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2022 Vol. 52, No. 8
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2022, 52(8): 1-8.
doi: 10.13204/j.gyjzG21121615
Abstract:
The long-span transmission tower-line system combines the characteristics of long-span, towering and flexibility, which is extremely sensitive to wind loads. Due to the coupling of the transmission wires, insulators and the spanning tower, its dynamic characteristics and wind-induced response are more complex. Taking the world’s tallest 500 kV transmission tower crossing the Yangtze River as an example, finite element models of single tower and tower-line system were established based on ABAQUS. The dynamic characteristics of single tower and tower-line systems were studied, and wind-induced vibration response together with wind-induced vibration coefficients were analyzed based on the results of wind load time-history analysis. The results showed the natural vibration frequency of the tower in transmission tower line system was less than that of single tower. Under different wind attack angles, the displacement of the tower line system at the apex of the tower was larger than that of a single tower, and the acceleration response was smaller.The weighted average value of wind-vibration coefficient calculated in the current code was greater than the time-history analysis results, which was partial to safety. However, the wind load in the concrete pouring area of main stressed tube might be underestimated, and the sudden change of wind-vibration coefficients caused by the change of mass and shape at the cross arm was not considered.
The long-span transmission tower-line system combines the characteristics of long-span, towering and flexibility, which is extremely sensitive to wind loads. Due to the coupling of the transmission wires, insulators and the spanning tower, its dynamic characteristics and wind-induced response are more complex. Taking the world’s tallest 500 kV transmission tower crossing the Yangtze River as an example, finite element models of single tower and tower-line system were established based on ABAQUS. The dynamic characteristics of single tower and tower-line systems were studied, and wind-induced vibration response together with wind-induced vibration coefficients were analyzed based on the results of wind load time-history analysis. The results showed the natural vibration frequency of the tower in transmission tower line system was less than that of single tower. Under different wind attack angles, the displacement of the tower line system at the apex of the tower was larger than that of a single tower, and the acceleration response was smaller.The weighted average value of wind-vibration coefficient calculated in the current code was greater than the time-history analysis results, which was partial to safety. However, the wind load in the concrete pouring area of main stressed tube might be underestimated, and the sudden change of wind-vibration coefficients caused by the change of mass and shape at the cross arm was not considered.
2022, 52(8): 9-15.
doi: 10.13204/j.gyjzG20101801
Abstract:
In order to study the wind drag coefficients on main rods and whole structure of an angle-steel transmission tower, high frequency force balance test was carried out to obtain drag force coefficients of main rods of the cross arm and tower body under various wind azimuths. Interference of surrounding rods on drag force was considered during the test. Meanwhile, drag force coefficients of a single plane and whole parts of the tower body and cross-arm were tested under different wind azimuths, respectively, and the corresponding shielding factors were also analyzed. In addition, the obtained experimental results were compared with the current national code provisions. The study showed that drag force coefficients of a main rod were significantly influenced by its location. Most rods of the cross arm and tower body had maximum drag force coefficients larger than 1.3 as recommended by Load Code for the Design of Building structures (GB 50009-2012). Wind loads acting on the upper and lower surfaces of the cross arm contributed a lot to overall wind loads on the cross arm, however. Technical Code for the Design of Tower and Pole Structures of Overhead Transmission Line (DL/T 5154-2012) only considered those on the windward and leeward surfaces of the cross arm, resulting in underestimation of overall wind drag force. The drag force coefficients of a single plane and whole parts of the tower-body were close to those given by the foreign codes, but slightly larger than those in Chinese codes. The tested shielding factors of leeward sides of the cross arm and tower body were 0.73 and 0.62, respectively. Comparing the test results with different code recommended values indicated that the shielding factors in Chinese codes were more conservative.
In order to study the wind drag coefficients on main rods and whole structure of an angle-steel transmission tower, high frequency force balance test was carried out to obtain drag force coefficients of main rods of the cross arm and tower body under various wind azimuths. Interference of surrounding rods on drag force was considered during the test. Meanwhile, drag force coefficients of a single plane and whole parts of the tower body and cross-arm were tested under different wind azimuths, respectively, and the corresponding shielding factors were also analyzed. In addition, the obtained experimental results were compared with the current national code provisions. The study showed that drag force coefficients of a main rod were significantly influenced by its location. Most rods of the cross arm and tower body had maximum drag force coefficients larger than 1.3 as recommended by Load Code for the Design of Building structures (GB 50009-2012). Wind loads acting on the upper and lower surfaces of the cross arm contributed a lot to overall wind loads on the cross arm, however. Technical Code for the Design of Tower and Pole Structures of Overhead Transmission Line (DL/T 5154-2012) only considered those on the windward and leeward surfaces of the cross arm, resulting in underestimation of overall wind drag force. The drag force coefficients of a single plane and whole parts of the tower-body were close to those given by the foreign codes, but slightly larger than those in Chinese codes. The tested shielding factors of leeward sides of the cross arm and tower body were 0.73 and 0.62, respectively. Comparing the test results with different code recommended values indicated that the shielding factors in Chinese codes were more conservative.
2022, 52(8): 16-21.
doi: 10.13204/j.gyjzG21081101
Abstract:
By considering the included angle between the front face of tower segments and the vertical plane, a refined JEC calculation method of wind loads acting on the frontal face and the segment of transmission towers based on the drag coefficients of single member was proposed, which was also called member assembly method. Drag coefficients of the frontal faces and segments of transmission towers with most commonly used solidarity ratios by member assembly method were calculated. Effects of the modification of main member slenderness ratio on drag coefficients were discussed. Drag coefficients calculated by the member assembly method were compared with those values regulated by total calculation method in applicable standards. The drag coefficients of tower segments calculated by the total calculation method in Chinese standard were lower than the member assembly method. Drag coefficients of tower segments calculated by the total calculation method in BS and JEC standards were close to the values calculated by the member assembly method. The relative variations of drag coefficients for tower segments with different solidarity ratios were lower than 10%. Drag coefficients by wind tunnel tests and the member assembly method for frontal faces and segments of typical transmission towers were compared. The relative variations were 5.7% and 7.5%, respectively. Property of the calculation method of wind loads acting on transmission towers based on single member drag coefficients was verified.
By considering the included angle between the front face of tower segments and the vertical plane, a refined JEC calculation method of wind loads acting on the frontal face and the segment of transmission towers based on the drag coefficients of single member was proposed, which was also called member assembly method. Drag coefficients of the frontal faces and segments of transmission towers with most commonly used solidarity ratios by member assembly method were calculated. Effects of the modification of main member slenderness ratio on drag coefficients were discussed. Drag coefficients calculated by the member assembly method were compared with those values regulated by total calculation method in applicable standards. The drag coefficients of tower segments calculated by the total calculation method in Chinese standard were lower than the member assembly method. Drag coefficients of tower segments calculated by the total calculation method in BS and JEC standards were close to the values calculated by the member assembly method. The relative variations of drag coefficients for tower segments with different solidarity ratios were lower than 10%. Drag coefficients by wind tunnel tests and the member assembly method for frontal faces and segments of typical transmission towers were compared. The relative variations were 5.7% and 7.5%, respectively. Property of the calculation method of wind loads acting on transmission towers based on single member drag coefficients was verified.
2022, 52(8): 22-27,63.
doi: 10.13204/j.gyjzG22011111
Abstract:
There are still many in-service 77/78 series transmission towers designed by the allowable stress method in the strong wind area. The power grid operation departments need to gradually carry out reinforcement and retrofit according to the applicable standards. According to the allowable stress method and the limit state method, the safety factor expressions of transmission tower members were given separately, and the wind load and structural design methods in the standards of different periods in China were compared and analyzed. Two 77/78 series transmission towers destroyed in 2021 wind disaster were selected as the research objects. The stress, stress ratios and safety factors of the transmission tower members were calculated according to the allowable stress method and the limit state method, respectively. The weak positions of the typical transmission towers under strong wind were determined. The safety factors of the transmission tower designed according to SDJ 3-1979 were significantly lower than that of SDGJ 94-90 and DL/T 5154-2002, and the difference in safety factors was more than 20%. The safety level of the transmission tower designed according to SDGJ 94-90 and DL/T 5154-2002 was basically the same.
There are still many in-service 77/78 series transmission towers designed by the allowable stress method in the strong wind area. The power grid operation departments need to gradually carry out reinforcement and retrofit according to the applicable standards. According to the allowable stress method and the limit state method, the safety factor expressions of transmission tower members were given separately, and the wind load and structural design methods in the standards of different periods in China were compared and analyzed. Two 77/78 series transmission towers destroyed in 2021 wind disaster were selected as the research objects. The stress, stress ratios and safety factors of the transmission tower members were calculated according to the allowable stress method and the limit state method, respectively. The weak positions of the typical transmission towers under strong wind were determined. The safety factors of the transmission tower designed according to SDJ 3-1979 were significantly lower than that of SDGJ 94-90 and DL/T 5154-2002, and the difference in safety factors was more than 20%. The safety level of the transmission tower designed according to SDGJ 94-90 and DL/T 5154-2002 was basically the same.
2022, 52(8): 28-33,118.
doi: 10.13204/j.gyjzG22011304
Abstract:
Wind tunnel tests were conducted on sectional models and whole tower models to obtain the wind loading on the elevator shaft of long-span transmission towers. The influence of climbing ladders and interference of tower body on the drag coefficient of the elevator shaft was analyzed. The test results were compared with those regulated in different countries’ codes. Finally, the drag coefficients of the elevator shaft were recommended for the design. The results showed that the drag coefficients of elevator shaft with climbing ladder was larger than that of shaft without climbing ladder. With the interference effect of tower body, the drag coefficients significantly varied with the wind azimuth, reaching their maximum value at 35 degree and their minimum value at 45 degree. The aerodynamic coefficients of the shaft obtained from sectional model and whole tower model tests were almost equaled. The drag coefficients of the shaft with respect to wind azimuth under the interference of tower body were recommended. The maximum value of elevator shaft without climbing ladder was 0.93, which was quite close to 0.9 that was the drag coefficient of smooth circular cylinder recommended by Load Code for the Design of Building Structures (GB 50009-2012).
Wind tunnel tests were conducted on sectional models and whole tower models to obtain the wind loading on the elevator shaft of long-span transmission towers. The influence of climbing ladders and interference of tower body on the drag coefficient of the elevator shaft was analyzed. The test results were compared with those regulated in different countries’ codes. Finally, the drag coefficients of the elevator shaft were recommended for the design. The results showed that the drag coefficients of elevator shaft with climbing ladder was larger than that of shaft without climbing ladder. With the interference effect of tower body, the drag coefficients significantly varied with the wind azimuth, reaching their maximum value at 35 degree and their minimum value at 45 degree. The aerodynamic coefficients of the shaft obtained from sectional model and whole tower model tests were almost equaled. The drag coefficients of the shaft with respect to wind azimuth under the interference of tower body were recommended. The maximum value of elevator shaft without climbing ladder was 0.93, which was quite close to 0.9 that was the drag coefficient of smooth circular cylinder recommended by Load Code for the Design of Building Structures (GB 50009-2012).
2022, 52(8): 34-40,47.
doi: 10.13204/j.gyjzG22030222
Abstract:
In view of the characteristics of many member intersections, complex spatial relations and special load conditions at the connection joint of cross arm and main rods in a 385-meter super long-span transmission tower crossing the Yangtze River, which is a national key project, cast steel joints were proposed to applied in the transmission tower for the first time. Considering the characteristics of complex shape and high importance of cast steel joints, two 1∶2 scaled models of joints were designed and the bearing capacity verification test and finite element analysis were carried out in order to verify its safety and rationality.The results showed that under the 90° gale test condition, the maximum stress location of the joint was the chamfer of the member, the strain basically changed linearly with the load, and the whole joint was in a linear elastic state. The experimental results were in good agreement with the finite element analysis results, which showed that the joint model could truly and effectively simulate the actual stress of the joint. The finite element elastic-plastic analysis results showed that the ultimate bearing capacity of the cast steel joint was 12.39 times of the design load, with a large safety redundancy, and the joint design was safe and reliable.
In view of the characteristics of many member intersections, complex spatial relations and special load conditions at the connection joint of cross arm and main rods in a 385-meter super long-span transmission tower crossing the Yangtze River, which is a national key project, cast steel joints were proposed to applied in the transmission tower for the first time. Considering the characteristics of complex shape and high importance of cast steel joints, two 1∶2 scaled models of joints were designed and the bearing capacity verification test and finite element analysis were carried out in order to verify its safety and rationality.The results showed that under the 90° gale test condition, the maximum stress location of the joint was the chamfer of the member, the strain basically changed linearly with the load, and the whole joint was in a linear elastic state. The experimental results were in good agreement with the finite element analysis results, which showed that the joint model could truly and effectively simulate the actual stress of the joint. The finite element elastic-plastic analysis results showed that the ultimate bearing capacity of the cast steel joint was 12.39 times of the design load, with a large safety redundancy, and the joint design was safe and reliable.
2022, 52(8): 41-47.
doi: 10.13204/j.gyjzG20121307
Abstract:
Reinforcing method, to constitute the box-shaped section by the angel of the transmission tower and the strengthening angle of the same size, was presented in the paper. In order to study the effect of every parameters on the bearing capacity of reinforced main member angle, analysis models of reinforced main member angles of single panel length and multi panel length were designed. Meanwhile, finite element analysis models of reinforced main member angles were also established by using ANSYS software. The reliability of finite element analysis was proved by comparing the results of finite element analysis and that from the experiments presented in references. The effects of the parameters such as the prestress force of high strength bolt P, the distance between ferrule assemblies Lt, the end clearance jx, the length of subsidiary angle steel Lf, the thickness of ferrule plate tg, the yield strength of angle fy, the friction coefficient mu, the wall leg thickness of angle used to strengthen the main member tc and the section dimension of main members on the bearing capacity of models was researched. The results showed that the length of subsidiary angle steel Lf,the thickness of ferrule plate tg,the friction coefficient mu had little effect on the ultimate bearing capacity of the reinforced main members. The end clearance jx and the prestress force of high strength bolt P had effects on the ultimate bearing capacity of NW series models with a small to medium slenderness ratio, and had little effect on the ultimate bearing capacity of other series models; the distance between ferrule assemblies had an effect on the ultimate bearing capacity of all reinforced main members.
Reinforcing method, to constitute the box-shaped section by the angel of the transmission tower and the strengthening angle of the same size, was presented in the paper. In order to study the effect of every parameters on the bearing capacity of reinforced main member angle, analysis models of reinforced main member angles of single panel length and multi panel length were designed. Meanwhile, finite element analysis models of reinforced main member angles were also established by using ANSYS software. The reliability of finite element analysis was proved by comparing the results of finite element analysis and that from the experiments presented in references. The effects of the parameters such as the prestress force of high strength bolt P, the distance between ferrule assemblies Lt, the end clearance jx, the length of subsidiary angle steel Lf, the thickness of ferrule plate tg, the yield strength of angle fy, the friction coefficient mu, the wall leg thickness of angle used to strengthen the main member tc and the section dimension of main members on the bearing capacity of models was researched. The results showed that the length of subsidiary angle steel Lf,the thickness of ferrule plate tg,the friction coefficient mu had little effect on the ultimate bearing capacity of the reinforced main members. The end clearance jx and the prestress force of high strength bolt P had effects on the ultimate bearing capacity of NW series models with a small to medium slenderness ratio, and had little effect on the ultimate bearing capacity of other series models; the distance between ferrule assemblies had an effect on the ultimate bearing capacity of all reinforced main members.
2022, 52(8): 48-56.
Abstract:
Combined with the structural characteristics, wind-induced response characteristics and load characteristics of transmission tower, a wind resistant reinforcement technique and design method of in-plane cable of self-supporting transmission tower were proposed. Taking 330ZM3-40 tower collapsed in "Hagupit" typhoon in 2020 as the research object, the influence of prestress of cable on the internal force of components of tower and wind-induced vibration time history analysis were carried out. The influence of prestress, section area, damping coefficient and inclination of cable on wind-induced vibration control of tower was analyzed. The research showed that, through reasonable design, setting multi-layer in-plane crossing cables on the body of tower could effectively control the displacement response and internal force of the tower under wind load. The section area of cable was the key factor to ensure the wind-induced vibration control effect of transmission tower, and section area of cable should be greater than 100 mm2; the prestress of cable should not be greater than 150 MPa to ensure that the internal force increase-yield ratio of tower components did not exceed 5%; the angle of installation of cable was 40°-60°; in order to achieve better wind-induced vibration control effect, additional dampings for the cable system should be added with the reasonable value range 5%-20%.
Combined with the structural characteristics, wind-induced response characteristics and load characteristics of transmission tower, a wind resistant reinforcement technique and design method of in-plane cable of self-supporting transmission tower were proposed. Taking 330ZM3-40 tower collapsed in "Hagupit" typhoon in 2020 as the research object, the influence of prestress of cable on the internal force of components of tower and wind-induced vibration time history analysis were carried out. The influence of prestress, section area, damping coefficient and inclination of cable on wind-induced vibration control of tower was analyzed. The research showed that, through reasonable design, setting multi-layer in-plane crossing cables on the body of tower could effectively control the displacement response and internal force of the tower under wind load. The section area of cable was the key factor to ensure the wind-induced vibration control effect of transmission tower, and section area of cable should be greater than 100 mm2; the prestress of cable should not be greater than 150 MPa to ensure that the internal force increase-yield ratio of tower components did not exceed 5%; the angle of installation of cable was 40°-60°; in order to achieve better wind-induced vibration control effect, additional dampings for the cable system should be added with the reasonable value range 5%-20%.
2022, 52(8): 57-63.
doi: 10.13204/j.gyjzG21071316
Abstract:
The safety of engineering steel structures such as transmission towers is often affected by cracks and other damages. Such damages often exhibit nonlinear characteristics of variable stiffness in structural vibration. In order to solve this kind of nonlinear damage detection problem, a nonlinear damage identification method based on AR/ARCH model conversion distance was presented. Firstly, the basic theory of AR/ARCH hybrid model was described, and the order determination and parameter estimation methods of modeling were given. Then, the time-varying stiffness characteristics of nonlinear damage were described, and the nonlinear damage identification strategy based on second-order variance index was given. On this basis, the relations between AR/ARCH model residual and condition variance and nonlinear damage was analyzed, and a conversion distance index based on AR/ARCH model was proposed. Finally, the related experimental research was carried out, and the three-layer frame experiment was used to verify the effectiveness of the index, and the damage identification experiment of the transmission tower model was also conducted. The experimental and calculation results showed that the conversion distance index based on AR/ARCH model was obviously superior to the traditional second-order variance index, and it had stronger nonlinear damage identification capability and reliability.
The safety of engineering steel structures such as transmission towers is often affected by cracks and other damages. Such damages often exhibit nonlinear characteristics of variable stiffness in structural vibration. In order to solve this kind of nonlinear damage detection problem, a nonlinear damage identification method based on AR/ARCH model conversion distance was presented. Firstly, the basic theory of AR/ARCH hybrid model was described, and the order determination and parameter estimation methods of modeling were given. Then, the time-varying stiffness characteristics of nonlinear damage were described, and the nonlinear damage identification strategy based on second-order variance index was given. On this basis, the relations between AR/ARCH model residual and condition variance and nonlinear damage was analyzed, and a conversion distance index based on AR/ARCH model was proposed. Finally, the related experimental research was carried out, and the three-layer frame experiment was used to verify the effectiveness of the index, and the damage identification experiment of the transmission tower model was also conducted. The experimental and calculation results showed that the conversion distance index based on AR/ARCH model was obviously superior to the traditional second-order variance index, and it had stronger nonlinear damage identification capability and reliability.
2022, 52(8): 64-70,90.
doi: 10.13204/j.gyjzG22042602
Abstract:
With the background of the construction of the transmission tower crossing the Yangtze River of Jiangsu Fengcheng-Meili 500 kV line, a set of construction and erection techniques for transmission towers based on finite element simulation and field measurement was proposed. First of all, according to the characteristics of lifting components, installation location, etc., a reasonable lifting and installation process was developed, and then a coupled finite element model of the tower and the crane in the key construction stages was established, the real measurement system was installed on the tower and crane structure to collect the dynamic information of the wind environment and the structure state, so as to ensure that the construction could be carried out safely. A computer vision displacement measurement method of relative displacement of overhead structures was developed to solve the problem of difficult displacement measurement of crane at high altitude. The finite element model was used to simulate the overall state of the structure, the computer vision method was used to measure the deformation and dynamic displacement of the structure, a new safe and high-efficienly technique for construction and erection of transmission towers was proposed.
With the background of the construction of the transmission tower crossing the Yangtze River of Jiangsu Fengcheng-Meili 500 kV line, a set of construction and erection techniques for transmission towers based on finite element simulation and field measurement was proposed. First of all, according to the characteristics of lifting components, installation location, etc., a reasonable lifting and installation process was developed, and then a coupled finite element model of the tower and the crane in the key construction stages was established, the real measurement system was installed on the tower and crane structure to collect the dynamic information of the wind environment and the structure state, so as to ensure that the construction could be carried out safely. A computer vision displacement measurement method of relative displacement of overhead structures was developed to solve the problem of difficult displacement measurement of crane at high altitude. The finite element model was used to simulate the overall state of the structure, the computer vision method was used to measure the deformation and dynamic displacement of the structure, a new safe and high-efficienly technique for construction and erection of transmission towers was proposed.
2022, 52(8): 71-77,15.
doi: 10.13204/j.gyjzG21091804
Abstract:
Floor area ratio (FAR) is the core index to reflect the intensity of land development, which can be used as the measurement index of urban spatial structure and form. The spatial difference analysis of FAR is of great significance to the research on the influencing mechanism of urban related factors and the evaluation of urban planning effect. Most of the existing studies focus on the FAR of residential areas, which is difficult to analyze the whole city. In this paper, the FAR was obtained by combining the architectural vector data of Gaode map with the surveying and mapping data, and its spatial characteristics were analyzed in different scales combined with the land use information, including the overall spatial characteristics, spatial agglomeration characteristics and spatial structure characteristics. The results showed that the main functions of the city were residential and productive functions, and there was a lot of room for improvement in land use intensity of the study area; the spatial agglomeration of FAR street scale was shown as a single center structure; the spatial agglomeration of FAR in plot scale was represented by multi-center structure; the circle structure model was used to calculate the FAR of the circle in different places, different regions showed different laws, the urban expansion trend was obvious, and the public service and other supporting construction were insufficient; 13 urban centers in Shenyang were identified by kernel density method according to FAR of plot. The current multi-center structure could not meet the needs of residents’ life and urban development.
Floor area ratio (FAR) is the core index to reflect the intensity of land development, which can be used as the measurement index of urban spatial structure and form. The spatial difference analysis of FAR is of great significance to the research on the influencing mechanism of urban related factors and the evaluation of urban planning effect. Most of the existing studies focus on the FAR of residential areas, which is difficult to analyze the whole city. In this paper, the FAR was obtained by combining the architectural vector data of Gaode map with the surveying and mapping data, and its spatial characteristics were analyzed in different scales combined with the land use information, including the overall spatial characteristics, spatial agglomeration characteristics and spatial structure characteristics. The results showed that the main functions of the city were residential and productive functions, and there was a lot of room for improvement in land use intensity of the study area; the spatial agglomeration of FAR street scale was shown as a single center structure; the spatial agglomeration of FAR in plot scale was represented by multi-center structure; the circle structure model was used to calculate the FAR of the circle in different places, different regions showed different laws, the urban expansion trend was obvious, and the public service and other supporting construction were insufficient; 13 urban centers in Shenyang were identified by kernel density method according to FAR of plot. The current multi-center structure could not meet the needs of residents’ life and urban development.
2022, 52(8): 78-84,126.
doi: 10.13204/j.gyjzG21081017
Abstract:
The co-existence between excellent experimental buildings and the surroundings is one of important engines for promoting regeneration of new functions of the cultural heritage and the prosperity of cultural tourism economy, as well as an important booster for rural revitalization.Chi Chu Art Museum on Choku Island, Japan and Zhangyan Cultural Center in Qingpu District, Shanghai are both typical cases of promoting rural cultural tourism economy through experimental buildings, which has played a critical leading role in local rural culture revitalization and rural cultural tourism construction. By comparative analysis for the two cases on integration of buildings with surroundings, design styles, organization of architecture spaces and intervention of arts in rural areas, the commonality for experimental buildings and artistry of in rural construction in rural revitalization was summarized and the thoughts for rural revitalization construction, planning and layout were presented.
The co-existence between excellent experimental buildings and the surroundings is one of important engines for promoting regeneration of new functions of the cultural heritage and the prosperity of cultural tourism economy, as well as an important booster for rural revitalization.Chi Chu Art Museum on Choku Island, Japan and Zhangyan Cultural Center in Qingpu District, Shanghai are both typical cases of promoting rural cultural tourism economy through experimental buildings, which has played a critical leading role in local rural culture revitalization and rural cultural tourism construction. By comparative analysis for the two cases on integration of buildings with surroundings, design styles, organization of architecture spaces and intervention of arts in rural areas, the commonality for experimental buildings and artistry of in rural construction in rural revitalization was summarized and the thoughts for rural revitalization construction, planning and layout were presented.
2022, 52(8): 85-90.
doi: 10.13204/j.gyjzG21123009
Abstract:
As the first high-voltage switch factory in China, Shenyang high-voltage switch factory is the most complete historical area of industrial heritage in Shenyang at present. Its industrial process reflects the national advanced high-voltage switch production technology level, plays an important role in the historical process of China’s industrial development, and has important historical, scientific and technological values.Taking the industrial process of industrial heritage as the starting point, historical map archaeology, field archaeology and information archaeology were carried out on the basis of field investigation and data collection, and the difficulties encountered in the protection and utilization of the industrial process of Shenyang high-voltage switch plant were summarized through analysis and summary, so as to the protection measures and display and utilization strategies of the core industrial process were put forward, which could provide the basis for the historical reappearance of industrial process in Shenyang high-voltage switch plant.
As the first high-voltage switch factory in China, Shenyang high-voltage switch factory is the most complete historical area of industrial heritage in Shenyang at present. Its industrial process reflects the national advanced high-voltage switch production technology level, plays an important role in the historical process of China’s industrial development, and has important historical, scientific and technological values.Taking the industrial process of industrial heritage as the starting point, historical map archaeology, field archaeology and information archaeology were carried out on the basis of field investigation and data collection, and the difficulties encountered in the protection and utilization of the industrial process of Shenyang high-voltage switch plant were summarized through analysis and summary, so as to the protection measures and display and utilization strategies of the core industrial process were put forward, which could provide the basis for the historical reappearance of industrial process in Shenyang high-voltage switch plant.
2022, 52(8): 91-96,151.
doi: 10.13204/j.gyjzG21111718
Abstract:
The COVID-19 has a huge impact and caused significant human and economic losses. Hub-airport terminals play an important role in epidemic prevention and control but are not conducive to the response, because of the lack of architectural theories and methods for epidemic control. Based on the usage pattern and guided by the problems, the paper proposed the concept of partitioned epidemic control in hub-airport terminals. Based on the departure process, the partitioned epidemic control mode was constructed by integrated key elements of epidemic control. Guided by the combination of epidemic control and normal condition, the partitioned epidemic control strategies and architectural design measures were formulated. The concept and strategies of partitioned epidemic control are beneficial attempt to the theory and method of epidemic control in hub-airport terminals.
The COVID-19 has a huge impact and caused significant human and economic losses. Hub-airport terminals play an important role in epidemic prevention and control but are not conducive to the response, because of the lack of architectural theories and methods for epidemic control. Based on the usage pattern and guided by the problems, the paper proposed the concept of partitioned epidemic control in hub-airport terminals. Based on the departure process, the partitioned epidemic control mode was constructed by integrated key elements of epidemic control. Guided by the combination of epidemic control and normal condition, the partitioned epidemic control strategies and architectural design measures were formulated. The concept and strategies of partitioned epidemic control are beneficial attempt to the theory and method of epidemic control in hub-airport terminals.
2022, 52(8): 97-102.
doi: 10.13204/j.gyjzG21101322
Abstract:
In order to study the seismic performance of existing reinforced concrete structures in cold and seismic regions, the results of the quasi-static tests of eight reinforced concrete columns subjected to freezing-thawing cycles were analyzed. Considering the impacts of freezing-thawing cycle times and axial compression ratio on the bearing capacity and hysteretic behavior of member columns, a trilinear skeleton curve was proposed. Besides, the calculation formula of unloading stiffness before and after yield and specific hysteretic rules were obtained, furthermore, the stiffness degradation trilinear restoring force model of "pointing point" of freezing-thawing damaged reinforced concrete columns was established. The comparative analysis between the test curves and the calculation curves showed that the proposed restoring force model had a certain accuracy, which could provide a theoretical basis for the seismic response analysis of reinforced concrete columns in freeze-thaw environment.
In order to study the seismic performance of existing reinforced concrete structures in cold and seismic regions, the results of the quasi-static tests of eight reinforced concrete columns subjected to freezing-thawing cycles were analyzed. Considering the impacts of freezing-thawing cycle times and axial compression ratio on the bearing capacity and hysteretic behavior of member columns, a trilinear skeleton curve was proposed. Besides, the calculation formula of unloading stiffness before and after yield and specific hysteretic rules were obtained, furthermore, the stiffness degradation trilinear restoring force model of "pointing point" of freezing-thawing damaged reinforced concrete columns was established. The comparative analysis between the test curves and the calculation curves showed that the proposed restoring force model had a certain accuracy, which could provide a theoretical basis for the seismic response analysis of reinforced concrete columns in freeze-thaw environment.
2022, 52(8): 103-110.
doi: 10.13204/j.gyjzG21092202
Abstract:
In order to study the influence of construction technology on the fatigue performance of pre-stressed composite beams, the constant-amplitude fatigue experiment was carried out.Four pre-stressed ceramsite concrete and ordinary concrete composite beams were fabricated, two of which were subjected to two-point static loading and two were subjected to two-point fatigue bending. The experiment results showed that the flexural performance of prestressed ceramsite concrete T-beam members was continuously attenuated with the increase of the number of fatigue cycles. As the number of fatigue loading increased, the deflection value and the strain value of steel bars under the static load of the same level generally showed an increasing trend, but the magnitude of the change was small. The maximum crack width and average crack width increased with the increase of the number of fatigue cycles. For the test beams that had experienced cyclic loading 2 million times without fatigue failure, the failure mode under static loading was still typical bending failure, and its residual bearing capacity was significantly lower than that of the test beams under static loading, and the post-tensioned prestressed beam had a more obvious decline compared to the pre-tensioned prestressed beam.
In order to study the influence of construction technology on the fatigue performance of pre-stressed composite beams, the constant-amplitude fatigue experiment was carried out.Four pre-stressed ceramsite concrete and ordinary concrete composite beams were fabricated, two of which were subjected to two-point static loading and two were subjected to two-point fatigue bending. The experiment results showed that the flexural performance of prestressed ceramsite concrete T-beam members was continuously attenuated with the increase of the number of fatigue cycles. As the number of fatigue loading increased, the deflection value and the strain value of steel bars under the static load of the same level generally showed an increasing trend, but the magnitude of the change was small. The maximum crack width and average crack width increased with the increase of the number of fatigue cycles. For the test beams that had experienced cyclic loading 2 million times without fatigue failure, the failure mode under static loading was still typical bending failure, and its residual bearing capacity was significantly lower than that of the test beams under static loading, and the post-tensioned prestressed beam had a more obvious decline compared to the pre-tensioned prestressed beam.
2022, 52(8): 111-118.
doi: 10.13204/j.gyjzG21123003
Abstract:
By conducting axial compression tests and finite element analysis on three double-faced precast concrete superposed shear wall(DPCW)specimens, the damage patterns, deformation and ultimate bearing capacity of double-faced precast concrete superposed shear walls under axial load were studied, and the effects of different connection methods between steel truss and distributed reinforcement mesh on the mechanical properties of double-faced precast concrete superposed shear wall specimens were analyzed. The test results showed that the damage of double-faced precast concrete superposed shear walls under axial load started from the cracking of the concrete laminated surface of the precast and post-cast layers, and when the ultimate load was reached, the cracks of laminated surface on both sides of wall slabs were penetrated, and concrete of wall slabs was crushed. In this test, the ultimate bearing capacity of the specimen of double-faced precast concrete superposed shear wall with tied connection of reinforcement joist and distribution bar mesh was higher than that of the specimen with welded connection. The finite element calculation results of double-faced precast concrete superposed shear wall specimens were in good agreement with the test results; the parameter analysis results showed that increasing the friction coefficient of precast-postcast concrete laminated surface and the diameter of web reinforcement of steel truss could significantly improve the ultimate bearing capacity of laminated wall slabs.
By conducting axial compression tests and finite element analysis on three double-faced precast concrete superposed shear wall(DPCW)specimens, the damage patterns, deformation and ultimate bearing capacity of double-faced precast concrete superposed shear walls under axial load were studied, and the effects of different connection methods between steel truss and distributed reinforcement mesh on the mechanical properties of double-faced precast concrete superposed shear wall specimens were analyzed. The test results showed that the damage of double-faced precast concrete superposed shear walls under axial load started from the cracking of the concrete laminated surface of the precast and post-cast layers, and when the ultimate load was reached, the cracks of laminated surface on both sides of wall slabs were penetrated, and concrete of wall slabs was crushed. In this test, the ultimate bearing capacity of the specimen of double-faced precast concrete superposed shear wall with tied connection of reinforcement joist and distribution bar mesh was higher than that of the specimen with welded connection. The finite element calculation results of double-faced precast concrete superposed shear wall specimens were in good agreement with the test results; the parameter analysis results showed that increasing the friction coefficient of precast-postcast concrete laminated surface and the diameter of web reinforcement of steel truss could significantly improve the ultimate bearing capacity of laminated wall slabs.
2022, 52(8): 119-126.
doi: 10.13204/j.gyjzG22022203
Abstract:
The composite passive control scheme of seismic isolation and tower damping was applied to the twin-tower structure with large-chassis, with the total structural vibration energy minimization as the optimal control objective, the stochastic response expression of the structure was derived, and the optimal control parameters and the influence law of the connecting control parameters on the control effect were analyzed in the equivalent single-DOF simplified model based on the Kanai-Tajimi spectral stochastic ground vibration model, and this parameter was applied to the twin-tower structure with large-chassis. The control effects on the structural response were analyzed in the time domain and frequency domain, and the control effects of the seismic scheme, the seismic isolation scheme and the composite passive control scheme were compared and analyzed to verify the rationality and effectiveness of the composite passive control scheme for the twin-tower structure with large chassis . The results showed that both the isolation scheme and the isolation and absorption composite passive control scheme could play a good control effect on the energy and displacement response of the twin-tower structure with large chassis, and the composite passive control scheme showed a better control effect.
The composite passive control scheme of seismic isolation and tower damping was applied to the twin-tower structure with large-chassis, with the total structural vibration energy minimization as the optimal control objective, the stochastic response expression of the structure was derived, and the optimal control parameters and the influence law of the connecting control parameters on the control effect were analyzed in the equivalent single-DOF simplified model based on the Kanai-Tajimi spectral stochastic ground vibration model, and this parameter was applied to the twin-tower structure with large-chassis. The control effects on the structural response were analyzed in the time domain and frequency domain, and the control effects of the seismic scheme, the seismic isolation scheme and the composite passive control scheme were compared and analyzed to verify the rationality and effectiveness of the composite passive control scheme for the twin-tower structure with large chassis . The results showed that both the isolation scheme and the isolation and absorption composite passive control scheme could play a good control effect on the energy and displacement response of the twin-tower structure with large chassis, and the composite passive control scheme showed a better control effect.
2022, 52(8): 127-131,174.
doi: 10.13204/j.gyjzG21052003
Abstract:
In order to research the stress and seismic performance of joints between the tank wall and ring beam of large-scale liquefied natural gas (LNG) concrete full-capacity storage tanks,a 160 000 m3LNG concretefull-capacity storage tank was used as a prototype to conduct model test.The bearing capacity, failure mode, stiffness and energy dissipation capacity were studied by quasi-static test.The results showed that the joint between the tank wall and ring beam of the 160 000 m3LNG concrete full-capacity storage tank was not damaged when the tank wall was damaged, which conformed to the design principle of "strong joint" for large-scale concrete structures. However,the energy dissipation capacity of the structure was poor, the maximum energy dissipation coefficient before failure was 0.685, the residual secant stiffness was 0.878 kN/mm, the stiffness degradation coefficient was 0.17, and the residual stiffness was small.
In order to research the stress and seismic performance of joints between the tank wall and ring beam of large-scale liquefied natural gas (LNG) concrete full-capacity storage tanks,a 160 000 m3LNG concretefull-capacity storage tank was used as a prototype to conduct model test.The bearing capacity, failure mode, stiffness and energy dissipation capacity were studied by quasi-static test.The results showed that the joint between the tank wall and ring beam of the 160 000 m3LNG concrete full-capacity storage tank was not damaged when the tank wall was damaged, which conformed to the design principle of "strong joint" for large-scale concrete structures. However,the energy dissipation capacity of the structure was poor, the maximum energy dissipation coefficient before failure was 0.685, the residual secant stiffness was 0.878 kN/mm, the stiffness degradation coefficient was 0.17, and the residual stiffness was small.
2022, 52(8): 132-139.
doi: 10.13204/j.gyjzG21112215
Abstract:
The prestressed tension overall structure represented by cable dome and suspended dome is novel and beautiful in appearance and has high structural efficiency.During the tensioning process of cable dome and suspended dome, the friction between the ring cable and the cable strut joint will cause the loss of prestress, which will lead to a significant decrease in the mechanical properties of the prestressed structure after forming. A new type of hemispherical sliding cable strut joint was proposed. The hemispherical cover plate is easy to connect multi-directional components, and the rollers are embedded with rolling bearings, which reduces the friction coefficient with the central axis and effectively reduces the prestress loss rate. The finite element analysis of the mechanical properties of the hemispherical sliding cable-strut joint was carried out by ABAQUS, and the reliability of the finite element model was verified by comparing the measured data of the experiment. Finite element analysis showed that the cable-strut joint had good performance and could meet the design requirements. By comparing the finite element and test results, the prestress loss of this joint was about 4.2% under the actual working conditions, which was greatly reduced compared to the traditional cable-strut joint with a prestress loss of more than 10%.
The prestressed tension overall structure represented by cable dome and suspended dome is novel and beautiful in appearance and has high structural efficiency.During the tensioning process of cable dome and suspended dome, the friction between the ring cable and the cable strut joint will cause the loss of prestress, which will lead to a significant decrease in the mechanical properties of the prestressed structure after forming. A new type of hemispherical sliding cable strut joint was proposed. The hemispherical cover plate is easy to connect multi-directional components, and the rollers are embedded with rolling bearings, which reduces the friction coefficient with the central axis and effectively reduces the prestress loss rate. The finite element analysis of the mechanical properties of the hemispherical sliding cable-strut joint was carried out by ABAQUS, and the reliability of the finite element model was verified by comparing the measured data of the experiment. Finite element analysis showed that the cable-strut joint had good performance and could meet the design requirements. By comparing the finite element and test results, the prestress loss of this joint was about 4.2% under the actual working conditions, which was greatly reduced compared to the traditional cable-strut joint with a prestress loss of more than 10%.
2022, 52(8): 140-146.
doi: 10.13204/j.gyjzG21102801
Abstract:
A three-span continuous rigid framed bridge model with a geometric similarity ratio of 1/10 was designed to carry out the corresponding shaking table tests. In the test, soil-structure interaction was considered. On the basis of the experiment, the finite element analysis model was established. Ten typical near-fault ground motions were selected to carry out the full-bridge numerical simulation analysis. Taking the Penzien model as a benchmark, a comparative study of the influence of the SSI effect on the seismic response of key components of rigid frame bridges was carried out. The results showed that SSI effect had significant influence on seismic response of rigid frame bridge. SSI effect could increase the displacement response and strain response by more than 0.2 times and 0.5 times respectively. Compared with the far-field earthquake, the internal force and deformation of the structure were increased by more than one time under the action of near-fault earthquake. Both near-fault and SSI effects would further amplify the adverse effects also should be considered. Both near-fault effect and SSI effect were unfavorable factors for seismic response of rigid frame bridge, which should be taken into precise consideration in seismic design to ensure structural safety.
A three-span continuous rigid framed bridge model with a geometric similarity ratio of 1/10 was designed to carry out the corresponding shaking table tests. In the test, soil-structure interaction was considered. On the basis of the experiment, the finite element analysis model was established. Ten typical near-fault ground motions were selected to carry out the full-bridge numerical simulation analysis. Taking the Penzien model as a benchmark, a comparative study of the influence of the SSI effect on the seismic response of key components of rigid frame bridges was carried out. The results showed that SSI effect had significant influence on seismic response of rigid frame bridge. SSI effect could increase the displacement response and strain response by more than 0.2 times and 0.5 times respectively. Compared with the far-field earthquake, the internal force and deformation of the structure were increased by more than one time under the action of near-fault earthquake. Both near-fault and SSI effects would further amplify the adverse effects also should be considered. Both near-fault effect and SSI effect were unfavorable factors for seismic response of rigid frame bridge, which should be taken into precise consideration in seismic design to ensure structural safety.
2022, 52(8): 147-151.
doi: 10.13204/j.gyjzG21070301
Abstract:
In order to promote the application of steel-concrete composite beam in bridge structures and crane beams, the fatigue performance of composite beams has attracted researchers' attention. However, the basis for judging the fatigue failure mode of composite beams has not given. In the paper, stress amplitude index was defined based on the main experimental results and reasoning at home and abroad, which was the basis for judging the fatigue failure mode of composite beams. The fatigue tests of composite beams with different shear connection degrees and different details of steel beams were carried out so that the specific criteria for fatigue failure modes was obtained combined with the related parameters of steel beam details given by Standard for Design of Steel Structures (GB 50017-2017). It verified the fatigue failure modes of 13 test beams with different shear connection degrees. The results showed that it was feasible to judge the fatigue failure mode by stress amplitude index.
In order to promote the application of steel-concrete composite beam in bridge structures and crane beams, the fatigue performance of composite beams has attracted researchers' attention. However, the basis for judging the fatigue failure mode of composite beams has not given. In the paper, stress amplitude index was defined based on the main experimental results and reasoning at home and abroad, which was the basis for judging the fatigue failure mode of composite beams. The fatigue tests of composite beams with different shear connection degrees and different details of steel beams were carried out so that the specific criteria for fatigue failure modes was obtained combined with the related parameters of steel beam details given by Standard for Design of Steel Structures (GB 50017-2017). It verified the fatigue failure modes of 13 test beams with different shear connection degrees. The results showed that it was feasible to judge the fatigue failure mode by stress amplitude index.
2022, 52(8): 152-159,8.
doi: 10.13204/j.gyjzG22010508
Abstract:
This study focused on improving the connection stiffness of modern bamboo structures. Total twelve groups, each including six identical glubam specimens with glued-in single threaded rod, were tested to failure in the pull-pull configuration. It was observed that the specimens exhibited four different failure modes, including two types of the shear failure at different interfaces, the yield failure of threaded rod, and the splitting failure of glubam. In order to control yield failure mode, the lower limit of bond length-diameter ratio could be taken as 12.5 and 15 for thread rods of M12 and M16, respectively. Analysis results showed that the bond strength of glued-in single threaded rod in glubam increased as increasing the drill-hole diameter, while it reduced as increasing the bond length-diameter ratio. Typical existing strength models for glued-in rod in timber were not fit to predict the bond strength of glued-in threaded rod in glubam. Based on test data in this investigation, a strength model was also proposed for the glued-in single threaded rod in glubam, and it showed a good prediction accuracy.
This study focused on improving the connection stiffness of modern bamboo structures. Total twelve groups, each including six identical glubam specimens with glued-in single threaded rod, were tested to failure in the pull-pull configuration. It was observed that the specimens exhibited four different failure modes, including two types of the shear failure at different interfaces, the yield failure of threaded rod, and the splitting failure of glubam. In order to control yield failure mode, the lower limit of bond length-diameter ratio could be taken as 12.5 and 15 for thread rods of M12 and M16, respectively. Analysis results showed that the bond strength of glued-in single threaded rod in glubam increased as increasing the drill-hole diameter, while it reduced as increasing the bond length-diameter ratio. Typical existing strength models for glued-in rod in timber were not fit to predict the bond strength of glued-in threaded rod in glubam. Based on test data in this investigation, a strength model was also proposed for the glued-in single threaded rod in glubam, and it showed a good prediction accuracy.
2022, 52(8): 160-167.
doi: 10.13204/j.gyjzG21030203
Abstract:
Based on Lemaitre’s hypothesis theory of strain equivalence, it was assumed that the micro-element strength of rock subjected to thermal-mechanical coupling damage followed the Weibull distribution. Considering the influence of temperature and confining pressure coupling on rock mechanical parameters, the thermal-mechanical damage variables were introduced by the damage mechanic theory. In the condition that the microelement failure conformed to the D-P criterion, the damage evolution equation for coupling of temperature and mechanics and the constitutive model of rock were established. The required model parameters were derived by the theory. Comparing between the peak points in the established constitutire model curves for thermal-mechanical coupling demage and experimental curves, the results showed that the two curves were in good agreement, the model could well reflect the damage evolution and the constitutive relation for rock in the coupling of temperature and confining pressure. The rationality and reliability of the model and the method to determine the model parameters were verified. The model parameters required by the model could be obtained by conventional triaxial tests in laboratory.
Based on Lemaitre’s hypothesis theory of strain equivalence, it was assumed that the micro-element strength of rock subjected to thermal-mechanical coupling damage followed the Weibull distribution. Considering the influence of temperature and confining pressure coupling on rock mechanical parameters, the thermal-mechanical damage variables were introduced by the damage mechanic theory. In the condition that the microelement failure conformed to the D-P criterion, the damage evolution equation for coupling of temperature and mechanics and the constitutive model of rock were established. The required model parameters were derived by the theory. Comparing between the peak points in the established constitutire model curves for thermal-mechanical coupling demage and experimental curves, the results showed that the two curves were in good agreement, the model could well reflect the damage evolution and the constitutive relation for rock in the coupling of temperature and confining pressure. The rationality and reliability of the model and the method to determine the model parameters were verified. The model parameters required by the model could be obtained by conventional triaxial tests in laboratory.
2022, 52(8): 168-174.
doi: 10.13204/j.gyjzG21011102
Abstract:
In view of the problem that the relation between pressure of brittleness to ductility transition on deep shale gas caprock and dip angles of stratification were indefinite, uniaxial and triaxial compression tests of rock were conducted from the perspective of physical and mechanical properties of rock. Based on Hoek-Brown Failure Criterion, stratification damage was introduced to predict the critical pressure of brittleness to ductility transition. The results showed that: to increase confining pressure could restrained the effect of stratification on mechanical properties of rock; with the increase of confining pressure, the failure mode of shale gradually tended to shear failure with a single fracture;stratification surfaces played a certain role in controlling the pressure of brittleness to ductility transition, and the pressure of brittleness to ductility transition in parallel and vertical stratification directions was significantly higher than that of rock at other dip angle directions with stratification.
In view of the problem that the relation between pressure of brittleness to ductility transition on deep shale gas caprock and dip angles of stratification were indefinite, uniaxial and triaxial compression tests of rock were conducted from the perspective of physical and mechanical properties of rock. Based on Hoek-Brown Failure Criterion, stratification damage was introduced to predict the critical pressure of brittleness to ductility transition. The results showed that: to increase confining pressure could restrained the effect of stratification on mechanical properties of rock; with the increase of confining pressure, the failure mode of shale gradually tended to shear failure with a single fracture;stratification surfaces played a certain role in controlling the pressure of brittleness to ductility transition, and the pressure of brittleness to ductility transition in parallel and vertical stratification directions was significantly higher than that of rock at other dip angle directions with stratification.
Experimental Study on the Influence of Joint Fillers on the Crack Initiation Strength of Rock Masses
2022, 52(8): 175-179.
doi: 10.13204/j.gyjzG21062915
Abstract:
Three kinds of materials—cement, mud and gypsum, were used as fillers to fill jointed rock specimens with single crack, and uniaxial compression tests were conducted on the specimens. The analytical expression about initiation strength of crack for closed crack under uniaxial compression was established and numerical simulations were performed to further study it. The results showed that under uniaxial compression, the initiation strength of crack for specimens simulated by the friction coefficient theory was basically consistent with the peak strength from indoor tests. The larger the friction coefficients of fillers were, the less easier the damage of jointed rock masses, and the initiation strength of crack for rock masses with fillers was greatly improved than that without fillers. The peak strength of cement-filled jointed specimens was highest and mud-filled jointed specimens was lowest. Shear failure was the main failure mode of specimens filled with mud, the failure form of specimens filled with cement and gypsum was complex. With the increase of filler strength, the failure mode of jointed rock mass would change from shear failure to tension failure.
Three kinds of materials—cement, mud and gypsum, were used as fillers to fill jointed rock specimens with single crack, and uniaxial compression tests were conducted on the specimens. The analytical expression about initiation strength of crack for closed crack under uniaxial compression was established and numerical simulations were performed to further study it. The results showed that under uniaxial compression, the initiation strength of crack for specimens simulated by the friction coefficient theory was basically consistent with the peak strength from indoor tests. The larger the friction coefficients of fillers were, the less easier the damage of jointed rock masses, and the initiation strength of crack for rock masses with fillers was greatly improved than that without fillers. The peak strength of cement-filled jointed specimens was highest and mud-filled jointed specimens was lowest. Shear failure was the main failure mode of specimens filled with mud, the failure form of specimens filled with cement and gypsum was complex. With the increase of filler strength, the failure mode of jointed rock mass would change from shear failure to tension failure.
2022, 52(8): 180-186.
doi: 10.13204/j.gyjzG21070808
Abstract:
In view of the phenomenon that the bearing capacity of anchor bolts in soil declines due to the large temperature differences between day and night and the geology of soft sand layer in Northwest China, the bearing characteristics of underreamed anchor bolts in aeolian sand and the influence of freeze-thaw cycles were studied. Based on 12 model test groups, the ultimate bearing capacity, load-displacement relations, stress in soil layers and the change of failure modes for anchor bolts with 6 types of anchor ends in different freeze-thaw cycles were obtained. The results showed that the ultimate bearing capacity of the underreamed anchor bolts had larger growth protential in the condition of high confining pressure (deep buried in aeolian sand). The increase of anchored end volumes could effectively improve the ultimate bearing capacity of underreamed bolts in aeolian sand, and existed an optimal design ratio of anchorage ends. With the increase of freeze-thaw cycles, the appearance of inflection points in load-displacement curves and the ultimate bearing capacity were advanced. The stress in the soil layer changed abruptly and the attenuation accelerated rapidly, then the deformation increased at the time of failure
In view of the phenomenon that the bearing capacity of anchor bolts in soil declines due to the large temperature differences between day and night and the geology of soft sand layer in Northwest China, the bearing characteristics of underreamed anchor bolts in aeolian sand and the influence of freeze-thaw cycles were studied. Based on 12 model test groups, the ultimate bearing capacity, load-displacement relations, stress in soil layers and the change of failure modes for anchor bolts with 6 types of anchor ends in different freeze-thaw cycles were obtained. The results showed that the ultimate bearing capacity of the underreamed anchor bolts had larger growth protential in the condition of high confining pressure (deep buried in aeolian sand). The increase of anchored end volumes could effectively improve the ultimate bearing capacity of underreamed bolts in aeolian sand, and existed an optimal design ratio of anchorage ends. With the increase of freeze-thaw cycles, the appearance of inflection points in load-displacement curves and the ultimate bearing capacity were advanced. The stress in the soil layer changed abruptly and the attenuation accelerated rapidly, then the deformation increased at the time of failure
2022, 52(8): 187-193,110.
doi: 10.13204/j.gyjzG21060212
Abstract:
Aiming at a new geotechnical reinforcing material—denti-geogrids, pullout tests were simulated by numerical simulations. The accuracy for calculation results of the ultimate pullout resistance for denti-geogrids with a single transverse rib by the flow-around model, Peterson-Anderson model, Jewell model, Chai model and Rankine model, as well as the numerical analysis model were comparatively researched. And the friction characteristics of the interfaces were studied and the formula for the ultimate pullout resistance of denti-geogrids with multi-ribs was put forward on the basis of factor analysis. Researches showed that: 1) For denti-geogrid with a single transverse rib, the ultimate pullout resistance calculated by Jewell model was closest to the numerical simulation result (with an average error of 5.35%), the Rankine model was relatively simple and precise for engineering application. 2) In the same test conditions, the pullout resistance of denti-geogrids was much higher than that of common geogrids. Also, the interface cohesion, friction angles, pullout coefficients, and apparent friction coefficients of denti-geogrids at all levels of normal stress were larger. 3) For denti-geogrids with multi-ribs, the relations for the ultimate pullout resistance between the detni-geogrid rib quantities, spacing and normal stress were separately exponential, logarithmic and linear. The ultimate pullout resistance for denti-geogrids with multi-ribs in different working conditions was calculated by the suggested formula, and the reliability was verified.
Aiming at a new geotechnical reinforcing material—denti-geogrids, pullout tests were simulated by numerical simulations. The accuracy for calculation results of the ultimate pullout resistance for denti-geogrids with a single transverse rib by the flow-around model, Peterson-Anderson model, Jewell model, Chai model and Rankine model, as well as the numerical analysis model were comparatively researched. And the friction characteristics of the interfaces were studied and the formula for the ultimate pullout resistance of denti-geogrids with multi-ribs was put forward on the basis of factor analysis. Researches showed that: 1) For denti-geogrid with a single transverse rib, the ultimate pullout resistance calculated by Jewell model was closest to the numerical simulation result (with an average error of 5.35%), the Rankine model was relatively simple and precise for engineering application. 2) In the same test conditions, the pullout resistance of denti-geogrids was much higher than that of common geogrids. Also, the interface cohesion, friction angles, pullout coefficients, and apparent friction coefficients of denti-geogrids at all levels of normal stress were larger. 3) For denti-geogrids with multi-ribs, the relations for the ultimate pullout resistance between the detni-geogrid rib quantities, spacing and normal stress were separately exponential, logarithmic and linear. The ultimate pullout resistance for denti-geogrids with multi-ribs in different working conditions was calculated by the suggested formula, and the reliability was verified.
2022, 52(8): 194-200,146.
doi: 10.13204/j.gyjzG21111009
Abstract:
Utilizing recycled rubber particles prepared from waste tires and recycled aggregates crushed from waste concrete is one of the important ways for the sustainable development of building materials. Incorporation of rubber modification significantly affects the damping characteristics and damage development of recycled aggregate concrete (RAC). Considering the effect of rubber replacement ratio by volume, silane coupling agent and defoamer, the first-order natural frequency and damping ratio of rubber modified recycled aggregate concrete (RRAC) subjected to cyclic loadings with different stress amplitudes were measured by suspension free vibration method, and its dynamic elastic modulus and loss modulus were quantitatively evaluated with the recorded data. The evolution of RRAC damping characteristics with damage index was revealed. The results showed that the first-order damping ratio of RRAC at the elastic stage increases by 10.2% to 30.6% with the increasing of rubber replacement ratio, while the dynamic elastic modulus decreased by 4.2% to 22.0%. The Presoaking of rubber particles with silane coupling agent and the addition of defoamer increased the dynamic elastic modulus of RRAC by 5.1% to 21.0%, but reduced the first-order damping ratio of RRAC by 7.1% to 17.2%. The damage index of RRAC increased rapidly first then slowly with increasing stress amplitude, which was opposite to that of RAC, and the damage index of RRAC was larger than that of RAC. This was mainly attributed to the weak interface of the rubber particles. Besides, the first-order damping ratio of RRAC increased linearly with the increase of damage index. 10% dosage of rubber content could increase the first-order damping ratio and loss modulus, and increase the energy dissipation capacity of RRAC.
Utilizing recycled rubber particles prepared from waste tires and recycled aggregates crushed from waste concrete is one of the important ways for the sustainable development of building materials. Incorporation of rubber modification significantly affects the damping characteristics and damage development of recycled aggregate concrete (RAC). Considering the effect of rubber replacement ratio by volume, silane coupling agent and defoamer, the first-order natural frequency and damping ratio of rubber modified recycled aggregate concrete (RRAC) subjected to cyclic loadings with different stress amplitudes were measured by suspension free vibration method, and its dynamic elastic modulus and loss modulus were quantitatively evaluated with the recorded data. The evolution of RRAC damping characteristics with damage index was revealed. The results showed that the first-order damping ratio of RRAC at the elastic stage increases by 10.2% to 30.6% with the increasing of rubber replacement ratio, while the dynamic elastic modulus decreased by 4.2% to 22.0%. The Presoaking of rubber particles with silane coupling agent and the addition of defoamer increased the dynamic elastic modulus of RRAC by 5.1% to 21.0%, but reduced the first-order damping ratio of RRAC by 7.1% to 17.2%. The damage index of RRAC increased rapidly first then slowly with increasing stress amplitude, which was opposite to that of RAC, and the damage index of RRAC was larger than that of RAC. This was mainly attributed to the weak interface of the rubber particles. Besides, the first-order damping ratio of RRAC increased linearly with the increase of damage index. 10% dosage of rubber content could increase the first-order damping ratio and loss modulus, and increase the energy dissipation capacity of RRAC.
2022, 52(8): 201-207.
doi: 10.13204/j.gyjzG22030604
Abstract:
The rebar sleeve grouting connection is often incompletely filled due to unsatisfactory fluidity of grouting material, which needs to be repaired properly. To improve the workability and quality of the grouting repairing construction, a cementitious repairing grouting material (CRGM) was first prepared, then the relevant properties of CRGM and ordinary rebar sleeve grouting material (ORSGM) were experimentally compared. The results showed that the 28 d compressive strength of present CRGM was 96.4 MPa, and early-age vertical expansion rate from 3 h to 24 h was 0.23, which both could meet the index requirements of ORSGM in Cementitious Grout for Sleeve of Rebar Splicing (JG/T 408—2019). Truncated cone fluidity,flow cone fluidity and their 30 minutes retention values of CRGM were obviously much better than that of ORSGM. Comparing with ORSGM at the age of 28 days, the mercury intrusion testing results and cluster analysis of nano-indentation data indicated that the pore structure of CRGM was finer, and the hardness and elastic modulus of the hardened cement paste were higher. The field application also showed that the CRGM had an obvious advantage in groutability, and could be used for repairing construction of the not-full-filled grouting of the reinforcement sleeve grouting connection in the future.
The rebar sleeve grouting connection is often incompletely filled due to unsatisfactory fluidity of grouting material, which needs to be repaired properly. To improve the workability and quality of the grouting repairing construction, a cementitious repairing grouting material (CRGM) was first prepared, then the relevant properties of CRGM and ordinary rebar sleeve grouting material (ORSGM) were experimentally compared. The results showed that the 28 d compressive strength of present CRGM was 96.4 MPa, and early-age vertical expansion rate from 3 h to 24 h was 0.23, which both could meet the index requirements of ORSGM in Cementitious Grout for Sleeve of Rebar Splicing (JG/T 408—2019). Truncated cone fluidity,flow cone fluidity and their 30 minutes retention values of CRGM were obviously much better than that of ORSGM. Comparing with ORSGM at the age of 28 days, the mercury intrusion testing results and cluster analysis of nano-indentation data indicated that the pore structure of CRGM was finer, and the hardness and elastic modulus of the hardened cement paste were higher. The field application also showed that the CRGM had an obvious advantage in groutability, and could be used for repairing construction of the not-full-filled grouting of the reinforcement sleeve grouting connection in the future.
2022, 52(8): 208-214,139.
doi: 10.13204/j.gyjzG21033001
Abstract:
Based on the understanding of the connotation of library, it is the dissemination of knowledge for people, the symbol of culture for regions, and the expression of civilization for times. Therefore, the construction of library needs to answer the question of coordination between regional culture and modern civilization. Taking the library of Guizhou Anshun Vocational and Technical College as an example, the project explored a way and strategy of 'dialogue between tradition and modernity’ based on an attitude of regression and introspection. The design applied the theory of local and thinking of place. Through the interpretation of the project site, the integration of terrain, the cause of climate and the reconstruction of space, the building returned to a local expression and reshaped a place spirit. The design exploration of the project is not a symbolic reappearance of tradition and place, but an interpretation of a regressive design strategy in a critical and introspective way in the context of the times. It is regarded as a reference of traditional regional architecture practice as well as a comparison of design methods.
Based on the understanding of the connotation of library, it is the dissemination of knowledge for people, the symbol of culture for regions, and the expression of civilization for times. Therefore, the construction of library needs to answer the question of coordination between regional culture and modern civilization. Taking the library of Guizhou Anshun Vocational and Technical College as an example, the project explored a way and strategy of 'dialogue between tradition and modernity’ based on an attitude of regression and introspection. The design applied the theory of local and thinking of place. Through the interpretation of the project site, the integration of terrain, the cause of climate and the reconstruction of space, the building returned to a local expression and reshaped a place spirit. The design exploration of the project is not a symbolic reappearance of tradition and place, but an interpretation of a regressive design strategy in a critical and introspective way in the context of the times. It is regarded as a reference of traditional regional architecture practice as well as a comparison of design methods.
2022, 52(8): 215-221,186.
doi: 10.13204/j.gyjzG21111814
Abstract:
The height of Kunming China Railway building project is 226 m, and the seismic fortification intensity is 8 degrees. The structure has some problems of exceeding codes limits, such as irregular torsion, eccentric layout, discontinuity floor slabs, inclined column and so on. In order to solve aforementioned problems, the project creatively adopted the "high ductility, high energy dissipation" structure system, and targeted research was carried out on the problem, and finally the elastic-plastic verification under rare earthquake and very rare earthquake was carried out. The results showed that the torsional displacement ratio could be controlled by adopting the dense columns and diagonal braces; the tower could be divided into low-rise tower and high-rise tower, the eccentricity of stiffness center and mass center of the two parts was adjusted recpectively, the whole tower would not be twisted; after linear assembly, the discontinuity of slabs had no effect on the integrity of tower; the cracks of floor slabs could be controlled by post pouring concrete; the tower had strong torsion resistance, and eccentric load had no effect on its mechanical properties under rare earthquake; the equivalent damping ratio of the structure under rare earthquake was 11.5%, and the corrugated web steel coupling beam and SRC coupling beam were used to realize high energy dissipation; 1.2 times of rare earthquake caused tower collapse; as the second line of defense of the structure, the outer frame was weak, and the shear walls in the collapse related area should be equipped with section steel to improve the collapse resistance of the structure.
The height of Kunming China Railway building project is 226 m, and the seismic fortification intensity is 8 degrees. The structure has some problems of exceeding codes limits, such as irregular torsion, eccentric layout, discontinuity floor slabs, inclined column and so on. In order to solve aforementioned problems, the project creatively adopted the "high ductility, high energy dissipation" structure system, and targeted research was carried out on the problem, and finally the elastic-plastic verification under rare earthquake and very rare earthquake was carried out. The results showed that the torsional displacement ratio could be controlled by adopting the dense columns and diagonal braces; the tower could be divided into low-rise tower and high-rise tower, the eccentricity of stiffness center and mass center of the two parts was adjusted recpectively, the whole tower would not be twisted; after linear assembly, the discontinuity of slabs had no effect on the integrity of tower; the cracks of floor slabs could be controlled by post pouring concrete; the tower had strong torsion resistance, and eccentric load had no effect on its mechanical properties under rare earthquake; the equivalent damping ratio of the structure under rare earthquake was 11.5%, and the corrugated web steel coupling beam and SRC coupling beam were used to realize high energy dissipation; 1.2 times of rare earthquake caused tower collapse; as the second line of defense of the structure, the outer frame was weak, and the shear walls in the collapse related area should be equipped with section steel to improve the collapse resistance of the structure.
