Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly devel...Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly developed and used in recent years,particularly in the construction industry.This paper presents an analytical and numerical study of assembled CFS two single channel-shaped columns with different slenderness and configurations(backto-back,face-to-face,and box).These columns were joined by double-row rivets for the back-to-back and box configurations,whereas they were welded together for the face-to-face design.The built-up columns were filled with ordinary concrete of good strength.Finite element models were applied,using ABAQUS software,to assess mechanical performance and study the influence of assembly techniques on the behavior of cold-formed columns under axial compression.Analytical approaches based on Eurocode 3 and Eurocode 4 recommendations for un-filled and concrete-filled columns respectively were followed for the numerical analysis,and concrete confinement effects were also considered per American Concrete Institute(ACI)standards for face-to-face and box configurations.The obtained results indicated a good correlation between the numerical results and the proposed analytical methodology which did not exceed 8%.The failure modes showed that the columns failed due to instabilities such as local and global buckling.展开更多
An experimental program was initiated to investigate the seismic performance of built-up laced steel brace members. Quasi-static testing of twelve typical steel built-up laced member （BLM） specimens was conducted. T...An experimental program was initiated to investigate the seismic performance of built-up laced steel brace members. Quasi-static testing of twelve typical steel built-up laced member （BLM） specimens was conducted. These were designed to span a range of parameters typically encountered for such members based on findings from a survey of commonly used shapes and details that have been historically used. The specimens were subdivided into groups of three different cross-sectional shapes, namely built-up I-shape section, and built-up box shapes buckling about the x or the y axis. Within each group, global and local buckling slenderness ratios had either kl/r values of 60 or 120, and b/t ratios of 8 or 16. The specific inelastic cyclic behavior germane to each specimen, and general observations on overall member hysteretic behavior as a function of the considered parameters, are reported. A companion paper （Lee and Bruneau 2008） investigates this observed response against predictions from analytical models, and behavior in the perspective of system performance.展开更多
Since the reform and opening-up program started in 1978,the level of urbanization has increased rapidly in China.Rapid urban expansion and restructuring have had significant impacts on the ecological environment espec...Since the reform and opening-up program started in 1978,the level of urbanization has increased rapidly in China.Rapid urban expansion and restructuring have had significant impacts on the ecological environment especially within built-up areas.In this study,ArcGIS 10,ENVI 4.5,and Visual FoxPro 6.0 were used to analyze the human impacts on vegetation in the built-up areas of 656Chinese cities from 1992 to 2010.Firstly,an existing algorithm was refined to extract the boundaries of the built-up areas based on the Defense Meteorological Satellite Program Operational Linescan System(DMSP_OLS)nighttime light data.This improved algorithm has the advantages of high accuracy and speed.Secondly,a mathematical model(Human impacts(HI))was constructed to measure the impacts of human factors on vegetation during rapid urbanization based on Advanced Very High Resolution Radiometer(AVHRR)Normalized Difference Vegetation Index(NDVI)and Moderate Resolution Imaging Spectroradiometer(MODIS)NDVI.HI values greater than zero indicate relatively beneficial effects while values less than zero indicate proportionally adverse effects.The results were analyzed from four aspects:the size of cities(metropolises,large cities,medium-sized cities,and small cities),large regions(the eastern,central,western,and northeastern China),administrative divisions of China(provinces,autonomous regions,and municipalities)and vegetation zones(humid and semi-humid forest zone,semi-arid steppe zone,and arid desert zone).Finally,we discussed how human factors impacted on vegetation changes in the built-up areas.We found that urban planning policies and developmental stages impacted on vegetation changes in the built-up areas.The negative human impacts followed an inverted′U′shape,first rising and then falling with increase of urban scales.China′s national policies,social and economic development affected vegetation changes in the built-up areas.The findings can provide a scientific basis for municipal planning departments,a decision-making reference for government,and scientific guidance for sustainable development in China.展开更多
The test results described in Part 1 of this paper （Lee and Bruneau, 2008） on twelve steel built-up laced members （BLMs） subjected to quasi-static loading are analyzed to provide better knowledge on their seismic ...The test results described in Part 1 of this paper （Lee and Bruneau, 2008） on twelve steel built-up laced members （BLMs） subjected to quasi-static loading are analyzed to provide better knowledge on their seismic behavior. Strength capacity of the BLM specimens is correlated with the strength predicted by the AISC LRFD Specifications. Assessments of hysteretic properties such as ductility capacity, energy dissipation capacity, and strength degradation after buckling of the specimen are performed. The compressive strength of BLMs is found to be relatively well predicted by the AISC LRFD Specifications. BLMs with smaller kl/r were ductile but failed to reach the target ductility of 3.0 before starting to fracture, while those with larger kl/r could meet the ductility demand in most cases. The normalized energy dissipation ratio, EC/ET and the normalized compressive strength degradation, Cr″/Cr of BLMs typically decrease as normalized displacements δ/δb,exp increase, and the ratios for specimens with larger kl/r dropped more rapidly than for specimens with smaller kl/r; similar trends were observed for the monolithic braces. The BLMs with a smaller slenderness ratio, kl/r, and width-to-thickness ratio, b/t, experienced a larger number of inelastic cycles than those with larger ratios.展开更多
Non-linear finite element models accounting for large displacements have been used to investigate the behavior of steel built-up shear links that had previously been tested using large-scale experiments. The links wer...Non-linear finite element models accounting for large displacements have been used to investigate the behavior of steel built-up shear links that had previously been tested using large-scale experiments. The links were designed using steel grades with yield points ranging from high to low strengths. The objectives of the numerical analyses were to further investigate the non-linear behavior and to correlate the numerical results with experimental observations. Elasto-plastic as well as cyclic stress-strain material properties were incorporated to study the influence of material behavior on the overall shear link response. Non-linear monotonie analyses of the shear links incorporating the cyclic stress-strain steel properties resulted in similar trends in the response as the backbone curves recorded from the physical experiments. The numerical models of built-up shear links utilizing structural grade steels closely correlated to the experimentally recorded shear strength. Models utilizing low yield point steels overestimated the shear strength, which was caused by the characteristics of cyclic behavior of those steels. The detailed numerical models also allowed for investigation of the plastic strain demands on the different components of the link. It was shown that finite element models combined with appropriate stress-strain relationship may be used with confidence to check the design of shear links of different steel grades and sectional geometries.展开更多
Municipal district adjustment and built-up area expansion are two main forms of urban spatial expansion. Using geometric methods, this study constructed a space-time path method to characterize the space-time relation...Municipal district adjustment and built-up area expansion are two main forms of urban spatial expansion. Using geometric methods, this study constructed a space-time path method to characterize the space-time relationship between municipal district adjustment and built-up area expansion, and drew the space-time path sets of major prefecture level cities from 2000 to 2010 by constructing a coordinate system of the standardized built-up areas and municipal district areas. This divided them into four quadrants, namely, H-H, L-H, L-L, and H-L, based on the relative mean value to evaluate overall and individual stability by three indexes of the trajectory vectors, namely, direction, length, and slope. Results provide the following conclusions. 1) Municipal district adjustment is an effective spatial expansion way for city-scale promotion in China. Since 2000, municipal district adjustments have been mainly distributed in the eastern coastal regions and mid-western capital cities along with their surrounding cities. 2) Municipal district adjustment affects the scale and status of a city in China. Many cities that have expanded municipal districts behave stably and cross quadrants. 3) Great majority second-tier cities have effectively promoted their scale and status through municipal district adjustment. The municipal district adjustment of medium and small cities in the mid-west area is relatively advanced compared with city development. 4) Municipal district adjustment with minimal magnitude is severely restricted from upgrading the scale and status of a city. The transformation from entirely incorporated counties or cities to municipal districts should be the mainstream in future municipal district adjustment.展开更多
The advantage of built-up sleeved backup roll was described. Based on the stress distribution analysis and simulation for the built-up sleeved backup roll by using finite element method, the effects of roll sleeve thi...The advantage of built-up sleeved backup roll was described. Based on the stress distribution analysis and simulation for the built-up sleeved backup roll by using finite element method, the effects of roll sleeve thickness and shrink range on the stress-strain field were studied. Finally, based on the methodology and strategy of the fatigue analysis, fatigue life of backup roll was estimated by using the stress-strain data obtained through finite element simulation. The results show that roll sleeve thickness and shrink range have a great influence on sleeve stress distribution of built-up sleeved roll. Under the circumstance of ensuring transferring enough torque, the shrink range should be kept small. However, thicker roll sleeve has longer roll service life when the shrink range is constant.展开更多
As an important goal of urban design research,the evaluation of urban spatial vitality has been widely concerned.Taking Shenzhen as an example,the urban built-up area of Shenzhen was identifi ed using improved DENsi-G...As an important goal of urban design research,the evaluation of urban spatial vitality has been widely concerned.Taking Shenzhen as an example,the urban built-up area of Shenzhen was identifi ed using improved DENsi-Graph analysis,from the perspective of quantifi cation of urban spatial morphological features.The accessibility of urban streets,degree of construction and architectural form,and degree of functional mixing were quantitatively analyzed through space syntax,space matrix and mixeduse index(MXI),and the spatial vitality of urban built-up area was evaluated.Research results demonstrated that the improved Densi-Graph analysis could better identify the built-up area of Shenzhen,and the overall classifi cation accuracy was 0.810.The analysis results of spatial vitality showed that the urban spatial vitality in Shenzhen urban built-up area was well created.The street accessibility of Shenzhen generally hindered the creation of urban vitality;the spatial matrix value in the north of Shenzhen urban built-up area was lower;and the MXI of most areas within the study area was above the medium.展开更多
Designing “liveable” cities as climate change effects are felt all over the world has become a priority to city authorities as ways are sought to reduce rising temperatures in urban areas. Urban Heat Island (UHI) ef...Designing “liveable” cities as climate change effects are felt all over the world has become a priority to city authorities as ways are sought to reduce rising temperatures in urban areas. Urban Heat Island (UHI) effect occurs when there is a difference in temperature between rural and urban areas. In urban areas, impervious surfaces absorb heat during the day and release it at night, making urban areas warmer compared to rural areas which cool faster at night. This Urban Heat Island effect is particularly noticeable at night. Noticeable negative effects of Urban Heat Islands include health problems, air pollution, water shortages and higher energy requirements. The main objective of this research paper was to analyze the spatial and temporal relationship between Land Surface Temperature (LST) and Normalized Density Vegetation Index (NDVI) and Built-Up Density Index (BDI) in Upper-Hill, Nairobi Kenya. The changes in land cover would be represented by analyzing the two indices NDVI and BDI. Results showed the greatest increase in temperature within Upper-Hill of up to 3.96°C between the years 2015 and 2017. There was also an increase in impervious surfaces as indicated by NDVI and BDI within Upper-Hill and its surroundings. The linear regression results showed a negative correlation between LST and NDVI and a positive correlation with BDI, which is a better predictor of Land Surface Temperature than NDVI. Data sets were analyzed from Landsat imagery for the periods 1987, 2002, 2015 and 2017 to determine changes in land surface temperatures over a 30 year period and it’s relation to land cover changes using indices. Visual comparisons between Temperature differences between the years revealed that temperatures decreased around the urban areas. Minimum and maximum temperatures showed an increase of 1.6°C and 3.65°C respectively between 1987 and 2017. The comparisons between LST, NDVI and BDI show the results to be significantly different. The use of NDVI and BDI to study changes in land cover due to urbanization, reduces the time taken to manually classify moderate resolution satellite imagery.展开更多
The built-up effect of inorganic compounds containing more active metal ions, such as Ca^2＋ , Al^3＋ , Cu^2＋ , and Zn^2＋ , as additives adding to phosphorus-containing flame retarding systems in suppression of smok...The built-up effect of inorganic compounds containing more active metal ions, such as Ca^2＋ , Al^3＋ , Cu^2＋ , and Zn^2＋ , as additives adding to phosphorus-containing flame retarding systems in suppression of smoke was studied. The data presented herein suggested that the amount of smoke in the burning process can be better suppressed after the cotton fabric finishing with built-up system was burnt. Some general principles were identified, and the likely causes of the observed effects were analyzed according to test data.展开更多
The flame retardants containing organophosphorus compounds have extensively been used in the flame retarding of polymer materials. Among others, dimethyl methyl phosphate (DMMP) was applied in flame retarding of polyu...The flame retardants containing organophosphorus compounds have extensively been used in the flame retarding of polymer materials. Among others, dimethyl methyl phosphate (DMMP) was applied in flame retarding of polyurethane owing to its so much merit. However, the water-soluble property of DMMP restricted its application in textile fabric. The flame retarding system containing DMMP will be microencapsulated to form a novel flame retardant that could be used in textiles. We have studied the built–up effect of DMMP with some inorganic compounds to improve the afterflame and afterglow suppression in the flame retarding system. The experimental data indicated that inorganic compounds containing various non-metal elements P, N, B and metal ions Mg2+, Al3+, Ca2+, Zn2+, Cu2+, Mn4+ could be applied in flame retarding systems as additives to effectively suppress afterflame or afterglow.展开更多
This paper is aimed at studying the environmental degradation of densely built-up areas in the process of urbanization in Qiina. In consideration of the severe environmental conditions of die densely built-up afeas, s...This paper is aimed at studying the environmental degradation of densely built-up areas in the process of urbanization in Qiina. In consideration of the severe environmental conditions of die densely built-up afeas, such as the lack of green space and. open space, ecological disturbance in some areas, poor landscape quality, this paper focused on the ecological space optimization in the process of urban renewal Firstly, theories related to this field were analyzed, and a comprehensive ecological efficiency evaluation sjrstem was established based on disciplines such as urban ecology, landscape ecology, urban sociology, behavioral psychology, biology, urban planning and design. Secondly, this system was used to judge the ecological efficiency of typical blocks on GIS platform and to find out the key spatial nodes that need to be updated. Thirdly, in different cases, space optimization projects witii different theories were designed, and the spatial model of influence was used to comprehensively evaluate their ecological efficiency. Finally, the parameters under different conditions were corrected to get a systematic system for evaluating the green space system in densely built-up areas＊ Due to the lack of undetstanding of the ecological fonction of green space in the past, die environmental condition of densely built-up areas is not good. Therefore, the most important task of urban oigauic renewal is ecological restoiation. In this paper, die exploiation is based on the reservation for built-up afeas to avoid repeated reconstruction and interference. Authors of this paper tried to find out a way to rebuild green space system that performed more complex functions with limited spatial resources. The application of “micfo-ttansfotmation” of green space system in densely built-up areas turns out to improve the quality of landscape while reducing the construction costrds展开更多
This paper aimed at incorporating the precautionary principles into the planning and development of GSM （global system for mobile communications） masts within the built-up areas of Jimeta. Using GIS （geographic inf...This paper aimed at incorporating the precautionary principles into the planning and development of GSM （global system for mobile communications） masts within the built-up areas of Jimeta. Using GIS （geographic information system） analysis technique, the zone of precautionary principle was defined to 500 meters radius as the zone within which precautionary measures are exercised. The criteria for siting GSM base station are also equally identified. For instance, the presence of certain elements within the precautionary zone like schools, hospitals, residential density and overlap of RF （radio frequency） occurrences, may disqualify any mast location. Analysis of the land use within precautionary zone has shown various proportions of exposure to RF, whereas, only 3.39% of the masts are suitably located and 94.92% are not and therefore should be relocated. The study recommend measures for addressing physical development within precautionary areas, including land conversion and mast sharing to reduce potential harmful effects of RF emanating from GSM base stations.展开更多
Urban river riparian spaces and their natural systems are valuable to urban dwellers;but are increasingly affected and ruined by human activities and in particular, urbanization processes. In this research, land sat a...Urban river riparian spaces and their natural systems are valuable to urban dwellers;but are increasingly affected and ruined by human activities and in particular, urbanization processes. In this research, land sat and sentinel satellite imagery apt for change detection in vegetation cover, both landsat and sentinel imagery, covering the period between 1970 and 2021 in epochs of 1973, 1984, 1993, 2003, 2015 and 2021 years were used to establish the correlation between vegetation cover and built-up area along River Riara river reserve. The images were analysed to extract the built-up areas along the river reserve, including the buildings, and the rate of human settlements, which influenced vegetation cover. Normalized Difference Built-Up Index (NDBI) and Normalized Difference Vegetation Index (NDVI) were computed using the Short-Wave Infrared (SWIR) and the Near Infra-Red (NIR) bands to show the rate of change over the years. Results indicate NDVI values were high, compared to NDBI values along river Riara in the years 1973 and 1993 implying that there was more vegetation cover then. However, in the year 2021, the NDVI indicated the highest value at 0.88, with the complementary NDBI indicating the highest NDBI value at 0.47. This represents a significant increase in built-up areas since 2015 more than in previous epochs. Either, there was a significant increase in NDBI values, from 0.24 in 1993 to 0.47 in 2021. More so, the R-squared value at 0.80 informed 80% relationship between NDBI and NDVI values indicating a negative correlation.展开更多
The development of spatial interactions of land resources enhances virtual built-up land flow,which contributes to China's inter-regional trade inequality.Little is known about the degree of inequality among regio...The development of spatial interactions of land resources enhances virtual built-up land flow,which contributes to China's inter-regional trade inequality.Little is known about the degree of inequality among regions.This work seeks to estimate the degree of inter-regional trade inequality through environmental-economic benefits.We combined a multiregional input-output model at the city level with a new classification to calculate the virtual built-up land flow among cities and analyzed its implications for the regional economy and carbon balance.The results indicate that developed regions were the main beneficiaries of inter-regional trade,as reflected in land-use efficiency.China's economic hub has been progressively shifting southward,and the inter-regional trade inequality has continuously increased.The flow of virtual service industry land among developed regions rose,while underdeveloped regions remained suppliers of raw materials,further increasing inter-regional trade inequality.展开更多
There is growing demand to develop methods that integrate environmental and economic assessment of more sustainabletechnologies incorporated into commercial and residential buildings. In this paper, we incorporate eco...There is growing demand to develop methods that integrate environmental and economic assessment of more sustainabletechnologies incorporated into commercial and residential buildings. In this paper, we incorporate economic and energyuse data obtained for a green roof operating in the Midwest U.S. at latitude 42.94N into an integrated approach toestimate and compare the economic and environmental impacts of an intensive (or extensive) green roof with a built-uproof. The life cycle stages included in the analysis were material acquisition life stage which including the transportationeffects from material extraction through manufacturing to the fi nished products, and the use and maintenance life stageof the building. Environmental impact analysis indicates that green roof emits three times more environmental pollutantsthan built-up roofs in the material acquisition life stage. However, in the use and maintenance life stage, built-uproof emits three times more pollutants than a green roof. Overall, when emissions from both material acquisition lifestage and use and maintenance life stage are combined, the built-up roof contributes almost 3 times more (or 46% more)environmental emissions than green roof over a 45-year building life span. Furthermore the overall energy use, specifi -cally energy involved in the transportation from material extraction through to the fi nished product indicate that greenroof uses 2.5 times less energy than a built-up roof. An Economic Input and Output life cycle assessment (EIO-LCA) wasused to estimate the environmental impacts. The economic impact over an assumed 45-year building life was determinedusing life cycle costing, taking into account Net Present Value (NPV) calculations. Life cycle costing results indicate thatgreen roof costs approximately 50% less to maintain over a 45 year-building life than a built-up roof. A Monte Carlosimulation is also performed to account for any variability in cost data. In addition, the paper presents a method toquantify the value incentive that a decision-maker has in adopting green technology. Results from the study indicate thatwhen a green roof is compared to the Midwest regional NPV of a built-up roof, we fi nd that the cost to maintain it ($35per square foot) lies well below the average regional NPV of $59 per square foot of a built-up roof.展开更多
An improved methodology for the extraction and mapping of urban built-up areas at a global scale is presented in this study.The Moderate Resolution Imaging Spectroradiometer(MODIS)-based multispectral data were combin...An improved methodology for the extraction and mapping of urban built-up areas at a global scale is presented in this study.The Moderate Resolution Imaging Spectroradiometer(MODIS)-based multispectral data were combined with the Visible Infrared Imager Radiometer Suite(VIIRS)-based nighttime light(NTL)data for robust extraction and mapping of urban built-up areas.The MODIS-based newly proposed Urban Built-up Index(UBI)was combined with NTL data,and the resulting Enhanced UBI(EUBI)was used as a single master image for global extraction of urban built-up areas.Due to higher variation of the EUBI with respect to geographical regions,a region-specific threshold approach was used to extract urban built-up areas.This research provided 500-m-resolution global urban built-up map of year 2014.The resulted map was compared with three existing moderate-resolution global maps and one high-resolution map in the United States.The comparative analysis demonstrated finer details of the urban built-up cover estimated by the resultant map.展开更多
文摘Given their numerous functional and architectural benefits,such as improved bearing capacity and increased resistance to elastic instability modes,cold-formed steel(CFS)built-up sections have become increasingly developed and used in recent years,particularly in the construction industry.This paper presents an analytical and numerical study of assembled CFS two single channel-shaped columns with different slenderness and configurations(backto-back,face-to-face,and box).These columns were joined by double-row rivets for the back-to-back and box configurations,whereas they were welded together for the face-to-face design.The built-up columns were filled with ordinary concrete of good strength.Finite element models were applied,using ABAQUS software,to assess mechanical performance and study the influence of assembly techniques on the behavior of cold-formed columns under axial compression.Analytical approaches based on Eurocode 3 and Eurocode 4 recommendations for un-filled and concrete-filled columns respectively were followed for the numerical analysis,and concrete confinement effects were also considered per American Concrete Institute(ACI)standards for face-to-face and box configurations.The obtained results indicated a good correlation between the numerical results and the proposed analytical methodology which did not exceed 8%.The failure modes showed that the columns failed due to instabilities such as local and global buckling.
基金Federal Highway Administration Under Grant No. DTFH61-98-C-00094
文摘An experimental program was initiated to investigate the seismic performance of built-up laced steel brace members. Quasi-static testing of twelve typical steel built-up laced member （BLM） specimens was conducted. These were designed to span a range of parameters typically encountered for such members based on findings from a survey of commonly used shapes and details that have been historically used. The specimens were subdivided into groups of three different cross-sectional shapes, namely built-up I-shape section, and built-up box shapes buckling about the x or the y axis. Within each group, global and local buckling slenderness ratios had either kl/r values of 60 or 120, and b/t ratios of 8 or 16. The specific inelastic cyclic behavior germane to each specimen, and general observations on overall member hysteretic behavior as a function of the considered parameters, are reported. A companion paper （Lee and Bruneau 2008） investigates this observed response against predictions from analytical models, and behavior in the perspective of system performance.
基金Under the auspices of National Natural Science Foundation of China(No.41171143,40771064)Program for New Century Excellent Talents in University(No.NCET-07-0398)Fundamental Research Funds for the Central Universities(No.lzu-jbky-2012-k35)
文摘Since the reform and opening-up program started in 1978,the level of urbanization has increased rapidly in China.Rapid urban expansion and restructuring have had significant impacts on the ecological environment especially within built-up areas.In this study,ArcGIS 10,ENVI 4.5,and Visual FoxPro 6.0 were used to analyze the human impacts on vegetation in the built-up areas of 656Chinese cities from 1992 to 2010.Firstly,an existing algorithm was refined to extract the boundaries of the built-up areas based on the Defense Meteorological Satellite Program Operational Linescan System(DMSP_OLS)nighttime light data.This improved algorithm has the advantages of high accuracy and speed.Secondly,a mathematical model(Human impacts(HI))was constructed to measure the impacts of human factors on vegetation during rapid urbanization based on Advanced Very High Resolution Radiometer(AVHRR)Normalized Difference Vegetation Index(NDVI)and Moderate Resolution Imaging Spectroradiometer(MODIS)NDVI.HI values greater than zero indicate relatively beneficial effects while values less than zero indicate proportionally adverse effects.The results were analyzed from four aspects:the size of cities(metropolises,large cities,medium-sized cities,and small cities),large regions(the eastern,central,western,and northeastern China),administrative divisions of China(provinces,autonomous regions,and municipalities)and vegetation zones(humid and semi-humid forest zone,semi-arid steppe zone,and arid desert zone).Finally,we discussed how human factors impacted on vegetation changes in the built-up areas.We found that urban planning policies and developmental stages impacted on vegetation changes in the built-up areas.The negative human impacts followed an inverted′U′shape,first rising and then falling with increase of urban scales.China′s national policies,social and economic development affected vegetation changes in the built-up areas.The findings can provide a scientific basis for municipal planning departments,a decision-making reference for government,and scientific guidance for sustainable development in China.
基金Federal Highway Administration Under Grant No.DTFH61-98-C-00094
文摘The test results described in Part 1 of this paper （Lee and Bruneau, 2008） on twelve steel built-up laced members （BLMs） subjected to quasi-static loading are analyzed to provide better knowledge on their seismic behavior. Strength capacity of the BLM specimens is correlated with the strength predicted by the AISC LRFD Specifications. Assessments of hysteretic properties such as ductility capacity, energy dissipation capacity, and strength degradation after buckling of the specimen are performed. The compressive strength of BLMs is found to be relatively well predicted by the AISC LRFD Specifications. BLMs with smaller kl/r were ductile but failed to reach the target ductility of 3.0 before starting to fracture, while those with larger kl/r could meet the ductility demand in most cases. The normalized energy dissipation ratio, EC/ET and the normalized compressive strength degradation, Cr″/Cr of BLMs typically decrease as normalized displacements δ/δb,exp increase, and the ratios for specimens with larger kl/r dropped more rapidly than for specimens with smaller kl/r; similar trends were observed for the monolithic braces. The BLMs with a smaller slenderness ratio, kl/r, and width-to-thickness ratio, b/t, experienced a larger number of inelastic cycles than those with larger ratios.
基金the Federal Highway Administration through the Highway Project at the Multidisciplinary Center for Earthquake Engineering Researchthe toll bridge retrofit program of the California Department of Transportation through the University of California,San Diego
文摘Non-linear finite element models accounting for large displacements have been used to investigate the behavior of steel built-up shear links that had previously been tested using large-scale experiments. The links were designed using steel grades with yield points ranging from high to low strengths. The objectives of the numerical analyses were to further investigate the non-linear behavior and to correlate the numerical results with experimental observations. Elasto-plastic as well as cyclic stress-strain material properties were incorporated to study the influence of material behavior on the overall shear link response. Non-linear monotonie analyses of the shear links incorporating the cyclic stress-strain steel properties resulted in similar trends in the response as the backbone curves recorded from the physical experiments. The numerical models of built-up shear links utilizing structural grade steels closely correlated to the experimentally recorded shear strength. Models utilizing low yield point steels overestimated the shear strength, which was caused by the characteristics of cyclic behavior of those steels. The detailed numerical models also allowed for investigation of the plastic strain demands on the different components of the link. It was shown that finite element models combined with appropriate stress-strain relationship may be used with confidence to check the design of shear links of different steel grades and sectional geometries.
基金Under the auspices of National Natural Science Foundation of China(No.41371178,41471126)
文摘Municipal district adjustment and built-up area expansion are two main forms of urban spatial expansion. Using geometric methods, this study constructed a space-time path method to characterize the space-time relationship between municipal district adjustment and built-up area expansion, and drew the space-time path sets of major prefecture level cities from 2000 to 2010 by constructing a coordinate system of the standardized built-up areas and municipal district areas. This divided them into four quadrants, namely, H-H, L-H, L-L, and H-L, based on the relative mean value to evaluate overall and individual stability by three indexes of the trajectory vectors, namely, direction, length, and slope. Results provide the following conclusions. 1) Municipal district adjustment is an effective spatial expansion way for city-scale promotion in China. Since 2000, municipal district adjustments have been mainly distributed in the eastern coastal regions and mid-western capital cities along with their surrounding cities. 2) Municipal district adjustment affects the scale and status of a city in China. Many cities that have expanded municipal districts behave stably and cross quadrants. 3) Great majority second-tier cities have effectively promoted their scale and status through municipal district adjustment. The municipal district adjustment of medium and small cities in the mid-west area is relatively advanced compared with city development. 4) Municipal district adjustment with minimal magnitude is severely restricted from upgrading the scale and status of a city. The transformation from entirely incorporated counties or cities to municipal districts should be the mainstream in future municipal district adjustment.
基金Project(E2010001155) supported by the Natural Science Foundation of Hebei Province, China
文摘The advantage of built-up sleeved backup roll was described. Based on the stress distribution analysis and simulation for the built-up sleeved backup roll by using finite element method, the effects of roll sleeve thickness and shrink range on the stress-strain field were studied. Finally, based on the methodology and strategy of the fatigue analysis, fatigue life of backup roll was estimated by using the stress-strain data obtained through finite element simulation. The results show that roll sleeve thickness and shrink range have a great influence on sleeve stress distribution of built-up sleeved roll. Under the circumstance of ensuring transferring enough torque, the shrink range should be kept small. However, thicker roll sleeve has longer roll service life when the shrink range is constant.
基金National Natural Science Foundation of China(416711800).
文摘As an important goal of urban design research,the evaluation of urban spatial vitality has been widely concerned.Taking Shenzhen as an example,the urban built-up area of Shenzhen was identifi ed using improved DENsi-Graph analysis,from the perspective of quantifi cation of urban spatial morphological features.The accessibility of urban streets,degree of construction and architectural form,and degree of functional mixing were quantitatively analyzed through space syntax,space matrix and mixeduse index(MXI),and the spatial vitality of urban built-up area was evaluated.Research results demonstrated that the improved Densi-Graph analysis could better identify the built-up area of Shenzhen,and the overall classifi cation accuracy was 0.810.The analysis results of spatial vitality showed that the urban spatial vitality in Shenzhen urban built-up area was well created.The street accessibility of Shenzhen generally hindered the creation of urban vitality;the spatial matrix value in the north of Shenzhen urban built-up area was lower;and the MXI of most areas within the study area was above the medium.
文摘Designing “liveable” cities as climate change effects are felt all over the world has become a priority to city authorities as ways are sought to reduce rising temperatures in urban areas. Urban Heat Island (UHI) effect occurs when there is a difference in temperature between rural and urban areas. In urban areas, impervious surfaces absorb heat during the day and release it at night, making urban areas warmer compared to rural areas which cool faster at night. This Urban Heat Island effect is particularly noticeable at night. Noticeable negative effects of Urban Heat Islands include health problems, air pollution, water shortages and higher energy requirements. The main objective of this research paper was to analyze the spatial and temporal relationship between Land Surface Temperature (LST) and Normalized Density Vegetation Index (NDVI) and Built-Up Density Index (BDI) in Upper-Hill, Nairobi Kenya. The changes in land cover would be represented by analyzing the two indices NDVI and BDI. Results showed the greatest increase in temperature within Upper-Hill of up to 3.96°C between the years 2015 and 2017. There was also an increase in impervious surfaces as indicated by NDVI and BDI within Upper-Hill and its surroundings. The linear regression results showed a negative correlation between LST and NDVI and a positive correlation with BDI, which is a better predictor of Land Surface Temperature than NDVI. Data sets were analyzed from Landsat imagery for the periods 1987, 2002, 2015 and 2017 to determine changes in land surface temperatures over a 30 year period and it’s relation to land cover changes using indices. Visual comparisons between Temperature differences between the years revealed that temperatures decreased around the urban areas. Minimum and maximum temperatures showed an increase of 1.6°C and 3.65°C respectively between 1987 and 2017. The comparisons between LST, NDVI and BDI show the results to be significantly different. The use of NDVI and BDI to study changes in land cover due to urbanization, reduces the time taken to manually classify moderate resolution satellite imagery.
文摘The built-up effect of inorganic compounds containing more active metal ions, such as Ca^2＋ , Al^3＋ , Cu^2＋ , and Zn^2＋ , as additives adding to phosphorus-containing flame retarding systems in suppression of smoke was studied. The data presented herein suggested that the amount of smoke in the burning process can be better suppressed after the cotton fabric finishing with built-up system was burnt. Some general principles were identified, and the likely causes of the observed effects were analyzed according to test data.
文摘The flame retardants containing organophosphorus compounds have extensively been used in the flame retarding of polymer materials. Among others, dimethyl methyl phosphate (DMMP) was applied in flame retarding of polyurethane owing to its so much merit. However, the water-soluble property of DMMP restricted its application in textile fabric. The flame retarding system containing DMMP will be microencapsulated to form a novel flame retardant that could be used in textiles. We have studied the built–up effect of DMMP with some inorganic compounds to improve the afterflame and afterglow suppression in the flame retarding system. The experimental data indicated that inorganic compounds containing various non-metal elements P, N, B and metal ions Mg2+, Al3+, Ca2+, Zn2+, Cu2+, Mn4+ could be applied in flame retarding systems as additives to effectively suppress afterflame or afterglow.
基金Sponsored by National Natural Science Fund of China(51578454)
文摘This paper is aimed at studying the environmental degradation of densely built-up areas in the process of urbanization in Qiina. In consideration of the severe environmental conditions of die densely built-up afeas, such as the lack of green space and. open space, ecological disturbance in some areas, poor landscape quality, this paper focused on the ecological space optimization in the process of urban renewal Firstly, theories related to this field were analyzed, and a comprehensive ecological efficiency evaluation sjrstem was established based on disciplines such as urban ecology, landscape ecology, urban sociology, behavioral psychology, biology, urban planning and design. Secondly, this system was used to judge the ecological efficiency of typical blocks on GIS platform and to find out the key spatial nodes that need to be updated. Thirdly, in different cases, space optimization projects witii different theories were designed, and the spatial model of influence was used to comprehensively evaluate their ecological efficiency. Finally, the parameters under different conditions were corrected to get a systematic system for evaluating the green space system in densely built-up areas＊ Due to the lack of undetstanding of the ecological fonction of green space in the past, die environmental condition of densely built-up areas is not good. Therefore, the most important task of urban oigauic renewal is ecological restoiation. In this paper, die exploiation is based on the reservation for built-up afeas to avoid repeated reconstruction and interference. Authors of this paper tried to find out a way to rebuild green space system that performed more complex functions with limited spatial resources. The application of “micfo-ttansfotmation” of green space system in densely built-up areas turns out to improve the quality of landscape while reducing the construction costrds
文摘This paper aimed at incorporating the precautionary principles into the planning and development of GSM （global system for mobile communications） masts within the built-up areas of Jimeta. Using GIS （geographic information system） analysis technique, the zone of precautionary principle was defined to 500 meters radius as the zone within which precautionary measures are exercised. The criteria for siting GSM base station are also equally identified. For instance, the presence of certain elements within the precautionary zone like schools, hospitals, residential density and overlap of RF （radio frequency） occurrences, may disqualify any mast location. Analysis of the land use within precautionary zone has shown various proportions of exposure to RF, whereas, only 3.39% of the masts are suitably located and 94.92% are not and therefore should be relocated. The study recommend measures for addressing physical development within precautionary areas, including land conversion and mast sharing to reduce potential harmful effects of RF emanating from GSM base stations.
文摘Urban river riparian spaces and their natural systems are valuable to urban dwellers;but are increasingly affected and ruined by human activities and in particular, urbanization processes. In this research, land sat and sentinel satellite imagery apt for change detection in vegetation cover, both landsat and sentinel imagery, covering the period between 1970 and 2021 in epochs of 1973, 1984, 1993, 2003, 2015 and 2021 years were used to establish the correlation between vegetation cover and built-up area along River Riara river reserve. The images were analysed to extract the built-up areas along the river reserve, including the buildings, and the rate of human settlements, which influenced vegetation cover. Normalized Difference Built-Up Index (NDBI) and Normalized Difference Vegetation Index (NDVI) were computed using the Short-Wave Infrared (SWIR) and the Near Infra-Red (NIR) bands to show the rate of change over the years. Results indicate NDVI values were high, compared to NDBI values along river Riara in the years 1973 and 1993 implying that there was more vegetation cover then. However, in the year 2021, the NDVI indicated the highest value at 0.88, with the complementary NDBI indicating the highest NDBI value at 0.47. This represents a significant increase in built-up areas since 2015 more than in previous epochs. Either, there was a significant increase in NDBI values, from 0.24 in 1993 to 0.47 in 2021. More so, the R-squared value at 0.80 informed 80% relationship between NDBI and NDVI values indicating a negative correlation.
基金supported by the National Natural Science Foundation of China(No.41871179)the China Postdoctoral Science Foundation under Grant(No.2024M751047).
文摘The development of spatial interactions of land resources enhances virtual built-up land flow,which contributes to China's inter-regional trade inequality.Little is known about the degree of inequality among regions.This work seeks to estimate the degree of inter-regional trade inequality through environmental-economic benefits.We combined a multiregional input-output model at the city level with a new classification to calculate the virtual built-up land flow among cities and analyzed its implications for the regional economy and carbon balance.The results indicate that developed regions were the main beneficiaries of inter-regional trade,as reflected in land-use efficiency.China's economic hub has been progressively shifting southward,and the inter-regional trade inequality has continuously increased.The flow of virtual service industry land among developed regions rose,while underdeveloped regions remained suppliers of raw materials,further increasing inter-regional trade inequality.
基金sponsored by the U.S.National Science Foundation(under Grant No.DGE 0333401)the NSF Bolivia International Sustainable Development Engineering Research Experience Project(OISE-0623558).
文摘There is growing demand to develop methods that integrate environmental and economic assessment of more sustainabletechnologies incorporated into commercial and residential buildings. In this paper, we incorporate economic and energyuse data obtained for a green roof operating in the Midwest U.S. at latitude 42.94N into an integrated approach toestimate and compare the economic and environmental impacts of an intensive (or extensive) green roof with a built-uproof. The life cycle stages included in the analysis were material acquisition life stage which including the transportationeffects from material extraction through manufacturing to the fi nished products, and the use and maintenance life stageof the building. Environmental impact analysis indicates that green roof emits three times more environmental pollutantsthan built-up roofs in the material acquisition life stage. However, in the use and maintenance life stage, built-uproof emits three times more pollutants than a green roof. Overall, when emissions from both material acquisition lifestage and use and maintenance life stage are combined, the built-up roof contributes almost 3 times more (or 46% more)environmental emissions than green roof over a 45-year building life span. Furthermore the overall energy use, specifi -cally energy involved in the transportation from material extraction through to the fi nished product indicate that greenroof uses 2.5 times less energy than a built-up roof. An Economic Input and Output life cycle assessment (EIO-LCA) wasused to estimate the environmental impacts. The economic impact over an assumed 45-year building life was determinedusing life cycle costing, taking into account Net Present Value (NPV) calculations. Life cycle costing results indicate thatgreen roof costs approximately 50% less to maintain over a 45 year-building life than a built-up roof. A Monte Carlosimulation is also performed to account for any variability in cost data. In addition, the paper presents a method toquantify the value incentive that a decision-maker has in adopting green technology. Results from the study indicate thatwhen a green roof is compared to the Midwest regional NPV of a built-up roof, we fi nd that the cost to maintain it ($35per square foot) lies well below the average regional NPV of $59 per square foot of a built-up roof.
文摘An improved methodology for the extraction and mapping of urban built-up areas at a global scale is presented in this study.The Moderate Resolution Imaging Spectroradiometer(MODIS)-based multispectral data were combined with the Visible Infrared Imager Radiometer Suite(VIIRS)-based nighttime light(NTL)data for robust extraction and mapping of urban built-up areas.The MODIS-based newly proposed Urban Built-up Index(UBI)was combined with NTL data,and the resulting Enhanced UBI(EUBI)was used as a single master image for global extraction of urban built-up areas.Due to higher variation of the EUBI with respect to geographical regions,a region-specific threshold approach was used to extract urban built-up areas.This research provided 500-m-resolution global urban built-up map of year 2014.The resulted map was compared with three existing moderate-resolution global maps and one high-resolution map in the United States.The comparative analysis demonstrated finer details of the urban built-up cover estimated by the resultant map.
