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2023 Vol. 53, No. 11
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2023, 53(11): 1-10,20.
doi: 10.13204/j.gyjzG23051908
Abstract:
Wenzhou has deep structural soft soil. To study the deformation of soft soil during metro tunnel construction, a typical section of the soil layer in Wenzhou Rail Transit Line M1 was taken as the research object. Based on the inherent compression characteristics of remolded soil, consolidation compression tests were conducted on intact and remolded specimens, to evaluate structure characteristics respectively from strength and deformation. Simultaneously, a three-dimensional elastic-plastic finite element model for the stratum and the shield tunnel was constructed by the software of PLAXIS 3D, to study the disturbance laws, the distribution of disturbance degrees, the additional settlement of the structural soil layer tunnelled with tunnel boring machines. The results indicated that the soft clay in the Wenzhou area was of strong structure, and the strength and deformation characteristics were influenced by the structure. The yield stress could not be used as an index to evaluate the structure of under-consolidated soil. The construction disturbance could be divided into the preliminary development stage, the rapid development stage and the stable stage, and different stages were influenced by different disturbance factors. The tunnelling with tunnel boring machines would caused larger additional settlement of strata after construction, which mainly concentrated in the soil around shield tunnels. Therefore, it was necessary to reinforce the stratum before construction.
Wenzhou has deep structural soft soil. To study the deformation of soft soil during metro tunnel construction, a typical section of the soil layer in Wenzhou Rail Transit Line M1 was taken as the research object. Based on the inherent compression characteristics of remolded soil, consolidation compression tests were conducted on intact and remolded specimens, to evaluate structure characteristics respectively from strength and deformation. Simultaneously, a three-dimensional elastic-plastic finite element model for the stratum and the shield tunnel was constructed by the software of PLAXIS 3D, to study the disturbance laws, the distribution of disturbance degrees, the additional settlement of the structural soil layer tunnelled with tunnel boring machines. The results indicated that the soft clay in the Wenzhou area was of strong structure, and the strength and deformation characteristics were influenced by the structure. The yield stress could not be used as an index to evaluate the structure of under-consolidated soil. The construction disturbance could be divided into the preliminary development stage, the rapid development stage and the stable stage, and different stages were influenced by different disturbance factors. The tunnelling with tunnel boring machines would caused larger additional settlement of strata after construction, which mainly concentrated in the soil around shield tunnels. Therefore, it was necessary to reinforce the stratum before construction.
2023, 53(11): 11-20.
doi: 10.13204/j.gyjzG22090204
Abstract:
Against the background of a expressway tunnel project in Guangxi, a 3D numerical model was constructed by the finite element analysis software ABAQUS to simulate and study the influence of insufficient lining thickness on the safety of lining structures and crack propagation laws. The results indicated that the insufficient thickness of tunnel linings would significantly affect the safety of lining structures, and the safety factors at thickness reduction positions decreased with the decrease of the thickness. The insufficient thickness at the vault had a greatest impact on the safety of lining structures, the dispersive distribution of the lining thinning had a greater impact on the safety of the vault and arch shoulders, and the concentrated distribution of the lining thinning had a greater impact on the safety of side walls. Crack first appeared in the inside of linings corresponding to the lining thinning area. With the decrease of lining thickness, the number of cracks increased, the cracking speed increased, and destruction advanced simultaneously. The cracking area generated by the concentrated distribution of lining thinning was larger than that by the dispersed distribution.
Against the background of a expressway tunnel project in Guangxi, a 3D numerical model was constructed by the finite element analysis software ABAQUS to simulate and study the influence of insufficient lining thickness on the safety of lining structures and crack propagation laws. The results indicated that the insufficient thickness of tunnel linings would significantly affect the safety of lining structures, and the safety factors at thickness reduction positions decreased with the decrease of the thickness. The insufficient thickness at the vault had a greatest impact on the safety of lining structures, the dispersive distribution of the lining thinning had a greater impact on the safety of the vault and arch shoulders, and the concentrated distribution of the lining thinning had a greater impact on the safety of side walls. Crack first appeared in the inside of linings corresponding to the lining thinning area. With the decrease of lining thickness, the number of cracks increased, the cracking speed increased, and destruction advanced simultaneously. The cracking area generated by the concentrated distribution of lining thinning was larger than that by the dispersed distribution.
2023, 53(11): 21-28.
doi: 10.13204/j.gyjzG22091803
Abstract:
To explore the mutual disturbance effect due to tunnelling of deeply buried the left and right tunnels with small clearance in soft rock, based on tunnel 1 of Dongmachang in Huali High-Speed Project, through field measured data analysis and numerical simulations, the deformation laws of tunnels with small clearance by dififerenent tunnelling methods for the and left and right tunnels in different clearances between working faces in deeply soft rock were studied. The results indicated that there was mutual disturbance between the left and right tunnels during tunnelling and the horizontal convergent deformation of the tunnel first was obviously larger than that of the tunnel later. The tunnelling method had a great influence on the deformation of tunnels, and the deformation by the three-step tunnelling for both double tunnels was 13% less than that by the two-step tunnelling. The deformation by the three-step tunnelling for the tunnel first and the two-step tunnelling for the tunnel later decreased by 12% than that by the three-step tunnelling for both tunnels, which was similar to that by the three-step tunnelling for both tunnels. The clearance between the left and right tunnels had a little influence on the settlement of the vault, but had a great influence on the horizontal convergence deformation of tunnels. With the increase of the clearance between working faces of the left and right tunnels, the time for deformation stability prolonged, the horizontal displacement gradually decreased, and the deformation decreased slowly when the clearance was up to 50 m. Comprehensively considering the construction period, construction cost and tunnel deformation control effect, the scheme for the tunnel first by the three-step tunnelling and the tunnel later by two-step tunnelling was suggested to tunnels with small clearance in deeply soft rock.If the clearance between working faces could be controlled beyond 50 m,the mutual disturbance between the both tunnels would be reduced.
To explore the mutual disturbance effect due to tunnelling of deeply buried the left and right tunnels with small clearance in soft rock, based on tunnel 1 of Dongmachang in Huali High-Speed Project, through field measured data analysis and numerical simulations, the deformation laws of tunnels with small clearance by dififerenent tunnelling methods for the and left and right tunnels in different clearances between working faces in deeply soft rock were studied. The results indicated that there was mutual disturbance between the left and right tunnels during tunnelling and the horizontal convergent deformation of the tunnel first was obviously larger than that of the tunnel later. The tunnelling method had a great influence on the deformation of tunnels, and the deformation by the three-step tunnelling for both double tunnels was 13% less than that by the two-step tunnelling. The deformation by the three-step tunnelling for the tunnel first and the two-step tunnelling for the tunnel later decreased by 12% than that by the three-step tunnelling for both tunnels, which was similar to that by the three-step tunnelling for both tunnels. The clearance between the left and right tunnels had a little influence on the settlement of the vault, but had a great influence on the horizontal convergence deformation of tunnels. With the increase of the clearance between working faces of the left and right tunnels, the time for deformation stability prolonged, the horizontal displacement gradually decreased, and the deformation decreased slowly when the clearance was up to 50 m. Comprehensively considering the construction period, construction cost and tunnel deformation control effect, the scheme for the tunnel first by the three-step tunnelling and the tunnel later by two-step tunnelling was suggested to tunnels with small clearance in deeply soft rock.If the clearance between working faces could be controlled beyond 50 m,the mutual disturbance between the both tunnels would be reduced.
2023, 53(11): 29-35,87.
doi: 10.13204/j.gyjzG22071706
Abstract:
Both bedding structure of rock and tunnel clearance are sensitive factors to the response of surrounding rock during tunnelling of adjacent tunnels, which easily cause deformation instability of surrounding rock and ground subsidence. Taking dip angles as the research variable, the construction response laws of the rock around tunnels were studied by the finite element software FLAC3D against the background for separate subway tunnels under construction in inclined stratification rocks, which was verified by comparison with the construction monitoring data. The results indicated that the conspicuousness of asymmetric deformation for rock around the tunnel increased first and decreased then with the increase of dip angles, while the vertical settlement trough of the ground gradually changed from the unimodal V-type to the bimodal W-type and tended to be obvious, and the width coefficient of the settlement trough decreased first and increase then. The characteristics of stress release of surrounding rock in the range of 0.75 times the diameter of tunnels was obvious and reached the peak value when the dip angle was 30°, but decreased nonlinearly with the increase of the radial depth. The discontinuous distribution characteristics of the stress field in surrounding rock on both sides of the stratification tended to be conspicuouse with the decrease of dip angle. In addition, the rock mass on both sides of the stratification was prone to conjugate shear failure at the intersection of the structural plane and the side wall outlines of tunnels, where might be reinforced locally during construction.
Both bedding structure of rock and tunnel clearance are sensitive factors to the response of surrounding rock during tunnelling of adjacent tunnels, which easily cause deformation instability of surrounding rock and ground subsidence. Taking dip angles as the research variable, the construction response laws of the rock around tunnels were studied by the finite element software FLAC3D against the background for separate subway tunnels under construction in inclined stratification rocks, which was verified by comparison with the construction monitoring data. The results indicated that the conspicuousness of asymmetric deformation for rock around the tunnel increased first and decreased then with the increase of dip angles, while the vertical settlement trough of the ground gradually changed from the unimodal V-type to the bimodal W-type and tended to be obvious, and the width coefficient of the settlement trough decreased first and increase then. The characteristics of stress release of surrounding rock in the range of 0.75 times the diameter of tunnels was obvious and reached the peak value when the dip angle was 30°, but decreased nonlinearly with the increase of the radial depth. The discontinuous distribution characteristics of the stress field in surrounding rock on both sides of the stratification tended to be conspicuouse with the decrease of dip angle. In addition, the rock mass on both sides of the stratification was prone to conjugate shear failure at the intersection of the structural plane and the side wall outlines of tunnels, where might be reinforced locally during construction.
2023, 53(11): 36-41,96.
doi: 10.13204/j.gyjzG22081603
Abstract:
The force and deformation forms of the supporting structure of tunnels are usually complicated in complex conditions. Especially in the landslide area, the supporting structure is in a eccentrically compressive state. Based on the entrance section of Sunshine Tunnel in Panzhihua, the force and deformation characteristics of the supporting structure of tunnels in the condition of existing anti-slide piles cut off by shallowly burized tunnels were studied. A three-dimensional model was constructed by the numerical simulation software MIDAS GTS NX to analyze the internal forces and stress in the supporting structure and predict the weakness of the supporting structure in the tunnelling process. According to the simulation results, the shed-pipe support produced overall displacement, and the maximum deformation was 35.35 mm. The initial support produced extrusion deformation, and the maximum deformation was 34.36 mm. The internal force in the left arch waist of the supporting structure was larger due to stress concentration, while the removal of temporary supports had a greater impact on the stress at the vault and invert. The monitored data showed that the pressure in surrounding rock was uneven, and the contact pressure at the vault was largest. The pressure on the right side of the supporting structure was greater than that on the left side, and the maximum pressure was 268.60 kPa.
The force and deformation forms of the supporting structure of tunnels are usually complicated in complex conditions. Especially in the landslide area, the supporting structure is in a eccentrically compressive state. Based on the entrance section of Sunshine Tunnel in Panzhihua, the force and deformation characteristics of the supporting structure of tunnels in the condition of existing anti-slide piles cut off by shallowly burized tunnels were studied. A three-dimensional model was constructed by the numerical simulation software MIDAS GTS NX to analyze the internal forces and stress in the supporting structure and predict the weakness of the supporting structure in the tunnelling process. According to the simulation results, the shed-pipe support produced overall displacement, and the maximum deformation was 35.35 mm. The initial support produced extrusion deformation, and the maximum deformation was 34.36 mm. The internal force in the left arch waist of the supporting structure was larger due to stress concentration, while the removal of temporary supports had a greater impact on the stress at the vault and invert. The monitored data showed that the pressure in surrounding rock was uneven, and the contact pressure at the vault was largest. The pressure on the right side of the supporting structure was greater than that on the left side, and the maximum pressure was 268.60 kPa.
2023, 53(11): 42-49.
doi: 10.13204/j.gyjzG22090118
Abstract:
The integrated prefabrication for internal structures of shield tunnels is of great significance to improve construction efficiency and guarantee construction quality. However, due to the difference in connection strength and quality of assembled components, the vibration response caused by the passage of trains on shield tunnel foundations on cavities will have negative effect on the force and deformation of the assembled internal structure. Against the background of Jintang Submarine Tunnel of Yongzhou Railway, two connection methods (fixed at both ends, fixed at one end and horizontally hinged at the other end) of integrated assembled internal structures with shield segments and partially assembled internal structures with unclosedly secondary linings were proposed, the influence of cavities in foundation under different internal structures on the cumulatively basal settlement and internal forces under vibration in operation of trains was studied. The research indicated that: 1) Cavities under foundations would increase the cumuletively basal settlement, but the cumulatively basal settlement of the integrated assembled internal structure fixed with shield segments at both ends was minimum, it showed that the strengthening of the connection between the internal structure and the segments could reduce cumulative deformation under reciprocating loads by trains; 2) Cavities under founndations would increase internal forces in shield segments and internal structures, and produce stress concentration in the lining in the corresponding area. Cavities would hinder transfer of vibration energy to segments, resulting in the sharp increase of shear amplitude in connecting bolts in the integrated assembled internal structure and the accumulation of vibration energy at the arch bottom, which would intensify the cumulative response of vibration.
The integrated prefabrication for internal structures of shield tunnels is of great significance to improve construction efficiency and guarantee construction quality. However, due to the difference in connection strength and quality of assembled components, the vibration response caused by the passage of trains on shield tunnel foundations on cavities will have negative effect on the force and deformation of the assembled internal structure. Against the background of Jintang Submarine Tunnel of Yongzhou Railway, two connection methods (fixed at both ends, fixed at one end and horizontally hinged at the other end) of integrated assembled internal structures with shield segments and partially assembled internal structures with unclosedly secondary linings were proposed, the influence of cavities in foundation under different internal structures on the cumulatively basal settlement and internal forces under vibration in operation of trains was studied. The research indicated that: 1) Cavities under foundations would increase the cumuletively basal settlement, but the cumulatively basal settlement of the integrated assembled internal structure fixed with shield segments at both ends was minimum, it showed that the strengthening of the connection between the internal structure and the segments could reduce cumulative deformation under reciprocating loads by trains; 2) Cavities under founndations would increase internal forces in shield segments and internal structures, and produce stress concentration in the lining in the corresponding area. Cavities would hinder transfer of vibration energy to segments, resulting in the sharp increase of shear amplitude in connecting bolts in the integrated assembled internal structure and the accumulation of vibration energy at the arch bottom, which would intensify the cumulative response of vibration.
2023, 53(11): 50-54,49.
doi: 10.13204/j.gyjzG22070507
Abstract:
Taking a shield tunnel section in Shanghai Rail Transit as the research object, considering different influencing factors including frozen and unfrozen construction and different frozen days, the thermal-mechanical coupling model of tunneling for shield tunnels was constructed and the simulation results were compared with the in-situ monitoring data. The results indicated that the overall trend of the calculated subsidence was consistent with the measured data; the ground subsidence at the entrance of tunnels was reduced by 82.3% in the horizontal frozen condition compared with not being horizontally frozen condition; simultaneously, the different horizontal-frozen days had little effect on the ground subsidence.
Taking a shield tunnel section in Shanghai Rail Transit as the research object, considering different influencing factors including frozen and unfrozen construction and different frozen days, the thermal-mechanical coupling model of tunneling for shield tunnels was constructed and the simulation results were compared with the in-situ monitoring data. The results indicated that the overall trend of the calculated subsidence was consistent with the measured data; the ground subsidence at the entrance of tunnels was reduced by 82.3% in the horizontal frozen condition compared with not being horizontally frozen condition; simultaneously, the different horizontal-frozen days had little effect on the ground subsidence.
2023, 53(11): 55-64.
doi: 10.13204/j.gyjzG22103112
Abstract:
To analyze, manage and control safety risks of construction with tunnel boring machines passing under existing tunnels, a risk analysis method based on the Gaussian Copula Bayesian Network (GCBN) model was proposed. Based on the fault tree, a set of the construction safety risk index system including 12 factors was established, and the dynamic inferential diagnosis of Bayesian Network was combined with the dependence expression of Copula Theory. The GCBN model for risk analysis of construction with tunnel boring machines passing under existing tunnels was constructed in the condition of uncertain and incomplete information. Taking the project of Wuhan Rail Transit Line 12 passing under the existing Line 7 as an example, the Gaussian Copula was used to identify marginal distribution types of each factor, calculate correlation coefficients between each factor, and connect nodes in the network. Through the model reasoning, qualitative analysis and quantitative analysis were conducted, the safety state under construction with tunnel boring machines passing under existing tunnels could be identified, the impact the risk factors on results of risks was analyzed. Eventually, preventive and control measures for high sensitivity factors were implemented. By comparison with the calculating results of models before and after being prevented and controlled, the real-time dynamic security warning and control for construction with tummel boring machines passing under existing tunnels were achieved. The application results indicated that the prediction results by the GCBN model were consistent with the evaluation results by experts, which verified the reliability of the established risk analysis model of GCBN.
To analyze, manage and control safety risks of construction with tunnel boring machines passing under existing tunnels, a risk analysis method based on the Gaussian Copula Bayesian Network (GCBN) model was proposed. Based on the fault tree, a set of the construction safety risk index system including 12 factors was established, and the dynamic inferential diagnosis of Bayesian Network was combined with the dependence expression of Copula Theory. The GCBN model for risk analysis of construction with tunnel boring machines passing under existing tunnels was constructed in the condition of uncertain and incomplete information. Taking the project of Wuhan Rail Transit Line 12 passing under the existing Line 7 as an example, the Gaussian Copula was used to identify marginal distribution types of each factor, calculate correlation coefficients between each factor, and connect nodes in the network. Through the model reasoning, qualitative analysis and quantitative analysis were conducted, the safety state under construction with tunnel boring machines passing under existing tunnels could be identified, the impact the risk factors on results of risks was analyzed. Eventually, preventive and control measures for high sensitivity factors were implemented. By comparison with the calculating results of models before and after being prevented and controlled, the real-time dynamic security warning and control for construction with tummel boring machines passing under existing tunnels were achieved. The application results indicated that the prediction results by the GCBN model were consistent with the evaluation results by experts, which verified the reliability of the established risk analysis model of GCBN.
2023, 53(11): 65-72.
doi: 10.13204/j.gyjzG22011206
Abstract:
During tunnelling with tunnel boring machines in karst, the complex geological environment has a larger impact on the stability of working faces of tunnels, which would caused risks such as destabilization of working faces. To accurately evaluate the stability of working faces and reduce construction risks, a safety evaluation method based on the cloud model and the D-S evidence theory was proposed to consider the complexity of effect factors, which could solve the problem of fuzzy uncertainty and high conflict of evaluation information. Based on a large number of engineering practices and literature research, a set of stability evaluation systems and criteria for working faces was established from 3 aspects: karst, construction and the influence of surrounding rock. The cloud model was used to obtain the correlation degree of evaluation indexes for risk levels and then transformed into basic probability assignment, and the D-S evidence theory was used to fuse and update the multi-source evidence information to realize the real-time evaluation for safety risk of working faces and determine the sensitivity factors based on the global sensitivity. The results of the practical application indicated that the stability grade for working faces of the evaluated section was Ⅱ and could keep relative stability, that was consistent with the actual construction situation.
During tunnelling with tunnel boring machines in karst, the complex geological environment has a larger impact on the stability of working faces of tunnels, which would caused risks such as destabilization of working faces. To accurately evaluate the stability of working faces and reduce construction risks, a safety evaluation method based on the cloud model and the D-S evidence theory was proposed to consider the complexity of effect factors, which could solve the problem of fuzzy uncertainty and high conflict of evaluation information. Based on a large number of engineering practices and literature research, a set of stability evaluation systems and criteria for working faces was established from 3 aspects: karst, construction and the influence of surrounding rock. The cloud model was used to obtain the correlation degree of evaluation indexes for risk levels and then transformed into basic probability assignment, and the D-S evidence theory was used to fuse and update the multi-source evidence information to realize the real-time evaluation for safety risk of working faces and determine the sensitivity factors based on the global sensitivity. The results of the practical application indicated that the stability grade for working faces of the evaluated section was Ⅱ and could keep relative stability, that was consistent with the actual construction situation.
2023, 53(11): 73-79.
doi: 10.13204/j.gyjzG22072104
Abstract:
The municipal cable duct banks characterized by a small cross-section, shallow burial depth and intricately laid conditions,which is mainly prefabricated in factory and connected by prestressed assembly on site. The stiffness of municipal cable duct banks have a great impact on their operation. To study the effect of prestress on connecting performances of municipal cable duct banks, taking a 10-pipe municipal cable duct bank with a cross section of 1 090 mm×650 mm as an example, the flexural and shear performances of prefabricated prestressed municipal cable duct banks were studied under different tensioning methods and prestresses with prestressed steel strands by the finite element method and experiments. The results of finite element analysis indicated that the lengths of prestressed steel strands had significant effect on the flexural stiffness of connections, the shorter the steel strands were, the greater the flexural stiffness of connections and the lower the ductility were; increasing the prestress and the friction coefficients of connection sections could improve the shear stiffness of connections significantly. Finally, the correctness of the finite element analysis results was verified by comparing test results of 3 full scale municipal cable duct banks.
The municipal cable duct banks characterized by a small cross-section, shallow burial depth and intricately laid conditions,which is mainly prefabricated in factory and connected by prestressed assembly on site. The stiffness of municipal cable duct banks have a great impact on their operation. To study the effect of prestress on connecting performances of municipal cable duct banks, taking a 10-pipe municipal cable duct bank with a cross section of 1 090 mm×650 mm as an example, the flexural and shear performances of prefabricated prestressed municipal cable duct banks were studied under different tensioning methods and prestresses with prestressed steel strands by the finite element method and experiments. The results of finite element analysis indicated that the lengths of prestressed steel strands had significant effect on the flexural stiffness of connections, the shorter the steel strands were, the greater the flexural stiffness of connections and the lower the ductility were; increasing the prestress and the friction coefficients of connection sections could improve the shear stiffness of connections significantly. Finally, the correctness of the finite element analysis results was verified by comparing test results of 3 full scale municipal cable duct banks.
2023, 53(11): 80-87.
doi: 10.13204/j.gyjzG23051516
Abstract:
Under the national policy of dual carbon emissions reduction, the development of resource-exhausted cities faces complex and ever-changing problems as well as heavy transformation pressure, especially the problem of recycling abandoned mines. Based on the "symbiosis theory", the paper analyzed the industrial relics and cultural industries of resource exhausted cities, analyzed the existing problems of the Fuxin Haizhou open-pit mine from three aspects: organization of symbiotic units, construction of symbiotic environment, and construction of symbiotic interface, and proposed corresponding design strategies and practical methods to achieve the healthy development of resource exhausted cities, So as to provide a certain reference for the renewal and development of relevant cities.
Under the national policy of dual carbon emissions reduction, the development of resource-exhausted cities faces complex and ever-changing problems as well as heavy transformation pressure, especially the problem of recycling abandoned mines. Based on the "symbiosis theory", the paper analyzed the industrial relics and cultural industries of resource exhausted cities, analyzed the existing problems of the Fuxin Haizhou open-pit mine from three aspects: organization of symbiotic units, construction of symbiotic environment, and construction of symbiotic interface, and proposed corresponding design strategies and practical methods to achieve the healthy development of resource exhausted cities, So as to provide a certain reference for the renewal and development of relevant cities.
2023, 53(11): 88-96.
doi: 10.13204/j.gyjzG22060205
Abstract:
Based on the application and development of vertical climbing green facde in high-density cities, the vertical climbing green facades on thermal and wind environment in hot-humid climate areas. Firstly, field measurements were conducted to record the thermal indices around a case of climbing green facade in typical extreme hot summer days in hot-humid climate areas. Secondly, a validation was conducted with a CFD simulation method with the software. Then, the combination condition of typical overhead transition space and climbing green facade was simulated and tested for human thermal comfort evaluation coupled with CFD and Ladybug+Honeybee tools. The results showed that: 1)field measurements results revealed that the temperature, globe temperature (Tg), and wind velocity (Va) of the shaded area was reduced by 0.06-0.53 ℃, 0.37-1.73 ℃, and 0-0.18 m/s compared to the unshaded area, relpectively. The mean radiant temperature(MRT) and physiological equivalent temperature(PET) were reduced by 0.58-2.74 ℃ and 0.27-1.43 ℃, respectively; 2)CFD simulation results revealed different greening models reduced the average temperature by 0.1-0.3 ℃ except the model FG-1; 3) the wind velocity of model FG-2 and FG-3 reduced by about 1.3 m/s, the wind velocity of DG model series reduced by about 0.8 m/s; 4) the PET of FG-2, FG-3, DG series and WG series models reduced by about 0.8-1.1 ℃. Furthermore, FG-2, FG-3 and DG series model presented better optimizations on the whole open floor space and could be the better choice for the greenery layout.
Based on the application and development of vertical climbing green facde in high-density cities, the vertical climbing green facades on thermal and wind environment in hot-humid climate areas. Firstly, field measurements were conducted to record the thermal indices around a case of climbing green facade in typical extreme hot summer days in hot-humid climate areas. Secondly, a validation was conducted with a CFD simulation method with the software. Then, the combination condition of typical overhead transition space and climbing green facade was simulated and tested for human thermal comfort evaluation coupled with CFD and Ladybug+Honeybee tools. The results showed that: 1)field measurements results revealed that the temperature, globe temperature (Tg), and wind velocity (Va) of the shaded area was reduced by 0.06-0.53 ℃, 0.37-1.73 ℃, and 0-0.18 m/s compared to the unshaded area, relpectively. The mean radiant temperature(MRT) and physiological equivalent temperature(PET) were reduced by 0.58-2.74 ℃ and 0.27-1.43 ℃, respectively; 2)CFD simulation results revealed different greening models reduced the average temperature by 0.1-0.3 ℃ except the model FG-1; 3) the wind velocity of model FG-2 and FG-3 reduced by about 1.3 m/s, the wind velocity of DG model series reduced by about 0.8 m/s; 4) the PET of FG-2, FG-3, DG series and WG series models reduced by about 0.8-1.1 ℃. Furthermore, FG-2, FG-3 and DG series model presented better optimizations on the whole open floor space and could be the better choice for the greenery layout.
2023, 53(11): 97-101,167.
doi: 10.13204/j.gyjzG21082301
Abstract:
Tree-shaped supporting structure in long-span buildings has been widely recognized and applied due to its unique force transmission mechanism and aesthetic characteristics, and many excellent building examples have also been produced. By summarizing the essential features of tree-shaped structures, combining with the graphic statics, structural morphology and fractional theory, the paper analyzed and summarized the tree-shaped structure from form and morphology, which could provide more design ideas for the creation of tree-shaped structure.
Tree-shaped supporting structure in long-span buildings has been widely recognized and applied due to its unique force transmission mechanism and aesthetic characteristics, and many excellent building examples have also been produced. By summarizing the essential features of tree-shaped structures, combining with the graphic statics, structural morphology and fractional theory, the paper analyzed and summarized the tree-shaped structure from form and morphology, which could provide more design ideas for the creation of tree-shaped structure.
2023, 53(11): 102-109,144.
doi: 10.13204/j.gyjzG22063008
Abstract:
Urban street green space is an important part of urban public space and one of the most direct places for people to perceive the city. From the perspective of supply and demand balance of urban street green space, taking Hongjialou block of Jinan City as an example, the supply and demand level of urban street green space was measured by street green visibility level and demand index. With the help of open platform data such as Baidu map and Gaode map, the supply and demand balance of urban street green space was evaluated by using ArcGIS network analysis technology and segnet semantic segmentation technology. The results showed that in terms of green space supply, the overall green space supply level of Hongjialou block in Jinan was not high, and only 24% of the sites with good green space supply were selected. The green space supply level of Huayuan road was higher than that of Hongjialou South Road and North Road. In terms of green space demand, the west section of Huayuan road had the highest street demand, showing a trend of gradually decreasing from west to east, and there were several spots with high street demand in the middle section, while Hongjialou South and North roads had higher street demand in the south and north sections, and lower in the middle. The street demand of Huayuan road was higher than that of Hongjialou South Road and North Road. In terms of supply-demand balance, Huayuan road had a high matching degree of supply and demand for green space, while Hongjialou South Road and North Road had a poor matching degree of supply and demand for green space, with 44.12% in the quadrant of "low supply and high demand". Finally, from the two aspects of supply and demand, the paper put forward targeted optimization strategies. The research could provide research ideas and methods for urban renewal.
Urban street green space is an important part of urban public space and one of the most direct places for people to perceive the city. From the perspective of supply and demand balance of urban street green space, taking Hongjialou block of Jinan City as an example, the supply and demand level of urban street green space was measured by street green visibility level and demand index. With the help of open platform data such as Baidu map and Gaode map, the supply and demand balance of urban street green space was evaluated by using ArcGIS network analysis technology and segnet semantic segmentation technology. The results showed that in terms of green space supply, the overall green space supply level of Hongjialou block in Jinan was not high, and only 24% of the sites with good green space supply were selected. The green space supply level of Huayuan road was higher than that of Hongjialou South Road and North Road. In terms of green space demand, the west section of Huayuan road had the highest street demand, showing a trend of gradually decreasing from west to east, and there were several spots with high street demand in the middle section, while Hongjialou South and North roads had higher street demand in the south and north sections, and lower in the middle. The street demand of Huayuan road was higher than that of Hongjialou South Road and North Road. In terms of supply-demand balance, Huayuan road had a high matching degree of supply and demand for green space, while Hongjialou South Road and North Road had a poor matching degree of supply and demand for green space, with 44.12% in the quadrant of "low supply and high demand". Finally, from the two aspects of supply and demand, the paper put forward targeted optimization strategies. The research could provide research ideas and methods for urban renewal.
2023, 53(11): 110-116.
doi: 10.13204/j.gyjzG22051211
Abstract:
Three new fabricated high-strength reinforced concrete beam-column joints with steel ends were subjected to quasi-static loading tests to investigate their mechanical properties. The failure characteristics moment-rotation hysteresis curves, sheared-rotation skeleton curves in core area, strength degradation, and strain laws of the joints were analyzed. The test results showed that the proposed new prefabricated high-strength reinforced concrete beam-column joints occurred the expected shear damage in the core area. The connection between the embedded steel connectors and reinforced concrete beams was reliable. The prefabricated high-strength reinforced concrete beam-column joints with steel ends could effectively transfer internal forces, showing high rotation capacity and gentle strength degradation. Thus the joints showed a good mechanical properties. The spacer and the web set in the steel end could be stressed with the stirrups and concrete. The joint with webs between horizontal connecting plates and post-cast concrete in the assembly area exhibited the best mechanical properties among the three specimens.
Three new fabricated high-strength reinforced concrete beam-column joints with steel ends were subjected to quasi-static loading tests to investigate their mechanical properties. The failure characteristics moment-rotation hysteresis curves, sheared-rotation skeleton curves in core area, strength degradation, and strain laws of the joints were analyzed. The test results showed that the proposed new prefabricated high-strength reinforced concrete beam-column joints occurred the expected shear damage in the core area. The connection between the embedded steel connectors and reinforced concrete beams was reliable. The prefabricated high-strength reinforced concrete beam-column joints with steel ends could effectively transfer internal forces, showing high rotation capacity and gentle strength degradation. Thus the joints showed a good mechanical properties. The spacer and the web set in the steel end could be stressed with the stirrups and concrete. The joint with webs between horizontal connecting plates and post-cast concrete in the assembly area exhibited the best mechanical properties among the three specimens.
2023, 53(11): 117-124,174.
doi: 10.13204/j.gyjzG23012801
Abstract:
In order to study the influence of the connection forms and positions of truss rebars and steel meshes on the performance of double-faced superposed shear walls under large eccentric compression loading, three double-faced superposed shear wall specimens were tested. The failure mode, deformability, bearing capacity and stiffness of each specimen under large eccentric loading were compared and analyzed. The test results showed that all specimens exhibited typical ductile failure characteristics under large eccentric compression. Under large eccentric compression, the failure modes, bearing capacity and stiffnesses of specimens with the lower stringed tendons and the steel mesh fully tied but the upper stringed tendons and the steel mesh tied only at two ends (DPCW-1) or the upper and lower stringed tendons and steel mesh fully tied (DPCW-2) were the same. The ultimate bearing capacity and stiffness of the specimen with truss rebars and steel meshes welded (DPCW-3) were higher than those of the specimen DPCW-2.The upper and lower stringed tendons of all the truss rebars yielded, and the strain variations of the upper and lower stringed tendons was were roughly similar to that of the vertical rebars, which indicated that the upper and lower strings of the truss rebars participated in the force when the double-faced superposed shear wall bore large eccentric compression loading. On the basis of the experimental study, the finite element software ABAQUS was used to model and analyze the specimens, and the calculated results were in good agreement with the experimental results. The results of parameter analysis showed that the ultimate bearing capacity of all specimens decreased and the ultimate deflection increased with the increase of eccentric distance. The bond coefficient of concrete superimposed surface had little effect on the ultimate bearing capacity and stiffness of superimposed shear walls under large eccentric compression.
In order to study the influence of the connection forms and positions of truss rebars and steel meshes on the performance of double-faced superposed shear walls under large eccentric compression loading, three double-faced superposed shear wall specimens were tested. The failure mode, deformability, bearing capacity and stiffness of each specimen under large eccentric loading were compared and analyzed. The test results showed that all specimens exhibited typical ductile failure characteristics under large eccentric compression. Under large eccentric compression, the failure modes, bearing capacity and stiffnesses of specimens with the lower stringed tendons and the steel mesh fully tied but the upper stringed tendons and the steel mesh tied only at two ends (DPCW-1) or the upper and lower stringed tendons and steel mesh fully tied (DPCW-2) were the same. The ultimate bearing capacity and stiffness of the specimen with truss rebars and steel meshes welded (DPCW-3) were higher than those of the specimen DPCW-2.The upper and lower stringed tendons of all the truss rebars yielded, and the strain variations of the upper and lower stringed tendons was were roughly similar to that of the vertical rebars, which indicated that the upper and lower strings of the truss rebars participated in the force when the double-faced superposed shear wall bore large eccentric compression loading. On the basis of the experimental study, the finite element software ABAQUS was used to model and analyze the specimens, and the calculated results were in good agreement with the experimental results. The results of parameter analysis showed that the ultimate bearing capacity of all specimens decreased and the ultimate deflection increased with the increase of eccentric distance. The bond coefficient of concrete superimposed surface had little effect on the ultimate bearing capacity and stiffness of superimposed shear walls under large eccentric compression.
2023, 53(11): 125-130,116.
doi: 10.13204/j.gyjzG22120802
Abstract:
To discuss the engineering application of steel reinforced concrete in the transfer beam of subway station, based on the shear performance tests on the specimens of twin I-steel reinforced concrete transfer beams, the finite element model of the transfer beams were established by using ABAQUS software in the study, and the shear performance of transfer beams were analyzed nonlinearly. The stress nephogram and load-displacement curves of transfer beams ware obtained. The calculation results of transfer beams were compared with the test results, so as to verify the rationality on the finite element model of transfer beams, and the influence of design parameters on the shear performance of transfer beams was also analyzed. The research showed that the transfer beams went though three stages of the initial crack, crack development and failure, and finally presented typical shear failure characteristics. Compared with the traditional reinforced concrete transfer beams, the twinle I-steel reinforced concrete transfer beams had higher bearing capacity and good ductility. With the increase of shear-span ratio, the bearing capacity of transfer beams decreased, but the ductility increased slightly. The bearing capacity and deformation capacity of transfer beams could be significantly improved by increasing the steel ratio of profile steel. In addition, improving the material strength of steel and concrete was beneficial to the shear bearing capacity of transfer beams.
To discuss the engineering application of steel reinforced concrete in the transfer beam of subway station, based on the shear performance tests on the specimens of twin I-steel reinforced concrete transfer beams, the finite element model of the transfer beams were established by using ABAQUS software in the study, and the shear performance of transfer beams were analyzed nonlinearly. The stress nephogram and load-displacement curves of transfer beams ware obtained. The calculation results of transfer beams were compared with the test results, so as to verify the rationality on the finite element model of transfer beams, and the influence of design parameters on the shear performance of transfer beams was also analyzed. The research showed that the transfer beams went though three stages of the initial crack, crack development and failure, and finally presented typical shear failure characteristics. Compared with the traditional reinforced concrete transfer beams, the twinle I-steel reinforced concrete transfer beams had higher bearing capacity and good ductility. With the increase of shear-span ratio, the bearing capacity of transfer beams decreased, but the ductility increased slightly. The bearing capacity and deformation capacity of transfer beams could be significantly improved by increasing the steel ratio of profile steel. In addition, improving the material strength of steel and concrete was beneficial to the shear bearing capacity of transfer beams.
2023, 53(11): 131-138.
doi: 10.13204/j.gyjzG22071309
Abstract:
To study the influence of reinforcement ratio and prestressing tendon on the bending fatigue performance and residual bearing capacity of UHPC-T beams, six UHPC-T beams and two concrete T beams were designed and constructed. Four of the beams were subjected to three-point bending fatigue tests, while the other four beams were subjected to three-point bending static load tests, in order to study the influence of the reinforcement ratio and prestressing tendon on the deflection (residual deflection), strain (residual strain), and residual bearing capacity. The results showed that increasing the reinforcement ratio and adding prestressing force had little effect on the concrete strain of the T beams based on a series of fatigue tests. Increasing the reinforcement ratio could reduce the rebar strain, whereas adding the prestressing tendon did not influence the rebar strain. The residual bearing capacity of the UHPC-T beams with 0.372% and 1.14%, and the prestressed UHPC-T beam decrease by 14.0%, 6.7%, and 16.7% compared to the corresponding static ultimate bearing capacity, respectively. It was indicated that the fatigue load decreased the bearing capacity of UHPC-T beams. The residual bearing capacity of UHPC-T beams gradually increased with the increasing of reinforcement ratio or the material performance, and the corresponding deflection and residual deflection decreased. The prestressing force application significantly improved the residual bearing capacity and mitigated the maximum crack width of UHPC-T beams under fatigue loads.
To study the influence of reinforcement ratio and prestressing tendon on the bending fatigue performance and residual bearing capacity of UHPC-T beams, six UHPC-T beams and two concrete T beams were designed and constructed. Four of the beams were subjected to three-point bending fatigue tests, while the other four beams were subjected to three-point bending static load tests, in order to study the influence of the reinforcement ratio and prestressing tendon on the deflection (residual deflection), strain (residual strain), and residual bearing capacity. The results showed that increasing the reinforcement ratio and adding prestressing force had little effect on the concrete strain of the T beams based on a series of fatigue tests. Increasing the reinforcement ratio could reduce the rebar strain, whereas adding the prestressing tendon did not influence the rebar strain. The residual bearing capacity of the UHPC-T beams with 0.372% and 1.14%, and the prestressed UHPC-T beam decrease by 14.0%, 6.7%, and 16.7% compared to the corresponding static ultimate bearing capacity, respectively. It was indicated that the fatigue load decreased the bearing capacity of UHPC-T beams. The residual bearing capacity of UHPC-T beams gradually increased with the increasing of reinforcement ratio or the material performance, and the corresponding deflection and residual deflection decreased. The prestressing force application significantly improved the residual bearing capacity and mitigated the maximum crack width of UHPC-T beams under fatigue loads.
2023, 53(11): 139-144.
doi: 10.13204/j.gyjzG21112303
Abstract:
Traditional empirical methods to predict the shear strength of steel fiber reinforced concrete (SFRC) beams are based on limited data and difficult to deal with strong nonlinear problems, so it is difficult to predict the shear strength effectively and quickly. A shear strength prediction method of SFRC beams based on ensemble learning was developed. The data included 330 groups of beams from literature. The input parameters included the effective size of the beam, longitudinal reinforcement ratio, concrete compressive strength, aggregate size, shear-span ratio, steel fiber factor and tensile strength of fibers. Firstly, the thermodynamic diagram and correlation coefficient of the data set were analyzed, and it was found that there was almost no redundancy between the input parameters, which could be used as effective input parameters for modeling, and the linear relations between the input and output parameters was obtained; then the data set was divided into test set and training set for different ensemble learning models to calculate and record the running process; finally, the results were compared with traditional regression methods. The results showed that the accuracy of the GradientBoost algorithm in predicting the shear strength in the ensemble learning was the highest, reaching 0.950, which was higher than the average accuracy of the traditional regression method. It proved that the method could be used to predict the shear strength of SFRC.
Traditional empirical methods to predict the shear strength of steel fiber reinforced concrete (SFRC) beams are based on limited data and difficult to deal with strong nonlinear problems, so it is difficult to predict the shear strength effectively and quickly. A shear strength prediction method of SFRC beams based on ensemble learning was developed. The data included 330 groups of beams from literature. The input parameters included the effective size of the beam, longitudinal reinforcement ratio, concrete compressive strength, aggregate size, shear-span ratio, steel fiber factor and tensile strength of fibers. Firstly, the thermodynamic diagram and correlation coefficient of the data set were analyzed, and it was found that there was almost no redundancy between the input parameters, which could be used as effective input parameters for modeling, and the linear relations between the input and output parameters was obtained; then the data set was divided into test set and training set for different ensemble learning models to calculate and record the running process; finally, the results were compared with traditional regression methods. The results showed that the accuracy of the GradientBoost algorithm in predicting the shear strength in the ensemble learning was the highest, reaching 0.950, which was higher than the average accuracy of the traditional regression method. It proved that the method could be used to predict the shear strength of SFRC.
2023, 53(11): 145-155,138.
doi: 10.13204/j.gyjzG23053107
Abstract:
A new cylindrical-cone steel cooling tower was proposed, and the concrete cooling tower was selected as a reference for the comparison study, which verified the technical achievability and structural reliability of the steel cooling tower, the results showed that its cost and duration were less than the concrete cooling tower. The calculation formulae for the axial, flexural, shear and torsional stiffness of the four-sided angle steel lattice type members was derived, on which the equivalent substitution principle and calculation method of the box-type thin-walled units were proposed, and the correction coefficients of the stiffness parameters were optained, which were analyzed and calibrated by using the finite element model. The results showed that the equivalent substitution of cross-sectional stiffness proposed in the paper had high accuracy and could meet the requcrements of engineering accuracy. By introducing the negative stiffness of axial force, the formula of calculated length coefficient applicable to general space structures was obtained.
A new cylindrical-cone steel cooling tower was proposed, and the concrete cooling tower was selected as a reference for the comparison study, which verified the technical achievability and structural reliability of the steel cooling tower, the results showed that its cost and duration were less than the concrete cooling tower. The calculation formulae for the axial, flexural, shear and torsional stiffness of the four-sided angle steel lattice type members was derived, on which the equivalent substitution principle and calculation method of the box-type thin-walled units were proposed, and the correction coefficients of the stiffness parameters were optained, which were analyzed and calibrated by using the finite element model. The results showed that the equivalent substitution of cross-sectional stiffness proposed in the paper had high accuracy and could meet the requcrements of engineering accuracy. By introducing the negative stiffness of axial force, the formula of calculated length coefficient applicable to general space structures was obtained.
2023, 53(11): 156-160,187.
doi: 10.13204/j.gyjzG21083107
Abstract:
Experimental and numerical investigation on ten ring-stiffened tube-gusset plate joints (RS-TGP joints) has been carried out. The mechanical properties and failure mode of RS-TGP joints under radial tension/compressive were studied. The failure criteria of RS-TGP joints were proposed. The failure mode of the RS-TGP joints under tension performed as tensile broken at the intersection of the gusset plate and ring stiffener while buckling of the ring stiffener at the location perpendicular to the loading direction. The failure mode of the RS-TGP joints under compressive was bulking of the ring stiffener. It was found that the RS-TGP joint was elastic when the ratio of joint deformation to chord diameter was less than or equal to 0.15%. However, the stiffness of the joint decreased rapidly as the ratio of the joint deformation to the chord diameter was greater than 0.15% and less than 2.0%. When the ratio of joint deformation to chord diameter was larger than 2.0%, the RS-TGP joint was in a plastic state and unable to carry the load. Thus, the ultimate bearing capality of the joint was determined by the failure criterion of the 2%D limit.
Experimental and numerical investigation on ten ring-stiffened tube-gusset plate joints (RS-TGP joints) has been carried out. The mechanical properties and failure mode of RS-TGP joints under radial tension/compressive were studied. The failure criteria of RS-TGP joints were proposed. The failure mode of the RS-TGP joints under tension performed as tensile broken at the intersection of the gusset plate and ring stiffener while buckling of the ring stiffener at the location perpendicular to the loading direction. The failure mode of the RS-TGP joints under compressive was bulking of the ring stiffener. It was found that the RS-TGP joint was elastic when the ratio of joint deformation to chord diameter was less than or equal to 0.15%. However, the stiffness of the joint decreased rapidly as the ratio of the joint deformation to the chord diameter was greater than 0.15% and less than 2.0%. When the ratio of joint deformation to chord diameter was larger than 2.0%, the RS-TGP joint was in a plastic state and unable to carry the load. Thus, the ultimate bearing capality of the joint was determined by the failure criterion of the 2%D limit.
2023, 53(11): 161-167.
doi: 10.13204/j.gyjzG21091406
Abstract:
It was discussed and proved that the element selection in eigenvalue buckling analysis of grid structure should adopt multi-section beam element. The stability of the hinged compression rod and the hinged truss was analyzed, and the analytical solution was compared with the approximate solution. It was pointed out that the key to element selection lies in the appropriate shape function. The eigenvalue buckling analysis of the single grid structure and the grid considering the lower frame was carried out by using the rod element, the non-segmented beam element and the segmented beam element (multi-segment beam element). Among them, the beam element considered different shape functions. The research showed that the lowest-order buckling load factor was too large for the eigenvalue buckling analysis of the grid frame using rod elements. However, if the beam element using higher-order shape functions was not segmented, a more accurate buckling load factor could be obtained, but the buckling mode could not reflect the member buckling. Using beam elements and considering segmentation, a more accurate critical load could be obtained, and its buckling mode could reflect the member buckling.
It was discussed and proved that the element selection in eigenvalue buckling analysis of grid structure should adopt multi-section beam element. The stability of the hinged compression rod and the hinged truss was analyzed, and the analytical solution was compared with the approximate solution. It was pointed out that the key to element selection lies in the appropriate shape function. The eigenvalue buckling analysis of the single grid structure and the grid considering the lower frame was carried out by using the rod element, the non-segmented beam element and the segmented beam element (multi-segment beam element). Among them, the beam element considered different shape functions. The research showed that the lowest-order buckling load factor was too large for the eigenvalue buckling analysis of the grid frame using rod elements. However, if the beam element using higher-order shape functions was not segmented, a more accurate buckling load factor could be obtained, but the buckling mode could not reflect the member buckling. Using beam elements and considering segmentation, a more accurate critical load could be obtained, and its buckling mode could reflect the member buckling.
2023, 53(11): 168-174.
doi: 10.13204/j.gyjzG21082504
Abstract:
Two 1∶2 scaled single-span pin-connected steel frame structures with two floors were designed and fabricated. One is pin-connected steel frame with common braces (FMB) as the comparison frame, and the other is pin-connected steel frame with self-centering energy dissipation braces (FMD). The experimental study and comparative analysis of the two frames under quasi-static loading were carried out. The results showed that the out-of-plane instability and buckling occured in FMB during the loading process, local warpage also occurred in the beam-brace connection zone. The FMB was almost no energy dissipation capacity or self-centering capability. Self-centering energy dissipation devices in FMD played the energy dissipation and self-centering function, and other components kept in the elastic. After loading, no damage occurred to the structure. The structure possessed good energy dissipation capability and could restored to its initial station after loading. Compared to FMB, FMD owned about the same yielding load, higher sidesway resistance, greater ductility, stronger energy dissipation and self-centering capacity.
Two 1∶2 scaled single-span pin-connected steel frame structures with two floors were designed and fabricated. One is pin-connected steel frame with common braces (FMB) as the comparison frame, and the other is pin-connected steel frame with self-centering energy dissipation braces (FMD). The experimental study and comparative analysis of the two frames under quasi-static loading were carried out. The results showed that the out-of-plane instability and buckling occured in FMB during the loading process, local warpage also occurred in the beam-brace connection zone. The FMB was almost no energy dissipation capacity or self-centering capability. Self-centering energy dissipation devices in FMD played the energy dissipation and self-centering function, and other components kept in the elastic. After loading, no damage occurred to the structure. The structure possessed good energy dissipation capability and could restored to its initial station after loading. Compared to FMB, FMD owned about the same yielding load, higher sidesway resistance, greater ductility, stronger energy dissipation and self-centering capacity.
2023, 53(11): 175-179.
doi: 10.13204/j.gyjzG21083004
Abstract:
In order to accurately and quickly analyze the stability bearing capacity of single-layer reticulated shells with initial geometric defects, through analyzing the initial geometric imperfection values of eigenvalue imperfection modal method (EIM) and random imperfection modal method (RIMM), and conducting the linear buckling analysis of K8 Kaiweite single-layer reticulated shell structure with 1/4, 1/5, 1/6, 1/7 rise-span ratio, it was found that the vertical geometry imperfection value of the EIM was smaller than that of the RIMM, and it would be more obvious when the rise-span ratio was relatively large. Furthermore, the reason for the low reliability of the EIM when the rise-span was relatively large was analyzed, and the eigenvalue imperfection modal method for controlling vertical geometric imperfections (EIM-CVGI) was proposed. Using the proposed method and the N-order eigenvalue imperfection modal method, the elastoplastic load-displacement whole process analysis of the above four kinds of rise-span ratio reticulated shell structures was carried out. The results showed that the errors of the calculation results of the EIM-CVGI and the N-order eigenvalue defect modal method were within 5% of the engineering allowable. Compared with EIM, the stability performance of the reticulated shell structure could be evaluated more safely.
In order to accurately and quickly analyze the stability bearing capacity of single-layer reticulated shells with initial geometric defects, through analyzing the initial geometric imperfection values of eigenvalue imperfection modal method (EIM) and random imperfection modal method (RIMM), and conducting the linear buckling analysis of K8 Kaiweite single-layer reticulated shell structure with 1/4, 1/5, 1/6, 1/7 rise-span ratio, it was found that the vertical geometry imperfection value of the EIM was smaller than that of the RIMM, and it would be more obvious when the rise-span ratio was relatively large. Furthermore, the reason for the low reliability of the EIM when the rise-span was relatively large was analyzed, and the eigenvalue imperfection modal method for controlling vertical geometric imperfections (EIM-CVGI) was proposed. Using the proposed method and the N-order eigenvalue imperfection modal method, the elastoplastic load-displacement whole process analysis of the above four kinds of rise-span ratio reticulated shell structures was carried out. The results showed that the errors of the calculation results of the EIM-CVGI and the N-order eigenvalue defect modal method were within 5% of the engineering allowable. Compared with EIM, the stability performance of the reticulated shell structure could be evaluated more safely.
2023, 53(11): 180-187.
doi: 10.13204/j.gyjzG22112702
Abstract:
In order to study the shear performance of large-diameter short studs in prefabricated steel-thin UHPC composite beams, push-out test models were established by finite element software ABAQUS, and the effects of stud diameter, hole size, hole shape and the number of studs configured in a single hole on shear performance of specimens were mainly investigated. The results showed that the failure mode of specimens was the shear failure of studs and the local crushing of concrete slabs. The stud diameter was the key factor affecting the shear bearing capacity, the hole size and hole shape had little effect on the shear bearing capacity, and the shear bearing capacity of prefabricated specimens was slightly higher than that of cast-in-place specimens. One large-diameter short stud in a single prefabricated hole could basically be replaced by two small diameter short studs with the same cross-sectional area. In addition, comparing the shear bearing capacity obtained by finite element method with the calculated values of the existed codes, it was found that the calculation values in GB 50010—2017 and EC 4 were conservative in prediction, and the calculation results in AASHTO LRFD was in good agreement with the results from finite element method, and the accuracy of its calculation method was verified by comparing six groups of relevant test data.
In order to study the shear performance of large-diameter short studs in prefabricated steel-thin UHPC composite beams, push-out test models were established by finite element software ABAQUS, and the effects of stud diameter, hole size, hole shape and the number of studs configured in a single hole on shear performance of specimens were mainly investigated. The results showed that the failure mode of specimens was the shear failure of studs and the local crushing of concrete slabs. The stud diameter was the key factor affecting the shear bearing capacity, the hole size and hole shape had little effect on the shear bearing capacity, and the shear bearing capacity of prefabricated specimens was slightly higher than that of cast-in-place specimens. One large-diameter short stud in a single prefabricated hole could basically be replaced by two small diameter short studs with the same cross-sectional area. In addition, comparing the shear bearing capacity obtained by finite element method with the calculated values of the existed codes, it was found that the calculation values in GB 50010—2017 and EC 4 were conservative in prediction, and the calculation results in AASHTO LRFD was in good agreement with the results from finite element method, and the accuracy of its calculation method was verified by comparing six groups of relevant test data.
2023, 53(11): 188-195.
doi: 10.13204/j.gyjzG21090908
Abstract:
Thin-walled open-section members are likely to occur distortional and local buckling, and the interaction between the buckling modes will result in the deterioration of mechanical properties of cold-formed steel columns. Whereas, this interaction is not included properly in the design calculation of the current specifications. A test program of 2 high-strength cold-formed steel C-section stub columns was conducted. This experiment studied the relations between the flange stiffener, flange plate size, plate thickness and the buckling interactions, and their influence on the bearing capacity of compression members. The results showed that: 1) distortional buckling should be considered in design calculation for the bearing capacity of stub columns; 2) the direct strength method and the effective width method overestimated the bearing capacity of compression members that failed by interaction of local and distortional buckling. The buckling mode identification was carried out according to the sequence of occurrence of buckling deformation, and the modified design curves of current direct strength method were proposed for local and distortional buckling, respectively. These modifications could accurately predict the ultimate strength of high-strength cold-formed stub columns that failed by interaction of local and distortional buckling.
Thin-walled open-section members are likely to occur distortional and local buckling, and the interaction between the buckling modes will result in the deterioration of mechanical properties of cold-formed steel columns. Whereas, this interaction is not included properly in the design calculation of the current specifications. A test program of 2 high-strength cold-formed steel C-section stub columns was conducted. This experiment studied the relations between the flange stiffener, flange plate size, plate thickness and the buckling interactions, and their influence on the bearing capacity of compression members. The results showed that: 1) distortional buckling should be considered in design calculation for the bearing capacity of stub columns; 2) the direct strength method and the effective width method overestimated the bearing capacity of compression members that failed by interaction of local and distortional buckling. The buckling mode identification was carried out according to the sequence of occurrence of buckling deformation, and the modified design curves of current direct strength method were proposed for local and distortional buckling, respectively. These modifications could accurately predict the ultimate strength of high-strength cold-formed stub columns that failed by interaction of local and distortional buckling.
2023, 53(11): 196-206,233.
doi: 10.13204/j.gyjzG23071406
Abstract:
A typical 220 kV transmission tower with high-low legs in mountainous slope areas of mining areas was taken as the object, and factors such as tower leg difference (0, 1, 2, 3 m), plate thickness (200, 400, 600 mm) and surface deformation direction (0°, 45°, 90°, 135°) were considered to study the surface deformation resistance of the split-type protective plate under the action of horizontal tension, horizontal compression, positive and negative curvature of the surface. The results indicated that the split-type protective plate could effectively reduce the axial force and relative displacement of the foundation of the transmission tower with high-low legs, and its protective effect was closely related to the type of surface deformation, direction of surface deformation, and tower leg level difference. The protective effect of the split-type protective plate increased with the increase of plate thickness, but when the plate thickness increased to a certain extent, its comprehensive protective effect no longer significantly increased with the increase of thickness. 400 mm was the optimal thickness for the split-type protective plate to balance the protective effect and economy. When the length direction of the split-type large plate was consistent with the direction of horizontal or curvature deformation on the surface, the protective effect of the large plate could be fully utilized, but the effect was relatively poor under surface deformation along other directions.
A typical 220 kV transmission tower with high-low legs in mountainous slope areas of mining areas was taken as the object, and factors such as tower leg difference (0, 1, 2, 3 m), plate thickness (200, 400, 600 mm) and surface deformation direction (0°, 45°, 90°, 135°) were considered to study the surface deformation resistance of the split-type protective plate under the action of horizontal tension, horizontal compression, positive and negative curvature of the surface. The results indicated that the split-type protective plate could effectively reduce the axial force and relative displacement of the foundation of the transmission tower with high-low legs, and its protective effect was closely related to the type of surface deformation, direction of surface deformation, and tower leg level difference. The protective effect of the split-type protective plate increased with the increase of plate thickness, but when the plate thickness increased to a certain extent, its comprehensive protective effect no longer significantly increased with the increase of thickness. 400 mm was the optimal thickness for the split-type protective plate to balance the protective effect and economy. When the length direction of the split-type large plate was consistent with the direction of horizontal or curvature deformation on the surface, the protective effect of the large plate could be fully utilized, but the effect was relatively poor under surface deformation along other directions.
2023, 53(11): 207-213,220.
doi: 10.13204/j.gyjzG23053001
Abstract:
In order to study the performance of desert sand concrete after sulfate attack, the mechanical properties of sulfate attacked desert sand concrete under the action of wet-dry cycles were tested. The mass loss rate, compressive corrosion resistance coefficient and dynamic elastic modulus were used to symbol the mechanical properties deterioration of desert sand concrete under the action of sulfate erosion and wet-dry cycles. Experimental results showed that with the increase of the number of dry-wet cycles, the mass loss rate of desert sand concrete decreased firstly and then increased. The compressive corrosion resistance coefficient and relative dynamic modulus of elasticity increased firstly and then decreased. When the number of wet-dry cycles was equal to 60, the mass loss rate of desert sand concrete reached the minimum, and the compressive corrosion resistance coefficient and relative dynamic modulus of elasticity arrived at maximum. The higher the sulfate solution concentration, the greater the decrease in compressive corrosion resistance coefficient and relative dynamic modulus. The compressive corrosion resistance coefficient and relative dynamic modulus of desert sand concrete with the desert sand replacement ratio of 40% were higher than that of ordinary concrete. Dynamic elastic modulus was used to define damage variable. The relative peak stress and peak strain were exponentially related to the damage variable, the correlation coefficients of which were all above 0.93.
In order to study the performance of desert sand concrete after sulfate attack, the mechanical properties of sulfate attacked desert sand concrete under the action of wet-dry cycles were tested. The mass loss rate, compressive corrosion resistance coefficient and dynamic elastic modulus were used to symbol the mechanical properties deterioration of desert sand concrete under the action of sulfate erosion and wet-dry cycles. Experimental results showed that with the increase of the number of dry-wet cycles, the mass loss rate of desert sand concrete decreased firstly and then increased. The compressive corrosion resistance coefficient and relative dynamic modulus of elasticity increased firstly and then decreased. When the number of wet-dry cycles was equal to 60, the mass loss rate of desert sand concrete reached the minimum, and the compressive corrosion resistance coefficient and relative dynamic modulus of elasticity arrived at maximum. The higher the sulfate solution concentration, the greater the decrease in compressive corrosion resistance coefficient and relative dynamic modulus. The compressive corrosion resistance coefficient and relative dynamic modulus of desert sand concrete with the desert sand replacement ratio of 40% were higher than that of ordinary concrete. Dynamic elastic modulus was used to define damage variable. The relative peak stress and peak strain were exponentially related to the damage variable, the correlation coefficients of which were all above 0.93.
2023, 53(11): 214-220.
doi: 10.13204/j.gyjzG22031505
Abstract:
With the continuous expansion of the scale of the subway, a long span, more spacious space, more comfortable ride feeling has become the requirements of the people. Long-span column-free station can effectively expand the use space of station structure and improve passengers’ transfer experience by canceling the pier columns on platform floor. However, the long-span structure without columns also brings great difficulties to the structural design of the station. Steel-concrete composite structure has excellent mechanical properties and convenient construction, and can obtain good comprehensive benefits in solving the problems of long-span structures. Relying on the South Third Ring Station project of Xuzhou Rail Transit Line 3, the steel-concrete composite structure scheme of transfer node station was proposed. MIDAS Gen was used to establish an overall model for analysis, and the mechanical properties of the structure and the stress states of key components were studied. The results showed that the steel-concrete composite structure scheme could significantly reduce the weight of the structure, save the building space, and exhibited the advantages of convenient and fast construction. The results of modeling analysis showed that the long-span transfer beam was in the state of bending, shear and torsion, which was the key point and difficulty of design. Finally, some design suggestions were put forward for the application of steel-concrete composite structure scheme in long-span column-free station structure, which could provide a reference for similar projects in the future.
With the continuous expansion of the scale of the subway, a long span, more spacious space, more comfortable ride feeling has become the requirements of the people. Long-span column-free station can effectively expand the use space of station structure and improve passengers’ transfer experience by canceling the pier columns on platform floor. However, the long-span structure without columns also brings great difficulties to the structural design of the station. Steel-concrete composite structure has excellent mechanical properties and convenient construction, and can obtain good comprehensive benefits in solving the problems of long-span structures. Relying on the South Third Ring Station project of Xuzhou Rail Transit Line 3, the steel-concrete composite structure scheme of transfer node station was proposed. MIDAS Gen was used to establish an overall model for analysis, and the mechanical properties of the structure and the stress states of key components were studied. The results showed that the steel-concrete composite structure scheme could significantly reduce the weight of the structure, save the building space, and exhibited the advantages of convenient and fast construction. The results of modeling analysis showed that the long-span transfer beam was in the state of bending, shear and torsion, which was the key point and difficulty of design. Finally, some design suggestions were put forward for the application of steel-concrete composite structure scheme in long-span column-free station structure, which could provide a reference for similar projects in the future.
2023, 53(11): 221-225.
doi: 10.13204/gyjzG22120508
Abstract:
In order to study the bending performance of reinforced concrete (RC) beams after fire, a high temperature numerical analysis model of RC beams was established considering the bond degradation between rebar and concrete and the characteristics of concrete spalling, and the validity of the numerical analysis model was verified by fire test. Based on the verified numerical analysis model, a numerical analysis sample library consisting of fire exposure time, spalling depth, spalling area ratio and flexural capacity was established. The multiple regression prediction method and SVM prediction model of residual flexural capacity of RC beams after fire were proposed. The new working condition sample data were used for verification. The results showed that the coefficient of determination of the two prediction methods were greater than 0.9. Compared with the numerical simulation results, the relative error of SVM prediction was small, ranging from 0.05% to 4.05%, which indicated that it should be feasible and accurate to predict the residual flexural capacity of RC beams after fire by SVM.
In order to study the bending performance of reinforced concrete (RC) beams after fire, a high temperature numerical analysis model of RC beams was established considering the bond degradation between rebar and concrete and the characteristics of concrete spalling, and the validity of the numerical analysis model was verified by fire test. Based on the verified numerical analysis model, a numerical analysis sample library consisting of fire exposure time, spalling depth, spalling area ratio and flexural capacity was established. The multiple regression prediction method and SVM prediction model of residual flexural capacity of RC beams after fire were proposed. The new working condition sample data were used for verification. The results showed that the coefficient of determination of the two prediction methods were greater than 0.9. Compared with the numerical simulation results, the relative error of SVM prediction was small, ranging from 0.05% to 4.05%, which indicated that it should be feasible and accurate to predict the residual flexural capacity of RC beams after fire by SVM.
2023, 53(11): 226-233.
doi: 10.13204/j.gyjzG22010711
Abstract:
A dynamic safety risk evaluation method combining cloud model and Bayesian network was proposed to study the safety of complex approaching excavation of shield tunnel undercrossing railway. Based on literature and a lot of engineering experience, the risk evaluation index system and evaluation standard of shield undercrossing railway construction were established. The state of continuous nodes was discretized through cloud model and the prior probability was obtained. The cloud bayesian network reasoning model was established to predict the aggregation probability distribution of the construction safety risk of shield tunneling railway, and the comprehensive cloud was generated to obtain quantitative risk values, which effectively realized the transformation of qualitative concept of risk and quantitative values. Combined with sensitivity analysis and risk diagnosis, real-time security dynamic control was realized in the stage before, during and after the event. Taking an undercrossing railway project as an example, the method was used to effectively evaluate the system risk level, and the key control factors were determined by reverse diagnosis. It was verified that the method could provide a strong support for the safety management and early warning decision of shield close construction.
A dynamic safety risk evaluation method combining cloud model and Bayesian network was proposed to study the safety of complex approaching excavation of shield tunnel undercrossing railway. Based on literature and a lot of engineering experience, the risk evaluation index system and evaluation standard of shield undercrossing railway construction were established. The state of continuous nodes was discretized through cloud model and the prior probability was obtained. The cloud bayesian network reasoning model was established to predict the aggregation probability distribution of the construction safety risk of shield tunneling railway, and the comprehensive cloud was generated to obtain quantitative risk values, which effectively realized the transformation of qualitative concept of risk and quantitative values. Combined with sensitivity analysis and risk diagnosis, real-time security dynamic control was realized in the stage before, during and after the event. Taking an undercrossing railway project as an example, the method was used to effectively evaluate the system risk level, and the key control factors were determined by reverse diagnosis. It was verified that the method could provide a strong support for the safety management and early warning decision of shield close construction.
