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2021 Vol. 51, No. 5
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2021, 51(5): 1-9,123.
doi: 10.13204/j.gyjzG20110502
Abstract:
Aiming at the problem of low accuracy and intelligence of cable force prediction in the cable tensioning process, an intelligent prediction method of prestressed cable force based on digital twins was proposed. According to the current research status of cable tension, the main factors affecting the cable force were analyzed, and the current method of prestressed cable force prediction were summarized. Under the theoretical framework of intelligent predictive closed-loop control, a predictive maintenance method based on digital twins was explored. On this basis, the framework of the fusion prediction method based on digital twins was established, and the implementation process of the fusion prediction and maintenance method was explored. The cable force was predicted from the working condition parameters through the fusion of data. A case analysis of the spoke-type cable truss verified the effectiveness of the method. The intelligent prediction method for prestressed cable force based on digital twins could directly predict the state of cable force from working condition parameters, which improve the accuracy and intelligence of the safety assessment of prestressed steel structures.
Aiming at the problem of low accuracy and intelligence of cable force prediction in the cable tensioning process, an intelligent prediction method of prestressed cable force based on digital twins was proposed. According to the current research status of cable tension, the main factors affecting the cable force were analyzed, and the current method of prestressed cable force prediction were summarized. Under the theoretical framework of intelligent predictive closed-loop control, a predictive maintenance method based on digital twins was explored. On this basis, the framework of the fusion prediction method based on digital twins was established, and the implementation process of the fusion prediction and maintenance method was explored. The cable force was predicted from the working condition parameters through the fusion of data. A case analysis of the spoke-type cable truss verified the effectiveness of the method. The intelligent prediction method for prestressed cable force based on digital twins could directly predict the state of cable force from working condition parameters, which improve the accuracy and intelligence of the safety assessment of prestressed steel structures.
2021, 51(5): 10-15.
doi: 10.13204/j.gyjzG20111112
Abstract:
In recent years, the overall scale, construction speed, complexity and difficulty of engineering construction in China are unprecedented. Large-scale complex structures have exceeded the structural design specifications in terms of complexity, structural form and system. The existing engineering verification methods have limitations and technical bottlenecks, the use of theoretical methods, numerical simulations, and laboratory tests cannot solve the engineering verification problem of complex structures. A technical challenge for understanding the performance of large-scale complex structures in real construction and service environments was proposed. For complex engineering structures such as high-rise buildings and long-span bridges, the paper proposed the distributed synchronous acquisition and mobile sensing data acquisition method. The automatic stochastic subspace method was used to identify structural modal parameters. It could lay a solid foundation for the interpretation of the mechanical mechanism of engineering structure behaviors under operating conditions.
In recent years, the overall scale, construction speed, complexity and difficulty of engineering construction in China are unprecedented. Large-scale complex structures have exceeded the structural design specifications in terms of complexity, structural form and system. The existing engineering verification methods have limitations and technical bottlenecks, the use of theoretical methods, numerical simulations, and laboratory tests cannot solve the engineering verification problem of complex structures. A technical challenge for understanding the performance of large-scale complex structures in real construction and service environments was proposed. For complex engineering structures such as high-rise buildings and long-span bridges, the paper proposed the distributed synchronous acquisition and mobile sensing data acquisition method. The automatic stochastic subspace method was used to identify structural modal parameters. It could lay a solid foundation for the interpretation of the mechanical mechanism of engineering structure behaviors under operating conditions.
2021, 51(5): 16-21,36.
doi: 10.13204/j.gyjzG20102908
Abstract:
The spatial grid structure is one of the main structural forms of urban public buildings, which plays a vital role in the public life or transportation lifeline of citizens, and its safety guarantee has important social and engineering significance. The paper reviewed the research status and engineering technology of saftety assurance of in-service spatial grid structures, summarized the 12 inspection indicators for the testing and monitoring of existing spatial grid structures in technical standard for in-site testing of steel structure (GB/T 50621-2010), and an in-depth discussion of the frequently occurring bending deformation defect and its obvious impact on structural safety was conducted. Through the introduction of three-dimensional laser scanning, digital image method of multi-view geometric three-dimensional reconstruction, and applications of reverse engineering technique in the detection and quantitative measurement of bending deformation members, the new ideas for the testing and monitoring of bending deformation damage of the members were proposed.
The spatial grid structure is one of the main structural forms of urban public buildings, which plays a vital role in the public life or transportation lifeline of citizens, and its safety guarantee has important social and engineering significance. The paper reviewed the research status and engineering technology of saftety assurance of in-service spatial grid structures, summarized the 12 inspection indicators for the testing and monitoring of existing spatial grid structures in technical standard for in-site testing of steel structure (GB/T 50621-2010), and an in-depth discussion of the frequently occurring bending deformation defect and its obvious impact on structural safety was conducted. Through the introduction of three-dimensional laser scanning, digital image method of multi-view geometric three-dimensional reconstruction, and applications of reverse engineering technique in the detection and quantitative measurement of bending deformation members, the new ideas for the testing and monitoring of bending deformation damage of the members were proposed.
2021, 51(5): 22-29.
doi: 10.13204/j.gyjzG20110602
Abstract:
Initial geometric imperfection of steel structure is an important factor that affects mechanical performance, construction and installation. Traditional measurement methods have shortages such as low efficiency, incomplete data, and insufficient accuracy. High-precision point clouds of shape of steel members can be efficiently obtained by three-dimensional laser scanning. However, the processing method of the point clouds need to be developed. First, a digital model of structural member is developed, composing of three levels:component, section, and geometric element. Second, a modeling method of the digital model based on laser point cloud was proposed, including calibration of the inherent coordinate system, slicing and labeling member point cloud, segmenting and labeling section point cloud. Third, the calculation method of global and local initial geometric imperfections based on the digital model is proposed. The digital model abstracts geometric features while retaining precise scanning details. Finally, using a handheld 3D laser scanning device and self-made software BCModeler, initial global or local geometric imperfections of an H-section steel column and outer steel tube of a hybrid column are obtained, thus the effectiveness of the method is verified.
Initial geometric imperfection of steel structure is an important factor that affects mechanical performance, construction and installation. Traditional measurement methods have shortages such as low efficiency, incomplete data, and insufficient accuracy. High-precision point clouds of shape of steel members can be efficiently obtained by three-dimensional laser scanning. However, the processing method of the point clouds need to be developed. First, a digital model of structural member is developed, composing of three levels:component, section, and geometric element. Second, a modeling method of the digital model based on laser point cloud was proposed, including calibration of the inherent coordinate system, slicing and labeling member point cloud, segmenting and labeling section point cloud. Third, the calculation method of global and local initial geometric imperfections based on the digital model is proposed. The digital model abstracts geometric features while retaining precise scanning details. Finally, using a handheld 3D laser scanning device and self-made software BCModeler, initial global or local geometric imperfections of an H-section steel column and outer steel tube of a hybrid column are obtained, thus the effectiveness of the method is verified.
2021, 51(5): 30-36.
doi: 10.13204/j.gyjzG20112504
Abstract:
Convolution neural network method of deep learning is a high robust method for image crack recognition at present, which is mainly divided into sliding window method and image segmentation method. Sliding window method has the problems of low precision of later threshold segmentation of cracks; global image segmentation method has the problem of serious unbalanced sample distribution between crack region and background region,which will affect the accuracy of crack segmentation. The method based on progressive cascade convolution neural network was used to detect concrete surface cracks:firstly, the fully convolution neural network was used to judge whether there were cracks in all the dense overlapped window areas in the image only once, and then the window blocks with cracks were extracted as the region of interest, and then the light-weight U-Net image segmentation network was used to act on the region of interest to extract the crack area accurately. Experimental results showed that the proposed progressive cascade convolution neural network was superior to sliding window method and global image segmentation method, and had a reliable application prospect.
Convolution neural network method of deep learning is a high robust method for image crack recognition at present, which is mainly divided into sliding window method and image segmentation method. Sliding window method has the problems of low precision of later threshold segmentation of cracks; global image segmentation method has the problem of serious unbalanced sample distribution between crack region and background region,which will affect the accuracy of crack segmentation. The method based on progressive cascade convolution neural network was used to detect concrete surface cracks:firstly, the fully convolution neural network was used to judge whether there were cracks in all the dense overlapped window areas in the image only once, and then the window blocks with cracks were extracted as the region of interest, and then the light-weight U-Net image segmentation network was used to act on the region of interest to extract the crack area accurately. Experimental results showed that the proposed progressive cascade convolution neural network was superior to sliding window method and global image segmentation method, and had a reliable application prospect.
2021, 51(5): 37-43.
doi: 10.13204.j/gyjzG20112202
Abstract:
Ancestor's Monastery, as one of the representative buildings of "The Center of Heaven and Earth" in Dengfeng city, has an important historical value. As the main hall of Ancestor's Monastery, it is the earliest wooden structure in the ancestor's monastery. It has a history of more than 800 years. Although after repeated repairs, there are still a lot of problems. In order to understand the damage of the main hall of Ancestor's Monastery, the number of lintels at six different positions in the main hall of Ancestor's Monastery was measured, and the parameters, such as external sizes, moisture content, and deflections, were obtained to evaluate the safety state of the lintels. Ultrasonic nondestructive testing technique was applied on testing and preliminary analysis for four lintels in the main hall. The analysis method of selecting abnormal points by boxplot and calculation formula was introduced, and different damage points were obtained. The dynamic elastic modulus and residual elastic modulus of four lintels were calculated and the mechanical and acoustic properties of those lintels were combined to judge, providing a basis for the subsequent survey and repair of this kind of buildings.
Ancestor's Monastery, as one of the representative buildings of "The Center of Heaven and Earth" in Dengfeng city, has an important historical value. As the main hall of Ancestor's Monastery, it is the earliest wooden structure in the ancestor's monastery. It has a history of more than 800 years. Although after repeated repairs, there are still a lot of problems. In order to understand the damage of the main hall of Ancestor's Monastery, the number of lintels at six different positions in the main hall of Ancestor's Monastery was measured, and the parameters, such as external sizes, moisture content, and deflections, were obtained to evaluate the safety state of the lintels. Ultrasonic nondestructive testing technique was applied on testing and preliminary analysis for four lintels in the main hall. The analysis method of selecting abnormal points by boxplot and calculation formula was introduced, and different damage points were obtained. The dynamic elastic modulus and residual elastic modulus of four lintels were calculated and the mechanical and acoustic properties of those lintels were combined to judge, providing a basis for the subsequent survey and repair of this kind of buildings.
2021, 51(5): 44-50,43.
doi: 10.13204/j.gyjzG20110321
Abstract:
This paper mainly studied the flexural behavior of damaged RC beams reinforced by FRP grids. A control beam was designed for a four-point bending test in this study. Based on the test data, a finite element model for analyzing the reinforcement effect of the FRP grid was established. The flexural behavior of the reinforcement scheme and the influence of grid spacing and FRP-concrete interface treatment on the reinforcement were obtained through the FEM analysis. The results showed that the reinforcement was very effective in improving the bearing capacity of the damaged beams, and the limit load of the beam was increased by 27.4%~43.4%. There was a greatly improvement in the overall stiffness of the beams after the reinforcement. The deflection at yield was slightly reduced and the deflection at failure hardly changed. For beams with different anchoring conditions, the limit load of the unanchored beams was about 10% higher than that of the anchored beams.
This paper mainly studied the flexural behavior of damaged RC beams reinforced by FRP grids. A control beam was designed for a four-point bending test in this study. Based on the test data, a finite element model for analyzing the reinforcement effect of the FRP grid was established. The flexural behavior of the reinforcement scheme and the influence of grid spacing and FRP-concrete interface treatment on the reinforcement were obtained through the FEM analysis. The results showed that the reinforcement was very effective in improving the bearing capacity of the damaged beams, and the limit load of the beam was increased by 27.4%~43.4%. There was a greatly improvement in the overall stiffness of the beams after the reinforcement. The deflection at yield was slightly reduced and the deflection at failure hardly changed. For beams with different anchoring conditions, the limit load of the unanchored beams was about 10% higher than that of the anchored beams.
2021, 51(5): 51-55,62.
doi: 10.13204/j.gyjzG20102907
Abstract:
Polymer cement mortar (PCM) has been widely used in the reinforcement of reinforced concrete structure because of its good bond with concrete, but the law of bond degradation between PCM and rebar at high temperatures is still unclear. Experimental studies were conducted on the bonding properties of rebar and PCM under different temperatures and cooling methods. The results showed that:1) the failure modes of the specimens under natural cooling were split and split pull-out, and the corresponding failure modes of the water-cooled specimens were split pull-out and pulled out; 2)the influence of cooling mode on bond strength increased with the increase of temperature; 3)different cooling methods would lead to different failure forms of specimens, which would affect the slip amount of specimens; 4)with the increases of temperature, the bond strength of the specimen decreased and the slip amount increased. According to the experimental results, the high temperature degradation model of rebar-PCM bond strength was established, which could provide a reference for practical engineering.
Polymer cement mortar (PCM) has been widely used in the reinforcement of reinforced concrete structure because of its good bond with concrete, but the law of bond degradation between PCM and rebar at high temperatures is still unclear. Experimental studies were conducted on the bonding properties of rebar and PCM under different temperatures and cooling methods. The results showed that:1) the failure modes of the specimens under natural cooling were split and split pull-out, and the corresponding failure modes of the water-cooled specimens were split pull-out and pulled out; 2)the influence of cooling mode on bond strength increased with the increase of temperature; 3)different cooling methods would lead to different failure forms of specimens, which would affect the slip amount of specimens; 4)with the increases of temperature, the bond strength of the specimen decreased and the slip amount increased. According to the experimental results, the high temperature degradation model of rebar-PCM bond strength was established, which could provide a reference for practical engineering.
2021, 51(5): 56-62.
doi: 10.13204/j.gyjz201908300010
Abstract:
A new type of prefabricated concrete shear wall, which is connected by the dark beam with a vertical seam, was proposed to reduce the quantity of cast-in-situ concrete in the edge members of the shear wall, and it also can facilitate the construction and improve the assembly rate. In order to verify the feasibility of the new prefabricated shear wall, quasi-static tests were carried out on the prefabricated and cast-in-situ T-shaped shear walls. The influence of dark beam height on the hysteretic behavior, stiffness degradation, ductility and energy dissipation capacity of T-shaped shear wall was studied. The experimental results showed that the failure modes of T-shaped precast shear walls were bending failures for integral component and shear failures for local joint, and the concrete at the bottom of the shear wall away from the flange side was crushed, which was similar to that of cast-in-situ shear wall; the hysteretic curves of shear walls were asymmetrical and very full, which showed a good energy dissipation capacity; comparing with the cast-in-situ shear walls, the bearing capacity of the prefabricated shear walls was reduced, but there was little difference between the deformation capacity and energy dissipation capacity.
A new type of prefabricated concrete shear wall, which is connected by the dark beam with a vertical seam, was proposed to reduce the quantity of cast-in-situ concrete in the edge members of the shear wall, and it also can facilitate the construction and improve the assembly rate. In order to verify the feasibility of the new prefabricated shear wall, quasi-static tests were carried out on the prefabricated and cast-in-situ T-shaped shear walls. The influence of dark beam height on the hysteretic behavior, stiffness degradation, ductility and energy dissipation capacity of T-shaped shear wall was studied. The experimental results showed that the failure modes of T-shaped precast shear walls were bending failures for integral component and shear failures for local joint, and the concrete at the bottom of the shear wall away from the flange side was crushed, which was similar to that of cast-in-situ shear wall; the hysteretic curves of shear walls were asymmetrical and very full, which showed a good energy dissipation capacity; comparing with the cast-in-situ shear walls, the bearing capacity of the prefabricated shear walls was reduced, but there was little difference between the deformation capacity and energy dissipation capacity.
2021, 51(5): 63-69.
doi: 10.13204/j.gyjzG20011903
Abstract:
Taking a five-story reinforced concrete frame structure as an example, the structural properties were compared and analyzed by using YJK and PERFORM-3D programs, and the seismic perfomance of the frame structure with multi-storey unbraced columns and a big opening on the first floor slab was studied. The research results showed that under frequent earthquakes, the natural vibration period of the multi-story frame structure was longer, and the elastic interstorey drift angles of the first floor and the second floor were increased by 10.3%. Under rare earthquakes, the base shear force of the structure had decreased, the floor displacement had increased, and the elastic-plastic interstorey drift angle of the first floor had increased by 16%. The opening led to the lateral resistance members of this layer and its adjacent layers to consume more energy than other layers, which resulted in more damage and stiffness degradation of the lateral resistance members. The maximum plastic tensile strain of steel bars in the multi-storey unbraced columns had increased by about 15% when there was an big opening, which reduced the ductile deformation capacity of the structure. Strengthening the reinforcement of the multi-storey unbraced columns according to the principle of proximity could significantly reduce the impact of aggravated damage of the multi-storey unbraced columns caused by the opening.
Taking a five-story reinforced concrete frame structure as an example, the structural properties were compared and analyzed by using YJK and PERFORM-3D programs, and the seismic perfomance of the frame structure with multi-storey unbraced columns and a big opening on the first floor slab was studied. The research results showed that under frequent earthquakes, the natural vibration period of the multi-story frame structure was longer, and the elastic interstorey drift angles of the first floor and the second floor were increased by 10.3%. Under rare earthquakes, the base shear force of the structure had decreased, the floor displacement had increased, and the elastic-plastic interstorey drift angle of the first floor had increased by 16%. The opening led to the lateral resistance members of this layer and its adjacent layers to consume more energy than other layers, which resulted in more damage and stiffness degradation of the lateral resistance members. The maximum plastic tensile strain of steel bars in the multi-storey unbraced columns had increased by about 15% when there was an big opening, which reduced the ductile deformation capacity of the structure. Strengthening the reinforcement of the multi-storey unbraced columns according to the principle of proximity could significantly reduce the impact of aggravated damage of the multi-storey unbraced columns caused by the opening.
2021, 51(5): 70-75,107.
doi: 10.13204/j.gyjzG20060810
Abstract:
To study the flexural behavior of waste fiber recycled concrete beams, the static loading test of beams were carried out with the replacement rate of recycled aggregates for 0, 50%, 100%, and the volume of waste fiber blending with 0, 0.08%, 0.12%, and 0.16%. At the same time, a calculation model of reinforced concrete beams was set up based on the finite element software ABAQUS, compared with the test results. The results showed that with the increase of the replacement rate of recycled aggregates, the ultimate bearing capacity of concrete beams decreased. At the meso-level, the waste fiber was the bridge function of fibers, which limited the development of cracks in cement matrix. At the macro level, it improved the flexural behavior of recycled concrete beams. Furthermore, when the replacement rate of recycled aggregates was 50% and the fiber content was 0.12%, the ultimate bearing capacity of waste fiber recycled concrete beams was increased by 0.4%, the calculated values of the finite element model were relatively consistent with the experimental values.
To study the flexural behavior of waste fiber recycled concrete beams, the static loading test of beams were carried out with the replacement rate of recycled aggregates for 0, 50%, 100%, and the volume of waste fiber blending with 0, 0.08%, 0.12%, and 0.16%. At the same time, a calculation model of reinforced concrete beams was set up based on the finite element software ABAQUS, compared with the test results. The results showed that with the increase of the replacement rate of recycled aggregates, the ultimate bearing capacity of concrete beams decreased. At the meso-level, the waste fiber was the bridge function of fibers, which limited the development of cracks in cement matrix. At the macro level, it improved the flexural behavior of recycled concrete beams. Furthermore, when the replacement rate of recycled aggregates was 50% and the fiber content was 0.12%, the ultimate bearing capacity of waste fiber recycled concrete beams was increased by 0.4%, the calculated values of the finite element model were relatively consistent with the experimental values.
2021, 51(5): 76-81,163.
doi: 10.13204/j.gyjzG20052403
Abstract:
A new type of bearing with vertical stiffness that can be adjusted precisely was designed. A 1/10 scale model was established on the basis of a high-rise building above a subway, and the vibration excitation of subway and road traffic environment was input, and the actual effect of vertical vibration isolation based on the new type of bearing was analyzed. The test results showed:1) the mix proportion of sand particles and rubber particles was adjusted, and the vertical stiffness of the new bearing could be precisely adjusted with a maximum error of no more than 3%; 2)the trend of irregular fluctuations of indoor vibration of high-rise buildings under the excitation of the subway upward along the floor was presented; 3)after applying the basic vertical vibration isolation measures, the vertical vibration level difference of each floor became smaller, and the trend of irregular fluctuations became gentle; 4)after the implementation of the basic vertical vibration isolation measures, the indoor comfort of the high-rise building had been significantly improved, and the floor 1/3 octave frequency division vibration level was reduced by a maximum of about 15 dB, and all floors had met the standard comfort requirements;5) the new bearing was affected by the friction energy dissipation among sand grains, which led to the base isolation structure had a stronger anti-interference resistance to low-frequency environmental vibration caused by road traffic and could suppress resonance phenomena.
A new type of bearing with vertical stiffness that can be adjusted precisely was designed. A 1/10 scale model was established on the basis of a high-rise building above a subway, and the vibration excitation of subway and road traffic environment was input, and the actual effect of vertical vibration isolation based on the new type of bearing was analyzed. The test results showed:1) the mix proportion of sand particles and rubber particles was adjusted, and the vertical stiffness of the new bearing could be precisely adjusted with a maximum error of no more than 3%; 2)the trend of irregular fluctuations of indoor vibration of high-rise buildings under the excitation of the subway upward along the floor was presented; 3)after applying the basic vertical vibration isolation measures, the vertical vibration level difference of each floor became smaller, and the trend of irregular fluctuations became gentle; 4)after the implementation of the basic vertical vibration isolation measures, the indoor comfort of the high-rise building had been significantly improved, and the floor 1/3 octave frequency division vibration level was reduced by a maximum of about 15 dB, and all floors had met the standard comfort requirements;5) the new bearing was affected by the friction energy dissipation among sand grains, which led to the base isolation structure had a stronger anti-interference resistance to low-frequency environmental vibration caused by road traffic and could suppress resonance phenomena.
2021, 51(5): 82-92.
doi: 10.13204/j.gyjzG20031809
Abstract:
In steel frame-tube structures (SFTSs), the plastic hinges usually form at column-ends before beam-ends due to the low span-to-height ratio of deep beams, which can lead to lower ductility and energy dissipation capacity of the SFTSs. To address this problem, a replaceable shear link, acting as a ductile fuse at the midspan of deep beams, was proposed. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings, and finite element models (FEMs) were established to study their hysteretic behaviors. The nonlinear static pushover analysis and dynamic analysis were undertaken in comparing the seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial elastic stiffness. Compared with the SFTS, the SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. The SFTS-RSL had lower interstory drift compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrated plasticity on the shear links. Other structural components remained elastic during the seismic loading. It could be expected that the SFTS-RSL would be a reliable dual resistant system, which could offer the benefit of being able to repair the structure rapidly by replacing the damaged shear links after earthquakes.
In steel frame-tube structures (SFTSs), the plastic hinges usually form at column-ends before beam-ends due to the low span-to-height ratio of deep beams, which can lead to lower ductility and energy dissipation capacity of the SFTSs. To address this problem, a replaceable shear link, acting as a ductile fuse at the midspan of deep beams, was proposed. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings, and finite element models (FEMs) were established to study their hysteretic behaviors. The nonlinear static pushover analysis and dynamic analysis were undertaken in comparing the seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial elastic stiffness. Compared with the SFTS, the SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. The SFTS-RSL had lower interstory drift compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrated plasticity on the shear links. Other structural components remained elastic during the seismic loading. It could be expected that the SFTS-RSL would be a reliable dual resistant system, which could offer the benefit of being able to repair the structure rapidly by replacing the damaged shear links after earthquakes.
2021, 51(5): 93-98,195.
doi: 10.13204/j.gyjzG20032402
Abstract:
Taking the cantilevered string structure of a stadium in Pujiang as a research object, the wind vibration response and equivalent static wind load of the structure based on wind tunnel test data were discussed. A finite element model considering the cable's geometric non-linear characteristics was established, and the wind speed time-history of the test points was equivalent to the load time-history of the finite element node by interpolation method, and the wind vibration response extraction was performed. The conclusions are as follows:the combination of wind load time-history and other loads would make the structural design process complicated, and then the load wind vibration coefficient was introduced to establish the relationship between the dynamic response of the structure and the static wind pressure, and it was converted into an equivalent static wind load. Meanwhile, based on the equivalent static wind load, a geometric nonlinear analysis of the cantilevered string structure was carried out. There were obvious differences in wind vibration coefficients at different locations of the canopy, and it was advisable to adopt a multi-partition wind vibration coefficient under 0°~180° wind angle when carrying out structural design to ensure safety and economy.
Taking the cantilevered string structure of a stadium in Pujiang as a research object, the wind vibration response and equivalent static wind load of the structure based on wind tunnel test data were discussed. A finite element model considering the cable's geometric non-linear characteristics was established, and the wind speed time-history of the test points was equivalent to the load time-history of the finite element node by interpolation method, and the wind vibration response extraction was performed. The conclusions are as follows:the combination of wind load time-history and other loads would make the structural design process complicated, and then the load wind vibration coefficient was introduced to establish the relationship between the dynamic response of the structure and the static wind pressure, and it was converted into an equivalent static wind load. Meanwhile, based on the equivalent static wind load, a geometric nonlinear analysis of the cantilevered string structure was carried out. There were obvious differences in wind vibration coefficients at different locations of the canopy, and it was advisable to adopt a multi-partition wind vibration coefficient under 0°~180° wind angle when carrying out structural design to ensure safety and economy.
2021, 51(5): 99-107.
doi: 10.13204/j.gyjzG20030706
Abstract:
A series of compression tests were conducted at ambient temperature to investigate the mechanical properties of cold-formed steel stub columns after a fire. The test specimens, including three types of 45 stub columns with open sections, were heated to the pre-selected temperature and then the compression tests were conducted on the specimens after cooling. Seven specified temperatures and two duration times were adopted in the test program to study the relations between the bearing capacity of components and the parameters of temperature field. The effects of longitudinal stiffeners on the local stability and fire resistance of open sections were also evaluated. The test results showed that:1) the heating temperature and duration time greatly affected the bearing capacity of stub columns; 2) the deterioration of material properties was not the only attribute that the stub columns lost their bearing capacity after being exposed to fire; 3) longitudinal stiffeners could improve the local stability of open sections, and web stiffeners performed better. The test results were also used to evaluate the appropriateness of the direst strength method (DSM). This evaluation showed that the mass loss of specimens should be taken into account in the design calculation when the heating temperature was above 700℃. It was also shown that the modified DSM, with consideration of the high-temperature effect, was accurate and reliable for calculating the bearing capacity of cold-formed steel stub columns with open sections.
A series of compression tests were conducted at ambient temperature to investigate the mechanical properties of cold-formed steel stub columns after a fire. The test specimens, including three types of 45 stub columns with open sections, were heated to the pre-selected temperature and then the compression tests were conducted on the specimens after cooling. Seven specified temperatures and two duration times were adopted in the test program to study the relations between the bearing capacity of components and the parameters of temperature field. The effects of longitudinal stiffeners on the local stability and fire resistance of open sections were also evaluated. The test results showed that:1) the heating temperature and duration time greatly affected the bearing capacity of stub columns; 2) the deterioration of material properties was not the only attribute that the stub columns lost their bearing capacity after being exposed to fire; 3) longitudinal stiffeners could improve the local stability of open sections, and web stiffeners performed better. The test results were also used to evaluate the appropriateness of the direst strength method (DSM). This evaluation showed that the mass loss of specimens should be taken into account in the design calculation when the heating temperature was above 700℃. It was also shown that the modified DSM, with consideration of the high-temperature effect, was accurate and reliable for calculating the bearing capacity of cold-formed steel stub columns with open sections.
2021, 51(5): 108-115,15.
doi: 10.13204/j.gyjzG20081506
Abstract:
It is of great significance to introduce manufactured sand and recycled coarse aggregate into concrete-filled steel tubular (CFST) structures to solve the problems of resource shortage and construction waste pollution. However, there are few studies on recycled concrete members with manufactured sand and no research has been made on the constitutive model of recycled concrete with manufactured sand which is suitable for finite element analysis. In this paper, through ABAQUS software modeling, combined with the test data in relevant literature, several commonly used constitutive models of recycled concrete were compared. According to the comparison results of load-displacement curve and ultimate bearing capacity, the optimal constitutive model of recycled concrete was determined; on the basis of the data in the literature, the calculation formula of the constitutive model was modified, and the infuence of manufactured sand was discussed. Finally, a constitutive model for the concrete core of recycled concrete with manufactured sand filled steel tube.
It is of great significance to introduce manufactured sand and recycled coarse aggregate into concrete-filled steel tubular (CFST) structures to solve the problems of resource shortage and construction waste pollution. However, there are few studies on recycled concrete members with manufactured sand and no research has been made on the constitutive model of recycled concrete with manufactured sand which is suitable for finite element analysis. In this paper, through ABAQUS software modeling, combined with the test data in relevant literature, several commonly used constitutive models of recycled concrete were compared. According to the comparison results of load-displacement curve and ultimate bearing capacity, the optimal constitutive model of recycled concrete was determined; on the basis of the data in the literature, the calculation formula of the constitutive model was modified, and the infuence of manufactured sand was discussed. Finally, a constitutive model for the concrete core of recycled concrete with manufactured sand filled steel tube.
2021, 51(5): 116-123.
doi: 10.13204/j.gyjzG20031020
Abstract:
A kind of T-shaped steel column wrapped with ceramsite concrete was proposed. With the good thermal insulation and impermeability performance of ceramsite concrete, it has been used as covering material to improve column's insulated and fireproof performances. Axial compression test and finite element analysis were carried out on two 1 720 mm high T-shaped columns to obtain the mechanical properties. The effects of stirrup end and steel web welded or not on the bearing capacity of specimens were discussed. The results indicated that the obvious cracking and ceramsite concrete's falling off did not occur until arrived the ultimate load, which proved that the concrete and steel had good bonding effects. Benefiting from the concrete cover, the strength of the steel column was fully utilized and the steel might reach the yield strength. Because ceramsite concrete provided an effective restraint for the inner steel, the local and overall buckling of the steel column were avoided, and the ductility and bearing capacity of the specimen were improved. Welding stirrup ends on the web of T-shaped steel had little effect on the bearing capacity of the specimen. The connections between the stirrup ends and steel were strengthened, which constrained the deformation of longitudinal reinforcement and reduced the damage of concrete.
A kind of T-shaped steel column wrapped with ceramsite concrete was proposed. With the good thermal insulation and impermeability performance of ceramsite concrete, it has been used as covering material to improve column's insulated and fireproof performances. Axial compression test and finite element analysis were carried out on two 1 720 mm high T-shaped columns to obtain the mechanical properties. The effects of stirrup end and steel web welded or not on the bearing capacity of specimens were discussed. The results indicated that the obvious cracking and ceramsite concrete's falling off did not occur until arrived the ultimate load, which proved that the concrete and steel had good bonding effects. Benefiting from the concrete cover, the strength of the steel column was fully utilized and the steel might reach the yield strength. Because ceramsite concrete provided an effective restraint for the inner steel, the local and overall buckling of the steel column were avoided, and the ductility and bearing capacity of the specimen were improved. Welding stirrup ends on the web of T-shaped steel had little effect on the bearing capacity of the specimen. The connections between the stirrup ends and steel were strengthened, which constrained the deformation of longitudinal reinforcement and reduced the damage of concrete.
MECHANICAL ANALYSIS OF THE INTEGRAL LIFTING PROCESS FOR A LONG-SPAN AND COMPLEX ASSEMBLED STEEL ROOF
2021, 51(5): 124-130,138.
doi: 10.13204/j.gyjzG201906170007
Abstract:
The roof of Fengyang Gymnasium is a long-span complex assembled steel structure composed of steel trusses, inner ring grids and steel cables, the height of the structure is 24 m, the span is 82.2 m, and the projected area is about 11 851 m2. According to the characteristics of the project, the three-dimensional computational model of the steel roof was established by means of large analysis software. Firstly, the integral lifting construction scheme was described, the selection of lifting points and main construction steps were determined. Secondly, through the mechanical analysis at each stage of construction, the comparisons between the forming at construction stage and the once-forming, the analysis of the influence of temperature change and elevation deviation of lifting point on the structure, the safety of the construction process and the rationality of the structure forming were verified, the design and mechanical analysis of lifting lug and lifting bracket in auxiliary structure were carried out. Finally, by means of safety monitoring, the reliability of the mechanical analysis was verified, and the basic guarantee for the safe construction of the steel roof structure was provided.
The roof of Fengyang Gymnasium is a long-span complex assembled steel structure composed of steel trusses, inner ring grids and steel cables, the height of the structure is 24 m, the span is 82.2 m, and the projected area is about 11 851 m2. According to the characteristics of the project, the three-dimensional computational model of the steel roof was established by means of large analysis software. Firstly, the integral lifting construction scheme was described, the selection of lifting points and main construction steps were determined. Secondly, through the mechanical analysis at each stage of construction, the comparisons between the forming at construction stage and the once-forming, the analysis of the influence of temperature change and elevation deviation of lifting point on the structure, the safety of the construction process and the rationality of the structure forming were verified, the design and mechanical analysis of lifting lug and lifting bracket in auxiliary structure were carried out. Finally, by means of safety monitoring, the reliability of the mechanical analysis was verified, and the basic guarantee for the safe construction of the steel roof structure was provided.
2021, 51(5): 131-138.
doi: 10.13204/j.gyjzG20031405
Abstract:
Under the seismic action, due to the features of the mortise-tenon joint of tenon-through style wooden structures, the relative rotation may be produced between the mortise and tenon, and the mutual extruding between the mortise and tenon will loosen the joint, as a result, the bearing capacity will decrease. The stiffness matrix equation of the tenon-through joint area reinforced by rubber pieces was derived by structure matrix, theoretically, the reinforcement effect was approximately obtained, the results of the quasi-static loading experiment and numerical simulation were compared, the hysteretic behavior of the rubber reinforced joint was obtained. The results showed that the reinforcement method could effectively utilize the good elastic-plastic properties of rubber, limit the relative rotation of columns, prolong the working status of mortise-tenon joint; the deformation of rubber could improve the energy dissipation capacity and hysteretic behavior of the joints.
Under the seismic action, due to the features of the mortise-tenon joint of tenon-through style wooden structures, the relative rotation may be produced between the mortise and tenon, and the mutual extruding between the mortise and tenon will loosen the joint, as a result, the bearing capacity will decrease. The stiffness matrix equation of the tenon-through joint area reinforced by rubber pieces was derived by structure matrix, theoretically, the reinforcement effect was approximately obtained, the results of the quasi-static loading experiment and numerical simulation were compared, the hysteretic behavior of the rubber reinforced joint was obtained. The results showed that the reinforcement method could effectively utilize the good elastic-plastic properties of rubber, limit the relative rotation of columns, prolong the working status of mortise-tenon joint; the deformation of rubber could improve the energy dissipation capacity and hysteretic behavior of the joints.
2021, 51(5): 139-144.
doi: 10.13204/j.gyjzG20070215
Abstract:
In bridge engineering, piles not only bear vertical loads, but also are subjectd to lateral loads such as waves, wind, earthquakes and impact loads impacted by carriers. Based on lateral static load tests of two large-diameter bored piles, the bearing characteristics of bored piles subjected to horizontal loads in deep soft soil foundation were analyzed. The results of tests showed that the results calculated by m-method deviated greatly from the measured values, the results calculated by the method of p-y curves were closer to the measured values and more safe.
In bridge engineering, piles not only bear vertical loads, but also are subjectd to lateral loads such as waves, wind, earthquakes and impact loads impacted by carriers. Based on lateral static load tests of two large-diameter bored piles, the bearing characteristics of bored piles subjected to horizontal loads in deep soft soil foundation were analyzed. The results of tests showed that the results calculated by m-method deviated greatly from the measured values, the results calculated by the method of p-y curves were closer to the measured values and more safe.
2021, 51(5): 145-150.
doi: 10.13204/j.gyjzG20022605
Abstract:
The simple conversion method is a common method for transform Q-s curves of self-balanced static load tests into curves of traditional static load tests. The calculation accuracy of compression for piles of being pushed-up determined the accuracy of the simple conversion method and the results of self-balanced static load tests.Aimed at the deficiency of the current simple conversion method, the compression calculations of the pushed-up piles were studied. Based on analysis of the force mechanisms for pushed-up piles and the finite element calculations, the distribution coefficient C of the side friction resistance for piles were obtained, which could influence the calculation accuracy of compression for pushed-up piles. Under the action of the thrust, the negative friction on the sides of piles decreased sharply upward along pile shafts, and the distribution of the negative friction was a concave hyperbola. With the increase of aspect ratios, the values of C increased.Therein, the calculation formula of pile compression was more accurate. Engineering examples showed that the improved simple transformation method was more accurate and practical.
The simple conversion method is a common method for transform Q-s curves of self-balanced static load tests into curves of traditional static load tests. The calculation accuracy of compression for piles of being pushed-up determined the accuracy of the simple conversion method and the results of self-balanced static load tests.Aimed at the deficiency of the current simple conversion method, the compression calculations of the pushed-up piles were studied. Based on analysis of the force mechanisms for pushed-up piles and the finite element calculations, the distribution coefficient C of the side friction resistance for piles were obtained, which could influence the calculation accuracy of compression for pushed-up piles. Under the action of the thrust, the negative friction on the sides of piles decreased sharply upward along pile shafts, and the distribution of the negative friction was a concave hyperbola. With the increase of aspect ratios, the values of C increased.Therein, the calculation formula of pile compression was more accurate. Engineering examples showed that the improved simple transformation method was more accurate and practical.
2021, 51(5): 151-157,144.
doi: 10.13204/j.gyjzG20062403
Abstract:
Be aimed at negative frictional resistance on the pile sides caused by collapsing in collapsible loess zones, two kinds of methods to reduce negative frictional resistauce were designed, which were to wrap piles with linoleum or with steel casing pipes. The model tests were conducted to contrast the laws of load transfer for the two novel piles in collapsible loess before and after immersion. The test results showed that in the condition of immersion, the piles wrapped with steel casing pipes could efficiently reduce negative friction resistance caused by collapsing; the piles wrapped with linoleum could reduce negative friction resistance of piles to a certain extent.
Be aimed at negative frictional resistance on the pile sides caused by collapsing in collapsible loess zones, two kinds of methods to reduce negative frictional resistauce were designed, which were to wrap piles with linoleum or with steel casing pipes. The model tests were conducted to contrast the laws of load transfer for the two novel piles in collapsible loess before and after immersion. The test results showed that in the condition of immersion, the piles wrapped with steel casing pipes could efficiently reduce negative friction resistance caused by collapsing; the piles wrapped with linoleum could reduce negative friction resistance of piles to a certain extent.
2021, 51(5): 158-163.
doi: 10.13204/j.gyjzG20072406
Abstract:
To explore the laws of fatigue damage for cement-solidified soil under the action of freeze-thaw cycle, the failure modes of strength for cement-solidified soil were defined based on analysis of the stress-strain curves for cement-solidified soil with different mass fractions of cement mix. The development processes of internal defects in freeze-thaw damage were analyzed, combined with the results of freeze-thaw damage tests. Taking elastic moduli as damage indexes, a freeze-thaw damage model of the cement-solidified soil characterized by elastic moduli was proposed. According to the model, the test data were fitted and the values of test parameters were obtained, the proposed model was checked by test results from other regions and in different test conditions, the results showed that the model could reflected the laws of fatigue damage for cement-solidified soil under the action of freeze-thaw cycle.
To explore the laws of fatigue damage for cement-solidified soil under the action of freeze-thaw cycle, the failure modes of strength for cement-solidified soil were defined based on analysis of the stress-strain curves for cement-solidified soil with different mass fractions of cement mix. The development processes of internal defects in freeze-thaw damage were analyzed, combined with the results of freeze-thaw damage tests. Taking elastic moduli as damage indexes, a freeze-thaw damage model of the cement-solidified soil characterized by elastic moduli was proposed. According to the model, the test data were fitted and the values of test parameters were obtained, the proposed model was checked by test results from other regions and in different test conditions, the results showed that the model could reflected the laws of fatigue damage for cement-solidified soil under the action of freeze-thaw cycle.
2021, 51(5): 164-167,187.
doi: 10.13204/j.gyjzG20061201
Abstract:
The Casagrande method is a famous graphic method to obtain pre-consolidation pressure from consolidation test data, in which the one of the procedures is fitting the second half curve of compression curves based on the point of the greatest curvature. In the light of complexity and hard to control proper scales for the traditional graphic method, a program was developed by the software of MATLAB to calculate pre-consolidation pressure. Analysis on the deficiency of Harris Model on processing compression curves and taking account of disturbed factors for soil specimens, a new parameter from test was adopted, and the modified calculation method about the pre-consolidation pressure was proposed based on Harris model. It was shown that the calculated results by the modified method accorded with the actal pre-consolidation pressure for tests at medium and high pressure. Furthermore, soil consolidation experiments should contain higher pressure which could be 1 600 to 3 200 kPa.
The Casagrande method is a famous graphic method to obtain pre-consolidation pressure from consolidation test data, in which the one of the procedures is fitting the second half curve of compression curves based on the point of the greatest curvature. In the light of complexity and hard to control proper scales for the traditional graphic method, a program was developed by the software of MATLAB to calculate pre-consolidation pressure. Analysis on the deficiency of Harris Model on processing compression curves and taking account of disturbed factors for soil specimens, a new parameter from test was adopted, and the modified calculation method about the pre-consolidation pressure was proposed based on Harris model. It was shown that the calculated results by the modified method accorded with the actal pre-consolidation pressure for tests at medium and high pressure. Furthermore, soil consolidation experiments should contain higher pressure which could be 1 600 to 3 200 kPa.
2021, 51(5): 168-172.
doi: 10.13204/j.gyjzG20041302
Abstract:
To verify the effectiveness of marine sand desalination and the accuracy of testing methods for chloride ion content from marine sand, submarine sand, desalted sea sand and seabeach sand immersed were respectively in three solvents that were deionized water, saturated calcium hydroxide, and filtrate of cement paste. The mass ratio of marine and solvent was 0.2. When the soaking time arrived at 3 h, 1 d, 7 d and 28 d, the dissolved quantities(DQ) of Cl-、SO42-、K+、Mg2+ and Na+ were measured. The experimental results showed that the DQ of five kinds of ion was related to the types of soaking solvents. As the soaking time went by, the DQ of Cl- in three solvents tended to stable, and it was hard to discover the continuous dissolution, while the test value in 24 h was 14%~25% higher than that in 3 h. If marine sand was grinded into power (<75 μm), the DQ of Cl- would decline. The dissolved mass of SO42- in the filtrate of cement paste and saturated calcium hydroxide was observed to decrease with the increase of soaking time, and it was not necessary to pay close attention to the influence of SO42- of sea sand concrete. Finally, the DQ of K+、Mg2+ and Na+ in deionized water would tend to stable with the increase of soaking time.
To verify the effectiveness of marine sand desalination and the accuracy of testing methods for chloride ion content from marine sand, submarine sand, desalted sea sand and seabeach sand immersed were respectively in three solvents that were deionized water, saturated calcium hydroxide, and filtrate of cement paste. The mass ratio of marine and solvent was 0.2. When the soaking time arrived at 3 h, 1 d, 7 d and 28 d, the dissolved quantities(DQ) of Cl-、SO42-、K+、Mg2+ and Na+ were measured. The experimental results showed that the DQ of five kinds of ion was related to the types of soaking solvents. As the soaking time went by, the DQ of Cl- in three solvents tended to stable, and it was hard to discover the continuous dissolution, while the test value in 24 h was 14%~25% higher than that in 3 h. If marine sand was grinded into power (<75 μm), the DQ of Cl- would decline. The dissolved mass of SO42- in the filtrate of cement paste and saturated calcium hydroxide was observed to decrease with the increase of soaking time, and it was not necessary to pay close attention to the influence of SO42- of sea sand concrete. Finally, the DQ of K+、Mg2+ and Na+ in deionized water would tend to stable with the increase of soaking time.
2021, 51(5): 173-180.
doi: 10.13204/j.gyjzG20010806
Abstract:
On the basis of constructing an evaluation index system for the coupling and coordination of the construction industry and the regional economy, taking various province in China as the research unit, the entropy method and the coupling coordination degree model were used to quantitatively measure the coupling and coordination degree between the construction industry and the regional economy in China, and combined with ArcGIS10.5 to analyze the coordinated and coordinated development level and time-space distribution law of the construction industry and regional economy in various provinces in China. The research showed that:from 2011 to 2017, the coupling and coordination of the construction industry and regional economy in China could be generally divided into three types, with significant differences between regions, and there were more provinces with lagging regional economic development. The comprehensive development level of the construction industry and the level of regional economic development were unbalanced among these provinces, and the regional polarization effect was obvious. In general, the spatial pattern of coastal provinces was higher than that of inland provinces; there was a certain degree of differences between the construction industry and regional economy. The differences were in the stage of development from "multi-polarity" to"planar", and the radiating effect was obvious. On the whole, the degree of coupling and coordination between the construction industry and the regional economy was at the intermediate level of coordination, the overall synergistic development effect tended to increase, and the spatial distribution had not changed significantly.
On the basis of constructing an evaluation index system for the coupling and coordination of the construction industry and the regional economy, taking various province in China as the research unit, the entropy method and the coupling coordination degree model were used to quantitatively measure the coupling and coordination degree between the construction industry and the regional economy in China, and combined with ArcGIS10.5 to analyze the coordinated and coordinated development level and time-space distribution law of the construction industry and regional economy in various provinces in China. The research showed that:from 2011 to 2017, the coupling and coordination of the construction industry and regional economy in China could be generally divided into three types, with significant differences between regions, and there were more provinces with lagging regional economic development. The comprehensive development level of the construction industry and the level of regional economic development were unbalanced among these provinces, and the regional polarization effect was obvious. In general, the spatial pattern of coastal provinces was higher than that of inland provinces; there was a certain degree of differences between the construction industry and regional economy. The differences were in the stage of development from "multi-polarity" to"planar", and the radiating effect was obvious. On the whole, the degree of coupling and coordination between the construction industry and the regional economy was at the intermediate level of coordination, the overall synergistic development effect tended to increase, and the spatial distribution had not changed significantly.
2021, 51(5): 181-187.
doi: 10.13204/j.gyjzG20011305
Abstract:
Fatigue failure is a common form of failure of welded steel bridges under cyclic loading. In order to extend its life, the cracked structure needs to be strengthened and repaired. Due to its excellent performance, CFRP has been widely used in the reinforcement of concrete structures, but rarely used in welding steel structures. In the paper, the effects of different initial crack depths, CFRP fabric thickness and elastic modulus on fatigue performance under cyclic loading were studied through experiments and finite element methods. The finite element software ABAQUS was used to analyze the change laws of stress intensity factors of reinforced or unreinforced welded cruciform joints, and compared with the analytical results. It was found that the error of the stress intensity factor obtained by the numerical simulation solution and the theoretical solution of the unreinforced specimen was very small, which verified the accuracy of the numerical simulation. The adhesive layer was simulated by using CPE8 and cohesive element, and the maximum deviation was found to be -3.4%. CFRP could effectively reduce the strength factor at the cracking tip and extend its fatigue life, with a maximum increase of 67%. When the elastic modulus and thickness of the CFRP cloth were larger, the decrease of the stress intensity factor at the cracking tip was more obvious. The remaining fatigue life of the cruciform joints was estimated based on the Paris formula, and the predicted life was compared with the test results, and it was found that the agreement was good.
Fatigue failure is a common form of failure of welded steel bridges under cyclic loading. In order to extend its life, the cracked structure needs to be strengthened and repaired. Due to its excellent performance, CFRP has been widely used in the reinforcement of concrete structures, but rarely used in welding steel structures. In the paper, the effects of different initial crack depths, CFRP fabric thickness and elastic modulus on fatigue performance under cyclic loading were studied through experiments and finite element methods. The finite element software ABAQUS was used to analyze the change laws of stress intensity factors of reinforced or unreinforced welded cruciform joints, and compared with the analytical results. It was found that the error of the stress intensity factor obtained by the numerical simulation solution and the theoretical solution of the unreinforced specimen was very small, which verified the accuracy of the numerical simulation. The adhesive layer was simulated by using CPE8 and cohesive element, and the maximum deviation was found to be -3.4%. CFRP could effectively reduce the strength factor at the cracking tip and extend its fatigue life, with a maximum increase of 67%. When the elastic modulus and thickness of the CFRP cloth were larger, the decrease of the stress intensity factor at the cracking tip was more obvious. The remaining fatigue life of the cruciform joints was estimated based on the Paris formula, and the predicted life was compared with the test results, and it was found that the agreement was good.
2021, 51(5): 188-195.
doi: 10.13204/j.gyjzG20050301
Abstract:
A kind of self-compacting micro-expanded reactive powder concrete (RPC) with high performance and high strength was prepared. The RPC was cured at conventional temperature and its fluidity was greater than 255 mm. The RPC was filled into glass fiber-reinforced plastic (GFRP) tubes. The axial compression performance tests of GFRP tube filled with self-compacting micro-expaned RPC tube filled with short column were carried out. The axial compression performance tests of GFRP tube filled with self-compacting micro-expanded RPC short column were carried out. The effects of design parameters such as GFRP tube forming process, concrete expansion agent and the stress mode of members on the mechanical properties of the structure were considered in the tests. The failure mode, stress-strain curve and member bearing capacity were analyzed emphatically. The results showed that the mechanical properties of GFRP tube RPC short column with GFRP filament wound ±45° were the best, and the stress-strain curve of the composite column increased in a quadratic linear manner. When the composite column was damaged, the GFRP fibers were broken and the confined concrete in the tube was crushed. Its ultimate bearing capacity was about 1.6 times that of the unconstrained RPC short column. The concrete expansion agent improved the deformability of the combined short column, and its ultimate strain was about 1.4 times that of the column without the expansion agent. The theoretical calculation model of Teng was suitable for the GFRP tube filled with self-compacting micro-expaned RPC short column under full-section compression.
A kind of self-compacting micro-expanded reactive powder concrete (RPC) with high performance and high strength was prepared. The RPC was cured at conventional temperature and its fluidity was greater than 255 mm. The RPC was filled into glass fiber-reinforced plastic (GFRP) tubes. The axial compression performance tests of GFRP tube filled with self-compacting micro-expaned RPC tube filled with short column were carried out. The axial compression performance tests of GFRP tube filled with self-compacting micro-expanded RPC short column were carried out. The effects of design parameters such as GFRP tube forming process, concrete expansion agent and the stress mode of members on the mechanical properties of the structure were considered in the tests. The failure mode, stress-strain curve and member bearing capacity were analyzed emphatically. The results showed that the mechanical properties of GFRP tube RPC short column with GFRP filament wound ±45° were the best, and the stress-strain curve of the composite column increased in a quadratic linear manner. When the composite column was damaged, the GFRP fibers were broken and the confined concrete in the tube was crushed. Its ultimate bearing capacity was about 1.6 times that of the unconstrained RPC short column. The concrete expansion agent improved the deformability of the combined short column, and its ultimate strain was about 1.4 times that of the column without the expansion agent. The theoretical calculation model of Teng was suitable for the GFRP tube filled with self-compacting micro-expaned RPC short column under full-section compression.
2021, 51(5): 196-203.
doi: 10.13204/j.gyjzG20050606
Abstract:
In order to monitor the damage process of confined concrete elements in buildings and establish an early-warning index to predict the failure status in real-time, four experimental tests of circular concrete columns confined by BFRP (Basalt Fiber Reinforced Polymer) tube (CCCBT) were carried out to collect the acoustic emission signals during the loading condition. Meanwhile, the characteristics of acoustic emission parameters, correlation analysis, and damage index calculation were conducted based on the experimental data. The variation of acoustic emission characteristic parameters of CCCBTs, which had different diameters and reinforcement ratios (with the same pipe thickness), was studied through experiments. It was indicated that the CCCBTs presented different characteristics of acoustic emission at different loading stages. The damage development of CCCBTs with smaller diameter (but with identical thickness) was slower relatively at the early loading stage, and then became faster until that the failure appeared. Through the RA-AF correlation analysis, it was concluded that most of tensile cracks formed at the elastic stage, while the shear cracks appeared mainly at the elastic-plastic stage. All the CCCBTs, whether having inner steel reinforcements or not, were brittle failure mode. However, the CCCBTs with inner steel reinforcements altered the variational features of acoustic emission signals. For this reason, some typical variational features could be chosen to predict the hazard ahead of the failure.
In order to monitor the damage process of confined concrete elements in buildings and establish an early-warning index to predict the failure status in real-time, four experimental tests of circular concrete columns confined by BFRP (Basalt Fiber Reinforced Polymer) tube (CCCBT) were carried out to collect the acoustic emission signals during the loading condition. Meanwhile, the characteristics of acoustic emission parameters, correlation analysis, and damage index calculation were conducted based on the experimental data. The variation of acoustic emission characteristic parameters of CCCBTs, which had different diameters and reinforcement ratios (with the same pipe thickness), was studied through experiments. It was indicated that the CCCBTs presented different characteristics of acoustic emission at different loading stages. The damage development of CCCBTs with smaller diameter (but with identical thickness) was slower relatively at the early loading stage, and then became faster until that the failure appeared. Through the RA-AF correlation analysis, it was concluded that most of tensile cracks formed at the elastic stage, while the shear cracks appeared mainly at the elastic-plastic stage. All the CCCBTs, whether having inner steel reinforcements or not, were brittle failure mode. However, the CCCBTs with inner steel reinforcements altered the variational features of acoustic emission signals. For this reason, some typical variational features could be chosen to predict the hazard ahead of the failure.
2021, 51(5): 204-211,203.
doi: 10.13204/j.gyjzG20052404
Abstract:
Soil work refers to the soil construction of foundation engineering of Chinese ancient buildings. To effectively protect Chinese ancient buildings, the foundations in the Forbidden City were taken as examples, their soil work techniques were studied by means of site investigation as well as literature analysis. Details such as the constitution of soil foundation, groundwater treatment, application of cementing material and so on were discussed. The results show that the foundations of the buildings in the Forbidden City were made up of alternative layers of brick blocks and lime-soil, or layers of lime-soil, both of which included complicated and strictly construction processes; to deal with groundwater, vertical timber piles and layers of gravels were used; cementing material such as lime, glutinous rice, tung oil, alumen had been found in the soil, which could benefit the strength, bonding performance and waterproof property of the foundation. Besides, the official codes of Yingzaofashi the in Song dynasty and the rules of Gongchengzuofa in the Qing dynasty played important roles in the soil work of the buildings in the Forbidden City.
Soil work refers to the soil construction of foundation engineering of Chinese ancient buildings. To effectively protect Chinese ancient buildings, the foundations in the Forbidden City were taken as examples, their soil work techniques were studied by means of site investigation as well as literature analysis. Details such as the constitution of soil foundation, groundwater treatment, application of cementing material and so on were discussed. The results show that the foundations of the buildings in the Forbidden City were made up of alternative layers of brick blocks and lime-soil, or layers of lime-soil, both of which included complicated and strictly construction processes; to deal with groundwater, vertical timber piles and layers of gravels were used; cementing material such as lime, glutinous rice, tung oil, alumen had been found in the soil, which could benefit the strength, bonding performance and waterproof property of the foundation. Besides, the official codes of Yingzaofashi the in Song dynasty and the rules of Gongchengzuofa in the Qing dynasty played important roles in the soil work of the buildings in the Forbidden City.
