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2024 Vol. 54, No. 11
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2024, 54(11): 1-8.
doi: 10.3724/j.gyjzG24060406
Abstract:
A damage assessment method for transmission tower members based on image recognition and finite element analysis was proposed. For damaged members, based on the images obtained from on-site inspection, combined with edge detection and curve fitting to locate the member contour, the bending and state of members could be quantitatively assessed. This method showed good robustness in complex conditions such as members crossing and existence of gusset plates. For undamaged members, a member importance analysis method was proposed by setting the damage conditions in the finite element model, which could accurately locate the position of associated element. Transmission tower collapse calculation and failure path analysis showed that initial damage to the tower member would change the failure path of transmission tower collapse. The associated elements of damaged elements had the risk of early failure, which further verified the accuracy of the member importance analysis method.
A damage assessment method for transmission tower members based on image recognition and finite element analysis was proposed. For damaged members, based on the images obtained from on-site inspection, combined with edge detection and curve fitting to locate the member contour, the bending and state of members could be quantitatively assessed. This method showed good robustness in complex conditions such as members crossing and existence of gusset plates. For undamaged members, a member importance analysis method was proposed by setting the damage conditions in the finite element model, which could accurately locate the position of associated element. Transmission tower collapse calculation and failure path analysis showed that initial damage to the tower member would change the failure path of transmission tower collapse. The associated elements of damaged elements had the risk of early failure, which further verified the accuracy of the member importance analysis method.
2024, 54(11): 9-14.
doi: 10.3724/j.gyjzG24042503
Abstract:
In order to study the mechanical properties of the composite structure system of modular integrated construction (MIC)-frame in Phoenix Tower during construction and use, a set of distributed optical fiber structure health monitoring system based on Brillouin scattering was designed and deployed, and then monitored during construction. Through the analysis of the monitoring data, the following conclusions were obtained: the test accuracy of the monitoring system met the engineering requirements; before the completion of the enclosure structure, the difference of temperature variation in different positions of the structure at the same time could reach 23 ℃, and the effect of temperature should be paid attention to in the construction stage. During the construction process, the temperature variation of the component was -18-16 ℃, the strain variation was (-150-210)×10-6, and the additional temperature stress was -26.8-36.7 MPa. No abnormal response or damage occurred. The design and application of this monitoring system could provide a reference for the popularization of modular buildings and the application of distributed optical fiber monitoring technology in the health monitoring of modular buildings.
In order to study the mechanical properties of the composite structure system of modular integrated construction (MIC)-frame in Phoenix Tower during construction and use, a set of distributed optical fiber structure health monitoring system based on Brillouin scattering was designed and deployed, and then monitored during construction. Through the analysis of the monitoring data, the following conclusions were obtained: the test accuracy of the monitoring system met the engineering requirements; before the completion of the enclosure structure, the difference of temperature variation in different positions of the structure at the same time could reach 23 ℃, and the effect of temperature should be paid attention to in the construction stage. During the construction process, the temperature variation of the component was -18-16 ℃, the strain variation was (-150-210)×10-6, and the additional temperature stress was -26.8-36.7 MPa. No abnormal response or damage occurred. The design and application of this monitoring system could provide a reference for the popularization of modular buildings and the application of distributed optical fiber monitoring technology in the health monitoring of modular buildings.
2024, 54(11): 15-23.
doi: 10.3724/j.gyjzG24040707
Abstract:
Wind turbines affected by alternating loads may cause their bolts to loosen due to fatigue. As an important part of connecting the wind turbine tower, flange bolt connection directly affects the safety and stability of the overall structure. Therefore, it is necessary to monitor the health status of flange bolts in real time. Based on strain monitoring theory, a strain based method of flange bolt loosening diagnosis was proposed, which can realize real-time monitoring of bolt health status. Firstly, the monitoring principle of flange bolts of tower barrel was proposed by using equivalent static method, and the relations between bolt loosening and dynamic strain near flanges were expounded. In order to reflect the strain changes before and after bolt loosening and eliminate the instantaneous error, the strain data were discretized and the RMS difference ratio RMSCR was proposed. The zone loosening index RDI was proposed to reflect the degree of bolt loosening in the zone. Through numerical simulation, a series of working conditions were designed to carry out flange bolt loosening research, and the feasibility of monitoring theory and the effectiveness of damage indexes were verified. The results showed that when the preload loss was small, the index change was not sensitive, as the preload decreased, the index began to change slowly when it reached 40%, and as the preload decreased, the change amplitude was more obvious. For the reverse balanced flange, the index was still applicable, and the monitoring effect in the tension area was better.
Wind turbines affected by alternating loads may cause their bolts to loosen due to fatigue. As an important part of connecting the wind turbine tower, flange bolt connection directly affects the safety and stability of the overall structure. Therefore, it is necessary to monitor the health status of flange bolts in real time. Based on strain monitoring theory, a strain based method of flange bolt loosening diagnosis was proposed, which can realize real-time monitoring of bolt health status. Firstly, the monitoring principle of flange bolts of tower barrel was proposed by using equivalent static method, and the relations between bolt loosening and dynamic strain near flanges were expounded. In order to reflect the strain changes before and after bolt loosening and eliminate the instantaneous error, the strain data were discretized and the RMS difference ratio RMSCR was proposed. The zone loosening index RDI was proposed to reflect the degree of bolt loosening in the zone. Through numerical simulation, a series of working conditions were designed to carry out flange bolt loosening research, and the feasibility of monitoring theory and the effectiveness of damage indexes were verified. The results showed that when the preload loss was small, the index change was not sensitive, as the preload decreased, the index began to change slowly when it reached 40%, and as the preload decreased, the change amplitude was more obvious. For the reverse balanced flange, the index was still applicable, and the monitoring effect in the tension area was better.
2024, 54(11): 24-32.
doi: 10.3724/j.gyjzG23082920
Abstract:
Based on the statistics on 32 cases of actual underground engineering projects in China where the foundation was excavated above existing tunnels, according to the composition of site soils, they could be divided into two types of strata: fine-grained soil containing sand and fine-grained soil containing gravel. Sorting and summarizing the relevant information including the plane sizes of excavated areas, the relative position and conventional control measures, etc., the main factors induced the maximum uplift displacement of tunnels were analyzed. On the basis, the prediction formula for the maximum uplift displacement of tunnels caused by deep excavation in the strata of fine-grained soil containing sand and fine-grained soil containing gravel were proposed, which were compared and analyzed with other prediction formula and actual engineering cases for verification. The results indicated that the larger the excavated area A, unloading ratio R and the shape factor of excavated areas α, and the longer the longth of tunnels passing under excavated areas Lt, the larger the maximum uplift displacement of tunnels caused by deep excavation wmax was, but the correlation between a single influencing factor and the maximum uplift displacement of tunnels was not strong. Thus, it was necessary to comprehensively consider the main influencing factors to scientifically predict tunnel deformation caused by foundation excavation. Eventually, αR(lg A+ln Lt) was used as the overall influence factor to characterize the maximum uplift displacement of tunnels induced by deep excavation of foundation, and it was found that wmax showed a good linear relation with αR(lg A+ln Lt).
Based on the statistics on 32 cases of actual underground engineering projects in China where the foundation was excavated above existing tunnels, according to the composition of site soils, they could be divided into two types of strata: fine-grained soil containing sand and fine-grained soil containing gravel. Sorting and summarizing the relevant information including the plane sizes of excavated areas, the relative position and conventional control measures, etc., the main factors induced the maximum uplift displacement of tunnels were analyzed. On the basis, the prediction formula for the maximum uplift displacement of tunnels caused by deep excavation in the strata of fine-grained soil containing sand and fine-grained soil containing gravel were proposed, which were compared and analyzed with other prediction formula and actual engineering cases for verification. The results indicated that the larger the excavated area A, unloading ratio R and the shape factor of excavated areas α, and the longer the longth of tunnels passing under excavated areas Lt, the larger the maximum uplift displacement of tunnels caused by deep excavation wmax was, but the correlation between a single influencing factor and the maximum uplift displacement of tunnels was not strong. Thus, it was necessary to comprehensively consider the main influencing factors to scientifically predict tunnel deformation caused by foundation excavation. Eventually, αR(lg A+ln Lt) was used as the overall influence factor to characterize the maximum uplift displacement of tunnels induced by deep excavation of foundation, and it was found that wmax showed a good linear relation with αR(lg A+ln Lt).
2024, 54(11): 33-40.
doi: 10.3724/j.gyjzG23052511
Abstract:
A hybrid model of genetic algorithm combined with residual network (the GA-ResNN dynamic prediction model) for multi-index variables during deep foundation excavation and the construction risk assessment method were established by combining the back propagation (BP) artificial neural network, genetic algorithm(GA), and residual network(ResNN) to address the problems of low training efficiency of existing machine learning prediction models, the possibility of a single algorithm falling into local optima, and inability to converge. An intelligent early warning platform for excavation construction risks was developed. Research showed that the proposed GA-ResNN dynamic prediction model was of better prediction accuracy compared with the BP neural network model and GA-BP network model and could realize quantitative prediction and qualitative risk level evaluation. The intelligent warning platform for foundation excavation construction risks could present the prediction curve and warning threshold, which could improve the intelligent management and risk control level for engineering projects of foundation excavation.
A hybrid model of genetic algorithm combined with residual network (the GA-ResNN dynamic prediction model) for multi-index variables during deep foundation excavation and the construction risk assessment method were established by combining the back propagation (BP) artificial neural network, genetic algorithm(GA), and residual network(ResNN) to address the problems of low training efficiency of existing machine learning prediction models, the possibility of a single algorithm falling into local optima, and inability to converge. An intelligent early warning platform for excavation construction risks was developed. Research showed that the proposed GA-ResNN dynamic prediction model was of better prediction accuracy compared with the BP neural network model and GA-BP network model and could realize quantitative prediction and qualitative risk level evaluation. The intelligent warning platform for foundation excavation construction risks could present the prediction curve and warning threshold, which could improve the intelligent management and risk control level for engineering projects of foundation excavation.
2024, 54(11): 41-49.
doi: 10.3724/j.gyjzG23091420
Abstract:
As a large-scale temporary enclosure structure for bridge foundation projects, steel pipe pile cofferdams face a large number of uncertain risk factors during the construction process. In order to accurately evaluate the safety risk level of steel pipe pile cofferdams and enhance project emergency management capabilities, after a year of on-site practice and investigation, a risk assessment model based on the combination weighting-cloud model was proposed, which adopted the Lagrangian minimum entropy principle to combine the determined subjective and objective weights, and output the evaluation language with the forward and reverse generators of the cloud model. The evaluation language presented quantitative evaluation results based on the three digital characteristics of Ex, En and He mapped by various data. Taking a highway and railway combined bridge under construction as the project background, a case analysis was conducted on the steel pipe pile cofferdam project in the water-rich sand geology. The results indicated that the evaluation results were good and basically in line with the actual situation on site. In the condition of a super entropy He of 0.03, the numerical characteristics of the overall evaluation cloud of the steel pipe pile cofferdam were 3.543 8, 0.815 4 and 0.328 5. It was reflected the cofferdam was in a relatively low risk. The proposed evaluation model could provided effective means and scientific basis for the safety management of steel pipe pile cofferdams.
As a large-scale temporary enclosure structure for bridge foundation projects, steel pipe pile cofferdams face a large number of uncertain risk factors during the construction process. In order to accurately evaluate the safety risk level of steel pipe pile cofferdams and enhance project emergency management capabilities, after a year of on-site practice and investigation, a risk assessment model based on the combination weighting-cloud model was proposed, which adopted the Lagrangian minimum entropy principle to combine the determined subjective and objective weights, and output the evaluation language with the forward and reverse generators of the cloud model. The evaluation language presented quantitative evaluation results based on the three digital characteristics of Ex, En and He mapped by various data. Taking a highway and railway combined bridge under construction as the project background, a case analysis was conducted on the steel pipe pile cofferdam project in the water-rich sand geology. The results indicated that the evaluation results were good and basically in line with the actual situation on site. In the condition of a super entropy He of 0.03, the numerical characteristics of the overall evaluation cloud of the steel pipe pile cofferdam were 3.543 8, 0.815 4 and 0.328 5. It was reflected the cofferdam was in a relatively low risk. The proposed evaluation model could provided effective means and scientific basis for the safety management of steel pipe pile cofferdams.
2024, 54(11): 50-60.
doi: 10.3724/j.gyjzG23071806
Abstract:
Affected by the seasonal precipitation and changes in water levels of reservoirs, parts of mountains will generate landslides in which the cumulative displacement-time curve of some landslides exhibits obvious "step type" dynamic deformation characteristics. In the light of that displacement, a landslide displacement prediction model was proposed, which was combined the particle swarm optimization (PSO) algorithm with the support vector regression (SVR) based on the recursive feature elimination (RFE) algorithm. and the research was performed combined with the Xinpu landslide. Firstly, the methods of outlier removal and missing value filling for landslide displacement data were explored. Outlier rejection was adopted a median-based method with ensemble empirical mode decomposition, and missing value filling was adopted a statistical variable-based method. Then, the "step type" cumulative displacement of landslides was split into the trend and period terms by the exponential smoothing method. The displacement of the trend term was fitted by Fourier curve. For the displacement of the periodic term, the influence factors with high correlation with the displacement of the periodic term were selected based on the SVR-RFE method, and the prediction model for the displacement of the periodic term was established. Subsequently, the prediction model parameters were optimized by the PSO algorithm. Finally, the predicted displacement of the period term was superimposed on the predicted displacement of the trend term to obtain the final predicted cumulative displacement of landslides, in which the goodness of fit was 0.999, the root mean square error was 9.974 mm, and the average absolute error was 7.037 mm. Comparing the proposed model with the GSCV-SVR model and the GA-SVR model, the proposed model was of a strong predictive capability for sudden displacement and was suitable for risk warning during periods of accelerated displacement changes of "step type" displacement of landslides.
Affected by the seasonal precipitation and changes in water levels of reservoirs, parts of mountains will generate landslides in which the cumulative displacement-time curve of some landslides exhibits obvious "step type" dynamic deformation characteristics. In the light of that displacement, a landslide displacement prediction model was proposed, which was combined the particle swarm optimization (PSO) algorithm with the support vector regression (SVR) based on the recursive feature elimination (RFE) algorithm. and the research was performed combined with the Xinpu landslide. Firstly, the methods of outlier removal and missing value filling for landslide displacement data were explored. Outlier rejection was adopted a median-based method with ensemble empirical mode decomposition, and missing value filling was adopted a statistical variable-based method. Then, the "step type" cumulative displacement of landslides was split into the trend and period terms by the exponential smoothing method. The displacement of the trend term was fitted by Fourier curve. For the displacement of the periodic term, the influence factors with high correlation with the displacement of the periodic term were selected based on the SVR-RFE method, and the prediction model for the displacement of the periodic term was established. Subsequently, the prediction model parameters were optimized by the PSO algorithm. Finally, the predicted displacement of the period term was superimposed on the predicted displacement of the trend term to obtain the final predicted cumulative displacement of landslides, in which the goodness of fit was 0.999, the root mean square error was 9.974 mm, and the average absolute error was 7.037 mm. Comparing the proposed model with the GSCV-SVR model and the GA-SVR model, the proposed model was of a strong predictive capability for sudden displacement and was suitable for risk warning during periods of accelerated displacement changes of "step type" displacement of landslides.
2024, 54(11): 61-66.
doi: 10.3724/j.gyjzG23033008
Abstract:
In order to effectively realize the assessment on healthy status of slopes and failure prediction of diversion projects, a fuzzy evaluation model was constructed to obtain the evaluation affiliation vector of slope status integrating multi-indicator monitored safety information, and then a healthy degree of slope status with higher recognition and more convenient application was proposed; and a prediction method for remaining useful life was established based on the nonlinear Wiener process taking healthy degrees as its performance degradation index; according to calculations of a slope in a water diversion project, the time-dependant healthy degree curve was obtained. The results showed that the method could not only evaluate the healthy status of slopes in diversion projects, but also predict the remaining life, and the prediction accuracy was ideal, which could provide a reliable monitoring method for operation status and preventive maintenance decision-making basis for slopes.
In order to effectively realize the assessment on healthy status of slopes and failure prediction of diversion projects, a fuzzy evaluation model was constructed to obtain the evaluation affiliation vector of slope status integrating multi-indicator monitored safety information, and then a healthy degree of slope status with higher recognition and more convenient application was proposed; and a prediction method for remaining useful life was established based on the nonlinear Wiener process taking healthy degrees as its performance degradation index; according to calculations of a slope in a water diversion project, the time-dependant healthy degree curve was obtained. The results showed that the method could not only evaluate the healthy status of slopes in diversion projects, but also predict the remaining life, and the prediction accuracy was ideal, which could provide a reliable monitoring method for operation status and preventive maintenance decision-making basis for slopes.
2024, 54(11): 67-77.
doi: 10.3724/j.gyjzG23110710
Abstract:
Aiming at the problem of uneven classification of apparent crack data and quantification of damage characteristics of concrete structures, a crack damage assessment method based on U2-Net and morphology was proposed. The Dice loss function and the loss weight were fused to construct the loss function, and the loss function was embedded in transfer learning. The U2-Net network was used to train the data set of apparent cracks of concrete members. The skeleton of the predicted crack map was extracted according to the predicted crack binary image, and finally the cracks were divided into linear cracks and mesh cracks. According to different types of cracks, the corresponding characteristic parameters were extracted by morphology, and the error analysis of the corresponding fracture characteristic parameters was carried out to verify the validity of the fracture characteristic parameters. The results showed that: the average relative errors of linear fracture length, maximum width and average width were -1.34%, 1.08% and 2.64%, respectively, and the average relative errors of mesh fracture area and coverage were 0.05% and 0.07%, respectively. It showed that this method had relatively high detection precision and had certain reference value for crack detection of concrete structures.
Aiming at the problem of uneven classification of apparent crack data and quantification of damage characteristics of concrete structures, a crack damage assessment method based on U2-Net and morphology was proposed. The Dice loss function and the loss weight were fused to construct the loss function, and the loss function was embedded in transfer learning. The U2-Net network was used to train the data set of apparent cracks of concrete members. The skeleton of the predicted crack map was extracted according to the predicted crack binary image, and finally the cracks were divided into linear cracks and mesh cracks. According to different types of cracks, the corresponding characteristic parameters were extracted by morphology, and the error analysis of the corresponding fracture characteristic parameters was carried out to verify the validity of the fracture characteristic parameters. The results showed that: the average relative errors of linear fracture length, maximum width and average width were -1.34%, 1.08% and 2.64%, respectively, and the average relative errors of mesh fracture area and coverage were 0.05% and 0.07%, respectively. It showed that this method had relatively high detection precision and had certain reference value for crack detection of concrete structures.
2024, 54(11): 78-86.
doi: 10.3724/j.gyjzG23102311
Abstract:
Aiming at the problem that the damage recognition accuracy of the deep learning model decreases under the influence of data sample imbalance and noise, a structural damage recognition method based on the combination of convolutional autoencoder and correlation function was proposed. Taking the stand scale test of Qatar University as an example, the sample data of healthy working conditions were input into the convolutional autoencoder model for learning, and the constructed convolutional autoencoder model was used to reconstruct the data samples of the healthy structural data samples, and the maximum error of data reconstruction was used as a threshold to judge whether the structure was damaged. Then, Gaussian white noise with different signal-to-noise ratios was added to the data set containing healthy working condition samples and damaged working condition samples, and the data samples added with noise were preprocessed by autocorrelation function. The data set processed by the autocorrelation function was input into the model for training and prediction respectively, and the prediction results of the model were compared and analyzed. The results showed that the method could accurately identify structural damage when the data samples without noise were not balanced, and the identification accuracy could reach 100%. However, under the influence of adding noise, the original characteristics of the data could be highlighted after being processed by the autocorrelation function. Under the noise condition with a signal-to-noise ratio of 5, the recognition accuracy could still reach 100%, which proved that the method could effectively improve the accuracy of damage recognition of the autoencoder model and had better noise resistance.
Aiming at the problem that the damage recognition accuracy of the deep learning model decreases under the influence of data sample imbalance and noise, a structural damage recognition method based on the combination of convolutional autoencoder and correlation function was proposed. Taking the stand scale test of Qatar University as an example, the sample data of healthy working conditions were input into the convolutional autoencoder model for learning, and the constructed convolutional autoencoder model was used to reconstruct the data samples of the healthy structural data samples, and the maximum error of data reconstruction was used as a threshold to judge whether the structure was damaged. Then, Gaussian white noise with different signal-to-noise ratios was added to the data set containing healthy working condition samples and damaged working condition samples, and the data samples added with noise were preprocessed by autocorrelation function. The data set processed by the autocorrelation function was input into the model for training and prediction respectively, and the prediction results of the model were compared and analyzed. The results showed that the method could accurately identify structural damage when the data samples without noise were not balanced, and the identification accuracy could reach 100%. However, under the influence of adding noise, the original characteristics of the data could be highlighted after being processed by the autocorrelation function. Under the noise condition with a signal-to-noise ratio of 5, the recognition accuracy could still reach 100%, which proved that the method could effectively improve the accuracy of damage recognition of the autoencoder model and had better noise resistance.
2024, 54(11): 87-94.
doi: 10.3724/j.gyjzG24022808
Abstract:
To explore the influence of polyvinyl alcohol fibers (PVA fibers) on the mechanical properties of ultra-high performance concrete (UHPC), this work adopted the Box-Behnken test design method in the response surface method to construct a quadratic polynomial regression model and studied the effects of different binder-sand ratio, dosage of silica fume, dosage of fly ash, and dosage of metakaolin on the compressive strength of UHPC matrix. The optimum ratio of UHPC containing PVA fibers was obtained by optimizing the design, and the microstructure of UHPC containing PVA fibers was described by scanning electron microscope (SEM). The results showed that the binder-sand ratio had the greatest influence on the compressive strength of UHPC matrix, followed by the dosage of fly ash, and the dosage of silica fume and metakaolin had a smaller influence; the compressive strength of the UHPC matrix reached its maximum value when the cement-sand ratio was 1.10, the silica fume dosing was 4.70%, the fly ash dosing was 18.30%, and the metakaolin dosing was 6.55%, at which time the 28 d compressive strength and tensile strength of the UHPC containing PVA fibers were 122 MPa and 11.5 MPa, respectively; PVA fibers showed good bonding performance with the matrix, had a denser microstructure, and exhibited excellent mechanical properties, especially in tensile properties.
To explore the influence of polyvinyl alcohol fibers (PVA fibers) on the mechanical properties of ultra-high performance concrete (UHPC), this work adopted the Box-Behnken test design method in the response surface method to construct a quadratic polynomial regression model and studied the effects of different binder-sand ratio, dosage of silica fume, dosage of fly ash, and dosage of metakaolin on the compressive strength of UHPC matrix. The optimum ratio of UHPC containing PVA fibers was obtained by optimizing the design, and the microstructure of UHPC containing PVA fibers was described by scanning electron microscope (SEM). The results showed that the binder-sand ratio had the greatest influence on the compressive strength of UHPC matrix, followed by the dosage of fly ash, and the dosage of silica fume and metakaolin had a smaller influence; the compressive strength of the UHPC matrix reached its maximum value when the cement-sand ratio was 1.10, the silica fume dosing was 4.70%, the fly ash dosing was 18.30%, and the metakaolin dosing was 6.55%, at which time the 28 d compressive strength and tensile strength of the UHPC containing PVA fibers were 122 MPa and 11.5 MPa, respectively; PVA fibers showed good bonding performance with the matrix, had a denser microstructure, and exhibited excellent mechanical properties, especially in tensile properties.
2024, 54(11): 95-102.
doi: 10.3724/j.gyjzG23083029
Abstract:
For the ultra-high performance concrete (UHPC) overlaying normal concrete (NC) structures, the reliable interface performance between UHPC and NC is the foundation for achieving their good co-work behavior. The paper focused on the experimental and theoretical research on the crack propagation at the interface of these UHPC-NC configurations under stress waves. A bi-material notched semi-circle bent (BNSCB) configuration was proposed, and the impact tests were conducted on the BNSCB specimens using a split Hopkinson pressure bar system (SHPB), examining the differences in the interfacial impact performance between UHPC with different strengths and NC. Based on the finite element method and crack propagation gauge, the complex stress intensity factor (CSIF) at the crack tip of the interface of BNSCB specimen was calculated. The results showed that: 1) under stress wave action, interface cracks in the BNSCB specimens tended to propagate along the aggregate-cement matrix interface; 2) the maximum velocity of interface crack propagation in the BNSCB specimen did not exceed the Rayleigh wave velocity of UHPC; 3) the parameter K2 at the crack tip of the BNSCB specimen was much smaller than K1, and the parameter K1 played a dominant role in crack initiation; 4) there was no obvious relations between the parameter K2 in CSIF and UHPC strength grades.
For the ultra-high performance concrete (UHPC) overlaying normal concrete (NC) structures, the reliable interface performance between UHPC and NC is the foundation for achieving their good co-work behavior. The paper focused on the experimental and theoretical research on the crack propagation at the interface of these UHPC-NC configurations under stress waves. A bi-material notched semi-circle bent (BNSCB) configuration was proposed, and the impact tests were conducted on the BNSCB specimens using a split Hopkinson pressure bar system (SHPB), examining the differences in the interfacial impact performance between UHPC with different strengths and NC. Based on the finite element method and crack propagation gauge, the complex stress intensity factor (CSIF) at the crack tip of the interface of BNSCB specimen was calculated. The results showed that: 1) under stress wave action, interface cracks in the BNSCB specimens tended to propagate along the aggregate-cement matrix interface; 2) the maximum velocity of interface crack propagation in the BNSCB specimen did not exceed the Rayleigh wave velocity of UHPC; 3) the parameter K2 at the crack tip of the BNSCB specimen was much smaller than K1, and the parameter K1 played a dominant role in crack initiation; 4) there was no obvious relations between the parameter K2 in CSIF and UHPC strength grades.
2024, 54(11): 103-111.
doi: 10.3724/j.gyjzG24042910
Abstract:
For steel-HSC(high-strength concrete) composite structures, the interface performance of steel and high-strength concrete is the key to determine the working mechanism of the two. To this end, the paper conducted experimental and theoretical research on the dynamic mechanical properties of the steel-HSC interface with shear studs under impact loads. The composite specimens under stress waves were experimentally studied using a split Hopkinson bar system, and the complex stress intensity factor at the crack tip of the composite specimen was obtained by an experimental numerical method. The research results showed that: 1) Under impact loads, the BNSCB specimen was not only prone to stress concentration at the shear studs, but also had a certain degree of inhibitory effect on the propagation of interface cracks. 2) When using a three-dimensional model to solve the stress intensity factor of the specimen, the average values of K1 and K2 along the thickness direction were taken as the numerical solution of the BNSCB specimen parameter K1 and K2. 3) The maximum and average velocities of the interface crack propagation of the BNSCB specimen increased with the increase of the high-strength concrete strength. 4) With the increase of the high-strength concrete strength, the fracture parameter K1 value at the interface crack tip of the BNSCB specimen would increase.
For steel-HSC(high-strength concrete) composite structures, the interface performance of steel and high-strength concrete is the key to determine the working mechanism of the two. To this end, the paper conducted experimental and theoretical research on the dynamic mechanical properties of the steel-HSC interface with shear studs under impact loads. The composite specimens under stress waves were experimentally studied using a split Hopkinson bar system, and the complex stress intensity factor at the crack tip of the composite specimen was obtained by an experimental numerical method. The research results showed that: 1) Under impact loads, the BNSCB specimen was not only prone to stress concentration at the shear studs, but also had a certain degree of inhibitory effect on the propagation of interface cracks. 2) When using a three-dimensional model to solve the stress intensity factor of the specimen, the average values of K1 and K2 along the thickness direction were taken as the numerical solution of the BNSCB specimen parameter K1 and K2. 3) The maximum and average velocities of the interface crack propagation of the BNSCB specimen increased with the increase of the high-strength concrete strength. 4) With the increase of the high-strength concrete strength, the fracture parameter K1 value at the interface crack tip of the BNSCB specimen would increase.
2024, 54(11): 112-120.
doi: 10.3724/j.gyjzG23102902
Abstract:
Ultra-high-performance concrete (UHPC) encased concrete-filled steel tubes (CFST) have advantages such as high bearing capacity and superior durability. In order to study their flexural performance, five pure bending tests of UHPC encased CFSTs members were designed. The main parameters were the steel fiber content and the ratio of concrete-filled steel tube. Based on the experimental study, the effects of different parameters on failure mode,midspan load-deflection curves, ultimate flexural capacity, flexural stiffness, and ductility were investigated. The results showed that UHPC encased CFSTs members exhibited excellent performance. Under bending, each component could maintain good collaboration. The flexural capacity increased with the increase of the UHPC steel fiber content and the ratio of concrete-filled steel tube, especially when the steel fiber content increased from 0% to 1%, the increase in bearing capacity was particularly significant. The predictions by current codes and standards for flexural capacity of UHPC encased CFST members were 11%-38% lower than the measured ones, and the predicted flexural stiffness was generally conservative.
Ultra-high-performance concrete (UHPC) encased concrete-filled steel tubes (CFST) have advantages such as high bearing capacity and superior durability. In order to study their flexural performance, five pure bending tests of UHPC encased CFSTs members were designed. The main parameters were the steel fiber content and the ratio of concrete-filled steel tube. Based on the experimental study, the effects of different parameters on failure mode,midspan load-deflection curves, ultimate flexural capacity, flexural stiffness, and ductility were investigated. The results showed that UHPC encased CFSTs members exhibited excellent performance. Under bending, each component could maintain good collaboration. The flexural capacity increased with the increase of the UHPC steel fiber content and the ratio of concrete-filled steel tube, especially when the steel fiber content increased from 0% to 1%, the increase in bearing capacity was particularly significant. The predictions by current codes and standards for flexural capacity of UHPC encased CFST members were 11%-38% lower than the measured ones, and the predicted flexural stiffness was generally conservative.
2024, 54(11): 121-128.
doi: 10.3724/j.gyjzG24022108
Abstract:
Ultral-high-performance concrete (UHPC) encased concrete-filled steel tubes (CFST) have advatages such as superior durability and high bearing capacity.Four CFST columns with varying eccentricity and slenderness ratios were experimentally tested to examine their mechanical properties.Based on the test results,the failure characteristics, load-deformation responses, ultimate eccentric bearing capacity, second-order effects, and ductility were investigated. The results revealed that the incorporation of steel fibers significantly reduced the failure degree of the outer UHPC, while the inner CFST offered the column specimens good ductility. It was noted that the eccentric bearing capacity decreased markedly with the increasing eccentricity, particularly in the range of 0-80 mm. Moreover, second-order effects had a substantial impact on the eccentric bearing capacity, contributing up to 36.5% of the total moment as eccentricity and slenderness ratio increased. The study’s findings were used to discuss the applicability of existing code provisions for calculating the eccentric bearing capacity of UHPC encased CFST columns.
Ultral-high-performance concrete (UHPC) encased concrete-filled steel tubes (CFST) have advatages such as superior durability and high bearing capacity.Four CFST columns with varying eccentricity and slenderness ratios were experimentally tested to examine their mechanical properties.Based on the test results,the failure characteristics, load-deformation responses, ultimate eccentric bearing capacity, second-order effects, and ductility were investigated. The results revealed that the incorporation of steel fibers significantly reduced the failure degree of the outer UHPC, while the inner CFST offered the column specimens good ductility. It was noted that the eccentric bearing capacity decreased markedly with the increasing eccentricity, particularly in the range of 0-80 mm. Moreover, second-order effects had a substantial impact on the eccentric bearing capacity, contributing up to 36.5% of the total moment as eccentricity and slenderness ratio increased. The study’s findings were used to discuss the applicability of existing code provisions for calculating the eccentric bearing capacity of UHPC encased CFST columns.
2024, 54(11): 129-135.
doi: 10.3724/j.gyjzG24021907
Abstract:
A ultra-high super-heavy drop hammer impact test system was employed to conduct lateral impact tests on four UHPC-Encased CFST composite columns (UECC) with fixed axial load ratio. The impact force and displacement responses of the specimens throughout the impact process were studied, and the damage and failure characteristics of the specimens during and after impact under different impact velocities and steel tube diameters were comparatively analyzed. The experimental results showed that the UECC specimens exhibited bending failure at medium to low impact velocities, with only few vertical cracks appearing. At higher impact velocities, the outer UHPC were not spalling, indicating excellent impact resistance of the UECC. Notably, an increase in impact velocity significantly improved the impact force and displacement response of the specimens, accompanied by a proportional rise in impact energy. Furthermore, enlarging the steel tube diameter proved effective in enhancing component stiffness, marginally reducing dynamic displacement response, while exerting minimal influence on impact force responses.
A ultra-high super-heavy drop hammer impact test system was employed to conduct lateral impact tests on four UHPC-Encased CFST composite columns (UECC) with fixed axial load ratio. The impact force and displacement responses of the specimens throughout the impact process were studied, and the damage and failure characteristics of the specimens during and after impact under different impact velocities and steel tube diameters were comparatively analyzed. The experimental results showed that the UECC specimens exhibited bending failure at medium to low impact velocities, with only few vertical cracks appearing. At higher impact velocities, the outer UHPC were not spalling, indicating excellent impact resistance of the UECC. Notably, an increase in impact velocity significantly improved the impact force and displacement response of the specimens, accompanied by a proportional rise in impact energy. Furthermore, enlarging the steel tube diameter proved effective in enhancing component stiffness, marginally reducing dynamic displacement response, while exerting minimal influence on impact force responses.
2024, 54(11): 136-143.
doi: 10.3724/j.gyjzG23103111
Abstract:
Concrete-encased concrete-filled steel tubular (CECFST) composite columns possess better durability and fire performance, and have been widly used in engineering practice. However, welding joints are generally used to connect the steel beam to CECFST column, leading significant difficulty in joint construction accompanied by a large amount of welding work. Moreover, welding joints are more likely to appear fracture under earthquake loads. The load transfer mechanism within the encased concrete was analyzed and its influence on the bearing capacity and stiffness of one-side bolts in tension and beam flanges in compression were discussed. The calculation model for the bearing capacity and stiffness of joints was established. OpenSEES software was employed to model the CECFST frame, in which the moment-rotation and shear force-shear curves were obtained based on the component method and superstition method, respectively. The accurary of the model was verified through test results, and the dynamic response of the CECFST frame with one-side bolted connections under different seismic intensities was studied. The seismic performance for such frame structures was investigated to determine whether it meets the requirements of current relevant specifications.
Concrete-encased concrete-filled steel tubular (CECFST) composite columns possess better durability and fire performance, and have been widly used in engineering practice. However, welding joints are generally used to connect the steel beam to CECFST column, leading significant difficulty in joint construction accompanied by a large amount of welding work. Moreover, welding joints are more likely to appear fracture under earthquake loads. The load transfer mechanism within the encased concrete was analyzed and its influence on the bearing capacity and stiffness of one-side bolts in tension and beam flanges in compression were discussed. The calculation model for the bearing capacity and stiffness of joints was established. OpenSEES software was employed to model the CECFST frame, in which the moment-rotation and shear force-shear curves were obtained based on the component method and superstition method, respectively. The accurary of the model was verified through test results, and the dynamic response of the CECFST frame with one-side bolted connections under different seismic intensities was studied. The seismic performance for such frame structures was investigated to determine whether it meets the requirements of current relevant specifications.
2024, 54(11): 144-151.
doi: 10.3724/j.gyjzG24030308
Abstract:
One-side bolted connecting technique ensures the access of inside into the closed-section column, which has been used in the assembled joints between concrete encased CFST (CECFST) columns and steel beams. However, the bulge of steel tube and outer concrete were detected for one-side bolted normal CECFST column joints owing to the limited strength of outer concrete. Therefore, UHPC was adopted as outer concrete to replace the traditional outer concrete in CECFST columns, which aimed to avoid the steel tube from being failure effectively and to omit reinforcements in outer concrete for convenient installation in one-side bolted joints. A finite element model was established by ABAQUS considering the constitutive relations of complex materials and the convergence of multi-contact in joint region. The accuracy of the model was verified through test results, systematically revealing the restraining effect of outer concrete on interral steel tubes, and indicating that the UHPC could effectively restrict the bulge of steel tube. A parametric analysis were conducted on typical UHPC encased CFST composite columns one-side bolted to steel beam joints. Finally, the analytical models on the moment resistance were developed based on the component method. The comparison results declared that the proposed analytical method provided a reasonable prediction of the moment resistance. The research results in the paper validated that replacing normal concrete of CECFST by UHPC could avoid column failure when using one-side bolted joints and gave a proper design method for UHPC-encased CFST composite column one-side bolted to steel beam joints.
One-side bolted connecting technique ensures the access of inside into the closed-section column, which has been used in the assembled joints between concrete encased CFST (CECFST) columns and steel beams. However, the bulge of steel tube and outer concrete were detected for one-side bolted normal CECFST column joints owing to the limited strength of outer concrete. Therefore, UHPC was adopted as outer concrete to replace the traditional outer concrete in CECFST columns, which aimed to avoid the steel tube from being failure effectively and to omit reinforcements in outer concrete for convenient installation in one-side bolted joints. A finite element model was established by ABAQUS considering the constitutive relations of complex materials and the convergence of multi-contact in joint region. The accuracy of the model was verified through test results, systematically revealing the restraining effect of outer concrete on interral steel tubes, and indicating that the UHPC could effectively restrict the bulge of steel tube. A parametric analysis were conducted on typical UHPC encased CFST composite columns one-side bolted to steel beam joints. Finally, the analytical models on the moment resistance were developed based on the component method. The comparison results declared that the proposed analytical method provided a reasonable prediction of the moment resistance. The research results in the paper validated that replacing normal concrete of CECFST by UHPC could avoid column failure when using one-side bolted joints and gave a proper design method for UHPC-encased CFST composite column one-side bolted to steel beam joints.
2024, 54(11): 152-162.
doi: 10.3724/j.gyjzG23100902
Abstract:
The purpose of the paper is to explore the design and transformation path of industrial heritage protection and renewal based on the "catalyst" theory, and to activate the spatial design strategy of industrial wasteland in old industrial cities. The paper analyzed the current situation of industrial heritage and established the enthusiasm and feasibility of catalyst theory in the design method of industrial heritage renewal. Taking Baotou Sugar Factory as an example, the value of "catalyst" elements was evaluated and screened out, the design of functional space and cultural elements was activated, and the activation of "catalyst style" industrial heritage space was explored. Based on the three-stage design strategy of catalyst preparation, catalyst element screening and activation, and catalyst reaction guidance, the paper adopted design strategies such as spatial organization, environmental system design, and event activities, the inventory space of industrial heritage was organically updated, enabling sustainable development of industrial culture and providing new ideas and research methods for the activation of industrial areas in old industrial cities.
The purpose of the paper is to explore the design and transformation path of industrial heritage protection and renewal based on the "catalyst" theory, and to activate the spatial design strategy of industrial wasteland in old industrial cities. The paper analyzed the current situation of industrial heritage and established the enthusiasm and feasibility of catalyst theory in the design method of industrial heritage renewal. Taking Baotou Sugar Factory as an example, the value of "catalyst" elements was evaluated and screened out, the design of functional space and cultural elements was activated, and the activation of "catalyst style" industrial heritage space was explored. Based on the three-stage design strategy of catalyst preparation, catalyst element screening and activation, and catalyst reaction guidance, the paper adopted design strategies such as spatial organization, environmental system design, and event activities, the inventory space of industrial heritage was organically updated, enabling sustainable development of industrial culture and providing new ideas and research methods for the activation of industrial areas in old industrial cities.
2024, 54(11): 163-171.
doi: 10.3724/j.gyjzG22030602
Abstract:
Spatial structure directly affects the pattern and spatial element distribution of traditional villages, and its characteristic analysis and optimal development is a strong support for the development and revitalization of traditional villages. Taking Chengyanggang Village in Shantou City as an example, the paper constructed variable parameters by using spatial syntax and social network theory to analyze the current situation, evolution law, commercial potential area and overall spatial intelligence of the village’s core block. The results show that: 1) the core block and commercial potential area gather in the middle east of the village, and the two areas basically overlap, indicating that there is a positive correlation between the core block and commercial potential area; 2) In recent years, the core block has been transferred from the old village area to the new and old combination area and new village area, showing a multi-core spatial structure; 3) At present, the village intelligence is low, so it is necessary to strengthen the classification of spatial structure. Finally, the research put forward corresponding optimization strategies according to the analysis results, in order to provide a basic basis for the future planning and construction of Chengyanggang Village.
Spatial structure directly affects the pattern and spatial element distribution of traditional villages, and its characteristic analysis and optimal development is a strong support for the development and revitalization of traditional villages. Taking Chengyanggang Village in Shantou City as an example, the paper constructed variable parameters by using spatial syntax and social network theory to analyze the current situation, evolution law, commercial potential area and overall spatial intelligence of the village’s core block. The results show that: 1) the core block and commercial potential area gather in the middle east of the village, and the two areas basically overlap, indicating that there is a positive correlation between the core block and commercial potential area; 2) In recent years, the core block has been transferred from the old village area to the new and old combination area and new village area, showing a multi-core spatial structure; 3) At present, the village intelligence is low, so it is necessary to strengthen the classification of spatial structure. Finally, the research put forward corresponding optimization strategies according to the analysis results, in order to provide a basic basis for the future planning and construction of Chengyanggang Village.
2024, 54(11): 172-180.
doi: 10.3724/j.gyjzG23111106
Abstract:
Classical gardens, as a kind of medium language for transferring information, can realize the information exchange between people. Taking the concept of linguistics as the theoretical basis, applying Morris’s theory of linguistic semiotics to the classical garden translation system, the classical garden design language was divided into three parts, namely, "pragmatics" "semantics" and "syntax", and the use of classical Chinese garden translation techniques in modern public display areas was analyzed from the perspective of language, and the embedded paths of spatial translation techniques, image translation techniques, formal translation techniques and emotional translation techniques were analyzed in detail from the aspects of spatial layout, garden images and gardening emotions, so as to make clear the design process, and to establish the complete classical garden design language translation system. On this basis, the empirical study of the translation system was carried out in combination with actual cases, obtaining high-quality design results, so as to provide a reference for the landscape design of modern public display areas.
Classical gardens, as a kind of medium language for transferring information, can realize the information exchange between people. Taking the concept of linguistics as the theoretical basis, applying Morris’s theory of linguistic semiotics to the classical garden translation system, the classical garden design language was divided into three parts, namely, "pragmatics" "semantics" and "syntax", and the use of classical Chinese garden translation techniques in modern public display areas was analyzed from the perspective of language, and the embedded paths of spatial translation techniques, image translation techniques, formal translation techniques and emotional translation techniques were analyzed in detail from the aspects of spatial layout, garden images and gardening emotions, so as to make clear the design process, and to establish the complete classical garden design language translation system. On this basis, the empirical study of the translation system was carried out in combination with actual cases, obtaining high-quality design results, so as to provide a reference for the landscape design of modern public display areas.
2024, 54(11): 181-188.
doi: 10.3724/j.gyjzG24063001
Abstract:
In order to cope with the complicated stress state at the material interface of the composite open-web sandwich plate and to improve the performance of the combined action of the structure, the paper proposed a PBL shear connectors with additional steel pipes and carried out experimental analyses and finite element simulation studies on it. The push-out tests of PBL shear connectors specimens with additional steel pipes and traditional PBL shear connectors specimens were carried out respectively. By analyzing the failure phenomenon, load-slip curves and shear stiffness of the two groups of specimens, it was found that the additional steel pipes can significantly improve the shear performance of PBL shear connectors. The stress distribution of each member of this type of PBL shear connectors and the influence of additional steel pipe parameters on the shear stiffness of this new type of PBL shear connectors were further revealed through the finite element parameter expansion analysis. It was found that the existence of additional steel pipe could avoid the phenomenon of stress concentration in the internal component and protect the internal component. The study showed that steel pipe parameters such as pipe diameter, pipe wall thickness and pipe length had different degrees of influence on the bearing capacity of this type of shear connector, with the most significant effect of pipe diameter.
In order to cope with the complicated stress state at the material interface of the composite open-web sandwich plate and to improve the performance of the combined action of the structure, the paper proposed a PBL shear connectors with additional steel pipes and carried out experimental analyses and finite element simulation studies on it. The push-out tests of PBL shear connectors specimens with additional steel pipes and traditional PBL shear connectors specimens were carried out respectively. By analyzing the failure phenomenon, load-slip curves and shear stiffness of the two groups of specimens, it was found that the additional steel pipes can significantly improve the shear performance of PBL shear connectors. The stress distribution of each member of this type of PBL shear connectors and the influence of additional steel pipe parameters on the shear stiffness of this new type of PBL shear connectors were further revealed through the finite element parameter expansion analysis. It was found that the existence of additional steel pipe could avoid the phenomenon of stress concentration in the internal component and protect the internal component. The study showed that steel pipe parameters such as pipe diameter, pipe wall thickness and pipe length had different degrees of influence on the bearing capacity of this type of shear connector, with the most significant effect of pipe diameter.
2024, 54(11): 189-195.
doi: 10.3724/j.gyjzG24073005
Abstract:
The full-frame thick slab transfer plate structure enables a skewed grids design between superstructure and substructure, maximizing the architectural potential of the space above and gaining significant attention in engineering. However, its application is recent, and seismic performance analysis for skewed grids designs is lacking. This study investigates a residential building with a thick slab transfer plate structure above metro depot. Due to the complex force transfer mechanism, a 1/40 scale seismic shaking table test was conducted to study the dynamic characteristics and responses under 7 to 8-degree seismic conditions. Numerical simulations were also performed to verify the test results. Findings indicate that after a 7-degree rare earthquake, all dynamic indicators remained within safe limits, showing good seismic performance. Under an 8-degree rare earthquake, the first natural frequency decreased by 27.93%, causing some damage mainly in the upper tower, while the thick slab transfer plate structure remained undamaged. This aligns with the expected "strong transfer floor, weak tower" failure mechanism.
The full-frame thick slab transfer plate structure enables a skewed grids design between superstructure and substructure, maximizing the architectural potential of the space above and gaining significant attention in engineering. However, its application is recent, and seismic performance analysis for skewed grids designs is lacking. This study investigates a residential building with a thick slab transfer plate structure above metro depot. Due to the complex force transfer mechanism, a 1/40 scale seismic shaking table test was conducted to study the dynamic characteristics and responses under 7 to 8-degree seismic conditions. Numerical simulations were also performed to verify the test results. Findings indicate that after a 7-degree rare earthquake, all dynamic indicators remained within safe limits, showing good seismic performance. Under an 8-degree rare earthquake, the first natural frequency decreased by 27.93%, causing some damage mainly in the upper tower, while the thick slab transfer plate structure remained undamaged. This aligns with the expected "strong transfer floor, weak tower" failure mechanism.
2024, 54(11): 196-202.
doi: 10.3724/j.gyjzG23021314
Abstract:
Three-center cylindrical latticed shell closed cargo shed is a typical wind-sensitive structure, and wind load is one of the control loads in structural design. Based on the background of three three-center cylindrical latticed shell closed cargo sheds in a comprehensive wharf project, wind tunnel tests and numerical analysis on various factors affecting wind load of closed sheds were carried out. The influence of the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions on the wind load of the closed cargo shed was studied, the calculation results of closed cargo sheds designed by the wind load in wind tunnel test results, load codes and related literature are compared. Through the research, it is found that the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions had great influence on the wind tunnel test results, there were potential safety hazards in the structural design of closed sheds by the wind load in load codes and related literatures, the wind tunnel test of this kind of long-span closed sheds should be conducted before the detailed design, and the various actual working conditions of the sheds should be taken into account and correctly reflected during the wind tunnel test.
Three-center cylindrical latticed shell closed cargo shed is a typical wind-sensitive structure, and wind load is one of the control loads in structural design. Based on the background of three three-center cylindrical latticed shell closed cargo sheds in a comprehensive wharf project, wind tunnel tests and numerical analysis on various factors affecting wind load of closed sheds were carried out. The influence of the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions on the wind load of the closed cargo shed was studied, the calculation results of closed cargo sheds designed by the wind load in wind tunnel test results, load codes and related literature are compared. Through the research, it is found that the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions had great influence on the wind tunnel test results, there were potential safety hazards in the structural design of closed sheds by the wind load in load codes and related literatures, the wind tunnel test of this kind of long-span closed sheds should be conducted before the detailed design, and the various actual working conditions of the sheds should be taken into account and correctly reflected during the wind tunnel test.
2024, 54(11): 203-210.
doi: 10.3724/j.gyjzG24061103
Abstract:
At present, the research on socket-type Disc-lock scaffolds at home and abroad mainly focuses on the vertical load working condition, while there is less research on the scaffold under lateral loads. An in-depth analysis of the mechanical properties and failure modes of the socket-type disc-lock scaffolds under lateral loads was conducted by combining physical experiments and ABAQUS finite element simulations.The study on the stress condition of the scaffold’s members under lateral loads showed that upright rods and diagonal braces played an essential role in restricting the lateral displacement of the lower and middle parts of the scaffold. The diagonal braces in the direction of the force enhanced the scaffold’s deformation resistance and stability. The arrangements of the tie-in rods effectively constrained the lateral displacement of the upper part of the scaffold. However, due to the limitation of the fastener’s strength, fastener slippage and fracture might occur as the load increased.
At present, the research on socket-type Disc-lock scaffolds at home and abroad mainly focuses on the vertical load working condition, while there is less research on the scaffold under lateral loads. An in-depth analysis of the mechanical properties and failure modes of the socket-type disc-lock scaffolds under lateral loads was conducted by combining physical experiments and ABAQUS finite element simulations.The study on the stress condition of the scaffold’s members under lateral loads showed that upright rods and diagonal braces played an essential role in restricting the lateral displacement of the lower and middle parts of the scaffold. The diagonal braces in the direction of the force enhanced the scaffold’s deformation resistance and stability. The arrangements of the tie-in rods effectively constrained the lateral displacement of the upper part of the scaffold. However, due to the limitation of the fastener’s strength, fastener slippage and fracture might occur as the load increased.
2024, 54(11): 211-219.
doi: 10.3724/j.gyjzG23071011
Abstract:
In order to study the influence of winding angle and axial compression ratio of GFRP fibers on the seismic performance of UHPC composite columns confined by GFRP tubes, six GFRP tube confined UHPC composite columns and one UHPC composite column were designed, and the quasi-static tests of the specimens under quasi-static load and axial force were carried out, and the skeleton curve characteristics of the structure were analyzed. In order to further explore the effects of diameter-thickness ratio, slenderness ratio, circumferential elastic modulus of confined tubes, and tensile strength of concrete on the seismic performance of the composite column, a finite element analysis model of composite column is established, and the energy dissipation capacity of the structure with different design schemes was analyzed. The results showed that GFRP tube was effective in improving the seismic performance of UHPC columns, and the failure mode, peak load and peak displacement of composite columns were improved, and the finite element analysis results were in good agreement with the experimental results, which verified the effectiveness of the analysis model. Through the extended analysis, it was found that the bearing capacity of the specimen increased and the energy dissipation capacity became worse with the decrease of diameter-thickness ratio and the increase of circumferential elastic modulus. With the decrease of slenderness ratio, the bearing capacity of the specimen increased, the ultimate displacement became smaller, and the energy dissipation capacity became worse. The tensile strength of concrete had an effect on the seismic performance of the specimen, but the effect was small. Through regression analysis, a formula of shear capacity of UHPC composite columns confined by GFRP tubes was proposed.
In order to study the influence of winding angle and axial compression ratio of GFRP fibers on the seismic performance of UHPC composite columns confined by GFRP tubes, six GFRP tube confined UHPC composite columns and one UHPC composite column were designed, and the quasi-static tests of the specimens under quasi-static load and axial force were carried out, and the skeleton curve characteristics of the structure were analyzed. In order to further explore the effects of diameter-thickness ratio, slenderness ratio, circumferential elastic modulus of confined tubes, and tensile strength of concrete on the seismic performance of the composite column, a finite element analysis model of composite column is established, and the energy dissipation capacity of the structure with different design schemes was analyzed. The results showed that GFRP tube was effective in improving the seismic performance of UHPC columns, and the failure mode, peak load and peak displacement of composite columns were improved, and the finite element analysis results were in good agreement with the experimental results, which verified the effectiveness of the analysis model. Through the extended analysis, it was found that the bearing capacity of the specimen increased and the energy dissipation capacity became worse with the decrease of diameter-thickness ratio and the increase of circumferential elastic modulus. With the decrease of slenderness ratio, the bearing capacity of the specimen increased, the ultimate displacement became smaller, and the energy dissipation capacity became worse. The tensile strength of concrete had an effect on the seismic performance of the specimen, but the effect was small. Through regression analysis, a formula of shear capacity of UHPC composite columns confined by GFRP tubes was proposed.
2024, 54(11): 220-225.
doi: 10.3724/j.gyjzG24050708
Abstract:
The formation of large and complex steel structures, including their geometric configuration and force state, has consistently been a key focus in construction, for large and complex steel structures have always been the key concerns during construction. There is usually a deviation in displacement and force distribution between constructional completed state and structural design state for large and complex steel structures. In order to realize the difference of completed construction and design in structural deformed and force states and ensure structural safety requirements, it is necessary to analyze and control them during construction. Based on the long-span cantilevered trusses of Shenzhen Free Trade Center project, the paper investigated the structural displacements and stress variations during construction by taking into account step-by-step loading and hardening of fluid concrete during pouring, especialy in the calculation and convergence of pre-set deformation values. The safety of the construction process was evaluated and the reasonable construction suggestions were put forward. The results highlighted the significant impact of the concrete hardening process on the pre-set deformation values and stresses, emphasizing that this factor could not be overlooked. The excellent convergence of the forward installation iteration on the pre-set deformation values of the cantilevered truss could ensure the accuracy of the results in the first iteration. The end of the concrete floor slab, if poured directly with the main structure, was constrained rigidly, which results in excessive stress under loads. To solve this problem, pour strips could be used for releasing stress.
The formation of large and complex steel structures, including their geometric configuration and force state, has consistently been a key focus in construction, for large and complex steel structures have always been the key concerns during construction. There is usually a deviation in displacement and force distribution between constructional completed state and structural design state for large and complex steel structures. In order to realize the difference of completed construction and design in structural deformed and force states and ensure structural safety requirements, it is necessary to analyze and control them during construction. Based on the long-span cantilevered trusses of Shenzhen Free Trade Center project, the paper investigated the structural displacements and stress variations during construction by taking into account step-by-step loading and hardening of fluid concrete during pouring, especialy in the calculation and convergence of pre-set deformation values. The safety of the construction process was evaluated and the reasonable construction suggestions were put forward. The results highlighted the significant impact of the concrete hardening process on the pre-set deformation values and stresses, emphasizing that this factor could not be overlooked. The excellent convergence of the forward installation iteration on the pre-set deformation values of the cantilevered truss could ensure the accuracy of the results in the first iteration. The end of the concrete floor slab, if poured directly with the main structure, was constrained rigidly, which results in excessive stress under loads. To solve this problem, pour strips could be used for releasing stress.
2024, 54(11): 226-233.
doi: 10.3724/j.gyjzG22122010
Abstract:
To study the influence law of vibration induced by rotary drilling during foundation excavation on surrounding buildings and the environment, the vibration of the adjacent ground and buildings were monitored under construction of rotary drilling for foundation excavation of the comprehensive well 5 in Shenzhen metro line 16. The following main conclusions were drawn based on time and frequency domain analysis on the field-recorded vibration data. Firstly, the vertical vibration of surrounding buildings caused by rotary drilling was stronger than horizontal vibration. Secondly, the vertical peak particle velocity (PPV) and the vertical vibration acceleration level on the floor of adjacent buildings linearly increased as the floor rosed. Thirdly, in the one-third octave spectrum of vibration acceleration, the maximum vibration acceleration in the vertical direction increased with the increase in the floor. The floor vibration in vertical and horizontal directions caused by rotary drilling was mainly in low and medium frequencies, mainly concentrated in 4 to 40 Hz. And the range of center frequency corresponding to the horizontal and vertical peak vibration acceleration of the nearby buildings was in 8 to 25 Hz. Finally, except the maximum vertical vibration level on the roof and the surrounding ground were larger than 75 dB, the maximum vertical vibration level measured at other observation points was below 75 dB. The relevant findings were of guiding significance for analysis of the impact of vibration induced by rotary drilling on surrounding buildings and the environment.
To study the influence law of vibration induced by rotary drilling during foundation excavation on surrounding buildings and the environment, the vibration of the adjacent ground and buildings were monitored under construction of rotary drilling for foundation excavation of the comprehensive well 5 in Shenzhen metro line 16. The following main conclusions were drawn based on time and frequency domain analysis on the field-recorded vibration data. Firstly, the vertical vibration of surrounding buildings caused by rotary drilling was stronger than horizontal vibration. Secondly, the vertical peak particle velocity (PPV) and the vertical vibration acceleration level on the floor of adjacent buildings linearly increased as the floor rosed. Thirdly, in the one-third octave spectrum of vibration acceleration, the maximum vibration acceleration in the vertical direction increased with the increase in the floor. The floor vibration in vertical and horizontal directions caused by rotary drilling was mainly in low and medium frequencies, mainly concentrated in 4 to 40 Hz. And the range of center frequency corresponding to the horizontal and vertical peak vibration acceleration of the nearby buildings was in 8 to 25 Hz. Finally, except the maximum vertical vibration level on the roof and the surrounding ground were larger than 75 dB, the maximum vertical vibration level measured at other observation points was below 75 dB. The relevant findings were of guiding significance for analysis of the impact of vibration induced by rotary drilling on surrounding buildings and the environment.
2024, 54(11): 234-241.
doi: 10.3724/j.gyjzG23022307
Abstract:
Slope treatment is an inevitable problem in engineering construction in karst regions. Take a large slope project on the karst stratum in Shenzhen as an example, the investigation and treatment measures for the large slope were introduced from the engineering background, potential factors of slope instability, monitored data of the project, rescue and reinforcement, which involved that:1) the monitoring and warning of the slope, and emergency treatment measures; 2) potential effects of the hydrogeological condition characteristics of the region on slope instability;3) the analysis for force-deformation characteristics of pile-anchor support structure based on long-term monitoring data. Eventually, the application of "grouting with sleeve valve pipes combined deep drainage with deep drainage holes,anti-slip piles,and retaining system reinforcement with supporting beams" in the slope reinforcement was introduced.
Slope treatment is an inevitable problem in engineering construction in karst regions. Take a large slope project on the karst stratum in Shenzhen as an example, the investigation and treatment measures for the large slope were introduced from the engineering background, potential factors of slope instability, monitored data of the project, rescue and reinforcement, which involved that:1) the monitoring and warning of the slope, and emergency treatment measures; 2) potential effects of the hydrogeological condition characteristics of the region on slope instability;3) the analysis for force-deformation characteristics of pile-anchor support structure based on long-term monitoring data. Eventually, the application of "grouting with sleeve valve pipes combined deep drainage with deep drainage holes,anti-slip piles,and retaining system reinforcement with supporting beams" in the slope reinforcement was introduced.
