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2024 Vol. 54, No. 10
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2024, 54(10): 1-8.
doi: 10.3724/j.gyjzG24091907
Abstract:
Prestressed concrete structure has undergone several decades of digestion and absorption, and re-innovation since its introduction to China, which has become one of important structural forms to achieve further enhancement of structural performances and meet diverse design demands. Prestressed concrete structure has been widely applied and a large number of prestressed concrete buildings and structures have been constructed up to now.The key techniques and development status in the field of the performance evaluation on prestressed concrete structures from the aspects of development history, performance evaluation needs, prestress detection and monitoring techniques, and performance evaluation methods were expounded. The future development trends of prestressed concrete structure from the three aspects of theory, techniques and application were envisaged. The future development directions involving uncertainty evaluation theory, material-structure-integrated evaluation techniques, and intelligent service performance evaluation methods were focused. It was expected to provide references to research and practice in the field of prestressed concrete structure.
Prestressed concrete structure has undergone several decades of digestion and absorption, and re-innovation since its introduction to China, which has become one of important structural forms to achieve further enhancement of structural performances and meet diverse design demands. Prestressed concrete structure has been widely applied and a large number of prestressed concrete buildings and structures have been constructed up to now.The key techniques and development status in the field of the performance evaluation on prestressed concrete structures from the aspects of development history, performance evaluation needs, prestress detection and monitoring techniques, and performance evaluation methods were expounded. The future development trends of prestressed concrete structure from the three aspects of theory, techniques and application were envisaged. The future development directions involving uncertainty evaluation theory, material-structure-integrated evaluation techniques, and intelligent service performance evaluation methods were focused. It was expected to provide references to research and practice in the field of prestressed concrete structure.
2024, 54(10): 9-20.
doi: 10.3724/j.gyjzG24100801
Abstract:
Precast prestressed concrete structures, possessing the characteristics of both precast concrete structures and prestressed concrete structures, exhibit promising application prospects in the fields of construction and infrastructure. The paper systematically summarized the research progress made by domestic and international research teams, including the authors’ group, on the mechanical properties of precast prestressed concrete frames, shear walls, and utility tunnel structures. The research objects primarily encompassed two types of precast prestressed concrete frame structures (with precast and cast-in-situ joint cores), precast prestressed concrete shear wall structures, and precast prestressed concrete utility tunnel structures. Existing research indicates that all three structures possessed excellent bearing capacity and deformation recovery capability. Precast prestressed concrete frame structures with precast joint cores exhibited limited ductility and energy dissipation capability, displaying typical semi-rigid characteristics, while those with cast-in-situ joint cores demonstrated good seismic performance. Precast prestressed concrete shear wall structures primarily underwent rigid body rotation during seismic events, with no significant damage or residual deformation to the main wall body, but their ductility and energy dissipation capacity were unsatisfactory. Precast prestressed concrete utility tunnel structures demonstrated good waterproof performance, high bearing capacity and recovery capability. Furthermore, the applications and codes for these three types of structures were summarized. Finally, the research prospects for precast prestressed concrete structures were discussed.
Precast prestressed concrete structures, possessing the characteristics of both precast concrete structures and prestressed concrete structures, exhibit promising application prospects in the fields of construction and infrastructure. The paper systematically summarized the research progress made by domestic and international research teams, including the authors’ group, on the mechanical properties of precast prestressed concrete frames, shear walls, and utility tunnel structures. The research objects primarily encompassed two types of precast prestressed concrete frame structures (with precast and cast-in-situ joint cores), precast prestressed concrete shear wall structures, and precast prestressed concrete utility tunnel structures. Existing research indicates that all three structures possessed excellent bearing capacity and deformation recovery capability. Precast prestressed concrete frame structures with precast joint cores exhibited limited ductility and energy dissipation capability, displaying typical semi-rigid characteristics, while those with cast-in-situ joint cores demonstrated good seismic performance. Precast prestressed concrete shear wall structures primarily underwent rigid body rotation during seismic events, with no significant damage or residual deformation to the main wall body, but their ductility and energy dissipation capacity were unsatisfactory. Precast prestressed concrete utility tunnel structures demonstrated good waterproof performance, high bearing capacity and recovery capability. Furthermore, the applications and codes for these three types of structures were summarized. Finally, the research prospects for precast prestressed concrete structures were discussed.
2024, 54(10): 21-30.
doi: 10.3724/j.gyjzG24090902
Abstract:
Prestressed structures, serving as key components in bridge and tunnel construction, frequently operate in high or variable humidity environments. To investigate the long-term deformation and prestress loss of prestressed beams under varying environmental humidities, this study employed the DuCOM-COM3 multi-physis and multi-scale finite element program to analyze prestressed concrete structures across different humidity levels and compared these findings with experimental results. The findings indicated that concrete beam prestress loss was influenced by environmental humidity; higher humidity reduced long-term deformation, thereby mitigating prestress loss and long-term deflection in these structures. This suggests that constitutive models based on multi-scale micro-pore structures could capture the micro-deformations within pore structures, enabling the determination of concrete structures’ mechanical properties through computations of micro-behavior and moisture transport within the concrete. Comparative experiments and calculations demonstrated that multi-field and multi-scale analysis of concrete structures could assess the effects of changing environments on the long-term performance of prestressed concrete structures. Through analyzing the mechanism of multi-physics and multi-scale analysis of moisture-heat-stress coupling, the paper simulated the prestress loss and long-term deflection of prestressed concrete beams under environmental humidity conditions of 40%, 60%, and 80%. The relations between environmental humidity and the shrinkage and creep,the long-term deformation,and the prestress loss were obtained.
Prestressed structures, serving as key components in bridge and tunnel construction, frequently operate in high or variable humidity environments. To investigate the long-term deformation and prestress loss of prestressed beams under varying environmental humidities, this study employed the DuCOM-COM3 multi-physis and multi-scale finite element program to analyze prestressed concrete structures across different humidity levels and compared these findings with experimental results. The findings indicated that concrete beam prestress loss was influenced by environmental humidity; higher humidity reduced long-term deformation, thereby mitigating prestress loss and long-term deflection in these structures. This suggests that constitutive models based on multi-scale micro-pore structures could capture the micro-deformations within pore structures, enabling the determination of concrete structures’ mechanical properties through computations of micro-behavior and moisture transport within the concrete. Comparative experiments and calculations demonstrated that multi-field and multi-scale analysis of concrete structures could assess the effects of changing environments on the long-term performance of prestressed concrete structures. Through analyzing the mechanism of multi-physics and multi-scale analysis of moisture-heat-stress coupling, the paper simulated the prestress loss and long-term deflection of prestressed concrete beams under environmental humidity conditions of 40%, 60%, and 80%. The relations between environmental humidity and the shrinkage and creep,the long-term deformation,and the prestress loss were obtained.
2024, 54(10): 31-37.
doi: 10.3724/j.gyjzG24091802
Abstract:
To promote the application of precast concrete frames in earthquake hazard areas, a new prestressed precast concrete frame with buckling-restrained braces (BRB-PPCF) was proposed, and the nonlinear dynamic time-history analysis of 6-story, 9-story and 12-story BRB-PPCF cases under 20 earthquake waves were carried out. The results showed that the average maximum inter-story drift ratios θmax of BRB-PPCFs were less than 2.0% and the maximum residual inter-story drift ratios θr were less than 0.5% under both rare and extremely rare seismic intensity. The θmax and θr values of BRB-PPCFs gradually decreased with the decrease of the initial stiffness ratio αc between the moment-resistant sub-frame (MSF) and the truss sub-system (TSS). Reducing the αc value of BRB-PPCF effectively improved its seismic performance and post-earthquake recoverability. The θmax and θr values of BRB-PPCFs decreased first and then increased with the increase of the ratio ψ of the MSF inter-story shear force at linear limit state and the TSS shear force at yield state, and the influence of the ψ was relatively small. The effects of the ratio σpi/σpl between the initial tensile stress and the proportional ultimate strength on the θmax and θr values of the BRB-PPCF could be ignored.
To promote the application of precast concrete frames in earthquake hazard areas, a new prestressed precast concrete frame with buckling-restrained braces (BRB-PPCF) was proposed, and the nonlinear dynamic time-history analysis of 6-story, 9-story and 12-story BRB-PPCF cases under 20 earthquake waves were carried out. The results showed that the average maximum inter-story drift ratios θmax of BRB-PPCFs were less than 2.0% and the maximum residual inter-story drift ratios θr were less than 0.5% under both rare and extremely rare seismic intensity. The θmax and θr values of BRB-PPCFs gradually decreased with the decrease of the initial stiffness ratio αc between the moment-resistant sub-frame (MSF) and the truss sub-system (TSS). Reducing the αc value of BRB-PPCF effectively improved its seismic performance and post-earthquake recoverability. The θmax and θr values of BRB-PPCFs decreased first and then increased with the increase of the ratio ψ of the MSF inter-story shear force at linear limit state and the TSS shear force at yield state, and the influence of the ψ was relatively small. The effects of the ratio σpi/σpl between the initial tensile stress and the proportional ultimate strength on the θmax and θr values of the BRB-PPCF could be ignored.
2024, 54(10): 38-45.
doi: 10.3724/j.gyjzG24091003
Abstract:
Due to the difficulty in meeting major earthquake demands with the stiffness and energy dissipation capabilities of traditional self-centering prestressed concrete (SCPC)frames, the inter-story drift of the structure becomes excessively large during seismic events. Additionally, to achieve full re-centering of the structure, high tensioning of steel strands is required, which further reduces the energy dissipation ratio (β) of the structure. A self-centering prestressed concrete frame with low prestressing and slope friction (SF-SCPC) was proposed, low prestressing and a high energy dissipation ratio β were incorporated into the self-centering prestressed concrete frame, allowing for some residual displacement in the structure to achieve high energy dissipation under large earthquakes. Using a reinforced concrete structure in an 8-degree seismic fortification area as a prototype, semi-self-centering prestressed concrete frames with low prestressing and slope friction (SF-PSCPC), semi-self-centering prestressed concrete (PF-PSCPC) frames with planar friction energy dissipating, and fully self-centering prestressed concrete frames with slope friction energy dissipating (SF-CSCPC) were designed. Nonlinear dynamic time-history analysis was conducted on the structures under design intensity, rarely occurred, and extremely rarely occurred earthquakes to study the impact of energy dissipator forms and initial prestressing parameters on the seismic performance indicators such as inter-story drift, residual inter-story drift, and beam-column damage. The results indicated that effectively combining the slope friction energy dissipation mechanism and low prestressing re-centering mechanism in self-centering prestressed concrete frames could significantly reduce the inter-story drift and decrease damage to main components. The hysteresis curve area of connections in the SF-PSCPC frame is significantly larger than that of the PF-PSCPC and SF-CSCPC frames, indicating higher energy dissipation capacity. Although the SF-PSCPC structure exhibited some residual displacement under rarely occurred earthquakes, it remained within the economically repairable limit of the structure.
Due to the difficulty in meeting major earthquake demands with the stiffness and energy dissipation capabilities of traditional self-centering prestressed concrete (SCPC)frames, the inter-story drift of the structure becomes excessively large during seismic events. Additionally, to achieve full re-centering of the structure, high tensioning of steel strands is required, which further reduces the energy dissipation ratio (β) of the structure. A self-centering prestressed concrete frame with low prestressing and slope friction (SF-SCPC) was proposed, low prestressing and a high energy dissipation ratio β were incorporated into the self-centering prestressed concrete frame, allowing for some residual displacement in the structure to achieve high energy dissipation under large earthquakes. Using a reinforced concrete structure in an 8-degree seismic fortification area as a prototype, semi-self-centering prestressed concrete frames with low prestressing and slope friction (SF-PSCPC), semi-self-centering prestressed concrete (PF-PSCPC) frames with planar friction energy dissipating, and fully self-centering prestressed concrete frames with slope friction energy dissipating (SF-CSCPC) were designed. Nonlinear dynamic time-history analysis was conducted on the structures under design intensity, rarely occurred, and extremely rarely occurred earthquakes to study the impact of energy dissipator forms and initial prestressing parameters on the seismic performance indicators such as inter-story drift, residual inter-story drift, and beam-column damage. The results indicated that effectively combining the slope friction energy dissipation mechanism and low prestressing re-centering mechanism in self-centering prestressed concrete frames could significantly reduce the inter-story drift and decrease damage to main components. The hysteresis curve area of connections in the SF-PSCPC frame is significantly larger than that of the PF-PSCPC and SF-CSCPC frames, indicating higher energy dissipation capacity. Although the SF-PSCPC structure exhibited some residual displacement under rarely occurred earthquakes, it remained within the economically repairable limit of the structure.
2024, 54(10): 46-52.
doi: 10.13204/j.gyjzG22122906
Abstract:
According to the stress principle of prestressed concrete composite flexural members, the paper put forward the calculation method of the steel stress about pretensioned prestressed concrete composite beams in service stage, which takes into account the two stages of stress in construction stage and service stage, filling the gap in the current standard in China. The paper also revised the calculation method of crack width in the service stage about prestressed concrete composite beams in the code. Referring to the relevant provisions of American ACI 318 Code on controlling the cracks of prestressed components through nominal tensile stress, based on specific projects, the recommended nominal tensile stress control values for different crack limits of pretensioned prestressed concrete T-shaped composite beams under the Chinese code system were proposed.
According to the stress principle of prestressed concrete composite flexural members, the paper put forward the calculation method of the steel stress about pretensioned prestressed concrete composite beams in service stage, which takes into account the two stages of stress in construction stage and service stage, filling the gap in the current standard in China. The paper also revised the calculation method of crack width in the service stage about prestressed concrete composite beams in the code. Referring to the relevant provisions of American ACI 318 Code on controlling the cracks of prestressed components through nominal tensile stress, based on specific projects, the recommended nominal tensile stress control values for different crack limits of pretensioned prestressed concrete T-shaped composite beams under the Chinese code system were proposed.
2024, 54(10): 53-61.
doi: 10.3724/j.gyjzG24061205
Abstract:
In order to investigate the stress distribution characteristics of the prestressed concrete thick plate anchorage zone with multiple blocks, a full-scale test was carried out on the anchorage zone of the longest cantilever beam in the staircase of Shanghai Grand Opera House. The stress development of the reinforcement and concrete at the location of the tensile stress concentration was obtained by tensioning the prestressed tendons in batches of each block. The finite element model was established and the parameters were analyzed. The force flow characteristics and the influence of various factors on the local action effect in the anchorage zone were obtained. The results of test and finite element calculation showed that the local bending effect was not obvious in the thick plate anchorage zone, and only the last anchor block had the tie-back tension effect. The bursting effect, root tension effect and deviation force effect of each anchor block were independent of each other. The stress of the stirrups resisting horizontal shear in the plate accumulated with the tension of the prestressed tendons of each anchor block. The tensile stress flow caused by the bursting effect in the thick plate anchorage zone was mainly distributed in the tension end to the half of the block length. And there was a bifurcation phenomenon of the tie-back tension effect force. The tie-back effect and root tension effect decrease with the increase of the angle of the block. The local bending effect increased with the decrease of the plate thickness and the increase of the distance from the block to the front end of the plate.
In order to investigate the stress distribution characteristics of the prestressed concrete thick plate anchorage zone with multiple blocks, a full-scale test was carried out on the anchorage zone of the longest cantilever beam in the staircase of Shanghai Grand Opera House. The stress development of the reinforcement and concrete at the location of the tensile stress concentration was obtained by tensioning the prestressed tendons in batches of each block. The finite element model was established and the parameters were analyzed. The force flow characteristics and the influence of various factors on the local action effect in the anchorage zone were obtained. The results of test and finite element calculation showed that the local bending effect was not obvious in the thick plate anchorage zone, and only the last anchor block had the tie-back tension effect. The bursting effect, root tension effect and deviation force effect of each anchor block were independent of each other. The stress of the stirrups resisting horizontal shear in the plate accumulated with the tension of the prestressed tendons of each anchor block. The tensile stress flow caused by the bursting effect in the thick plate anchorage zone was mainly distributed in the tension end to the half of the block length. And there was a bifurcation phenomenon of the tie-back tension effect force. The tie-back effect and root tension effect decrease with the increase of the angle of the block. The local bending effect increased with the decrease of the plate thickness and the increase of the distance from the block to the front end of the plate.
2024, 54(10): 62-69.
doi: 10.3724/j.gyjzG24082107
Abstract:
Taking the design of the cable mesh curtain wall of CICC Tower as a case study, and design method of a cross-corner micro-curved cable mesh curtain wall was studied and analyzed, and the key technical details were put forward from the overall analysis and calculation of the cable mesh structure, the analysis of key joints, and the design of the curtain wall system. The results showed that the "micro-curved" single-layer cable network structure supported building curtain wall could realize the modeling demand of the corner of the building facade; the overall analysis of the cable network structure should consider the rigidity of the main supporting structure and the influence of the construction process, and should also consider the spatial relations between different components at the joints of the cable network; when designing the curtain wall system, the focus should be on the displacement of the glass panel support points in and out of the plane of the curtain wall, the warping of the control panel should be strictly controlled, and measures should be taken to prevent the panel from sliding out of the range of the connectors.
Taking the design of the cable mesh curtain wall of CICC Tower as a case study, and design method of a cross-corner micro-curved cable mesh curtain wall was studied and analyzed, and the key technical details were put forward from the overall analysis and calculation of the cable mesh structure, the analysis of key joints, and the design of the curtain wall system. The results showed that the "micro-curved" single-layer cable network structure supported building curtain wall could realize the modeling demand of the corner of the building facade; the overall analysis of the cable network structure should consider the rigidity of the main supporting structure and the influence of the construction process, and should also consider the spatial relations between different components at the joints of the cable network; when designing the curtain wall system, the focus should be on the displacement of the glass panel support points in and out of the plane of the curtain wall, the warping of the control panel should be strictly controlled, and measures should be taken to prevent the panel from sliding out of the range of the connectors.
2024, 54(10): 70-76.
doi: 10.3724/j.gyjzG24090204
Abstract:
Four sets of 12 bending tests of prestressed glued laminated timber (glulam)-concrete composite beams with different shear connections were tested. The test parameter is the shear connection form, including notch connections, notch plus screw connections, and the combination of multi connections. The results of the bending test showed that the main failure mode of the composite beams was the bending failure of the timber. For beams with the same notch plus screw connection, applying prestress increased the average bending bearing capacity by 20.3%, the average collapse bending stiffness by 10.1%. At failure, obvious slip occurred at the shear connection. The beam with notch plus screw connection showed better integrity and flexural capacity when it failed compared to the other two sets of composite beams, which meant that the notch plus screw connection presented a better connection effect.
Four sets of 12 bending tests of prestressed glued laminated timber (glulam)-concrete composite beams with different shear connections were tested. The test parameter is the shear connection form, including notch connections, notch plus screw connections, and the combination of multi connections. The results of the bending test showed that the main failure mode of the composite beams was the bending failure of the timber. For beams with the same notch plus screw connection, applying prestress increased the average bending bearing capacity by 20.3%, the average collapse bending stiffness by 10.1%. At failure, obvious slip occurred at the shear connection. The beam with notch plus screw connection showed better integrity and flexural capacity when it failed compared to the other two sets of composite beams, which meant that the notch plus screw connection presented a better connection effect.
2024, 54(10): 77-83.
doi: 10.3724/j.gyjzG21081606
Abstract:
Prestressed steel reinforced concrete (PSRC) is the combination of modern prestressed concrete technology and steel composite structure technology, which can create conditions for the realization of larger span and larger space of building structures. The redistribution of plastic internal force and moment of PSRC continuous beams have different characteristics. The existing research is rarely reported, and there is no regulation in the relevant national codes. Therefore, it is necessary to study the theory of moment redistribution of PSRC continuous beams. In the study, the influence of the relative compression area height of the bearing section, the strength ratio of bearing to midspan, the steel ratio and the secondary moment on the redistribution of plastic internal force and the moment of the two-span PSRC continuous beams were studied by the redistribution of plastic internal force and the moment redistribution of the two-span PSRC continuous beams.
Prestressed steel reinforced concrete (PSRC) is the combination of modern prestressed concrete technology and steel composite structure technology, which can create conditions for the realization of larger span and larger space of building structures. The redistribution of plastic internal force and moment of PSRC continuous beams have different characteristics. The existing research is rarely reported, and there is no regulation in the relevant national codes. Therefore, it is necessary to study the theory of moment redistribution of PSRC continuous beams. In the study, the influence of the relative compression area height of the bearing section, the strength ratio of bearing to midspan, the steel ratio and the secondary moment on the redistribution of plastic internal force and the moment of the two-span PSRC continuous beams were studied by the redistribution of plastic internal force and the moment redistribution of the two-span PSRC continuous beams.
2024, 54(10): 84-93.
doi: 10.3724/j.gyjzG24093001
Abstract:
In order to predict the nonlinear creep of concrete, it is necessary to establish a reasonable meso-finite element model of concrete. Base on the computational methods and principles of nonlinear creep in concrete, a mesoscale three-phase numerical model of concrete, which considering aggregates, cement paste, and the interfacial transition zone, was developed by using ABAQUS finite element analysis software through secondary development. The "aggregate scaling method" was proposed to generate a uniform interface transition zone in the two-phase finite element model, which was subsequently used to establish a three-phase model. By introducing strain increments caused by damage based on linear creep, the nonlinear creep effect was effectively simulated. The mesoscale three-phase numerical model of concrete successfully simulated the complex mesoscale structure of concrete and computed creep behavior by using recursive formulas, demonstrating good performance in simulating strain changes in concrete under sustained loads. Finally, the accuracy of the model was validated through existing creep test data from concrete cylindrical and prismatic specimens.
In order to predict the nonlinear creep of concrete, it is necessary to establish a reasonable meso-finite element model of concrete. Base on the computational methods and principles of nonlinear creep in concrete, a mesoscale three-phase numerical model of concrete, which considering aggregates, cement paste, and the interfacial transition zone, was developed by using ABAQUS finite element analysis software through secondary development. The "aggregate scaling method" was proposed to generate a uniform interface transition zone in the two-phase finite element model, which was subsequently used to establish a three-phase model. By introducing strain increments caused by damage based on linear creep, the nonlinear creep effect was effectively simulated. The mesoscale three-phase numerical model of concrete successfully simulated the complex mesoscale structure of concrete and computed creep behavior by using recursive formulas, demonstrating good performance in simulating strain changes in concrete under sustained loads. Finally, the accuracy of the model was validated through existing creep test data from concrete cylindrical and prismatic specimens.
2024, 54(10): 94-105.
doi: 10.3724/j.gyjzG23091217
Abstract:
Nanhua Village in Yangjiang, Guangdong Province, is one of the few large-scale traditional Hakka Walled Village of the Qing Dynasty preserved in western Guangdong. Through field research, the village was recorded in detail, and the spatial morphological characteristics of Nanhua Village were analyzed in aspects of historical background, axis rank and order, enclosure and centrality, integration of ancestral hall and living rooms, etc. In addition, spatial gene theory was also used to compare and refine how traditional Walled Village architecture adapted to the regional "replication-expression" mechanism. In order to provide auxiliary references for the excavation of traditional architectural spatial form organization and in-depth cognition of Hakka cultural connotation.
Nanhua Village in Yangjiang, Guangdong Province, is one of the few large-scale traditional Hakka Walled Village of the Qing Dynasty preserved in western Guangdong. Through field research, the village was recorded in detail, and the spatial morphological characteristics of Nanhua Village were analyzed in aspects of historical background, axis rank and order, enclosure and centrality, integration of ancestral hall and living rooms, etc. In addition, spatial gene theory was also used to compare and refine how traditional Walled Village architecture adapted to the regional "replication-expression" mechanism. In order to provide auxiliary references for the excavation of traditional architectural spatial form organization and in-depth cognition of Hakka cultural connotation.
2024, 54(10): 106-116.
doi: 10.3724/j.gyjzG23063009
Abstract:
Urban ventilation corridor is one of the effective ways to improve urban microclimate, reduce urban heat island effect and alleviate air pollution. By constructing a theoretical framework for evaluating the ventilation performance of urban neighborhoods and quantitatively assessing the ventilation performance of 57 neighborhoods in the main urban area of Hefei City, the worst ventilation performance was found in Shuanggang Street, and then a spatial optimization strategy for the wind environment based on the old neighborhoods was proposed. The results showed that: 1)Hefei ventilation efficiency formed a "one main and one time" dual-center distribution structure mainly in the old city (within the Second Ring Road) and the new city (Binhu New District), and the ventilation efficiency decreased slightly and then increased from the core outward, with an average value of 3.27. 2)CFD numerical simulation was used to analyze a variety of spatial layout schemes in winter and summer, and it was concluded that it was necessary to build a new ventilation system that conformed to the dominant wind direction. The spatial optimization strategies, such as constructing potential ventilation corridors that follow the dominant wind direction and changing the height and density of buildings at the block obstruction points, can improve the quality of the wind environment of the block, promote the diffusion of pollutants, and improve the comfort of the residents, thus providing theoretical support for the ecological renewal and reconstruction of the old block.
Urban ventilation corridor is one of the effective ways to improve urban microclimate, reduce urban heat island effect and alleviate air pollution. By constructing a theoretical framework for evaluating the ventilation performance of urban neighborhoods and quantitatively assessing the ventilation performance of 57 neighborhoods in the main urban area of Hefei City, the worst ventilation performance was found in Shuanggang Street, and then a spatial optimization strategy for the wind environment based on the old neighborhoods was proposed. The results showed that: 1)Hefei ventilation efficiency formed a "one main and one time" dual-center distribution structure mainly in the old city (within the Second Ring Road) and the new city (Binhu New District), and the ventilation efficiency decreased slightly and then increased from the core outward, with an average value of 3.27. 2)CFD numerical simulation was used to analyze a variety of spatial layout schemes in winter and summer, and it was concluded that it was necessary to build a new ventilation system that conformed to the dominant wind direction. The spatial optimization strategies, such as constructing potential ventilation corridors that follow the dominant wind direction and changing the height and density of buildings at the block obstruction points, can improve the quality of the wind environment of the block, promote the diffusion of pollutants, and improve the comfort of the residents, thus providing theoretical support for the ecological renewal and reconstruction of the old block.
2024, 54(10): 117-130.
doi: 10.3724/j.gyjzG23083146
Abstract:
As a 'Chinese-style’ industrial heritage that witnesses technological innovation, promotes historical progress, and reflects multiple values, the reasonable preservation and continuation of the heritage built by the third-front construction is the purpose and significance of this study. The number of industrial building sites left over from the third-front construction period is huge, and not all of them have preservation value. Therefore, the idea of holistic protection has become the primary idea in the context of land incremental conversion and urban organic renewal. Under the background, the paper studied the series of elements of the built heritage of the third-front construction to clarify the four-in-one value system of architectural value, environmental value, intangible value and contemporary value, so as to establish a systematic value evaluation system, and introduce oral history and fair value range to jointly determine the rates of evaluation factors. Empirically, the system could provide conditions for vertical and horizontal, single and multiple comparisons for the evaluation results. It could not only horizontally compare and analyze the value differences of different plant areas, but also vertically compare the relative importance of various values of the same plant area, and ultimately guide the integrity protection of third-front construction, also provide a tool and method for transforming the industrial'rust belt’ into the 'show belt’ of life in China’s urban renewal in the future.
As a 'Chinese-style’ industrial heritage that witnesses technological innovation, promotes historical progress, and reflects multiple values, the reasonable preservation and continuation of the heritage built by the third-front construction is the purpose and significance of this study. The number of industrial building sites left over from the third-front construction period is huge, and not all of them have preservation value. Therefore, the idea of holistic protection has become the primary idea in the context of land incremental conversion and urban organic renewal. Under the background, the paper studied the series of elements of the built heritage of the third-front construction to clarify the four-in-one value system of architectural value, environmental value, intangible value and contemporary value, so as to establish a systematic value evaluation system, and introduce oral history and fair value range to jointly determine the rates of evaluation factors. Empirically, the system could provide conditions for vertical and horizontal, single and multiple comparisons for the evaluation results. It could not only horizontally compare and analyze the value differences of different plant areas, but also vertically compare the relative importance of various values of the same plant area, and ultimately guide the integrity protection of third-front construction, also provide a tool and method for transforming the industrial'rust belt’ into the 'show belt’ of life in China’s urban renewal in the future.
2024, 54(10): 131-137.
doi: 10.3724/j.gyjzG23092503
Abstract:
Wind tunnel tests were used to study the wind load of high-rise building sail-shaped tower crown. The distribution characteristics of average wind pressure and fluctuating wind pressure of sail-shaped tower crown under typical wind direction were obtained, as well as the variation of shape coefficient of each face with wind direction. The extreme value analysis method was used to obtain the extreme net wind pressure distribution of sail-shaped tower crown. The wind load spectrum characteristics of tower crown under typical wind direction were discussed and compared with the middle of tower body.The results showed that a semi-open cavity was formed by three sides of the sail-shaped tower crown, and the distribution of wind pressure inside was relatively uniform. When the sail opening was facing the wind, a significant wind-catching effect was formed. However, the net wind shape coefficient of the sails open to the wind was only 1.09 because of the upward flow from the top of the high-rise building. Due to the separation of air flow, strong wind suction and pressure pulsation were generated on the two edges of the tower crown, and the local net wind pressure extreme value was large. The special shape of the sail-shaped tower crown made the intensity of the cross wind vortex shedding when the sail opening was windward or leeward was obviously weaker than that when the flank was windward.
Wind tunnel tests were used to study the wind load of high-rise building sail-shaped tower crown. The distribution characteristics of average wind pressure and fluctuating wind pressure of sail-shaped tower crown under typical wind direction were obtained, as well as the variation of shape coefficient of each face with wind direction. The extreme value analysis method was used to obtain the extreme net wind pressure distribution of sail-shaped tower crown. The wind load spectrum characteristics of tower crown under typical wind direction were discussed and compared with the middle of tower body.The results showed that a semi-open cavity was formed by three sides of the sail-shaped tower crown, and the distribution of wind pressure inside was relatively uniform. When the sail opening was facing the wind, a significant wind-catching effect was formed. However, the net wind shape coefficient of the sails open to the wind was only 1.09 because of the upward flow from the top of the high-rise building. Due to the separation of air flow, strong wind suction and pressure pulsation were generated on the two edges of the tower crown, and the local net wind pressure extreme value was large. The special shape of the sail-shaped tower crown made the intensity of the cross wind vortex shedding when the sail opening was windward or leeward was obviously weaker than that when the flank was windward.
2024, 54(10): 138-146.
doi: 10.3724/j.gyjzG22020911
Abstract:
Flat panel stiffened plates are the basic components of steel box, steel tower and steel arch in steel structure bridges. In order to study the overall stability of flat panel stiffened plates, the finite element models verified by experiments were established for overall stability analysis. The effects of different constitutive relations, initial geometric defects and welding residual stresses on the overall stability bearing capacity were considered. It was found that: the ideal elastic-plastic constitutive model could be used to safely analyze the overall stability of flat plate stiffened panel under compression. Increasing the initial bending amplitude and loading eccentricity of the model would weaken the plates’ overall stability capacity.When the defect amplitude was 1/1 000 of the calculated length, the bearing capacity of model initially bent on the side of the plate rib was relatively low, but the model initially bent on the side of the stiffened plate was more sensitive to the defect; increasing the peak value of welding residual compressive stress would reduce the overall axial stiffness and ultimate average stress of flat plate stiffened panels.Within the range of the relative slenderness ratio studied, the fitted calculation formula curve was lower than the test value and the curve of equal strength steel u-rib column, and was generally close to the class B column curve in the Specifications for Design of Highway Steel Bridge (JTG D64—2015), higher than the column curve corresponding to the Japanese and American codes, which could be safely used for the overall stability calculation of flat panel stiffened plates.
Flat panel stiffened plates are the basic components of steel box, steel tower and steel arch in steel structure bridges. In order to study the overall stability of flat panel stiffened plates, the finite element models verified by experiments were established for overall stability analysis. The effects of different constitutive relations, initial geometric defects and welding residual stresses on the overall stability bearing capacity were considered. It was found that: the ideal elastic-plastic constitutive model could be used to safely analyze the overall stability of flat plate stiffened panel under compression. Increasing the initial bending amplitude and loading eccentricity of the model would weaken the plates’ overall stability capacity.When the defect amplitude was 1/1 000 of the calculated length, the bearing capacity of model initially bent on the side of the plate rib was relatively low, but the model initially bent on the side of the stiffened plate was more sensitive to the defect; increasing the peak value of welding residual compressive stress would reduce the overall axial stiffness and ultimate average stress of flat plate stiffened panels.Within the range of the relative slenderness ratio studied, the fitted calculation formula curve was lower than the test value and the curve of equal strength steel u-rib column, and was generally close to the class B column curve in the Specifications for Design of Highway Steel Bridge (JTG D64—2015), higher than the column curve corresponding to the Japanese and American codes, which could be safely used for the overall stability calculation of flat panel stiffened plates.
2024, 54(10): 147-152.
doi: 10.3724/j.gyjzG24051001
Abstract:
In order to study the interface bonding performance of concrete-filled aluminum tubular columns at room temperatures, three factors including concrete strength and component slenderness ratio were considered. A bond-slip push-out test was conducted on concrete-filled aluminum tubular stub columns, and the load-slip correlation, and longitudinal strain distribution of aluminum tubes under different loads were obtained. The feasibility of existing constitutive models for bond-slip of concrete-filled steel tube columns in evaluating the peak bonding strength and residual bonding strength of concrete-filled aluminum tubular concrete columns was analyzed. The research results indicated that the trend of the load-slip curve of each specimen was basically consistent; the longitudinal strain on the surface of the aluminum tube was proportional to its distance from the loading end, and the bonding stress was uniformly distributed within the interface length range; the decrease in concrete strength and interface bonding length would lead to a decrease in ultimate bonding strength and residual bonding strength, and the impact of concrete strength was greater. On this basis, a calculation formula for the interfacial bonding strength of concrete-filled aluminum tubular columns at room temperatures was proposed.
In order to study the interface bonding performance of concrete-filled aluminum tubular columns at room temperatures, three factors including concrete strength and component slenderness ratio were considered. A bond-slip push-out test was conducted on concrete-filled aluminum tubular stub columns, and the load-slip correlation, and longitudinal strain distribution of aluminum tubes under different loads were obtained. The feasibility of existing constitutive models for bond-slip of concrete-filled steel tube columns in evaluating the peak bonding strength and residual bonding strength of concrete-filled aluminum tubular concrete columns was analyzed. The research results indicated that the trend of the load-slip curve of each specimen was basically consistent; the longitudinal strain on the surface of the aluminum tube was proportional to its distance from the loading end, and the bonding stress was uniformly distributed within the interface length range; the decrease in concrete strength and interface bonding length would lead to a decrease in ultimate bonding strength and residual bonding strength, and the impact of concrete strength was greater. On this basis, a calculation formula for the interfacial bonding strength of concrete-filled aluminum tubular columns at room temperatures was proposed.
2024, 54(10): 153-159.
doi: 10.3724/j.gyjzG22011910
Abstract:
The neutral plane position of double modulus rectangular glass under external load was solved with the static equilibrium equation, in which the neutral plane tension of single-layer glass was considered; the relations between the volume change of insulating glass cavity and the gas pressure in the cavity under external load were studied; the deflection differential equation of inner and outer glass was derived with the static balance equation, geometric deformation equation and physical equation, and the deflection calculation formula of insulating glass reflecting the force transfer performance between inner and outer layers of insulating glass was established. The theoretical calculation results considering the force transfer between inner and outer layers of insulating glass were compared with those obtained by standard formula and the finite element. The results showed that the theoretical above was reliable.
The neutral plane position of double modulus rectangular glass under external load was solved with the static equilibrium equation, in which the neutral plane tension of single-layer glass was considered; the relations between the volume change of insulating glass cavity and the gas pressure in the cavity under external load were studied; the deflection differential equation of inner and outer glass was derived with the static balance equation, geometric deformation equation and physical equation, and the deflection calculation formula of insulating glass reflecting the force transfer performance between inner and outer layers of insulating glass was established. The theoretical calculation results considering the force transfer between inner and outer layers of insulating glass were compared with those obtained by standard formula and the finite element. The results showed that the theoretical above was reliable.
2024, 54(10): 160-167.
doi: 10.3724/j.gyjzG23091701
Abstract:
A type of stone curtain wall connection with attached L-shaped stone back hook is put forward. In order to investigate the mechanical properties of this type of connection, out-of-plane loading tests were carried out on 81 specimens, and the failure mode and bearing capacity of the connections with different hook thicknesses, hook-curtain wall panel bond widths, and thicknesses of curtain wall panel were analyzed. The experimental results showed that, three different types of failure modes, i.e., fracture of back hook at corner, facture of back hook near bonding area, and fracture of curtain wall panel, would occur for the connection. All the failure modes exhibited brittle characteristic, and the deformation of connection before failure was unobvious. When the thickness of curtain wall panel was kept constant, increasing the hook thickness and hook-curtain wall panel bond widths could improve the ultimate bearing capacity of the connection until the fracture of curtain wall panel occured, that is, the "strong joint" principle was achieved. Based on force analysis, calculation methods for the out-of-plane bearing capacities of connections under different failure modes were proposed, and configuration suggestions were also obtained.
A type of stone curtain wall connection with attached L-shaped stone back hook is put forward. In order to investigate the mechanical properties of this type of connection, out-of-plane loading tests were carried out on 81 specimens, and the failure mode and bearing capacity of the connections with different hook thicknesses, hook-curtain wall panel bond widths, and thicknesses of curtain wall panel were analyzed. The experimental results showed that, three different types of failure modes, i.e., fracture of back hook at corner, facture of back hook near bonding area, and fracture of curtain wall panel, would occur for the connection. All the failure modes exhibited brittle characteristic, and the deformation of connection before failure was unobvious. When the thickness of curtain wall panel was kept constant, increasing the hook thickness and hook-curtain wall panel bond widths could improve the ultimate bearing capacity of the connection until the fracture of curtain wall panel occured, that is, the "strong joint" principle was achieved. Based on force analysis, calculation methods for the out-of-plane bearing capacities of connections under different failure modes were proposed, and configuration suggestions were also obtained.
2024, 54(10): 168-174.
doi: 10.3724/j.gyjzG22101822
Abstract:
To study the mechanical characteristics of peat soil under the action of seasonal temperature differences at high altitudes, through the shear strength tests in freeze and freeze thawing in the laboratory, the strength variation law of soil during freeze-thaw was analyzed, and the fitting curve for cohesion of peat soil in freeze-thaw cycles was obtained. The results showed that reducing freeze temperatures and prolonging freeze times could increase shear strength of soil, and the freeze time had a more significant effect on the strength; in the process of freeze-thaw, the deterioration effect at the thaw stage on soil strength was greater than that at the freeze stage. The lower the water content was, the greater the deterioration effect was. With the increase in rounds of freeze-thaw cycles, the sensitivity of soil cohesion to the water content decreased, while the sensitivity of internal friction angle to the water content increased. The water content of 51% to 63% was the control threshold of freeze-thaw and lubrication for soil cohesive strength; the deterioration of freeze-thaw strength was not only affected by the phase change in pore water, but also affected by the organic matter content. The relation among the round of freeze-thaw cycles, the water content and the soil cohesion was fitted, which could better predict the deterioration of soil strength.
To study the mechanical characteristics of peat soil under the action of seasonal temperature differences at high altitudes, through the shear strength tests in freeze and freeze thawing in the laboratory, the strength variation law of soil during freeze-thaw was analyzed, and the fitting curve for cohesion of peat soil in freeze-thaw cycles was obtained. The results showed that reducing freeze temperatures and prolonging freeze times could increase shear strength of soil, and the freeze time had a more significant effect on the strength; in the process of freeze-thaw, the deterioration effect at the thaw stage on soil strength was greater than that at the freeze stage. The lower the water content was, the greater the deterioration effect was. With the increase in rounds of freeze-thaw cycles, the sensitivity of soil cohesion to the water content decreased, while the sensitivity of internal friction angle to the water content increased. The water content of 51% to 63% was the control threshold of freeze-thaw and lubrication for soil cohesive strength; the deterioration of freeze-thaw strength was not only affected by the phase change in pore water, but also affected by the organic matter content. The relation among the round of freeze-thaw cycles, the water content and the soil cohesion was fitted, which could better predict the deterioration of soil strength.
2024, 54(10): 175-182.
doi: 10.3724/j.gyjzG22120217
Abstract:
Debris flow were often triggered by rainfall and other extreme events. The occurrence characteristics and probability of debris flow after extreme rainfall were explored in the Chenyulan watershed in central Taiwan, China, which was affected by the Chi-Chi earthquake and extreme rainfall. The results showed that the critical rainfall intensity to induce debris flow after extreme rainfall events would decrease and then recover the original value. The reduction of critical rainfall intensity and the required recovery period were significantly correlated with the rainfall intensity of extreme rainfall events. The relation model between the occurrence probability of the debris flow P and the return period T showed that the occurrence probability of the debris flow increased significantly after extreme rainfall events, and the further verification on the P-T relation showed that the model could better predict the occurrence of debris flow disasters. The rainfall intensity triggering the debris flow before and after earthquakes was significantly different, and the combined effect of earthquakes and extreme rainfall was more apt to trigger the occurrence of debris flow disasters.
Debris flow were often triggered by rainfall and other extreme events. The occurrence characteristics and probability of debris flow after extreme rainfall were explored in the Chenyulan watershed in central Taiwan, China, which was affected by the Chi-Chi earthquake and extreme rainfall. The results showed that the critical rainfall intensity to induce debris flow after extreme rainfall events would decrease and then recover the original value. The reduction of critical rainfall intensity and the required recovery period were significantly correlated with the rainfall intensity of extreme rainfall events. The relation model between the occurrence probability of the debris flow P and the return period T showed that the occurrence probability of the debris flow increased significantly after extreme rainfall events, and the further verification on the P-T relation showed that the model could better predict the occurrence of debris flow disasters. The rainfall intensity triggering the debris flow before and after earthquakes was significantly different, and the combined effect of earthquakes and extreme rainfall was more apt to trigger the occurrence of debris flow disasters.
2024, 54(10): 183-190.
doi: 10.13204/j.gyjzG22100503
Abstract:
To study the reasonable pile spacing of anti-slide piles, based on the soil arching effect, it was proposed a hypothesis that in the reasonable pile spacing, the soil arches at pile ends and pile sides were simultaneously activated to resist the slide forces of landslides. According to the static equilibrium condition between piles and the Mohr-Coulomb strength criterion of soil,a formula for pile spacing was deduced and checked through engineering cases. In the condition of a certain safety margin, the rationality of the formula was verified. Subsequently, the impact of variable parameters of the formula on pile spacing was analyzed. Eventually, the rationality of the formula was further verified by three-dimensional numerical simulations. The results indicated that in the condition of reasonable pile spacing, the spacing linearly increased with the cohesion of soil, front and side widths and increased with internal friction angles of soil as a quadratic function, and simultaneously, it dropped sharply as a quadratic function with the increase in uniform thrust of landslides. The three-dimensional numerical simulations demonstrated the earth arch effect decreased constantly with the increase in pile spacing, and the anti-slide effect of anti-slide piles also decreased. With the increase in pile spacing, the displacement of soil beside piles was larger and larger, and the closer to the middle section of earth arches, the greater the displacement was. However, the displacement of soil at pile ends was less influenced by pile spacing and changed slightly away from anti-slide piles compared to that closer to anti-slide piles.
To study the reasonable pile spacing of anti-slide piles, based on the soil arching effect, it was proposed a hypothesis that in the reasonable pile spacing, the soil arches at pile ends and pile sides were simultaneously activated to resist the slide forces of landslides. According to the static equilibrium condition between piles and the Mohr-Coulomb strength criterion of soil,a formula for pile spacing was deduced and checked through engineering cases. In the condition of a certain safety margin, the rationality of the formula was verified. Subsequently, the impact of variable parameters of the formula on pile spacing was analyzed. Eventually, the rationality of the formula was further verified by three-dimensional numerical simulations. The results indicated that in the condition of reasonable pile spacing, the spacing linearly increased with the cohesion of soil, front and side widths and increased with internal friction angles of soil as a quadratic function, and simultaneously, it dropped sharply as a quadratic function with the increase in uniform thrust of landslides. The three-dimensional numerical simulations demonstrated the earth arch effect decreased constantly with the increase in pile spacing, and the anti-slide effect of anti-slide piles also decreased. With the increase in pile spacing, the displacement of soil beside piles was larger and larger, and the closer to the middle section of earth arches, the greater the displacement was. However, the displacement of soil at pile ends was less influenced by pile spacing and changed slightly away from anti-slide piles compared to that closer to anti-slide piles.
2024, 54(10): 191-198.
doi: 10.3724/j.gyjzG22100604
Abstract:
During foundation excavation of metro stations, the dry working surface was needed, and dewatering in site is essential. After construction of dewatering wells, the pre-dewatering must be performed to check whether it can meet the excavation condition and the water interception effect for curtain of cutting-off water. However, some construction enterprises do not attach importance to the issues, and often ignore or abandon the preparation for the dewatering test due to considering of time and economic costs, laying a certain potential safety hazard for project construction. Based on data analysis on the dewatering test at the deep excavation site of a metro station in Tianjin, it was found that because the construction quality of dewatering wells did not strictly meet the design requirements, the aquifers were interconnected, and led to the foundation dewatering not to meet the design requirements. Subsequently, a grouting reinforcement measure, which alternately injected water glass and calcium chloride solutions into water-resisting layer, was adopted to block water leakage and ensure its water resisting effect and meet the design requirements of dewatering, and simultaneously prevent the impacts of the significant change in groundwater levels caused by dewatering for deep excavation on the surrounding environment.
During foundation excavation of metro stations, the dry working surface was needed, and dewatering in site is essential. After construction of dewatering wells, the pre-dewatering must be performed to check whether it can meet the excavation condition and the water interception effect for curtain of cutting-off water. However, some construction enterprises do not attach importance to the issues, and often ignore or abandon the preparation for the dewatering test due to considering of time and economic costs, laying a certain potential safety hazard for project construction. Based on data analysis on the dewatering test at the deep excavation site of a metro station in Tianjin, it was found that because the construction quality of dewatering wells did not strictly meet the design requirements, the aquifers were interconnected, and led to the foundation dewatering not to meet the design requirements. Subsequently, a grouting reinforcement measure, which alternately injected water glass and calcium chloride solutions into water-resisting layer, was adopted to block water leakage and ensure its water resisting effect and meet the design requirements of dewatering, and simultaneously prevent the impacts of the significant change in groundwater levels caused by dewatering for deep excavation on the surrounding environment.
2024, 54(10): 199-204.
doi: 10.3724/j.gyjzG23102513
Abstract:
The dynamic compaction method for reinforcing foundation has the advantages of significant effectiveness, saving in materials and short construction period, which is suitable for reinforcing coral reef sand foundation. To conduct the mechanism of strengthening coral reef sand foundation by dynamic compaction method, a numerical model was established based on discrete element method which could simulate both the shape of coral reef sand and the characteristics of soil porosity changes during the dynamic compaction process. The numerical model reliability was verified by field test results, and finally the coral reef sand particle crushing process, force chain development and foundation settlement under different tamping energy were analyzed, so as to clarify the internal mechanism of foundation reinforcement.The research results showed that the foundation settlement of adopted discrete numerical model showed a good alignment with that of field results, proving that the model had low error and high reliability; under the action of dynamic compaction method, the pores of coral reef particles decreased, the particle fragmentation zone gradually developed to both ends of the ramming pit, and the force chain was concentrated and radially distributed towards the center of the ramming pit; the greater the tamping energy, the greater the surface and foundation settlement within a certain depth range, and the particle fragmentation zone and force chain developed in both depth and breadth.
The dynamic compaction method for reinforcing foundation has the advantages of significant effectiveness, saving in materials and short construction period, which is suitable for reinforcing coral reef sand foundation. To conduct the mechanism of strengthening coral reef sand foundation by dynamic compaction method, a numerical model was established based on discrete element method which could simulate both the shape of coral reef sand and the characteristics of soil porosity changes during the dynamic compaction process. The numerical model reliability was verified by field test results, and finally the coral reef sand particle crushing process, force chain development and foundation settlement under different tamping energy were analyzed, so as to clarify the internal mechanism of foundation reinforcement.The research results showed that the foundation settlement of adopted discrete numerical model showed a good alignment with that of field results, proving that the model had low error and high reliability; under the action of dynamic compaction method, the pores of coral reef particles decreased, the particle fragmentation zone gradually developed to both ends of the ramming pit, and the force chain was concentrated and radially distributed towards the center of the ramming pit; the greater the tamping energy, the greater the surface and foundation settlement within a certain depth range, and the particle fragmentation zone and force chain developed in both depth and breadth.
2024, 54(10): 205-214.
doi: 10.3724/j.gyjzG24022706
Abstract:
To study the effects of load and erosion dimension on the characteristics of chloride ion erosion in concrete and its analysis method, dry-wet cycle experiments of chloride salt solution were carried out on components under continuous loads for a long time,including axially compressed, eccentrically compressed, and stress-free components, in both one-dimensional and two-dimensional manners. The distribution of free chloride ion content under different load properties and erosion dimensions was analyzed. The results showed that under a stress-free condition,the two-dimensional chloride ion erosion concentration at the same erosion depth was higher than that of one-dimensional erosion; axial compressive load had an inhibitory effect on the transmission of chloride ions, within the 0-40 mm depth range of the concrete surface, the two-dimensional chloride ion erosion concentration was greater than that at the same depth of one-dimensional erosion, but less than the one-dimensional erosion concentration under a stress-free condition; eccentric tensile stress accelerated the transmission of chloride ions, during both one-dimensional and two-dimensional erosion,the degree of chloride ion erosion in the eccentric tension zone was more severe than in the eccentric compression zone;in terms of erosion degree,the area above the horizontal plane of the erosion face > inclined plane > bottom face downwards. The influence of load effects on the diffusive properties of chloride ions was characterized by the "equivalent apparent chloride ion diffusion coefficient", and its applicability had been verified through experiments. Based on the experimental research and theoretical analysis, a dimension influence function was introduced to modify the Fick diffusion model. The modified model’s calculated results were in good agreement with the measured two-dimensional chloride ion erosion results, indicating that it was feasible to describe the characteristics of two-dimensional chloride ion erosion using the modified model.
To study the effects of load and erosion dimension on the characteristics of chloride ion erosion in concrete and its analysis method, dry-wet cycle experiments of chloride salt solution were carried out on components under continuous loads for a long time,including axially compressed, eccentrically compressed, and stress-free components, in both one-dimensional and two-dimensional manners. The distribution of free chloride ion content under different load properties and erosion dimensions was analyzed. The results showed that under a stress-free condition,the two-dimensional chloride ion erosion concentration at the same erosion depth was higher than that of one-dimensional erosion; axial compressive load had an inhibitory effect on the transmission of chloride ions, within the 0-40 mm depth range of the concrete surface, the two-dimensional chloride ion erosion concentration was greater than that at the same depth of one-dimensional erosion, but less than the one-dimensional erosion concentration under a stress-free condition; eccentric tensile stress accelerated the transmission of chloride ions, during both one-dimensional and two-dimensional erosion,the degree of chloride ion erosion in the eccentric tension zone was more severe than in the eccentric compression zone;in terms of erosion degree,the area above the horizontal plane of the erosion face > inclined plane > bottom face downwards. The influence of load effects on the diffusive properties of chloride ions was characterized by the "equivalent apparent chloride ion diffusion coefficient", and its applicability had been verified through experiments. Based on the experimental research and theoretical analysis, a dimension influence function was introduced to modify the Fick diffusion model. The modified model’s calculated results were in good agreement with the measured two-dimensional chloride ion erosion results, indicating that it was feasible to describe the characteristics of two-dimensional chloride ion erosion using the modified model.
2024, 54(10): 215-222.
doi: 10.3724/j.gyjzG24040907
Abstract:
In order to study the influence of wood viscoelasticity characteristics on the propagation behavior of acoustic emission (AE) signals, a finite element simulation model of wood specimens was established by setting the viscosity coefficients of wood in COMSOL software. The effectiveness of the simulation model was verified by combining the results of wood AE experiments. Firstly, a Hanning window modulated sine pulse signal was generated by a signal generator at a distance of 100 mm from the left end face on the surface of the fir specimen. Two AE sensors were placed at a distance of 200 mm from the left end face at a distance of 300 mm on the surface of the specimen to collect the AE signals. Then, a filter was used to denoise the AE signals collected by the sensors. Secondly, finite element simulations were conducted on the fir specimen to obtain the displacement cloud map of elastic wave propagation in the specimen and the propagation law in viscoelastic materials. Finally, the time difference of arrival (TDOA) method was used to compare the transverse and longitudinal wave velocities and time-domain waveforms obtained from the simulations and experimental measurements. The results showed that the simulated transverse and longitudinal wave velocities were 1 118 m/s and 5 245 m/s, and the experimental transverse and longitudinal wave velocities were 1 290 m/s and 5 209 m/s, respectively. The amplitude attenuation and the time-domain waveforms were in good agreement when comparing the simulated and measured waveforms with the experimental waveforms. Therefore, the effects of viscoelasticity on Chinese fir specimens and the validity of the simulation model were confirmed.
In order to study the influence of wood viscoelasticity characteristics on the propagation behavior of acoustic emission (AE) signals, a finite element simulation model of wood specimens was established by setting the viscosity coefficients of wood in COMSOL software. The effectiveness of the simulation model was verified by combining the results of wood AE experiments. Firstly, a Hanning window modulated sine pulse signal was generated by a signal generator at a distance of 100 mm from the left end face on the surface of the fir specimen. Two AE sensors were placed at a distance of 200 mm from the left end face at a distance of 300 mm on the surface of the specimen to collect the AE signals. Then, a filter was used to denoise the AE signals collected by the sensors. Secondly, finite element simulations were conducted on the fir specimen to obtain the displacement cloud map of elastic wave propagation in the specimen and the propagation law in viscoelastic materials. Finally, the time difference of arrival (TDOA) method was used to compare the transverse and longitudinal wave velocities and time-domain waveforms obtained from the simulations and experimental measurements. The results showed that the simulated transverse and longitudinal wave velocities were 1 118 m/s and 5 245 m/s, and the experimental transverse and longitudinal wave velocities were 1 290 m/s and 5 209 m/s, respectively. The amplitude attenuation and the time-domain waveforms were in good agreement when comparing the simulated and measured waveforms with the experimental waveforms. Therefore, the effects of viscoelasticity on Chinese fir specimens and the validity of the simulation model were confirmed.
2024, 54(10): 223-229.
doi: 10.3724/j.gyjzG23051108
Abstract:
In order to investigate the feasibility of a non-destructive testing method based on modal testing to assess the structural stiffness of ancient architectural bridges under environmental excitation, a 29 m span stone arch bridge was used as the research object, a virtual load test was designed based on the finite element model to determine the minimum modal order that meet the engineering accuracy requirements under symmetrical and eccentric load conditions; the vertical vibration information of the main girders of the stone arch bridge was collected under environmental excitation and the modal parameters were identified, and then the modal displacement flexibility matrix of the structure was identified; the modal deflection of the stone arch bridge under equivalent test load was predicted, compared with the design deflection of the finite element model, the deflection check factor was calculated, and the bridge stiffness condition was evaluated in conjunction with the current code. The results showed that the modal parameters of the stone arch bridge could be accurately identified based on the environmental excitation; the modal deflection predicted by the first two mode parameters could meet the engineering accuracy requirements under the symmetrical load condition and the first three mode parameters under the eccentric condition; the calculated mid-span deflection check coefficient was less than 1 under both conditions, which indicated that the actual condition of the bridge was better; modal testing, as a non-destructive testing method to replace load testing in evaluating the stiffness of ancient stone arch bridge structures, showed good engineering feasibility.
In order to investigate the feasibility of a non-destructive testing method based on modal testing to assess the structural stiffness of ancient architectural bridges under environmental excitation, a 29 m span stone arch bridge was used as the research object, a virtual load test was designed based on the finite element model to determine the minimum modal order that meet the engineering accuracy requirements under symmetrical and eccentric load conditions; the vertical vibration information of the main girders of the stone arch bridge was collected under environmental excitation and the modal parameters were identified, and then the modal displacement flexibility matrix of the structure was identified; the modal deflection of the stone arch bridge under equivalent test load was predicted, compared with the design deflection of the finite element model, the deflection check factor was calculated, and the bridge stiffness condition was evaluated in conjunction with the current code. The results showed that the modal parameters of the stone arch bridge could be accurately identified based on the environmental excitation; the modal deflection predicted by the first two mode parameters could meet the engineering accuracy requirements under the symmetrical load condition and the first three mode parameters under the eccentric condition; the calculated mid-span deflection check coefficient was less than 1 under both conditions, which indicated that the actual condition of the bridge was better; modal testing, as a non-destructive testing method to replace load testing in evaluating the stiffness of ancient stone arch bridge structures, showed good engineering feasibility.
2024, 54(10): 230-239.
doi: 10.3724/j.gyjzG23051515
Abstract:
Earthquake disasters have a great impact on cultural heritage. In order to predict the impact of earthquake disasters on grotto temples, an earthquake disaster risk assessment model for grotto temples was established from four aspects: disaster-causing factors, disaster-pregnant environment, disaster-bearing bodies, and disaster prevention and mitigation capabilities. The evaluation index system,which consists of 23 factors such as peak ground motion acceleration and site category,was determined, and the Yungang Grottoes was taken as an example. The results showed that 44 % of the caves in the Yungang Grottoes had higher earthquake risk, mainly concentrated in the western area, showing a trend of high in the west and low in the east as a whole, which was in good agreement with the actual results. It showed that the model could quantitatively evaluate the earthquake disaster risk of grotto temples, and provide scientific basis for the preventive conservation and earthquake prevention and disaster reduction managements of grotto temples.
Earthquake disasters have a great impact on cultural heritage. In order to predict the impact of earthquake disasters on grotto temples, an earthquake disaster risk assessment model for grotto temples was established from four aspects: disaster-causing factors, disaster-pregnant environment, disaster-bearing bodies, and disaster prevention and mitigation capabilities. The evaluation index system,which consists of 23 factors such as peak ground motion acceleration and site category,was determined, and the Yungang Grottoes was taken as an example. The results showed that 44 % of the caves in the Yungang Grottoes had higher earthquake risk, mainly concentrated in the western area, showing a trend of high in the west and low in the east as a whole, which was in good agreement with the actual results. It showed that the model could quantitatively evaluate the earthquake disaster risk of grotto temples, and provide scientific basis for the preventive conservation and earthquake prevention and disaster reduction managements of grotto temples.
2024, 54(10): 240-246.
doi: 10.3724/j.gyjzG24050707
Abstract:
With the advancement of construction technology, the structural forms of high-rise buildings are becoming increasingly diverse. Among them, the applications of elevated corridors and cantilevered structures are also becoming more widespread. The installation construction of elevated corridors often adopts an integral lifting construction scheme, which can significantly reduce the difficulty of installation construction. Integral lifting requires high structural stiffness and advanced construction techniques. Accurate calculation of the deformation pre-adjustment value during pre-assembly and precise control of the lifting force during the entire elevation process are crucial for smooth construction. Based on the engineering research of the Shenzhen Free Trade Center project, the installation and construction techniques of elevated corridors with integral lifting were investigated. The finite element numerical analysis method was utilized to simulate the corridor deformation throughout the construction process, achieving precise control over both "deformation" and "force variation." Additionally, the study examined various lifting schemes for integral lifting, analyzing the lifting forces associated with different approaches, providing valuable references for determining the optimal integral lifting scheme. The findings of the research had significant implications for subsequent simulations and calculations of integral lifting for similar elevated corridor structures. Finally, the paper discussed the key problems in the construction process, such as the integrated simulation method of the lifting, lateral stiffness, forming internal force, etc., which could provide a reference for the design and construction.
With the advancement of construction technology, the structural forms of high-rise buildings are becoming increasingly diverse. Among them, the applications of elevated corridors and cantilevered structures are also becoming more widespread. The installation construction of elevated corridors often adopts an integral lifting construction scheme, which can significantly reduce the difficulty of installation construction. Integral lifting requires high structural stiffness and advanced construction techniques. Accurate calculation of the deformation pre-adjustment value during pre-assembly and precise control of the lifting force during the entire elevation process are crucial for smooth construction. Based on the engineering research of the Shenzhen Free Trade Center project, the installation and construction techniques of elevated corridors with integral lifting were investigated. The finite element numerical analysis method was utilized to simulate the corridor deformation throughout the construction process, achieving precise control over both "deformation" and "force variation." Additionally, the study examined various lifting schemes for integral lifting, analyzing the lifting forces associated with different approaches, providing valuable references for determining the optimal integral lifting scheme. The findings of the research had significant implications for subsequent simulations and calculations of integral lifting for similar elevated corridor structures. Finally, the paper discussed the key problems in the construction process, such as the integrated simulation method of the lifting, lateral stiffness, forming internal force, etc., which could provide a reference for the design and construction.
