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2023 Vol. 53, No. 6
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2023, 53(6): 1-12.
doi: 10.13204/j.gyjzG23022210
Abstract:
The impact of diameters of piles, wall thickness of tubular steel piles and layout radii of piles for high-rise pile cap foundations of offshore wind turbines on the static performances and load effects of piles were analyzed by the SESAM software. The results indicated that: in certain conditions of external loads and environmental parameters, the changes in diameters of piles, wall thicknesses and layout radii of tube piles had different influences on the axial compression, axial tension, shear force and bending moment of the structure. Based on the calculation data, an optimized design method for the structure was proposed. By analyzing the rules of the vertical and horizontal displacement and rotation angle at the mud surface in changes of the structural parameters, the regression curves were obtained, which were verified by examples in different sea conditions and was of good accuracy.
The impact of diameters of piles, wall thickness of tubular steel piles and layout radii of piles for high-rise pile cap foundations of offshore wind turbines on the static performances and load effects of piles were analyzed by the SESAM software. The results indicated that: in certain conditions of external loads and environmental parameters, the changes in diameters of piles, wall thicknesses and layout radii of tube piles had different influences on the axial compression, axial tension, shear force and bending moment of the structure. Based on the calculation data, an optimized design method for the structure was proposed. By analyzing the rules of the vertical and horizontal displacement and rotation angle at the mud surface in changes of the structural parameters, the regression curves were obtained, which were verified by examples in different sea conditions and was of good accuracy.
2023, 53(6): 13-18.
doi: 10.13204/j.gyjzG22122304
Abstract:
The horizontal bearing capacity and deformation characteristics for monopile foundations of offshore wind turbines directly influenced the stability and safety of the whole structure and wind turbine operation. In order to study the horizontal bearing capacity and deformation characteristics of monopile foundations, finite element numerical simulations were used to analyze the pile-soil contact model, soil parameters and variable characteristics of horizontal displacement and bending moment of piles based on the in-situ static load tests of single piles. Moreover, the method of the p-y curve recommended by the specification of API RP 2A-WSD was applied to compare the numerical simulation results with that from in-situ tests. It indicated that the simulation results were in good agreement with the measured data from in-situ tests at different load levels. The errors between the horizontal displacement of piles by the p-y curve method and in-situ tests increased with the increase of horizontal loads, which indicated that the p-y curve method was conservative. With the increase of horizontal loads, the horizontal deformation of piles gradually increased, the maximum bending moment points tended to move down, and the reverse bending point was about 14 m to16 m below the mud surface. The deformation and plastic zone of foundation soil gradually extended from the surface to the deep. Therefore, the model of pile-soil interfaces and the selection of geotechnical parameters were basically reasonable, and the rationality and effectiveness of finite element numerical simulations were verified.
The horizontal bearing capacity and deformation characteristics for monopile foundations of offshore wind turbines directly influenced the stability and safety of the whole structure and wind turbine operation. In order to study the horizontal bearing capacity and deformation characteristics of monopile foundations, finite element numerical simulations were used to analyze the pile-soil contact model, soil parameters and variable characteristics of horizontal displacement and bending moment of piles based on the in-situ static load tests of single piles. Moreover, the method of the p-y curve recommended by the specification of API RP 2A-WSD was applied to compare the numerical simulation results with that from in-situ tests. It indicated that the simulation results were in good agreement with the measured data from in-situ tests at different load levels. The errors between the horizontal displacement of piles by the p-y curve method and in-situ tests increased with the increase of horizontal loads, which indicated that the p-y curve method was conservative. With the increase of horizontal loads, the horizontal deformation of piles gradually increased, the maximum bending moment points tended to move down, and the reverse bending point was about 14 m to16 m below the mud surface. The deformation and plastic zone of foundation soil gradually extended from the surface to the deep. Therefore, the model of pile-soil interfaces and the selection of geotechnical parameters were basically reasonable, and the rationality and effectiveness of finite element numerical simulations were verified.
2023, 53(6): 19-24.
doi: 10.13204/j.gyjzG22060620
Abstract:
A series of triaxial consolidated undrained shear tests were conducted on marine soil with different contents of fine particles, and the influence of contents of fine particles on nonlinear deformation properties of marine soil was obtained. The results indicated that when the content of illite was between 0% to 18%, the maximum strength of soil was in the illite content of 12%. When it was less than 12%, the properties of soil were mainly determined by sandy soil, and the deformation of the soil exhibited strain-softening properties. When the illite content was more than 12%, the properties of soil were dominated by the illite content, which exhibited strain-hardening properties. Coupled with the nonlinear deformation characteristics of different contents of fine particles in marine soil, a three-dimensionally numerically dynamic response model for a foundation-pile-superstructure under wave dynamic loads was constructed. The analysis results indicated that when the peak strength of soil was larger, the deformation of strain-softening characteristics would cause more serious damage to wharfs. When the peak strength was lower, the deformation of strain-hardening characteristics would cause more serious damage to wharfs. At the same peak strength, the peak values of the maximum equivalent stress and the maximum shear stress in the dock panels on the hardened foundation were larger than that on the softened foundation, and the stress of the dock panel on the foundation with low peak strength of the foundation soil was larget than that on the foundation with high peak strength. In the foundation with the same peak strength, the maximum stress of strain-softening soil foundation was larger than that of strain-hardening soil foundation, the larger the stress in foundation soil, the smaller the peak strength was. It indicated that the fine particle content of marine soil had a significant impact on the dynamic stability of wharfs, and the nonlinear responses of foundation soil with different mechanical properties should be considered in design.
A series of triaxial consolidated undrained shear tests were conducted on marine soil with different contents of fine particles, and the influence of contents of fine particles on nonlinear deformation properties of marine soil was obtained. The results indicated that when the content of illite was between 0% to 18%, the maximum strength of soil was in the illite content of 12%. When it was less than 12%, the properties of soil were mainly determined by sandy soil, and the deformation of the soil exhibited strain-softening properties. When the illite content was more than 12%, the properties of soil were dominated by the illite content, which exhibited strain-hardening properties. Coupled with the nonlinear deformation characteristics of different contents of fine particles in marine soil, a three-dimensionally numerically dynamic response model for a foundation-pile-superstructure under wave dynamic loads was constructed. The analysis results indicated that when the peak strength of soil was larger, the deformation of strain-softening characteristics would cause more serious damage to wharfs. When the peak strength was lower, the deformation of strain-hardening characteristics would cause more serious damage to wharfs. At the same peak strength, the peak values of the maximum equivalent stress and the maximum shear stress in the dock panels on the hardened foundation were larger than that on the softened foundation, and the stress of the dock panel on the foundation with low peak strength of the foundation soil was larget than that on the foundation with high peak strength. In the foundation with the same peak strength, the maximum stress of strain-softening soil foundation was larger than that of strain-hardening soil foundation, the larger the stress in foundation soil, the smaller the peak strength was. It indicated that the fine particle content of marine soil had a significant impact on the dynamic stability of wharfs, and the nonlinear responses of foundation soil with different mechanical properties should be considered in design.
2023, 53(6): 25-30.
doi: 10.13204/j.gyjzG22071601
Abstract:
The wellhead suction anchor has been first used in the second round of trial production tests for natural gas hydrates in China. Be directed against anchorage foundations with wellheed suction anchors, the mechanism of the foundation under vertical loads was studied. The three-dimensional model of the foundation was constructed by finite element software, and the coupled Euler-Lagrangian (CEL) method was used to simulate the vertical large-deformation process of the foundation. The validity of the CEL method for analyzing the ultimate bearing capacity of the wellhead suction anchor was verified by comparing the numerical analysis results with the theoretical calculation results. By comparing between the characteristics of vertical displacement-load curves of traditional suction anchors and wellhead suction anchors, it was found that the side wall serionsly confined the soil plug inside wellhead suction anchors, and its vertical ultimate bearing capacity was higher. The model coupled the Euler-Lagrangian method provided reference to the optimal design of anchorage foundations with wellhead suction anchors.
The wellhead suction anchor has been first used in the second round of trial production tests for natural gas hydrates in China. Be directed against anchorage foundations with wellheed suction anchors, the mechanism of the foundation under vertical loads was studied. The three-dimensional model of the foundation was constructed by finite element software, and the coupled Euler-Lagrangian (CEL) method was used to simulate the vertical large-deformation process of the foundation. The validity of the CEL method for analyzing the ultimate bearing capacity of the wellhead suction anchor was verified by comparing the numerical analysis results with the theoretical calculation results. By comparing between the characteristics of vertical displacement-load curves of traditional suction anchors and wellhead suction anchors, it was found that the side wall serionsly confined the soil plug inside wellhead suction anchors, and its vertical ultimate bearing capacity was higher. The model coupled the Euler-Lagrangian method provided reference to the optimal design of anchorage foundations with wellhead suction anchors.
2023, 53(6): 31-36.
doi: 10.13204/j.gyjzG22102905
Abstract:
The stability evaluation of foundation trench slopes of immersed tube tunnels in the marine dynamic environment has an important research value. As a key link in the construction process of immersed tube tunnels, the sinking of tube segments of tunnels may have an adverse impact on the stability of foundation trench slopes. The dynamic stability of submarine foundation trench slopes in the sinking stage of tube segments of tunnels was numerically simulated and analyzed. The wave-current pressure calculated by wave-current fields was applied to the slope of the foundation trench and the ambient seabed surface near it, and the pore pressure caused by the wave pressure in the seabed was calculated by Darcy's law. Mohr-Coulomb model was used for seabed soil, and the slope stability coefficient was calculated by the strength reduction method. The safety factors of the slope at different times were continuously obtained, and the minimum value of the dynamic safety factor was taken as the stability evaluation index of the slope in the whole process under wave dynamic action. The flow field distribution of the foundation trench slope and its influence on the stability of foundation trench slope were discussed in the cases of with or without wave loads, with or without tube segments of tunnels in the wave-current environment, in the same or different directions between waves and currents, different sinking depths of tube segments of tunnels and other working conditions. The results indicated that the sinking of tube segments of tunnels had an adverse impact on the foundation trench slope, and the stability of the foundation trench slope was the worst when the tube segments of tunnels sinked to a certain position in the wave-current environment. When the waves and currents were in the same direction and descended along the slope, the slope was most prone to lose stability. Therefore, considering the influence of skining of tube segments of tunnels was helpful to improve the scientificity and accuracy of design and construction for foundation trench slopes of immersed tunnels.
The stability evaluation of foundation trench slopes of immersed tube tunnels in the marine dynamic environment has an important research value. As a key link in the construction process of immersed tube tunnels, the sinking of tube segments of tunnels may have an adverse impact on the stability of foundation trench slopes. The dynamic stability of submarine foundation trench slopes in the sinking stage of tube segments of tunnels was numerically simulated and analyzed. The wave-current pressure calculated by wave-current fields was applied to the slope of the foundation trench and the ambient seabed surface near it, and the pore pressure caused by the wave pressure in the seabed was calculated by Darcy's law. Mohr-Coulomb model was used for seabed soil, and the slope stability coefficient was calculated by the strength reduction method. The safety factors of the slope at different times were continuously obtained, and the minimum value of the dynamic safety factor was taken as the stability evaluation index of the slope in the whole process under wave dynamic action. The flow field distribution of the foundation trench slope and its influence on the stability of foundation trench slope were discussed in the cases of with or without wave loads, with or without tube segments of tunnels in the wave-current environment, in the same or different directions between waves and currents, different sinking depths of tube segments of tunnels and other working conditions. The results indicated that the sinking of tube segments of tunnels had an adverse impact on the foundation trench slope, and the stability of the foundation trench slope was the worst when the tube segments of tunnels sinked to a certain position in the wave-current environment. When the waves and currents were in the same direction and descended along the slope, the slope was most prone to lose stability. Therefore, considering the influence of skining of tube segments of tunnels was helpful to improve the scientificity and accuracy of design and construction for foundation trench slopes of immersed tunnels.
2023, 53(6): 37-42.
doi: 10.13204/j.gyjzG22052707
Abstract:
To estimate parameters of physical and mechanical properties of marine soil correctly plays a significant role in ensuring the safety of ocean engineering. A probabilistic prediction method was proposed, based on the Ensemble Kalman Filters and combined with the measured date of acoustic impectance and acoustic impedance-porosity transfer model, to predict the porosity of marine soil and quantify the relevant uncertainty of the transfer model and transfer states. First, an initial set representing the primary porosity estimation was generated based on the prior information. Then, the soil porosity along the depth was predicted and updated by combining the measurements of acoustic impedance obtained by multi-sensor core loggers and the probabilistic transfer model. Finally, the influence of errors of the transfer model, the initial set and the numbers of observation data on the prediction results were analyzed. An example was given to illustrate and verify the proposed method. The result indicated that the proposed method could effectively predict the distribution of soil porosity along the depth and reasonably quantify the relevant uncertainty.
To estimate parameters of physical and mechanical properties of marine soil correctly plays a significant role in ensuring the safety of ocean engineering. A probabilistic prediction method was proposed, based on the Ensemble Kalman Filters and combined with the measured date of acoustic impectance and acoustic impedance-porosity transfer model, to predict the porosity of marine soil and quantify the relevant uncertainty of the transfer model and transfer states. First, an initial set representing the primary porosity estimation was generated based on the prior information. Then, the soil porosity along the depth was predicted and updated by combining the measurements of acoustic impedance obtained by multi-sensor core loggers and the probabilistic transfer model. Finally, the influence of errors of the transfer model, the initial set and the numbers of observation data on the prediction results were analyzed. An example was given to illustrate and verify the proposed method. The result indicated that the proposed method could effectively predict the distribution of soil porosity along the depth and reasonably quantify the relevant uncertainty.
2023, 53(6): 51-58,12.
doi: 10.13204/j.gyjzG21081207
Abstract:
Under the background of focusing on urban regeneration and improving the quality of the stock spaces, how to better reuse railway heritage in China’s mega cities is a key to achieve the goal of high-quality development. Through the analysis of international and domestic cases of railway heritage conservation, the paper focused on interpreting the practice process of the section of Shanghai-Wusong Railway and Shanghai-Hangzhou Railway and surrounding areas from the obsolescence of important transportation arteries and functions to new transportation forms, which can drive activation so as to lead the urban composite regeneration functional corridor. Based on the summary of experience trends, the research proposed that railway heritage areas should play an important driving role in urban historic inheritance and comprehensive regeneration of mega cities. The study proposed the need to coordinate the railway heritage and surrounding areas with high correlation, form the new concept of railway heritage areas, comprehensively recognize and conserve the multi value system of society, economy, culture, history, and other aspects, expand and improve the object system, which including intrinsic elements, derivative elements, and intangible elements, establish characteristic functional guidance, implement policies in zones and sections, and the multiple renewal measures that can integrate the macro structure of city and drive the revitalization of surrounding communities were adopted, the supporting work mechanisms and specific policy supply for diversified integrated governance were established, so as to ultimately achieve the regeneration goal of driving high-quality urban development, providing high-quality life, and enhancing the comprehensive competitiveness of the city.
Under the background of focusing on urban regeneration and improving the quality of the stock spaces, how to better reuse railway heritage in China’s mega cities is a key to achieve the goal of high-quality development. Through the analysis of international and domestic cases of railway heritage conservation, the paper focused on interpreting the practice process of the section of Shanghai-Wusong Railway and Shanghai-Hangzhou Railway and surrounding areas from the obsolescence of important transportation arteries and functions to new transportation forms, which can drive activation so as to lead the urban composite regeneration functional corridor. Based on the summary of experience trends, the research proposed that railway heritage areas should play an important driving role in urban historic inheritance and comprehensive regeneration of mega cities. The study proposed the need to coordinate the railway heritage and surrounding areas with high correlation, form the new concept of railway heritage areas, comprehensively recognize and conserve the multi value system of society, economy, culture, history, and other aspects, expand and improve the object system, which including intrinsic elements, derivative elements, and intangible elements, establish characteristic functional guidance, implement policies in zones and sections, and the multiple renewal measures that can integrate the macro structure of city and drive the revitalization of surrounding communities were adopted, the supporting work mechanisms and specific policy supply for diversified integrated governance were established, so as to ultimately achieve the regeneration goal of driving high-quality urban development, providing high-quality life, and enhancing the comprehensive competitiveness of the city.
2023, 53(6): 59-65.
doi: 10.13204/j.gyjzG22082309
Abstract:
The development of a multi-source data analysis system has broadened the perspective of urban commercial space research, but discussions on the vitality of commercial space often focus on a single dimension of the built-up environment or social network impact, lacking comprehensive multi-dimensional practice. Therefore, an indicator system for measuring the factors affecting the vitality of commercial districts was constructed from the perspective of medium and micro, from multiple levels of physical environment, service formats and vitality atmosphere creation, and with the support of multi-source data, road network, POI, street view pictures and internet comment data were used to explore the impact of various factors on the vitality of commercial blocks during the interaction process, with the help of Arcgis technology platform, spatial syntax sDNA model construction, street view semantic analysis and other analysis tools. The results showed a positive correlation between 14 specific measurement indicators and spatial vitality to varying degrees, while expanding the applicability of multi-source data in meso and micro spatial research.
The development of a multi-source data analysis system has broadened the perspective of urban commercial space research, but discussions on the vitality of commercial space often focus on a single dimension of the built-up environment or social network impact, lacking comprehensive multi-dimensional practice. Therefore, an indicator system for measuring the factors affecting the vitality of commercial districts was constructed from the perspective of medium and micro, from multiple levels of physical environment, service formats and vitality atmosphere creation, and with the support of multi-source data, road network, POI, street view pictures and internet comment data were used to explore the impact of various factors on the vitality of commercial blocks during the interaction process, with the help of Arcgis technology platform, spatial syntax sDNA model construction, street view semantic analysis and other analysis tools. The results showed a positive correlation between 14 specific measurement indicators and spatial vitality to varying degrees, while expanding the applicability of multi-source data in meso and micro spatial research.
2023, 53(6): 66-74.
doi: 10.13204/j.gyjzG21061804
Abstract:
To resolve the contradiction between pedestrian and motor vehicle traffic in mixed urban residential and industrial land-use blocks, this study established a set of models for the quantitative analysis of spatial movement based on the principle of space syntax. These were applied to the optimal design of walkways in a mixed land sample area of the Changsha Tianxin Economic Development Zone. The investigation data showed that the traffic flow of motor vehicles in the sample area was significantly related to the spatial movement attribute of the road network; the local pedestrian flow was weakly related to the spatial moving attribute of the pedestrian network which presented a hollow state of peripheral street agglomeration and internal streets isolation. Two optimization schemes of walkways layout were put forward, and the current situation and the optimization schemes were compared and analyzed. The results showed that increasing the street crossing was beneficial to the pass-through ability for pedestrians, and increasing the density of the walkways network was beneficial to the accessibility for pedestrians. The spatial movement attribute analysis method could effectively evaluate the rationality of walkways structure and help to realize the urban demands for improving the living and business enviroment and production-city integration.
To resolve the contradiction between pedestrian and motor vehicle traffic in mixed urban residential and industrial land-use blocks, this study established a set of models for the quantitative analysis of spatial movement based on the principle of space syntax. These were applied to the optimal design of walkways in a mixed land sample area of the Changsha Tianxin Economic Development Zone. The investigation data showed that the traffic flow of motor vehicles in the sample area was significantly related to the spatial movement attribute of the road network; the local pedestrian flow was weakly related to the spatial moving attribute of the pedestrian network which presented a hollow state of peripheral street agglomeration and internal streets isolation. Two optimization schemes of walkways layout were put forward, and the current situation and the optimization schemes were compared and analyzed. The results showed that increasing the street crossing was beneficial to the pass-through ability for pedestrians, and increasing the density of the walkways network was beneficial to the accessibility for pedestrians. The spatial movement attribute analysis method could effectively evaluate the rationality of walkways structure and help to realize the urban demands for improving the living and business enviroment and production-city integration.
2023, 53(6): 75-83.
doi: 10.13204/j.gyjzG22081308
Abstract:
The spatial morphology of urban metro entrances and exits is essential in optimizing metro design and its built-up environment improvement. Based on literature research, satellite remote sensing and field research, the paper analyzed the typology of spatial forms of subway entrances in hot-summer and cold-winter regions from four aspects, including combination and orientation, opening forms, geometric forms and spatial parameters, and design elements, and deduced the differences of spatial forms of subway entrances, and then analyzed the influence of urban development orientation, climate, topography and landscape, cultural heritage and low-carbon technology on them. Finally, the paper proposed measures and strategies to enrich the diversity of materials and structures of subway entrances and exits, enhance the humanized design of subway entrances and exits, improve the directionality of subway entrances and exits, and improve the functional connection of subway entrances and exits. The research aimed to provide a theoretical basis and technical support for the design of urban spatial environments and ecological environment quality.
The spatial morphology of urban metro entrances and exits is essential in optimizing metro design and its built-up environment improvement. Based on literature research, satellite remote sensing and field research, the paper analyzed the typology of spatial forms of subway entrances in hot-summer and cold-winter regions from four aspects, including combination and orientation, opening forms, geometric forms and spatial parameters, and design elements, and deduced the differences of spatial forms of subway entrances, and then analyzed the influence of urban development orientation, climate, topography and landscape, cultural heritage and low-carbon technology on them. Finally, the paper proposed measures and strategies to enrich the diversity of materials and structures of subway entrances and exits, enhance the humanized design of subway entrances and exits, improve the directionality of subway entrances and exits, and improve the functional connection of subway entrances and exits. The research aimed to provide a theoretical basis and technical support for the design of urban spatial environments and ecological environment quality.
2023, 53(6): 84-90,121.
doi: 10.13204/j.gyjzG22122307
Abstract:
Large office buildings in severe cold regions have high energy consumption and great energy-saving potential. It is of typical and practical significance to study the law of building form energy-saving design. From the perspective of day-lighting and thermal performance, the paper proposed the influence of building form parameters on energy consumption for high-rise office buildings in severe cold C-rigion by using computer simulation method and orthogonal test method.The results showed that:1)the difference of light climate could not be the dominant factor causing the difference of building energy consumption under the same thermal region;2)plane volume,floor height and window-wall ratio always had a significant impact on the building energy consumption;3)in general, the improvement of building envelope performance would reduce the sensitivity of form design parameters to energy consumption;4)the optimal parameter combination and the worst parameter combination would not change because of the difference of light climate and building envelope performance.The research conclusions could provide a reference for the primary stage of architectural design from the perspective of energy saving.
Large office buildings in severe cold regions have high energy consumption and great energy-saving potential. It is of typical and practical significance to study the law of building form energy-saving design. From the perspective of day-lighting and thermal performance, the paper proposed the influence of building form parameters on energy consumption for high-rise office buildings in severe cold C-rigion by using computer simulation method and orthogonal test method.The results showed that:1)the difference of light climate could not be the dominant factor causing the difference of building energy consumption under the same thermal region;2)plane volume,floor height and window-wall ratio always had a significant impact on the building energy consumption;3)in general, the improvement of building envelope performance would reduce the sensitivity of form design parameters to energy consumption;4)the optimal parameter combination and the worst parameter combination would not change because of the difference of light climate and building envelope performance.The research conclusions could provide a reference for the primary stage of architectural design from the perspective of energy saving.
2023, 53(6): 91-99.
doi: 10.13204/j.gyjzG22091808
Abstract:
The research summarized the development and evolution process of silk industry in Hangzhou-Jiaxing-Huzhou area, defined the research scope of modern silk industrial heritages in Hangzhou-Jiaxing-Huzhou area from three aspects: time, space and type, put forward the "modern silk industrial heritages in Hangzhou-Jiaxing-Huzhou area list", and investigated the information data of research cases in the list. Accordingly, the database system framework and operation mode were designed, and the "comprehensive information database of modern silk industrial heritages in Hangzhou-Jiaxing-Huzhou area" composed of meta database and 8 sub databases was constructed by using SQL Server database platform. On this basis, the application of database in heritage protection research was discussed, including the overview of the overall characteristics of silk industrial heritage in Hangzhou-Jiaxing-Huzhou area based on comprehensive information database, analyzing the spatial distribution characteristics of silk industrial heritages by using GIS database, and analyzing the architectural noumenon characteristics and "type-mode" characteristics of silk industrial heritages by using "image and model information database".
The research summarized the development and evolution process of silk industry in Hangzhou-Jiaxing-Huzhou area, defined the research scope of modern silk industrial heritages in Hangzhou-Jiaxing-Huzhou area from three aspects: time, space and type, put forward the "modern silk industrial heritages in Hangzhou-Jiaxing-Huzhou area list", and investigated the information data of research cases in the list. Accordingly, the database system framework and operation mode were designed, and the "comprehensive information database of modern silk industrial heritages in Hangzhou-Jiaxing-Huzhou area" composed of meta database and 8 sub databases was constructed by using SQL Server database platform. On this basis, the application of database in heritage protection research was discussed, including the overview of the overall characteristics of silk industrial heritage in Hangzhou-Jiaxing-Huzhou area based on comprehensive information database, analyzing the spatial distribution characteristics of silk industrial heritages by using GIS database, and analyzing the architectural noumenon characteristics and "type-mode" characteristics of silk industrial heritages by using "image and model information database".
2023, 53(6): 100-104,74.
doi: 10.13204/j.gyjzG21120701
Abstract:
The effect of temperature on ultra-long concrete structures is very significant. Bending cracks may occur on the structure under service loads, while the tensile stress generated by temperature effect will further crack the structures, and thus the stiffness of the members will be reduced significantly. A simplified elastic analysis method was proposed in the paper, which considered the stiffness reduction of reinforced concrete tension-flexure members under temperature effect, and could obtain the effective axial stiffness of cracked tension-flexure members through simple iterations. The internal force of a single-span statically indeterminate beam under combined service load and temperature reduction was analyzed with the proposed method and finite element program ANSYS respectively to obtain the axial force versus temperature effect curve. The comparison between these two methods indicated that the calculated axial force by proposed method coincided well with finite element modeling results. The proposed simplified method could avoid complicated nonlinear analysis and had reasonable feasibility and accuracy.
The effect of temperature on ultra-long concrete structures is very significant. Bending cracks may occur on the structure under service loads, while the tensile stress generated by temperature effect will further crack the structures, and thus the stiffness of the members will be reduced significantly. A simplified elastic analysis method was proposed in the paper, which considered the stiffness reduction of reinforced concrete tension-flexure members under temperature effect, and could obtain the effective axial stiffness of cracked tension-flexure members through simple iterations. The internal force of a single-span statically indeterminate beam under combined service load and temperature reduction was analyzed with the proposed method and finite element program ANSYS respectively to obtain the axial force versus temperature effect curve. The comparison between these two methods indicated that the calculated axial force by proposed method coincided well with finite element modeling results. The proposed simplified method could avoid complicated nonlinear analysis and had reasonable feasibility and accuracy.
2023, 53(6): 105-110,147.
doi: 10.13204/j.gyjzG20100901
Abstract:
An experiment scheme for monitoring the temperature field of cylindrical concrete caisson outer wall under surrounding temperature was designed, which was built at Yingkou Port in northeast China. The 7-day continuous monitoring of concrete temperature in each season was measured in winter, spring, summer and autumn from 2018 to 2019. The finite element model of the experimental caisson was established by LS-DYNA finite element software, and the temperature field and temperature effect of the caisson concrete under surrounding temperature were analyzed. The results showed that the temperature of inside concrete caisson changed slowly under sunshine, while that of concrete outside changed rapidly. In winter, the temperature difference between the inside and outside of the concrete caisson was the largest, and the concrete tensile stress was the largest which exceeded the tensile strength. Moreover, the initial temperature of the structure had a great influence on the temperature stress of concrete in winter. When the initial temperature exceeded 10 ℃, there was a risk of cracking on the outer wall of caisson concrete. Therefore, the temperature effect of surrounding temperature on concrete caissons in northeast China should be considered in the design.
An experiment scheme for monitoring the temperature field of cylindrical concrete caisson outer wall under surrounding temperature was designed, which was built at Yingkou Port in northeast China. The 7-day continuous monitoring of concrete temperature in each season was measured in winter, spring, summer and autumn from 2018 to 2019. The finite element model of the experimental caisson was established by LS-DYNA finite element software, and the temperature field and temperature effect of the caisson concrete under surrounding temperature were analyzed. The results showed that the temperature of inside concrete caisson changed slowly under sunshine, while that of concrete outside changed rapidly. In winter, the temperature difference between the inside and outside of the concrete caisson was the largest, and the concrete tensile stress was the largest which exceeded the tensile strength. Moreover, the initial temperature of the structure had a great influence on the temperature stress of concrete in winter. When the initial temperature exceeded 10 ℃, there was a risk of cracking on the outer wall of caisson concrete. Therefore, the temperature effect of surrounding temperature on concrete caissons in northeast China should be considered in the design.
2023, 53(6): 111-121.
doi: 10.13204/j.gyjzG20040807
Abstract:
The high-strength steel composite Y-type eccentrically braced structure is a new type structure. Ordinary steel (fy≤345 MPa) is utilized in links to ensure the structure has good plastic deformation capacity under strong earthquake, and high-strength steel (fy≥460 MPa) is used in frame beams and columns to reduce the cross-sectional size while ensuring the elastic stress state of non-energy consuming components. The new structure has good ductility and energy-dissipating capacity. The structural influence coefficient R is a crucial part of the performance-based seismic design method. If a reasonable value of R is used, the seismic design of structure will be safer, more reasonable, and more economical. It is obviously not reasonable to hide the concept of the structural influence coefficient and adopt a fixed value for all structural systems in the 2016 edition of China’s Code for Seismic Design of Buildings (GB 50011—2010). The research can not only improve the structural performance design method, but also provide a reference for the future design of the structure. The static elastic-plastic analysis (Pushover analysis) and incremental dynamic analysis (IDA analysis) were carried out on 12 finite element models of high-strength steel composite Y-type eccentrically braced frames, and the data obtained by IDA analysis were fitted to reach the IDA performance curve of the structure. The R, Cd, Rμ and RΩ of each prototype structure were calculated by the capability spectrum method, the effects of the number of structural story N and the length of link e on performance coefficients were analyzed. Comparing the results of Pushover analysis and IDA analysis, the proposed values of each performance coefficient were proposed to provide a reference for the performance design of the new structural systems in the future.
The high-strength steel composite Y-type eccentrically braced structure is a new type structure. Ordinary steel (fy≤345 MPa) is utilized in links to ensure the structure has good plastic deformation capacity under strong earthquake, and high-strength steel (fy≥460 MPa) is used in frame beams and columns to reduce the cross-sectional size while ensuring the elastic stress state of non-energy consuming components. The new structure has good ductility and energy-dissipating capacity. The structural influence coefficient R is a crucial part of the performance-based seismic design method. If a reasonable value of R is used, the seismic design of structure will be safer, more reasonable, and more economical. It is obviously not reasonable to hide the concept of the structural influence coefficient and adopt a fixed value for all structural systems in the 2016 edition of China’s Code for Seismic Design of Buildings (GB 50011—2010). The research can not only improve the structural performance design method, but also provide a reference for the future design of the structure. The static elastic-plastic analysis (Pushover analysis) and incremental dynamic analysis (IDA analysis) were carried out on 12 finite element models of high-strength steel composite Y-type eccentrically braced frames, and the data obtained by IDA analysis were fitted to reach the IDA performance curve of the structure. The R, Cd, Rμ and RΩ of each prototype structure were calculated by the capability spectrum method, the effects of the number of structural story N and the length of link e on performance coefficients were analyzed. Comparing the results of Pushover analysis and IDA analysis, the proposed values of each performance coefficient were proposed to provide a reference for the performance design of the new structural systems in the future.
2023, 53(6): 122-128.
doi: 10.13204/j.gyjzG22031808
Abstract:
According to the excellent characteristics of steel structure, a kinds of steel girder with segmental assembly and web opening, truss-ring girder, was presented. Based on the theory of Timoshenko beam, the deflection of truss-ring girder under vertical load was obtained by deriving the bending and shear stiffness of the girder. In order to study the bending properties of the girder, two scale model specimens were fabricated according to the requirements of Specifications for Design of Highway Steel Bridge (JTG D64—2015), which were carried out by four-point loading and three-point loading tests, respectively. Two nonlinear analysis models of the specimens were established based on the finite element software ABAQUS, whose results were compared with the test results. The results showed that: 1) the proposed deflection calculation method could effectively calculate the deflection of the girder in the elastic deformation stage; 2) in four-point loading test, the edge of the top deck was prone to lose stability under pressure, which needed to be reinforced; 3) in three-point loading test, the girder reached the yield load, and the compression buckling of the top deck occurred, and the stress level of the top deck and bottom deck were close to the yield strength of Q235.
According to the excellent characteristics of steel structure, a kinds of steel girder with segmental assembly and web opening, truss-ring girder, was presented. Based on the theory of Timoshenko beam, the deflection of truss-ring girder under vertical load was obtained by deriving the bending and shear stiffness of the girder. In order to study the bending properties of the girder, two scale model specimens were fabricated according to the requirements of Specifications for Design of Highway Steel Bridge (JTG D64—2015), which were carried out by four-point loading and three-point loading tests, respectively. Two nonlinear analysis models of the specimens were established based on the finite element software ABAQUS, whose results were compared with the test results. The results showed that: 1) the proposed deflection calculation method could effectively calculate the deflection of the girder in the elastic deformation stage; 2) in four-point loading test, the edge of the top deck was prone to lose stability under pressure, which needed to be reinforced; 3) in three-point loading test, the girder reached the yield load, and the compression buckling of the top deck occurred, and the stress level of the top deck and bottom deck were close to the yield strength of Q235.
2023, 53(6): 129-137.
doi: 10.13204/j.gyjzG20121409
Abstract:
In order to investigate the mechanical properties and failure mechanism of the new type of gusset-plate connections to slotted tubular members, four specimens of this kind of joint were designed for monotonic static loading test. The test parameters studied included plate thickness and load form. The failure mode, joint ultimate bearing capacity of joint, joint displacement and strain distribution of different parts of the joint (circular tube, transverse gusset-plate and vertical gusset-plate) were discussed. The structural parameters affecting the performance indexes of joint specimens (tube wall thickness, tube diameter, plate thickness and number of branches) were analyzed by finite element parametric analysis. Results indicated that there were two types of joint failure modes, gusset-plate failure and tube failure, under the action of axial load on tube; the relative relations between tube wall thickness and gusset-plate thickness mainly determined the plastic deformation capacity of joints. For the joint specimens with two branches, when the thickness of the gusset-plate was greater than that of the tube wall, the specimen failed at the junction of the circular tube and gusset-plate, and this damage was ductile failure; when the thickness of the gusset-plate was less than that of the tube wall, the specimen bent or broke at the bottom of the gusset-plate, and this damage was brittle failure. For the joint specimens with four branches, the gusset-plate thickness should be 2 times the tube wall thickness to ensure the plastic development and ultimate bearing capacity of the joint.
In order to investigate the mechanical properties and failure mechanism of the new type of gusset-plate connections to slotted tubular members, four specimens of this kind of joint were designed for monotonic static loading test. The test parameters studied included plate thickness and load form. The failure mode, joint ultimate bearing capacity of joint, joint displacement and strain distribution of different parts of the joint (circular tube, transverse gusset-plate and vertical gusset-plate) were discussed. The structural parameters affecting the performance indexes of joint specimens (tube wall thickness, tube diameter, plate thickness and number of branches) were analyzed by finite element parametric analysis. Results indicated that there were two types of joint failure modes, gusset-plate failure and tube failure, under the action of axial load on tube; the relative relations between tube wall thickness and gusset-plate thickness mainly determined the plastic deformation capacity of joints. For the joint specimens with two branches, when the thickness of the gusset-plate was greater than that of the tube wall, the specimen failed at the junction of the circular tube and gusset-plate, and this damage was ductile failure; when the thickness of the gusset-plate was less than that of the tube wall, the specimen bent or broke at the bottom of the gusset-plate, and this damage was brittle failure. For the joint specimens with four branches, the gusset-plate thickness should be 2 times the tube wall thickness to ensure the plastic development and ultimate bearing capacity of the joint.
2023, 53(6): 138-147.
doi: 10.13204/j.gyjzG21072206
Abstract:
In order to study the seismic performance of steel frame with rotational friction damper parameters, the finite element calculation model of rotational friction damper was established by using ABAQUS. The seismic mechanism of the structure was analyzed, and the restoring force model of steel frame with rotational friction damper was proposed. The stress distribution and failure mode of steel frame structures with rotational friction damper under monotonic and quasi-static load were studied, as well as the influence of high-strength bolt preload and friction coefficient of friction plate on the seismic performance of the structure. The results showed that the initial stiffness and bearing capacity of the steel frame with rotational friction damper were significantly improved compared with the ordinary steel frame. When the damper reached the maximum rotational range, it worked with the structure and provided a certain stiffness; by increasing the preload of high-strength bolts and friction coefficient of friction plate, the initial stiffness of the structure could be improved, but there was no obvious effect on the ultimate load and sliding stiffness of the structure; the hysteretic curve of the steel frame model with rotational friction damper was full and had good ductility and energy dissipation capacity.
In order to study the seismic performance of steel frame with rotational friction damper parameters, the finite element calculation model of rotational friction damper was established by using ABAQUS. The seismic mechanism of the structure was analyzed, and the restoring force model of steel frame with rotational friction damper was proposed. The stress distribution and failure mode of steel frame structures with rotational friction damper under monotonic and quasi-static load were studied, as well as the influence of high-strength bolt preload and friction coefficient of friction plate on the seismic performance of the structure. The results showed that the initial stiffness and bearing capacity of the steel frame with rotational friction damper were significantly improved compared with the ordinary steel frame. When the damper reached the maximum rotational range, it worked with the structure and provided a certain stiffness; by increasing the preload of high-strength bolts and friction coefficient of friction plate, the initial stiffness of the structure could be improved, but there was no obvious effect on the ultimate load and sliding stiffness of the structure; the hysteretic curve of the steel frame model with rotational friction damper was full and had good ductility and energy dissipation capacity.
2023, 53(6): 148-152,160.
doi: 10.13204/j.gyjzG21101208
Abstract:
The solar tower in CSP (concentrating solar power) station is usually characterized by large height-width ratio, low frequency and small damping which makes its response is rather sensitivity to wind loads. In order to study the wind-induced responses laws of the tower, a full-scale aeroelastic model for a 243-meter-high solar tower was designed and manufactured in the paper. Measurements of the model’s dynamic response indicated a good simulation of the parameters for the prototype tower and the first-order damping ratio was as low as 0.3%. Then wind tunnel test for the aeroelastic model was conducted, the influence of the damping ratio of the model on the wind-induced responses of the tower was studied, as well as the response laws of the structure in cross-wind and along-wind directions at vortex-induced vibration resonance and design wind speed. The results indicated that vortex-induced resonance occurred significantly at a velocity of about 22.1 m/s for the prototype tower. When the damping ratio was 0.7%, there was an obvious vortex-induced response, however, when the damping ratio of the structure increased to 1.0% or more, the vortex-indused response became less obvious. In addition, the maximum peak acceleration of the tower occurred in the cross-wind direction at the vortex-induced vibration wind speed while the maximum base shear response occurred in the along-wind direction at the design wind speed.
The solar tower in CSP (concentrating solar power) station is usually characterized by large height-width ratio, low frequency and small damping which makes its response is rather sensitivity to wind loads. In order to study the wind-induced responses laws of the tower, a full-scale aeroelastic model for a 243-meter-high solar tower was designed and manufactured in the paper. Measurements of the model’s dynamic response indicated a good simulation of the parameters for the prototype tower and the first-order damping ratio was as low as 0.3%. Then wind tunnel test for the aeroelastic model was conducted, the influence of the damping ratio of the model on the wind-induced responses of the tower was studied, as well as the response laws of the structure in cross-wind and along-wind directions at vortex-induced vibration resonance and design wind speed. The results indicated that vortex-induced resonance occurred significantly at a velocity of about 22.1 m/s for the prototype tower. When the damping ratio was 0.7%, there was an obvious vortex-induced response, however, when the damping ratio of the structure increased to 1.0% or more, the vortex-indused response became less obvious. In addition, the maximum peak acceleration of the tower occurred in the cross-wind direction at the vortex-induced vibration wind speed while the maximum base shear response occurred in the along-wind direction at the design wind speed.
2023, 53(6): 153-160.
doi: 10.13204/j.gyjzG22110911
Abstract:
To investigate the effects of profiled steel sheets on the flexural capacity, short-term and long-term stiffness of steel-bars truss slabs, typical design methods for reinforced concrete slabs and composite steel-concrete slabs were first summarised and evaluated, and benchmarked against the test results reported by the authors and other researchers. Design procedures were then proposed for steel-bars truss slabs considering the influence of profiled steel sheets. The results indicated that the profiled steel sheets in steel-bars truss slabs could reach their yield strength under ultimate limit state, and therefore an increase of 47.0%-60.3% in the flexural capacity was observed for steel-bars truss slabs when compared to slab samples without profiled steel sheets; the contribution of profiled steel sheets to the short-term stiffness was significant, and the increase magnitudes were 112.1%-180.0%, despite the strains of profiled steel sheets under the normal service load were smaller than expected; the sealing effect of profiled steel sheets resulted in uneven distribution of shrinkage deformation of concrete along the height of cross section, and an additional 119.7% deflection could be obtained accordingly. Span-to-depth ratio and ambient relative humidity were the key factors that influenced the shrinkage performance of steel-bars truss slabs, and the proposed design procedures accounting for non-uniform shrinkage distributions showed good accuracy with the test results, with the ratio of 0.951-0.979 and the correlation coefficient R2 of 0.657-0.873.
To investigate the effects of profiled steel sheets on the flexural capacity, short-term and long-term stiffness of steel-bars truss slabs, typical design methods for reinforced concrete slabs and composite steel-concrete slabs were first summarised and evaluated, and benchmarked against the test results reported by the authors and other researchers. Design procedures were then proposed for steel-bars truss slabs considering the influence of profiled steel sheets. The results indicated that the profiled steel sheets in steel-bars truss slabs could reach their yield strength under ultimate limit state, and therefore an increase of 47.0%-60.3% in the flexural capacity was observed for steel-bars truss slabs when compared to slab samples without profiled steel sheets; the contribution of profiled steel sheets to the short-term stiffness was significant, and the increase magnitudes were 112.1%-180.0%, despite the strains of profiled steel sheets under the normal service load were smaller than expected; the sealing effect of profiled steel sheets resulted in uneven distribution of shrinkage deformation of concrete along the height of cross section, and an additional 119.7% deflection could be obtained accordingly. Span-to-depth ratio and ambient relative humidity were the key factors that influenced the shrinkage performance of steel-bars truss slabs, and the proposed design procedures accounting for non-uniform shrinkage distributions showed good accuracy with the test results, with the ratio of 0.951-0.979 and the correlation coefficient R2 of 0.657-0.873.
2023, 53(6): 161-170.
doi: 10.13204/j.gyjzG22093006
Abstract:
In order to solve the situation that it is impossible to install temporary piers in the bridge span for special reasons such as flood season, a kind of walking jacking construction without temporary piers scheme for long-span steel-concrete composite bridges was studied, it has more advantages than the original design of trestle straight lifting, side sliding and other construction schemes. The scheme simulated hundreds of construction conditions and selected the optimal construction conditions for finite element analysis. Through the finite element analysis of the bearing capacity of steel bridge permanent pier, assembling platform, steel guide beam and steel beam itself, the results showed that the jacking construction without temporary piers scheme for steel-concrete composite bridges was safe, economical and reliable, and was worth popularizing.
In order to solve the situation that it is impossible to install temporary piers in the bridge span for special reasons such as flood season, a kind of walking jacking construction without temporary piers scheme for long-span steel-concrete composite bridges was studied, it has more advantages than the original design of trestle straight lifting, side sliding and other construction schemes. The scheme simulated hundreds of construction conditions and selected the optimal construction conditions for finite element analysis. Through the finite element analysis of the bearing capacity of steel bridge permanent pier, assembling platform, steel guide beam and steel beam itself, the results showed that the jacking construction without temporary piers scheme for steel-concrete composite bridges was safe, economical and reliable, and was worth popularizing.
2023, 53(6): 171-180.
doi: 10.13204/j.gyjzG22031003
Abstract:
In order to provide data support for the fire protection work of the Back Hall of Yangxin Hall (hereinafter referred to as the Back Hall), and provide useful guidance for the fire safety management of ancient wooden structures in China, the fixed fire load value of the Back Hall was counted, and the FDS software was used to simulate and analyze the changes of heat release rate, fire spread, temperature, visibility, smoke and toxic and harmful gas concentration under different disaster causing factors. The results showed that the fixed fire load value of the Back Hall was 11 096.85 MJ·m-2. The flashover time in the fire scenario was short, and secondary flashover would occur in the process. The roof was the most threatened by the fire. The temperature and toxic and harmful gas concentration in the fire site exceeded the safe bearing range of the human body. The evacuation of movable cultural relics was greatly affected by smoke and visibility, and the opening and closing status of windows had a great impact on the development of the fire. Based on the research results, the paper put forward countermeasures and suggestions for the fire safety management of the Back Hall.
In order to provide data support for the fire protection work of the Back Hall of Yangxin Hall (hereinafter referred to as the Back Hall), and provide useful guidance for the fire safety management of ancient wooden structures in China, the fixed fire load value of the Back Hall was counted, and the FDS software was used to simulate and analyze the changes of heat release rate, fire spread, temperature, visibility, smoke and toxic and harmful gas concentration under different disaster causing factors. The results showed that the fixed fire load value of the Back Hall was 11 096.85 MJ·m-2. The flashover time in the fire scenario was short, and secondary flashover would occur in the process. The roof was the most threatened by the fire. The temperature and toxic and harmful gas concentration in the fire site exceeded the safe bearing range of the human body. The evacuation of movable cultural relics was greatly affected by smoke and visibility, and the opening and closing status of windows had a great impact on the development of the fire. Based on the research results, the paper put forward countermeasures and suggestions for the fire safety management of the Back Hall.
2023, 53(6): 181-186,193.
doi: 10.13204/j.gyjzG22052706
Abstract:
Through the experiments of concrete with normal water content experiencing cryogenic temperatures of 0 ℃, -20 ℃, -40 ℃, -60 ℃, -80 ℃, -100 ℃, -120 ℃, -140 ℃ and -160 ℃, the changing regularity of the preloading stress of prestressed concrete under different cryogenic temperatures was discussed, and the difference of the effect of higher water content on it was given by the experiments from lower and higher cryogenic temperature actions. The test results showed that the preloading stress loss rate of prestressed concrete at the cooling target points and the temperature uniformity target points increased rapidly first and then slowly with the decreased in the exerted cryogenic temperatures. But its preloading stress changing rate at the cooling stages was different from that at the constant temperature stages. The former showed a trend of rapid increase first and then basically linear decrease, and the latter showed a trend of rapid first and then gradually slow decrease. The loss of preloading stress of the prestressed concrete no longer increased but recovered at the constant temperature stages after reaching the cooling target points. The influence of water content on the preloading stress loss rate and the preloading stress changing rate of prestressed concrete was complex, and it was related to the exerted cryogenic temperatures. These results could provide a reference for the design and safety evaluation of prestressed concrete structures as LNG storage tanks.
Through the experiments of concrete with normal water content experiencing cryogenic temperatures of 0 ℃, -20 ℃, -40 ℃, -60 ℃, -80 ℃, -100 ℃, -120 ℃, -140 ℃ and -160 ℃, the changing regularity of the preloading stress of prestressed concrete under different cryogenic temperatures was discussed, and the difference of the effect of higher water content on it was given by the experiments from lower and higher cryogenic temperature actions. The test results showed that the preloading stress loss rate of prestressed concrete at the cooling target points and the temperature uniformity target points increased rapidly first and then slowly with the decreased in the exerted cryogenic temperatures. But its preloading stress changing rate at the cooling stages was different from that at the constant temperature stages. The former showed a trend of rapid increase first and then basically linear decrease, and the latter showed a trend of rapid first and then gradually slow decrease. The loss of preloading stress of the prestressed concrete no longer increased but recovered at the constant temperature stages after reaching the cooling target points. The influence of water content on the preloading stress loss rate and the preloading stress changing rate of prestressed concrete was complex, and it was related to the exerted cryogenic temperatures. These results could provide a reference for the design and safety evaluation of prestressed concrete structures as LNG storage tanks.
2023, 53(6): 187-193.
doi: 10.13204/j.gyjzG20101007
Abstract:
The specimens of concrete (C), recycled concrete (RC), steel fiber reinforced recycled concrete (SFRC) and silicon carbide recycled concrete (SiCRC) at different soaking ages were studied by compression test and splitting tensile test. Four types of standard concrete cube test blocks were immersed in a NaCl solution with a mass fraction of 5%. Soaking time was 0 d, 30 d, 60 d and 90 d, then finished the test. The mechanical properties of recycled concrete such as RC、SFRC、SiCRC were compared with ordinary concrete, the relations between the compressive strength and splitting tensile strength of different types of concrete with age were obtained by fitting the test data, and the influence mechanism of chloride salt immersion at different ages on recycled concrete was analyzed.The results showed that the compressive strength and splitting tensile strength of C,RC,SiCRC and other concrete increased with the increase of chlorine salt immersion age, while the strength performance of SFRC concrete was opposite. The color of SFRC specimens after being subjected to chlorine salt immersion was deepened and the surface was corroded. There was no obvious change in other types of concrete specimens, which indicated that SiCRC、RC and C were more suitable for chlorine salt environment than SFRC.
The specimens of concrete (C), recycled concrete (RC), steel fiber reinforced recycled concrete (SFRC) and silicon carbide recycled concrete (SiCRC) at different soaking ages were studied by compression test and splitting tensile test. Four types of standard concrete cube test blocks were immersed in a NaCl solution with a mass fraction of 5%. Soaking time was 0 d, 30 d, 60 d and 90 d, then finished the test. The mechanical properties of recycled concrete such as RC、SFRC、SiCRC were compared with ordinary concrete, the relations between the compressive strength and splitting tensile strength of different types of concrete with age were obtained by fitting the test data, and the influence mechanism of chloride salt immersion at different ages on recycled concrete was analyzed.The results showed that the compressive strength and splitting tensile strength of C,RC,SiCRC and other concrete increased with the increase of chlorine salt immersion age, while the strength performance of SFRC concrete was opposite. The color of SFRC specimens after being subjected to chlorine salt immersion was deepened and the surface was corroded. There was no obvious change in other types of concrete specimens, which indicated that SiCRC、RC and C were more suitable for chlorine salt environment than SFRC.
2023, 53(6): 194-201.
doi: 10.13204/j.gyjzG22122706
Abstract:
It is of great significance for geopolymer grouting material as a low-carbon material to replace high energy consumption cement-based grouting material in tunnel reinforcement engineering. In order to reasonably design the ratio of slag-based geopolymer grouting material and reveal the mechanism of alkali-activated reaction, firstly the ratio of fly ash was determined through single factor experiment, then the response surface methodology and central composite design were applied for establishing the prediction models of compressive strength for geopolymer grouting material. In the design, alkali activator modulus, alkali activator concentration and liquid-solid ratio were taken as independent variates, and the compressive strength of cementation body as the response values. The quadratic prediction equations of compressive strength were established and verified through significance analysis, variance analysis and the comprehensive analysis of response surface figure, and XRD, SEM and FT-IR methods were applied to analyze the component and microstructure of geopolymer. The results showed that the response surface method was more accurate to optimize the ratio of geopolymer injection paste. The concentration of activator became the most important factor affecting the compressive strength, and the interaction between activator concentration and liquid-solid ratio was significant. The coexistence of C-(A)-S-H and N-A-S-H multi-gels appeared in the alkali-activated slag-fly ash system. The coagulation and hardening of the gel phase provided strength for the harden paste. With the extension of the age, the gel content increased, the microstructure of the system became denser, and the macroscopic mechanical properties were further improved. Considering the development of slurry strength and construction performance, it was concluded that when the dosage of slag and fly ash was 9∶1, the modulus and concentration of activator were 1.2 and 15%, respectively, and the liquid-solid ratio was 0.6, the comprehensive performance of geopolymer grouting material was the best. The research could provide a reference for the engineering application of geopolymer grouting materials.
It is of great significance for geopolymer grouting material as a low-carbon material to replace high energy consumption cement-based grouting material in tunnel reinforcement engineering. In order to reasonably design the ratio of slag-based geopolymer grouting material and reveal the mechanism of alkali-activated reaction, firstly the ratio of fly ash was determined through single factor experiment, then the response surface methodology and central composite design were applied for establishing the prediction models of compressive strength for geopolymer grouting material. In the design, alkali activator modulus, alkali activator concentration and liquid-solid ratio were taken as independent variates, and the compressive strength of cementation body as the response values. The quadratic prediction equations of compressive strength were established and verified through significance analysis, variance analysis and the comprehensive analysis of response surface figure, and XRD, SEM and FT-IR methods were applied to analyze the component and microstructure of geopolymer. The results showed that the response surface method was more accurate to optimize the ratio of geopolymer injection paste. The concentration of activator became the most important factor affecting the compressive strength, and the interaction between activator concentration and liquid-solid ratio was significant. The coexistence of C-(A)-S-H and N-A-S-H multi-gels appeared in the alkali-activated slag-fly ash system. The coagulation and hardening of the gel phase provided strength for the harden paste. With the extension of the age, the gel content increased, the microstructure of the system became denser, and the macroscopic mechanical properties were further improved. Considering the development of slurry strength and construction performance, it was concluded that when the dosage of slag and fly ash was 9∶1, the modulus and concentration of activator were 1.2 and 15%, respectively, and the liquid-solid ratio was 0.6, the comprehensive performance of geopolymer grouting material was the best. The research could provide a reference for the engineering application of geopolymer grouting materials.
2023, 53(6): 202-208,42.
doi: 10.13204/j.gyjzG22081906
Abstract:
In order to study the shear fatigue performance of concrete beams using CFRP strips instead of steel stirrups, constant-amplitude fatigue experiment was carried out on 4 concrete beams reinforced with CFRP strip stirrups and 2 concrete beams with steel stirrups. The effects of shear-span ratio (a/d=1.0, 2.5) and the configuration way of CFRP strips on the shear fatigue performance of the concrete beams were investigated. The results showed that the fatigue life of beams with CFRP strip stirrups was much higher than that of reinforced concrete beams, the beams with CFRP strip stirrups were not damaged after being subjected to more than 2 million cycles of cyclic loading under equal-amplitude fatigue loading conditions. Moreover, compared with the reinforced concrate beams, the residual deflection and stirrup strain of the beams reinforced with CFRP strip stirrups showed a better performance. Based on the existing shear damage theory and the truss-arch model, the maximum strain of CFRP strip stirrups under cyclic loading was predicted, and results were in good agreement with the test data. Therefore, using CFRP strip stirrups instead of ordinary steel stirrups could effectively improve the shear resistance of concrete beams under fatigue loading.
In order to study the shear fatigue performance of concrete beams using CFRP strips instead of steel stirrups, constant-amplitude fatigue experiment was carried out on 4 concrete beams reinforced with CFRP strip stirrups and 2 concrete beams with steel stirrups. The effects of shear-span ratio (a/d=1.0, 2.5) and the configuration way of CFRP strips on the shear fatigue performance of the concrete beams were investigated. The results showed that the fatigue life of beams with CFRP strip stirrups was much higher than that of reinforced concrete beams, the beams with CFRP strip stirrups were not damaged after being subjected to more than 2 million cycles of cyclic loading under equal-amplitude fatigue loading conditions. Moreover, compared with the reinforced concrate beams, the residual deflection and stirrup strain of the beams reinforced with CFRP strip stirrups showed a better performance. Based on the existing shear damage theory and the truss-arch model, the maximum strain of CFRP strip stirrups under cyclic loading was predicted, and results were in good agreement with the test data. Therefore, using CFRP strip stirrups instead of ordinary steel stirrups could effectively improve the shear resistance of concrete beams under fatigue loading.
2023, 53(6): 209-217.
doi: 10.13204/j.gyjzG22061601
Abstract:
Aiming at the defects of low strength and ductility of recycled aggregate, low utilization rate of tailings and relative brittleness of geopolymer concrete, fiber reinforced polymer (FRP) was adopted to restraint concrete for enhancing the utilization rate of resources and ameliorating the mechanical properties such as strength and ductility. Therefore, taking the type of FRP, the number of FRP layers and the axial strength grade of core concrete as variables, a total of 42 specimens in 14 groups were designed to carry out axial compressive performance test research and theoretical model analysis of FRP-constrained geopolymeric recycled concrete mixed with tailing powder (FRP-GRC-TP) in the paper. The results showed that the FRP-GRC-TP composite structure significantly improved the strength and ductility of core concrete, and the more layers of FRP, the stronger the enhancement effect. In addition, the enhancement effect of FRP-constrained low-strength concrete was more obvious. The two suggested fitting strength models and one suggested fitting limit strain model proposed in the study had small errors between theoretical calculated values and experimental values, and showed a high prediction accuracy for the strength and ultimate strain of FRP-GRC-TP.
Aiming at the defects of low strength and ductility of recycled aggregate, low utilization rate of tailings and relative brittleness of geopolymer concrete, fiber reinforced polymer (FRP) was adopted to restraint concrete for enhancing the utilization rate of resources and ameliorating the mechanical properties such as strength and ductility. Therefore, taking the type of FRP, the number of FRP layers and the axial strength grade of core concrete as variables, a total of 42 specimens in 14 groups were designed to carry out axial compressive performance test research and theoretical model analysis of FRP-constrained geopolymeric recycled concrete mixed with tailing powder (FRP-GRC-TP) in the paper. The results showed that the FRP-GRC-TP composite structure significantly improved the strength and ductility of core concrete, and the more layers of FRP, the stronger the enhancement effect. In addition, the enhancement effect of FRP-constrained low-strength concrete was more obvious. The two suggested fitting strength models and one suggested fitting limit strain model proposed in the study had small errors between theoretical calculated values and experimental values, and showed a high prediction accuracy for the strength and ultimate strain of FRP-GRC-TP.
2023, 53(6): 218-223,24.
doi: 10.13204/j.gyjzG23042307
Abstract:
In view of the problem of comprehensive evaluation for the safety state of long-span space steel structures, a three-level comprehensive evaluation index system for monitoring long-span steel structures was established, in which the criterion layer included the bearing capacity, deformation, dynamic characteristics, and load environment. By constructing the fuzzy judgment matrix of criterion layer and index layer, the weights of the monitoring indexes were obtained, and the representative values of the comprehensive evaluation for structural safety and its calculation method were put forward. The comprehensive index system proposed in the paper was used to evaluate the static load test of single-layer reticulated shell and the steel structure roof of Hangzhou West Railway Station during construction. These two engineering examples verified the correctness and effectiveness of the method proposed in the paper and provided a reference for the comprehensive evaluation of similar structural monitoring.
In view of the problem of comprehensive evaluation for the safety state of long-span space steel structures, a three-level comprehensive evaluation index system for monitoring long-span steel structures was established, in which the criterion layer included the bearing capacity, deformation, dynamic characteristics, and load environment. By constructing the fuzzy judgment matrix of criterion layer and index layer, the weights of the monitoring indexes were obtained, and the representative values of the comprehensive evaluation for structural safety and its calculation method were put forward. The comprehensive index system proposed in the paper was used to evaluate the static load test of single-layer reticulated shell and the steel structure roof of Hangzhou West Railway Station during construction. These two engineering examples verified the correctness and effectiveness of the method proposed in the paper and provided a reference for the comprehensive evaluation of similar structural monitoring.
