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2023 Vol. 53, No. 10
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2023, 53(10): 1-9.
doi: 10.13204/j.gyjzG22080820
Abstract:
With the development of national fitness activities and the improvement of people's living standards, the development of sports buildings is in full swing today. However, the traditional sports venues have exposed problems such as inconvenient transportation, single function, decentralized facilities, low utilization ratios, and the requirements of urban land intensification have re-examined the configuration of sports buildings. It is a new design concept to use the building height to put the mass sports function into more compact vertical space. Based on the appropriate space scale and functional characteristics of the national fitness facilities, as well as the structural technology and material application of today's long-span buildings, the design strategy was studied from the perspective of "overlapping space", taking the comprehensive sports halls with 4 to 5 stories as a typical representative. While promoting such buildings to provide public space and vitality for cities, it also achieved the sustainable development objects of today's large-scale public buildings.
With the development of national fitness activities and the improvement of people's living standards, the development of sports buildings is in full swing today. However, the traditional sports venues have exposed problems such as inconvenient transportation, single function, decentralized facilities, low utilization ratios, and the requirements of urban land intensification have re-examined the configuration of sports buildings. It is a new design concept to use the building height to put the mass sports function into more compact vertical space. Based on the appropriate space scale and functional characteristics of the national fitness facilities, as well as the structural technology and material application of today's long-span buildings, the design strategy was studied from the perspective of "overlapping space", taking the comprehensive sports halls with 4 to 5 stories as a typical representative. While promoting such buildings to provide public space and vitality for cities, it also achieved the sustainable development objects of today's large-scale public buildings.
2023, 53(10): 10-16.
doi: 10.13204/j.gyjzG22020907
Abstract:
The canal waterfront area is one of the important urban public spaces, and the quality of its waterfront landscape is an important criterion to measure the quality of the urban waterfront landscape. However, the current lack of quantitative data support and the lack of prioritization of the influencing factors of waterfront landscape quality make it impossible to propose targeted strategies to promote the improvement of waterfront landscape quality. Taking Shangtang River in Suzhou as an example, through questionnaire survey and IPA-KANO model and other analytical methods, the waterfront landscape quality evaluation of Shangtang River in Suzhou was studied. Relying on the index system and constructing an "explicit-recessive matrix", the paper formed three types of elements that affected the quality of the waterfront landscape of the ancient canal. Combined with the actual performance of the three types of elements, optimization strategies were proposed to create characteristic cultural landscape nodes, construct ecological cultural spaces, and excavate ancient canal water cultural resources.
The canal waterfront area is one of the important urban public spaces, and the quality of its waterfront landscape is an important criterion to measure the quality of the urban waterfront landscape. However, the current lack of quantitative data support and the lack of prioritization of the influencing factors of waterfront landscape quality make it impossible to propose targeted strategies to promote the improvement of waterfront landscape quality. Taking Shangtang River in Suzhou as an example, through questionnaire survey and IPA-KANO model and other analytical methods, the waterfront landscape quality evaluation of Shangtang River in Suzhou was studied. Relying on the index system and constructing an "explicit-recessive matrix", the paper formed three types of elements that affected the quality of the waterfront landscape of the ancient canal. Combined with the actual performance of the three types of elements, optimization strategies were proposed to create characteristic cultural landscape nodes, construct ecological cultural spaces, and excavate ancient canal water cultural resources.
2023, 53(10): 17-22.
doi: 10.13204/j.gyjzG22062304
Abstract:
China's urban development has entered a new stage of stock upgrading, and the industrial remain sites vacated after urban areas have become an important part of urban regeneration. Based on the theory of landscape urbanism, the principles of landscape as the overall spatial form, site memory intervention in the diachronic process, open boundary activation of spatial vitality, and the integrity of ecological sustainable development were proposed for Industrial remain sites. The old brewery plot in Pingyuan County adopted the updated design strategy from integrating into the urban public spaces, continuing the historical memory of the site, enriching the interface space of the site, and building the site ecosystem, so as to tap the potential of landscape urbanism in urban regeneration, with a view to providing a reference for the renewal of industrial remain sites.
China's urban development has entered a new stage of stock upgrading, and the industrial remain sites vacated after urban areas have become an important part of urban regeneration. Based on the theory of landscape urbanism, the principles of landscape as the overall spatial form, site memory intervention in the diachronic process, open boundary activation of spatial vitality, and the integrity of ecological sustainable development were proposed for Industrial remain sites. The old brewery plot in Pingyuan County adopted the updated design strategy from integrating into the urban public spaces, continuing the historical memory of the site, enriching the interface space of the site, and building the site ecosystem, so as to tap the potential of landscape urbanism in urban regeneration, with a view to providing a reference for the renewal of industrial remain sites.
2023, 53(10): 23-28.
doi: 10.13204/j.gyjzG22042606
Abstract:
Inner Mongolia has a vast territory, bordering Gansu in the west and Russia in the east, with a straight-line distance of more than 2 400 kilometers from east to west. As a province on the border of northern China and one of the major industrial provinces, regional differences and historical backgrounds have resulted in obvious differences in the architectural styles of industrial heritage in the eastern and western regions. The paper adopted research methods such as field investigation and literature review, selected some representative industrial architectural heritages in eastern and central and western Inner Mongolia, and conducted a comparative analysis of the architectural structure and craftsmanship, and decorative arts of the industrial heritage in Inner Mongolia, and presented the industrial heritage of Inner Mongolia. The richness and diversity of industrial heritage provide a realistic basis for the overall protection strategy of regional industrial heritage.
Inner Mongolia has a vast territory, bordering Gansu in the west and Russia in the east, with a straight-line distance of more than 2 400 kilometers from east to west. As a province on the border of northern China and one of the major industrial provinces, regional differences and historical backgrounds have resulted in obvious differences in the architectural styles of industrial heritage in the eastern and western regions. The paper adopted research methods such as field investigation and literature review, selected some representative industrial architectural heritages in eastern and central and western Inner Mongolia, and conducted a comparative analysis of the architectural structure and craftsmanship, and decorative arts of the industrial heritage in Inner Mongolia, and presented the industrial heritage of Inner Mongolia. The richness and diversity of industrial heritage provide a realistic basis for the overall protection strategy of regional industrial heritage.
2023, 53(10): 29-35.
doi: 10.13204/j.gyjzG22060901
Abstract:
A large number of old industrial buildings, facilities and productive environments in rural areas are important resources in the process of current rural revitalization. The concept of rural industrial heritage was identified according to international views and national contexts. In addition, the types and characteristics of rural industrial heritage were summarized through the field investigation in Southern Jiangsu. Based on the existing value system of industrial heritage and the feature of rural areas, the dimensions of value cognition were supplemented. Clear concept and cognition of rural industrial heritage provide the theoretical foundation for relevant research and practices, also are necessities for the sustainable rural-urban environment and keeping nostalgia.
A large number of old industrial buildings, facilities and productive environments in rural areas are important resources in the process of current rural revitalization. The concept of rural industrial heritage was identified according to international views and national contexts. In addition, the types and characteristics of rural industrial heritage were summarized through the field investigation in Southern Jiangsu. Based on the existing value system of industrial heritage and the feature of rural areas, the dimensions of value cognition were supplemented. Clear concept and cognition of rural industrial heritage provide the theoretical foundation for relevant research and practices, also are necessities for the sustainable rural-urban environment and keeping nostalgia.
2023, 53(10): 36-43,35.
doi: 10.13204/j.gyjzG21111518
Abstract:
Building morphology, as a design factor to be focused on in the design phase of building scheme, has a direct impact on several performance indicators of the building. The meteorological parameters of different sub-climatic zones in severe cold regions were used as the research background, and the building form was decomposed into 8 quantitative factors, and the building energy consumption and the annual discomfort time of the building based on Thermal Environmental Conditions for Human Occupancy(ANSI/ASHRAE 55-2004) evaluation standard were used as the optimization indexes. Based on the EnergyPlus simulation platform, the original data of the evaluation indexes was obtained, the radial basis function neural network was introduced to establish the rapid response model between the influencing factors and the optimization indexes, combined with the orthogonal test method, the single-objective optimization calculation of the building energy consumption and the annual discomfort time in each study area were carried out, and the influence weight and optimization potential of the three morphological factors representing urban buildings in severe cold regions on different optimization indexes were analyzed. The optimal combination of energy saving and comfort based on morphological factors in each study area was further investigated. The results showed that the quantitative design parameters of building morphology had considerable optimization potential for reducing building energy consumption and building discomfort time throughout the year.
Building morphology, as a design factor to be focused on in the design phase of building scheme, has a direct impact on several performance indicators of the building. The meteorological parameters of different sub-climatic zones in severe cold regions were used as the research background, and the building form was decomposed into 8 quantitative factors, and the building energy consumption and the annual discomfort time of the building based on Thermal Environmental Conditions for Human Occupancy(ANSI/ASHRAE 55-2004) evaluation standard were used as the optimization indexes. Based on the EnergyPlus simulation platform, the original data of the evaluation indexes was obtained, the radial basis function neural network was introduced to establish the rapid response model between the influencing factors and the optimization indexes, combined with the orthogonal test method, the single-objective optimization calculation of the building energy consumption and the annual discomfort time in each study area were carried out, and the influence weight and optimization potential of the three morphological factors representing urban buildings in severe cold regions on different optimization indexes were analyzed. The optimal combination of energy saving and comfort based on morphological factors in each study area was further investigated. The results showed that the quantitative design parameters of building morphology had considerable optimization potential for reducing building energy consumption and building discomfort time throughout the year.
2023, 53(10): 44-50.
doi: 10.13204/j.gyjzG22042520
Abstract:
The evaluation of prestress transfer length of corroded pretensioned prestressed concrete (PC) members plays a significant role in assessing the performance of these structures. Firstly, the concrete cracking at member end and mechanical characteristics at the transfer interface caused by prestress releasing were analyzed based on the thick-walled cylinder model. Then, considering the rust expansion characteristics of seven-wire cross-section of steel strands, the further cracking characteristics of concrete along the transfer length under corrosion were analyzed by combining initial releasing cracking and corrosion-induced cracking, the relations between corrosion depth, corrosion loss and interfacial rust expansion displacement were established along the transfer length, considering the tensile softening of cracked concrete, the radial confining stress model of strands under the combined confinement of cracked concrete and stirrups was derived along the transfer length, then the bond stress distribution was obtained. Finally, based on the equilibrium relations between bond stress and prestress, the strain distribution of steel strands and concrete was obtained, and the prestress transfer length under corrosion-induced concrete cracking was determined. The comparison between analytical and experimental results showed that this method could reasonably predict the development laws of transfer length of corroded pretensioned PC members with various corrosion locations and degrees.
The evaluation of prestress transfer length of corroded pretensioned prestressed concrete (PC) members plays a significant role in assessing the performance of these structures. Firstly, the concrete cracking at member end and mechanical characteristics at the transfer interface caused by prestress releasing were analyzed based on the thick-walled cylinder model. Then, considering the rust expansion characteristics of seven-wire cross-section of steel strands, the further cracking characteristics of concrete along the transfer length under corrosion were analyzed by combining initial releasing cracking and corrosion-induced cracking, the relations between corrosion depth, corrosion loss and interfacial rust expansion displacement were established along the transfer length, considering the tensile softening of cracked concrete, the radial confining stress model of strands under the combined confinement of cracked concrete and stirrups was derived along the transfer length, then the bond stress distribution was obtained. Finally, based on the equilibrium relations between bond stress and prestress, the strain distribution of steel strands and concrete was obtained, and the prestress transfer length under corrosion-induced concrete cracking was determined. The comparison between analytical and experimental results showed that this method could reasonably predict the development laws of transfer length of corroded pretensioned PC members with various corrosion locations and degrees.
2023, 53(10): 51-60.
doi: 10.13204/j.gyjzG22092406
Abstract:
To study the effect of flange notch on the mechanical properties of inverted T-shaped concrete beam, two inverted T-shaped beam were designed for static tests, and the bearing capacity, failure mode, crack development and stress and strain of reinforcement were analyzed by comparing the two specimens.The finite element software ANSYS was used to model and verify the rationality. Based on this, the influence of material strength, longitudinal reinforcement ratio and stirrup spacing on the mechanical properties of notch beam was quantitatively analyzed. The results showed that the intact flanks of the inverted T-shaped notched beam gradually participated in the compression during the loading pro-cess, and the failure state was a typical bending-torsional failure. Compared with the intact inverted T-shaped beam,the inverted T-shaped notched beam had a significantly decrease in flexural capacity, but showed a better displacement ductility. Decreasing the stirrup spacing and increasing the longitudinal reinforcement ratio could significantly increase the characteristic load and bearing capacity of the inverted T-shaped notched beam in normal service limit state, improve the flexural stiffness of the notch beam, reduce the structural deformation, and make the notched beam effectively resist torsion.
To study the effect of flange notch on the mechanical properties of inverted T-shaped concrete beam, two inverted T-shaped beam were designed for static tests, and the bearing capacity, failure mode, crack development and stress and strain of reinforcement were analyzed by comparing the two specimens.The finite element software ANSYS was used to model and verify the rationality. Based on this, the influence of material strength, longitudinal reinforcement ratio and stirrup spacing on the mechanical properties of notch beam was quantitatively analyzed. The results showed that the intact flanks of the inverted T-shaped notched beam gradually participated in the compression during the loading pro-cess, and the failure state was a typical bending-torsional failure. Compared with the intact inverted T-shaped beam,the inverted T-shaped notched beam had a significantly decrease in flexural capacity, but showed a better displacement ductility. Decreasing the stirrup spacing and increasing the longitudinal reinforcement ratio could significantly increase the characteristic load and bearing capacity of the inverted T-shaped notched beam in normal service limit state, improve the flexural stiffness of the notch beam, reduce the structural deformation, and make the notched beam effectively resist torsion.
2023, 53(10): 61-67,93.
doi: 10.13204/j.gyjzG22092808
Abstract:
Currently, the construction of floor slabs of 3D printed concrete buildings mainly adopts the method of on-site assembly of prefabricated printed slabs, but with the in-depth research and development of large concrete 3D printers, the practice of in-situ printing of floor slabs is also accelerating in the exploration. The in-situ printing of floor slabs requires a base mold to achieve, so by simulating the in-situ printing of temporary base mold and the construction method of using printed concrete laminated slab and profiled steel sheet as permanent base mold respectively, the in-situ printed concrete slab specimens were designed to study the damage pattern, crack distribution, deflection development and characteristic load. The tests showed that both the specimens with printed concrete slabs as permanent base mold and the specimens with temporary base mold exhibited similar overall damage patterns as those of ordinary concrete slabs, and good bonds could be formed between the superimposed printed concrete layers and between the prefabricated superimposed printed concrete layers; while the slab specimens with profiled steel sheet applied as permanent base mold showed slippage between the profiled steel sheet and the printed concrete.
Currently, the construction of floor slabs of 3D printed concrete buildings mainly adopts the method of on-site assembly of prefabricated printed slabs, but with the in-depth research and development of large concrete 3D printers, the practice of in-situ printing of floor slabs is also accelerating in the exploration. The in-situ printing of floor slabs requires a base mold to achieve, so by simulating the in-situ printing of temporary base mold and the construction method of using printed concrete laminated slab and profiled steel sheet as permanent base mold respectively, the in-situ printed concrete slab specimens were designed to study the damage pattern, crack distribution, deflection development and characteristic load. The tests showed that both the specimens with printed concrete slabs as permanent base mold and the specimens with temporary base mold exhibited similar overall damage patterns as those of ordinary concrete slabs, and good bonds could be formed between the superimposed printed concrete layers and between the prefabricated superimposed printed concrete layers; while the slab specimens with profiled steel sheet applied as permanent base mold showed slippage between the profiled steel sheet and the printed concrete.
2023, 53(10): 68-74.
doi: 10.13204/j.gyjzG20102914
Abstract:
The hospital building reinforcement project in Jinnan District of Tianjin was taken as the engineering background in this study. Based on the performance-based seismic reduction control objectives, three reinforcement schemes of energy dissipation and seismic reduction were adopted, namely scheme 1 (buckling restrained brace), scheme 2 (viscous damper) and scheme 3 (buckling restrained brace + viscous damper). The damping effects of the three reinforcement schemes of energy dissipating and seismic reduction in high-rise structures were compared in according to the time-history analysis results of SAUSAGE software. The study showed that:under the action of frequently occurred earthquakes, using scheme 2 to strengthen the structure had the best damping effect; under the action of rarely occurred earthquakes, schemes 1 and 3 were better than scheme 2; using scheme 2 to reinforce the structure could achieve the damping target of performance 3, but could not meet the requirements of the building's uninterrupted operation under rarely occurred earthquake. The use of scheme 1 and scheme 3 to strengthen the structure could achieve the seismic reduction target of performance 2. As far as the control of the vertex displacement of the weak axis of the structure, the reinforcement effect of scheme 3 was better than scheme 1.
The hospital building reinforcement project in Jinnan District of Tianjin was taken as the engineering background in this study. Based on the performance-based seismic reduction control objectives, three reinforcement schemes of energy dissipation and seismic reduction were adopted, namely scheme 1 (buckling restrained brace), scheme 2 (viscous damper) and scheme 3 (buckling restrained brace + viscous damper). The damping effects of the three reinforcement schemes of energy dissipating and seismic reduction in high-rise structures were compared in according to the time-history analysis results of SAUSAGE software. The study showed that:under the action of frequently occurred earthquakes, using scheme 2 to strengthen the structure had the best damping effect; under the action of rarely occurred earthquakes, schemes 1 and 3 were better than scheme 2; using scheme 2 to reinforce the structure could achieve the damping target of performance 3, but could not meet the requirements of the building's uninterrupted operation under rarely occurred earthquake. The use of scheme 1 and scheme 3 to strengthen the structure could achieve the seismic reduction target of performance 2. As far as the control of the vertex displacement of the weak axis of the structure, the reinforcement effect of scheme 3 was better than scheme 1.
2023, 53(10): 75-82.
doi: 10.13204/j.gyjzG21072302
Abstract:
Based on the study of cold-formed steel yurts in grassland areas, a one-bay planar rigid frame was used as the research object. Stability tests and finite element simulations were carried out on a 5-bay rigid frame to analyze its damage modalities, bearing capacity, column top lateral displacement and yielding mechanism, etc., and to investigate the effects of inclined beam slope and depth-span ratio on the stability of the rigid frame. The results showed that the damage of rigid frame was mainly caused by the local buckling of C-beam at the top and bottom of the beam, which led to the overall in-plane instability; increasing the slope of inclined beam and decreasing the depth-span ratio could advance the bearing capacity and the overall stability of rigid frame; the lateral shift of the top of rigid frame column increased with the raise of slope of slanted beam, but the depth-span ratio had less effect on the lateral shift of the top of column; the increase of slope of inclined beam and depth-span ratio would advance the buckling damage of the top of rigid frame column and change the overall damage modality of rigid frame; the design should consider the influence of slope of inclined beam on column top lateral shift and bearing capacity, and increase the rigidity of rigid hing column reasonably to prevent the column top lateral shift from causing the instability of rigid frame;comparison and cross-validation between finite elements and tests were used to provide a reference for further research into such structures.
Based on the study of cold-formed steel yurts in grassland areas, a one-bay planar rigid frame was used as the research object. Stability tests and finite element simulations were carried out on a 5-bay rigid frame to analyze its damage modalities, bearing capacity, column top lateral displacement and yielding mechanism, etc., and to investigate the effects of inclined beam slope and depth-span ratio on the stability of the rigid frame. The results showed that the damage of rigid frame was mainly caused by the local buckling of C-beam at the top and bottom of the beam, which led to the overall in-plane instability; increasing the slope of inclined beam and decreasing the depth-span ratio could advance the bearing capacity and the overall stability of rigid frame; the lateral shift of the top of rigid frame column increased with the raise of slope of slanted beam, but the depth-span ratio had less effect on the lateral shift of the top of column; the increase of slope of inclined beam and depth-span ratio would advance the buckling damage of the top of rigid frame column and change the overall damage modality of rigid frame; the design should consider the influence of slope of inclined beam on column top lateral shift and bearing capacity, and increase the rigidity of rigid hing column reasonably to prevent the column top lateral shift from causing the instability of rigid frame;comparison and cross-validation between finite elements and tests were used to provide a reference for further research into such structures.
2023, 53(10): 83-87,99.
doi: 10.13204/j.gyjzG21071404
Abstract:
Long-span spatial structures are highly sensitive to wind loads, and are vulnerable to downbursts. In view of the lack of performance evaluation method for downburst-resistance of such structures, fragility of the single-layer spherical reticulated shell subjected to downbursts was studied, and a structural fragility analysis method for downburst loads was proposed. Considering the randomness of downburst loads and the uncertainty of structural parameters, the random incremental dynamic analysis (IDA) method was used to solve the structural response under different load intensity. Combined with the fragility analysis theory and quadratic regression analysis, the fragility function of the structure was calculated, and the fragility curves were further drawn to evaluate the downburst-resistance performance of the structure. The results showed that the combination of stochastic IDA method and fragility analysis could effectively evaluate the structural downburst-resistance performance. With the action of downbursts, the single-layer spherical reticulated shell might reach the CP performance point, while the probability of reaching the GI performance point was relatively small.
Long-span spatial structures are highly sensitive to wind loads, and are vulnerable to downbursts. In view of the lack of performance evaluation method for downburst-resistance of such structures, fragility of the single-layer spherical reticulated shell subjected to downbursts was studied, and a structural fragility analysis method for downburst loads was proposed. Considering the randomness of downburst loads and the uncertainty of structural parameters, the random incremental dynamic analysis (IDA) method was used to solve the structural response under different load intensity. Combined with the fragility analysis theory and quadratic regression analysis, the fragility function of the structure was calculated, and the fragility curves were further drawn to evaluate the downburst-resistance performance of the structure. The results showed that the combination of stochastic IDA method and fragility analysis could effectively evaluate the structural downburst-resistance performance. With the action of downbursts, the single-layer spherical reticulated shell might reach the CP performance point, while the probability of reaching the GI performance point was relatively small.
2023, 53(10): 88-93.
doi: 10.13204/j.gyjzG21081001
Abstract:
The effect of temperature on long-span space structures cannot be ignored. Temperature effect values related to the area, taking Urumqi Railway Station steel roof space truss structure as engineering example, combined with Urumqi meteorological data and the result of flow field analysis, different types of temperature effect accessor methods were put forward, and then the different types of temperature effects were taken into account in structural finite element model for temperature effect analysis, according to the deformation and force of the structure, it was concluded that the extreme daily temperature difference and the extreme annual temperature difference were the most unfavorable loads, which should be considered in the future structure design.
The effect of temperature on long-span space structures cannot be ignored. Temperature effect values related to the area, taking Urumqi Railway Station steel roof space truss structure as engineering example, combined with Urumqi meteorological data and the result of flow field analysis, different types of temperature effect accessor methods were put forward, and then the different types of temperature effects were taken into account in structural finite element model for temperature effect analysis, according to the deformation and force of the structure, it was concluded that the extreme daily temperature difference and the extreme annual temperature difference were the most unfavorable loads, which should be considered in the future structure design.
2023, 53(10): 94-99.
doi: 10.13204/j.gyjzG22071404
Abstract:
Based on L9(34) orthogonal test design method, choosing four basic influence factors in masonry structures, a set of quasi-static loading tests with nine specimens were carried out to study the shear performance and stiffness degradaion of the small concrete block masonry walls. Four influence factors include:the aspect ratio of the walls, the strength of mortars, the axial compression and the grouted masonry strips. The results showed that the mortar strength was the greatest influential factor to the shear performance of the walls; the axial compression was in the second. For the stiffness degraadation, the greatest influential factor was the grouted masonry strips. Otherwise, a new computational model was suggested for describing the stiffness degradation of the concrete block walls. This model can describe stiffness-degrading of the walls in a better way, and provide some reasonable parameters for statistical analysis.
Based on L9(34) orthogonal test design method, choosing four basic influence factors in masonry structures, a set of quasi-static loading tests with nine specimens were carried out to study the shear performance and stiffness degradaion of the small concrete block masonry walls. Four influence factors include:the aspect ratio of the walls, the strength of mortars, the axial compression and the grouted masonry strips. The results showed that the mortar strength was the greatest influential factor to the shear performance of the walls; the axial compression was in the second. For the stiffness degraadation, the greatest influential factor was the grouted masonry strips. Otherwise, a new computational model was suggested for describing the stiffness degradation of the concrete block walls. This model can describe stiffness-degrading of the walls in a better way, and provide some reasonable parameters for statistical analysis.
2023, 53(10): 100-104.
doi: 10.13204/j.gyjzG22070902
Abstract:
Loess is a kind of unsaturated soil with special structure. To explore the quantitative relations between structural degrees of unsaturated loess and matric suction or compressive yield deformation, uniaxial compressive strength tests were conducted on loess specimens from different sites in intact, remolded and saturated intact conditions, and the variation laws of structural degrees of loess with different contents of water were analyzed. The soil-water characteristic curves of corresponding loess specimens were tested, and the matric suction indexes of intact loess with different contents of water were measured. Based on the quantitative relations between the physical quantity and the structural degree, the relation between matric suction and the structural degree was established, and its applicability was demonstrated. Through isotropic compression tests, the relation between the yield stress and the structural degree was determined, and the relations between the yield stress and the structured degree of Q2 loess or Q3 loess were established. Through the relations between the structural degree of loess and the compressive yield stress or isotropic compressive yield deformation, the relations among the structural degree of Q2 loess or Q3 loess, compressive yield and compressive deformation were established.
Loess is a kind of unsaturated soil with special structure. To explore the quantitative relations between structural degrees of unsaturated loess and matric suction or compressive yield deformation, uniaxial compressive strength tests were conducted on loess specimens from different sites in intact, remolded and saturated intact conditions, and the variation laws of structural degrees of loess with different contents of water were analyzed. The soil-water characteristic curves of corresponding loess specimens were tested, and the matric suction indexes of intact loess with different contents of water were measured. Based on the quantitative relations between the physical quantity and the structural degree, the relation between matric suction and the structural degree was established, and its applicability was demonstrated. Through isotropic compression tests, the relation between the yield stress and the structural degree was determined, and the relations between the yield stress and the structured degree of Q2 loess or Q3 loess were established. Through the relations between the structural degree of loess and the compressive yield stress or isotropic compressive yield deformation, the relations among the structural degree of Q2 loess or Q3 loess, compressive yield and compressive deformation were established.
2023, 53(10): 105-111.
doi: 10.13204/j.gyjzG22070421
Abstract:
To study the influence of different factors on mechanical properties of frozen soft clay of Tianjin Metro Line 7, triaxial compression tests were conducted on artificially frozen soft clay at different temperatures, confining pressures, and loading rates. The results indicated that the stress-strain curves of frozen soft clay at different temperatures and confining pressures were all strain hardening. In experimental conditions, the peak compressive strength of frozen soft clay was positively correlated with confining pressures and loading rates and negatively correlated with temperatures. With the decrease of frozen negative temperature, the failure mode of specimens changed from bulging deformation to local shear failure, and the influence of confining pressure levels on compressive strength gradually decreased. In the frozen negative temperature range of tests, with the decrease of frozen negative temperatures, the cohesive strength increased range of 0.897 to 3.281 MPa, the internal frictional angle decreased varying in the range of 7.7° to 20.6°. Both of them had good linear relations with frozen negative temperature. Four kinds of frozen soil relations between stress and strain were used to fit the measured data, and the applicability of the improved Duncan-Chang's model to frozen soft clay was verified.
To study the influence of different factors on mechanical properties of frozen soft clay of Tianjin Metro Line 7, triaxial compression tests were conducted on artificially frozen soft clay at different temperatures, confining pressures, and loading rates. The results indicated that the stress-strain curves of frozen soft clay at different temperatures and confining pressures were all strain hardening. In experimental conditions, the peak compressive strength of frozen soft clay was positively correlated with confining pressures and loading rates and negatively correlated with temperatures. With the decrease of frozen negative temperature, the failure mode of specimens changed from bulging deformation to local shear failure, and the influence of confining pressure levels on compressive strength gradually decreased. In the frozen negative temperature range of tests, with the decrease of frozen negative temperatures, the cohesive strength increased range of 0.897 to 3.281 MPa, the internal frictional angle decreased varying in the range of 7.7° to 20.6°. Both of them had good linear relations with frozen negative temperature. Four kinds of frozen soil relations between stress and strain were used to fit the measured data, and the applicability of the improved Duncan-Chang's model to frozen soft clay was verified.
2023, 53(10): 112-118.
doi: 10.13204/j.gyjzG22070517
Abstract:
To study response laws of piles, free field soil and pile-soil interfaces under different propertions of seismic waves, the pile-soil model was constructed by the OpenSees software. The contact between pile and soil was simulated by p-y, q-z and τ-z spring elements separately. The waves with proportions of 50%, 75% and 100% of the El Centro wave and Kobe wave were respectively input into the model. The results showed that the accelerations of soil and pile bodies in the free field were amplified, and the amplified ranges of the peak ground acceleration and pile cap were from 1.73 to 2.26 and 2.63 to 3.92 respectively; with the increase of the proportion of input seismic waves, the amplified times of acceleration at the ground and the pile cap decreased gradually; the maximum displacement ratio at pile caps and the maximum shear force ratio of piles were approximately linear with the peak ground acceleration; the resistances of soil at 3 m below the ground or at the pile bottom were larger, and the resistance at the ground was smallest; the residual displacement at the ground was caused by plastic deformation. For the soil at different depths, the phenomenon of shear contraction followed shear dilation occurred in soil at different depths under earthquakes.
To study response laws of piles, free field soil and pile-soil interfaces under different propertions of seismic waves, the pile-soil model was constructed by the OpenSees software. The contact between pile and soil was simulated by p-y, q-z and τ-z spring elements separately. The waves with proportions of 50%, 75% and 100% of the El Centro wave and Kobe wave were respectively input into the model. The results showed that the accelerations of soil and pile bodies in the free field were amplified, and the amplified ranges of the peak ground acceleration and pile cap were from 1.73 to 2.26 and 2.63 to 3.92 respectively; with the increase of the proportion of input seismic waves, the amplified times of acceleration at the ground and the pile cap decreased gradually; the maximum displacement ratio at pile caps and the maximum shear force ratio of piles were approximately linear with the peak ground acceleration; the resistances of soil at 3 m below the ground or at the pile bottom were larger, and the resistance at the ground was smallest; the residual displacement at the ground was caused by plastic deformation. For the soil at different depths, the phenomenon of shear contraction followed shear dilation occurred in soil at different depths under earthquakes.
2023, 53(10): 119-125.
doi: 10.13204/j.gyjzG22071510
Abstract:
To predict rock burst tendencies in deep underground engineering, a prediction model of rock burst tendencies combining the principal component analysis (PCA) and improved GWO-SVM algorithm was proposed. Based on the formation mechanism of rock burst, the maximum tangential stress of rock σθ, the uniaxial compressive strength of rock σc, the uniaxial tensile strength of rock σt, the rock stress coefficient σθ/σc, the rock brittleness coefficient σc/σt, and the elastic energy index Wet were selected as estimate indexes for rock burst tendencies, and the three estimate indexes including F1, F2 and F3 were obtained to optimize estimation index structure by PCA,which reduced the complexity of calculations. The original data set of rock burst was constructed by collecting 64 sets of rock burst cases at home and abroad, and the original rock burst data set and the pre-processed rock burst data set by PCA were used as input vectors of four machine learning models including the PNN model, the Elman model, the SVM model and the GWO-SVM model, and the prediction performances of each model were compared in different combinations of inputs in terms of prediction accuracy and running times. The results indicated that the overall performances of models were significantly improved after optimization by PCA. Comparison with those models before optimization by PCA, the calculation accuracy of improved models was enhanced by 6.25% to 12.5%, running times was shortened by 11.20% to 58.42%, and the prediction accuracy of the GWO-SVM model combined with PCA was up to 93.75%.
To predict rock burst tendencies in deep underground engineering, a prediction model of rock burst tendencies combining the principal component analysis (PCA) and improved GWO-SVM algorithm was proposed. Based on the formation mechanism of rock burst, the maximum tangential stress of rock σθ, the uniaxial compressive strength of rock σc, the uniaxial tensile strength of rock σt, the rock stress coefficient σθ/σc, the rock brittleness coefficient σc/σt, and the elastic energy index Wet were selected as estimate indexes for rock burst tendencies, and the three estimate indexes including F1, F2 and F3 were obtained to optimize estimation index structure by PCA,which reduced the complexity of calculations. The original data set of rock burst was constructed by collecting 64 sets of rock burst cases at home and abroad, and the original rock burst data set and the pre-processed rock burst data set by PCA were used as input vectors of four machine learning models including the PNN model, the Elman model, the SVM model and the GWO-SVM model, and the prediction performances of each model were compared in different combinations of inputs in terms of prediction accuracy and running times. The results indicated that the overall performances of models were significantly improved after optimization by PCA. Comparison with those models before optimization by PCA, the calculation accuracy of improved models was enhanced by 6.25% to 12.5%, running times was shortened by 11.20% to 58.42%, and the prediction accuracy of the GWO-SVM model combined with PCA was up to 93.75%.
2023, 53(10): 126-134.
doi: 10.13204/j.gyjzG23030409
Abstract:
Due to the uneven distribution of the temperature field inside the concrete, mass concrete is prone to produce temperature cracks of varying degrees. These temperature cracks often directly affect the construction quality of concrete and the structural safety of buildings. Therefore, it is particularly important to accurately estimate the temperature field of mass concrete, which can provide effective basis and measures for the control of temperature cracks. However, traditional one-dimensional difference method does not take into consideration the fact that thermal parameters of concrete change with the hydration reaction of cementitious materials, which makes some disparities between the calculated result and the actual temperature. Incorporating thermal parameters changes during cement hydration, a phase adjustment coefficient of thermal parameters was proposed. Based on one-dimensional difference method, a new method for calculating theoretical temperature of mass concrete by incorporating the cement hydration and periodic variation law of ambient temperature was proposed. Through the comparison and analysis of the results from mass concrete cube temperature test, it showed that the proposed method could more accurately reflect the maximum temperature at the center of concrete and the time when the maximum temperature occurred.
Due to the uneven distribution of the temperature field inside the concrete, mass concrete is prone to produce temperature cracks of varying degrees. These temperature cracks often directly affect the construction quality of concrete and the structural safety of buildings. Therefore, it is particularly important to accurately estimate the temperature field of mass concrete, which can provide effective basis and measures for the control of temperature cracks. However, traditional one-dimensional difference method does not take into consideration the fact that thermal parameters of concrete change with the hydration reaction of cementitious materials, which makes some disparities between the calculated result and the actual temperature. Incorporating thermal parameters changes during cement hydration, a phase adjustment coefficient of thermal parameters was proposed. Based on one-dimensional difference method, a new method for calculating theoretical temperature of mass concrete by incorporating the cement hydration and periodic variation law of ambient temperature was proposed. Through the comparison and analysis of the results from mass concrete cube temperature test, it showed that the proposed method could more accurately reflect the maximum temperature at the center of concrete and the time when the maximum temperature occurred.
2023, 53(10): 135-142.
doi: 10.13204/j.gyjzG23050809
Abstract:
In order to study the effects of hybrid fibers on the workability and mechanical properties of rubber concrete, the slump, axial compression, splitting tensile and four-point bending tests were carried out. Taking the hybrid steel-glass fibers reinforced rubber concrete as the research object, the influence of steel fibers content, glass fibers content and glass fibers length on the workability, mechanical properties and brittle coefficient of rubber concrete was analyzed. The results showed that adding steel fibers and glass fibers decreased the workability of rubber concrete, and the influence of glass fibers were greater when the volume content was the same; as the steel fibers content increased, the mechanical properties of rubber concrete increased; as the glass fibers content increased, the mechanical properties of rubber concrete first increased and then decreased; longer glass fibers could inhibit the development of cracks more effectively, thus longer fibers improved the mechanical properties of rubber concrete more; hybrid fibers could effectively reduce the brittleness coefficient of rubber concrete and improve the toughness of rubber concrete.
In order to study the effects of hybrid fibers on the workability and mechanical properties of rubber concrete, the slump, axial compression, splitting tensile and four-point bending tests were carried out. Taking the hybrid steel-glass fibers reinforced rubber concrete as the research object, the influence of steel fibers content, glass fibers content and glass fibers length on the workability, mechanical properties and brittle coefficient of rubber concrete was analyzed. The results showed that adding steel fibers and glass fibers decreased the workability of rubber concrete, and the influence of glass fibers were greater when the volume content was the same; as the steel fibers content increased, the mechanical properties of rubber concrete increased; as the glass fibers content increased, the mechanical properties of rubber concrete first increased and then decreased; longer glass fibers could inhibit the development of cracks more effectively, thus longer fibers improved the mechanical properties of rubber concrete more; hybrid fibers could effectively reduce the brittleness coefficient of rubber concrete and improve the toughness of rubber concrete.
2023, 53(10): 143-150,82.
doi: 10.13204/j.gyjzG23051513
Abstract:
To investigate the influence of recycled aggregate incorporation on the dilation behavior of concrete, the paper conducted the compressive tests for 14 groups of 150 mm×150 mm×300 mm prisms (totally 42 specimens) with different coarse recycled aggregate (CRA) and fine recycled aggregate (FRA) replacement ratios and water-cement ratios (w/c), and then quantified the influence of recycled aggregate (RA) replacement ratio on the dilation ratio of concrete with different w/c. Based on two-phase composite material theory, a new dilation ratio prediction model for RAC was proposed, which could consider the difference of replacement ratio influence with different w/c. The proposed model was benchmarked against the available test data. It was found that the CRA and FRA had a significant compounding effect on dilation ratio, which could be amplified by the increasing w/c ratio;the mean value and coefficient of variation (COV) for the ratio of predictions by proposed model to the available test results were 1.000 and 0.250, respectively.
To investigate the influence of recycled aggregate incorporation on the dilation behavior of concrete, the paper conducted the compressive tests for 14 groups of 150 mm×150 mm×300 mm prisms (totally 42 specimens) with different coarse recycled aggregate (CRA) and fine recycled aggregate (FRA) replacement ratios and water-cement ratios (w/c), and then quantified the influence of recycled aggregate (RA) replacement ratio on the dilation ratio of concrete with different w/c. Based on two-phase composite material theory, a new dilation ratio prediction model for RAC was proposed, which could consider the difference of replacement ratio influence with different w/c. The proposed model was benchmarked against the available test data. It was found that the CRA and FRA had a significant compounding effect on dilation ratio, which could be amplified by the increasing w/c ratio;the mean value and coefficient of variation (COV) for the ratio of predictions by proposed model to the available test results were 1.000 and 0.250, respectively.
2023, 53(10): 151-156,28.
doi: 10.13204/j.gyjzG23021512
Abstract:
In order to improve the drying shrinkage performance of 3D printed cement-based materials, two mineral admixtures of fly ash (FA) and mineral powder (S) were added to the 3D printed cement-based materials prepared by machine-made sand in the form of single admixture and compound admixture. Scanning electron microscope and mercury intrusion porosimetry were used to research the microstructure and pore structure of 3D printed cement-based materials. The test results showed that:in the case of single addition, lower activity of fly ash and mineral powder inhibited the development of strength, and the inhibition effect of fly ash in the X, direction was the strongest, which reduced the 28 d compressive strength and flexural strength by 41% and 23%, respectively. However, the skeleton filling effect and pozzolanic effect of mineral admixtures could improve the pore structure, reduce the connectivity between pores, reduce water consumption, and inhibit the drying shrinkage of 3D printed cement-based materials. With the same content of fly ash and mineral powder, the total porosity was reduced by 15.2% and 9.8%, and the most probable pore size was reduced by 43.2% and 16.5%. Test group with 30% fly ash and 20% mineral powder reduced the 28d drying shrinkage by 41% and 22%, respectively. When fly ash and mineral powder were paired together, compressive strength and flexural strength decreased by 27.5% and 13.9%, respectively, and the inhibition effect on drying shrinkage was between that of single admixture, reduced the 28 d drying shrinkage by 23%-25%.
In order to improve the drying shrinkage performance of 3D printed cement-based materials, two mineral admixtures of fly ash (FA) and mineral powder (S) were added to the 3D printed cement-based materials prepared by machine-made sand in the form of single admixture and compound admixture. Scanning electron microscope and mercury intrusion porosimetry were used to research the microstructure and pore structure of 3D printed cement-based materials. The test results showed that:in the case of single addition, lower activity of fly ash and mineral powder inhibited the development of strength, and the inhibition effect of fly ash in the X, direction was the strongest, which reduced the 28 d compressive strength and flexural strength by 41% and 23%, respectively. However, the skeleton filling effect and pozzolanic effect of mineral admixtures could improve the pore structure, reduce the connectivity between pores, reduce water consumption, and inhibit the drying shrinkage of 3D printed cement-based materials. With the same content of fly ash and mineral powder, the total porosity was reduced by 15.2% and 9.8%, and the most probable pore size was reduced by 43.2% and 16.5%. Test group with 30% fly ash and 20% mineral powder reduced the 28d drying shrinkage by 41% and 22%, respectively. When fly ash and mineral powder were paired together, compressive strength and flexural strength decreased by 27.5% and 13.9%, respectively, and the inhibition effect on drying shrinkage was between that of single admixture, reduced the 28 d drying shrinkage by 23%-25%.
2023, 53(10): 157-163,134.
doi: 10.13204/j.gyjzG23010509
Abstract:
In recent years, steel bridges, steel-concrete composite girder bridges and other steel bridges have been widely used in China. In order to ensure the safety and durability of bridges, it is very important to carry out in-depth research on fatigue state assessment of steel bridges. Among them, the application of modern technology such as digital image acquisition and transmission in fatigue monitoring and assessment is one of the research hotspots. In order to understand the morphological and data characteristics of digital image in the fatigue research of steel bridge structure details, the fatigue and three-dimensional digital strain image measurement tests were carried out synchronously by using common bridge steel Q345qD specimens. Automatic processing and fast extraction methods were explored for the maximum strain on the image. The morphological characteristics of the maximum strain of the image with the number change of fatigue cycles were analyzed. In addition the test data were fitted to form a measured curve function and were optimized. Combined with the fatigue S-N curve equation, the general formula for calculating the strain changes with the fatigue process was determined. The results showed that the measured maximum strain value image could be cropped, identified and converted digitally by a batch program, which could meet the requirements of fast extraction. The measured strain curve showed an upward trend of exponential function with the increase of number of fatigue cycles, and the trend curve had a certain width with the cyclic loading of fatigue. By extracting the peak point data, the strain showed a significant upward change at approximately 70% of fatigue life, or earlier. It was shown that the curve of digital image strain was the refinement of the damage process at a single measuring point on the fatigue S-N curve. The proposed ε-N' general formula integrated strain curve with S-N curve exhibited the inherent damage characteristics of the structural details.
In recent years, steel bridges, steel-concrete composite girder bridges and other steel bridges have been widely used in China. In order to ensure the safety and durability of bridges, it is very important to carry out in-depth research on fatigue state assessment of steel bridges. Among them, the application of modern technology such as digital image acquisition and transmission in fatigue monitoring and assessment is one of the research hotspots. In order to understand the morphological and data characteristics of digital image in the fatigue research of steel bridge structure details, the fatigue and three-dimensional digital strain image measurement tests were carried out synchronously by using common bridge steel Q345qD specimens. Automatic processing and fast extraction methods were explored for the maximum strain on the image. The morphological characteristics of the maximum strain of the image with the number change of fatigue cycles were analyzed. In addition the test data were fitted to form a measured curve function and were optimized. Combined with the fatigue S-N curve equation, the general formula for calculating the strain changes with the fatigue process was determined. The results showed that the measured maximum strain value image could be cropped, identified and converted digitally by a batch program, which could meet the requirements of fast extraction. The measured strain curve showed an upward trend of exponential function with the increase of number of fatigue cycles, and the trend curve had a certain width with the cyclic loading of fatigue. By extracting the peak point data, the strain showed a significant upward change at approximately 70% of fatigue life, or earlier. It was shown that the curve of digital image strain was the refinement of the damage process at a single measuring point on the fatigue S-N curve. The proposed ε-N' general formula integrated strain curve with S-N curve exhibited the inherent damage characteristics of the structural details.
2023, 53(10): 164-168.
doi: 10.13204/j.gyjzG23040405
Abstract:
In order to improve the anchoring performance and tensile properties of carbon fibre reinforced plastics (CFRP) plates, the influence of failure phenomenon, types of anchoring resin, types of matrix resin, and fiber volume content on the tensile properties of carbon fiber plates were studied by static load test. The results showed that explosive failure was the most reasonable failure mode, which could best reflect the real performance of CFRP plates, and the tensile strength was greater than that of brittle fracture. The greater the shear strength of the anchoring resin, the more conducive to anchoring, and it was recommended to use epoxy film for anchoring; the viscosity of the matrix resin had a great influence on the tensile properties; for 1.2 mm CFRP plates, with the increase of fiber volume content, the tensile strength first increased and then decreased, and the elastic modulus gradually increased, and the optimal fit ratio was 66%.
In order to improve the anchoring performance and tensile properties of carbon fibre reinforced plastics (CFRP) plates, the influence of failure phenomenon, types of anchoring resin, types of matrix resin, and fiber volume content on the tensile properties of carbon fiber plates were studied by static load test. The results showed that explosive failure was the most reasonable failure mode, which could best reflect the real performance of CFRP plates, and the tensile strength was greater than that of brittle fracture. The greater the shear strength of the anchoring resin, the more conducive to anchoring, and it was recommended to use epoxy film for anchoring; the viscosity of the matrix resin had a great influence on the tensile properties; for 1.2 mm CFRP plates, with the increase of fiber volume content, the tensile strength first increased and then decreased, and the elastic modulus gradually increased, and the optimal fit ratio was 66%.
2023, 53(10): 169-178,118.
doi: 10.13204/j.gyjzG22070904
Abstract:
Since 1964, there have been many destructive earthquakes that caused large-scale liquefaction phenomena around the world, such as Niigata Earthquake, Cobe Earthquake, Tangshan Earthquake, and Wenchuan Earthquake, etc. During earthquakes, many cases of earthquake-induced damage to bridge pile foundations in liquefiable sites caused significant economic losses and casualties. Based on investigations of a large number of relevant documents at home and abroad, the typical cases of earthquake-induced damage to bridge foundations at home and abroad in recent years were summed.the research progress of domestic and foreign scholars on anti-liquefaction tests, numerical simulations, and theoretical analysis for anti-liquefaction of pile foundations were emphasized introduction. Relevant summaries and analysis were performed to provide reference to further research on anti-liquefaction of bridge pile foundations.
Since 1964, there have been many destructive earthquakes that caused large-scale liquefaction phenomena around the world, such as Niigata Earthquake, Cobe Earthquake, Tangshan Earthquake, and Wenchuan Earthquake, etc. During earthquakes, many cases of earthquake-induced damage to bridge pile foundations in liquefiable sites caused significant economic losses and casualties. Based on investigations of a large number of relevant documents at home and abroad, the typical cases of earthquake-induced damage to bridge foundations at home and abroad in recent years were summed.the research progress of domestic and foreign scholars on anti-liquefaction tests, numerical simulations, and theoretical analysis for anti-liquefaction of pile foundations were emphasized introduction. Relevant summaries and analysis were performed to provide reference to further research on anti-liquefaction of bridge pile foundations.
2023, 53(10): 179-183.
doi: 10.13204/j.gyjzG23091908
Abstract:
The partial revision of Technical Specification for Grout Sleeve Splicing of Rebars (JGJ 355-2015) has been initiated since 2019. The revised provisions of the 2023 Version have been approved for publication and will be implemented from November 1, 2023. The background and key contents of partial revision were analyzed, which could be convenient for relevant technicians to fully understand the main technical contents of standard revision and accurately carry out the application of standard in new engineering applications.
The partial revision of Technical Specification for Grout Sleeve Splicing of Rebars (JGJ 355-2015) has been initiated since 2019. The revised provisions of the 2023 Version have been approved for publication and will be implemented from November 1, 2023. The background and key contents of partial revision were analyzed, which could be convenient for relevant technicians to fully understand the main technical contents of standard revision and accurately carry out the application of standard in new engineering applications.
2023, 53(10): 184-189,60.
doi: 10.13204/j.gyjzG23042608
Abstract:
The combination of ultrasonic method and tomographic imaging technology is a common method to realize the visual defection of concrete hole defects. Herein, a comprehensive identification method was proposed to address the problem of defect misjudgment and missing judgment caused by using a single acoustic parameter as the criterion for ultrasonic testing. Additionally, an image reconstruction method based on inversion initial value correction was used to address the problem of low accuracy in tomographic imaging, which is often characterized by empirical assignment of initial wave velocity and uniform distribution of travel time error. The effectiveness of the modified method was verified through experiments on concrete specimens with different hole sizes and numbers. The results showed that the comprehensive defect discrimination based on the coupling of sound velocity, amplitude and frequency could accurately identify hole defects in concrete, with better accuracy than single-parameter or two-parameter coupling method. The ultrasonic tomography method based on inversion initial value correction could accurately assign the initial value of wave velocity iteration and make the distribution of travel time error more consistent with the defect distribution law.The method was effective for identifying holes larger than 5 mm.
The combination of ultrasonic method and tomographic imaging technology is a common method to realize the visual defection of concrete hole defects. Herein, a comprehensive identification method was proposed to address the problem of defect misjudgment and missing judgment caused by using a single acoustic parameter as the criterion for ultrasonic testing. Additionally, an image reconstruction method based on inversion initial value correction was used to address the problem of low accuracy in tomographic imaging, which is often characterized by empirical assignment of initial wave velocity and uniform distribution of travel time error. The effectiveness of the modified method was verified through experiments on concrete specimens with different hole sizes and numbers. The results showed that the comprehensive defect discrimination based on the coupling of sound velocity, amplitude and frequency could accurately identify hole defects in concrete, with better accuracy than single-parameter or two-parameter coupling method. The ultrasonic tomography method based on inversion initial value correction could accurately assign the initial value of wave velocity iteration and make the distribution of travel time error more consistent with the defect distribution law.The method was effective for identifying holes larger than 5 mm.
