The host plants of 8emisia tabaci （Gennadius） in Shaanxi were investigated, and its damage degree was evaluated by hazard index in 2013 and 2014. There were 73 species （variants） of host plants of B. tabaci belong...The host plants of 8emisia tabaci （Gennadius） in Shaanxi were investigated, and its damage degree was evaluated by hazard index in 2013 and 2014. There were 73 species （variants） of host plants of B. tabaci belonging to 28 families, mainly concentrated in Cueurbitaceae, Crueiferae, Solanaceae, Laguminosae md Malvaceae. There were seven species of vegetables that suffered the damage of grade 4. B. tabaci was more serious in southern Shaanxi and lighter in northern Shaanxi. According to the distribution of host plants, the occurrence status of B. tabaci in Shamvd Province was analyzed and its development tendency was oredicted.展开更多
The species of main diseases and pests in foxtail millet and their damage status were investigated in 15 survey points in Longhua, Weichang, Chengde, Fengning and Luanping counties, Chengde City from 2015 to 2017. It ...The species of main diseases and pests in foxtail millet and their damage status were investigated in 15 survey points in Longhua, Weichang, Chengde, Fengning and Luanping counties, Chengde City from 2015 to 2017. It was preliminarily cleared that there were 11 species of main diseases and 8 species of pests in continuous cropping millet field. The diseases damaged severely were millet downy mildew and kernel smut, and pests were yellow-legged lema, millet shoot fly and soil insects. The results provided a scientific basis for green control of millet pests and diseases and safe production in Chengde area.展开更多
This study aimed to investigate the performance evolution characteristics of concrete under permafrost ambient temperatures and to explore methods to mitigate the thermal perturbation by concrete on the permafrost env...This study aimed to investigate the performance evolution characteristics of concrete under permafrost ambient temperatures and to explore methods to mitigate the thermal perturbation by concrete on the permafrost environment.A program was designed to investigate the properties of various concretes at three curing conditions.The compressive strength development pattern of each group was evaluated and the concrete's performance was characterized by compressive strength damage degree,hydration temperature and SEM analysis in a low temperature environment.The experimental results show that the incorporation of fly ash alone or incombination with other admixtures in concrete under low-temperature curing does not deteriorate its microstructure,and at the same time,it can slow down the hydration rate of cement and significantly reduce the exothermic heat of hydration of concrete.These findings are expected to provide valuable references for the proportioning design of concrete in permafrost environments.展开更多
Low pore sedimentary rocks(from Guangxi, China) were subjected to uniaxial compression loading experiment under different initial stresses. The rock samples were investigated by nuclear magnetic resonance before and a...Low pore sedimentary rocks(from Guangxi, China) were subjected to uniaxial compression loading experiment under different initial stresses. The rock samples were investigated by nuclear magnetic resonance before and after the loading. The relationships between the mesoscopic rock damage and macroscopic mechanical parameters were established, and the initial damage stress of the low-porosity sedimentary rock was determined. The results showed that this type of rock has the initial stress of damage. When the initial loading stress is lower than the initial stress of damage, the T2 spectrum area of the rock sample gradually decreases, and the primary pores of the rock are further closed under the stress. The range of the initial stress of damage for this type of rock is 8-16 MPa. When the loading stress exceeds the initial stress of damage, the T2 spectrum area gradually increases, indicating that the porosity of the rock increases and microscopic damage of the rock appears. The rock damage degree is defined, and the nonlinear function between the rock damage degree and the initial loading stress is established.展开更多
The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparat...The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparatus. The blasting test was carried out for ten times at some tunnels of Changba Lead-Zinc Mine. The damage depth of surrounding rock caused by old blasting excavation （0.8-1.2 m） was confirmed. The relation between the cumulative damage degree and blast times was obtained. The results show that the sonic velocity decreases gradually with increasing blast times, hut the damage degree （D） increases. The damage cumulative law is non-linear. The damage degree caused by blast decreases with increasing distance, and damage effects become indistinct. The blasting damage of rock mass is anisotropic. The damage degree of rock mass within charging range is maximal. And the more the charge is, the more severe the damage degree of rock mass is. The test results provide references for researches of mechanical parameters of rock mass and dynamic stability analysis of underground chambers.展开更多
To clarify association between armyworm（Mythimna separata） damage level and the corn growth and weed occurrence, we investigated corn plant height, stem diameter and vigor as well as weed coverage and biomass. The i...To clarify association between armyworm（Mythimna separata） damage level and the corn growth and weed occurrence, we investigated corn plant height, stem diameter and vigor as well as weed coverage and biomass. The investigations were conducted at three locations of Shaanxi Province, China which were suffered seriously from armyworm. Significant correlations were found between the parameters analyzed. At stunted corn growth and presence of plenty of weeds, the armyworm damage tended to be heavy; oppositely, when corn grew well and weed density were low, armyworm harm was the minimal. Therefore, corn growing status and weed density can significantly affect armyworm damage level. Our results imply that promoting corn growth and timely removal of weeds are conducive to reducing armyworm occurrence.展开更多
An equivalent sliding mode fault-tolerant control method with continuous switching is proposed for vertical tail damage.First,the nonlinear damage model of aircraft and the estimation of stability and control derivati...An equivalent sliding mode fault-tolerant control method with continuous switching is proposed for vertical tail damage.First,the nonlinear damage model of aircraft and the estimation of stability and control derivatives are introduced.Secondly,the linear sliding surface and the equivalent sliding mode controller are constructed,and the sufficient conditions for the stability of the damaged aircraft motion model are given by using the Lyapunov technique.The damage-tolerant controller is designed based on an adaptive sliding mode control for analyzing damaged aircraft systems.Furthermore,the hyperbolic tangent function is utilized to replace the symbolic function in the controller.The feasibility of the hyperbolic tangent function as the switching function is analyzed theoretically.Finally,the Boeing-747100/200 model is taken as an example to demonstrate the efficiency of theoretical results by recognizing the structural fault of aircraft.Numerical results show that the control law has a positive impact on the performance of the closed-loop system,and it also has a better fault tolerance and robustness towards external disturbance compared with traditional methods of damaged aircraft stabilization control.展开更多
In this paper, we researched the regional seismic status by using theories of the Damage Mechanics. The macroscopic damage status of the earth crust block, which is caused by earthquake fracture, is described with sev...In this paper, we researched the regional seismic status by using theories of the Damage Mechanics. The macroscopic damage status of the earth crust block, which is caused by earthquake fracture, is described with several concepts—the damage degree, the damage rate and the strain rate. In the earthquake process, the average strain rate of the studied block is equal to the sum of all seismic moment tensors of the earthquakes taking place in unit time and physical volume. To describe the anisotropy of microdamage of the crust block, we use the damage tensor that is expressed in the fissure density. By means of the transformation from the focal coordinate system to the observation system, we obtained the external normal vector of the focal fault plane expressed in its observation system and obtained the macrodamage degree of the researched block, which is calculated in dyadic. This provides a new analysis method for recognizing the underground damage status and the stress status.展开更多
Background:Anoplophora glabripennis(Motschulsky),commonly known as Asian longhorned beetle(ALB),is a wood-boring insect that can cause lethal infestation to multiple borer leaf trees.In Gansu Province,northwest China,...Background:Anoplophora glabripennis(Motschulsky),commonly known as Asian longhorned beetle(ALB),is a wood-boring insect that can cause lethal infestation to multiple borer leaf trees.In Gansu Province,northwest China,ALB has caused a large number of deaths of a local tree species Populus gansuensis.The damaged area belongs to Gobi desert where every single tree is artificially planted and is extremely difficult to cultivate.Therefore,the monitoring of the ALB infestation at the individual tree level in the landscape is necessary.Moreover,the determination of an abnormal phenotype that can be obtained directly from remote-sensing images to predict the damage degree can greatly reduce the cost of field investigation and management.Methods:Multispectral WorldView-2(WV-2)images and 5 tree physiological factors were collected as experimental materials.One-way ANOVA of the tree’s physiological factors helped in determining the phenotype to predict damage degrees.The original bands of WV-2 and derived vegetation indices were used as reference data to construct the dataset of a prediction model.Variance inflation factor and stepwise regression analyses were used to eliminate collinearity and redundancy.Finally,three machine learning algorithms,i.e.,Random Forest(RF),Support Vector Machine(SVM),Classification And Regression Tree(CART),were applied and compared to find the best classifier for predicting the damage stage of individual P.gansuensis.Results:The confusion matrix of RF achieved the highest overall classification accuracy(86.2%)and the highest Kappa index value(0.804),indicating the potential of using WV-2 imaging to accurately detect damage stages of individual trees.In addition,the canopy color was found to be positively correlated with P.gansuensis’damage stages.Conclusions:A novel method was developed by combining WV-2 and tree physiological index for semi-automatic classification of three damage stages of P.gansuensis infested with ALB.The canopy color was determined as an abnormal phenotype that could be directly assessed using remote-sensing images at the tree level to predict the damage degree.These tools are highly applicable for driving quick and effective measures to reduce damage to pure poplar forests in Gansu Province,China.展开更多
After the outbreak of Dendrolimus superans Buter in 2002, many insect borers quickly invaded larch （Larix gmelinii Rupr.） forests in the Aershan of Inner Mongolia. Methods involved included setting sample plots, col...After the outbreak of Dendrolimus superans Buter in 2002, many insect borers quickly invaded larch （Larix gmelinii Rupr.） forests in the Aershan of Inner Mongolia. Methods involved included setting sample plots, collecting adults in iron traps and measuring areas of galleries to study the invasive sequence, their ecological niche and the extent of the different effects by the main insect borers to their hosts. The results showed that the damage of D. superans weakened L. gmelinii, first Ips subelongatus Motschulsky invaded, followed by Acanthocinus carinulatus Gebler, Monochamus urussovi Fisher and M. sutor L. After the outbreak of D. superans, the average density of longhorn beetles per L. gmelinii tree increased. The ecological niche of Ips subelongatus stretches almost from the base to the top of the trunk. The number of insects in older stands of L. gmelinii is larger than those in middle aged stands. They do not damage healthy trees of L. gmelinii. The ecological niche of A. carinulatus is higher in dead L. gmelinii trees than in weak ones. The degree of damage is directly proportional with age and depth of bark. M. urussovi mainly damages trunks below 4 m in weak trees; in dead trees they can do damage up to 6 m in height. M. sutor mainly damages trunks below 5 m in weak L. gmelinii trees; in dead trees they cause damage up to 7 m. Again, the degree of damage is directly proportional with age. None of the three species of longhorn beetles damage healthy L. gmelinii and younger trees. Among the main insect borers, the degree of damage caused by I. subelongatus is more serious than that of other insects.展开更多
In this paper, based on consultation to tens of bridge exberts and a vast amount of investigation and study, experts knowledge on bridge assessment has been sorted out. A new concept Damage Value (DV) is put forward t...In this paper, based on consultation to tens of bridge exberts and a vast amount of investigation and study, experts knowledge on bridge assessment has been sorted out. A new concept Damage Value (DV) is put forward to measure bridge damage, and Fuzzy theory is used to create comprehensive Fuzzy system to assess bridge service property. The setup of an experts system for bridge assessment is tried as well. This system is programmed in Turbo C 2.0 and has been run successfully at IBM-PC (AT/XT).展开更多
This study proposed a damage identification method compared with the existing ones,based on relative curvature difference and frequency perturbation theory,showing sensitivity to local damage by changes in the curvatu...This study proposed a damage identification method compared with the existing ones,based on relative curvature difference and frequency perturbation theory,showing sensitivity to local damage by changes in the curvature mode and high recognition accuracy of frequencies.Considering the relative curvature difference as a damage index,numerical simulation is used for a simply supported beam under single and multiple damage conditions for different damage degrees.The damage is located according to the curvature mode curves,and the damage degree is qualitatively determined.Based on the perturbation theory,the damage equations are established by the changes between frequencies before and after damage,and the damage localization and degree are verified and determined.Effectiveness of the proposed method for identifying damage at different conditions is numerically investigated.This method potentially promotes the development of damage identification of beam structures.展开更多
For the first time, degree of damage of the disease Botrytis cinerea Pers. is founded in decorative colors in the Tashkent region. Chemical preparations are the most effective methods of struggle in the fight against ...For the first time, degree of damage of the disease Botrytis cinerea Pers. is founded in decorative colors in the Tashkent region. Chemical preparations are the most effective methods of struggle in the fight against diseases of ornamental crops.展开更多
In this article, the fragility of reinforced concrete and steel structures in Bucharest, a city of high seismic hazard, designed using the recent building codes in Romania, is assessed. A total of 24 reinforced concre...In this article, the fragility of reinforced concrete and steel structures in Bucharest, a city of high seismic hazard, designed using the recent building codes in Romania, is assessed. A total of 24 reinforced concrete and steel structures with heights varying from five stories to 13 stories were analyzed. Their seismic fragility was evaluated using two procedures from the literature. In the first procedure(SPO2 FRAG), the fragility was derived based on the pushover curves using the SPO2 IDA algorithm, while in the second procedure(FRACAS), the fragility was derived from nonlinear time-history analyses. The analyzed structures were designed for three levels of peak ground accelerations, corresponding to mean return periods of 100,225, and 475 years. Subsequently, the damage assessment of the analyzed structures was performed using ground motions generated from a Monte-Carlo simulated earthquake catalogue for the Vrancea intermediate-depth seismic source. The damage degrees that were estimated using the SPO2 FRAG approach are higher than those estimated using the FRACAS approach. The life-cycle analysis of the structures shows that a further increase of the design peak ground acceleration for Bucharest is feasible from an economic point of view using the SPO2 FRAG results.However, based on the FRACAS results, the opposite conclusion can be drawn. Finally, generic lognormal fragility functions are proposed as a function of building height and structural system.展开更多
A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on...A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses.Five T-joints were physically tested:one bare joint to obtain the peak load and corresponding displacement(D1m),two reinforced joints to provide a reference,and two pre-damaged then retrofitted joints to serve as the primary research objects.The ratio of the pre-loaded specimen chord displacement to the value of D1m was considered to be the degree of damage of the two retrofitted joints,and was set to 0.80 and 1.20.The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06%over the corresponding unreinforced specimens.However,the capacity of the retrofitted specimen was 2.51%–22.77%lesser compared with that of the directly reinforced specimens.Next,111 numerical analysis models(0.63≤b≤0.76,9.70≤g≤16.92)were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage.The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping,and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters.Finally,reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results.The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.展开更多
基金Supported by Special Research Project of Shaanxi Department of Education(14JK1822)Doctoral Scientific Research Program of Yan'an University(YDBK2013-3)+1 种基金Science and Technology Research Program of Yan'an City(2014CGZH-09)Science and Technology Project of Shaanxi Tobacco Company(YAYC-2014-FW-01)
文摘The host plants of 8emisia tabaci （Gennadius） in Shaanxi were investigated, and its damage degree was evaluated by hazard index in 2013 and 2014. There were 73 species （variants） of host plants of B. tabaci belonging to 28 families, mainly concentrated in Cueurbitaceae, Crueiferae, Solanaceae, Laguminosae md Malvaceae. There were seven species of vegetables that suffered the damage of grade 4. B. tabaci was more serious in southern Shaanxi and lighter in northern Shaanxi. According to the distribution of host plants, the occurrence status of B. tabaci in Shamvd Province was analyzed and its development tendency was oredicted.
基金Supported by Science and Technology Research and Development Project of Chengde City(201701A152)
文摘The species of main diseases and pests in foxtail millet and their damage status were investigated in 15 survey points in Longhua, Weichang, Chengde, Fengning and Luanping counties, Chengde City from 2015 to 2017. It was preliminarily cleared that there were 11 species of main diseases and 8 species of pests in continuous cropping millet field. The diseases damaged severely were millet downy mildew and kernel smut, and pests were yellow-legged lema, millet shoot fly and soil insects. The results provided a scientific basis for green control of millet pests and diseases and safe production in Chengde area.
基金Funded by the National Natural Science Foundation of China(Nos.52068035,52078372,and 52478272)。
文摘This study aimed to investigate the performance evolution characteristics of concrete under permafrost ambient temperatures and to explore methods to mitigate the thermal perturbation by concrete on the permafrost environment.A program was designed to investigate the properties of various concretes at three curing conditions.The compressive strength development pattern of each group was evaluated and the concrete's performance was characterized by compressive strength damage degree,hydration temperature and SEM analysis in a low temperature environment.The experimental results show that the incorporation of fly ash alone or incombination with other admixtures in concrete under low-temperature curing does not deteriorate its microstructure,and at the same time,it can slow down the hydration rate of cement and significantly reduce the exothermic heat of hydration of concrete.These findings are expected to provide valuable references for the proportioning design of concrete in permafrost environments.
基金Project(41672298)supported by the National Natural Science Foundation of China。
文摘Low pore sedimentary rocks(from Guangxi, China) were subjected to uniaxial compression loading experiment under different initial stresses. The rock samples were investigated by nuclear magnetic resonance before and after the loading. The relationships between the mesoscopic rock damage and macroscopic mechanical parameters were established, and the initial damage stress of the low-porosity sedimentary rock was determined. The results showed that this type of rock has the initial stress of damage. When the initial loading stress is lower than the initial stress of damage, the T2 spectrum area of the rock sample gradually decreases, and the primary pores of the rock are further closed under the stress. The range of the initial stress of damage for this type of rock is 8-16 MPa. When the loading stress exceeds the initial stress of damage, the T2 spectrum area gradually increases, indicating that the porosity of the rock increases and microscopic damage of the rock appears. The rock damage degree is defined, and the nonlinear function between the rock damage degree and the initial loading stress is established.
基金Project (50490272) supported by the National Natural Science Foundation of ChinaProject(040109) supported by the Doctor Degree Paper Innovation Engineering of Central South University
文摘The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparatus. The blasting test was carried out for ten times at some tunnels of Changba Lead-Zinc Mine. The damage depth of surrounding rock caused by old blasting excavation （0.8-1.2 m） was confirmed. The relation between the cumulative damage degree and blast times was obtained. The results show that the sonic velocity decreases gradually with increasing blast times, hut the damage degree （D） increases. The damage cumulative law is non-linear. The damage degree caused by blast decreases with increasing distance, and damage effects become indistinct. The blasting damage of rock mass is anisotropic. The damage degree of rock mass within charging range is maximal. And the more the charge is, the more severe the damage degree of rock mass is. The test results provide references for researches of mechanical parameters of rock mass and dynamic stability analysis of underground chambers.
基金supported by the National Public Welfare Industry(Agriculture)Scientific Research of China(201403031)the National Key Research and Development Program of China(2017YFD0201807)the Project of Agricultural Science and Technology Innovation Transformation in Shaanxi Province,China
文摘To clarify association between armyworm（Mythimna separata） damage level and the corn growth and weed occurrence, we investigated corn plant height, stem diameter and vigor as well as weed coverage and biomass. The investigations were conducted at three locations of Shaanxi Province, China which were suffered seriously from armyworm. Significant correlations were found between the parameters analyzed. At stunted corn growth and presence of plenty of weeds, the armyworm damage tended to be heavy; oppositely, when corn grew well and weed density were low, armyworm harm was the minimal. Therefore, corn growing status and weed density can significantly affect armyworm damage level. Our results imply that promoting corn growth and timely removal of weeds are conducive to reducing armyworm occurrence.
基金The National Natural Science Foundation of China(No.61973172,61973175)the Key Technologies R&D Program of Tianjin(No.19JCZDJC32800).
文摘An equivalent sliding mode fault-tolerant control method with continuous switching is proposed for vertical tail damage.First,the nonlinear damage model of aircraft and the estimation of stability and control derivatives are introduced.Secondly,the linear sliding surface and the equivalent sliding mode controller are constructed,and the sufficient conditions for the stability of the damaged aircraft motion model are given by using the Lyapunov technique.The damage-tolerant controller is designed based on an adaptive sliding mode control for analyzing damaged aircraft systems.Furthermore,the hyperbolic tangent function is utilized to replace the symbolic function in the controller.The feasibility of the hyperbolic tangent function as the switching function is analyzed theoretically.Finally,the Boeing-747100/200 model is taken as an example to demonstrate the efficiency of theoretical results by recognizing the structural fault of aircraft.Numerical results show that the control law has a positive impact on the performance of the closed-loop system,and it also has a better fault tolerance and robustness towards external disturbance compared with traditional methods of damaged aircraft stabilization control.
基金This research was supported by the Joint EarthquakeScience Foundation,CEA(105004) the 10th Five-Year Program of Research on Short-term Strong EarthquakeForecast and Disaster Relieving Technology (2004BA601B01-02) .
文摘In this paper, we researched the regional seismic status by using theories of the Damage Mechanics. The macroscopic damage status of the earth crust block, which is caused by earthquake fracture, is described with several concepts—the damage degree, the damage rate and the strain rate. In the earthquake process, the average strain rate of the studied block is equal to the sum of all seismic moment tensors of the earthquakes taking place in unit time and physical volume. To describe the anisotropy of microdamage of the crust block, we use the damage tensor that is expressed in the fissure density. By means of the transformation from the focal coordinate system to the observation system, we obtained the external normal vector of the focal fault plane expressed in its observation system and obtained the macrodamage degree of the researched block, which is calculated in dyadic. This provides a new analysis method for recognizing the underground damage status and the stress status.
基金supported by National Key Research&Development Program of China“Research on key technologies for prevention and control of major disasters in plantation”(Grant No.2018YFD0600200)Beijing’s Science and Technology Planning Project“Key technologies for prevention and control of major pests in Beijing ecological public welfare forests”(Grant Nos.Z191100008519004 and Z201100008020001).
文摘Background:Anoplophora glabripennis(Motschulsky),commonly known as Asian longhorned beetle(ALB),is a wood-boring insect that can cause lethal infestation to multiple borer leaf trees.In Gansu Province,northwest China,ALB has caused a large number of deaths of a local tree species Populus gansuensis.The damaged area belongs to Gobi desert where every single tree is artificially planted and is extremely difficult to cultivate.Therefore,the monitoring of the ALB infestation at the individual tree level in the landscape is necessary.Moreover,the determination of an abnormal phenotype that can be obtained directly from remote-sensing images to predict the damage degree can greatly reduce the cost of field investigation and management.Methods:Multispectral WorldView-2(WV-2)images and 5 tree physiological factors were collected as experimental materials.One-way ANOVA of the tree’s physiological factors helped in determining the phenotype to predict damage degrees.The original bands of WV-2 and derived vegetation indices were used as reference data to construct the dataset of a prediction model.Variance inflation factor and stepwise regression analyses were used to eliminate collinearity and redundancy.Finally,three machine learning algorithms,i.e.,Random Forest(RF),Support Vector Machine(SVM),Classification And Regression Tree(CART),were applied and compared to find the best classifier for predicting the damage stage of individual P.gansuensis.Results:The confusion matrix of RF achieved the highest overall classification accuracy(86.2%)and the highest Kappa index value(0.804),indicating the potential of using WV-2 imaging to accurately detect damage stages of individual trees.In addition,the canopy color was found to be positively correlated with P.gansuensis’damage stages.Conclusions:A novel method was developed by combining WV-2 and tree physiological index for semi-automatic classification of three damage stages of P.gansuensis infested with ALB.The canopy color was determined as an abnormal phenotype that could be directly assessed using remote-sensing images at the tree level to predict the damage degree.These tools are highly applicable for driving quick and effective measures to reduce damage to pure poplar forests in Gansu Province,China.
文摘After the outbreak of Dendrolimus superans Buter in 2002, many insect borers quickly invaded larch （Larix gmelinii Rupr.） forests in the Aershan of Inner Mongolia. Methods involved included setting sample plots, collecting adults in iron traps and measuring areas of galleries to study the invasive sequence, their ecological niche and the extent of the different effects by the main insect borers to their hosts. The results showed that the damage of D. superans weakened L. gmelinii, first Ips subelongatus Motschulsky invaded, followed by Acanthocinus carinulatus Gebler, Monochamus urussovi Fisher and M. sutor L. After the outbreak of D. superans, the average density of longhorn beetles per L. gmelinii tree increased. The ecological niche of Ips subelongatus stretches almost from the base to the top of the trunk. The number of insects in older stands of L. gmelinii is larger than those in middle aged stands. They do not damage healthy trees of L. gmelinii. The ecological niche of A. carinulatus is higher in dead L. gmelinii trees than in weak ones. The degree of damage is directly proportional with age and depth of bark. M. urussovi mainly damages trunks below 4 m in weak trees; in dead trees they can do damage up to 6 m in height. M. sutor mainly damages trunks below 5 m in weak L. gmelinii trees; in dead trees they cause damage up to 7 m. Again, the degree of damage is directly proportional with age. None of the three species of longhorn beetles damage healthy L. gmelinii and younger trees. Among the main insect borers, the degree of damage caused by I. subelongatus is more serious than that of other insects.
文摘In this paper, based on consultation to tens of bridge exberts and a vast amount of investigation and study, experts knowledge on bridge assessment has been sorted out. A new concept Damage Value (DV) is put forward to measure bridge damage, and Fuzzy theory is used to create comprehensive Fuzzy system to assess bridge service property. The setup of an experts system for bridge assessment is tried as well. This system is programmed in Turbo C 2.0 and has been run successfully at IBM-PC (AT/XT).
基金This study is supported by the National Natural Science Foundation of China under Grant No.51278420the Natural Science Foundation of Shaanxi Province under Grant No.2017JM5021.
文摘This study proposed a damage identification method compared with the existing ones,based on relative curvature difference and frequency perturbation theory,showing sensitivity to local damage by changes in the curvature mode and high recognition accuracy of frequencies.Considering the relative curvature difference as a damage index,numerical simulation is used for a simply supported beam under single and multiple damage conditions for different damage degrees.The damage is located according to the curvature mode curves,and the damage degree is qualitatively determined.Based on the perturbation theory,the damage equations are established by the changes between frequencies before and after damage,and the damage localization and degree are verified and determined.Effectiveness of the proposed method for identifying damage at different conditions is numerically investigated.This method potentially promotes the development of damage identification of beam structures.
文摘For the first time, degree of damage of the disease Botrytis cinerea Pers. is founded in decorative colors in the Tashkent region. Chemical preparations are the most effective methods of struggle in the fight against diseases of ornamental crops.
文摘In this article, the fragility of reinforced concrete and steel structures in Bucharest, a city of high seismic hazard, designed using the recent building codes in Romania, is assessed. A total of 24 reinforced concrete and steel structures with heights varying from five stories to 13 stories were analyzed. Their seismic fragility was evaluated using two procedures from the literature. In the first procedure(SPO2 FRAG), the fragility was derived based on the pushover curves using the SPO2 IDA algorithm, while in the second procedure(FRACAS), the fragility was derived from nonlinear time-history analyses. The analyzed structures were designed for three levels of peak ground accelerations, corresponding to mean return periods of 100,225, and 475 years. Subsequently, the damage assessment of the analyzed structures was performed using ground motions generated from a Monte-Carlo simulated earthquake catalogue for the Vrancea intermediate-depth seismic source. The damage degrees that were estimated using the SPO2 FRAG approach are higher than those estimated using the FRACAS approach. The life-cycle analysis of the structures shows that a further increase of the design peak ground acceleration for Bucharest is feasible from an economic point of view using the SPO2 FRAG results.However, based on the FRACAS results, the opposite conclusion can be drawn. Finally, generic lognormal fragility functions are proposed as a function of building height and structural system.
基金This research work was supported and funded by Shandong Provincial Science and Technology Plan Project(No.J13LG05).
文摘A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses.Five T-joints were physically tested:one bare joint to obtain the peak load and corresponding displacement(D1m),two reinforced joints to provide a reference,and two pre-damaged then retrofitted joints to serve as the primary research objects.The ratio of the pre-loaded specimen chord displacement to the value of D1m was considered to be the degree of damage of the two retrofitted joints,and was set to 0.80 and 1.20.The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06%over the corresponding unreinforced specimens.However,the capacity of the retrofitted specimen was 2.51%–22.77%lesser compared with that of the directly reinforced specimens.Next,111 numerical analysis models(0.63≤b≤0.76,9.70≤g≤16.92)were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage.The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping,and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters.Finally,reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results.The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.
