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2022 Vol. 52, No. 1
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2022, 52(1): 1-7.
doi: 10.13204/j.gyjzG21112411
Abstract:
Uniaxial compression tests were carried out on 14 short ceramsite concrete columns confined by circular steel tubes. The effects of the yield strength of steel tube, the ratio of diameter to thickness, and the contact between steel tube and ceramsite concrete on the failure mode, load-displacement curve, load-strain curve, load-lateral deformation coefficient, and bearing capacity were studied experimentally. The results showed that all specimens exhibited shear failure under axial compression, and the shear angle was about 60°, and the load-displacement curve had no obvious descending section. When D/t ≥ 19, the ultimate bearing capacity increased with the decrease of the ratio of diameter to thickness. The higher the yield strength of steel pipe and the film between the steel pipe and the concrete, the greater the restraint effect of the steel pipe on the concrete. The calculation results were in good agreement with the test results without considering the influence of the contact between steel tube and concrete.
Uniaxial compression tests were carried out on 14 short ceramsite concrete columns confined by circular steel tubes. The effects of the yield strength of steel tube, the ratio of diameter to thickness, and the contact between steel tube and ceramsite concrete on the failure mode, load-displacement curve, load-strain curve, load-lateral deformation coefficient, and bearing capacity were studied experimentally. The results showed that all specimens exhibited shear failure under axial compression, and the shear angle was about 60°, and the load-displacement curve had no obvious descending section. When D/t ≥ 19, the ultimate bearing capacity increased with the decrease of the ratio of diameter to thickness. The higher the yield strength of steel pipe and the film between the steel pipe and the concrete, the greater the restraint effect of the steel pipe on the concrete. The calculation results were in good agreement with the test results without considering the influence of the contact between steel tube and concrete.
2022, 52(1): 8-16.
doi: 10.13204/j.gyjzG20102106
Abstract:
To investigate the mechanical properties of concrete-filled double-skin square steel tubular (oblique inside & straight outside) columns under axial compression, 8 composite column specimens and 1 ordinary concrete-filled square steel tubular columns specimen SC1 were prepared for the experiment. The parameters include the side length and thickness of inner square steel tube, the thickness of outer square steel tube, the slenderness ratio, and the core area proportion. In this study, the failure process and load-displacement curves were obtained. The failure modes, axial compressive bearing capacity, ductility, energy dissipation, stifness degradation and the effects of variable parameters on the mechanical properties of specimens were analyzed. The results showed that there were two failure modes:local buckling failure and bending failure in plastic plase. The inner tube showed continuous folds under the combined action of core concrete and sandwich concrete, while the outer tube heaved outward caused by the squeezing action of concrete. The steel tube bulged out in different degrees in the debonding area, and debonding area with large area and close distance had obvious influence on the final failure mode of the specimens. Compared with specimen SC1, the bearing capacity of composite column specimen with little difference in steel ratio had been increased by 35%. The load-displacement curves had no descending section and showed excellent plastic hardening characteristics. The initial stiffness and peak load of the specimen increased with the increasing of the width-thickness ratio of the inner steel tube. Affected by the uneven mixing of concrete, increasing the steel tube thickness (inside or outside) could effectively improve the mechanical properties of the specimen, but the peak load remained unchanged. Increasing the area ratio of core column could give full play to the advantages of steel tube and concrete when the steel content was not different. The calcuation method considering the effects of constratints of the superposition of double-skin square steel tube concrete on the inner was used to calculate the bearing capacity of specimens, which is in good agreement with the measured results.
To investigate the mechanical properties of concrete-filled double-skin square steel tubular (oblique inside & straight outside) columns under axial compression, 8 composite column specimens and 1 ordinary concrete-filled square steel tubular columns specimen SC1 were prepared for the experiment. The parameters include the side length and thickness of inner square steel tube, the thickness of outer square steel tube, the slenderness ratio, and the core area proportion. In this study, the failure process and load-displacement curves were obtained. The failure modes, axial compressive bearing capacity, ductility, energy dissipation, stifness degradation and the effects of variable parameters on the mechanical properties of specimens were analyzed. The results showed that there were two failure modes:local buckling failure and bending failure in plastic plase. The inner tube showed continuous folds under the combined action of core concrete and sandwich concrete, while the outer tube heaved outward caused by the squeezing action of concrete. The steel tube bulged out in different degrees in the debonding area, and debonding area with large area and close distance had obvious influence on the final failure mode of the specimens. Compared with specimen SC1, the bearing capacity of composite column specimen with little difference in steel ratio had been increased by 35%. The load-displacement curves had no descending section and showed excellent plastic hardening characteristics. The initial stiffness and peak load of the specimen increased with the increasing of the width-thickness ratio of the inner steel tube. Affected by the uneven mixing of concrete, increasing the steel tube thickness (inside or outside) could effectively improve the mechanical properties of the specimen, but the peak load remained unchanged. Increasing the area ratio of core column could give full play to the advantages of steel tube and concrete when the steel content was not different. The calcuation method considering the effects of constratints of the superposition of double-skin square steel tube concrete on the inner was used to calculate the bearing capacity of specimens, which is in good agreement with the measured results.
2022, 52(1): 17-25.
doi: 10.13204/j.gyjzG20090604
Abstract:
For deeply understanding of the mechanical properties of concrete filled circular carbon fiber reinforced polymer (CFRP) steel tubular under compression and torsion, 8 concrete filled CFRP-steel tubular members under compression and torsion were conducted. The results of test observation, the torque-rotation angle curves, the coordination between steel tube and carbon fiber, and plane across-section assumption were analyzed. ABAQUS was used to simulate the torque-rotation angle and the failure modes. The simulating results coincided well with the test results. Based on above-mentioned study results, the whole loading process analysis was carried out. The results of analysis of parameters showed that the transverse carbon fiber layer, the concrete strength, and steel ratio had none obvious influence on the torque-rotation angle curves. Increasing the transverse carbon fiber layer, steel yield strength, concrete strength and steel ratio could improve the bearing capacity of members. The proper axial compression ratio could also increase the bearing capacity. Based on the performance analysis and a large number of calculation results, the equation for the bearing capacity of concrete filled circular CFRP-steel tubular under compression and torsion was proposed, the calculated results were in good agreement with the experimental results.
For deeply understanding of the mechanical properties of concrete filled circular carbon fiber reinforced polymer (CFRP) steel tubular under compression and torsion, 8 concrete filled CFRP-steel tubular members under compression and torsion were conducted. The results of test observation, the torque-rotation angle curves, the coordination between steel tube and carbon fiber, and plane across-section assumption were analyzed. ABAQUS was used to simulate the torque-rotation angle and the failure modes. The simulating results coincided well with the test results. Based on above-mentioned study results, the whole loading process analysis was carried out. The results of analysis of parameters showed that the transverse carbon fiber layer, the concrete strength, and steel ratio had none obvious influence on the torque-rotation angle curves. Increasing the transverse carbon fiber layer, steel yield strength, concrete strength and steel ratio could improve the bearing capacity of members. The proper axial compression ratio could also increase the bearing capacity. Based on the performance analysis and a large number of calculation results, the equation for the bearing capacity of concrete filled circular CFRP-steel tubular under compression and torsion was proposed, the calculated results were in good agreement with the experimental results.
2022, 52(1): 26-30,38.
doi: 10.13204/j.gyjzG20112707
Abstract:
By using self-stressing concrete can improve the coordination between steel tube and concrete and meet the practical engineering requirements. In order to predict the ultimate bearing capacity, the stress analysis of self-stressing CFST column under axial compression was carried out based on twin-shear unified strength theory. The reduction factor of slenderness ratio was introduced and the self-stressing of concrete was considered for calculating constraint coefficient k. A new theoretical calculation method for the ultimate bearing capacity of self-stressing CFST column was established. The results obtained by this method were in good agreement with available experimental data, and the effects of concrete strength, steel yield strength, self-stress value, steel tube wall thickness and steel tube outer diameter on the ultimate bearing capacity of self-stressing CFST column were further analyzed, the influencing order of each factor was:steel tube outer diameter>steel tube wall thickness>concrete strength>steel yield strength>self-stress value.
By using self-stressing concrete can improve the coordination between steel tube and concrete and meet the practical engineering requirements. In order to predict the ultimate bearing capacity, the stress analysis of self-stressing CFST column under axial compression was carried out based on twin-shear unified strength theory. The reduction factor of slenderness ratio was introduced and the self-stressing of concrete was considered for calculating constraint coefficient k. A new theoretical calculation method for the ultimate bearing capacity of self-stressing CFST column was established. The results obtained by this method were in good agreement with available experimental data, and the effects of concrete strength, steel yield strength, self-stress value, steel tube wall thickness and steel tube outer diameter on the ultimate bearing capacity of self-stressing CFST column were further analyzed, the influencing order of each factor was:steel tube outer diameter>steel tube wall thickness>concrete strength>steel yield strength>self-stress value.
2022, 52(1): 31-38.
doi: 10.13204/j.gyjzG20102702
Abstract:
To facilitate the simulation of concrete-filled square steel tube (SCFT) column connected by H-shaped steel, three types of models were established, including the simplified double-beam single-shell element models (based on the equivalent axial stiffness and bending stiffness) as well as the normal solid element model. The mechanical properties of models under compression and bending were discussed considering test results. On the basis of the solid element model and both the single-beam single-shell element model and double-beam single-shell element model converted by equivalent stiffness, the typical SCFT frame models were established by using the general analysis and design software MIDAS. The responses of these frame models were compared under different load conditions. The results showed that the failure modes and bearing capacity obtained by three models were consistent and in good agreement with the test results, and the natural vibration characteristics, story drift and column bottom reaction of SCFT frame were consistent, indicating the results of the simplified models were accurate and the simplified models of SCFT column based on the equivalent stiffness were proved to be feasible for structural analysis.
To facilitate the simulation of concrete-filled square steel tube (SCFT) column connected by H-shaped steel, three types of models were established, including the simplified double-beam single-shell element models (based on the equivalent axial stiffness and bending stiffness) as well as the normal solid element model. The mechanical properties of models under compression and bending were discussed considering test results. On the basis of the solid element model and both the single-beam single-shell element model and double-beam single-shell element model converted by equivalent stiffness, the typical SCFT frame models were established by using the general analysis and design software MIDAS. The responses of these frame models were compared under different load conditions. The results showed that the failure modes and bearing capacity obtained by three models were consistent and in good agreement with the test results, and the natural vibration characteristics, story drift and column bottom reaction of SCFT frame were consistent, indicating the results of the simplified models were accurate and the simplified models of SCFT column based on the equivalent stiffness were proved to be feasible for structural analysis.
2022, 52(1): 39-46.
doi: 10.13204/j.gyjzG20061012
Abstract:
In order to improve the low bearing capacity, brittle failure and poor ductility of timber columns, the pre-stressed steel-timber circular column was proposed. The axial compression tests were carried out on the components, and the failure forms, failure modes, ductility index, load-displacement curves and load-strain curves of each specimen were obtained. The results showed that compared with the sum of ultimate load(Pmax) of thin-walled steel cylinder and timber column, the ultimate load of the prestressed steel-timber circular column and the prestressed steel-timber circular column wrapped with CFRP increased by 16.12% and 24.49% respectively. Compared with the timber column, the ductility index(DI) increased by 268.73% and 340% respectively. The model of the prestressed steel-timber circular column was built by the finite element analysis software ABAQUS, and the load-displacement curve which was obtained by means of displacement loading was in good agreement with the test results. The finite elements analysis results showed that when the prestressing of lateral steel equalled 0.1,0.15 and 0.2 times of its tensile yield, the Pmax increased obviously. The Pmax would be reduced when the prestressing of lateral steel reached 0.25 times of its tensile yield, but it was still larger than the Pmax of unstressed specimen. Confinement effect coefficient λ increased with the increase of pre-stressing of steel and use of CFRP sheets.
In order to improve the low bearing capacity, brittle failure and poor ductility of timber columns, the pre-stressed steel-timber circular column was proposed. The axial compression tests were carried out on the components, and the failure forms, failure modes, ductility index, load-displacement curves and load-strain curves of each specimen were obtained. The results showed that compared with the sum of ultimate load(Pmax) of thin-walled steel cylinder and timber column, the ultimate load of the prestressed steel-timber circular column and the prestressed steel-timber circular column wrapped with CFRP increased by 16.12% and 24.49% respectively. Compared with the timber column, the ductility index(DI) increased by 268.73% and 340% respectively. The model of the prestressed steel-timber circular column was built by the finite element analysis software ABAQUS, and the load-displacement curve which was obtained by means of displacement loading was in good agreement with the test results. The finite elements analysis results showed that when the prestressing of lateral steel equalled 0.1,0.15 and 0.2 times of its tensile yield, the Pmax increased obviously. The Pmax would be reduced when the prestressing of lateral steel reached 0.25 times of its tensile yield, but it was still larger than the Pmax of unstressed specimen. Confinement effect coefficient λ increased with the increase of pre-stressing of steel and use of CFRP sheets.
2022, 52(1): 47-51,7.
doi: 10.13204/j.gyjzG21040811
Abstract:
After abandoning Deconstructivism, complexity architecture turned to seek alliances with complexity science to form an exact and rigorous design system with nonlinear algorithm generation as the core, so as to break through the modernism architectural paradigm. Through discussion on the problems that the alliance has always faced such as catering to fashion trends and business culture, destroying "complexity" due to compromise in the process of implementation, the necessity of logic and reality, the applicability of complexity science in the research of architecture as basic element of urban space were analyzed. Based on that, the alliance between complexity architecture and complexity science was considered to be not stable. The alliance with complexity science seemed to increase the scientific quality of complexity architecture and the proportion of scientific judgment in its creation, however, architecture as a social product could not be separated from value judgment, otherwise it would inevitably damage the applicability of architecture.
After abandoning Deconstructivism, complexity architecture turned to seek alliances with complexity science to form an exact and rigorous design system with nonlinear algorithm generation as the core, so as to break through the modernism architectural paradigm. Through discussion on the problems that the alliance has always faced such as catering to fashion trends and business culture, destroying "complexity" due to compromise in the process of implementation, the necessity of logic and reality, the applicability of complexity science in the research of architecture as basic element of urban space were analyzed. Based on that, the alliance between complexity architecture and complexity science was considered to be not stable. The alliance with complexity science seemed to increase the scientific quality of complexity architecture and the proportion of scientific judgment in its creation, however, architecture as a social product could not be separated from value judgment, otherwise it would inevitably damage the applicability of architecture.
2022, 52(1): 52-58.
doi: 10.13204/j.gyjzG20102504
Abstract:
Taking the Zhongfu mining heritage in Jiaozuo as the main research object, meanwhile the paper focused on the community level, which has the most extensive contact with mining heritage. The paper analyzed in detail the relation between single mining heritage, group mining heritage and community, put forward the viewpoint of combining the protection and reuse of mining heritage with community renewal, and discussed the reform strategy of site reconstruction and space integration to build community centers and community unities. Finally, the reform strategy was applied to two design examples,and it could provide specific methods in community level and urban life for the exploration of mining heritage protection and mining urban construction.
Taking the Zhongfu mining heritage in Jiaozuo as the main research object, meanwhile the paper focused on the community level, which has the most extensive contact with mining heritage. The paper analyzed in detail the relation between single mining heritage, group mining heritage and community, put forward the viewpoint of combining the protection and reuse of mining heritage with community renewal, and discussed the reform strategy of site reconstruction and space integration to build community centers and community unities. Finally, the reform strategy was applied to two design examples,and it could provide specific methods in community level and urban life for the exploration of mining heritage protection and mining urban construction.
2022, 52(1): 59-64.
doi: 10.13204/j.gyjzG21090303
Abstract:
ANSYS software was used to simulate the fire resistance of ALC board, carbon steel plate, rock wool board, aluminum silicate plate and multilayer composite panels (steel plate-aluminum silicate plate-air layer-aluminum silicate plate-steel plate) under the condition of HC standard temperature rise for 3 hours, so as to obtain the temperature rise curve and fire resistance limit of the backfire surface of each board.The results showed that the time to reach the fire resistance limit of carbon steel plate was 2 743 s, and the heat resistance of carbon steel plate was the worst.ALC board and aluminum silicate plate had the best fire resistance, both of which reached the fire resistance limit after 8 000 s. However, the heating trend of aluminum silicate plate was slower than that of ALC board. If the heating time became longer, the fire resistance of aluminum silicate plate would exceed that of ALC board.For composite sandwich panels, when the thickness of aluminum silicate plate was equal, the temperature of the backfire surface decreased with the increase of the thickness of air layer. Only when the thickness of air layer was 20 mm, the fire resistance limit of sandwich board reached 180℃ at 9 543 s. When the thickness of aluminum silicate board was 30 mm, the temperature of the backfire surface reached the fire resistance limit value of 180℃ at 9 372 s, and the other boards with different thicknesses did not reach the fire resistance limit. In order to verity the fire resistance of the proposed sandwich panel, a three-hour fire test was carried out, the results showed that the sandwich panel could meet the requirements of fire-resistant limit.
ANSYS software was used to simulate the fire resistance of ALC board, carbon steel plate, rock wool board, aluminum silicate plate and multilayer composite panels (steel plate-aluminum silicate plate-air layer-aluminum silicate plate-steel plate) under the condition of HC standard temperature rise for 3 hours, so as to obtain the temperature rise curve and fire resistance limit of the backfire surface of each board.The results showed that the time to reach the fire resistance limit of carbon steel plate was 2 743 s, and the heat resistance of carbon steel plate was the worst.ALC board and aluminum silicate plate had the best fire resistance, both of which reached the fire resistance limit after 8 000 s. However, the heating trend of aluminum silicate plate was slower than that of ALC board. If the heating time became longer, the fire resistance of aluminum silicate plate would exceed that of ALC board.For composite sandwich panels, when the thickness of aluminum silicate plate was equal, the temperature of the backfire surface decreased with the increase of the thickness of air layer. Only when the thickness of air layer was 20 mm, the fire resistance limit of sandwich board reached 180℃ at 9 543 s. When the thickness of aluminum silicate board was 30 mm, the temperature of the backfire surface reached the fire resistance limit value of 180℃ at 9 372 s, and the other boards with different thicknesses did not reach the fire resistance limit. In order to verity the fire resistance of the proposed sandwich panel, a three-hour fire test was carried out, the results showed that the sandwich panel could meet the requirements of fire-resistant limit.
2022, 52(1): 65-73.
doi: 10.13204/j.gyjzG21062601
Abstract:
A new self-centering prefabricated RC frame structure was proposed. Two single-floor and one-bay frame specimen were designed and constructed, including one cast-in-situ concrete frame and one new type of prefabricated RC frame. Two quasi-static tests were carried out for the self-centering prefabricated RC frame specimen, and the second test was carried out after the completion of the first test and the energy-dissipation rebars of the structure were replaced. The results showed that the bearing capacity and energy-dissipation capacity of the new prefabricated RC frame was slightly lower than the conventional concrete frame, but the ductility was enhanced substantially compared with the conventional concrete frame. When the drift ratio was larger than 1/50, the bearing capacity of the prefabricated RC frame still did not decrease. The residual deformation of the new prefabricated RC frame after the first quasi-static test was approximately 15% of that of the cast-in-situ concrete frame. The damage degree of the components was slight and the self-centering performance of the structure could be achieved. The bearing capacity of the new prefabricated RC frame in the second test was decreased slightly, and the residual deformation was larger compared with the results of first test. The self-centering performance still existed, and the damage degree of component was still slight. It could be shown that the seismic performance of the new self-centering prefabricated RC frame could be basically restored through the simple replacement of the energy-dissipation rebar.
A new self-centering prefabricated RC frame structure was proposed. Two single-floor and one-bay frame specimen were designed and constructed, including one cast-in-situ concrete frame and one new type of prefabricated RC frame. Two quasi-static tests were carried out for the self-centering prefabricated RC frame specimen, and the second test was carried out after the completion of the first test and the energy-dissipation rebars of the structure were replaced. The results showed that the bearing capacity and energy-dissipation capacity of the new prefabricated RC frame was slightly lower than the conventional concrete frame, but the ductility was enhanced substantially compared with the conventional concrete frame. When the drift ratio was larger than 1/50, the bearing capacity of the prefabricated RC frame still did not decrease. The residual deformation of the new prefabricated RC frame after the first quasi-static test was approximately 15% of that of the cast-in-situ concrete frame. The damage degree of the components was slight and the self-centering performance of the structure could be achieved. The bearing capacity of the new prefabricated RC frame in the second test was decreased slightly, and the residual deformation was larger compared with the results of first test. The self-centering performance still existed, and the damage degree of component was still slight. It could be shown that the seismic performance of the new self-centering prefabricated RC frame could be basically restored through the simple replacement of the energy-dissipation rebar.
2022, 52(1): 74-78,46.
doi: 10.13204/j.gyjzG20041303
Abstract:
Truss connector is an important component to connect the inner and outer leaves of concrete sandwich wall panels. In order to study the shear resistance of truss connector, two groups of 4 shear specimens with different insulation thickness were tested and analyzed by finite element method. The test results indicated that the failure modes of truss connector of sandwich wall under the action of shear force were that the tensioned web members were ruptured or pulled out after the compression buckling. Based on the test, the shear resistance of the truss connection of the wall was analyzed with variable parameters, such as the diameter of the truss web member, the distance between joints, and the thickness of the insulation layer were mainly taken into account, the simulation results showed that the yield and ultimate bearing capacity of sandwich wall increased with the increase of the diameter of web member, and increase with the decrease of joint spacing, the shear yield capacity of wall increased with the decrease of the thickness of insulation layer, but the correlation between the ultimate load and the thickness of insulation layer was not obvious due to the high-pressure shrinkage of insulation board.
Truss connector is an important component to connect the inner and outer leaves of concrete sandwich wall panels. In order to study the shear resistance of truss connector, two groups of 4 shear specimens with different insulation thickness were tested and analyzed by finite element method. The test results indicated that the failure modes of truss connector of sandwich wall under the action of shear force were that the tensioned web members were ruptured or pulled out after the compression buckling. Based on the test, the shear resistance of the truss connection of the wall was analyzed with variable parameters, such as the diameter of the truss web member, the distance between joints, and the thickness of the insulation layer were mainly taken into account, the simulation results showed that the yield and ultimate bearing capacity of sandwich wall increased with the increase of the diameter of web member, and increase with the decrease of joint spacing, the shear yield capacity of wall increased with the decrease of the thickness of insulation layer, but the correlation between the ultimate load and the thickness of insulation layer was not obvious due to the high-pressure shrinkage of insulation board.
2022, 52(1): 79-82,73.
doi: 10.13204/j.gyjzG20092304
Abstract:
Based on flexural experiment of the partially prestressed concrete beams with 600 MPa steel bars, the development laws and influencing factors of stress increment of unbonded prestressed tendons were analyzed. The formula for calculating the ultimate stress increment of the unbonded prestressed tendons, adopted to partially prestressed concrete beams with 600 MPa steel bars was proposed.The results indicated that there was only a slight growth of stress increment of unbonded prestressed tendons in earlier stage, while the non-prestressed steel bars bore the majority of tensile stress. The growth of stress increment of tendons accelerated obviously after steel bars yielding, resulting in full use of strength of 600 MPa steel bars.Through checking and calculating the ultimate stress increment for 69 beams,the results showed that the proposed formula had the reasonable applied scope and high accuracy.
Based on flexural experiment of the partially prestressed concrete beams with 600 MPa steel bars, the development laws and influencing factors of stress increment of unbonded prestressed tendons were analyzed. The formula for calculating the ultimate stress increment of the unbonded prestressed tendons, adopted to partially prestressed concrete beams with 600 MPa steel bars was proposed.The results indicated that there was only a slight growth of stress increment of unbonded prestressed tendons in earlier stage, while the non-prestressed steel bars bore the majority of tensile stress. The growth of stress increment of tendons accelerated obviously after steel bars yielding, resulting in full use of strength of 600 MPa steel bars.Through checking and calculating the ultimate stress increment for 69 beams,the results showed that the proposed formula had the reasonable applied scope and high accuracy.
2022, 52(1): 83-89,58.
doi: 10.13204/j.gyjzG20122307
Abstract:
In order to study the calculation method for the bearing capacity of wet joints of beam bridges equipped with circular steel bars, collected the test data and calculation methods were collected systematically, and it was found that:1) the existing calculation methods for the bearing capacity of joints were based on the bearing capacity of the specimen under tension, the main difference was the calculation of the tensile strength of the core concrete area and the control factors of the tensile strength of the specimen; 2) the theoretical values obtained by the plastic work model calculation method proposed by Joergensen was closer to the experimental values, and the data dispersion was small and more stable; 3) strut-and-tie model of HE Z-Q reflected the failure mode and stress mechanism of wet joints of circular steel bars better than other models. Since the current calculation method still had a certain error from the actual situation, it was recommended that the calculation method that was more suitable for the bearing capacity of the wet joints of beam equipped with circular steel bars should be derived from the failure mode and the stress mechanism in the future.
In order to study the calculation method for the bearing capacity of wet joints of beam bridges equipped with circular steel bars, collected the test data and calculation methods were collected systematically, and it was found that:1) the existing calculation methods for the bearing capacity of joints were based on the bearing capacity of the specimen under tension, the main difference was the calculation of the tensile strength of the core concrete area and the control factors of the tensile strength of the specimen; 2) the theoretical values obtained by the plastic work model calculation method proposed by Joergensen was closer to the experimental values, and the data dispersion was small and more stable; 3) strut-and-tie model of HE Z-Q reflected the failure mode and stress mechanism of wet joints of circular steel bars better than other models. Since the current calculation method still had a certain error from the actual situation, it was recommended that the calculation method that was more suitable for the bearing capacity of the wet joints of beam equipped with circular steel bars should be derived from the failure mode and the stress mechanism in the future.
2022, 52(1): 90-97.
doi: 10.13204/j.gyjzG21122107
Abstract:
Taking the example of simply-supported beams under uniform load, the elastic analysis of the effects of web opening and stiffening method on the steel beam was conducted. The analysis revealed that:the increment of deflection due to openings was a trilinear curve, the openings at mid-span had little effect on the defection of the beam; when the openings with the same size were eccentrically positioned, the deflection increment was smaller, the stresses in the opening segments were also smaller;however, the opening had a significant effect on the local buckling of the web. After analysis,an equation for the increased deflection of simply-supported beams was proposed;the width-to-thickness ratio of the unstiffened opening should be limited.For the sizes of the openings in high-shear or low-shear segments, the British SCI regulations were introduced for reference; the openings in high-shear segment had significant effect on the strength and local buckling of the beam, it was suggested that horizontal stiffeners should be used to avoid local buckling and increase the strength.
Taking the example of simply-supported beams under uniform load, the elastic analysis of the effects of web opening and stiffening method on the steel beam was conducted. The analysis revealed that:the increment of deflection due to openings was a trilinear curve, the openings at mid-span had little effect on the defection of the beam; when the openings with the same size were eccentrically positioned, the deflection increment was smaller, the stresses in the opening segments were also smaller;however, the opening had a significant effect on the local buckling of the web. After analysis,an equation for the increased deflection of simply-supported beams was proposed;the width-to-thickness ratio of the unstiffened opening should be limited.For the sizes of the openings in high-shear or low-shear segments, the British SCI regulations were introduced for reference; the openings in high-shear segment had significant effect on the strength and local buckling of the beam, it was suggested that horizontal stiffeners should be used to avoid local buckling and increase the strength.
2022, 52(1): 98-101.
doi: 10.13204/j.gyjzG20122210
Abstract:
In order to determine snow cover distribution exactly, reduce the snow and wind disasters, the field survey of snow cover distribution of building was carried out. By using the software Fluent, the numerical models of wind-induced snow cover on arched roof were set up considering air-phase relative velocity, air-phase velocity, air-phase relative angular velocity, snow density and other factors to simulate the distribution of wind-induced snow cover on arched roof. By analyzing the data, the main factors affecting the snow cover distribution on the roof were found out, the turbulence model of wind and snow effect was established, and the statistical data of the pressure generated by the snow cover on the arched roof was analyzed in detail, and suggestion of the value of the uneven distribution coefficient of the snow cover on the arched roof was proposed, in order to make up for the situation that the current norms in China have more adequate consideration for the value of the uniform distribution coefficient of snow cover, but inadequate consideration for the value of the uneven distribution coefficient.
In order to determine snow cover distribution exactly, reduce the snow and wind disasters, the field survey of snow cover distribution of building was carried out. By using the software Fluent, the numerical models of wind-induced snow cover on arched roof were set up considering air-phase relative velocity, air-phase velocity, air-phase relative angular velocity, snow density and other factors to simulate the distribution of wind-induced snow cover on arched roof. By analyzing the data, the main factors affecting the snow cover distribution on the roof were found out, the turbulence model of wind and snow effect was established, and the statistical data of the pressure generated by the snow cover on the arched roof was analyzed in detail, and suggestion of the value of the uneven distribution coefficient of the snow cover on the arched roof was proposed, in order to make up for the situation that the current norms in China have more adequate consideration for the value of the uniform distribution coefficient of snow cover, but inadequate consideration for the value of the uneven distribution coefficient.
2022, 52(1): 102-107,115.
doi: 10.13204/j.gyjzG21120501
Abstract:
A super high-rise commercial and residential building was taken as an example, combined with the calculation results of frequent earthquake using YJK and MIDAS software, the overrun situations in terms of total height, the ratio of inter-story drift angle to torsional inter-story drift, local conversion of vertical structural members, and the adopted strengthening measures were analyzed. The analysis results showed that:less-wall frame structure system with partial column-wall conversion was suitable for this kind of building, the elastic inter-story drift angle limits could be interpolated according to the proportion of the overturning moment at the bottom. The results of floor comfort check for the long-span cantilevering area could meet the requirements of Technical Standard for Human Comfort of the Floor Vibration (JGJ/T 441-2019).The results of elastic time-history analysis should be taken into account to adjust the floor seismic force in the design of components, the elastic-plastic inter-story drift angle obtained by static pushover under severe earthquakes was less than 1/100, which could meet the performance design requirements.
A super high-rise commercial and residential building was taken as an example, combined with the calculation results of frequent earthquake using YJK and MIDAS software, the overrun situations in terms of total height, the ratio of inter-story drift angle to torsional inter-story drift, local conversion of vertical structural members, and the adopted strengthening measures were analyzed. The analysis results showed that:less-wall frame structure system with partial column-wall conversion was suitable for this kind of building, the elastic inter-story drift angle limits could be interpolated according to the proportion of the overturning moment at the bottom. The results of floor comfort check for the long-span cantilevering area could meet the requirements of Technical Standard for Human Comfort of the Floor Vibration (JGJ/T 441-2019).The results of elastic time-history analysis should be taken into account to adjust the floor seismic force in the design of components, the elastic-plastic inter-story drift angle obtained by static pushover under severe earthquakes was less than 1/100, which could meet the performance design requirements.
2022, 52(1): 108-115.
doi: 10.13204/j.gyjzG21102107
Abstract:
As a temporary steel structure in construction, the importance of treatment for the foundation of framework is often neglected in engineering. Due to many factors such as the decrease of temperature and the high moisture content of soil, the foundation of framework is prone to heave which seriously endangers the construction safety of supporting frame. In order to study the actual mechanical properties of framework with cuplok brackets on the heave foundation, the relations between the height of framework and the allowable heave displacement was analyzed based on the theory of multi-segment continuous compression bars, and the model of framework with cuplok brackets was established with ABAQUS. The results showed that the stability bearing capacity of the framework decreased up to 57.92% after the foundation was heaved, which was the instability failure of a single rod; when failure occurred, the stability bearing capacity of the framework was less related to the number of heave members than to the stiffness of the heave members; the allowable heave displacement was the smallest under the condition of heave of upright rods at foundation corner while the allowable heave displacement was the maximum under the condition of heave of upright rods at the middle of foundation; the allowable heave displacement of the uprighty rods increased with the height of the framework.
As a temporary steel structure in construction, the importance of treatment for the foundation of framework is often neglected in engineering. Due to many factors such as the decrease of temperature and the high moisture content of soil, the foundation of framework is prone to heave which seriously endangers the construction safety of supporting frame. In order to study the actual mechanical properties of framework with cuplok brackets on the heave foundation, the relations between the height of framework and the allowable heave displacement was analyzed based on the theory of multi-segment continuous compression bars, and the model of framework with cuplok brackets was established with ABAQUS. The results showed that the stability bearing capacity of the framework decreased up to 57.92% after the foundation was heaved, which was the instability failure of a single rod; when failure occurred, the stability bearing capacity of the framework was less related to the number of heave members than to the stiffness of the heave members; the allowable heave displacement was the smallest under the condition of heave of upright rods at foundation corner while the allowable heave displacement was the maximum under the condition of heave of upright rods at the middle of foundation; the allowable heave displacement of the uprighty rods increased with the height of the framework.
2022, 52(1): 116-121.
doi: 10.13204/j.gyjzG21101903
Abstract:
The inversion hydraulic lifting technique of computer multi-point control was used for the construction of a LNG storage tank. During the lifting process, due to the long span, thin wall and heavy mass of the tank, the tank wall was prone to deformation and even instability damage during the lifting process, so it was necessary to conduct mechanical simulation of the lifting process. ABAQUS was used to establish the finite element model of the tank body and simulate the asynchronous lifting caused by the lifting error under the construction state, it was found that there was a 12.9% probability of occurrence of stress concentration, which would result in local buckling of the structure. The improved model based on expanding circle method was established and compared with the asynchronous lifting results, the results showed that the maximum stress of the structure should be reduced to 135 MPa, so as to meet the requirements of structural stability.
The inversion hydraulic lifting technique of computer multi-point control was used for the construction of a LNG storage tank. During the lifting process, due to the long span, thin wall and heavy mass of the tank, the tank wall was prone to deformation and even instability damage during the lifting process, so it was necessary to conduct mechanical simulation of the lifting process. ABAQUS was used to establish the finite element model of the tank body and simulate the asynchronous lifting caused by the lifting error under the construction state, it was found that there was a 12.9% probability of occurrence of stress concentration, which would result in local buckling of the structure. The improved model based on expanding circle method was established and compared with the asynchronous lifting results, the results showed that the maximum stress of the structure should be reduced to 135 MPa, so as to meet the requirements of structural stability.
2022, 52(1): 122-128.
doi: 10.13204/j.gyjzG21110408
Abstract:
Cable-supported grid structure with large opening is a new roof structure proposed in recent years, and its pre-stressed construction process is quite complicated. Based on Bazhong sports center project under construction as the background, combined with the actual project, the key elements to the composition of the cable-supported grid structure with large opening were discussed.According to the actual project of tensioning scheme,the improved tension compensation method was proposed for the control values of prestress of cable in different stages of tensioning, and the finite element analysis model was established, and then the cable forces and displacement variation in different tension stages were obtained. The analysis results show that the simulated cable forces were in good agreement with the design values, and the maximum and minimum cable forces of the circumferential cables are the same after the installation of diagonal braces. At the same time, the field monitoring of construction tension process showed that the simulated value was basically consistent with the measured value. The results showed that the improved tension compensation method could effectively simulate the control values of pre-stress in cable construction in different tension stages, which had a good reference value for the prestressed tension construction of cable-supported grid structures.
Cable-supported grid structure with large opening is a new roof structure proposed in recent years, and its pre-stressed construction process is quite complicated. Based on Bazhong sports center project under construction as the background, combined with the actual project, the key elements to the composition of the cable-supported grid structure with large opening were discussed.According to the actual project of tensioning scheme,the improved tension compensation method was proposed for the control values of prestress of cable in different stages of tensioning, and the finite element analysis model was established, and then the cable forces and displacement variation in different tension stages were obtained. The analysis results show that the simulated cable forces were in good agreement with the design values, and the maximum and minimum cable forces of the circumferential cables are the same after the installation of diagonal braces. At the same time, the field monitoring of construction tension process showed that the simulated value was basically consistent with the measured value. The results showed that the improved tension compensation method could effectively simulate the control values of pre-stress in cable construction in different tension stages, which had a good reference value for the prestressed tension construction of cable-supported grid structures.
2022, 52(1): 129-136,97.
doi: 10.13204/j.gyjzG21051203
Abstract:
With the help of data mining technology, the selection of probability distribution of geotechnical parameters for test samples was systematized. 19 groups of geotechnical parameters for test samples were selected, the beta distribution and the normal information diffusion method were chosen as two methods to infer the probability density of geotechnical parameters. Based on the fuzzy C-means clustering method in data mining technology, 19 groups of geotechnical parameters for test samples were clustered into 4 categories according to the numerical eigenvalues of samples, and then the inference method of probability density functions was determined according to the distribution law of each category for samples. For test samples with serious fluctuation and discreteness, an optimal determination method on window width was proposed, the method took the minimum mean square error as the constraint goal and changed the size of window width on the basis of window width. When the probability density function was deduced by the normal information diffusion method, in order to determine window width, an optimal determination method on window width of samples by changing the width value of the window on the basis of the minimum mean square error was proposed. For a group of new test samples, it was probable to infer the density function of samples by the numerical eigenvalue.
With the help of data mining technology, the selection of probability distribution of geotechnical parameters for test samples was systematized. 19 groups of geotechnical parameters for test samples were selected, the beta distribution and the normal information diffusion method were chosen as two methods to infer the probability density of geotechnical parameters. Based on the fuzzy C-means clustering method in data mining technology, 19 groups of geotechnical parameters for test samples were clustered into 4 categories according to the numerical eigenvalues of samples, and then the inference method of probability density functions was determined according to the distribution law of each category for samples. For test samples with serious fluctuation and discreteness, an optimal determination method on window width was proposed, the method took the minimum mean square error as the constraint goal and changed the size of window width on the basis of window width. When the probability density function was deduced by the normal information diffusion method, in order to determine window width, an optimal determination method on window width of samples by changing the width value of the window on the basis of the minimum mean square error was proposed. For a group of new test samples, it was probable to infer the density function of samples by the numerical eigenvalue.
2022, 52(1): 137-142.
doi: 10.13204/j.gyjzG20112802
Abstract:
A feasible approach of secant slopes was proposed to determine the safety state of plastic landslides, which was based on the typical accumulation displacement-time curve of plastic landslides. The secant slope-time (St-t) curve was used to determine the stages of landslide deformation. If the St-t curve was negative and the curve descended steeply, the landslide was judged in the initial deformation stage. The landslide was in the constant deformation stage if the curve's secant was negative and the curve kept falling slowly; if the curve's secant was from negative to positive and its upward trend was determined, the time point with zero slope could be defined as the critical point of the transformation for landslides from the constant speed deformation stage to accelerated deformation stage; the ratio of the current secant slope to the secant slope of the near five periods could be used to determine the time point from the accelerated deformation stage to rapid deformation stage. If the ratios were greater than 2.0 for the first time and 1.0 for the second time, the landslide entered the rapid deformation stage. According to the example verification, the feasibility and reasonability of the above method were proved.
A feasible approach of secant slopes was proposed to determine the safety state of plastic landslides, which was based on the typical accumulation displacement-time curve of plastic landslides. The secant slope-time (St-t) curve was used to determine the stages of landslide deformation. If the St-t curve was negative and the curve descended steeply, the landslide was judged in the initial deformation stage. The landslide was in the constant deformation stage if the curve's secant was negative and the curve kept falling slowly; if the curve's secant was from negative to positive and its upward trend was determined, the time point with zero slope could be defined as the critical point of the transformation for landslides from the constant speed deformation stage to accelerated deformation stage; the ratio of the current secant slope to the secant slope of the near five periods could be used to determine the time point from the accelerated deformation stage to rapid deformation stage. If the ratios were greater than 2.0 for the first time and 1.0 for the second time, the landslide entered the rapid deformation stage. According to the example verification, the feasibility and reasonability of the above method were proved.
2022, 52(1): 143-149,64.
doi: 10.13204/j.gyjzG20110501
Abstract:
Field tests of drag loads for prestressed pipes pile were performed in a petrochemical engineering in Zhoushan in which the backfill and underlying soft soil were 10 m and 50 m respectively. After unloading of surcharge preloading, prestressed pipe piles with different length were piled. Based on field tests, influences of relative displacement and relative displacement rates between piles and soil on drag loads, coefficients of negative friction and neutral points were studied. The results showed that there existed a positive correlation between drag loads and relative displacement between piles and soil. Growth rates of drag loads decreased with decrease of relative displacement rates between piles and soil. When relative displacement rates between piles and soil reduced to 0.1 to 0.2 mm/d, drag loads tended to be stable. Average values of negative friction could be tested by the suspension method. The calculation methods about coefficients of negative friction and neutral points were proposed according to the measured values in different pile length. The field test results showed that negative friction increased with time and the depth of neutral points in piles would increase as well. In the end, the increase of the depth for neutral points tended to be stable,negative friction was much less than the ultimate value of positive friction. The characteristic value of the bearing capacity of single piles was checked by the comprehensiely safe factor method considering the negative friction from JGJ 94-2018 Technical Code for Building Pile Foundation, the results showed the piles could meet safety requirements.
Field tests of drag loads for prestressed pipes pile were performed in a petrochemical engineering in Zhoushan in which the backfill and underlying soft soil were 10 m and 50 m respectively. After unloading of surcharge preloading, prestressed pipe piles with different length were piled. Based on field tests, influences of relative displacement and relative displacement rates between piles and soil on drag loads, coefficients of negative friction and neutral points were studied. The results showed that there existed a positive correlation between drag loads and relative displacement between piles and soil. Growth rates of drag loads decreased with decrease of relative displacement rates between piles and soil. When relative displacement rates between piles and soil reduced to 0.1 to 0.2 mm/d, drag loads tended to be stable. Average values of negative friction could be tested by the suspension method. The calculation methods about coefficients of negative friction and neutral points were proposed according to the measured values in different pile length. The field test results showed that negative friction increased with time and the depth of neutral points in piles would increase as well. In the end, the increase of the depth for neutral points tended to be stable,negative friction was much less than the ultimate value of positive friction. The characteristic value of the bearing capacity of single piles was checked by the comprehensiely safe factor method considering the negative friction from JGJ 94-2018 Technical Code for Building Pile Foundation, the results showed the piles could meet safety requirements.
2022, 52(1): 150-158.
doi: 10.13204/j.gyjzG20110601
Abstract:
Based on the viscoelastic theory expressed by fractional derivatives and the theory of porous media, the torsional dynamic control equations in the form of displacement for viscoelastic saturated soil expressed by fractional derivatives were obtained by considering the soil-plug effect of pipe piles, the torsionally dynamic interaction model to describe viscoelastic saturated soil expressed by fractional derivatives and partially exposed pipe piles was constructed. The equivalent stiffness and damping coefficients of the equivalent Winkler torsional spring-damper model were obtained by considering properties of fractional derivatives and Bessel Function, and boundary conditions of soil. Considering the effect of saturated soil around and in pipe piles, the torsional vibration of partially exposed pipe piles in saturated soil was solved by using the transfer matrix method, and the torsional stiffness factor and equivalent damping coefficient at tops pipe piles were obtained. The influences of mechanical and geometric parameters of pipe piles and soil on torsional vibration of pipe piles were discussed by numerical examples. The results showed that the effect of the geometric parameters for pipe piles on torsional vibration of partially exposed pipe piles in viscoelastic saturated soil expressed by fractional derivative was greater than that of mechanical properties for materials. When considering the soil-plug effect, the influence of soil viscosity could not be ignored on torsional vibration of partially exposed pipe piles in viscoelastic saturated soil, but the difference of properties between saturated soil around and in pipe piles could be ignored. The wall thickness of pipe piles was sensitive to the torsional vibration.
Based on the viscoelastic theory expressed by fractional derivatives and the theory of porous media, the torsional dynamic control equations in the form of displacement for viscoelastic saturated soil expressed by fractional derivatives were obtained by considering the soil-plug effect of pipe piles, the torsionally dynamic interaction model to describe viscoelastic saturated soil expressed by fractional derivatives and partially exposed pipe piles was constructed. The equivalent stiffness and damping coefficients of the equivalent Winkler torsional spring-damper model were obtained by considering properties of fractional derivatives and Bessel Function, and boundary conditions of soil. Considering the effect of saturated soil around and in pipe piles, the torsional vibration of partially exposed pipe piles in saturated soil was solved by using the transfer matrix method, and the torsional stiffness factor and equivalent damping coefficient at tops pipe piles were obtained. The influences of mechanical and geometric parameters of pipe piles and soil on torsional vibration of pipe piles were discussed by numerical examples. The results showed that the effect of the geometric parameters for pipe piles on torsional vibration of partially exposed pipe piles in viscoelastic saturated soil expressed by fractional derivative was greater than that of mechanical properties for materials. When considering the soil-plug effect, the influence of soil viscosity could not be ignored on torsional vibration of partially exposed pipe piles in viscoelastic saturated soil, but the difference of properties between saturated soil around and in pipe piles could be ignored. The wall thickness of pipe piles was sensitive to the torsional vibration.
2022, 52(1): 159-164.
doi: 10.13204/j.gyjzG20081106
Abstract:
Subsidence predictions of reclaimed airports on soft soil foundation is an important issue for airport construction. Based on an airport under construction in Xiamen,the subsidence and average consolidation degrees of soft soil foundation during the preloading period were studied by the measured curve fitting method,finite element analysis method and theoretical calculation method,and the consolidation degree of the current airport foundation was estimated. The results showed that:the subsidence and consolidation degrees calculated by the three methods were in few different,which could well explain the preloading effect of the airport foundation of being preloaded; the calculation results of the three methods were comparatively consonant with the measured results, and the three results could be compared with each other to study the law of subsidence evolution in soft soil areas; the average consolidation degree of the airport construction area subjected to the preloading loads of the last stage had exceeded 90%,and the main consolidation had completed.
Subsidence predictions of reclaimed airports on soft soil foundation is an important issue for airport construction. Based on an airport under construction in Xiamen,the subsidence and average consolidation degrees of soft soil foundation during the preloading period were studied by the measured curve fitting method,finite element analysis method and theoretical calculation method,and the consolidation degree of the current airport foundation was estimated. The results showed that:the subsidence and consolidation degrees calculated by the three methods were in few different,which could well explain the preloading effect of the airport foundation of being preloaded; the calculation results of the three methods were comparatively consonant with the measured results, and the three results could be compared with each other to study the law of subsidence evolution in soft soil areas; the average consolidation degree of the airport construction area subjected to the preloading loads of the last stage had exceeded 90%,and the main consolidation had completed.
2022, 52(1): 165-173.
doi: 10.13204/j.gyjzG21120813
Abstract:
In order to study the stability of airport pavement underpass tunnel structure under aircraft load, a mechanical model of cooperative deformation of airport pavement-base-soil-tunnel lining structure was established, and the stability of pavement-base-soil-tunnel lining structure under aircraft load was deeply analyzed, focusing on the displacement response, velocity response and stress evolution law of tunnel lining structure under the influence of in-situ stress, tunnel dead weight and impact effect of aircraft load. It was found that the dead weight and in-situ stress of the tunnel had great influence on the overall stability of the soil-tunnel structure, while the impact effect of aircraft load was relatively small. The tunnel structure with circular cross section had the best stability; with the increase of buried depth of tunnel structure, the influence of in-situ stress on the stability of tunnel structure was more serious. The higher the concrete strength of lining structure, the better its stability; with the different positions of aircraft loads, the deformation of tunnel structure changed greatly, and with the increase of lining thickness, the impact effect of aircraft loads on tunnel structure gradually weakened.
In order to study the stability of airport pavement underpass tunnel structure under aircraft load, a mechanical model of cooperative deformation of airport pavement-base-soil-tunnel lining structure was established, and the stability of pavement-base-soil-tunnel lining structure under aircraft load was deeply analyzed, focusing on the displacement response, velocity response and stress evolution law of tunnel lining structure under the influence of in-situ stress, tunnel dead weight and impact effect of aircraft load. It was found that the dead weight and in-situ stress of the tunnel had great influence on the overall stability of the soil-tunnel structure, while the impact effect of aircraft load was relatively small. The tunnel structure with circular cross section had the best stability; with the increase of buried depth of tunnel structure, the influence of in-situ stress on the stability of tunnel structure was more serious. The higher the concrete strength of lining structure, the better its stability; with the different positions of aircraft loads, the deformation of tunnel structure changed greatly, and with the increase of lining thickness, the impact effect of aircraft loads on tunnel structure gradually weakened.
2022, 52(1): 174-179.
doi: 10.13204/j.gyjzG21032911
Abstract:
In order to solve the durability of concrete in the Salt Lake area of Western and extend its service life, the sulfate resistance of semi-immersed nano-CaCO3 modified concrete was studied. The quality loss and relative dynamic modulus of elasticity were evaluated regularly, and the durability of the concrete was analyzed; at the same time, the durability degradation model of nano-CaCO3 modified concrete was established by Weibull function. The results showed that the relative mass and relative dynamic modulus of elasticity of the specimens were obviously enhanced in the age of 0-180 d. After 180 d, the durability of the specimens gradually degenerated, among which the evaluation parameters of relative dynamic modulus of elasticity were more sensitive, which could clearly reflect the durability degradation of the specimens; the probability density function and reliability function were obtained by Weibull function modeling and calculation. The longest service life of nano-CaCO3 modified concrete could reach 693 d in sulfate environment.
In order to solve the durability of concrete in the Salt Lake area of Western and extend its service life, the sulfate resistance of semi-immersed nano-CaCO3 modified concrete was studied. The quality loss and relative dynamic modulus of elasticity were evaluated regularly, and the durability of the concrete was analyzed; at the same time, the durability degradation model of nano-CaCO3 modified concrete was established by Weibull function. The results showed that the relative mass and relative dynamic modulus of elasticity of the specimens were obviously enhanced in the age of 0-180 d. After 180 d, the durability of the specimens gradually degenerated, among which the evaluation parameters of relative dynamic modulus of elasticity were more sensitive, which could clearly reflect the durability degradation of the specimens; the probability density function and reliability function were obtained by Weibull function modeling and calculation. The longest service life of nano-CaCO3 modified concrete could reach 693 d in sulfate environment.
2022, 52(1): 180-186,179.
doi: 10.13204/j.gyjzG21020903
Abstract:
In order to study the mechanical properties of steel slag fine aggregate concrete, mortar and concrete with steel slag substitution rate of 0, 10%, 20% and 30% were prepared.The compressive strength of mortar, the compressive strength of concrete cube, the splitting tensile strength and flexural strength were tested.The results showed that the granulated steel slag had interface transition zone, which could weaken the compressive strength of steel slag mortar.Steel slag had a certain hydration activity, which could improve the water-cement ratio of mortar, and then improve the compressive strength of mortar.When the substitution rate of steel slag was 20%, the compressive strength and splitting tensile strength of concrete specimens were the largest. When the substitution rate of steel slag was 30%, the flexural strength of concrete specimen was the highest.Based on the meso scale, the steel slag concrete was regarded as a five-phase composite composed of mortar, coarse aggregate, steel slag particles, the interface of mortar and coarse aggregate, and the interface of mortar and steel slag particles.The meso numerical model of steel slag concrete was established to simulate the compressive strength, flexural strength and load-deflection curves of concrete cubes with different steel slag contents.The simulation results were in good agreement with the experimental results, which verified the correctness of the meso model.
In order to study the mechanical properties of steel slag fine aggregate concrete, mortar and concrete with steel slag substitution rate of 0, 10%, 20% and 30% were prepared.The compressive strength of mortar, the compressive strength of concrete cube, the splitting tensile strength and flexural strength were tested.The results showed that the granulated steel slag had interface transition zone, which could weaken the compressive strength of steel slag mortar.Steel slag had a certain hydration activity, which could improve the water-cement ratio of mortar, and then improve the compressive strength of mortar.When the substitution rate of steel slag was 20%, the compressive strength and splitting tensile strength of concrete specimens were the largest. When the substitution rate of steel slag was 30%, the flexural strength of concrete specimen was the highest.Based on the meso scale, the steel slag concrete was regarded as a five-phase composite composed of mortar, coarse aggregate, steel slag particles, the interface of mortar and coarse aggregate, and the interface of mortar and steel slag particles.The meso numerical model of steel slag concrete was established to simulate the compressive strength, flexural strength and load-deflection curves of concrete cubes with different steel slag contents.The simulation results were in good agreement with the experimental results, which verified the correctness of the meso model.
2022, 52(1): 187-193,142.
doi: 10.13204/j.gyjzG21090911
Abstract:
Natural pumice stone was used as coarse aggregate, and part of river sand was replaced by desert aeolian sand as fine aggregate. Aeolian sand pumice concrete was prepared and tested for frost resistance and durability. With the help of nuclear magnetic resonance, the pore structure of pumice concrete with different replacement rates of aeolian sand under the action of freeze-thaw cycles was tested, and the relations between the pore structure of aeolian sand pumice concrete under the action of freeze-thaw cycles and the fractal dimension was revealed. The results showed that:the replacement rate of aeolian sand lower than 40% had little effect on the frost resistance of pumice concrete, but the frost resistance of pumice concrete with the replacement rate of aeolian sand 60% did not meet the design requirements; a greater proportion of large pores in the aeolian sand pumice concrete (100 nm<r ≤ 1 000 nm) could increase its frost resistance, while a greater proportion of harmful pores (r>1 000 nm) could weaken its frost resistance; the change of fractal dimension Dmax could reflect the change in the proportion micropores (r ≤ 100 nm) and harmful pores (r>1 000 nm) of concrete. The research could provide theoretical support for the applications of aeolian sand pumice concrete in civil and water conservancy projects in cold regions.
Natural pumice stone was used as coarse aggregate, and part of river sand was replaced by desert aeolian sand as fine aggregate. Aeolian sand pumice concrete was prepared and tested for frost resistance and durability. With the help of nuclear magnetic resonance, the pore structure of pumice concrete with different replacement rates of aeolian sand under the action of freeze-thaw cycles was tested, and the relations between the pore structure of aeolian sand pumice concrete under the action of freeze-thaw cycles and the fractal dimension was revealed. The results showed that:the replacement rate of aeolian sand lower than 40% had little effect on the frost resistance of pumice concrete, but the frost resistance of pumice concrete with the replacement rate of aeolian sand 60% did not meet the design requirements; a greater proportion of large pores in the aeolian sand pumice concrete (100 nm<r ≤ 1 000 nm) could increase its frost resistance, while a greater proportion of harmful pores (r>1 000 nm) could weaken its frost resistance; the change of fractal dimension Dmax could reflect the change in the proportion micropores (r ≤ 100 nm) and harmful pores (r>1 000 nm) of concrete. The research could provide theoretical support for the applications of aeolian sand pumice concrete in civil and water conservancy projects in cold regions.
2022, 52(1): 194-199,173.
doi: 10.13204/j.gyjzG21042709
Abstract:
In order to further reveal the influence of aggregate type on the performance of concrete under axial compression after being subjected to high temperatures and spray cooling, uniaxial compressive strength tests of concrete after being subjected to different fire temperatures and spray cooling were carried out on standard prismatic specimens of ordinary concrete, high-strength concrete, and recycled aggregate concrete. The stress-strain curves during the whole axial compression process were obtained. The effects on the peak stress, peak strain, elastic modulus of three kinds of concrete specimens and their damage process after being subjected to high temperatures and spray cooling were compared and analyzed. The test results showed that:after being subjected to high temperatures and spray cooling, the cracks of high strength concrete surface developed earlier and faster; the peak point of recycled aggregate concrete curve moved to the right most obviously as temperature increased, and the peak point of high strength concrete curve decreased the least; with the increase of temperature, the peak stress of ordinary concrete decreased most obviously, the peak strain of recycled aggregate concrete increased the most; the elastic modulus of high-strength concrete decreased least after being subjected to high temperatures and spray cooling. With the increase of temperature, the difference of damage development of recycled aggregate concrete was the most significant, while the energy consumption was the lowest. Based on the test results, the strength evaluation formulas and uniaxial stress-strain constitutive equation of different concrete after being subjected to different fire temperatures and spray cooling were put forward, and the calculated values were in good agreement with the actual values.
In order to further reveal the influence of aggregate type on the performance of concrete under axial compression after being subjected to high temperatures and spray cooling, uniaxial compressive strength tests of concrete after being subjected to different fire temperatures and spray cooling were carried out on standard prismatic specimens of ordinary concrete, high-strength concrete, and recycled aggregate concrete. The stress-strain curves during the whole axial compression process were obtained. The effects on the peak stress, peak strain, elastic modulus of three kinds of concrete specimens and their damage process after being subjected to high temperatures and spray cooling were compared and analyzed. The test results showed that:after being subjected to high temperatures and spray cooling, the cracks of high strength concrete surface developed earlier and faster; the peak point of recycled aggregate concrete curve moved to the right most obviously as temperature increased, and the peak point of high strength concrete curve decreased the least; with the increase of temperature, the peak stress of ordinary concrete decreased most obviously, the peak strain of recycled aggregate concrete increased the most; the elastic modulus of high-strength concrete decreased least after being subjected to high temperatures and spray cooling. With the increase of temperature, the difference of damage development of recycled aggregate concrete was the most significant, while the energy consumption was the lowest. Based on the test results, the strength evaluation formulas and uniaxial stress-strain constitutive equation of different concrete after being subjected to different fire temperatures and spray cooling were put forward, and the calculated values were in good agreement with the actual values.
2022, 52(1): 200-204,121.
doi: 10.13204/j.gyjzG21060913
Abstract:
The shear performance of new-to-old concrete interface with different loading modes is the key to the reinforcement structure. Therefore, the experimental tests of dip angle and normal stress of new-to-old concrete interface on shear performance were carried out, and the shear failure characteristics were analyzed. The results showed that the curves of shear stress and shear displacement about new-to-old concrete were roughly divided into the linear elastic change stage, the failure stage, and the residual strength stage. The peak shear stress of new-to-old concrete increased exponentially with the increase of interface dip angle and linearly with the increase of normal stress. During the shear process of the specimen, the shear failure of new-to-old concrete was generally characterized by dilatancy and shrinkage. The dip angle and normal stress of interface had significant effects on the crack propagation mode and the crack distribution.
The shear performance of new-to-old concrete interface with different loading modes is the key to the reinforcement structure. Therefore, the experimental tests of dip angle and normal stress of new-to-old concrete interface on shear performance were carried out, and the shear failure characteristics were analyzed. The results showed that the curves of shear stress and shear displacement about new-to-old concrete were roughly divided into the linear elastic change stage, the failure stage, and the residual strength stage. The peak shear stress of new-to-old concrete increased exponentially with the increase of interface dip angle and linearly with the increase of normal stress. During the shear process of the specimen, the shear failure of new-to-old concrete was generally characterized by dilatancy and shrinkage. The dip angle and normal stress of interface had significant effects on the crack propagation mode and the crack distribution.
2022, 52(1): 205-210.
doi: 10.13204/j.gyjzG20090102
Abstract:
The present precast bottom slab of prefabricated concrete two-way composite floor slab cannot work without the overhanging steel bar, and the cast-in-place strip joint method has disadvantages such as low-efficiency and high cost. In order to solve these problems, based on the previous research on common joints without gap between composite floor slabs, a joint method of pasting carbon fiber composite strips across the bottom of the slab without gap was proposed. Through the static load comparison test of 6 rectangular single-seam two-way composite floor slab connected without gap simply supported on four sides, the flexural properties of CFRP-concrete two-way composite floor slab connected without gap were studied from three aspects:stress characteristics, failure modes, and deformation capacity. The results showed that the four-sided simply-supported composite floor slab connected without gap could achieve two-way force transmission without the phenomenon of crack concentration at the joint; CFRP could effectively participate in the cross-section stress, and contribute significantly to the increase of cracking load of the component and the load value of the test in use. The flexural stiffness of composite floor slabs could be increased by about 25%, and the restraining effect of it on the slab gap was very obvious. The use of polymer mortar to fill the joints of slab could enhance the structural integrity, increase the flexural stiffness of composite floor slabs by about 23%, and reduce the increase of the gap width at the bottom
The present precast bottom slab of prefabricated concrete two-way composite floor slab cannot work without the overhanging steel bar, and the cast-in-place strip joint method has disadvantages such as low-efficiency and high cost. In order to solve these problems, based on the previous research on common joints without gap between composite floor slabs, a joint method of pasting carbon fiber composite strips across the bottom of the slab without gap was proposed. Through the static load comparison test of 6 rectangular single-seam two-way composite floor slab connected without gap simply supported on four sides, the flexural properties of CFRP-concrete two-way composite floor slab connected without gap were studied from three aspects:stress characteristics, failure modes, and deformation capacity. The results showed that the four-sided simply-supported composite floor slab connected without gap could achieve two-way force transmission without the phenomenon of crack concentration at the joint; CFRP could effectively participate in the cross-section stress, and contribute significantly to the increase of cracking load of the component and the load value of the test in use. The flexural stiffness of composite floor slabs could be increased by about 25%, and the restraining effect of it on the slab gap was very obvious. The use of polymer mortar to fill the joints of slab could enhance the structural integrity, increase the flexural stiffness of composite floor slabs by about 23%, and reduce the increase of the gap width at the bottom
2022, 52(1): 211-215.
doi: 10.13204/j.gyjzG20031209
Abstract:
To study the anti-implosion performance of steel pipes strengthened with carbon fiber reinforced plastic (CFRP) sheets, a total of 8 specimens were tested under implosion impact. The weight of emulsion explosive and the number of CFRP sheets for strengthening were taken into account in the experiments. The experimental results demonstrated that, for specimens strengthened with the same number of CFRP sheets, the axial cracks on the pipe wall increased with the increase of the emulsion explosive weight. Besides, for these specimens, the CFRP layer failed from cracking failure to fragmentation failure with the increase of the emulsion explosive weight. Additionally, for specimens with the same emulsion explosive weight, the cracks on the pipe wall developed marginally in the axial direction, and then developed in the hoop direction, which demonstrated the anti-implosion effect of the strengthened CFRP layer. Finally, by conducting the mechanical analysis, a theoretical model was proposed for analyzing CFRP strengthened steel pipes under implosion impact.
To study the anti-implosion performance of steel pipes strengthened with carbon fiber reinforced plastic (CFRP) sheets, a total of 8 specimens were tested under implosion impact. The weight of emulsion explosive and the number of CFRP sheets for strengthening were taken into account in the experiments. The experimental results demonstrated that, for specimens strengthened with the same number of CFRP sheets, the axial cracks on the pipe wall increased with the increase of the emulsion explosive weight. Besides, for these specimens, the CFRP layer failed from cracking failure to fragmentation failure with the increase of the emulsion explosive weight. Additionally, for specimens with the same emulsion explosive weight, the cracks on the pipe wall developed marginally in the axial direction, and then developed in the hoop direction, which demonstrated the anti-implosion effect of the strengthened CFRP layer. Finally, by conducting the mechanical analysis, a theoretical model was proposed for analyzing CFRP strengthened steel pipes under implosion impact.
