Finite Element Model for Predicting Stiffness of Metal-Plate-Connected Tension-Splice and Heel Joints of Wood Trusses

A finite element model that predicts axial stiffness of metal-plate-connected (MPC) tension-splice and heel joints of wood trusses is developed. The commercial software ABAQUS was used in developing the model. The model was based on: (1) the assumption that the joints are two-dimensional, (2) plane-strain modeling, and (3) the assumption that the properties of the wood and metal plate are linearly isotropic. The interface between the wood and the teeth of the metal plate is modeled with a finite sliding formulation. Contact surfaces (rather than contact elements) model the slip of the teeth of the metal plate and shear at the wood-tooth interface. The tangential contact properties are set to a specified coefficient of friction while the normal contact properties are set to a "hard" contact formulation, allowing for a possible separation of the nodes after contact is achieved. Model predictions are validated against experimentally measured stiffness values obtained in the literature. The data cover two wood species and three levels of modulus of elasticity (MOE). On the average, the model predicts within 5% of the experimentally measured stiffness values. The unique features of the model include: (1) accounting for friction at the tooth-wood interface, (2) accounting for tooth slip, (3) requiring no empirical factor (such as foundation modulus) in predicting axial stiffness, and (4) using the same methodology in modeling tension-splice and heel joints

Criterios de rotura en miembros de madera

Los procedimientos de diseño tienden a simplificar los estados multitensionales de tensión como uniaxiales. Esta simplificación puede no ser adecuada en el caso de materiales ortotrópicos como la madera, uno de cuyos modos de rotura habituales es la tracción perpendicular a la fibra. No es el único inconveniente al analizar la rotura de la madera: sus propiedades resistentes se obtienen a partir de especímenes libres de defectos, y las teorías de rotura aplicadas se derivan de las desarrolladas para materiales compuestos. Pero algunos de estos criterios de rotura, relativamente sencillos, sólo son válidos bajo ciertas condiciones: Norris y Tsai-Hill asumen que las resistencias a tracción y compresión son iguales (lo que no es cierto en el caso de la madera). Otros criterios se basan habitualmente en superficies cuadráticas, y algunas de sus restricciones se derivan de criterios estrictamente geométricos para asegurar una envolvente cerrada. Puesto que estas condiciones no se basan en criterios físicos, parte de ellas puede carecer de sentido. En otros casos, se requiere evaluar un término de interacción, para lo que se requieren numerosos ensayos experimentales. La investigación aquí presentada revisa y compara algunos de los criterios de rotura más comúnmente empleados. Sus predicciones se comparan con los resultados de ensayos biaxiales en madera de abeto libre de defectos. In most cases, design procedures assume uniaxial stress conditions. This assumption may not be adequate for orthotropic materials such as timber. Initial failure mode in lumber is usually tension perpendicular to the grain or axial tension around natural defects such as knots. It is not the only problem when analyzing wood failure: strength properties of lumber have been obtained from clearwood specimens and in-grade testing of full-scale lumber, whereas failure criteria are usually those originally developed for composite materials. Some of the existing failure criteria are relatively easy to use, but prove valid only under special orthotropic conditions. Norris and Tsai-Hill criteria assume the tension and compression strengths to be equal, which is not the case for wood. Other criteria are usually based on quadric surfaces, in which certain constraints are taken strictly from geometrical considerations to achieve a closed envelope. Since these conditions are not defined from a physical stand point, some parts of the resulting curve leads to errors in failure predictions. These quadric criteria also require evaluation of interaction coefficients for bi-axial stress conditions, which demands extensive experimental testing. The proposed paper will review the existing failure criteria. Their predictions will be validated by means of biaxial experimental results on clear spruce wood

Mapping geographical inequalities in childhood diarrhoeal morbidity and mortality in low-income and middle-income countries, 2000–17 : analysis for the Global Burden of Disease Study 2017

Background Across low-income and middle-income countries (LMICs), one in ten deaths in children younger than 5 years is attributable to diarrhoea. The substantial between-country variation in both diarrhoea incidence and mortality is attributable to interventions that protect children, prevent infection, and treat disease. Identifying subnational regions with the highest burden and mapping associated risk factors can aid in reducing preventable childhood diarrhoea. Methods We used Bayesian model-based geostatistics and a geolocated dataset comprising 15 072 746 children younger than 5 years from 466 surveys in 94 LMICs, in combination with findings of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017, to estimate posterior distributions of diarrhoea prevalence, incidence, and mortality from 2000 to 2017. From these data, we estimated the burden of diarrhoea at varying subnational levels (termed units) by spatially aggregating draws, and we investigated the drivers of subnational patterns by creating aggregated risk factor estimates. Findings The greatest declines in diarrhoeal mortality were seen in south and southeast Asia and South America, where 54·0% (95% uncertainty interval [UI] 38·1–65·8), 17·4% (7·7–28·4), and 59·5% (34·2–86·9) of units, respectively, recorded decreases in deaths from diarrhoea greater than 10%. Although children in much of Africa remain at high risk of death due to diarrhoea, regions with the most deaths were outside Africa, with the highest mortality units located in Pakistan. Indonesia showed the greatest within-country geographical inequality; some regions had mortality rates nearly four times the average country rate. Reductions in mortality were correlated to improvements in water, sanitation, and hygiene (WASH) or reductions in child growth failure (CGF). Similarly, most high-risk areas had poor WASH, high CGF, or low oral rehydration therapy coverage. Interpretation By co-analysing geospatial trends in diarrhoeal burden and its key risk factors, we could assess candidate drivers of subnational death reduction. Further, by doing a counterfactual analysis of the remaining disease burden using key risk factors, we identified potential intervention strategies for vulnerable populations. In view of the demands for limited resources in LMICs, accurately quantifying the burden of diarrhoea and its drivers is important for precision public health

Global, regional, and national age-sex-specific mortality and life expectancy, 1950–2017: a systematic analysis for the Global Burden of Disease Study 2017

BACKGROUND: Assessments of age-specific mortality and life expectancy have been done by the UN Population Division, Department of Economics and Social Affairs (UNPOP), the United States Census Bureau, WHO, and as part of previous iterations of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD). Previous iterations of the GBD used population estimates from UNPOP, which were not derived in a way that was internally consistent with the estimates of the numbers of deaths in the GBD. The present iteration of the GBD, GBD 2017, improves on previous assessments and provides timely estimates of the mortality experience of populations globally. METHODS: The GBD uses all available data to produce estimates of mortality rates between 1950 and 2017 for 23 age groups, both sexes, and 918 locations, including 195 countries and territories and subnational locations for 16 countries. Data used include vital registration systems, sample registration systems, household surveys (complete birth histories, summary birth histories, sibling histories), censuses (summary birth histories, household deaths), and Demographic Surveillance Sites. In total, this analysis used 8259 data sources. Estimates of the probability of death between birth and the age of 5 years and between ages 15 and 60 years are generated and then input into a model life table system to produce complete life tables for all locations and years. Fatal discontinuities and mortality due to HIV/AIDS are analysed separately and then incorporated into the estimation. We analyse the relationship between age-specific mortality and development status using the Socio-demographic Index, a composite measure based on fertility under the age of 25 years, education, and income. There are four main methodological improvements in GBD 2017 compared with GBD 2016: 622 additional data sources have been incorporated; new estimates of population, generated by the GBD study, are used; statistical methods used in different components of the analysis have been further standardised and improved; and the analysis has been extended backwards in time by two decades to start in 1950. FINDINGS: Globally, 18·7% (95% uncertainty interval 18·4–19·0) of deaths were registered in 1950 and that proportion has been steadily increasing since, with 58·8% (58·2–59·3) of all deaths being registered in 2015. At the global level, between 1950 and 2017, life expectancy increased from 48·1 years (46·5–49·6) to 70·5 years (70·1–70·8) for men and from 52·9 years (51·7–54·0) to 75·6 years (75·3–75·9) for women. Despite this overall progress, there remains substantial variation in life expectancy at birth in 2017, which ranges from 49·1 years (46·5–51·7) for men in the Central African Republic to 87·6 years (86·9–88·1) among women in Singapore. The greatest progress across age groups was for children younger than 5 years; under-5 mortality dropped from 216·0 deaths (196·3–238·1) per 1000 livebirths in 1950 to 38·9 deaths (35·6–42·83) per 1000 livebirths in 2017, with huge reductions across countries. Nevertheless, there were still 5·4 million (5·2–5·6) deaths among children younger than 5 years in the world in 2017. Progress has been less pronounced and more variable for adults, especially for adult males, who had stagnant or increasing mortality rates in several countries. The gap between male and female life expectancy between 1950 and 2017, while relatively stable at the global level, shows distinctive patterns across super-regions and has consistently been the largest in central Europe, eastern Europe, and central Asia, and smallest in south Asia. Performance was also variable across countries and time in observed mortality rates compared with those expected on the basis of development. INTERPRETATION: This analysis of age-sex-specific mortality shows that there are remarkably complex patterns in population mortality across countries. The findings of this study highlight global successes, such as the large decline in under-5 mortality, which reflects significant local, national, and global commitment and investment over several decades. However, they also bring attention to mortality patterns that are a cause for concern, particularly among adult men and, to a lesser extent, women, whose mortality rates have stagnated in many countries over the time period of this study, and in some cases are increasing

Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017

A double burden of malnutrition occurs when individuals, household members or communities experience both undernutrition and overweight. Here, we show geospatial estimates of overweight and wasting prevalence among children under 5 years of age in 105 low- and middle-income countries (LMICs) from 2000 to 2017 and aggregate these to policy-relevant administrative units. Wasting decreased overall across LMICs between 2000 and 2017, from 8.4 (62.3 (55.1�70.8) million) to 6.4 (58.3 (47.6�70.7) million), but is predicted to remain above the World Health Organization�s Global Nutrition Target of <5 in over half of LMICs by 2025. Prevalence of overweight increased from 5.2 (30 (22.8�38.5) million) in 2000 to 6.0 (55.5 (44.8�67.9) million) children aged under 5 years in 2017. Areas most affected by double burden of malnutrition were located in Indonesia, Thailand, southeastern China, Botswana, Cameroon and central Nigeria. Our estimates provide a new perspective to researchers, policy makers and public health agencies in their efforts to address this global childhood syndemic. © 2020, The Author(s)

Author Correction: Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017 (Nature Medicine, (2020), 26, 5, (750-759), 10.1038/s41591-020-0807-6)

An amendment to this paper has been published and can be accessed via a link at the top of the paper. © 2020, The Author(s)

Author Correction: Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017 (Nature Medicine, (2020), 26, 5, (750-759), 10.1038/s41591-020-0807-6)

An amendment to this paper has been published and can be accessed via a link at the top of the paper. © 2020, The Author(s)

Assessment of Failures of Post-Frame Buildings in New York State Due to Snow Load

A series of winter storm events during early January, 1999 resulted in significant accumulations of precipitation in many areas of New York State. Several agricultural structures failed as a result of the excessive snow load. Many of these were post-frame buildings constructed to house dairy cattle. A field investigation was conducted with the objective of evaluating why the buildings failed