the design principle of "the three-line defenses seismic fortification" could be realized. Under the aftershocks, the overall damage indexes of structures increased significantly, and "the secondary damage" caused by the aftershocks were obviously; under larger aftershocks, hinges in the transfer columns were more widespread, and even a "mechanism of story lateral displacement" occured, so it was necessary to strengthen the moment magnifying measures of the transfer columns.
Based on the design method of "three-line defenses seismic fortification", two pieces of first aseismic grade frames with PSRC vierendeel truss transfer story and different numbers of the upper stories were designed under eight degree (0.2g) of seismic fortification level, and a series of elastic-plastic time-history analysis had been completed under rare intensity level of different intensity aftershocks (ΔPGA=0, 0.5, 0.8, 1.0). After that, the seismic performance and damage of components, defenses, and structures were studied with inter-story drift ratios, ratios of demand to capacity of plastic hinge rotation, damage indexes and others. The results showed that the structures could avoid overall damage under the main-after shocks, and the damage indexes of a few upper beams appeared local damage when the aftershocks were strong; a "beam-column mixed hinge mechanism" could be formed to dissipate energy mainly with the beam hinges in the first line defense, and the damage indexes of the last two defenses were obviously smaller than the first one, so the design principle of "the three-line defenses seismic fortification" could be realized. Under the aftershocks, the overall damage indexes of structures increased significantly, and "the secondary damage" caused by the aftershocks were obviously; under larger aftershocks, hinges in the transfer columns were more widespread, and even a "mechanism of story lateral displacement" occured, so it was necessary to strengthen the moment magnifying measures of the transfer columns.
2021, 51(8): 53-59,33.
doi: 10.13204/j.gyjzG20053102
Abstract:
In order to study the seismic performance and restoring force characteristics of steel-polypropylene-fiber-reinforced concrete shear wall with lithium slag, three shear walls were tested by quasi-static test. The components had gone through the elastic stage, elastic-plastic stage, yield stage, and failure stage. Based on test results, taking cracking points, yield points, peak points and breaking-down points as characteristic points, the stress form and failure results of the specimen were analyzed, and the four-fold-line skeleton curve model, stiffness degradation law and restoring force model of the new shear wall were proposed. The results showed that under the same axial compression ratio, the hybrid fiber could effectively improve the ductility and ultimate deformation capacity of the component. As the axial compression ratio increased, the specimen mixed with the hybrid fiber would increase the bearing capacity and ductility, reduce the residual deformation and stiffness. According to the test results, the four-fold-line skeleton curve model fitted well with the test results, which could better reflect the stress state of the specimen at each stage. The stiffness degradation equation established by regressive and theoretical analysis of test data could better describe the stiffness degradation law of members at each stage. The restoring force model based on the hysteresis rule was preposed.
In order to study the seismic performance and restoring force characteristics of steel-polypropylene-fiber-reinforced concrete shear wall with lithium slag, three shear walls were tested by quasi-static test. The components had gone through the elastic stage, elastic-plastic stage, yield stage, and failure stage. Based on test results, taking cracking points, yield points, peak points and breaking-down points as characteristic points, the stress form and failure results of the specimen were analyzed, and the four-fold-line skeleton curve model, stiffness degradation law and restoring force model of the new shear wall were proposed. The results showed that under the same axial compression ratio, the hybrid fiber could effectively improve the ductility and ultimate deformation capacity of the component. As the axial compression ratio increased, the specimen mixed with the hybrid fiber would increase the bearing capacity and ductility, reduce the residual deformation and stiffness. According to the test results, the four-fold-line skeleton curve model fitted well with the test results, which could better reflect the stress state of the specimen at each stage. The stiffness degradation equation established by regressive and theoretical analysis of test data could better describe the stiffness degradation law of members at each stage. The restoring force model based on the hysteresis rule was preposed.
2021, 51(8): 60-67,18.
doi: 10.13204/j.gyjzG20052801
Abstract:
In order to study the shear behavior of ultra-high performance concrete beams, based on the MCFT theory, the bending moment effect was superimposed and the UHPC (ultra-high performance concrete) constitutive relation of this part was modified. The contribution of tensile strength of UHPC to its shear performance after cracking was considered. The cross-section analysis model of prestressed UHPC beam under the conmbined action of bending and shearing was established, and the calculation program was compiled. In order to verify the correctness of the model, the shear test of three prestressed UHPC beams with the shear-span ratio as the main factor was conducted. The failure mode, crack distribution characteristics and bearing capacity of the beams were obtained. After using this model to validate the experiment results of other literatures, the results showed that the contrast results were in good agreement and the coefficient of variation was small. Combined with the MCFT model and the test results of a large number of existing literatures, the shearing empirical formula of UHPC beam was proposed considering the influence of shear-span ratio, hooping ratio, prestress and UHPC strength. The calculated value well coincided with the test.
In order to study the shear behavior of ultra-high performance concrete beams, based on the MCFT theory, the bending moment effect was superimposed and the UHPC (ultra-high performance concrete) constitutive relation of this part was modified. The contribution of tensile strength of UHPC to its shear performance after cracking was considered. The cross-section analysis model of prestressed UHPC beam under the conmbined action of bending and shearing was established, and the calculation program was compiled. In order to verify the correctness of the model, the shear test of three prestressed UHPC beams with the shear-span ratio as the main factor was conducted. The failure mode, crack distribution characteristics and bearing capacity of the beams were obtained. After using this model to validate the experiment results of other literatures, the results showed that the contrast results were in good agreement and the coefficient of variation was small. Combined with the MCFT model and the test results of a large number of existing literatures, the shearing empirical formula of UHPC beam was proposed considering the influence of shear-span ratio, hooping ratio, prestress and UHPC strength. The calculated value well coincided with the test.
2021, 51(8): 68-73.
doi: 10.13204/j.gyjzG20041307
Abstract:
The dynamic pressure of silo discharging is the main cause of silo wall failure, and the type of storage material were is an important factor affecting dynamic pressure. The silo discharging tests were conducted on the silos infilled with three kinds of storage materials: soybean, wheat and sand. Based on the test, a numerical simulation model of grain flow during discharging was established.The dynamic side pressures and overpressure coefficients of different storage materials during discharging process were compared to explore the influence law of different storage materials on dynamic pressure.The results showed that:1) The maximum overpressure coefficients of the three kinds of storage materials were 2.27, 1.52 and 1.24 respectively, located near 1/3 of the silo height. 2) The falling speed of the silo side wall was less than that of the middle part of the silo, because the dense force chain network on the silo wall inhibited the flow of the storage material near the silo wall and led to the increase of side pressure. 3) By observing the particle force chain network, it was found that the contact forces were concentrated near the silo wall, and it was sparse at the middle part of silo, presenting the form of dynamic arch. The contact force of arch foot was used for the silo wall, which was the main reason for the increase of dynamic pressure.
The dynamic pressure of silo discharging is the main cause of silo wall failure, and the type of storage material were is an important factor affecting dynamic pressure. The silo discharging tests were conducted on the silos infilled with three kinds of storage materials: soybean, wheat and sand. Based on the test, a numerical simulation model of grain flow during discharging was established.The dynamic side pressures and overpressure coefficients of different storage materials during discharging process were compared to explore the influence law of different storage materials on dynamic pressure.The results showed that:1) The maximum overpressure coefficients of the three kinds of storage materials were 2.27, 1.52 and 1.24 respectively, located near 1/3 of the silo height. 2) The falling speed of the silo side wall was less than that of the middle part of the silo, because the dense force chain network on the silo wall inhibited the flow of the storage material near the silo wall and led to the increase of side pressure. 3) By observing the particle force chain network, it was found that the contact forces were concentrated near the silo wall, and it was sparse at the middle part of silo, presenting the form of dynamic arch. The contact force of arch foot was used for the silo wall, which was the main reason for the increase of dynamic pressure.
2021, 51(8): 74-78,86.
doi: 10.13204/j.gyjzG20041904
Abstract:
In order to study the structural response and damage form under earthquake, a two-bay-three-span three-story space steel frame structure with incomplete scale was selected. Ninghe wave, El Centro wave, and Taft wave were used as excitation to conduct shaking table tests. The paper analyzed the dynamic performance of the model frame, and conducted seismic performance research and damage analysis of the structure in terms of acceleration response, displacement response and strain response. The results showed that as the earthquake intensity increased and the structural damage accumulated, the structural dynamic amplification factor decreased and the displacement response increased. The seismic performance of the structure was evaluated based on the IDA method, so as to provide a reference for the selection of sub-structures in structural seismic experimental analysis.
In order to study the structural response and damage form under earthquake, a two-bay-three-span three-story space steel frame structure with incomplete scale was selected. Ninghe wave, El Centro wave, and Taft wave were used as excitation to conduct shaking table tests. The paper analyzed the dynamic performance of the model frame, and conducted seismic performance research and damage analysis of the structure in terms of acceleration response, displacement response and strain response. The results showed that as the earthquake intensity increased and the structural damage accumulated, the structural dynamic amplification factor decreased and the displacement response increased. The seismic performance of the structure was evaluated based on the IDA method, so as to provide a reference for the selection of sub-structures in structural seismic experimental analysis.
2021, 51(8): 79-86.
doi: 10.13204/j.gyjzG20012301
Abstract:
In order to solve the problem that the residual defomation at the bean ends of steel frame caused by platic damage after the earthquake is too large to be repaired, a new resilient steel beam-column joint featured with low damage and easy maintenance is proposed. The top of the upper flanges of the beams adopt suspended shear connections to form the center of rotation. The bottom flanges of the beams are connected by buckling-restrained plate (BRP), which is used to dissipate seismic energy. ABAQUS finite element software was used to study the mechanical performance of the new joint, in which the suspended connections with steel angle bolted configuration and steel angle welded configuration on the top flange were considered, and their performance was compared with the traditional welded joint. The results showed that the new joint had comparable stiffness to the traditional one, and energy dissipation was concentrated in the BRP. Thus, damage and local buckling near the beam end could be avoided and resiliency of the joint could be significantly improved. In elasto-plastic range, the rotation center of the new joint concentrated near the beam top flange, and bending moment was contributed mainly by the axial force from the BRP and the suspended connection, with stable cyclic performance. The configuration of suspended connection did had little effect on the performance of the new joint.
In order to solve the problem that the residual defomation at the bean ends of steel frame caused by platic damage after the earthquake is too large to be repaired, a new resilient steel beam-column joint featured with low damage and easy maintenance is proposed. The top of the upper flanges of the beams adopt suspended shear connections to form the center of rotation. The bottom flanges of the beams are connected by buckling-restrained plate (BRP), which is used to dissipate seismic energy. ABAQUS finite element software was used to study the mechanical performance of the new joint, in which the suspended connections with steel angle bolted configuration and steel angle welded configuration on the top flange were considered, and their performance was compared with the traditional welded joint. The results showed that the new joint had comparable stiffness to the traditional one, and energy dissipation was concentrated in the BRP. Thus, damage and local buckling near the beam end could be avoided and resiliency of the joint could be significantly improved. In elasto-plastic range, the rotation center of the new joint concentrated near the beam top flange, and bending moment was contributed mainly by the axial force from the BRP and the suspended connection, with stable cyclic performance. The configuration of suspended connection did had little effect on the performance of the new joint.
2021, 51(8): 87-92,172.
doi: 10.13204/j.gyjzG20012901
Abstract:
For the problems of residential steel structure buildings that steel members protrude from the wall surface and the building decoration at the joint is difficult, based on the actual engineering, the paper proposed a new type of diaphragm-through steel beam-column joint. According to the current specifications, five joints models were established by the finite element analysis software ABAQUS. The elastoplastic contrast analysis of the new joint and traditional diaphragm-through joint was carried out under cyclic loads. The mechanical properties of the joints in the major and secondary axial direction were analyzed. The research showed that the ductility, stiffness and energy consumption of the new joint were basically the same as those of the common joint; the plasticity development law of the new joint was different from that of the common joint, mainly reflected in the panel zone and the diaphragm; when connected to the secondary axis of the rectangular steel tube column, the shear deformation of panel zone should be paid enough attention, and its influence should be considered in the calculation of structural deformation. It was recommended to make a strong panel zone design when using new joint, and increase the thickness of new-type diaphragm.
For the problems of residential steel structure buildings that steel members protrude from the wall surface and the building decoration at the joint is difficult, based on the actual engineering, the paper proposed a new type of diaphragm-through steel beam-column joint. According to the current specifications, five joints models were established by the finite element analysis software ABAQUS. The elastoplastic contrast analysis of the new joint and traditional diaphragm-through joint was carried out under cyclic loads. The mechanical properties of the joints in the major and secondary axial direction were analyzed. The research showed that the ductility, stiffness and energy consumption of the new joint were basically the same as those of the common joint; the plasticity development law of the new joint was different from that of the common joint, mainly reflected in the panel zone and the diaphragm; when connected to the secondary axis of the rectangular steel tube column, the shear deformation of panel zone should be paid enough attention, and its influence should be considered in the calculation of structural deformation. It was recommended to make a strong panel zone design when using new joint, and increase the thickness of new-type diaphragm.
2021, 51(8): 93-98.
doi: 10.13204/j.gyjzG19112810
Abstract:
In order to study the influence of corrosion damage on the bearing capacity of H-shaped steel members under compression, especially the local buckling performance, six short H-shaped steel short columns with different degrees of corrosion were designed. Firstly, the outdoor accelerated corrosion test for up to 15 months was carried out, then the monotonic tensile test of plates and the eccentric compression test of short columns were carried out, finally the relationship between corrosion degree and mechanical property parameters, such as failure mode, ultimate bearing capacity, and deformation property, was analyzed. The results showed that with the increase of corrosion degree, the ultimate load and critical buckling load of H-shaped steel columns decreased gradually; corrosion led to the decrease of the half wavelength of local buckling, which weakened the plastic deformation capacity of the specimen and reduced the bearing capacity of the member under eccentric compression.
In order to study the influence of corrosion damage on the bearing capacity of H-shaped steel members under compression, especially the local buckling performance, six short H-shaped steel short columns with different degrees of corrosion were designed. Firstly, the outdoor accelerated corrosion test for up to 15 months was carried out, then the monotonic tensile test of plates and the eccentric compression test of short columns were carried out, finally the relationship between corrosion degree and mechanical property parameters, such as failure mode, ultimate bearing capacity, and deformation property, was analyzed. The results showed that with the increase of corrosion degree, the ultimate load and critical buckling load of H-shaped steel columns decreased gradually; corrosion led to the decrease of the half wavelength of local buckling, which weakened the plastic deformation capacity of the specimen and reduced the bearing capacity of the member under eccentric compression.
2021, 51(8): 99-105.
doi: 10.13204/j.gyjzG20072110
Abstract:
With the development of green prefabricated rural building in decades, the traditional cold-formed steel (CFS) wall reveals some shortcomings, such as poor sound insulation, low bearing capacity and weak thermal insulation. In order to improve the performance of walls and the degree of assembly, a novel type of prefabricated light mortar-filled CFS composite walls was developed. A total of six composite walls were tested under axial loading. The failure modes, load-displacement relations, load-strain relations, bearing capacities were studied comprehensively. The parameters including sheathing, filling type, wall thickness, and the number of steel mesh layers were studied. The test results showed that the sheathing, filling type and the thickness of wall panel had great effect on the performance of composite wall panels under axial compression. The number of steel mesh layers appeared no obvious influence on the bearing capacity. Additionally, the calculation method of bearing capacity of the wall panels under axial compression was proposed, and its accuracy was verified by experimental data.
2021, 51(8): 106-113,136.
doi: 10.13204/j.gyjzG20101908
Abstract:
Cold-formed thin-walled steel composite wall has been widely used in steel multi-story dwellings at home and abroad. When it is taken as double-layer-load-bearing walls, the weak part is located in the floor connection between the upper and lower wall segments, which becomes the primary part of shear failure.Considering different the axial compression, wall cross-section height and anchor factors at a total of 9 pieces of wall were designed, to test their shear performance under quasi-static loading, the results showed that: 1) for the walls designed according to Technical Standards for Cold-Formed Thin-Walled Steel Multi-Storey Residential Buldings (JGJ/T 421—2018), pulling a screw under shear effect, the existence of axial compression accelerated the failure of screw resulted in the decrease of bearing capacity quickly; 2) the height of the wall section and the axial compression had a great impact on the bearing performance of the wall, so the axial compression of the wall should be strictly limited in the design; 3) the wall had experienced the gradual damage of multiple components, the bearing capacity and stiffness degradation were relatively slow, and the failure was the result of cumulative damage; 4) in the early stage of loading applied on the walls, the screws on the pull-out parts of the double-nut bolts bore shear force, and in the stage of large displacement, the inclined screws of the bolts bore tension-shear force. The failure of the screws led to the rapid destruction of the bolts, and the second-order effect made the lower wall prone to interlayer failure; 5) after adding truss strengthening parts at the floor joints, the screws on the pull-out parts only bore the shear force, so that the anti-damage ability of the wall was significantly improved, and the bearing capacity of the wall could be significantly improved.
Cold-formed thin-walled steel composite wall has been widely used in steel multi-story dwellings at home and abroad. When it is taken as double-layer-load-bearing walls, the weak part is located in the floor connection between the upper and lower wall segments, which becomes the primary part of shear failure.Considering different the axial compression, wall cross-section height and anchor factors at a total of 9 pieces of wall were designed, to test their shear performance under quasi-static loading, the results showed that: 1) for the walls designed according to Technical Standards for Cold-Formed Thin-Walled Steel Multi-Storey Residential Buldings (JGJ/T 421—2018), pulling a screw under shear effect, the existence of axial compression accelerated the failure of screw resulted in the decrease of bearing capacity quickly; 2) the height of the wall section and the axial compression had a great impact on the bearing performance of the wall, so the axial compression of the wall should be strictly limited in the design; 3) the wall had experienced the gradual damage of multiple components, the bearing capacity and stiffness degradation were relatively slow, and the failure was the result of cumulative damage; 4) in the early stage of loading applied on the walls, the screws on the pull-out parts of the double-nut bolts bore shear force, and in the stage of large displacement, the inclined screws of the bolts bore tension-shear force. The failure of the screws led to the rapid destruction of the bolts, and the second-order effect made the lower wall prone to interlayer failure; 5) after adding truss strengthening parts at the floor joints, the screws on the pull-out parts only bore the shear force, so that the anti-damage ability of the wall was significantly improved, and the bearing capacity of the wall could be significantly improved.
2021, 51(8): 114-119.
doi: 10.13204/j.gyjzG20031704
Abstract:
The girder bridges which have been widely used are prone to occur lateral girder-falling damage under the earthquake action. In order to improve the limit and energy dissipation effect of the retainers under the earthquake action, based on the characteristics of the energy dissipation of the honeycomb structure under axial compression and combined with the design concept of double-retainer in preventing girder falling, a honeycomb type seismic energy-dissipation retainer was designed. The ABAQUS software was used for numerical simulation and analysis of the retainers, and a full-scale quasi-static test was carried out. The results of the numerical simulation and test were compared. It was found that the numerical simulation analysis and the test results were in good agreement, the structural hysteresis curve was full, and the mechanical model was clear. The following conclusions were drawn: the honeycomb-type seismic energy-dissipation block showed a good bearing capacity, and there was no obvious stiffness degradation during the cyclic loading; the structure had good energy dissipation effect, simple structural form, clear force transmission, which could be widely applied to practical engineering.
The girder bridges which have been widely used are prone to occur lateral girder-falling damage under the earthquake action. In order to improve the limit and energy dissipation effect of the retainers under the earthquake action, based on the characteristics of the energy dissipation of the honeycomb structure under axial compression and combined with the design concept of double-retainer in preventing girder falling, a honeycomb type seismic energy-dissipation retainer was designed. The ABAQUS software was used for numerical simulation and analysis of the retainers, and a full-scale quasi-static test was carried out. The results of the numerical simulation and test were compared. It was found that the numerical simulation analysis and the test results were in good agreement, the structural hysteresis curve was full, and the mechanical model was clear. The following conclusions were drawn: the honeycomb-type seismic energy-dissipation block showed a good bearing capacity, and there was no obvious stiffness degradation during the cyclic loading; the structure had good energy dissipation effect, simple structural form, clear force transmission, which could be widely applied to practical engineering.
2021, 51(8): 120-125.
doi: 10.13204/j.gyjzG21010409
Abstract:
Aiming at the problem that the research on the calculation of the lateral pressure of self-compacting concrete formwork is not perfect enough, a calculation model of the lateral pressure of self-compacting concrete formwork was established based on Janssen theory, and the calculation formula of the lateral pressure was deduced. The time-varying effect of friction coefficient μ and lateral pressure reduction coefficient K between self-compacting concrete and formwork was studied by self-designed test device, and the parameters of the deduced formula were modified. The validity of the modified formula was verified based on the measured data of lateral pressure. The results showed that the error between the calculated and the measured values was small and the correction formula considering the time-varying effect could predict the lateral pressure of the formwork relatively accurately.
Aiming at the problem that the research on the calculation of the lateral pressure of self-compacting concrete formwork is not perfect enough, a calculation model of the lateral pressure of self-compacting concrete formwork was established based on Janssen theory, and the calculation formula of the lateral pressure was deduced. The time-varying effect of friction coefficient μ and lateral pressure reduction coefficient K between self-compacting concrete and formwork was studied by self-designed test device, and the parameters of the deduced formula were modified. The validity of the modified formula was verified based on the measured data of lateral pressure. The results showed that the error between the calculated and the measured values was small and the correction formula considering the time-varying effect could predict the lateral pressure of the formwork relatively accurately.
2021, 51(8): 126-136.
doi: 10.13204/j.gyjzG20091602
Abstract:
Metal roof systems have been widely used in various important landmark buildings, and are often affected by periodic solar radiation, temperature changes and other environmental influences. The deformation and stress distribution of the standing seaming aluminum alloy roof system under the action of the temperature field were studied by experiments. The stress and deformation characteristics of roof slab, support and slab rib under static temperature were analyzed, and the mechanical properties, deformation and wear characteristics of roof slab were evaluated by cyclic temperature loading test. The results showed that with the increase of temperature, the stresses of slab rib, support, slab bottom and surface gradually increased, and the stress concentration was obvious. When the temperature increased by 1 ℃, the maximum temperature stress of roof slab increased by about 1.2 MPa. The slab rib stress was the largest, followed by the slab surface, the slab bottom stress was the smallest, and the stress of each part was in the elastic stage. The thermal expansion displacement of the roof slab was significant, and the longitudinal horizontal displacement of the roof slab was obviously larger than the vertical displacement of slab bottom, and the maximum longitudinal horizontal displacement was about 20.4 mm. Under cyclic loading, the wear characteristics of roof slab were greatly affected by the number of cycles, and the maximum wear thickness was about 18.20 μm.
Metal roof systems have been widely used in various important landmark buildings, and are often affected by periodic solar radiation, temperature changes and other environmental influences. The deformation and stress distribution of the standing seaming aluminum alloy roof system under the action of the temperature field were studied by experiments. The stress and deformation characteristics of roof slab, support and slab rib under static temperature were analyzed, and the mechanical properties, deformation and wear characteristics of roof slab were evaluated by cyclic temperature loading test. The results showed that with the increase of temperature, the stresses of slab rib, support, slab bottom and surface gradually increased, and the stress concentration was obvious. When the temperature increased by 1 ℃, the maximum temperature stress of roof slab increased by about 1.2 MPa. The slab rib stress was the largest, followed by the slab surface, the slab bottom stress was the smallest, and the stress of each part was in the elastic stage. The thermal expansion displacement of the roof slab was significant, and the longitudinal horizontal displacement of the roof slab was obviously larger than the vertical displacement of slab bottom, and the maximum longitudinal horizontal displacement was about 20.4 mm. Under cyclic loading, the wear characteristics of roof slab were greatly affected by the number of cycles, and the maximum wear thickness was about 18.20 μm.
2021, 51(8): 137-140,218.
doi: 10.13204/j.gyjzG20122104
Abstract:
In recent years, as the demand of cultural tour increases continuously, the theme park engineering starts to get more attention in the civil engineering field. Compared with regular structural design, the design work of building in theme park is different. Firstly, the overall analysis model was introduced in order to illustrate the relationship among the decoration materials, the decoration structure and the main structure. Secondly, the characteristics of design work for the decoration structure and the main structure were summarized respectively. Finally, the development trend of the applications of new structural techniques in theme park construction was provided. The paper analyzed and summarized the structural design for the single buildings in theme park, hoping to provide a reference to designers and improve the development of study of theme park engineering.
In recent years, as the demand of cultural tour increases continuously, the theme park engineering starts to get more attention in the civil engineering field. Compared with regular structural design, the design work of building in theme park is different. Firstly, the overall analysis model was introduced in order to illustrate the relationship among the decoration materials, the decoration structure and the main structure. Secondly, the characteristics of design work for the decoration structure and the main structure were summarized respectively. Finally, the development trend of the applications of new structural techniques in theme park construction was provided. The paper analyzed and summarized the structural design for the single buildings in theme park, hoping to provide a reference to designers and improve the development of study of theme park engineering.
2021, 51(8): 141-147,38.
doi: 10.13204/j.gyjzG20100902
Abstract:
Aiming at the problem of insufficient or excessive support for parallel single-row or double-row pile support systems in a large amount of shallow foundation excavation, a series of indoor model tests were conducted, the load-bearing characteristics of composite support systems were studied between the conventional single-row pile-soil-nail system and the dentate pile-soil-nail system. To different composite support structure, the distribution and evolution of laws on stress of piles, ground subsidence, horizontal displacement of pile tops and axial forces in soil nails were analyzed. The results showed that the piles arranged in serration bore a large part of loads acting on the composite support structure and the maximum positive and negative bending moments were 263.04 N·m and 198.25 N·m respectively, which were all less than the homologous ones in the structure of the sing-row pile support system. At the same time, the pile support system arranged in serration had a better capacity to restrain the displacement of the pile tops than the single-row pile support system. The axial stress of soil nails in the two types of support systems also showed the tend of "large in the middle parts and small in both ends", and the soil nails in the new support system had higher pullout resistance. It initially showed that the serrated bamboo-pile-soil-nail composite support system could be applied to shallow foundation excavation, and the support capacity was stronger than the traditional single-row pile composite support system, which could meet the temporary support requirements of foundation excavation.
Aiming at the problem of insufficient or excessive support for parallel single-row or double-row pile support systems in a large amount of shallow foundation excavation, a series of indoor model tests were conducted, the load-bearing characteristics of composite support systems were studied between the conventional single-row pile-soil-nail system and the dentate pile-soil-nail system. To different composite support structure, the distribution and evolution of laws on stress of piles, ground subsidence, horizontal displacement of pile tops and axial forces in soil nails were analyzed. The results showed that the piles arranged in serration bore a large part of loads acting on the composite support structure and the maximum positive and negative bending moments were 263.04 N·m and 198.25 N·m respectively, which were all less than the homologous ones in the structure of the sing-row pile support system. At the same time, the pile support system arranged in serration had a better capacity to restrain the displacement of the pile tops than the single-row pile support system. The axial stress of soil nails in the two types of support systems also showed the tend of "large in the middle parts and small in both ends", and the soil nails in the new support system had higher pullout resistance. It initially showed that the serrated bamboo-pile-soil-nail composite support system could be applied to shallow foundation excavation, and the support capacity was stronger than the traditional single-row pile composite support system, which could meet the temporary support requirements of foundation excavation.
2021, 51(8): 148-153.
doi: 10.13204/j.gyjzG20080403
Abstract:
In the light of many monuments and metro lines around the excavated foundation of the large public landmark buildings and their joint facilities for the Central Green in Beijing Municipal Administrative Center,the underground pedestrian passage of the Grand Theatre for Beijing Municipal Administrative Center passing below it,as well as in considerations of complex engineering geology and hydrogeology and the complexity of construction,the cement-soil walls by the trench cutting remixing deep wall method (TRD) were proposed to be adopted in Beijing first to control groundwater of the project. Comparisons of sealing effects for the cement-soil walls by TRD and the soil-mixing with cutters (SMC) showed curtains by TRD had better performances of isolating groundwater than that by SMC. The construction processes of SMC needed to be improved further.
In the light of many monuments and metro lines around the excavated foundation of the large public landmark buildings and their joint facilities for the Central Green in Beijing Municipal Administrative Center,the underground pedestrian passage of the Grand Theatre for Beijing Municipal Administrative Center passing below it,as well as in considerations of complex engineering geology and hydrogeology and the complexity of construction,the cement-soil walls by the trench cutting remixing deep wall method (TRD) were proposed to be adopted in Beijing first to control groundwater of the project. Comparisons of sealing effects for the cement-soil walls by TRD and the soil-mixing with cutters (SMC) showed curtains by TRD had better performances of isolating groundwater than that by SMC. The construction processes of SMC needed to be improved further.
2021, 51(8): 154-159.
doi: 10.13204/j.gyjzG20122807
Abstract:
The hydro-mechanical coupling relaxation characteristics is one of the key factors for long-term safety and stability of surrounding rocks. The hydro-mechanical coupling tests on effective confining pressure laws and sensitivity loading rates of saturated grey sandstone were conducted by the multi-field coupling triaxial test system. According to the relaxation characteristics, the generalized Maxwell relaxation constitutive model with three elements was adopted for the implementation of numerical verifications. The results showed that: 1) In the condition of hydro-mechanical coupling, saturated sandstone had the characteristics of incomplete attenuation relaxation. 2) Under the same effective confining pressure, the relaxation degrees of specimens without pore water pressure were slightly lower than that with pore pressure, while relaxation rates in the steady state were only about 45% of that with pore pressure. 3) The relaxation characteristics of sandstone depended significantly on loading rates. The relaxation degrees and initial relaxation rates increased with loading rates, in which the initial relaxation rates of specimens with the highest loading rate were almost six times rates for specimens with the lowest loading rate, while the relaxation rates in the stead state were no obvious different. 4) The whole process of hydro-mechanical coupling relaxation of sandstone could be accurately described by the three element generalized Maxwell relaxation constitutive model with three elements.
The hydro-mechanical coupling relaxation characteristics is one of the key factors for long-term safety and stability of surrounding rocks. The hydro-mechanical coupling tests on effective confining pressure laws and sensitivity loading rates of saturated grey sandstone were conducted by the multi-field coupling triaxial test system. According to the relaxation characteristics, the generalized Maxwell relaxation constitutive model with three elements was adopted for the implementation of numerical verifications. The results showed that: 1) In the condition of hydro-mechanical coupling, saturated sandstone had the characteristics of incomplete attenuation relaxation. 2) Under the same effective confining pressure, the relaxation degrees of specimens without pore water pressure were slightly lower than that with pore pressure, while relaxation rates in the steady state were only about 45% of that with pore pressure. 3) The relaxation characteristics of sandstone depended significantly on loading rates. The relaxation degrees and initial relaxation rates increased with loading rates, in which the initial relaxation rates of specimens with the highest loading rate were almost six times rates for specimens with the lowest loading rate, while the relaxation rates in the stead state were no obvious different. 4) The whole process of hydro-mechanical coupling relaxation of sandstone could be accurately described by the three element generalized Maxwell relaxation constitutive model with three elements.
2021, 51(8): 160-165.
doi: 10.13204/j.gyjzG20091004
Abstract:
The tests for the limit moisture content and compaction on Malan loess from Sanmenxia in Henan mixed with different proportions of bentonite and HDTMA were conducted to explore the effect mechanism of bentonite and HDTMA on the workability of loess liners in landfills. The plasticity index of loess increased from silt to clay when the mass content of bentonite was more than 10%, and to mix HDTMA with a mass content less than 4% could optimize the physical properties of loess. Besides, both of the bentonite and HDTMA could buffer the negative effects of salts on physical properties of loess. The maximum dry density and optimal moisture content of the loess would respectively be increased and reduced with the increase of the bentonite content. The addition of HDTMA was benefit to reduce the maximum dry density of loess, but had a little influence on the optimal moisture content. In the microstructure, the HDTMA changed the structure of clay particles; the increase of bentonite made clay particles of being adhered to coarse particles occupy more spaces. Based on the data by tests,a linear function relation between the maximum dry density and the optimal moisture content for the modified loess was proposed. From the perspective of workability, the proportion of bentonite should be more than 10% and the proportion of HDTMA should be less than 2% in loess for liners of landfills.
The tests for the limit moisture content and compaction on Malan loess from Sanmenxia in Henan mixed with different proportions of bentonite and HDTMA were conducted to explore the effect mechanism of bentonite and HDTMA on the workability of loess liners in landfills. The plasticity index of loess increased from silt to clay when the mass content of bentonite was more than 10%, and to mix HDTMA with a mass content less than 4% could optimize the physical properties of loess. Besides, both of the bentonite and HDTMA could buffer the negative effects of salts on physical properties of loess. The maximum dry density and optimal moisture content of the loess would respectively be increased and reduced with the increase of the bentonite content. The addition of HDTMA was benefit to reduce the maximum dry density of loess, but had a little influence on the optimal moisture content. In the microstructure, the HDTMA changed the structure of clay particles; the increase of bentonite made clay particles of being adhered to coarse particles occupy more spaces. Based on the data by tests,a linear function relation between the maximum dry density and the optimal moisture content for the modified loess was proposed. From the perspective of workability, the proportion of bentonite should be more than 10% and the proportion of HDTMA should be less than 2% in loess for liners of landfills.
2021, 51(8): 166-172.
doi: 10.13204/j.gyjzG20111903
Abstract:
Ring-reinforced lime-soil piers could be used to treat collapsible loess and soft soil foundation. Modulus calculation method is an important factor in engineering design. The deformation characteristics and failure mode of ring-reinforced lime-soil piers were analyzed by numerical method. The influence of confining pressure, the characteristics of lime-soil pier and the properties of ring-reinforced materials on the deformation characteristics of ring-reinforced lime-soil piers were studied. Considering the lateral restraint effect of reinforced materials, the calculation method of elastic modulus was deduced. By comparing the theoretical and numerical results, the theoretical calculation method for the elastic modulus of reinforced lime-soil pier was modified. The research results could provide a theoretical method and basis for engineering design.
Ring-reinforced lime-soil piers could be used to treat collapsible loess and soft soil foundation. Modulus calculation method is an important factor in engineering design. The deformation characteristics and failure mode of ring-reinforced lime-soil piers were analyzed by numerical method. The influence of confining pressure, the characteristics of lime-soil pier and the properties of ring-reinforced materials on the deformation characteristics of ring-reinforced lime-soil piers were studied. Considering the lateral restraint effect of reinforced materials, the calculation method of elastic modulus was deduced. By comparing the theoretical and numerical results, the theoretical calculation method for the elastic modulus of reinforced lime-soil pier was modified. The research results could provide a theoretical method and basis for engineering design.
2021, 51(8): 173-178.
doi: 10.13204/j.gyjzG20070301
Abstract:
In order to study the static and dynamic impact properties of concrete with different contents of steel fibers and rubber powder, 8 groups of 48 cubic specimens were designed for compressive and splitting tensile strength tests, 8 groups of 24 cubic specimens were designed for compressive stress-strain curve test, 6 slabs were designed for impact test,whose content of steel fibers was 0%, 0.5%, 1.0% and 1.5%, and rubber powder was 0%, 5%, 10% and 15%. The results showed that the compressive strength of concrete decreased with the increase of rubber powder content. When the rubber powder content was costant, the steel fiber content of 0.5% had little effect on the compressive strength and impact toughness of rubber concrete, but it could improve the tensile strength of rubber concrete by 7% to 28%. When the content of steel fiber rubber powder was 1% and the content of rubber powder was 10%, it was the optimal mixing amount of steel-fiber reinforced rubber concrete. The suggested constitutive relation of steel-fiber reinforced rubber concrete was in good agreement with the experimental data.
In order to study the static and dynamic impact properties of concrete with different contents of steel fibers and rubber powder, 8 groups of 48 cubic specimens were designed for compressive and splitting tensile strength tests, 8 groups of 24 cubic specimens were designed for compressive stress-strain curve test, 6 slabs were designed for impact test,whose content of steel fibers was 0%, 0.5%, 1.0% and 1.5%, and rubber powder was 0%, 5%, 10% and 15%. The results showed that the compressive strength of concrete decreased with the increase of rubber powder content. When the rubber powder content was costant, the steel fiber content of 0.5% had little effect on the compressive strength and impact toughness of rubber concrete, but it could improve the tensile strength of rubber concrete by 7% to 28%. When the content of steel fiber rubber powder was 1% and the content of rubber powder was 10%, it was the optimal mixing amount of steel-fiber reinforced rubber concrete. The suggested constitutive relation of steel-fiber reinforced rubber concrete was in good agreement with the experimental data.
2021, 51(8): 179-183.
doi: 10.13204/j.gyjzG21010416
Abstract:
By changing the carbonation temperature, relative humidity and carbonation time, the best carbonation process parameters of recycled aggregate were determined; on this basis, natural aggregate, un-carbonized recycled aggregate and three kinds of carbonized aggregate were selected to prepare concrete. The influence of carbonation of recycled aggregate on the performance of recycled concrete in the corrosion of chloride and sulfuric acid was explored. The results showed that the apparent density, water absorption rate and crushing value of recycled aggregate increased significantly after carbonation. The optimal carbonation process parameters were as follows: temperature 20℃, relative humidity 55% and carbonation time 24 h. Compared with recycled concrete, the chloride ion penetration resistance of carbonated aggregate concrete was improved by 5.1%~22.1%, but lower than that of ordinary concrete. Unlike the chloride ion resistance, the sulphate attack resistance of carbonated recycled aggregate concrete was not only better than recycled concrete, but also higher than ordinary concrete.
By changing the carbonation temperature, relative humidity and carbonation time, the best carbonation process parameters of recycled aggregate were determined; on this basis, natural aggregate, un-carbonized recycled aggregate and three kinds of carbonized aggregate were selected to prepare concrete. The influence of carbonation of recycled aggregate on the performance of recycled concrete in the corrosion of chloride and sulfuric acid was explored. The results showed that the apparent density, water absorption rate and crushing value of recycled aggregate increased significantly after carbonation. The optimal carbonation process parameters were as follows: temperature 20℃, relative humidity 55% and carbonation time 24 h. Compared with recycled concrete, the chloride ion penetration resistance of carbonated aggregate concrete was improved by 5.1%~22.1%, but lower than that of ordinary concrete. Unlike the chloride ion resistance, the sulphate attack resistance of carbonated recycled aggregate concrete was not only better than recycled concrete, but also higher than ordinary concrete.
2021, 51(8): 184-189,125.
doi: 10.13204/j.gyjzG19122508
Abstract:
The accelerated corrosion test of Q690 high-strength steel was carried out for 0-100 d in the periodic wetting and humid hot environment. The degradation law of mechanical properties of steel was studied by uniaxial tensile test. The stress-strain degradation constitutive model of corroded specimen was established by using secondary plastic flow model, and the relationships between parameters s1 and corrosion time, s2 and corrosion time were obtained. The results were compared with the experimental results. It could be concluded that the yield strength, tensile strength and elongation after fracture and other mechanical properties of Q690 high-strength steel decreased in varying degrees due to the increasing corrosion. The elastic modulus of Q690 high-strength steel had no obvious change in the early stage of corrosion, but it decreased by 10.2% in the later stage of corrosion. The secondary plastic flow model could better reflect the constitutive relationship of corroded steel. The finite element simulation of corrosion pit exploitation of steel could better reflect the degradation of bearing capacity of corroded high-strength steel, which was in good agreement with the test results.
The accelerated corrosion test of Q690 high-strength steel was carried out for 0-100 d in the periodic wetting and humid hot environment. The degradation law of mechanical properties of steel was studied by uniaxial tensile test. The stress-strain degradation constitutive model of corroded specimen was established by using secondary plastic flow model, and the relationships between parameters s1 and corrosion time, s2 and corrosion time were obtained. The results were compared with the experimental results. It could be concluded that the yield strength, tensile strength and elongation after fracture and other mechanical properties of Q690 high-strength steel decreased in varying degrees due to the increasing corrosion. The elastic modulus of Q690 high-strength steel had no obvious change in the early stage of corrosion, but it decreased by 10.2% in the later stage of corrosion. The secondary plastic flow model could better reflect the constitutive relationship of corroded steel. The finite element simulation of corrosion pit exploitation of steel could better reflect the degradation of bearing capacity of corroded high-strength steel, which was in good agreement with the test results.
2021, 51(8): 190-198,44.
doi: 10.13204/j.gyjzG21020308
Abstract:
At present, the ecological risk of mining cities in China is highly complex and severe. Building a perfect land spatial planning and governance system can provide specific implementation ways for the ecological risk regulation of mining cities, and the two are endogenous related. This paper comprehensively combs the relevant research on ecological risk regulation of mining cities, and uses CiteSpace software for literature visual analysis. The research results show that the research objects and elements of ecological risk of mining cities have evolved from single to multiple, and the risk regulation and management methods also show a systematic and diverse trend, The disciplines and theories involved have changed from independent dispersion to pluralistic integration; The preparation of land spatial planning can provide regulatory guarantee and control basis for the implementation of risk regulation in mining cities, but there is no systematic planning method from risk mechanism analysis, risk quantitative evaluation to risk process intervention. From the perspective of landscape ecology of the interaction between landscape pattern and ecological process, under the idea of interdisciplinary technical support and multi-objective optimization, this paper puts forward the spatial planning response technical framework of ecological risk regulation of mining cities, which provides innovative ideas for solving the problems of ecological risk regulation and ecological restoration of mining cities.
At present, the ecological risk of mining cities in China is highly complex and severe. Building a perfect land spatial planning and governance system can provide specific implementation ways for the ecological risk regulation of mining cities, and the two are endogenous related. This paper comprehensively combs the relevant research on ecological risk regulation of mining cities, and uses CiteSpace software for literature visual analysis. The research results show that the research objects and elements of ecological risk of mining cities have evolved from single to multiple, and the risk regulation and management methods also show a systematic and diverse trend, The disciplines and theories involved have changed from independent dispersion to pluralistic integration; The preparation of land spatial planning can provide regulatory guarantee and control basis for the implementation of risk regulation in mining cities, but there is no systematic planning method from risk mechanism analysis, risk quantitative evaluation to risk process intervention. From the perspective of landscape ecology of the interaction between landscape pattern and ecological process, under the idea of interdisciplinary technical support and multi-objective optimization, this paper puts forward the spatial planning response technical framework of ecological risk regulation of mining cities, which provides innovative ideas for solving the problems of ecological risk regulation and ecological restoration of mining cities.
2021, 51(8): 199-205,178.
doi: 10.13204/j.gyjzG21010507
Abstract:
In order to investigate the fracture damage and constitutive softening characteristics of basalt fiber reinforced concrete (BFRC) subjected to freeze-thaw cycles, five groups of specimens with five different basalt fiber volume percentages (0%, 0.1%, 0.2%, 0.3% and 0.4%) were designed and subjected to different freeze-thaw cycles (0, 25, 50, 75, 100 and 125 times), and then the three-point bending loading test was conducted on the concrete specimens. The results showed that when the content of fiber was less than 0.3%, the higher the content of basalt fibers, the higher the initial fracture toughness, instability toughness and fracture energy of BFRC. While the content of fibers more than 0.3%, the increase of initial fracture toughness of BFRC was not obvious, but the instability toughness and fracture energy would decrease slightly. The freeze-thaw damage of concrete reduced the fracture toughness and fracture energy of concrete. Basalt fibers could restrain the freeze-thaw damage of concrete to a certain extent. The higher the content of fibers, the smaller the freeze-thaw loss of fracture toughness and fracture energy of BFRC were. Based on the bilinear softening constitutive relation of Petersson for concrete, the bilinear softening constitutive relation curve of BFRC subjected to freeze-thaw cycles was derived by fitting freeze-thaw damage.
In order to investigate the fracture damage and constitutive softening characteristics of basalt fiber reinforced concrete (BFRC) subjected to freeze-thaw cycles, five groups of specimens with five different basalt fiber volume percentages (0%, 0.1%, 0.2%, 0.3% and 0.4%) were designed and subjected to different freeze-thaw cycles (0, 25, 50, 75, 100 and 125 times), and then the three-point bending loading test was conducted on the concrete specimens. The results showed that when the content of fiber was less than 0.3%, the higher the content of basalt fibers, the higher the initial fracture toughness, instability toughness and fracture energy of BFRC. While the content of fibers more than 0.3%, the increase of initial fracture toughness of BFRC was not obvious, but the instability toughness and fracture energy would decrease slightly. The freeze-thaw damage of concrete reduced the fracture toughness and fracture energy of concrete. Basalt fibers could restrain the freeze-thaw damage of concrete to a certain extent. The higher the content of fibers, the smaller the freeze-thaw loss of fracture toughness and fracture energy of BFRC were. Based on the bilinear softening constitutive relation of Petersson for concrete, the bilinear softening constitutive relation curve of BFRC subjected to freeze-thaw cycles was derived by fitting freeze-thaw damage.
2021, 51(8): 206-213,119.
doi: 10.13204/j.gyjzG20110320
Abstract:
The four-point bending static loading tests of seven test beams were carried out to study the interface mechanism and failure mode of reinforced concrete beams strengthened with FRP grids and epoxy mortar in the shear process. The shear reinforcement effect of this method with different reinforcement parameters and the actual stress behaviors of FRP grids were analyzed. The five calculation models were analyzed and compared based on the collected test data. The results showed that the specimens strengthened with FRP grid could constrain the development of diagonal cracks, delay the formation of main oblique cracks, greatly improve the ultimate bearing capacity and deformation capacity of specimens, and the reinforcement effect was remarkable. When the width of the shear diagonal crack of the original concrete beam was too large or the shear compression failure occured, the interface between the reinforcement layer and the original concrete beam was easy to produce different degrees of peeling failure. In a certain range, the shear contribution of FRP grids was negatively correlated with the concrete strength or shear-span ratio, and positively correlated with the reinforcement amount of FRP grids, and the greater the concrete strength or shear-span ratio, the higher the possibility of interface peeling off in advance.
The four-point bending static loading tests of seven test beams were carried out to study the interface mechanism and failure mode of reinforced concrete beams strengthened with FRP grids and epoxy mortar in the shear process. The shear reinforcement effect of this method with different reinforcement parameters and the actual stress behaviors of FRP grids were analyzed. The five calculation models were analyzed and compared based on the collected test data. The results showed that the specimens strengthened with FRP grid could constrain the development of diagonal cracks, delay the formation of main oblique cracks, greatly improve the ultimate bearing capacity and deformation capacity of specimens, and the reinforcement effect was remarkable. When the width of the shear diagonal crack of the original concrete beam was too large or the shear compression failure occured, the interface between the reinforcement layer and the original concrete beam was easy to produce different degrees of peeling failure. In a certain range, the shear contribution of FRP grids was negatively correlated with the concrete strength or shear-span ratio, and positively correlated with the reinforcement amount of FRP grids, and the greater the concrete strength or shear-span ratio, the higher the possibility of interface peeling off in advance.
2021, 51(8): 214-218.
doi: 10.13204/j.gyjzG20081010
Abstract:
In order to evaluate the impact of environmental effects on the shearing reliability of reinforced concrete (RC) beams strengthened with side near surface mounted (SNSM) carbon fiber-reinforced polymer (CFRP), the time-varying function model of the shear bearing capacity of the strengthened beams considering environmental impacts was established. Then, based on the JC method, the time-varying shear reliability of RC beams with different ratios of standard values of dead load and live load before and after reinforcement was calculated, and then the service life of the strengthened one was evaluated. The results showed that the shear reliability of RC beams decreased slowly with the increase of service time in the early stage, and decreased rapidly and linearly in the later stage. Compared with unstrengthened beams, the reliability of strengthened beams had been improved to a certain extent. When the RC beams were serviced 80% of the base period, its shear reliability could continue to be serviced about 8% of the base period after strengthened with SNSM CFRP technique.
In order to evaluate the impact of environmental effects on the shearing reliability of reinforced concrete (RC) beams strengthened with side near surface mounted (SNSM) carbon fiber-reinforced polymer (CFRP), the time-varying function model of the shear bearing capacity of the strengthened beams considering environmental impacts was established. Then, based on the JC method, the time-varying shear reliability of RC beams with different ratios of standard values of dead load and live load before and after reinforcement was calculated, and then the service life of the strengthened one was evaluated. The results showed that the shear reliability of RC beams decreased slowly with the increase of service time in the early stage, and decreased rapidly and linearly in the later stage. Compared with unstrengthened beams, the reliability of strengthened beams had been improved to a certain extent. When the RC beams were serviced 80% of the base period, its shear reliability could continue to be serviced about 8% of the base period after strengthened with SNSM CFRP technique.
2021, 51(8): 219-223,98.
doi: 10.13204/j.gyjzG21012104
Abstract:
In order to strike a balance between urban renewal and historic preservation, the United States protects historic resources with rich historical accumulation and regional characteristics through the inventory and registration system of historic properties. By clarifying the concept of "historic", California military historic buildings and structures inventory were studied. The key points of evaluation process and the innovation of evaluation methods of military historic properties were explained from three aspects of time construction, integrity and significance assessment. The method of increasing strengthening the comprehensiveness of the preliminary study of preservation planning and perfecting the identification and evaluation methods of historic properties could provide beneficial references for preservation planning in China.
In order to strike a balance between urban renewal and historic preservation, the United States protects historic resources with rich historical accumulation and regional characteristics through the inventory and registration system of historic properties. By clarifying the concept of "historic", California military historic buildings and structures inventory were studied. The key points of evaluation process and the innovation of evaluation methods of military historic properties were explained from three aspects of time construction, integrity and significance assessment. The method of increasing strengthening the comprehensiveness of the preliminary study of preservation planning and perfecting the identification and evaluation methods of historic properties could provide beneficial references for preservation planning in China.
