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2022 Vol. 52, No. 4
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2022, 52(4): 1-9.
doi: 10.13204/j.gyjzG21052801
Abstract:
Housing performance evaluation is the basis and key for the improvement of the performance of beautiful rural houses under the national village revitalization strategy. Moreover, the performance of beautiful rural houses not only includes "safety and functionality" (basic requirements), but also emphasizes "beauty and livability" (development requirements). Thus, from the perspective of "architectural ontology", a comprehensive performance evaluation system for beautiful rural houses was put forward, which could be used to evaluate the overall performance level of house and indentify the focuses of performance improvement. Focusing on the construction goal of safety, comfort, beauty, and livability of beautiful rural houses, the system constructed and quantized four characteristic indexes "locality, safety, functionality and comfort" and 18 sub-factor layer indexes, covering many fields such as architecture, structure, water and electricity, fire protection, ect.,so that the housing performance evaluation was more comprehensive and objective. In view of the large amount and wide range of rural houses, the two-level progressive evaluation strategy of "overall evaluation and special evaluation" was proposed. Secondly, according to the characteristics of each layer, the integrated weighting method was used to determine the index weight, which showed that the key indexes included structural safety, use function, thermal and humidity environment, etc. Moreover, a score probability distribution method was proposed to determine the four evaluation levels of house. Finally, taking the houses in different places,different ages, before and after reconstruction, it was shown that the system had strong feasibility and practicability for the comprehensive and efficient evaluation of housing performance; the houses built after 2000 should focus on improving the performance of local characteristics, thermal and humidity environment, etc.
Housing performance evaluation is the basis and key for the improvement of the performance of beautiful rural houses under the national village revitalization strategy. Moreover, the performance of beautiful rural houses not only includes "safety and functionality" (basic requirements), but also emphasizes "beauty and livability" (development requirements). Thus, from the perspective of "architectural ontology", a comprehensive performance evaluation system for beautiful rural houses was put forward, which could be used to evaluate the overall performance level of house and indentify the focuses of performance improvement. Focusing on the construction goal of safety, comfort, beauty, and livability of beautiful rural houses, the system constructed and quantized four characteristic indexes "locality, safety, functionality and comfort" and 18 sub-factor layer indexes, covering many fields such as architecture, structure, water and electricity, fire protection, ect.,so that the housing performance evaluation was more comprehensive and objective. In view of the large amount and wide range of rural houses, the two-level progressive evaluation strategy of "overall evaluation and special evaluation" was proposed. Secondly, according to the characteristics of each layer, the integrated weighting method was used to determine the index weight, which showed that the key indexes included structural safety, use function, thermal and humidity environment, etc. Moreover, a score probability distribution method was proposed to determine the four evaluation levels of house. Finally, taking the houses in different places,different ages, before and after reconstruction, it was shown that the system had strong feasibility and practicability for the comprehensive and efficient evaluation of housing performance; the houses built after 2000 should focus on improving the performance of local characteristics, thermal and humidity environment, etc.
2022, 52(4): 16-22.
doi: 10.13204/j.gyjzG21052504
Abstract:
Jingyu Street, which is centered on the historical block of Baroque, has not been effective after two phases of renovation. The activation of the old district is in a dilemma, so it is urgent to inject fresh vitality from the perspective of transformation. As the phase Ⅱ project of Harbin Metro Line 3 is under construction, the planned line network is parallel to Jingyu Street. This paper took this opportunity to consider the new method of activating the historical district from the perspective of rail transit station planning. Based on TOD theory and the current situation of Chinese cities, the efficiency of subway station was analyzed from three aspects: land use, pedestrian system and public transport system. The results showed that there were some unreasonable problems in land use, bus stop proportion and location distribution in Wudao Street and Mosque station area. The pedestrian environment of Beima Road station was blocked and the public transportation system was weak. Jingyu Park station was perfect except for the single land type. Based on this, the paper proposed an optimization strategy and summarized the intrinsic value and potential efficiency of TOD model. The purpose is to improve the application and linkage of rail transit, provide a new perspective for the reuse of historical blocks, and put forward new methods for creating a convenient and comfortable living environment and building a compact and efficient regional structure system.
Jingyu Street, which is centered on the historical block of Baroque, has not been effective after two phases of renovation. The activation of the old district is in a dilemma, so it is urgent to inject fresh vitality from the perspective of transformation. As the phase Ⅱ project of Harbin Metro Line 3 is under construction, the planned line network is parallel to Jingyu Street. This paper took this opportunity to consider the new method of activating the historical district from the perspective of rail transit station planning. Based on TOD theory and the current situation of Chinese cities, the efficiency of subway station was analyzed from three aspects: land use, pedestrian system and public transport system. The results showed that there were some unreasonable problems in land use, bus stop proportion and location distribution in Wudao Street and Mosque station area. The pedestrian environment of Beima Road station was blocked and the public transportation system was weak. Jingyu Park station was perfect except for the single land type. Based on this, the paper proposed an optimization strategy and summarized the intrinsic value and potential efficiency of TOD model. The purpose is to improve the application and linkage of rail transit, provide a new perspective for the reuse of historical blocks, and put forward new methods for creating a convenient and comfortable living environment and building a compact and efficient regional structure system.
2022, 52(4): 23-34.
doi: 10.13204/j.gyjzG21061702
Abstract:
The regional architecture in China is of the strong features of form orientation. The study of traditional green construction wisdom with great regionality not only responds to the country’s calls to develop green buildings, but also pays attention to the regional characteristics of buildings and traces the local culture. Based on the tracing and inheritance of ancestral temple buildings in the Huizhou area, four kinds of planning and site-selection methods for ancestral temple buildings in the Huizhou area were analyzed and summerized investigated by 30 ancestral temple buildings in the Huizhou area, including the central axis core, "backing against Yin and facing to Yang" "reversing Yin and Yang" and "location in the east of the settlements", and then, from the external environment to the buildings, five kinds of green techniques were analyzed and summarized. Finaly, simulation softwares were used to simulate and verify the construction effect. It could be seen that speeding up the ventilation around the ancestral temple buildings, adjusting the duration of light and the ways of drainage could play a positive and important role in optimizing the environment.
The regional architecture in China is of the strong features of form orientation. The study of traditional green construction wisdom with great regionality not only responds to the country’s calls to develop green buildings, but also pays attention to the regional characteristics of buildings and traces the local culture. Based on the tracing and inheritance of ancestral temple buildings in the Huizhou area, four kinds of planning and site-selection methods for ancestral temple buildings in the Huizhou area were analyzed and summerized investigated by 30 ancestral temple buildings in the Huizhou area, including the central axis core, "backing against Yin and facing to Yang" "reversing Yin and Yang" and "location in the east of the settlements", and then, from the external environment to the buildings, five kinds of green techniques were analyzed and summarized. Finaly, simulation softwares were used to simulate and verify the construction effect. It could be seen that speeding up the ventilation around the ancestral temple buildings, adjusting the duration of light and the ways of drainage could play a positive and important role in optimizing the environment.
2022, 52(4): 35-39.
doi: 10.13204/j.gyjzG21060706
Abstract:
The current urban planning is paying more and more attention to the mixed-use development mode, and the development of urban stock also puts forward new requirements for the regeneration of the fast-growing industrial heritage. Through sorting out the problems of industrial heritage regeneration, analyzing the feasibility of the development and application of mixed functions, combining with case studies on the problems of mixed function development in the renewal of old industrial areas, a mixed-use regeneration mode that could meet the current urban goals in China was proposed. Trying to improve the cognitive limitation of the traditional transformation mode in the industrial areas, so that transformed the regeneration mode controlled by the traditional single main function into a mode that combined project resources with corresponding functions.
The current urban planning is paying more and more attention to the mixed-use development mode, and the development of urban stock also puts forward new requirements for the regeneration of the fast-growing industrial heritage. Through sorting out the problems of industrial heritage regeneration, analyzing the feasibility of the development and application of mixed functions, combining with case studies on the problems of mixed function development in the renewal of old industrial areas, a mixed-use regeneration mode that could meet the current urban goals in China was proposed. Trying to improve the cognitive limitation of the traditional transformation mode in the industrial areas, so that transformed the regeneration mode controlled by the traditional single main function into a mode that combined project resources with corresponding functions.
2022, 52(4): 40-49,97.
doi: 10.13204/j.gyjzG21060107
Abstract:
The longitudinal steel bars of beams generally produce a obvious bond-slip deformation in reinforced concrete (RC) beam-column joints under strong earthquake excitation. The key issue of finite element model of RC joint is to correctly describe the bond-slip laws of longitudinal steel bars of beams based on a reasonable material constitutive model. In the "super joint" model and OpenSees software platform, the stress-slippage constitutive model for longitudinal steel bars of beams was established on the basis of monotonic tensile test for traditional anchorage of single steel bars, the influence of axial compression and cyclic tension-compression on the anchorage performance of the longitudinal steel bars of beams in the joint was not considered. The mechanical properties of 11 specimens were tested under monotonic tension or cyclic tension-compression, and the bond-slip deformations of the bars were measured. By comparing the stress-slippage test results of the anchorage steel bars, the effects of loading method, axial compression, relative anchorage length and yield strength of the steel bars on the slip deformation were analyzed. The results showed that the anchorage performance of the steel bars was relatively the best under monotonic tension, the bond-slip deformation of the steel bars was larger under tension-tension cyclic loading, and the slip deformation of the steel bars would be further increased under tension-compression cyclic loading. The application of axial compression load was beneficial to improve the bond performance of the steel bar, and reduce the bond-slip deformation. With the increase of the relative anchorage length, the slip deformation of the steel bars at the tensile yield would decrease. The material constitutive model based on the monotonic tensile test of anchorage steel bar did not consider the influence of axial compression and loading method, it was difficult to reasonably simulate the slip deformation of longitudinal steel bars of beams in RC joints under strong earthquake.
The longitudinal steel bars of beams generally produce a obvious bond-slip deformation in reinforced concrete (RC) beam-column joints under strong earthquake excitation. The key issue of finite element model of RC joint is to correctly describe the bond-slip laws of longitudinal steel bars of beams based on a reasonable material constitutive model. In the "super joint" model and OpenSees software platform, the stress-slippage constitutive model for longitudinal steel bars of beams was established on the basis of monotonic tensile test for traditional anchorage of single steel bars, the influence of axial compression and cyclic tension-compression on the anchorage performance of the longitudinal steel bars of beams in the joint was not considered. The mechanical properties of 11 specimens were tested under monotonic tension or cyclic tension-compression, and the bond-slip deformations of the bars were measured. By comparing the stress-slippage test results of the anchorage steel bars, the effects of loading method, axial compression, relative anchorage length and yield strength of the steel bars on the slip deformation were analyzed. The results showed that the anchorage performance of the steel bars was relatively the best under monotonic tension, the bond-slip deformation of the steel bars was larger under tension-tension cyclic loading, and the slip deformation of the steel bars would be further increased under tension-compression cyclic loading. The application of axial compression load was beneficial to improve the bond performance of the steel bar, and reduce the bond-slip deformation. With the increase of the relative anchorage length, the slip deformation of the steel bars at the tensile yield would decrease. The material constitutive model based on the monotonic tensile test of anchorage steel bar did not consider the influence of axial compression and loading method, it was difficult to reasonably simulate the slip deformation of longitudinal steel bars of beams in RC joints under strong earthquake.
2022, 52(4): 50-55,90.
doi: 10.13204/j.gyjzG20092801
Abstract:
The seismic performance of low-rise cold-formed thin-walled steel buildings is good, it is not clear when the structural system changes from low-rise building to multi-story building. In addition, the seismic action increased with the increase of building height. Thus, to ensure the safety of multi-story cold-formed thin-walled steel structures, a definite seismic design method is necessary. In the paper, the damage structural parameters were determined and the damage criterion was established based on the results of existing shaking table tests of full-scale buildings, combined with tests of the double-layer composite wall and the joint of composite wall and floor. Furthermore, the simplified mechanical analysis model of the structure was established by using the equivalent rod method. The SAP 2000 was adopted to analyze the seismic performance of 4-6 stories structure, and the damage indexes and displacement angles of the structure under different rare earthquakes were obtained. Then, according to the damage criterion and the requirements of "three-level" seismic fortification, the seismic design of the structure was completed by adjusting the characteristic values of the restoring force skeleton curves. The main results were shown that: 1) under the action of 7 degree or 8 degree rare earthquakes, the structure appeared "medium damage" and the top displacement angle satisfied the limit value. Under the action of 9 degree rare earthquake, the interlayer displacement angle exceeded the limit value of "serious damage". Therefore, the interlayer strengthening was required to satisfy the requirements of "large earthquake no collapse" under large earthquake. 2) The seismic capacity of the structure could be improved by adding truss strengthening components to meet the seismic fortification requirements of the structure.
The seismic performance of low-rise cold-formed thin-walled steel buildings is good, it is not clear when the structural system changes from low-rise building to multi-story building. In addition, the seismic action increased with the increase of building height. Thus, to ensure the safety of multi-story cold-formed thin-walled steel structures, a definite seismic design method is necessary. In the paper, the damage structural parameters were determined and the damage criterion was established based on the results of existing shaking table tests of full-scale buildings, combined with tests of the double-layer composite wall and the joint of composite wall and floor. Furthermore, the simplified mechanical analysis model of the structure was established by using the equivalent rod method. The SAP 2000 was adopted to analyze the seismic performance of 4-6 stories structure, and the damage indexes and displacement angles of the structure under different rare earthquakes were obtained. Then, according to the damage criterion and the requirements of "three-level" seismic fortification, the seismic design of the structure was completed by adjusting the characteristic values of the restoring force skeleton curves. The main results were shown that: 1) under the action of 7 degree or 8 degree rare earthquakes, the structure appeared "medium damage" and the top displacement angle satisfied the limit value. Under the action of 9 degree rare earthquake, the interlayer displacement angle exceeded the limit value of "serious damage". Therefore, the interlayer strengthening was required to satisfy the requirements of "large earthquake no collapse" under large earthquake. 2) The seismic capacity of the structure could be improved by adding truss strengthening components to meet the seismic fortification requirements of the structure.
2022, 52(4): 56-61.
doi: 10.13204/j.gyjzG20082905
Abstract:
At present, steel tubular structures have been widely used in engineering. When a circular hollow sections (CHS) T-joint transmits the axial compression through its brace, the joint often damages due to large deformation at the joint zone. In order to improve the bearing capacity of the joint, the study of reinforcing the joint with channel steel connection was carried out. Firstly, the finite element software ABAQUS was used to simulate the axial bearing capacity test of three groups of six T-joints without and with external stiffeners. The finite element simulation results were consistent with the test results, which verified the reliability of the finite element method. Then ABAQUS software was used to study the bearing capacity of channel steel connection joints under axial compression, and three sets of simulation of different β (brace-to-chord diameter, d1/d0) were conducted to analyze the influence of different channel steel models and different lengths of the same channel steel on the bearing capacity and deformation of the joints. The finite element simulation results showed that the bearing capacity of the joints connected by channel steel was at least 130% and at most 252% higher than that of the unreinforced joints, and the deformation of the chord was improved. With the increase of the cross-section size of channel steel, the bearing capacity of channel steel joints was firstly increased and then decreased. When β was 0.25, the bearing capacity increased from 130% to 252%, and then decreased to 196%; When β was 0.5, the bearing capacity increased from 133% to 293%, and then decreased to 170%. With the increase of channel steel cross-section size, the failure mode was also changed from chord deformation to channel sag. When β was 0.5 and the 22b channel steel was selected, the ultimate bearing capacity decreased from 212% to 142% with the increase of channel steel length.
At present, steel tubular structures have been widely used in engineering. When a circular hollow sections (CHS) T-joint transmits the axial compression through its brace, the joint often damages due to large deformation at the joint zone. In order to improve the bearing capacity of the joint, the study of reinforcing the joint with channel steel connection was carried out. Firstly, the finite element software ABAQUS was used to simulate the axial bearing capacity test of three groups of six T-joints without and with external stiffeners. The finite element simulation results were consistent with the test results, which verified the reliability of the finite element method. Then ABAQUS software was used to study the bearing capacity of channel steel connection joints under axial compression, and three sets of simulation of different β (brace-to-chord diameter, d1/d0) were conducted to analyze the influence of different channel steel models and different lengths of the same channel steel on the bearing capacity and deformation of the joints. The finite element simulation results showed that the bearing capacity of the joints connected by channel steel was at least 130% and at most 252% higher than that of the unreinforced joints, and the deformation of the chord was improved. With the increase of the cross-section size of channel steel, the bearing capacity of channel steel joints was firstly increased and then decreased. When β was 0.25, the bearing capacity increased from 130% to 252%, and then decreased to 196%; When β was 0.5, the bearing capacity increased from 133% to 293%, and then decreased to 170%. With the increase of channel steel cross-section size, the failure mode was also changed from chord deformation to channel sag. When β was 0.5 and the 22b channel steel was selected, the ultimate bearing capacity decreased from 212% to 142% with the increase of channel steel length.
2022, 52(4): 62-69,208.
doi: 10.13204/j.gyjzG20041801
Abstract:
A novel buckling-restrained butterfly-shaped steel plate wall that restrict the overall buckling by channel steel was proposed, which can provide certain lateral stiffness together with improving the energy dissipation capacity for the structure. The configuration and principle of buckling-restrained butterfly-shaped steel plate wall were presented. The finite element software ABAQUS performed a numerical simulation analysis on the butterfly-shaped steel plate wall under quasi-static loading and calibrated by theoretical lateral stiffness. Then, the parametric studies were carried out to inspect the hysteretic curves, load-displacement curves, stiffness degradation curves, ductility and energy dissipation of the structure and the effects of the buckling-restrained methods were also compared. The results showed that overall stability, ductility and energy dissipation of the buckling-restrained butterfly-shaped steel plate wall could be enhanced; when the ratio of width to thickness of butterfly link (b/t) and ratio of butterfly link height to steel plate wall thickness (L/h) declined, the bearing capacity and stiffness both increased, accompanied with a fuller hysteretic curves and enhanced energy dissipation capacity.
A novel buckling-restrained butterfly-shaped steel plate wall that restrict the overall buckling by channel steel was proposed, which can provide certain lateral stiffness together with improving the energy dissipation capacity for the structure. The configuration and principle of buckling-restrained butterfly-shaped steel plate wall were presented. The finite element software ABAQUS performed a numerical simulation analysis on the butterfly-shaped steel plate wall under quasi-static loading and calibrated by theoretical lateral stiffness. Then, the parametric studies were carried out to inspect the hysteretic curves, load-displacement curves, stiffness degradation curves, ductility and energy dissipation of the structure and the effects of the buckling-restrained methods were also compared. The results showed that overall stability, ductility and energy dissipation of the buckling-restrained butterfly-shaped steel plate wall could be enhanced; when the ratio of width to thickness of butterfly link (b/t) and ratio of butterfly link height to steel plate wall thickness (L/h) declined, the bearing capacity and stiffness both increased, accompanied with a fuller hysteretic curves and enhanced energy dissipation capacity.
2022, 52(4): 70-73.
doi: 10.13204/j.gyjzG20060112
Abstract:
In order to study the ultimate bearing capacity of the single-layer spherical reticulated shell structure, based on the BP neural network algorithm of TensorFlow, a neural network model was established to predict the ultimate bearing capacity of the K8 single-layer spherical reticulated shell structure by considering the complex mapping relationship in the nonlinear analysis. Moreover, another new neural network model was established to predict the ultimate bearing capacity of the Kn-type single-layer spherical reticulated shell structure. The prediction results were compared with the calculation results of the finite element and literature regression formulas. The results showed that the error mean between the predicted ultimate bearing capacity of the K8 single-layer spherical reticulated shell structure and the finite element calculation results was 1.666%, and that between the formula calculation results and the finite element calculation results was 3.994%; the error mean between the predicted ultimate bearing capacity of the Kn-type single-layer spherical reticulated shell structure and the finite element calculation was 4.774%, and that between the formula calculation results and the finite element calculation results was 5.163%. The feasibility of using neural network to predict the ultimate bearing capacity of single-layer reticulated shell structure is demonstrated.
In order to study the ultimate bearing capacity of the single-layer spherical reticulated shell structure, based on the BP neural network algorithm of TensorFlow, a neural network model was established to predict the ultimate bearing capacity of the K8 single-layer spherical reticulated shell structure by considering the complex mapping relationship in the nonlinear analysis. Moreover, another new neural network model was established to predict the ultimate bearing capacity of the Kn-type single-layer spherical reticulated shell structure. The prediction results were compared with the calculation results of the finite element and literature regression formulas. The results showed that the error mean between the predicted ultimate bearing capacity of the K8 single-layer spherical reticulated shell structure and the finite element calculation results was 1.666%, and that between the formula calculation results and the finite element calculation results was 3.994%; the error mean between the predicted ultimate bearing capacity of the Kn-type single-layer spherical reticulated shell structure and the finite element calculation was 4.774%, and that between the formula calculation results and the finite element calculation results was 5.163%. The feasibility of using neural network to predict the ultimate bearing capacity of single-layer reticulated shell structure is demonstrated.
2022, 52(4): 74-83.
doi: 10.13204/j.gyjzG21010406
Abstract:
A modular composite joint suitable for the industrialization of buildings was proposed. Three basic specimens were designed with the concept of beam-column-joint core area separation and modular prefabrication. Through the quasi-static test, the failure process and failure characteristics of each joint with different beam-to-column liner stiffness ratios (ki) were obtained. The seismic performance of joints such as hysteresis curve, skeleton curve, ductility, energy consumption, and stiffness degradation were analyzed. The results showed that with the increase of ki value, the failure mode of the joints developed from beam-end bending to joint shear and column-end compression bending, and had experienced three stages of elasticity, elastoplasticity, and failure. The hysteresis curve of the joints was full, and the skeleton curve was in the shape of 'S’. The overall stiffness degradation performance of the joints was stable, the mean ductility coefficients were in the range of 3.71-4.25, the limit rotation angles were in the range of 0.064 6-0.076 0 rad, and the mean equivalent viscous damping coefficients were in the range of 0.32-0.33, and the joints showed good mechanical and hysteretic properties. The beam-to-column linear stiffness ratio had a greater impact on the strain of longitudinal reinforcement and concrete but had a smaller impact on the strain of H-shaped steel skeleton, steel beam webs, and flange connecting plates. The shear mechanism of the joint core area was consistent with that of the 'oblique strut’.
A modular composite joint suitable for the industrialization of buildings was proposed. Three basic specimens were designed with the concept of beam-column-joint core area separation and modular prefabrication. Through the quasi-static test, the failure process and failure characteristics of each joint with different beam-to-column liner stiffness ratios (ki) were obtained. The seismic performance of joints such as hysteresis curve, skeleton curve, ductility, energy consumption, and stiffness degradation were analyzed. The results showed that with the increase of ki value, the failure mode of the joints developed from beam-end bending to joint shear and column-end compression bending, and had experienced three stages of elasticity, elastoplasticity, and failure. The hysteresis curve of the joints was full, and the skeleton curve was in the shape of 'S’. The overall stiffness degradation performance of the joints was stable, the mean ductility coefficients were in the range of 3.71-4.25, the limit rotation angles were in the range of 0.064 6-0.076 0 rad, and the mean equivalent viscous damping coefficients were in the range of 0.32-0.33, and the joints showed good mechanical and hysteretic properties. The beam-to-column linear stiffness ratio had a greater impact on the strain of longitudinal reinforcement and concrete but had a smaller impact on the strain of H-shaped steel skeleton, steel beam webs, and flange connecting plates. The shear mechanism of the joint core area was consistent with that of the 'oblique strut’.
2022, 52(4): 84-90.
doi: 10.13204/j.gyjzG20050712
Abstract:
A quasi-static loading test was conducted on four full-scaled models of prefabricated steel-concrete composite tube (SRCT) shear walls to evaluate the seismic performance. The test results were analyzed in terms of failure mode, bearing capacity, hysteretic curves, ductility, stiffness degradation and energy dissipation capacity. The results showed that the SRCT shear wall had high bearing capacity, stiffness, ductility and energy dissipation capacity. As the thickness of the steel plate increased, the failure mode of SRCT shear wall changed from steel plate yielding to weld failure. Measures should be taken to ensure the welding quality of U-shaped steel and steel plates to achieve the design failure mode. The average value of the yield displacement angle of the specimens was 0.005 rad, and the average ultimate displacement angle was 0.013 rad, indicating that the deformation capacity of SRCT shear wall was higher than the specification limit. In the range of 200-250 mm spacing between stud-tie bars, properly reducing the spacing between stud-tie bars could improve the ductility and energy dissipation capacity of the shear wall.
A quasi-static loading test was conducted on four full-scaled models of prefabricated steel-concrete composite tube (SRCT) shear walls to evaluate the seismic performance. The test results were analyzed in terms of failure mode, bearing capacity, hysteretic curves, ductility, stiffness degradation and energy dissipation capacity. The results showed that the SRCT shear wall had high bearing capacity, stiffness, ductility and energy dissipation capacity. As the thickness of the steel plate increased, the failure mode of SRCT shear wall changed from steel plate yielding to weld failure. Measures should be taken to ensure the welding quality of U-shaped steel and steel plates to achieve the design failure mode. The average value of the yield displacement angle of the specimens was 0.005 rad, and the average ultimate displacement angle was 0.013 rad, indicating that the deformation capacity of SRCT shear wall was higher than the specification limit. In the range of 200-250 mm spacing between stud-tie bars, properly reducing the spacing between stud-tie bars could improve the ductility and energy dissipation capacity of the shear wall.
2022, 52(4): 91-97.
doi: 10.13204/j.gyjzG21012609
Abstract:
The existing experimental studies showed that the seismic performance of prefabricated cylindrical pier with hybrid joint was better than that of cast-in-place pier, but the experimental research on the mechanical properties of this kind of assembled pier under eccentric compression was rare. The mechanical properties tests of four kinds of cylindrical piers under large or small eccentric compression were carried out, including the assembled pier with hybrid joints, the assembled pier with grouting sleeve connection, the assembled pier with CFST shear key connection and the integral cast-in-place pier. The damage mechanism and failure mode of different types of piers were compared and analyzed, and the bearing capacity of the specimens under compression was calculated by JTG 3362—2018. The results showed that: the failure mode and damage process of the pier connected by hybrid joints were similar to that of the integral bridge pier, which showed that the concrete on the compression side was crushed in the state of small eccentric compression, and the steel bar in the tensile side was yielding failure in the state of large eccentric compression. Compared with the integral cast-in-place specimens, the bearing capacity of the hybrid joint connection specimens increased by 6% under large eccentric compression and increased by 2% under small eccentric compression. The bearing capacity of the specimens connected by the grouting sleeve was reduced by 6% under large eccentric compression and increased by 8% under small eccentric compression. The bearing capacity of the specimens connected by the CFST shear key decreased by 20% under large eccentric compression and decreased by 27% under small eccentric compression. Different from other types of assembled pier specimens, the measured bearing capacity of composite pier specimens connected with hybrid joints was greater than the calculation results of JTG 3362—2018.
The existing experimental studies showed that the seismic performance of prefabricated cylindrical pier with hybrid joint was better than that of cast-in-place pier, but the experimental research on the mechanical properties of this kind of assembled pier under eccentric compression was rare. The mechanical properties tests of four kinds of cylindrical piers under large or small eccentric compression were carried out, including the assembled pier with hybrid joints, the assembled pier with grouting sleeve connection, the assembled pier with CFST shear key connection and the integral cast-in-place pier. The damage mechanism and failure mode of different types of piers were compared and analyzed, and the bearing capacity of the specimens under compression was calculated by JTG 3362—2018. The results showed that: the failure mode and damage process of the pier connected by hybrid joints were similar to that of the integral bridge pier, which showed that the concrete on the compression side was crushed in the state of small eccentric compression, and the steel bar in the tensile side was yielding failure in the state of large eccentric compression. Compared with the integral cast-in-place specimens, the bearing capacity of the hybrid joint connection specimens increased by 6% under large eccentric compression and increased by 2% under small eccentric compression. The bearing capacity of the specimens connected by the grouting sleeve was reduced by 6% under large eccentric compression and increased by 8% under small eccentric compression. The bearing capacity of the specimens connected by the CFST shear key decreased by 20% under large eccentric compression and decreased by 27% under small eccentric compression. Different from other types of assembled pier specimens, the measured bearing capacity of composite pier specimens connected with hybrid joints was greater than the calculation results of JTG 3362—2018.
2022, 52(4): 98-106.
doi: 10.13204/j.gyjzG20081704
Abstract:
The effect of shear connectors on mechanical and deformation properties of steel-plate concrete composite walls subjected to axial compressive loading was studied through experiment and finite element numerical simulation. The testing program involved four composite wall specimens with different ratios (the number of studs-to-tie bars). The results showed that the four walls failed in a similar brittle failure mode characterized by compressive yielding of the steel plates, then outward local buckling of the steel plates, crushing of inner concrete, and failure of the weld, except for DSW-12. The yielding and outward local buckling of the steel plates had little influence on the stiffness of the walls. The relative proportion of the tie bar had little effect on the axial compressive stiffness, bearing capacity, local buckling load of steel plate, and failure mode, but the tie bar could restrain outward local deformation. With the same section and distance-to-thickness ratio, the higher the proportion of the tie bar, the smaller the outward local buckling deformation of the steel plate.
The effect of shear connectors on mechanical and deformation properties of steel-plate concrete composite walls subjected to axial compressive loading was studied through experiment and finite element numerical simulation. The testing program involved four composite wall specimens with different ratios (the number of studs-to-tie bars). The results showed that the four walls failed in a similar brittle failure mode characterized by compressive yielding of the steel plates, then outward local buckling of the steel plates, crushing of inner concrete, and failure of the weld, except for DSW-12. The yielding and outward local buckling of the steel plates had little influence on the stiffness of the walls. The relative proportion of the tie bar had little effect on the axial compressive stiffness, bearing capacity, local buckling load of steel plate, and failure mode, but the tie bar could restrain outward local deformation. With the same section and distance-to-thickness ratio, the higher the proportion of the tie bar, the smaller the outward local buckling deformation of the steel plate.
2022, 52(4): 107-113.
doi: 10.13204/j.gyjzG21081309
Abstract:
A kind of cross laminated timber (CLT) wall-to-floor joint with angle brackets was studied. Firstly, the smooth-thread shear, transverse shear, withdrawal resistance and failure modes of two self-tapping screws in CLT plate were studied to estimate the bearing capacity of the CLT wall-to-floor joints with angle brackets. Then monotonic loading test and cyclic loading test in both directions of uplift and shear were conducted on the joints. The main failure modes were bending of the screws and the compressive failure of wood. The results showed that the connection had good ductility and energy dissipation capacity.
A kind of cross laminated timber (CLT) wall-to-floor joint with angle brackets was studied. Firstly, the smooth-thread shear, transverse shear, withdrawal resistance and failure modes of two self-tapping screws in CLT plate were studied to estimate the bearing capacity of the CLT wall-to-floor joints with angle brackets. Then monotonic loading test and cyclic loading test in both directions of uplift and shear were conducted on the joints. The main failure modes were bending of the screws and the compressive failure of wood. The results showed that the connection had good ductility and energy dissipation capacity.
2022, 52(4): 114-121.
doi: 10.13204/j.gyjzG21050610
Abstract:
In order to describe the stress-strain characteristics of strain-softening soil subjected to freeze-thaw cycling, an improved hyperbolic model was proposed. Based on the traditional Kondner hyperbolic model and the definition of secant modulus, the basic relation between dimensionless secant modulus Es/Ei and dimensionless deviation stress q/qmax was deduced through transformation of the hyperbolic model function. A set of triaxial tests were conducted on compacted silty clay specimens subjected to different confining pressures and freeze-thaw cycles. The q/qmax-Es/Ei relations before and after strain softening could be fitted by the power function, respectively. An improved hyperbolic model, which contained 8 parameters including c, φ, K, n, f, g, α and β, was proposed to reflect the strain softening characteristics. The influence of freeze-thaw cycles on soil characteristics was formulated by determining the laws of the model parameters changed with freeze-thaw cycles. The results showed with the increase of freeze-thaw cycles, the peak strength of specimens and cohesion c decreased gradually, the internal friction angle φ increased ceaselessly; the initial secant modulus decreased increasely, and the corresponding parameter K decreased at the same time, the parameter n increased steadily. The parameters f and α were the limit values which reflected secant moduli of picewise functions in the period of strain-softening, they increased or decreased gradually respectively with increase of freeze-thaw cycles.The parameters g and β reflected the shape of Es/Ei-q/q curves before and after strain-softening, and g decreased steadily with the increasing of freeze-thaw cycles and β changed in fluctuation. The relations of the above parameters to freeze-thaw cycles could be fitted by the Logistic function. The improved model and representation expressions for model parameters were programmed into a calculation software, which taking the confining pressure and freeze-thaw cycles as the variables. The calculation results by the model could reflect the influence of confining pressure and freeze-thaw cycles on the mechanical properties of soil.
In order to describe the stress-strain characteristics of strain-softening soil subjected to freeze-thaw cycling, an improved hyperbolic model was proposed. Based on the traditional Kondner hyperbolic model and the definition of secant modulus, the basic relation between dimensionless secant modulus Es/Ei and dimensionless deviation stress q/qmax was deduced through transformation of the hyperbolic model function. A set of triaxial tests were conducted on compacted silty clay specimens subjected to different confining pressures and freeze-thaw cycles. The q/qmax-Es/Ei relations before and after strain softening could be fitted by the power function, respectively. An improved hyperbolic model, which contained 8 parameters including c, φ, K, n, f, g, α and β, was proposed to reflect the strain softening characteristics. The influence of freeze-thaw cycles on soil characteristics was formulated by determining the laws of the model parameters changed with freeze-thaw cycles. The results showed with the increase of freeze-thaw cycles, the peak strength of specimens and cohesion c decreased gradually, the internal friction angle φ increased ceaselessly; the initial secant modulus decreased increasely, and the corresponding parameter K decreased at the same time, the parameter n increased steadily. The parameters f and α were the limit values which reflected secant moduli of picewise functions in the period of strain-softening, they increased or decreased gradually respectively with increase of freeze-thaw cycles.The parameters g and β reflected the shape of Es/Ei-q/q curves before and after strain-softening, and g decreased steadily with the increasing of freeze-thaw cycles and β changed in fluctuation. The relations of the above parameters to freeze-thaw cycles could be fitted by the Logistic function. The improved model and representation expressions for model parameters were programmed into a calculation software, which taking the confining pressure and freeze-thaw cycles as the variables. The calculation results by the model could reflect the influence of confining pressure and freeze-thaw cycles on the mechanical properties of soil.
2022, 52(4): 122-125,73.
doi: 10.13204/j.gyjzG21021603
Abstract:
The remolded saturated cohesive soil with the same initial state was consolidated at different loading rates, and the specimens were measured by nuclear magnetic resonance (NMR) in different loading stages. And then the relation of transverse relaxation time T2 distribution or T2 spectrum area change with porosity was qualitatively analyzed to study its microscopic response of deformation.The results showed that the T2 spectrum of saturated remolded cohesive soil in the initial stage of consolidation was consisted of two peaks. With the development of consolidation, the large pores gradually closed to small pores, and the final T2 spectrum turned out to be a single peak; for faster loading soil specimens influenced by lagging of drainage at the beginning of loading,the change trend of the T2 spectrum was not obvious.And after a long time of constant loading, the final shape for the T2 spectrum of the soil specimens was very similar regardless of the loading rate.It indicated that the loading rate only influenced the intermediate state of the soil specimens, the final state was dominated by the initial state of the specimens.
The remolded saturated cohesive soil with the same initial state was consolidated at different loading rates, and the specimens were measured by nuclear magnetic resonance (NMR) in different loading stages. And then the relation of transverse relaxation time T2 distribution or T2 spectrum area change with porosity was qualitatively analyzed to study its microscopic response of deformation.The results showed that the T2 spectrum of saturated remolded cohesive soil in the initial stage of consolidation was consisted of two peaks. With the development of consolidation, the large pores gradually closed to small pores, and the final T2 spectrum turned out to be a single peak; for faster loading soil specimens influenced by lagging of drainage at the beginning of loading,the change trend of the T2 spectrum was not obvious.And after a long time of constant loading, the final shape for the T2 spectrum of the soil specimens was very similar regardless of the loading rate.It indicated that the loading rate only influenced the intermediate state of the soil specimens, the final state was dominated by the initial state of the specimens.
2022, 52(4): 126-132.
doi: 10.13204/j.gyjzG21051110
Abstract:
In order to study the relations among the constant resistance value of sliding anchor bolts with expanded heads and the anchor bolt sizes, the elastoplastic theoretical formula was deduced based on the elastic theory for the constant resistance of large deformation bolts, which could be suitable to predict the constant resistance values of sliding auchor bolts with expanded heads. The numerical simulation software was researched the constant resistance values in five working conditions, and the simulation results of the three working conditions were contrasted with the results from indoor experiments, and the results showed that the numerical simulation model had less differences from the experimental results, and the model was more reasonable; the theoretical resistance values calculated by the elastoplastic theoretical formula were in good agreement with the ones by numerical simulations.
In order to study the relations among the constant resistance value of sliding anchor bolts with expanded heads and the anchor bolt sizes, the elastoplastic theoretical formula was deduced based on the elastic theory for the constant resistance of large deformation bolts, which could be suitable to predict the constant resistance values of sliding auchor bolts with expanded heads. The numerical simulation software was researched the constant resistance values in five working conditions, and the simulation results of the three working conditions were contrasted with the results from indoor experiments, and the results showed that the numerical simulation model had less differences from the experimental results, and the model was more reasonable; the theoretical resistance values calculated by the elastoplastic theoretical formula were in good agreement with the ones by numerical simulations.
2022, 52(4): 133-139.
doi: 10.13204/j.gyjzG21032405
Abstract:
The stability of karst foundation is an important guarantee for the safety of ground buildings. Taking an actual engineering of treatment for a giant karst cave under a high-rise building in Guizhou Province as an example, the stability for the roof subjected to building loads was analyzed used by the structural mechanics approximation method and finite element method. By the numerical simulation software FLAC3D, the calculation models of foundation with karst caves filled with different materials and ranges were constructed to calculate the characteristics of the strain field and stress field in the cave roof and ground under building loads. The materials filled in karst caves were fine aggregate concrete and crushed stone respectively, and the filling ranges included the whole void and the partial void in the side of the building. The deformation characteristics of overlying foundation in four working conditions were compared and analyzed. The results showed that the numerical analysis consonant with the actual monitoring data, and the treated foundation with complex karst cavities was stable under the action of pile loads, and the filling effect of fine aggregate concrete was better than that filled by gravel material. On the basis of ensuring the safety for the building, the partial filling scheme could save more cost for the project.
The stability of karst foundation is an important guarantee for the safety of ground buildings. Taking an actual engineering of treatment for a giant karst cave under a high-rise building in Guizhou Province as an example, the stability for the roof subjected to building loads was analyzed used by the structural mechanics approximation method and finite element method. By the numerical simulation software FLAC3D, the calculation models of foundation with karst caves filled with different materials and ranges were constructed to calculate the characteristics of the strain field and stress field in the cave roof and ground under building loads. The materials filled in karst caves were fine aggregate concrete and crushed stone respectively, and the filling ranges included the whole void and the partial void in the side of the building. The deformation characteristics of overlying foundation in four working conditions were compared and analyzed. The results showed that the numerical analysis consonant with the actual monitoring data, and the treated foundation with complex karst cavities was stable under the action of pile loads, and the filling effect of fine aggregate concrete was better than that filled by gravel material. On the basis of ensuring the safety for the building, the partial filling scheme could save more cost for the project.
2022, 52(4): 140-145,83.
doi: 10.13204/j.gyjzG21080909
Abstract:
The flexural fatigue tests of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) were investigated at three different stress levels (S=0.6, 0.7, 0.9) to study the fatigue properties and fatigue reliability of recycled aggregate concrete, the longitudinal strain and fatigue life at different stress levels were obtained. The two-parameter Weibull distribution was analyzed, and the S-N-Pf equation was established. And since the logarithmic fatigue life generally follows a lognormal distribution, based on the Miner fatigue model, the reliability formula was derived and the fatigue reliability was calculated. The results showed that under different stress levels, the fatigue life of RAC was smaller than that of NAC, the longitudinal strain of RAC was larger than that of NAC, the flexural fatigue resistance and the fatigue reliability of RAC were lower than that of NAC. It was assumed that the fatigue life obeyed the Weibull distribution, the predicted fatigue life under different reliability was closer to the critical value than if it obeyed the lognormal distribution in the analysis of NAC. The results were not much different in the analysis of RAC.
The flexural fatigue tests of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) were investigated at three different stress levels (S=0.6, 0.7, 0.9) to study the fatigue properties and fatigue reliability of recycled aggregate concrete, the longitudinal strain and fatigue life at different stress levels were obtained. The two-parameter Weibull distribution was analyzed, and the S-N-Pf equation was established. And since the logarithmic fatigue life generally follows a lognormal distribution, based on the Miner fatigue model, the reliability formula was derived and the fatigue reliability was calculated. The results showed that under different stress levels, the fatigue life of RAC was smaller than that of NAC, the longitudinal strain of RAC was larger than that of NAC, the flexural fatigue resistance and the fatigue reliability of RAC were lower than that of NAC. It was assumed that the fatigue life obeyed the Weibull distribution, the predicted fatigue life under different reliability was closer to the critical value than if it obeyed the lognormal distribution in the analysis of NAC. The results were not much different in the analysis of RAC.
2022, 52(4): 146-151,106.
doi: 10.13204/j.gyjzG20100804
Abstract:
The paper presented the results of the in-situ test and experimental study on a reinforced concrete industrial plant in Xi'an. The pH values of the pore solution in the cylinder samples were measured layer-by-layer by expression method. The length of semi-carbonated zone was determined according to the test results. The mass balance in the carbonation process was analyzed and the change of substance content in the carbonation process was calculated by numerical method, and the numerical model of semi-carbonated zone length of concrete was obtained. The accuracy of the numerical model was valid by comparing the numerical analysis results with the experimental results. The results showed that the semi-carbonated zone length increased with the increase of water-cement ratio, while decreasing with the increase of cement content and relative humidity. Relative humidity had the most significant effect on the semi-carbonated zone length. When RH ≥ 80%, the semi-carbonated zone disappearred. The semi-carbonated zone length was relatively short at RH = 70%, which could be ignored. The CO2 concentration and carbonation time had little effect on the semi-carbonated zone length.
The paper presented the results of the in-situ test and experimental study on a reinforced concrete industrial plant in Xi'an. The pH values of the pore solution in the cylinder samples were measured layer-by-layer by expression method. The length of semi-carbonated zone was determined according to the test results. The mass balance in the carbonation process was analyzed and the change of substance content in the carbonation process was calculated by numerical method, and the numerical model of semi-carbonated zone length of concrete was obtained. The accuracy of the numerical model was valid by comparing the numerical analysis results with the experimental results. The results showed that the semi-carbonated zone length increased with the increase of water-cement ratio, while decreasing with the increase of cement content and relative humidity. Relative humidity had the most significant effect on the semi-carbonated zone length. When RH ≥ 80%, the semi-carbonated zone disappearred. The semi-carbonated zone length was relatively short at RH = 70%, which could be ignored. The CO2 concentration and carbonation time had little effect on the semi-carbonated zone length.
2022, 52(4): 152-157,132.
doi: 10.13204/j.gyjzG21112105
Abstract:
In order to research the influence of sustained loads on the mechanical properties of concrete, taking the Tianjin Metro Line 6 Lushuidao station as the engineering background, the creep development of concrete under different sustained times and sustained stresses was tested, as well as the static performance of concrete after creep. At the same time, the static loading test for shrinkage specimens with the same environmental conditions of creep specimens was also carried out. The results showed that under 15% and 30% stress level, the elastic modulus of concrete after creep increased gradually with the sustained time, but its increase rate reduced. The elastic modulus of shrinkage specimens under the same environmental conditions also had a certain growth, and the value was about 5% lower than that of holding specimens at 0.3 stress level. With the increase of sustained time, the slope of the stress-strain curve of concrete after creep increased in the elastic stage, and the peak stress also increased. Under the same environmental conditions, the slope of the stress-strain curve of the shrinkage specimen without sustained loads also increased in the elastic stage, the peak stress was lower than that of the creep specimen, which was about 65% of that of the creep specimen.
In order to research the influence of sustained loads on the mechanical properties of concrete, taking the Tianjin Metro Line 6 Lushuidao station as the engineering background, the creep development of concrete under different sustained times and sustained stresses was tested, as well as the static performance of concrete after creep. At the same time, the static loading test for shrinkage specimens with the same environmental conditions of creep specimens was also carried out. The results showed that under 15% and 30% stress level, the elastic modulus of concrete after creep increased gradually with the sustained time, but its increase rate reduced. The elastic modulus of shrinkage specimens under the same environmental conditions also had a certain growth, and the value was about 5% lower than that of holding specimens at 0.3 stress level. With the increase of sustained time, the slope of the stress-strain curve of concrete after creep increased in the elastic stage, and the peak stress also increased. Under the same environmental conditions, the slope of the stress-strain curve of the shrinkage specimen without sustained loads also increased in the elastic stage, the peak stress was lower than that of the creep specimen, which was about 65% of that of the creep specimen.
2022, 52(4): 158-162,185.
doi: 10.13204/j.gyjzG21070809
Abstract:
The thermal and mechanical properties of slag sulfoaluminate cement (S-SAC) and ordinary Portland cement (OPC) were compared and analyzed by isothermal calorimetry, adiabatic temperature rise and compressive strength tests. The results showed that the total hydration heat of S-SAC cement was 33.5% lower than that of OPC cement at 7 days, and the 28 days compressive strength of S-SAC concrete was 36.4% higher than that of OPC concrete. With different water-binder ratios, the later strength of S-SAC concrete was 50% higher than that of OPC concrete, and the adiabatic temperature rise of S-SAC concrete was 49% of that of OPC concrete at the same ratio. Adding fly ash and granulated blast furnace slag powder could not only maintain the early strength of S-SAC concrete, but also increase the growth rate of later strength; the higher the content of fly ash, the slower the heat release rate of S-SAC concrete, and the lower the adiabatic temperature rise. Compared with OPC concrete, S-SAC concrete showed the advantages of low heat and high strength growth rate in the later stage.
The thermal and mechanical properties of slag sulfoaluminate cement (S-SAC) and ordinary Portland cement (OPC) were compared and analyzed by isothermal calorimetry, adiabatic temperature rise and compressive strength tests. The results showed that the total hydration heat of S-SAC cement was 33.5% lower than that of OPC cement at 7 days, and the 28 days compressive strength of S-SAC concrete was 36.4% higher than that of OPC concrete. With different water-binder ratios, the later strength of S-SAC concrete was 50% higher than that of OPC concrete, and the adiabatic temperature rise of S-SAC concrete was 49% of that of OPC concrete at the same ratio. Adding fly ash and granulated blast furnace slag powder could not only maintain the early strength of S-SAC concrete, but also increase the growth rate of later strength; the higher the content of fly ash, the slower the heat release rate of S-SAC concrete, and the lower the adiabatic temperature rise. Compared with OPC concrete, S-SAC concrete showed the advantages of low heat and high strength growth rate in the later stage.
2022, 52(4): 163-170,139.
doi: 10.13204/j.gyjzG21091202
Abstract:
In order to study the dynamic mechanical properties of rubber concrete under freeze-thaw cycles, the longitudinal wave velocity of rubber concrete specimens with 10% rubber volume was measured by non-metallic ultrasonic detector, the impact compression tests of rubber concrete specimens with different freeze-thaw cycles (0, 25, 50, 75, 100, 125) were carried out by using the 74 mm diameter variable cross-section split Hopkinson compression bar test device under different impact air pressures (0.3, 0.4, 0.5, 0.6 MPa), and the change laws of stress-strain curve, peak stress, ultimate strain dynamic intensity enhancement factor (DIF) and energy absorption effect were analyzed. The results showed that the strength of concrete decreased with the addition of rubber, but its toughness and energy absorption effect increased obviously. With the increase of freeze-thaw cycles, the longitudinal wave velocity of rubber concrete decreased and the damage degree increased. Freeze-thaw action would damage rubber concrete and reduce the longitudinal wave velocity of specimens. Under the same freeze-thaw cycles, with the increase of strain rate, the peak stress, limit strain, DIF and absorbed energy of specimen increased, and there was an obvious strain rate effect. Under the pressure of 0.6 MPa, the peak stresses of 25, 50, 75, 100 and 125 freeze-thaw cycles were reduced by 25.1%, 37.1%, 46%, 52.5% and 54.8%, respectively. With the increase of the number of freeze-thaw cycles, the peak stress of specimens decreased and the decreasing amplitude decreased gradually. After the number of cycles exceeded 100, the decreasing amplitude of stress of specimens was no longer obvious. The ultimate strain increased and the absorbed energy decreased. The freeze-thaw environment significantly reduced the strength and integrity of rubber concrete materials.
In order to study the dynamic mechanical properties of rubber concrete under freeze-thaw cycles, the longitudinal wave velocity of rubber concrete specimens with 10% rubber volume was measured by non-metallic ultrasonic detector, the impact compression tests of rubber concrete specimens with different freeze-thaw cycles (0, 25, 50, 75, 100, 125) were carried out by using the 74 mm diameter variable cross-section split Hopkinson compression bar test device under different impact air pressures (0.3, 0.4, 0.5, 0.6 MPa), and the change laws of stress-strain curve, peak stress, ultimate strain dynamic intensity enhancement factor (DIF) and energy absorption effect were analyzed. The results showed that the strength of concrete decreased with the addition of rubber, but its toughness and energy absorption effect increased obviously. With the increase of freeze-thaw cycles, the longitudinal wave velocity of rubber concrete decreased and the damage degree increased. Freeze-thaw action would damage rubber concrete and reduce the longitudinal wave velocity of specimens. Under the same freeze-thaw cycles, with the increase of strain rate, the peak stress, limit strain, DIF and absorbed energy of specimen increased, and there was an obvious strain rate effect. Under the pressure of 0.6 MPa, the peak stresses of 25, 50, 75, 100 and 125 freeze-thaw cycles were reduced by 25.1%, 37.1%, 46%, 52.5% and 54.8%, respectively. With the increase of the number of freeze-thaw cycles, the peak stress of specimens decreased and the decreasing amplitude decreased gradually. After the number of cycles exceeded 100, the decreasing amplitude of stress of specimens was no longer obvious. The ultimate strain increased and the absorbed energy decreased. The freeze-thaw environment significantly reduced the strength and integrity of rubber concrete materials.
2022, 52(4): 171-178.
doi: 10.13204/j.gyjzG21072605
Abstract:
National Speed Skating Oval is the landmark of the 2022 Winter Olympic Games, and the waterproofing of the unitary roofing system for the flexible cable net area is a key issue which needs to be solved. Firstly, based on the relevant cases, the mechanical properties and micro failure mechanism of common polymer waterproofing membrane were analyzed, including internal enhanced TPO, homogeneous EPDM and EPDM pressure-sensitive self-curing flashing. The test results showed that EPDM had better dimensional stability than TPO, and with the increase of curing time, the performance of EPDM pressure-sensitive self-curing flashing material gradually started to show the elastic performance of finished EPDM membrane from its initial plasticity, completely met the requirements of waterproofing membrane. Finally, EPDM membrane with self-curing flashing was selected for the waterproofing of National Speed Skating Oval, and some suggestions on the vulcanization research of the self-curing flashing materials were put forward.
National Speed Skating Oval is the landmark of the 2022 Winter Olympic Games, and the waterproofing of the unitary roofing system for the flexible cable net area is a key issue which needs to be solved. Firstly, based on the relevant cases, the mechanical properties and micro failure mechanism of common polymer waterproofing membrane were analyzed, including internal enhanced TPO, homogeneous EPDM and EPDM pressure-sensitive self-curing flashing. The test results showed that EPDM had better dimensional stability than TPO, and with the increase of curing time, the performance of EPDM pressure-sensitive self-curing flashing material gradually started to show the elastic performance of finished EPDM membrane from its initial plasticity, completely met the requirements of waterproofing membrane. Finally, EPDM membrane with self-curing flashing was selected for the waterproofing of National Speed Skating Oval, and some suggestions on the vulcanization research of the self-curing flashing materials were put forward.
2022, 52(4): 179-185.
doi: 10.13204/j.gyjzG21040204
Abstract:
To predict the lateral pressure of formwork more accurately, an experiment aims to investigate the influence on lateral pressure of formwork caused by the time-varying characteristics of friction coefficient μ and reduction coefficient K was conducted. Based on the method of stratified summation, a model for calculating the lateral pressure of formwork was established, the modified calculation formula was deduced and verified. The results showed that the modified formula that considering the time-varying characteristics of key coefficients could perform well in predicting the lateral pressure of formwork.
To predict the lateral pressure of formwork more accurately, an experiment aims to investigate the influence on lateral pressure of formwork caused by the time-varying characteristics of friction coefficient μ and reduction coefficient K was conducted. Based on the method of stratified summation, a model for calculating the lateral pressure of formwork was established, the modified calculation formula was deduced and verified. The results showed that the modified formula that considering the time-varying characteristics of key coefficients could perform well in predicting the lateral pressure of formwork.
2022, 52(4): 186-191,121.
doi: 10.13204/j.gyjzG21101503
Abstract:
Engineering leakage is a long-term "stubborn disease" of engineering quality, which is the key problem during promoting the high-quality development of engineering construction. For the sake of implementing of people-oriented development concept, improving the project quality, the paper investigated many waterproof projects in China and analyzed the solutions to the problem of leakage management. Various research methods were applied in the paper, such as literature research, field survey, questionaire survey and expert interviews. Based on the investigation of the current situation and main problems of engineering leakage in China, the development trend of treatment of engineering leakage in the future was pointed out: speeding up the research and development of high-performance waterproof materials, providing waterproof materials systematically, improving the techniques and management ability during constructing, speeding up the research and development of portable tools for detecting the position of leakage, and strengthening the training of industrial workers. And some suggestions for the industry of engineering leakage treatment were put forward, such as establishing a new system of waterproof industry, building a management system with clear responsibility, setting up professional waterproof companies, strengthening the culturing of waterproof talents and deepening international exchanges and cooperation.
Engineering leakage is a long-term "stubborn disease" of engineering quality, which is the key problem during promoting the high-quality development of engineering construction. For the sake of implementing of people-oriented development concept, improving the project quality, the paper investigated many waterproof projects in China and analyzed the solutions to the problem of leakage management. Various research methods were applied in the paper, such as literature research, field survey, questionaire survey and expert interviews. Based on the investigation of the current situation and main problems of engineering leakage in China, the development trend of treatment of engineering leakage in the future was pointed out: speeding up the research and development of high-performance waterproof materials, providing waterproof materials systematically, improving the techniques and management ability during constructing, speeding up the research and development of portable tools for detecting the position of leakage, and strengthening the training of industrial workers. And some suggestions for the industry of engineering leakage treatment were put forward, such as establishing a new system of waterproof industry, building a management system with clear responsibility, setting up professional waterproof companies, strengthening the culturing of waterproof talents and deepening international exchanges and cooperation.
2022, 52(4): 192-201,218.
doi: 10.13204/j.gyjzG21053111
Abstract:
In order to improve the automation level of bridge disease detection, solve the current manual detection time-consuming and laborious, traditional image segmentation methods have problems such as non-obvious denoising effect and poor crack continuity after segmentation. A bridge crack automatic segmentation model of BCI-AS(Bridge Crack Image-Automatic Segmentation) based on full convolutional neural network and a crack width measurement algorithm of least square fitting center line based on projection technology were proposed.Based on the BCI-AS model, the image data set of bridge cracks was segmented at the pixel level accurately, and the segmentation accuracy reached 94.45%.The width of the segmented crack binary map was measured by the least square center line fitting algorithm based on the projection technology. The results showed that the relative error was less than 7%, which could prove the feasibility of the proposed algorithm for crack segmentation and crack width calculation.
In order to improve the automation level of bridge disease detection, solve the current manual detection time-consuming and laborious, traditional image segmentation methods have problems such as non-obvious denoising effect and poor crack continuity after segmentation. A bridge crack automatic segmentation model of BCI-AS(Bridge Crack Image-Automatic Segmentation) based on full convolutional neural network and a crack width measurement algorithm of least square fitting center line based on projection technology were proposed.Based on the BCI-AS model, the image data set of bridge cracks was segmented at the pixel level accurately, and the segmentation accuracy reached 94.45%.The width of the segmented crack binary map was measured by the least square center line fitting algorithm based on the projection technology. The results showed that the relative error was less than 7%, which could prove the feasibility of the proposed algorithm for crack segmentation and crack width calculation.
2022, 52(4): 202-208.
doi: 10.13204/j.gyjzG21062919
Abstract:
Three-dimensional (3D) laser scanner with high-accuracy data, little environment-induced effect and easy operation is preferred to reconstruction of building information models. Well-selected locations of 3D laser scanner depend on knowledge, experience and on-site decision of specialized persons, where it is difficult to find a balance between completeness of scanned object and scanning time. Besides, for large and complex space frames, a large number of scanned objects and heavy occlusions will significantly increase the difficulty of scan planning. To address above-mentioned issues, an optimization model for scan planning of large and complex space frames was built, considering the objective function, constraints, and optimization method. Further, a novel optimization process, including data extraction, scanning location optimization, and scanning route optimization, was proposed based on application programming interface of CAD and BIM, 3D laser scanning, weighted greedy algorithm and ant colony algorithm. It was stated that the proposed process was efficient and feasible in solving optimization model for scan planning of large and complex space frames, providing an efficient guide to data collection for generating as-built model of large and complex space frames.
Three-dimensional (3D) laser scanner with high-accuracy data, little environment-induced effect and easy operation is preferred to reconstruction of building information models. Well-selected locations of 3D laser scanner depend on knowledge, experience and on-site decision of specialized persons, where it is difficult to find a balance between completeness of scanned object and scanning time. Besides, for large and complex space frames, a large number of scanned objects and heavy occlusions will significantly increase the difficulty of scan planning. To address above-mentioned issues, an optimization model for scan planning of large and complex space frames was built, considering the objective function, constraints, and optimization method. Further, a novel optimization process, including data extraction, scanning location optimization, and scanning route optimization, was proposed based on application programming interface of CAD and BIM, 3D laser scanning, weighted greedy algorithm and ant colony algorithm. It was stated that the proposed process was efficient and feasible in solving optimization model for scan planning of large and complex space frames, providing an efficient guide to data collection for generating as-built model of large and complex space frames.
2022, 52(4): 209-218.
doi: 10.13204/j.gyjzG21021702
Abstract:
In order to deal with a series of urban problems caused by social, economic, cultural, transportation and other multidimensional factors under the background of rapid urbanization, researchers have turned to the public transport-oriented urban land development (TOD) mode.The typical TOD areas in the United States and Japan were taken as a case study, and its traffic characteristics, spatial from and land use characteristics were compared and analyzed. Firstly, the general characteristics of TOD models in the United States and Japan were analyzed, the basis for the division of urban-centered TOD areas was proposed, and the selection principles and basic information of research cases were expounded. Secondly, taking the B-R corridor area in Arlington County of the United States and the Minatomirai Line area in Yokohama City of Japan as examples, a comparative analysis was conducted from three aspects: traffic characteristics, spatial form and land use. Finally, the characteristics of urban-centered TOD areas in the United States and Japan were summarized, and the causes of differences were compared from the perspectives of transportation system, land use and spatial form, in order to provide a reference for the design and practice of similar TOD areas in China.
In order to deal with a series of urban problems caused by social, economic, cultural, transportation and other multidimensional factors under the background of rapid urbanization, researchers have turned to the public transport-oriented urban land development (TOD) mode.The typical TOD areas in the United States and Japan were taken as a case study, and its traffic characteristics, spatial from and land use characteristics were compared and analyzed. Firstly, the general characteristics of TOD models in the United States and Japan were analyzed, the basis for the division of urban-centered TOD areas was proposed, and the selection principles and basic information of research cases were expounded. Secondly, taking the B-R corridor area in Arlington County of the United States and the Minatomirai Line area in Yokohama City of Japan as examples, a comparative analysis was conducted from three aspects: traffic characteristics, spatial form and land use. Finally, the characteristics of urban-centered TOD areas in the United States and Japan were summarized, and the causes of differences were compared from the perspectives of transportation system, land use and spatial form, in order to provide a reference for the design and practice of similar TOD areas in China.
