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The dynamics of built-up height are a crucial aspect of urban form, enabling the characterization of urban growth patterns and the attainment of sustainable development goals. While past studies have focused on urban extent mapping, little has been done to reveal changes in vertical structures in built-up areas. In this study, we reconstructed annual urban form dynamics in Beijing, China, from 1990 to 2020, utilizing Landsat time-series data. First, we identified urban growth and renewal years using a temporal segmentation approach. Then, we reconstructed the annual dynamics of built-up heights through logical reasoning, using the reference height in 2020 and the identified changing years. We evaluated the derived dataset and analyzed the urban growth patterns (i.e., upward and outward) over the past three decades. The detected change years are reliable, with an overall accuracy of 88% (± 1 year). Meanwhile, the reconstructed built-up height data showed good agreement with surveyed results (R2: 0.92), with a root mean square error of 2.87 m and a mean absolute error of 2.07 m. Most expanded built-up areas during 1990–2020 were located at the fringe of the central city, and about 16% experiencing multiple changes. Overall, outward growth was prominent in Beijing during the first decade, while upward growth became dominant in most districts thereafter. The proposed framework provides a new way to reveal annual urban form dynamics through time series analysis, with great potential to support relevant studies such as urban climate modeling and carbon emissions studies. [ABSTRACT FROM AUTHOR]

This study investigates the effects of perforations on the buckling behavior and load-bearing capacity of advanced high-strength steel I-shaped built-up compression members. The built-up section was fabricated by connecting two identical lipped channel sections made of complex phrase steel HC700CP980 using pull rivets. The perforations were classified into two groups: holes in web and holes in both web and flanges. A comprehensive parametric study, combining both experimental results and finite element analysis, demonstrated the decrease in load-bearing capacity caused by the presence of perforations, particularly noticeable in specimens featuring holes in both web and flanges. The extend of the reduction is closely linked to the quantity and dimensions of the holes, with a higher hole-element width ratio resulting in a more substantial loss of load-bearing capacity. Additionally, the obtained test and FE results were used to evaluate the accuracy of direct strength method (DSM) for the examined advanced high-strength steel I-shaped built-up compression members. The evaluation findings highlight the limitations of the DSM in the design predictions for built-up columns featuring multiple web holes and holes on both web and flanges. Therefore, a modified calculation method was proposed, which integrated strength reduction factors to consider the influence of the position of holes relative to the flexural buckling axis of built-up sections. The modified method has shown notably improved design accuracy and consistency for the perforated advanced high-strength steel I-shaped built-up sections. • Tests and numerical analysis conducted on advanced high-strength steel I-shaped built-up columns with perforations. • Influence of perforations on the buckling instability and capacities of columns examined. • Applicability of the Direct Strength Method (DSM) assessed. • Modified DSM methods proposed for improved design accuracy and consistency. [ABSTRACT FROM AUTHOR]

• Two new indices, IBUI opt and IBUI sar proposed for mapping impervious features. • IBUI opt uses Green, Red, NIR and SWIR spectral band information. • IBUI sar uses SAR L-band HH and HV polarization information. • IBUI sar outperformed in semi-urban and rural areas. • IBUI opt performed better in high dense urban scenario. In order to cope up with the emerging demand of interpreting and detecting urban features from remotely sensed imagery, this study proposes an innovative unique yet practically easy approach to extract impervious surfaces and features using certain built-up indices (BUIs) that are developed from space-borne optical and SAR remotely sensed sensors. Resourcesat-2 LISS III and HH/HV dual polarized L-band ALOS PALSAR data are respectively the space-borne optical and synthetic aperture radar (SAR) data used for designing the BUIs used for impervious feature detection. BUI generated from optical sensor uses green (G), red (R), near infrared (NIR) and short wave infrared (SWIR) channels simultaneously. BUI designed from SAR sensor uses horizontal-horizontal (HH) co-polarized and horizontal-vertical (HV) cross-polarized L-band backscatter coefficient/sigma nought (σ°) data. The feature extraction performed by two new indices, one derived from existing indices using spectral-based information from optical sensors– an Impervious Built-up Index (IBUI opt); and the other from SAR HH/HV σ° backscatter information– an Impervious Built-up Index (IBUI sar); are cross-checked and validated with Ground Truth (GT) data that revealed the performance of the indices designed and proposed in the study for three sample sites bearing completely different biophysical environments; for easy and rapid extraction of impervious land features in satellite imageries. Overall accuracies of impervious feature extraction using IBUI opt are 92.3%, 95% and 75.6% in comparison to 90%, 98% and 87.6% using IBUI sar for the three study areas respectively. The approach adopted in this study is henceforth acceptable due to its high accuracy, simplicity and reliability; and hence easy to replicate. [ABSTRACT FROM AUTHOR]

Built-up land/impervious surface expansion links urbanization and environmental change. To enable large-scale long-term spatially-explicit studies, we took a data-driven approach exploiting newly-available time series of fine-spatial-resolution remote sensing observations, and developed the Spatially-Explicit, Long-term, Empirical City developmenT (SELECT) model. Closely calibrated to observational data, SELECT functions at several spatial scales, with multiple design traits capturing local variations of urbanization, and ensuring performance for long-term extrapolations in scenario analyses (e.g. the Shared Socioeconomic Pathways). It showed low estimation residuals, explained high fractions of the response's variations, and scored well in all robustness and generalizability tests we ran. When compared with a typical spatial-interaction-based model for projecting global built-up land in 2030, SELECT allocated more new development to areas with similar characteristics to locations that exhibited expansive urban growth historically, while the example spatial-interaction-based model allocated more new development to areas with high amounts of existing built-up land. • A large-scale long-term spatially-explicit built-up/impervious land model is developed. • Newly-available time series of fine-spatial-resolution remote sensing data are used. • SELECT is a land cover change model based on statistical learning and data mining techniques. • SELECT captures local spatial variations for long-term extrapolations in scenario analyses. • SELECT scored highly in evaluations and model comparisons. [ABSTRACT FROM AUTHOR]

Highlights • This paper introduces two essential societal variables (ESV) – global built-up area and global population density. • The two ESVs are the building blocks for quantifying the human societal system as they measure the human presence on Earth. • The two ESVs complement the essential climate variables in modelling climate impact on societies. • The two ESVs are already used in disaster early warning systems, within disaster risk models, in system of indicators and in crisis management. • The two ESVs are also tested for use in system of indicators used to measure progress towards the 2030 Development Agenda. Abstract Scientists use Essential Climate Variables to understand and model the Earth's climate. Complementary to the Climate Variables this paper introduces global built-up area and population density, referred to as Essential Societal Variables, that can be used to model human activities and the impact of climate induced hazards on society. Climate impact scenarios inform policy makers on current and future risk and on the cost for mitigation and adaptation measures. The global built-up area and global population densities are generated from Earth observation image archives and from national population census data in the framework of the Global Human Settlement Layer (GHSL) project. The layers are produced with fine granularity for four epochs: 1975, 1990, 2000 and 2015, and will be updated on a regular basis with open satellite imagery. The paper discusses the relevance of global built-up area and population density for a number of policy areas, in particular to understand regional and global urbanization processes and for use in operational crisis management and risk assessment. The paper also provides examples of global statistics on exposure to natural hazards based on the two ESVs and their use in policy making. Finally, the paper discusses the potential of using population and built-up area for developing indicators to monitor the progress in Agenda 2030 including the Sustainable Development Goals (SDGs). [ABSTRACT FROM AUTHOR]

This paper reports on experiments addressing the buckling and collapse behavior of common built-up cold-formed steel (CFS) columns. The built-up column consists of two individual CFS lipped channels placed back-to-back and connected at the web using two self-drilling screw fasteners at specified spacing along the column length. The experiments aim to quantify ultimate strength, composite action, member end fixity, and buckling interactions and collapse behavior for common built-up CFS members. The testing also explicitly explores the effect of sheathing, as typically employed in cold-formed steel framing, on the response. The experiments provide benchmarks for design that include specific considerations for both thin-walled buckling and fastener behavior. A total of 17 monotonic, concentric compression tests with a column length of 1.83 m (6 ft) are completed with an array of position transducers monitoring displacements at key locations. Tests are conducted with the built-up member seated in CFS tracks. Results indicate a large range of deformation behavior, with local-global interaction and flexural-torsional modes common in many of the unsheathed specimens. Columns sheathed with oriented strand board on both flanges behave as braced against global buckling in the plane of the wall, and local buckling induced failures prevail. The end condition for the tested built-up members seated in track is determined to be semi-rigid, but generally closer to fixed than pinned. [ABSTRACT FROM AUTHOR]

This paper reports on experiments addressing the buckling and collapse behavior of back-to-back lipped channel built-up cold-formed steel (CFS) columns assembled using 16 different CFS lipped channel sizes. The lipped channel sections are connected at the web using a pair of self-drilling screw fasteners at a specified spacing along the column length of 1.83 m (6 ft). These experiments aim to quantify the effect of two web fastener layouts on composite action for each section size, study member end fixity, observe buckling and collapse behavior, and provide benchmarks for design that includes specific considerations for thin-walled member buckling. A total of 32 monotonic, displacement-controlled, concentric compression tests are completed with up to 17 position transducers monitoring displacements at key locations. All tests are conducted with the built-up member seated in CFS tracks, as would be found in practice. Local–global interaction is shown to be a prevalent failure mode, and the stud-to-track end condition is determined to be semi-rigid, but generally closer to a fixed condition. End rigidities are estimated using a Southwell approach. Rational design approaches extending the application of the Direct Strength Method (DSM) and employing current state-of-the-art numerical modeling techniques are proposed and validated with test data. In addition, the development of definitive design recommendations that help reduce the complexity of fastener designs and incorporates the DSM framework when predicting built-up member strength is underway. [ABSTRACT FROM AUTHOR]

Built-up cold-formed steel structural members can provide technically and economically advantageous solutions in cold-formed steel construction. However, there is a need for a deeper understanding of their stability behaviour, and this paper demonstrates that detailed, accurate and reliable finite element models provide an excellent means to achieve this. Apart from the typical issues to be considered in the high-fidelity modelling of thin-walled members, which include geometric and material nonlinearity, element type, mesh density, and the modelling of imperfections and boundary conditions, the paper focuses on two additional complications which arise in built-up members: the modelling of connectors, and contact between constituent parts. A number of alternative techniques to model connector behaviour are investigated and their effect on the predictions of the ultimate capacity quantified by benchmarking against experimental data. Various successful strategies to mitigate stubborn convergence problems, which almost inevitable originate when modelling complex contact problems, are also presented. It is demonstrated, however, that the inclusion of contact as a model feature does not have a significant effect on the predicted capacity in the majority of the considered cases, with its influence typically remaining limited below 10%. The validated models were further used in parametric studies which showed that once the connector spacing is short enough to prevent global instabilities of the component sections between connector points, its effect on the ultimate capacity of the built-up column is very small within the practical range of connector spacings. Modelling connector lines as continuous longitudinal constraints tying surfaces together, on the other hand, is bound to significantly overestimate the capacity. • Convergence issues can be overcome by Adding artificial damping and modifying solution control parameters. • Modelling connectors with PLANAR elements and assigning them the load-slip behaviour leads to best results. • Effect of connector spacing becomes noticeable when shorter than the local buckling half-wavelength. • Contact between the components only has a modest effect on the ultimate capacity. [ABSTRACT FROM AUTHOR]

Built-up area supports human settlements and activities, and its spatial distribution and temporal dynamics have significant impacts on ecosystem services and global environment change. To date, most of urban remote sensing has generated the maps of impervious surfaces, and limited effort has been made to explicitly identify the area, location and density of built-up in the complex and fragmented landscapes based on the freely available datasets. In this study, we took the lower Yangtze River Delta (Landsat Path/Row: 118/038), China, where extensive urbanization and industrialization have occurred, as a case study site. We analyzed the structure and optical features of typical land cover types from (1) the HH and HV gamma-naught imagery from the Advanced Land Observation Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR), and (2) time series Landsat imagery. We proposed a pixel- and rule-based decision tree approach to identify and map built-up area at 30-m resolution from 2007 to 2010, using PALSAR HH gamma-naught and Landsat annual maximum Normalized Difference Vegetation Index (NDVI max ). The accuracy assessment showed that the resultant annual maps of built-up had relatively high user (87–93%) and producer accuracies (91–95%) from 2007 to 2010. The built-up area was 2805 km 2 in 2010, about 16% of the total land area of the study site. The annual maps of built-up in 2007–2010 show relatively small changes in the urban core regions, but large outward expansion along the peri-urban regions. The average annual increase of built-up area s was about 80 km 2 per year from 2007 to 2010. Our annual maps of built-up in the lower Yangtze River Delta clearly complement the existing maps of impervious surfaces in the region. This study provides a promising new approach to identify and map built-up area, which is critical to investigate the interactions between human activities and ecosystem services in urban-rural systems. [ABSTRACT FROM AUTHOR]

This paper presents an assessment on the current yield slenderness limits under axial compression for cold-formed and built-up high strength carbon and stainless steel hollow sections. The definition of high strength steel in this paper refers to the materials with nominal yield strength or 0.2% proof stress which is greater than 700 MPa (Eurocode 3: Part 1-12) for carbon steel and greater than 480 MPa (Eurocode 3: Part 1-4) for stainless steel. A total of 147 stub column experimental results was compiled and assessed. Companion 46 finite element simulations were performed in this study and the results concurred with the experimental observations. The structural performance data showed that the current slenderness limits adopted in Eurocode 3, American and Australian Standards for both carbon and stainless steel under axial compression can be safely adopted for the high strength steel counterparts. New slenderness parameters and limits were also proposed to improve the design efficiency. [ABSTRACT FROM AUTHOR]

Abstract: As a result of the SAC project, rolled T-stub connections have been demonstrated to be a viable alternative to welded connections for steel frames in seismic areas. One difficulty with these connections is that oftentimes the rolled profiles needed to fabricate the T-stub needed for deep beams are not immediately available to fabricators and so built-up sections are the only alternative. The goal of this investigation is to demonstrate through experimental and finite element studies that built-up T-stub connections can be successfully detailed for use in special and intermediate moment frames in seismic areas. The results of a series of component tests on built-up T-stubs, obtained by means of complete joint penetration welding (CJP) and fillet welding are presented and discussed, providing supporting evidence for the best fabrication choice. Component tests investigating hole fabrication practices are also presented, studying their effect on ductility under monotonic and cyclic loads. Furthermore, finite element models of thick flange T-stub connections is presented and finite element simulation results are compared to experimental results to demonstrate the applicability of built-up T-stub connections for use in special and intermediate moment frames. The finite element results show an acceptable agreement with the experimental results and describe the behavior. A partial yielding of the T-stub flange followed by bolt fracture is highlighted as a failure mode based on the finite element and the experimental results. It is anticipated that the data collected from a forthcoming series of full-scale tests will lead to the prequalification of this connection typology. [Copyright &y& Elsevier]

Abstract: A series of tests on curved concrete filled steel tubular (CCFST) built-up members subjected to axial compression is described in this paper. Twenty specimens, including 18 CCFST built-up members and 2 curved hollow tubular built-up columns, were tested to investigate the influence of variations in the tube shape (circular and square), initial curvature ratio (β r, from 0 to 7.4%), nominal slenderness ratio (λ n, from 9.9 to 18.9), section pattern (two main components, three main components and four main components), as well as brace pattern (battened and laced) on the performance of such composite built-up members. The experimental results showed that the ultimate strength and stiffness of CCFST built-up specimens decreased with increasing β r or λ n. Different load-bearing capacities and failure modes were obtained for the battened and laced built-up members. A simplified method using an equivalent slenderness ratio was suggested to calculate the strength of CCFST built-up members under axial compression. [Copyright &y& Elsevier]

Abstract: ‘Natural’ treatment systems such as wetlands and reed beds have been proposed as sustainable means of reducing fluxes of faecal indicator organisms (FIOs) to recreational and shellfish harvesting waters. This is because FIO fluxes to coastal waters from both point (effluent) and diffuse (catchment) sources can cause non-compliance with microbiological standards for bathing and shellfish harvesting waters. The Water Framework Directive requires competent authorities in the member states to manage both point and diffuse sources of FIOs in an integrated manner to achieve compliance with ‘good’ water quality as defined in a series of daughter Directives. This study was undertaken to investigate the relative sources of FIOs to the popular bathing waters around Clacton, UK. In this predominantly arable (mainly cereal cropping) farming area, the principal land use predictor, explaining 76% of the variance in geometric mean presumptive Escherichia coli concentration at sub-catchment outlets during the bathing season, was the proportion of built-up (i.e. urbanised) land in each sub-catchment. This new finding contrasts with earlier studies in livestock farming regions where the proportion of improved grassland has proven to be the strongest predictor of microbial concentration. Also novel in this investigation, a flood defence wall has been built creating a wetland area which discharges every tidal cycle. The wetland produces over 97% reduction in the flux and concentrations of FIOs to the marine recreational waters. Also, FIO concentrations in water draining through the wetland to the sea were similar to concentrations measured in six UK sewage treatment plant effluents subject to secondary (biological) treatment followed by UV disinfection. [Copyright &y& Elsevier]

Analysis of cutting forces in fine turning is most frequently related to workpiece-material hardness and strength under different machining conditions. Material hardness and strength as well as material machinability, however, can be related to the material microstructure. Consequently, an additional influence exerted by the microstructure was included in the present study to find the relationship between the size of the soft phase described by intercept lengths and the magnitude of the cutting force measured during the fine-turning process. The magnitude of cutting force is usually treated in terms of its static and dynamic components. In our case, both the components are of importance. Because of different types of aluminium–silicon alloys, significant differences occur in the magnitude of the static and dynamic components of the cutting force mainly because of different types of microstructures. The latter can be described by the fraction and quantity of individual microstructure phases. The results obtained are represented by an average magnitude of static and dynamic components of the cutting force in relation to the intercept lengths of the soft phase. [Copyright &y& Elsevier]

This paper presents an experimental investigation on the behavior of cold-formed steel (CFS) battened built-up columns with unstiffened channel chords. A total of five specimens were fabricated, wherein the slenderness ratios of the unbraced chords and the overall column slenderness ratios of the specimens were varied. The structural performance was evaluated in terms of peak axial resistance, load-displacement response, and mode of failure. The test results were also validated using ABAQUS. The observed axial strengths of the CFS built-up columns have been compared with the design strengths computed using North American and Eurocode provisions. Both these standards over-predicted the axial strengths of the battened columns, except for the short columns with the unbraced chord slenderness ratio of less than 25% of the overall column slenderness. Based on this study, guidelines for design and detailing for built-up battened CFS columns have been recommended. • Monotonic tests are performed on CFS battened columns using unstiffened channels. • NAS's limiting value of 0.5 for unbraced chord's relative slenderness is inadequate. • NAS/EC3 can be adopted safely if unbraced chord's relative slenderness ≤0.25. • The overall column slenderness ≤50 to prevent large lateral displacements. • The width of end batten should at least be equal to the column width. [ABSTRACT FROM AUTHOR]

The increasing impact of humans on land and ongoing global population growth requires an improved understanding of land cover (LC) and land use (LU) processes related to settlements. The heterogeneity of built-up areas and infrastructures as well as the importance of not only mapping, but also characterizing anthropogenic structures suggests using a sub-pixel mapping approach for analysing related LC from space. We implement a regression-based unmixing approach for mapping built-up surfaces and infrastructure , woody vegetation and non-woody vegetation for all of Germany and Austria at 10 m resolution to demonstrate the potential of sub-pixel mapping. We map LC fractions for one point in time, using all available Sentinel-2 data from 2017 and 2018 (<70% cloud cover). We combine the concept of synthetically mixed training data with statistical aggregations from spectral-temporal metrics (STM) derived from Sentinel-2 reflectance time series. We specifically examine how STM can be used for creating synthetically mixed training data. STM are known to facilitate large area mapping by being largely independent of image acquisition dates and inherently incorporate phenological information. Vegetation is an important part of settlements and time series information supports its mapping. Synthetically mixed training data facilitates a streamlined training by using pure reference spectra to generate artificial mixtures as input to regression modelling of LC fractions in mixed pixels. We here show how combining both offers great potential for wall-to-wall LC fraction mapping. We further investigate the positive effect of STM on map results by comparing the performance of different subsets of STM combinations. Our results indicate that many STM combinations containing spectral variability and vegetation indices provide suitable input to creating synthetic training data for regression-based fraction mapping. Results for built-up surfaces and infrastructure (MAE 0.13/RMSE 0.18 at 20 m resolution), woody vegetation (0.18, 0.22) and non-woody vegetation (0.14, 0.19) are highly consistent across Germany and Austria. Only a few surface types were not accurately predicted in our nation-wide mapping. Further research is required to optimize mapping of temporally invariant bare soil and rock surfaces that show spectral similarity to built-up surfaces and infrastructure. The proposed methodology combines benefits of both regression-based modelling with synthetically mixed training data and STM, and thus facilitates mapping of LC fractions on a national scale and at high resolution. Such information will allow to better characterize settlements and identifying processes such as densification that are best represented by continuous LC mapping. • Sub-pixel built-up, woody & non-woody vegetation fractions mapped at national scale. • Wide range of rural and urban settings investigated for Germany and Austria. • Synthetic training data from spectral-temporal metrics leads to robust results. • A single model achieved MAE of 13–18% (RMSE 18–22%) from coastal to alpine regions. • Sub-pixel fractions structurally characterize settlements in Germany and Austria. [ABSTRACT FROM AUTHOR]

A comprehensive assessment of ecosystem health of wetlands is needed to guide protection and restoration activities. However, the conventional methods used in evaluating ecosystem health of wetlands largely rely on field observational data which often do not provide spatio-temporal perspectives to the assessment. Geospatial assessment of remotely sensed data has enormous potentials for assessing ecosystem health of wetlands at different temporal and spatial scales. This study employed geospatial techniques to assess ecosystem health of Densu Delta, Sakumo II and Muni-Pomadze Ramsar Sites over a 32-year period using structure, function and resilience indicators. Landsat satellite images of 1985, 2002 and 2017 were obtained for this study. Analytic hierarchy process (AHP) was used to weight the indicators. The importance of the ecosystem health indicators in decreasing order was as follows: Structure > Resilience > Function. The findings of the study also indicated that ecosystem health of the wetlands progressively deteriorated in 2002 and 2017 compared to the reference year of 1985. In 2002, the Densu Delta experienced the least decline (11.8%) from the 1985 state among the three wetlands and Sakumo II recorded the highest deterioration (38.0%). Unlike 2002, in 2017 the health of the Densu Delta experienced the worse deterioration (46.3%) whereas Sakumo II recorded the least decline (26.2%). Ecosystem health of Muni-Pomadze Ramsar Site deteriorated at a similar magnitude, 27.0% and 29.1% in 2002 and 2017, respectively. The critical underlying factor for the degradation of the wetlands is urbanization largely due to increase in human population which led to the expansion of built-up areas in the wetlands, fragmentation of natural land use and land cover (LULC) classes and reduction of vegetation cover. Image 1 • Geospatial assessment was used to characterise and quantify wetland ecosystem health indicators. • Wetland ecosystem health was assessed using structure, function and resilience indicators. • Analytic hierarchy process was used to weight the health indicators. • The ecosystem health of the wetland progressively deteriorated over the study period. [ABSTRACT FROM AUTHOR]