摘要：
In this study, we propose an accurate gain method for ground-penetrating radar (GPR) signals based on the characteristics of refined time-frequency analysis and translation invariance offered by the Stationary Wavelet Packet Transform (SWPT), combined with the conventional signal gain approach. This method aims to address the issue of low signal resolution resulting from the direct gain processing of GPR signals with a low signal-to-noise ratio (SNR). Specifically, the GPR signals are initially decomposed into appropriate wavelet packet coefficients using SWPT, wherein only those coefficients with high SNR undergo gain processing, followed by reconstruction of the signals through SWPT. By employing accurate gain processing on low SNR GPR signals acquired during concrete crack detection tests, we have confirmed that the proposed method effectively distinguishes the target reflected signals from most noise, thereby achieving accurate amplification of the desired reflected signals and significantly enhancing the GPR signals resolution under low SNR conditions.
In this study, we propose an accurate gain method for ground-penetrating radar (GPR) signals based on the characteristics of refined time-frequency analysis and translation invariance offered by the Stationary Wavelet Packet Transform (SWPT), combined with the conventional signal gain approach. This method aims to address the issue of low signal resolution resulting from the direct gain processing of GPR signals with a low signal-to-noise ratio (SNR). Specifically, the GPR signals are initially decomposed into appropriate wavelet packet coefficients using SWPT, wherein only those coefficients with high SNR undergo gain processing, followed by reconstruction of the signals through SWPT. By employing accurate gain processing on low SNR GPR signals acquired during concrete crack detection tests, we have confirmed that the proposed method effectively distinguishes the target reflected signals from most noise, thereby achieving accurate amplification of the desired reflected signals and significantly enhancing the GPR signals resolution under low SNR conditions.
摘要：
To estimate the progressive collapse resistance capacity of a multi-column frame tube structure with an assembled truss beam composite floor (ATBCF), pushdown analysis and nonlinear dynamic analysis are conducted for such a structure using the alternate load path (ALP) method. The bearing capacities of the remaining structures under three different work conditions, which are the side middle column removal, the edge middle column removal, and the corner column removal, are individually studied, and the collapse mechanism of the remaining structures is analyzed based on the aspects of the internal force redistribution and the failure mode of the second defense line. Simultaneously, the influence of the column failure time on the dynamic response of the remaining structure and the dynamic amplification coefficient is discussed. The results indicate that the residual bearing capacity of the remaining structure following the bottom corner column removal is higher than that of the one following the side or edge middle column removal, while the latter has a stronger plastic deformation capacity. When the ALP method is adopted to operate the progressive collapse analysis, it is reasonable to take the column failure time as 0.1 times the period of the first-order vertical vibration mode of the remaining structure, and it is suitable to set the dynamic amplification coefficient as 2.0, which is the ratio of the maximum dynamic displacement to the static displacement of the remaining structure under the transient loading condition.
摘要：
The river safety improvement project can restore and improve the surrounding ecological environment through measures such as ecological restoration. Based on the grey correlation analysis method, this paper analyses the impact of river safety regulation projects on the surrounding ecological environment. The development stage and existing problems of river safety regulation projects are identified, and the influencing factors are analysed using grey correlation analysis to determine the impact of river safety regulation projects on the surrounding ecological environment. The river safety regulation projects have a positive impact on water quality and terrain, which can stabilise sediment changes in the water area. The experimental results indicate that the river safety improvement project also has a positive impact on the surrounding ecological environment, with the surrounding water pollution index consistently below 0.4 and a relatively small impact on the surrounding terrain loss.
摘要：
The longitudinal displacement at the girder ends of long-span suspension bridges is a crucial issue that affects structural safety, durability, as well as traffic safety and ride comfort. The primary cause of these reciprocating displacements is the action of moving live loads, which induces quasi-static displacements in the longitudinal direction. This paper theoretically investigates the static longitudinal displacements of suspension bridges under a moving vertical concentrated load and elucidates the underlying deformation mechanisms. Considering geometrical nonlinearity, analytical equations are established for the longitudinal deformations of the main cable and stiffening girder under a vertical concentrated load. By analyzing the geometrical deformation conditions of the suspenders, the relationship between the longitudinal displacements of the stiffening girder and the main cable is derived. Due to the coupling between longitudinal and vertical displacements, the vertical displacement of the stiffening girder must be solved to obtain its longitudinal displacement. Based on deflection theory and considering the bending stiffness of the stiffening girder, this paper derives the vertical deformations of the stiffening girder for single-span suspension bridges and those with short continuous side spans under a vertical concentrated load, which is then used to calculate the longitudinal displacement. Finite element models are used to verify the accuracy of the analytical solutions. Differences between the proposed solutions and previous solutions neglecting the bending stiffness of the stiffening girder are compared and analyzed. The effects of neglecting the longitudinal displacement at the bridge tower top and the presence of short continuous side spans on the longitudinal displacement of stiffening girder are also investigated. The results demonstrate the high accuracy of the proposed analytical solution for the longitudinal displacement at the girder ends of suspension bridges. Importantly, the bending stiffness of the stiffening girder cannot be neglected in calculating the longitudinal displacement. The longitudinal displacement at the girder ends is primarily caused by the longitudinal deformation of the main cable, while the contribution from the flexural deformation of the girder is negligible. Furthermore, the longitudinal displacement at the bridge tower top has a negligible effect on the longitudinal displacement of the girder, and the presence of short continuous side spans is beneficial for reducing the longitudinal displacement of the stiffening girder. The proposed analytical solution method provides a rapid approach for calculating the static longitudinal displacement at the girder ends of suspension bridges under passing live loads and reveals the deformation mechanism. This is beneficial for preliminary design and structural optimization, as it avoids the complex finite element modeling and solution process.
摘要：
As a waterless fracturing fluids for gas shale stimulation with low viscosity and strong diffusibility, supercritical CO2 is promising than the water by avoiding the clay hydration expansion and reducing reservoir damage. The permeability evolution influenced by the changes of the temperature and stress is the key to gas extraction in deep buried shale reservoirs. Thus, the study focuses on the coupling influence of effective stress, temperature, and CO2 adsorption expansion effects on the seepage characteristics of Silurian Longmaxi shale fractured by supercritical CO2. The results show that when the gas pressure is 1–3 MPa, the permeability decreases significantly with the increase in gas pressure, and the Klinkenberg effects plays a predominant role at this stage. When the gas pressure is 3–5 MPa, the permeability increases with the increase in gas pressure, and the influence of effective stress on permeability is dominant. The permeability decreases exponentially with the increase in effective stress. The permeability of shale after the adsorption of CO2 gas is significantly lower than that of before adsorption; the permeability decreases with the increase in temperature at 305.15 K–321.15 K, and with the increase in temperature, the permeability sensitivity to the temperature decreases. The permeability is closely related to supercritical CO2 injection pressure and volume stress; when the injection pressure of supercritical CO2 is constant, the permeability decreases with the increase in volume stress. The results can be used for the dynamic prediction of reservoir permeability and gas extraction in CO2-enhanced shale gas development.
通讯机构：
[Jiang, H ] C;Changsha Univ Sci & Technol, 960,2nd Sect,Wanjiali RD S, Changsha 410004, Hunan, Peoples R China.
关键词：
lining void;ground penetrating radar;reverse time migration;digital morphology;edge detection
摘要：
Diseases such as voids behind the initial support of the tunnel will lead to problems such as lining rupture and concrete damage in the tunnel structure, which seriously affects the driving safety in the tunnel. In tunnel construction, ground penetrating radar is frequently employed as a method for detecting hidden defects. However, when the cavity size is small, there will be a large error when the original radar data is directly interpreted, which cannot meet the needs of practical engineering. To enhance the precision in tunnel detection, the Finite-Difference Time-Domain method is used to simulate various small cavities of different shapes located behind the primary support lining of the tunnel, and the study involves examining the electromagnetic response characteristics of different kinds of holes. The migration techniques of KIRCHHOFF, F-K, and reverse time are employed to reconstruct the hole target. Furthermore, digital morphology is employed to enhance the clarity of the image. Finally, the edge detection technology is used to further extract the hole features. After that, small cavities of different shapes are buried in the established outdoor concrete model box and radar detection is carried out. The detection position of the reconstructed radar image and the actual position of the cavity in the model box are verified. The results show that compared with KIRCHHOFF migration and F-K migration, the image processed by reverse time migration is clearer and more intuitive, and can restore the contour of small holes well. The research findings can serve as a reference for the interpretation of radar data of the cavity behind the initial support of the tunnel.
摘要：
Reasonable prediction of concrete creep is the basis of studying long-term deflection of concrete structures. In this paper, a hybrid model-driven and data-driven (HMD) method for predicting concrete creep is proposed by using the sequence integration strategy. Then, a novel uncertainty prediction model (UPM) is developed considering uncertainty quantification. Finally, the effectiveness of the proposed method is validated by using the North-western University (NU) database of creep, and the effect of uncertainty on prediction results are also discussed. The analysis results show that the proposed HMD method outperforms the model-driven and three data-driven methods, including the genetic algorithm-back propagation neural network (GA-BPNN), particle swarm optimization-support vector regression (PSO-SVR) and convolutional neural network only method, in accuracy and time efficiency. The proposed UPM of concrete creep not only ensures relatively good prediction accuracy, but also quantifies the model and measurement uncertainties during the prediction process. Additionally, although incorporating measurement uncertainty into concrete creep prediction can improve the prediction performance of UPM, the prediction interval of the creep compliance is more sensitive to model uncertainty than to measurement uncertainty, and the mean contribution of variance attributed to the model uncertainty to the total variance is about 90%.
通讯机构：
[Zhu, X ] H;Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.;Changsha Univ Sci & Technol, Natl Engn Res Ctr Highway Maintenance Technol, Changsha 410114, Peoples R China.
关键词：
construction solid waste;recycled aggregate;brick slag content;subgrade
摘要：
In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5–19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling.
摘要：
Steel strands subjected to marine salt spray environments are prone to corrosion, which can lead to degradation of their mechanical properties and ultimately affecting the safety of prestressed structures in service. Therefore, one of the most urgent scientific issues for prestressed structures is the assessment of the deterioration caused by long-term corrosion in steel strands. In this study, based on the environmental conditions of a specific coastal area, a similar neutral salt spray environment is simulated in an artificial climate chamber to analyze its influence on the mechanical behavior of prestressing strands. Long-term corrosion experiments on prestressing strands are conducted over a period of 10 months. Different corrosion periods, corrosion environments, and stress levels are considered to assess the prestressing force loss of strands in marine salt spray environments. The test results indicate that prestressing force loss increases with the growth in corrosion duration under combined stress and corrosion. Furthermore, the prestressing force of the strands enters an accelerated stage of plastic degradation after 9–10% corrosion loss. After the long-term corrosion test is completed, tensile tests are conducted on the strands to study the effect of corrosion on the tensile mechanical properties of strands. The results show that the ultimate strength of the corroded strands decreases as the corrosion loss increases. When the corrosion loss exceeds 17%, the strands in the tensile process directly exhibit brittle fracture without experiencing ductile development stage. Subsequently, a novel time-dependent model is proposed to predict the prestressing force loss caused by the corrosion in strands, and a finite element model is established to analyze the tensile mechanical properties of corroded strands. Finally, the experimental results are employed to validate the two proposed models. The results demonstrate that the proposed models can reasonably predict the prestressing force and constitutive relationship of prestressing steel strands.
Steel strands subjected to marine salt spray environments are prone to corrosion, which can lead to degradation of their mechanical properties and ultimately affecting the safety of prestressed structures in service. Therefore, one of the most urgent scientific issues for prestressed structures is the assessment of the deterioration caused by long-term corrosion in steel strands. In this study, based on the environmental conditions of a specific coastal area, a similar neutral salt spray environment is simulated in an artificial climate chamber to analyze its influence on the mechanical behavior of prestressing strands. Long-term corrosion experiments on prestressing strands are conducted over a period of 10 months. Different corrosion periods, corrosion environments, and stress levels are considered to assess the prestressing force loss of strands in marine salt spray environments. The test results indicate that prestressing force loss increases with the growth in corrosion duration under combined stress and corrosion. Furthermore, the prestressing force of the strands enters an accelerated stage of plastic degradation after 9–10% corrosion loss. After the long-term corrosion test is completed, tensile tests are conducted on the strands to study the effect of corrosion on the tensile mechanical properties of strands. The results show that the ultimate strength of the corroded strands decreases as the corrosion loss increases. When the corrosion loss exceeds 17%, the strands in the tensile process directly exhibit brittle fracture without experiencing ductile development stage. Subsequently, a novel time-dependent model is proposed to predict the prestressing force loss caused by the corrosion in strands, and a finite element model is established to analyze the tensile mechanical properties of corroded strands. Finally, the experimental results are employed to validate the two proposed models. The results demonstrate that the proposed models can reasonably predict the prestressing force and constitutive relationship of prestressing steel strands.
作者机构：
[Tan, Wanyu; Nie, Yixun] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Tan, WY ] H;Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.
关键词：
radon concentration;inhalation;annual effective dose;lifetime risk probability
摘要：
Radon is one of the important natural sources of radiation and pollutants. When radon and its progeny are inhaled by the human body, they can cause radiation damage to the respiratory system and can lead to lung cancer. Indoor and outdoor radon concentrations were measured in five villages near Shizhuyuan W-polymetallic deposit using a RAD7 detector; moreover, the corresponding radiation dose and lifetime risk probability were evaluated. The results show that the average value of indoor radon concentration was 216.6 +/- 121.1 Bq m-3, which is above the worldwide average indoor radon level of 40 Bq m-3, and the average outdoor value was 34.6 +/- 13.4 Bq m-3, which is higher than the worldwide outdoor average of 10 Bq m-3. A total of 42% of the dwellings investigated in our study had a higher radon level than the Chinese permissible indoor radon level of 200 Bq m-3. The total annual effective dose ranged from 5.21 mSv y-1 to 49.38 mSv y-1, with an average value of 14.63 mSv y-1, which is higher than the ICRP recommended value of 3-10 mSv y-1. This average total dose value corresponds to an average lifetime risk probability of 5.8% for residents in the whole study area.
摘要：
Corrosion accelerates the propagation of fatigue damage and significantly reduces the fatigue life of the orthotropic steel bridge deck (OSBD). This paper experimentally investigates the effects of local corrosion on the fatigue behavior of rib-to-deck (RD) joints in OSBDs. Firstly, an accelerated corrosion test was conducted to obtain corrosive effects for various corroded RD joint specimens. Next, the 3D scanning technology was used to test the geometric characteristics of corrosion regions. Then, the strain, failure mode, crack growth, and fatigue performance of corroded RD joints subjected to various fatigue cycles are discussed based on the fatigue loading test. Finally, a three-dimensional solid model of RD joint was established utilizing ABAQUS-FRANC3D (F-A) technology to analyze fatigue crack stress intensity factors (SIFs). The results indicated that corrosion has the greatest impact on the strain of the top plate weld toe, followed by the top plate weld root, with the least impact on the U-rib weld toe. The crack initiation life of specimens with a corrosion rate of 10.81%, 20.47%, and 30.14% decreased by 24.24%, 30.30%, and 60.61%, respectively, and the crack propagation life decreased by 2.11%, 21.05%, and 78.95%, respectively. The fatigue crack propagation of locally corroded RD joint is jointly controlled by type I, II, and III SIFs, and belongs to a composite fatigue crack dominated by type I cracking. The SIF at the welding toe of the top plate during U-rib bottom plate corrosion is greater than that of the top plate corrosion. The effects of the initial crack shape ratio and deflection angle on the SIF increase as the corrosion rate increases.
Corrosion accelerates the propagation of fatigue damage and significantly reduces the fatigue life of the orthotropic steel bridge deck (OSBD). This paper experimentally investigates the effects of local corrosion on the fatigue behavior of rib-to-deck (RD) joints in OSBDs. Firstly, an accelerated corrosion test was conducted to obtain corrosive effects for various corroded RD joint specimens. Next, the 3D scanning technology was used to test the geometric characteristics of corrosion regions. Then, the strain, failure mode, crack growth, and fatigue performance of corroded RD joints subjected to various fatigue cycles are discussed based on the fatigue loading test. Finally, a three-dimensional solid model of RD joint was established utilizing ABAQUS-FRANC3D (F-A) technology to analyze fatigue crack stress intensity factors (SIFs). The results indicated that corrosion has the greatest impact on the strain of the top plate weld toe, followed by the top plate weld root, with the least impact on the U-rib weld toe. The crack initiation life of specimens with a corrosion rate of 10.81%, 20.47%, and 30.14% decreased by 24.24%, 30.30%, and 60.61%, respectively, and the crack propagation life decreased by 2.11%, 21.05%, and 78.95%, respectively. The fatigue crack propagation of locally corroded RD joint is jointly controlled by type I, II, and III SIFs, and belongs to a composite fatigue crack dominated by type I cracking. The SIF at the welding toe of the top plate during U-rib bottom plate corrosion is greater than that of the top plate corrosion. The effects of the initial crack shape ratio and deflection angle on the SIF increase as the corrosion rate increases.
作者机构：
[Li, Kegang; Huang, Kaibo; He, Chong; Abbas, Naeem; Du, Xidong; Du, XD] Kunming Univ Sci & Technol, Fac Land Resources Engn, Yunnan Key Lab Sino German Blue Min & Utilizat Spe, Kunming 650093, Yunnan, Peoples R China.;[Du, Xidong] China Univ Min & Technol, Key Lab Coalbed Methane Resources & Reservoir Form, Minist Educ, Xuzhou 221008, Jiangsu, Peoples R China.;[Du, Xidong] Anhui Engn Res Ctr Exploitat & Utilizat Closed Aba, Huainan 232001, Anhui, Peoples R China.;[Zhou, Junping] Chongqing Univ, Sch Resources & Safety Engn, Chongqing 400044, Peoples R China.;[Zhang, Dengfeng] Kunming Univ Sci & Technol, Fac Chem Engn, Kunming 650500, Yunnan, Peoples R China.
通讯机构：
[Li, KG ; Du, XD] K;Kunming Univ Sci & Technol, Fac Land Resources Engn, Yunnan Key Lab Sino German Blue Min & Utilizat Spe, Kunming 650093, Yunnan, Peoples R China.
摘要：
The main reason for CO 2 enhanced coalbed methane recovery is the competitive adsorption of CO 2 and CH 4 on coal. Therefore, it is necessary to study the equilibrium adsorption of CO 2 , CH 4 and their mixed gases on coal over a wide range of pressures. This work investigates the mechanism adsorption of CO 2 /CH 4 on coal by thermodynamics. The findings indicate that CO 2 demonstrates a greater increase in Gibbs free energy and a larger decrease in entropy loss related to CH 4 , indicating that the adsorption process of CO 2 is more to occur spontaneously. In CO 2 /CH 4 mixed gas adsorption system, the amount of gas adsorbed for different gas ratios ( y CO2 : y CH4 = 1:3; y CO2 : y CH4 = 2:2; y CO2 : y CH4 = 3:1) falls between the amounts adsorbed for pure CO 2 and CH 4 components. As CO 2 concentration rises, the amount of mixed gases adsorbed similarly increases. Additionally, the amount of CH 4 adsorbed in any combination is lower than that of CO 2 , suggesting that CO 2 has a predominant influence regarding the adsorption process. Furthermore, isosteric heat of adsorption for CO 2 in the mixed gases exceeds that of CH 4 , suggesting a stronger connection between CO 2 and the surface of the coal matrix during the competitive adsorption stage.
The main reason for CO 2 enhanced coalbed methane recovery is the competitive adsorption of CO 2 and CH 4 on coal. Therefore, it is necessary to study the equilibrium adsorption of CO 2 , CH 4 and their mixed gases on coal over a wide range of pressures. This work investigates the mechanism adsorption of CO 2 /CH 4 on coal by thermodynamics. The findings indicate that CO 2 demonstrates a greater increase in Gibbs free energy and a larger decrease in entropy loss related to CH 4 , indicating that the adsorption process of CO 2 is more to occur spontaneously. In CO 2 /CH 4 mixed gas adsorption system, the amount of gas adsorbed for different gas ratios ( y CO2 : y CH4 = 1:3; y CO2 : y CH4 = 2:2; y CO2 : y CH4 = 3:1) falls between the amounts adsorbed for pure CO 2 and CH 4 components. As CO 2 concentration rises, the amount of mixed gases adsorbed similarly increases. Additionally, the amount of CH 4 adsorbed in any combination is lower than that of CO 2 , suggesting that CO 2 has a predominant influence regarding the adsorption process. Furthermore, isosteric heat of adsorption for CO 2 in the mixed gases exceeds that of CH 4 , suggesting a stronger connection between CO 2 and the surface of the coal matrix during the competitive adsorption stage.
