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2022 Vol. 52, No. 9
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2022, 52(9): 1-9.
doi: 10.13204/j.gyjzG22030410
Abstract:
In order to solve the corrosion problems caused by seawater and sea sand concrete in the engineering practice and enhance the seismic performance of structure, a novel structure called double-tube seawater and sea sand concrete columns with built-in CFRP tubes was proposed. Axial compression test was performed on 12 double-tube seawater and sea sand concrete columns with built-in CFRP tubes and 4 concrete-filled steel tube columns. The effect of the thickness of steel tube and the layers of CFRP tube was investigated. Test results indicated that the built-in CFRP tube could improve the bearing capacity and deformation capacity of the structure. The failure of double-tube seawater and sea sand concrete columns with built-in CFRP tubes was usually accompanied by the failure of one of built-in CFRP tubes, while the rest of CFRP tubes could still provide confinement and broke in turn during loading. Based on the theory of area equivalence and area segmentation, a model for ultimate load of double-tube seawater and sea sand concrete columns with built-in CFRP tubes was proposed. Finally, the prediction accuracy and dispersion of the formula were evaluated.
In order to solve the corrosion problems caused by seawater and sea sand concrete in the engineering practice and enhance the seismic performance of structure, a novel structure called double-tube seawater and sea sand concrete columns with built-in CFRP tubes was proposed. Axial compression test was performed on 12 double-tube seawater and sea sand concrete columns with built-in CFRP tubes and 4 concrete-filled steel tube columns. The effect of the thickness of steel tube and the layers of CFRP tube was investigated. Test results indicated that the built-in CFRP tube could improve the bearing capacity and deformation capacity of the structure. The failure of double-tube seawater and sea sand concrete columns with built-in CFRP tubes was usually accompanied by the failure of one of built-in CFRP tubes, while the rest of CFRP tubes could still provide confinement and broke in turn during loading. Based on the theory of area equivalence and area segmentation, a model for ultimate load of double-tube seawater and sea sand concrete columns with built-in CFRP tubes was proposed. Finally, the prediction accuracy and dispersion of the formula were evaluated.
2022, 52(9): 10-17.
doi: 10.13204/j.gyjzg22011918
Abstract:
In order to realize rapid longitudinal connection of composite thin-walled circular tubes, a lightweight all-composite flange joint was proposed. Three specimens were subjected to axial compression tests. Load-axial displacement curves were obtained, and the loading process and damage pattern of bolt-flange joints were analyzed. Then, axial compression tests were carried out on two assembled columns under the same boundary condition. The failure modes of the specimens were observed and the instability mechanism of the columns were analyzed. The results showed that under the same thickness design of the tube and flange, the flexure performance of the bolt-flange joint was significantly lower than that of the tube; compared with metal flanges, the failure modes of bolt yield or tube wall buckling were less likely to occur in the composite flange tube, and the junction of the flange and tube was the weak area of the composite flange joint, which was prone to material damage and had a great influence on the rotational stiffness of the joint; the assembled column could be regarded as a strut with a non-rigid connecting joint in the middle, and the change of rotational stiffness of the joint due to material damage had a direct impact on the overall stability of the strut; the lateral instability model of struts could be used to describe the instability mechanism of the assembled column.
In order to realize rapid longitudinal connection of composite thin-walled circular tubes, a lightweight all-composite flange joint was proposed. Three specimens were subjected to axial compression tests. Load-axial displacement curves were obtained, and the loading process and damage pattern of bolt-flange joints were analyzed. Then, axial compression tests were carried out on two assembled columns under the same boundary condition. The failure modes of the specimens were observed and the instability mechanism of the columns were analyzed. The results showed that under the same thickness design of the tube and flange, the flexure performance of the bolt-flange joint was significantly lower than that of the tube; compared with metal flanges, the failure modes of bolt yield or tube wall buckling were less likely to occur in the composite flange tube, and the junction of the flange and tube was the weak area of the composite flange joint, which was prone to material damage and had a great influence on the rotational stiffness of the joint; the assembled column could be regarded as a strut with a non-rigid connecting joint in the middle, and the change of rotational stiffness of the joint due to material damage had a direct impact on the overall stability of the strut; the lateral instability model of struts could be used to describe the instability mechanism of the assembled column.
2022, 52(9): 18-27.
doi: 10.13204/j.gyjzG22022314
Abstract:
Compared with the steel wires, carbon fiber reinforced polymer (CFRP) composite has the excellent properties, such as light weight, high strength, superior corrosion, fatigue and creep resistance. When CFRP are used in civil engineering structures, the weight of the structures can be reduced and life can be prolonged. Unidirectional CFRP has the typical orthotropic characteristics with poor shear and transverse compressive properties, which makes the anchorage of CFRP to become a difficult problem. In this paper, the experiment and finite element simulation were used to study the bearing performance and stress distribution of multi-bundle parallel carbon fiber cables anchorage system. The results showed that when the multi-cone anchors were used to anchor multi-bundle parallel carbon fiber cables, the stress concentration caused by the anchors would destory the surface of the CFRP bars at the load end, resulting in a decrease of bearing capacity of the CFRP cables. A finite element simulation method was proposed with the interface behavior of CFRP bars and epoxy resin characterized by bond-slip constitutive. The failure modes and stress distribution of anchorage system of CFRP cable were studied, the damage mechanism of carbon fiber cable caused by the anchor extrusion was revealed, and the ultimate bearing capacity of anchorage of CFRP cables was predicted. Finally, through optimizing the anchorage system, it was found that increaseing anchoring length for carbon fiber cable could improve the anchoring efficiency of the anchoring system from 70% to 90%.
Compared with the steel wires, carbon fiber reinforced polymer (CFRP) composite has the excellent properties, such as light weight, high strength, superior corrosion, fatigue and creep resistance. When CFRP are used in civil engineering structures, the weight of the structures can be reduced and life can be prolonged. Unidirectional CFRP has the typical orthotropic characteristics with poor shear and transverse compressive properties, which makes the anchorage of CFRP to become a difficult problem. In this paper, the experiment and finite element simulation were used to study the bearing performance and stress distribution of multi-bundle parallel carbon fiber cables anchorage system. The results showed that when the multi-cone anchors were used to anchor multi-bundle parallel carbon fiber cables, the stress concentration caused by the anchors would destory the surface of the CFRP bars at the load end, resulting in a decrease of bearing capacity of the CFRP cables. A finite element simulation method was proposed with the interface behavior of CFRP bars and epoxy resin characterized by bond-slip constitutive. The failure modes and stress distribution of anchorage system of CFRP cable were studied, the damage mechanism of carbon fiber cable caused by the anchor extrusion was revealed, and the ultimate bearing capacity of anchorage of CFRP cables was predicted. Finally, through optimizing the anchorage system, it was found that increaseing anchoring length for carbon fiber cable could improve the anchoring efficiency of the anchoring system from 70% to 90%.
2022, 52(9): 28-34.
doi: 10.13204/j.gyjzG21060603
Abstract:
A steel fiber-reinforced self-compacting reactive powder concrete with greater than 255 mm flowability was proposed. Seven fiber-reinforced self-compacting RPC long columns restricted to GFRP tubes were designed. Their mechanical properties under axial load was studied experimentally, with steel fiber admixture, GFRP tube winding angle, and length-to-fine ratio as design parameters. According to the experiment, the steel fiber could improve the compressive and shear resistance of concrete material but had little influence on the column damage characteristics. The ±80°GFRP tubes significantly improved the ultimate bearing capacity and deformation performance compared with the ±45°GFRP tubes. The larger the slenderness ratio, the smaller the initial stiffness and peak load of curve. Based on the calculation model of fiber-reinforced self-compacting RPC short columns restricted to GFRP tubes, the ultimate bearing capacity calculation equation of fiber-reinforced self-compacting RPC long columns restricted to GFRP tubes was proposed based on the discount factor of the length to slenderness ratio relations. The calculation results were in good agreement with the test results, and the error was more acceptable compared with the past test data.
A steel fiber-reinforced self-compacting reactive powder concrete with greater than 255 mm flowability was proposed. Seven fiber-reinforced self-compacting RPC long columns restricted to GFRP tubes were designed. Their mechanical properties under axial load was studied experimentally, with steel fiber admixture, GFRP tube winding angle, and length-to-fine ratio as design parameters. According to the experiment, the steel fiber could improve the compressive and shear resistance of concrete material but had little influence on the column damage characteristics. The ±80°GFRP tubes significantly improved the ultimate bearing capacity and deformation performance compared with the ±45°GFRP tubes. The larger the slenderness ratio, the smaller the initial stiffness and peak load of curve. Based on the calculation model of fiber-reinforced self-compacting RPC short columns restricted to GFRP tubes, the ultimate bearing capacity calculation equation of fiber-reinforced self-compacting RPC long columns restricted to GFRP tubes was proposed based on the discount factor of the length to slenderness ratio relations. The calculation results were in good agreement with the test results, and the error was more acceptable compared with the past test data.
2022, 52(9): 35-41,9.
doi: 10.13204/j.gyjzG21080406
Abstract:
Basalt fiber is added into the concrete substrate as a reinforcing material to form a cement composite which calls basalt fiber reinforced concrete (BFRC). Taking the aspect ratio of basalt fiber as the test variable, the four-point bending static loading test for BFRC beams was carried out to study its mechanical behavior and the reinforcement effect of basalt fiber; based on the collected mechanical property test data of fiber reinforced concrete, the relations between the tensile and compressive strength of fiber reinforced concrete and the compressive strength of matrix concrete, fiber content and fiber length diameter ratio was established, the prediction model of characteristic bearing capacity of BFRC beam was proposed based on RC beam model. The results showed that BFRC beams could meet the plane section assumption, and the addition of basalt fiber could improve the cracking and ultimate bearing capacity of BFRC beams, among which the characteristic bearing capacity of BFRC beams with length diameter ratio of 1200 was the most obvious; at the same time, the addition of basalt fiber could reduce the maximum crack width, increase the number of cracks and increase the bending stiffness of the beam; the calculation results of the improved characteristic bearing capacity prediction model of BFRC beams proposed in the paper could fit well with the test results, which could better predict the cracking and ultimate bearing capacity of BFRC beams, and reflect the gain effect of fiber in concrete beams.
Basalt fiber is added into the concrete substrate as a reinforcing material to form a cement composite which calls basalt fiber reinforced concrete (BFRC). Taking the aspect ratio of basalt fiber as the test variable, the four-point bending static loading test for BFRC beams was carried out to study its mechanical behavior and the reinforcement effect of basalt fiber; based on the collected mechanical property test data of fiber reinforced concrete, the relations between the tensile and compressive strength of fiber reinforced concrete and the compressive strength of matrix concrete, fiber content and fiber length diameter ratio was established, the prediction model of characteristic bearing capacity of BFRC beam was proposed based on RC beam model. The results showed that BFRC beams could meet the plane section assumption, and the addition of basalt fiber could improve the cracking and ultimate bearing capacity of BFRC beams, among which the characteristic bearing capacity of BFRC beams with length diameter ratio of 1200 was the most obvious; at the same time, the addition of basalt fiber could reduce the maximum crack width, increase the number of cracks and increase the bending stiffness of the beam; the calculation results of the improved characteristic bearing capacity prediction model of BFRC beams proposed in the paper could fit well with the test results, which could better predict the cracking and ultimate bearing capacity of BFRC beams, and reflect the gain effect of fiber in concrete beams.
2022, 52(9): 42-47,128.
doi: 10.13204/j.gyjzG22031210
Abstract:
In order to study the effect of basalt fiber (BF) on the impact resistance of acicular rubber concrete, the impact resistance of acicular rubber concrete with different BF content, and lengths was analyzed through drop weight impact test, its microstructure was observed combined with scanning electron microscope (SEM) and the reinforcement mechanism was discussed. Finally, the results of impact resistance test were fitted by Weibull distribution model.The results showed that BF could improve the impact resistance of acicular rubber concrete. When the BF length was 12 mm and the content was 0.1%, the impact energy consumption of acicular rubber concrete was the largest, which was 54%. At this time, compared with ordinary concrete, the impact energy consumption of basalt fiber rubber concrete (BFRC) was increased by 516%; under the action of impact kinetic energy, acicular rubber could absorb deformation, rebound and release part of the consumed kinetic energy. BF dissipated part of the kinetic energy through adhesion and friction with the matrix for fiber drawing deformation and damage. The two materials jointly reduced the damage of impact kinetic energy to the concrete matrix and achieved the purpose of toughening and crack resistance;the impact times of BFRC could be statistically analyzed by two parameter Weibull distribution.
In order to study the effect of basalt fiber (BF) on the impact resistance of acicular rubber concrete, the impact resistance of acicular rubber concrete with different BF content, and lengths was analyzed through drop weight impact test, its microstructure was observed combined with scanning electron microscope (SEM) and the reinforcement mechanism was discussed. Finally, the results of impact resistance test were fitted by Weibull distribution model.The results showed that BF could improve the impact resistance of acicular rubber concrete. When the BF length was 12 mm and the content was 0.1%, the impact energy consumption of acicular rubber concrete was the largest, which was 54%. At this time, compared with ordinary concrete, the impact energy consumption of basalt fiber rubber concrete (BFRC) was increased by 516%; under the action of impact kinetic energy, acicular rubber could absorb deformation, rebound and release part of the consumed kinetic energy. BF dissipated part of the kinetic energy through adhesion and friction with the matrix for fiber drawing deformation and damage. The two materials jointly reduced the damage of impact kinetic energy to the concrete matrix and achieved the purpose of toughening and crack resistance;the impact times of BFRC could be statistically analyzed by two parameter Weibull distribution.
2022, 52(9): 48-52,66.
doi: 10.13204/j.gyjzg21112207
Abstract:
Rapid chloride ion migration coefficient method(RCM)was used to measure the unsteady migration coefficient of chloride ion in concrete, so as to evaluate the resistance of concrete to chloride penetration. The effects of basalt fiber with different volume ratio, calcium sulfate whisker with different mass contents and different hybrid fiber contents of basalt fiber and calcium sulfate whisker on resistance of concrete to chloride penetration were studied. The results showed that the influence of single basalt fiber on the resistance of concrete to chloride penetration was not obvious. Resistance of concrete to chloride permeability could be improved by adding calcium sulfate whisker alone. With increase of the whisker content, the resistance of concrete to chloride permeability increased first and then decreased, but it was all higher than that of ordinary concrete. The optimal whisker content was 2%, and the chloride ion permeability resistance of concrete was improved by 36.8% compared with that of ordinary concrete. An appropriate hybrid fiber content of basalt fiber and calcium sulfate whisker could improve the resistance of concrete to chloride penetration, and the maximum improvement rate was 33.7%. The improvement of chloride penetration resistance of hybrid fiber concrete with basalt fiber and calcium sulfate whisker was mainly from calcium sulfate whisker.
Rapid chloride ion migration coefficient method(RCM)was used to measure the unsteady migration coefficient of chloride ion in concrete, so as to evaluate the resistance of concrete to chloride penetration. The effects of basalt fiber with different volume ratio, calcium sulfate whisker with different mass contents and different hybrid fiber contents of basalt fiber and calcium sulfate whisker on resistance of concrete to chloride penetration were studied. The results showed that the influence of single basalt fiber on the resistance of concrete to chloride penetration was not obvious. Resistance of concrete to chloride permeability could be improved by adding calcium sulfate whisker alone. With increase of the whisker content, the resistance of concrete to chloride permeability increased first and then decreased, but it was all higher than that of ordinary concrete. The optimal whisker content was 2%, and the chloride ion permeability resistance of concrete was improved by 36.8% compared with that of ordinary concrete. An appropriate hybrid fiber content of basalt fiber and calcium sulfate whisker could improve the resistance of concrete to chloride penetration, and the maximum improvement rate was 33.7%. The improvement of chloride penetration resistance of hybrid fiber concrete with basalt fiber and calcium sulfate whisker was mainly from calcium sulfate whisker.
2022, 52(9): 53-59,79.
doi: 10.13204/j.gyjzG21090209
Abstract:
The minimal surface generated by mathematical formulas and algorithms, which has special mathematical aesthetic feelings and artistic states, provides novel and rich creative themes for architectural space. However, due to its high complexity of shapes, extreme lightweight masses and thin thickness, it poses a high challenge to structural design and curved surface fabrication. Based on the analysis of the relation between forces and shapes, the concepts and methods how to transform the mathematical model to the mechanical model by the experimental scheme combining qualitative analysis with quantitative calculations were discussed and demonstrated. Based on economic considerations, the problems how to decompose, fit, fabricate and assemble the minimal surface effectively through the combination of parametric design with Computer Numerical Control (CNC) technology were discussed. As a demonstration for quantitative experiments and preliminary explorations of technical routes, it could provide empirical reference and the problems theoretical pathes for the research on collaborative forming of architectural parametric design and structural mechanics.
The minimal surface generated by mathematical formulas and algorithms, which has special mathematical aesthetic feelings and artistic states, provides novel and rich creative themes for architectural space. However, due to its high complexity of shapes, extreme lightweight masses and thin thickness, it poses a high challenge to structural design and curved surface fabrication. Based on the analysis of the relation between forces and shapes, the concepts and methods how to transform the mathematical model to the mechanical model by the experimental scheme combining qualitative analysis with quantitative calculations were discussed and demonstrated. Based on economic considerations, the problems how to decompose, fit, fabricate and assemble the minimal surface effectively through the combination of parametric design with Computer Numerical Control (CNC) technology were discussed. As a demonstration for quantitative experiments and preliminary explorations of technical routes, it could provide empirical reference and the problems theoretical pathes for the research on collaborative forming of architectural parametric design and structural mechanics.
2022, 52(9): 60-66.
doi: 10.13204/j.gyjzG21090603
Abstract:
In view of the current situation of low utilization ratio and poor accessibility of sports buildings, the paper explored the combination of old industrial buildings and sports functions from the perspective of the stock of buildings, compared the form and structure choices of old industrial buildings and long-span sports spaces, combined with the life mode of modern society and the exposure of emerging industries. The possibility of combining sports with other functions to enhance the vitality of the city was explored, as well as to awaken and retain the memory of old industrial buildings.
In view of the current situation of low utilization ratio and poor accessibility of sports buildings, the paper explored the combination of old industrial buildings and sports functions from the perspective of the stock of buildings, compared the form and structure choices of old industrial buildings and long-span sports spaces, combined with the life mode of modern society and the exposure of emerging industries. The possibility of combining sports with other functions to enhance the vitality of the city was explored, as well as to awaken and retain the memory of old industrial buildings.
2022, 52(9): 67-73,93.
doi: 10.13204/j.gyjzG22032906
Abstract:
Coal gangue is a typical kind of solid waste produced during the process of coal mining, and crushing it to replace natural aggregate in concrete can realize its recycling. To study the flexural properties of reinforced truss spontaneous-combustion coal gangue aggregate concrete (RTSCGAC) composite slab, the finite element model of RTSCCGA composite slab was established by using ABAQUS software, and the reliability of the model was verified by the load-deflection and load-stiffness results from 8 groups of full-scale specimens; a parametric study was conducted and the influence of replacement ratio of spontaneous-combustion coal gangue aggregate (SCGA) on the flexural properties (flexural capacity and flexural stiffness) of RTSCGAC composite slab was quantified; based on the results of parametric analysis, the existing code design methods were reviewed. The results showed that the flexural properties of RTSCGAC composite slab decreased with the incorporation of SCGA, and the ultimate bearing capacity was slightly affected by the replacement ratio of SCGA. When the replacement ratio was 100%, the bending moment was only reduced by 0.15%~0.69%, while the flexural stiffness decreased by 30.65%~30.99%; Code for Design of Concrete Structures (GB 50010—2017) could be used for predicting the flexural stiffness of RTSCGAC composite slabs.
Coal gangue is a typical kind of solid waste produced during the process of coal mining, and crushing it to replace natural aggregate in concrete can realize its recycling. To study the flexural properties of reinforced truss spontaneous-combustion coal gangue aggregate concrete (RTSCGAC) composite slab, the finite element model of RTSCCGA composite slab was established by using ABAQUS software, and the reliability of the model was verified by the load-deflection and load-stiffness results from 8 groups of full-scale specimens; a parametric study was conducted and the influence of replacement ratio of spontaneous-combustion coal gangue aggregate (SCGA) on the flexural properties (flexural capacity and flexural stiffness) of RTSCGAC composite slab was quantified; based on the results of parametric analysis, the existing code design methods were reviewed. The results showed that the flexural properties of RTSCGAC composite slab decreased with the incorporation of SCGA, and the ultimate bearing capacity was slightly affected by the replacement ratio of SCGA. When the replacement ratio was 100%, the bending moment was only reduced by 0.15%~0.69%, while the flexural stiffness decreased by 30.65%~30.99%; Code for Design of Concrete Structures (GB 50010—2017) could be used for predicting the flexural stiffness of RTSCGAC composite slabs.
2022, 52(9): 74-79.
doi: 10.13204/j.gyjzg21093002
Abstract:
In order to study the seismic performance of core grouted congruent concrete prefabricated shear walls with vertical mixed reinforcement on the wall, 1 cast-in-place concrete shear wall specimen and 2 core grouted congruent concrete prefabricated shear walls were designed and full-scale fabricated. The walls of the two prefabricated specimens adopted the method of vertical symmetrical reinforcement and vertical mixed reinforcement respectively, quasi-static tests were conducted according to the axial compression ratio of 0.3. The test results showed that the failure patterns of the shear wall specimens with mixed reinforcement and the shear wall specimens with symmetrical reinforcement were similar, and both had compression and bending failure; there was no obvious slip phenomenon between the prefabricated member and the core grouted concrete; the seismic performance of shear wall specimens with symmetrical reinforcement was slightly higher than that of shear wall specimens with mixed reinforcement; the core grouted congruent concrete prefabricated shear walls with vertical mixed reinforcement on the wall could meet the requirements of Code for Seismic Design of Buildings (GB 50011—2010).
In order to study the seismic performance of core grouted congruent concrete prefabricated shear walls with vertical mixed reinforcement on the wall, 1 cast-in-place concrete shear wall specimen and 2 core grouted congruent concrete prefabricated shear walls were designed and full-scale fabricated. The walls of the two prefabricated specimens adopted the method of vertical symmetrical reinforcement and vertical mixed reinforcement respectively, quasi-static tests were conducted according to the axial compression ratio of 0.3. The test results showed that the failure patterns of the shear wall specimens with mixed reinforcement and the shear wall specimens with symmetrical reinforcement were similar, and both had compression and bending failure; there was no obvious slip phenomenon between the prefabricated member and the core grouted concrete; the seismic performance of shear wall specimens with symmetrical reinforcement was slightly higher than that of shear wall specimens with mixed reinforcement; the core grouted congruent concrete prefabricated shear walls with vertical mixed reinforcement on the wall could meet the requirements of Code for Seismic Design of Buildings (GB 50011—2010).
2022, 52(9): 80-86.
doi: 10.13204/j.gyjzg21040102
Abstract:
The mega column design is one of the key points in the structural design of CITIC Tower. The integrated design method of building structure is adopted to control the geometry of the mega-column to realize the unity of architectural effect and structural force transmission. Through appropriate cavity structure design, it can solve the complicated cross-section changes of the mega column, while ensuring its reliable force transmission and convenient construction. The slab stiffness has a significant influence on the effective length of the mega column. By analyzing the variation of the effective length, the economical value of the effective length was determined. Through the finite element analysis, the safety of the key joints such as the mega column branching joint, the mega column and the transfer truss joint was verified. In this project, non-embedded column foot was adopted, and wing wall was set to diffusion the column force. The column foot reliability under non-yielding in rare seismic was verified by finite element.
The mega column design is one of the key points in the structural design of CITIC Tower. The integrated design method of building structure is adopted to control the geometry of the mega-column to realize the unity of architectural effect and structural force transmission. Through appropriate cavity structure design, it can solve the complicated cross-section changes of the mega column, while ensuring its reliable force transmission and convenient construction. The slab stiffness has a significant influence on the effective length of the mega column. By analyzing the variation of the effective length, the economical value of the effective length was determined. Through the finite element analysis, the safety of the key joints such as the mega column branching joint, the mega column and the transfer truss joint was verified. In this project, non-embedded column foot was adopted, and wing wall was set to diffusion the column force. The column foot reliability under non-yielding in rare seismic was verified by finite element.
2022, 52(9): 87-93.
doi: 10.13204/j.gyjzg22031516
Abstract:
A new calculation method of bond strength between steel bars and concrete with different aggregate types was proposed. Combined with 748 groups of test data and the introduction to dynamic renewal theories of the neural network, a prediction model with multi parameters for bond strength based on neural network method was established, the significance analysis of influencing factors of bond strength was conducted, the prediction model was simplified by the parameter elimination method of the neural network, and the formula for critical anchorage length was put forward. Important factors that influenced bond performances were tensile strength, anchorage length, diameters of steel bars, and thickness of concrete covers. The proposed model was of higher prediction accuracy and the mean value and coefficient of variation for the ratio of the prediction values to test values were 1.056 and 0.377 respectively. It provided a new method to predict bond strength between steel bars and concrete.
A new calculation method of bond strength between steel bars and concrete with different aggregate types was proposed. Combined with 748 groups of test data and the introduction to dynamic renewal theories of the neural network, a prediction model with multi parameters for bond strength based on neural network method was established, the significance analysis of influencing factors of bond strength was conducted, the prediction model was simplified by the parameter elimination method of the neural network, and the formula for critical anchorage length was put forward. Important factors that influenced bond performances were tensile strength, anchorage length, diameters of steel bars, and thickness of concrete covers. The proposed model was of higher prediction accuracy and the mean value and coefficient of variation for the ratio of the prediction values to test values were 1.056 and 0.377 respectively. It provided a new method to predict bond strength between steel bars and concrete.
2022, 52(9): 94-100,107.
doi: 10.13204/j.gyjzg21052302
Abstract:
The seismic isolation effect of different isolation schemes for high-rise buildings in high-intensity area were compared and analyzed, including single lead rubber bearing isolation, single natural rubber bearing isolation, lead rubber and natural rubber bearing mixed isolation, and the above schemes were combined with viscous dampers. Based on the optimal damping indexes and damping coefficients obtained from the analysis, the influence of reducing natural vibration period of non-isolated structure on the seismic isolation effect was analyzed by using the mixed damping scheme of viscous damper and natural rubber bearing. The analysis showed that adding viscous damper in the isolation layer could significantly improve the seismic isolation effect, reduce the horizontal damping coefficient, and reduce the tensile stress and displacement of the bearing. For high-rise isolated buildings with flexible superstructures, it might be difficult to achieve the expected damping target only by adjusting the layout or parameters of rubber bearings and viscous dampers. The more effective method should be improving the stiffness of superstructure and reducing the natural vibration period of superstructure. Increasing damper output could not necessarily reduce horizontal damping coefficient and bearing tensile stress. The damping coefficient and damping index had an optimal value for the influence of horizontal damping coefficient and bearing tensile stress.
The seismic isolation effect of different isolation schemes for high-rise buildings in high-intensity area were compared and analyzed, including single lead rubber bearing isolation, single natural rubber bearing isolation, lead rubber and natural rubber bearing mixed isolation, and the above schemes were combined with viscous dampers. Based on the optimal damping indexes and damping coefficients obtained from the analysis, the influence of reducing natural vibration period of non-isolated structure on the seismic isolation effect was analyzed by using the mixed damping scheme of viscous damper and natural rubber bearing. The analysis showed that adding viscous damper in the isolation layer could significantly improve the seismic isolation effect, reduce the horizontal damping coefficient, and reduce the tensile stress and displacement of the bearing. For high-rise isolated buildings with flexible superstructures, it might be difficult to achieve the expected damping target only by adjusting the layout or parameters of rubber bearings and viscous dampers. The more effective method should be improving the stiffness of superstructure and reducing the natural vibration period of superstructure. Increasing damper output could not necessarily reduce horizontal damping coefficient and bearing tensile stress. The damping coefficient and damping index had an optimal value for the influence of horizontal damping coefficient and bearing tensile stress.
2022, 52(9): 101-107.
doi: 10.13204/j.gyjzg21060914
Abstract:
In order to study the creep effect of prestressed concrete continuous beam bridge in the construction process based on cantilever construction method, the construction process of Hai’an Xintongyang Grand Canal was monitored. The approximate calculation formula of bridge creep effect at any time was deduced. The concept of influence coefficient was proposed. The creep coefficient formula was obtained by linear regression. The results showed that the creep coefficient of single loading age obtained by regression could be extended to any loading age by aging theory. Compared with the current bridge codes in China and America, the calculated results and the measured results only had errors within 15 percent of the range, and the agreement was good. However, the strain deviation calculated by the current bridge code in China and the American code was more than 15%, and the deflection deviation was larger on the whole. Therefore, the calculation method obtained in this paper showed a good accuracy.
In order to study the creep effect of prestressed concrete continuous beam bridge in the construction process based on cantilever construction method, the construction process of Hai’an Xintongyang Grand Canal was monitored. The approximate calculation formula of bridge creep effect at any time was deduced. The concept of influence coefficient was proposed. The creep coefficient formula was obtained by linear regression. The results showed that the creep coefficient of single loading age obtained by regression could be extended to any loading age by aging theory. Compared with the current bridge codes in China and America, the calculated results and the measured results only had errors within 15 percent of the range, and the agreement was good. However, the strain deviation calculated by the current bridge code in China and the American code was more than 15%, and the deflection deviation was larger on the whole. Therefore, the calculation method obtained in this paper showed a good accuracy.
2022, 52(9): 108-114.
doi: 10.13204/j.gyjzG20121908
Abstract:
To study the mechanical properties of aluminum alloy bolt ball joint used in composite space truss structures under axial compression, tensile and compression tests of aluminum alloy ball joints with high-strength stainless steel bolts and high-strength aluminum alloy bolts were conducted. Axial tensile and compression tests were carried out respectively for aluminum alloy bolt ball joints with different bolt materials, sealing plates and sleeve sizes, and the axial tensile-compression bearing response laws and failure modes of aluminum alloy bolt ball joints with different joint size parameters were obtained. The test results showed that S51740 high-strength stainless steel was superior to 7075-T6 high-strength aluminum alloy in terms of elastic modulus, strength and ductility; due to the difference of bolt material and thickness of sealing plate, the aluminum alloy bolt ball joint would occur bolt fracture failure, sealing plate shear failure and ball internal thread shear failure under tensile load, and the selection of high-strength stainless steel and increasing the thickness of sealing plate could significantly improve the initial stiffness of joints; due to the different sizes of the sleeve and thickness of the sealing plate, the aluminum alloy bolt ball joint would occur sleeve compression failure and sealing plate shear failure, and the bearing area of sleeve was the main control parameter of the joint bearing design; when the aluminum alloy bolt ball joint parts entered into plasticity, the tensile stiffness and compression stiffness of the joint were significantly reduced.
To study the mechanical properties of aluminum alloy bolt ball joint used in composite space truss structures under axial compression, tensile and compression tests of aluminum alloy ball joints with high-strength stainless steel bolts and high-strength aluminum alloy bolts were conducted. Axial tensile and compression tests were carried out respectively for aluminum alloy bolt ball joints with different bolt materials, sealing plates and sleeve sizes, and the axial tensile-compression bearing response laws and failure modes of aluminum alloy bolt ball joints with different joint size parameters were obtained. The test results showed that S51740 high-strength stainless steel was superior to 7075-T6 high-strength aluminum alloy in terms of elastic modulus, strength and ductility; due to the difference of bolt material and thickness of sealing plate, the aluminum alloy bolt ball joint would occur bolt fracture failure, sealing plate shear failure and ball internal thread shear failure under tensile load, and the selection of high-strength stainless steel and increasing the thickness of sealing plate could significantly improve the initial stiffness of joints; due to the different sizes of the sleeve and thickness of the sealing plate, the aluminum alloy bolt ball joint would occur sleeve compression failure and sealing plate shear failure, and the bearing area of sleeve was the main control parameter of the joint bearing design; when the aluminum alloy bolt ball joint parts entered into plasticity, the tensile stiffness and compression stiffness of the joint were significantly reduced.
2022, 52(9): 115-120.
doi: 10.13204/j.gyjzG22041108
Abstract:
The construction period of LNG stainless steel storage tank is generally 6 to 8 months. During the construction, the steel surface is affected by solar radiation and the temperature effect will affect the structure. Through the finite element simulation, the non-uniform temperature field distribution of the tank wall under solar radiation was obtained, and it was found that when the latitude increased by every 10°, the maximum temperature increased by 3%. Considering the solar radiation, the maximum stress and maximum radial displacement of the tank wall increased by 96% and 832%, respectively, compared with the working condition considering only the effect of gravity. During the construction of cold insulation layer, a gap of 30 mm should be reserved to ensure the structural integrity.
The construction period of LNG stainless steel storage tank is generally 6 to 8 months. During the construction, the steel surface is affected by solar radiation and the temperature effect will affect the structure. Through the finite element simulation, the non-uniform temperature field distribution of the tank wall under solar radiation was obtained, and it was found that when the latitude increased by every 10°, the maximum temperature increased by 3%. Considering the solar radiation, the maximum stress and maximum radial displacement of the tank wall increased by 96% and 832%, respectively, compared with the working condition considering only the effect of gravity. During the construction of cold insulation layer, a gap of 30 mm should be reserved to ensure the structural integrity.
2022, 52(9): 121-128.
doi: 10.13204/j.gyjzg22030601
Abstract:
In order to investigate the performance of shear connections of new profabricated steel-concrete composite beam, 4 types of shear connection construction were designed, including connections with local laminated region, with UHPC (ultra-high performance concrete) post-casting belt, with UHPC slotted post-casting belt and with slotted post-casting belt having post-placed shear rebar. Totally 10 specimens were fabricated and tested by static push-out test. Using the experimental phenomena and test data, the effects of different configurations, including diameter of studs, strength of post-casting concrete, shear slot and shear rebar in slot, on the failure mode, crack mode, load-slip characteristics and ultimate bearing capacity of prefabricated composite beams were analyzed. The results indicated the bearing capacity of prefabricated composite beams increased with the increase of stud diameter and post-casting concrete strength. UHPC post-casting belt configuration and post-placed shear rebars could significantly improve the shear capacity of specimens. The longitudinal shear mechanism of the prefabricated composite beam with post-casted UHPC was different from the traditional composite beam, and the interface between prefabricated slab and post-casted UHPC might become weak area under the interfacial shear force, and fail before studs or the concrete around studs.
In order to investigate the performance of shear connections of new profabricated steel-concrete composite beam, 4 types of shear connection construction were designed, including connections with local laminated region, with UHPC (ultra-high performance concrete) post-casting belt, with UHPC slotted post-casting belt and with slotted post-casting belt having post-placed shear rebar. Totally 10 specimens were fabricated and tested by static push-out test. Using the experimental phenomena and test data, the effects of different configurations, including diameter of studs, strength of post-casting concrete, shear slot and shear rebar in slot, on the failure mode, crack mode, load-slip characteristics and ultimate bearing capacity of prefabricated composite beams were analyzed. The results indicated the bearing capacity of prefabricated composite beams increased with the increase of stud diameter and post-casting concrete strength. UHPC post-casting belt configuration and post-placed shear rebars could significantly improve the shear capacity of specimens. The longitudinal shear mechanism of the prefabricated composite beam with post-casted UHPC was different from the traditional composite beam, and the interface between prefabricated slab and post-casted UHPC might become weak area under the interfacial shear force, and fail before studs or the concrete around studs.
2022, 52(9): 129-137.
doi: 10.13204/j.gyjzg21081705
Abstract:
In order to study the buckling performance of webs of castellated steel-concrete composite beams under the combined action of negative bending moment and shear force, two castellated steel-concrete composite beams and one castellated steel beam were designed for static loading test. Based on the test results, the nonlinear finite element model of castellated steel-concrete composite beam with initial geometric imperfections was established. The finite element model was verified, and the effects of parameters, such as opening ratio and web height-thickness ratio, on the buckling performance of castellated steel-concrete composite beams were analyzed. The results showed that concrete slabs on beams could increase the yield load and ultimate load of specimens, and improve the buckling resistance of webs to a certain extent. The web height-thickness ratio had a significant effect on the buckling performance of webs. Reducing the web height-thickness ratio could improve the buckling load of webs and enhance the buckling performance of webs of specimens, The opening ratio had a great influence on the buckling performance of webs, the buckling load of composite beams increased with the decrease of opening ratio. When the height-thickness ratio was below 58, the strength failure of castellated steel-concrete composite beams occurred before the stability failure.
In order to study the buckling performance of webs of castellated steel-concrete composite beams under the combined action of negative bending moment and shear force, two castellated steel-concrete composite beams and one castellated steel beam were designed for static loading test. Based on the test results, the nonlinear finite element model of castellated steel-concrete composite beam with initial geometric imperfections was established. The finite element model was verified, and the effects of parameters, such as opening ratio and web height-thickness ratio, on the buckling performance of castellated steel-concrete composite beams were analyzed. The results showed that concrete slabs on beams could increase the yield load and ultimate load of specimens, and improve the buckling resistance of webs to a certain extent. The web height-thickness ratio had a significant effect on the buckling performance of webs. Reducing the web height-thickness ratio could improve the buckling load of webs and enhance the buckling performance of webs of specimens, The opening ratio had a great influence on the buckling performance of webs, the buckling load of composite beams increased with the decrease of opening ratio. When the height-thickness ratio was below 58, the strength failure of castellated steel-concrete composite beams occurred before the stability failure.
2022, 52(9): 138-146.
doi: 10.13204/j.gyjzg21072201
Abstract:
A new type of column-column connection is proposed, which is composed of upper and lower steel tubular columns, hooks and bending plates. There is no need to weld between the upper and lower columns, which can effectively improve the construction efficiency and shorten the construction period. The tensile tests of nine specimens were carried out, and the load-displacement and load-strain variation laws were analyzed. The design bearing capacity, ductility performance and ultimate bearing capacity of the specimens were obtained. Through parameter analysis, the influence of bending plate thickness, bending plate width, bending plate length, hook length, rebar diameter, bolt and bending plate on the bearing capacity of column-column connection was obtained. According to the test results, some reasonable suggestions were put forward for the practical application of the column-column connections.
A new type of column-column connection is proposed, which is composed of upper and lower steel tubular columns, hooks and bending plates. There is no need to weld between the upper and lower columns, which can effectively improve the construction efficiency and shorten the construction period. The tensile tests of nine specimens were carried out, and the load-displacement and load-strain variation laws were analyzed. The design bearing capacity, ductility performance and ultimate bearing capacity of the specimens were obtained. Through parameter analysis, the influence of bending plate thickness, bending plate width, bending plate length, hook length, rebar diameter, bolt and bending plate on the bearing capacity of column-column connection was obtained. According to the test results, some reasonable suggestions were put forward for the practical application of the column-column connections.
2022, 52(9): 147-152,120.
doi: 10.13204/j.gyjzg22010519
Abstract:
According to the existing calculation formula of the bearing capacity of steel tubed steel reinforced concrete (TSRC) columns under axial and eccentric compression, the neural network analysis model of the bearing capacity of TSRC columns under axial and eccentric compression was proposed. Ten sensitive parameters affecting the bearing capacity were selected to determine the number of nodes in the input layer, and the bearing capacity of TSRC cylinder was taken as the output layer. The number of nodes in the hidden layer was determined as 12 according to the mean square error MSE and correlation coefficient R by trial and error method, and the N10-12-1 neural network analysis model was established. The prediction results of the neural network analysis model show that the maximum error was only 6.08%, indicating that the established neural network analysis model for the bearing capacity of TSRC cylinder under axial compression and eccentric londing was a good method. Finally, sensitivity analysis based on Garson algorithm was carried out to obtain the influence degree of each input parameter on the bearing capacity of TSRC cylinder, which could be used for reference in engineering design.
According to the existing calculation formula of the bearing capacity of steel tubed steel reinforced concrete (TSRC) columns under axial and eccentric compression, the neural network analysis model of the bearing capacity of TSRC columns under axial and eccentric compression was proposed. Ten sensitive parameters affecting the bearing capacity were selected to determine the number of nodes in the input layer, and the bearing capacity of TSRC cylinder was taken as the output layer. The number of nodes in the hidden layer was determined as 12 according to the mean square error MSE and correlation coefficient R by trial and error method, and the N10-12-1 neural network analysis model was established. The prediction results of the neural network analysis model show that the maximum error was only 6.08%, indicating that the established neural network analysis model for the bearing capacity of TSRC cylinder under axial compression and eccentric londing was a good method. Finally, sensitivity analysis based on Garson algorithm was carried out to obtain the influence degree of each input parameter on the bearing capacity of TSRC cylinder, which could be used for reference in engineering design.
2022, 52(9): 153-160.
doi: 10.13204/j.gyjzG22030702
Abstract:
The quasi-static test was carried out on 6 sets of H-steel beam to column connections with restraint at beam ends (JD2-2 had not passed the fire test), hysteretic curves and skeleton curves of joints were obtained, the bearing capacity, stiffness degradation, ductility and energy dissipation capacity of specimens were analyzed. The results showed that two-end extended end-plate connection joint had good deformation and energy dissipation capacity, the energy dissipation capacity of the one-end extended end-plate connection joint was weak and applicable to non-seismic zone; the strength, stiffness and ductility of joint were reduced by fire, and there was no effect on the energy dissipation capacity; Increasing the end-plate thickness could improve the bearing capacity and energy dissipation capacity of the joint after fire, it had little effect on improving the ductility of joint after fire; the ductility and energy dissipation capacity of the joint could be improved by setting stiffeners at beam ends and shear brackets at the bottom of the end plate, but the bearing capacity of the joint was not improved obviously after fire.
The quasi-static test was carried out on 6 sets of H-steel beam to column connections with restraint at beam ends (JD2-2 had not passed the fire test), hysteretic curves and skeleton curves of joints were obtained, the bearing capacity, stiffness degradation, ductility and energy dissipation capacity of specimens were analyzed. The results showed that two-end extended end-plate connection joint had good deformation and energy dissipation capacity, the energy dissipation capacity of the one-end extended end-plate connection joint was weak and applicable to non-seismic zone; the strength, stiffness and ductility of joint were reduced by fire, and there was no effect on the energy dissipation capacity; Increasing the end-plate thickness could improve the bearing capacity and energy dissipation capacity of the joint after fire, it had little effect on improving the ductility of joint after fire; the ductility and energy dissipation capacity of the joint could be improved by setting stiffeners at beam ends and shear brackets at the bottom of the end plate, but the bearing capacity of the joint was not improved obviously after fire.
2022, 52(9): 161-169.
doi: 10.13204/j.gyjzg20112911
Abstract:
In order to simplify the seismic response analysis model of the steel reinforced concrete spatial frame with special-shaped columns, a two-direction two-bay eight-story steel reinforced concrete spatial frame with special-shaped columns was taken as the original analysis model. Based on the finite element software platform of OpenSees Navigator, the spatial frame under bidirectional earthquakes, the spatial frame under unidirectional earthquakes, and the plane frame under unidirectional earthquakes were established as the research objects. In particular, the plane frame had the same period with the spactial frame by adjusting the width of subordinate area. By comparing and analyzing the seismic response of the three models, such as acceleration responses, displacement responses, basement shear versus top displacement hysteresis curve, energy dissipation capacity, et al, the rationality of simplified method was verified. The results showed that the dynamic responses of the three models under different earthquakes were similar, and it was feasible to carry out seismic response analysis by using the steel reinforced concrete plane frame with special-shaped columns after quality adjustment to replace the spatial frame.
In order to simplify the seismic response analysis model of the steel reinforced concrete spatial frame with special-shaped columns, a two-direction two-bay eight-story steel reinforced concrete spatial frame with special-shaped columns was taken as the original analysis model. Based on the finite element software platform of OpenSees Navigator, the spatial frame under bidirectional earthquakes, the spatial frame under unidirectional earthquakes, and the plane frame under unidirectional earthquakes were established as the research objects. In particular, the plane frame had the same period with the spactial frame by adjusting the width of subordinate area. By comparing and analyzing the seismic response of the three models, such as acceleration responses, displacement responses, basement shear versus top displacement hysteresis curve, energy dissipation capacity, et al, the rationality of simplified method was verified. The results showed that the dynamic responses of the three models under different earthquakes were similar, and it was feasible to carry out seismic response analysis by using the steel reinforced concrete plane frame with special-shaped columns after quality adjustment to replace the spatial frame.
2022, 52(9): 170-177,185.
doi: 10.13204/j.gyjzG21090615
Abstract:
Considering the difficulty of construction and low assembly degree of ring plate outer joint, a new type of ring plate beam column outer joint was proposed. The force transfer mechanism, yield mechanism, failure mode, stiffness and energy dissipation capacity of typical specimens were numerically simulated by using the finite element analysis software ABAQUS. Based on the above research, the effects of cover plate size, aspect ratio of tube and CFRP configuration rate on the seismic performance of the joint were deeply analyzed. The results showed that the yield of the joint began in the middle of the flange of the steel beam in the plastic hinge area, extended to the web through the flange, and then yielded in the whole section. The ultimate rotation angle of the joint was 0.053 rad, and its rotation performance was good, which showed semi-rigid connection. The bearing capacity of the joint could be enhanced by adding the measurement of the cover plate and the aspect ratio of tube. The most suitable size should be: the width of the cover plate should be 0.7~0.9 times the height of the steel beam; the thickness of cover plate should be 0.7~1.2 times the thickness of steel beam flange; the ratio of aspect ratio of tube should be 30~50; the CFRP configuration rate could satisfy the bearing capacity and deformation capacity of the column itself.
Considering the difficulty of construction and low assembly degree of ring plate outer joint, a new type of ring plate beam column outer joint was proposed. The force transfer mechanism, yield mechanism, failure mode, stiffness and energy dissipation capacity of typical specimens were numerically simulated by using the finite element analysis software ABAQUS. Based on the above research, the effects of cover plate size, aspect ratio of tube and CFRP configuration rate on the seismic performance of the joint were deeply analyzed. The results showed that the yield of the joint began in the middle of the flange of the steel beam in the plastic hinge area, extended to the web through the flange, and then yielded in the whole section. The ultimate rotation angle of the joint was 0.053 rad, and its rotation performance was good, which showed semi-rigid connection. The bearing capacity of the joint could be enhanced by adding the measurement of the cover plate and the aspect ratio of tube. The most suitable size should be: the width of the cover plate should be 0.7~0.9 times the height of the steel beam; the thickness of cover plate should be 0.7~1.2 times the thickness of steel beam flange; the ratio of aspect ratio of tube should be 30~50; the CFRP configuration rate could satisfy the bearing capacity and deformation capacity of the column itself.
2022, 52(9): 178-185.
doi: 10.13204/j.gyjzg21091006
Abstract:
The wind-induced effect is one of the important control factors of chimney in design. A chimney with rectangular section (about 100 meters high) located in Wuhan is decorated with fishscale surface, which can not only play a decorative effect, but also restrain its wind load. In addition, an adjacent factory building (about 50 meters high) will also have a significant aerodynamic interference effect on the chimney. Therefore, the wind load (shape factor) and wind-induced response (equivalent static wind load) of the chimney were studied by means of wind tunnel test of rigid model for pressures measured. The research showed that: the fishscale treatment could significantly reduce the windward wind load (shape factor) and the across-wind vortex shedding effect of the chimney; the aerodynamic interference effect of the nearby factory building on the chimney was very obvious: when it was located in the upstream, the wind pressure on the windward side of the chimney became negative; when it was located in the downstream, the negative pressure on the crosswind side of the chimney became positive pressure, when it was located in one side, the negative pressure on the crosswind side near the factory building became larger, and even the windward side became negative pressure due to the influence of the separated flow and vortex shedding of the factory building; the along-wind equivalent static wind load based on CQC inversion method was close to that of Load Code for the Design of Building Structures (GB 5009—2012), while that of across wind and torsion direction were quite different.
The wind-induced effect is one of the important control factors of chimney in design. A chimney with rectangular section (about 100 meters high) located in Wuhan is decorated with fishscale surface, which can not only play a decorative effect, but also restrain its wind load. In addition, an adjacent factory building (about 50 meters high) will also have a significant aerodynamic interference effect on the chimney. Therefore, the wind load (shape factor) and wind-induced response (equivalent static wind load) of the chimney were studied by means of wind tunnel test of rigid model for pressures measured. The research showed that: the fishscale treatment could significantly reduce the windward wind load (shape factor) and the across-wind vortex shedding effect of the chimney; the aerodynamic interference effect of the nearby factory building on the chimney was very obvious: when it was located in the upstream, the wind pressure on the windward side of the chimney became negative; when it was located in the downstream, the negative pressure on the crosswind side of the chimney became positive pressure, when it was located in one side, the negative pressure on the crosswind side near the factory building became larger, and even the windward side became negative pressure due to the influence of the separated flow and vortex shedding of the factory building; the along-wind equivalent static wind load based on CQC inversion method was close to that of Load Code for the Design of Building Structures (GB 5009—2012), while that of across wind and torsion direction were quite different.
2022, 52(9): 186-192,213.
doi: 10.13204/j.gyjzG22012005
Abstract:
Large scale construction projects have been carried out on varieties of cold areas with deepening of the Western Development and the Northeast Revitalization Strategy. To ensure the life of construction projects and maintain their normal working states in service periods, the higher bearing capacity and stability are needed to keep for frozen soil and structures. It is characteristic of frozen soil-structure interfaces that the frozen mechanics is the most direct mirror, and the roughness of interfaces is one of important factors influencing characteristics. Therefore,taking roughness as an influencing factor, based on the existing scientific research achievements of shear test research on frozen soil-structure interfaces at home and abroad, it was systematically analyzed from roughness evaluation, effect laws of roughness on mechanical properties and microscopic mechanisms. Based on the Gompertz model, a constitutive model between shear stress and displacement on interfaces was presented by considering the effect of roughness, which could well describe the evolution laws between stress and displacement of interfaces.
Large scale construction projects have been carried out on varieties of cold areas with deepening of the Western Development and the Northeast Revitalization Strategy. To ensure the life of construction projects and maintain their normal working states in service periods, the higher bearing capacity and stability are needed to keep for frozen soil and structures. It is characteristic of frozen soil-structure interfaces that the frozen mechanics is the most direct mirror, and the roughness of interfaces is one of important factors influencing characteristics. Therefore,taking roughness as an influencing factor, based on the existing scientific research achievements of shear test research on frozen soil-structure interfaces at home and abroad, it was systematically analyzed from roughness evaluation, effect laws of roughness on mechanical properties and microscopic mechanisms. Based on the Gompertz model, a constitutive model between shear stress and displacement on interfaces was presented by considering the effect of roughness, which could well describe the evolution laws between stress and displacement of interfaces.
2022, 52(9): 193-197.
doi: 10.13204/j.gyjzg21082515
Abstract:
In order to explore the influence of joint factors on the stability for surrounding rock of pilot tunnels under the construction of underground station by the pile-beam-arch approach. Against the background of Yatai Street Station in Changchun, the pilot tunnel model around the ubiquitous joints was constructed. For parts of the joint parameters, a six factors and five levels orthogonal scheme was built and parameter sensitivity was analyzed. The results showed that the order of joint factors that influenced the stability for surrounding rock of pilot tunnels from large to small was the internal friction angle of joints, the cohesion of joints, the dip angles of joints, the dilatancy angle of joints, the tensile strength of joints and the inclination of joints. With the increase of internal friction angles and cohesion of joints, the stability of surrounding rock increased gradually.
In order to explore the influence of joint factors on the stability for surrounding rock of pilot tunnels under the construction of underground station by the pile-beam-arch approach. Against the background of Yatai Street Station in Changchun, the pilot tunnel model around the ubiquitous joints was constructed. For parts of the joint parameters, a six factors and five levels orthogonal scheme was built and parameter sensitivity was analyzed. The results showed that the order of joint factors that influenced the stability for surrounding rock of pilot tunnels from large to small was the internal friction angle of joints, the cohesion of joints, the dip angles of joints, the dilatancy angle of joints, the tensile strength of joints and the inclination of joints. With the increase of internal friction angles and cohesion of joints, the stability of surrounding rock increased gradually.
2022, 52(9): 198-205.
doi: 10.13204/j.gyjzG21082101
Abstract:
Taking energy piles as the reasearch object, combined with the actual geological layered seepage, the differential equation for heat transfer of energy piles was established according to the principle of energy conservation. The excess temperature equation for heat transfer of energy piles in layered seepage soil was obtained by the method of seperation variables and Laplace Transform. The calculation software was programmed to verify the accuracy of the heat transfer model. Based on the model, the influence for thermophysical properties of soil and seepage velocities on the distribution of excess temperature was discussed. The results showed that changes in thermophysical properties of adjacent soil layers under and below the piles would influence the excess temperature distribution at the top and bottom of the piles, and had a certain impact on the total heat transfer of piles. Seepage had a significant impact on the distribution of excess temperature in stratified soil. At the same distance apart from the centers of energy piles, the excess temperature of the upper-stream was lower than that of the lower-stream in the same soil layer. The higher the seepage velocity, the more significant the isotherm deviation of excess temperature in the soil layer; the more obvious the heat transfer, and the higher the heat exchange efficiency of energy piles.
Taking energy piles as the reasearch object, combined with the actual geological layered seepage, the differential equation for heat transfer of energy piles was established according to the principle of energy conservation. The excess temperature equation for heat transfer of energy piles in layered seepage soil was obtained by the method of seperation variables and Laplace Transform. The calculation software was programmed to verify the accuracy of the heat transfer model. Based on the model, the influence for thermophysical properties of soil and seepage velocities on the distribution of excess temperature was discussed. The results showed that changes in thermophysical properties of adjacent soil layers under and below the piles would influence the excess temperature distribution at the top and bottom of the piles, and had a certain impact on the total heat transfer of piles. Seepage had a significant impact on the distribution of excess temperature in stratified soil. At the same distance apart from the centers of energy piles, the excess temperature of the upper-stream was lower than that of the lower-stream in the same soil layer. The higher the seepage velocity, the more significant the isotherm deviation of excess temperature in the soil layer; the more obvious the heat transfer, and the higher the heat exchange efficiency of energy piles.
2022, 52(9): 206-213.
doi: 10.13204/j.gyjzG21082505
Abstract:
Based on an engineering case of static load tests on super-long large-diameter cast-in-place piles by the method of reaction piles combined the stacking loads, the effect of reaction piles and stacking weight on settlement of test piles was discussed. According to test conditions, a 3D model was constructed, the influence on test piles during loading and unloading processes of cribbings and reaction piles was analyzed, involving pile-soil settlement, axial force of pile shafts, displacement of monitoring points and bearing characteristics of test piles. The results showed that during the static loading test on super-long large-diameter cast-in-place piles by reaction pile methods combined stacking loads, the uplift of reaction piles would drive soil surrounding test piles upward, and promote the development of side friction in advance. Attention should be paid to reduction in vertical displacement of test piles due to uplift of reaction piles. The space between reaction piles and test piles should be arranged large enough to satisfy the requirements of design specifications. Larger space would be expected when conditions permitted. A high precision level or total station was suggested to be used to monitor and check the vertical displacement of test piles, so that influences of reaction piles and cribbings during the loading and unloading process on displacement of reference points could be eliminated to avoid misjudgment.
Based on an engineering case of static load tests on super-long large-diameter cast-in-place piles by the method of reaction piles combined the stacking loads, the effect of reaction piles and stacking weight on settlement of test piles was discussed. According to test conditions, a 3D model was constructed, the influence on test piles during loading and unloading processes of cribbings and reaction piles was analyzed, involving pile-soil settlement, axial force of pile shafts, displacement of monitoring points and bearing characteristics of test piles. The results showed that during the static loading test on super-long large-diameter cast-in-place piles by reaction pile methods combined stacking loads, the uplift of reaction piles would drive soil surrounding test piles upward, and promote the development of side friction in advance. Attention should be paid to reduction in vertical displacement of test piles due to uplift of reaction piles. The space between reaction piles and test piles should be arranged large enough to satisfy the requirements of design specifications. Larger space would be expected when conditions permitted. A high precision level or total station was suggested to be used to monitor and check the vertical displacement of test piles, so that influences of reaction piles and cribbings during the loading and unloading process on displacement of reference points could be eliminated to avoid misjudgment.
2022, 52(9): 214-218,160.
doi: 10.13204/j.gyjzg21062506
Abstract:
Seismic response analysis on underground engineering must consider the dynamic interaction between structures and foundation, in which the free field response analysis of soil strata is an essential issue to determine the seismic input. Studying free field responses of soil strata subjected to vertical compression waves combined with horizontal shear waves, it was found that compared with under the action of horizontal shear wave only, the composition of short period harmonic waves in the upper soil stratum was more abundant under the action of the horizontal shear wave combined with vertical compression wave, and the corresponding horizontal response of the earth’s surface in free fields increased. Therefore, it was necessary to consider the influence of the vertical compression wave on field responses to ensure the safety of underground engineering with high seismic safety level requirements. Moreover, the effects of groundwater level variation and loading intensity on dynamic responses of soil strata were also analyzed. The analysis showed that with the increase of earthquake strength, the stress state of soil strata changed, the amplification factor in the earth surface gradually increased along the vertical direction and decreased along the horizontal direction. As the fluctuation of groundwater level, the frequency response curve of the surface changed steadily, the drop of groundwater level induced the decrease of horizontal vibration and the increase of vertical vibration in the earth surface.
Seismic response analysis on underground engineering must consider the dynamic interaction between structures and foundation, in which the free field response analysis of soil strata is an essential issue to determine the seismic input. Studying free field responses of soil strata subjected to vertical compression waves combined with horizontal shear waves, it was found that compared with under the action of horizontal shear wave only, the composition of short period harmonic waves in the upper soil stratum was more abundant under the action of the horizontal shear wave combined with vertical compression wave, and the corresponding horizontal response of the earth’s surface in free fields increased. Therefore, it was necessary to consider the influence of the vertical compression wave on field responses to ensure the safety of underground engineering with high seismic safety level requirements. Moreover, the effects of groundwater level variation and loading intensity on dynamic responses of soil strata were also analyzed. The analysis showed that with the increase of earthquake strength, the stress state of soil strata changed, the amplification factor in the earth surface gradually increased along the vertical direction and decreased along the horizontal direction. As the fluctuation of groundwater level, the frequency response curve of the surface changed steadily, the drop of groundwater level induced the decrease of horizontal vibration and the increase of vertical vibration in the earth surface.
2022, 52(9): 219-223,146.
doi: 10.13204/j.gyjzG22062508
Abstract:
Based on the overlap shield tunnel beneath the water supply pipe between Xiandaidadao Station and Loujiangdadao Station of Suzhou Metro Line 3, numerical method was used to analyze the mechanical properties of new structure-existing structure-earth’s surface under different construction sequences ("first lower then upper" or "first upper then lower"). And the better construction sequence was recommended considering the earth’s surface settlement, the water supply pipe deformation and the shield lining deformation. Combined with site monitor results, the influence of construction on water supply pipe was analyzed. Through the above research, the following conclusions were obtained: 1) constructions of overlapping tunnels caused two disturbances to the water supply pipe, and the adverse effects gradually increased; 2) the influence of lower tunnel construction on earth’s surface settlement and water supply pipe deformation was less than that of upper tunnel construction; 3) the construction sequence "first lower then upper" should be recommended; 4) the deformation of the water supply pipe caused by the construction of overlapping tunnels could meet the requirements of normal use of the water supply pipe.
Based on the overlap shield tunnel beneath the water supply pipe between Xiandaidadao Station and Loujiangdadao Station of Suzhou Metro Line 3, numerical method was used to analyze the mechanical properties of new structure-existing structure-earth’s surface under different construction sequences ("first lower then upper" or "first upper then lower"). And the better construction sequence was recommended considering the earth’s surface settlement, the water supply pipe deformation and the shield lining deformation. Combined with site monitor results, the influence of construction on water supply pipe was analyzed. Through the above research, the following conclusions were obtained: 1) constructions of overlapping tunnels caused two disturbances to the water supply pipe, and the adverse effects gradually increased; 2) the influence of lower tunnel construction on earth’s surface settlement and water supply pipe deformation was less than that of upper tunnel construction; 3) the construction sequence "first lower then upper" should be recommended; 4) the deformation of the water supply pipe caused by the construction of overlapping tunnels could meet the requirements of normal use of the water supply pipe.
2022, 52(9): 224-228.
doi: 10.13204/j.gyjzG22062006
Abstract:
The structures of nuclear containment vessel usually work under biaxial pre-compressive stresses. The existed uniaxial creep theory cannot be used to calculate the creep deformation of concrete under biaxial compressive stresses. Considering the effect of biaxial compressive stresses, the matrix of creep Poisson’s ratio was established by introducing the parameter of stress ratio. Meanwhile, based on the B4 creep model of uniaxial stress, the creep function under biaxial stresses was developed using Dirichlet series. Combining the Poisson effect with material viscoelastic property, the nonlinear creep model under biaxial compressive stresses was proposed. The proposed model was verified by taking the comparison between numerical and experimental results. Finally, the proposed model was also employed to numerically analyze the pre-stress loss for a containment vessel. It is expected that the proposed model could be useful for the containment vessel structures on assessment of time-dependent prestress loss and prediction of further working life.
The structures of nuclear containment vessel usually work under biaxial pre-compressive stresses. The existed uniaxial creep theory cannot be used to calculate the creep deformation of concrete under biaxial compressive stresses. Considering the effect of biaxial compressive stresses, the matrix of creep Poisson’s ratio was established by introducing the parameter of stress ratio. Meanwhile, based on the B4 creep model of uniaxial stress, the creep function under biaxial stresses was developed using Dirichlet series. Combining the Poisson effect with material viscoelastic property, the nonlinear creep model under biaxial compressive stresses was proposed. The proposed model was verified by taking the comparison between numerical and experimental results. Finally, the proposed model was also employed to numerically analyze the pre-stress loss for a containment vessel. It is expected that the proposed model could be useful for the containment vessel structures on assessment of time-dependent prestress loss and prediction of further working life.
2022, 52(9): 229-233.
doi: 10.13204/j.gyjzG22041823
Abstract:
In order to study the effect of different dosages of metakaolin and silica fume on the physical and mechanical properties of EPS concrete, metakaolin and silica fume with different contents were used as auxiliary cementing materials, and the contents of 0%, 5%, 10% and 15% were used to replace part of the cement, respectively, and 16 groups of EPS concrete specimens with different proportions were prepared. The water absorption, compressive strength, flexural strength and splitting tensile strength were measured. The results showed that the addition of a certain amount of silica fume and metakaolin could reduce the water absorption of EPS concrete and improve its compressive strength, bending and splitting tensile strength, but when the dosage was too high, the water absorption would increase and the strength would decrease, and when the content of both was 10%, EPS concrete had the lowest water absorption and the best mechanical properties. Although the particle size of metakaolin was larger than that of silica fume, its "pozzolanic effect" was stronger, so the improvement of the mechanical properties of EPS concrete was better than that of silica fume. Metakaolin and silica fume could improve the adhesion of EPS particles to the gel matrix.
In order to study the effect of different dosages of metakaolin and silica fume on the physical and mechanical properties of EPS concrete, metakaolin and silica fume with different contents were used as auxiliary cementing materials, and the contents of 0%, 5%, 10% and 15% were used to replace part of the cement, respectively, and 16 groups of EPS concrete specimens with different proportions were prepared. The water absorption, compressive strength, flexural strength and splitting tensile strength were measured. The results showed that the addition of a certain amount of silica fume and metakaolin could reduce the water absorption of EPS concrete and improve its compressive strength, bending and splitting tensile strength, but when the dosage was too high, the water absorption would increase and the strength would decrease, and when the content of both was 10%, EPS concrete had the lowest water absorption and the best mechanical properties. Although the particle size of metakaolin was larger than that of silica fume, its "pozzolanic effect" was stronger, so the improvement of the mechanical properties of EPS concrete was better than that of silica fume. Metakaolin and silica fume could improve the adhesion of EPS particles to the gel matrix.
Experimental Research on Basic Mechanical Properties of Brick Aggregate Geopolymer Recycled Concrete
2022, 52(9): 234-240.
doi: 10.13204/j.gyjzG22070207
Abstract:
To promote the reuse of wasted clay bricks produced by the buliding demolition, 45 geopolymer recycled brick aggregate concrete (GRBAC) specimens (15 cubic specimens and 30 prism specimens)with different replacement ratios of brick aggregates (BA) (0%,30%, 50%, 70%, 100%) were designed and tested to investigate the mechanical properties. Through monotonic compression tests, the relations between compressive strength and replacement ratio of BA was studied, and the stress-strain curves of prism specimens were obtained to analyze the peak stress, modulus, peak strain and ultimate strain. The results showed the GRBAC fell off gradually and finally that the damage of GRBAC exhibited oblique shear cracking damage due to the penetrative crack. With the increase of replacement ratio of BA, the compressive strength tended to decrease while the ductility was enhanced. When σ≤0.35 fck, the specimen was in elastic state without cracking; when 0.35fck≤σ≤0.85 fck, some visible cracks developed and the specimens transformed from elastic state to elasto-plastic stage; when 0.85 fck≤σ≤1.0 fck, the damage was aggravated with serious cracks development and audible noise. After reaching the peak load, the specimen was damaged and lost bearing capacity. With the increase of replacement ratio of BA, the strength of concrete decreased in a gradient, the elastic modulus decreased significantly, while the peak strain and ultimate strain increased. Based on the uniaxial compression constitutive model, the stress-strain constitutive model with different BA replacement ratios was obtained, and the fitting results obtained by the proposed model were in good agreement with the experimental results.
To promote the reuse of wasted clay bricks produced by the buliding demolition, 45 geopolymer recycled brick aggregate concrete (GRBAC) specimens (15 cubic specimens and 30 prism specimens)with different replacement ratios of brick aggregates (BA) (0%,30%, 50%, 70%, 100%) were designed and tested to investigate the mechanical properties. Through monotonic compression tests, the relations between compressive strength and replacement ratio of BA was studied, and the stress-strain curves of prism specimens were obtained to analyze the peak stress, modulus, peak strain and ultimate strain. The results showed the GRBAC fell off gradually and finally that the damage of GRBAC exhibited oblique shear cracking damage due to the penetrative crack. With the increase of replacement ratio of BA, the compressive strength tended to decrease while the ductility was enhanced. When σ≤0.35 fck, the specimen was in elastic state without cracking; when 0.35fck≤σ≤0.85 fck, some visible cracks developed and the specimens transformed from elastic state to elasto-plastic stage; when 0.85 fck≤σ≤1.0 fck, the damage was aggravated with serious cracks development and audible noise. After reaching the peak load, the specimen was damaged and lost bearing capacity. With the increase of replacement ratio of BA, the strength of concrete decreased in a gradient, the elastic modulus decreased significantly, while the peak strain and ultimate strain increased. Based on the uniaxial compression constitutive model, the stress-strain constitutive model with different BA replacement ratios was obtained, and the fitting results obtained by the proposed model were in good agreement with the experimental results.
