Snow Load Research Articles

Effect of the number of design variables in thickness optimization of concrete barrel roof shells using evolutionary algorithms

This study looks into some practical implications of using evolutionary algorithms for optimization of free-form concrete shells in search of methods for automating design representation and determining the number of design variables. This study reports the insights and learnings from a set of numerical experiments, by changing the number of parameters, on thickness optimization of a barrel roof shell subjected to self-weight, an additional snow load, and an earthquake response spectrum. The practical advantages and challenges of two methods, parametric and direct representations, are analysed, and a spectrum of methods between these two extremes are investigated through experiments. The results demonstrate how changing the number of variables affects the quality of the design and the performance of the algorithm and why a systematic problem-dependent method for finding the best design representation and number of variables outside this spectrum can be beneficial.

Modeling of the Snowdrift in Cold Regions: Introduction and Evaluation of a New Approach

Unbalanced, or non-uniform, snow loads caused by snow drifting or sliding in cold regions with heavy snowfalls, can be a serious problem for the building industry. However, the methods for predicting snow distribution still need to be improved. Field observation is the most direct and reliable method to study snow distribution, but because the natural environment is uncontrollable and varies dramatically, sometimes conclusions may be confused under the influence of the many variables in the investigation. This paper proposes a snowing experiment approach using an outdoor snow–wind combined experiment facility for the study of snow distribution. The facility can produce a stable and controllable wind field and snowfall environment. Experiments which focused on snowdrift around a building were conducted during the winter to make an evaluation of the repeatability and reliability of the new approach. Finally, from the analysis of results, it was demonstrated that the experimental facility was stable and that the similarity criterion adopted for the snowing pattern was reliable. Especially, the minimum value of the friction speed ratio was suggested to ensure the test accuracy.

Stochastic Description of Loads on the Steel Storage Capacities

This paper deals with the study of stochastic parameters of external loads, which are used in the tasks of determining the level of reliability of steel storage capacities. To describe the random load process, the normal law and the double exponential distribution of Gumbel were used. It was formulated the technique of transition from the study of the entire random process to the consideration of its maximums. It was obtained quantitative values of the stochastic characteristics of snow and wind loads on the territory of Ukraine, without reference to the zoning maps. A general procedure for determining the probability of failure was formulated, depending from a given characteristic maximum. This index corresponds to the basic level of load. The average intersection of this level by a random load process is equal to one. Analytical formulas are obtained to determine the scale and position of the double exponential distribution of Gumbel, which depend on the characteristic maximum, as well as formulas, which help to calculate the statistical characteristics (standard, expected value and coefficient of variation) of the random value of the load maximums. The possibility of using this approach is theoretically confirmed when the density distribution of the ordinate of a random process follows the normal law. It was proposed expressions for the parameters of the distribution maximums of the random processes, which are described by the polynomial exponent and the Weibull law.

Den‐site characteristics and selection by brown bears (Ursus arctos) in the central Brooks Range of Alaska

AbstractSelection and use of dens is a critical behavioral adaption of bears (Ursus spp.) to survive extended periods of resource limitation. We analyzed selection of den sites by brown bears (Ursus arctos) in an arctic montane environment from 2014 to 2017. We used GPS data from 51 instrumented bears to physically locate, identify, and describe den sites (n = 33) and to quantitatively model the selection of denning habitat (n = 65 dens over 3 yr). We conducted an analysis of den‐site selection at the home range (third order) scale using variables describing topographic, vegetative, and spatially‐explicit fish and wildlife models. We hypothesized four main factors influence den‐site selection by brown bears: (1) physiography, (2) proximity to food resources, (3) thermal insulation, and (4) den‐area fidelity. We used kernel density estimates to define space use and conditional logistic regression to estimate den selection within individual home ranges. Brown bears selected den sites on steep slopes (>31°) with high snow load potential near their previously used den site. Our results supported our hypothesis that den selection by brown bears was related to thermal insulation, structural stability, drainage, and den‐area fidelity.

Wind tunnel model tests of snow precipitation and redistribution on rooftops, terraces and in the vicinity of high-rise buildings

This paper describes the model tests conducted in the Wind Engineering Laboratory of the Cracow University of Technology aimed at determining the shape coefficients of snow load on high-rise buildings of The Warsaw Hub. The shape coefficient was measured at two different situations: snow precipitation and its subsequent redistribution. The model tests were conducted independently for rooftops and terraces in the scale of 1:120 and for the neighbouring area of the buildings in the scale of 1:300. The results allowed for creation of snow shape coefficient maps on the investigated areas both for snow precipitation and redistribution for the use of designers, constructors and architects.

Comparing Design Ground Snow Load Prediction in Utah and Idaho

AbstractSnow loads in the western United States are largely undefined due to complex geography and climates, leaving the individual states to publish detailed studies for their region, usually thro...

Site-specific assessment of mechanical loads on photovoltaic modules from meteorological reanalysis data

This work demonstrates the capability of meteorological reanalysis data for estimating mechanical stresses due to wind gusts on photovoltaic modules. Besides the immediate power loss caused by the inactive solar cell areas within the module, the influence of cracks induced by such mechanical loads on the ageing and degradation behavior of PV modules is in the focus of current PV reliability research. To choose and/or design the optimum module for a given deployment site at the most economical cost, the mechanical loads the module will be exposed to during its service life need to be estimated. Hence, this paper introduces a new methodology for assessing and deducing site-specific mechanical load scenarios which are expected to be imposed on photovoltaic modules by wind gusts for a given location. The approach presented here is based on the linear calibration of meteorological reanalysis data with publicly available and standardized high-quality surface weather station data of local weather services. In this fashion, site-specific mechanical load scenarios can be deduced for virtually any site covered by the respective reanalysis data set. These scenarios can be used for developing site-specific module qualification tests, thereby providing a methodology enabling climate-specific module designs or specifications. This methodology can also be transferred to virtually any location and other climate and weather parameters such as snow loads, UV dose, etc. Hence a complete assessment of all weather-related degradation scenarios could be deduced eventually.

«Шуховский пролет» листопрокатного цеха Нижне-Выксунского завода

Рассматриваются проблемы сохранения объекта культур­ного наследия «Листопрокатный цех Нижне-Выксунского завода» (АО «ВМЗ»), выполненного по проекту выдающегося русского учёного и инженера В.Г. Шухова, его перемещения в центральную часть города Выксы и дальнейшей реставрации. В статье приведена история создания и эксплуатации листо­прокатного цеха, материалы ранее проведённых обследова­ний, результаты комплексного научного исследованияи 2018 года, включающего натурное обследование, при выполнении которого были зафиксированы многочисленные дефекты и повреждения металлических конструкций, наиболее опасные из которых - щелевая коррозия в узлах сопряжений элемен­тов, глубокая язвенной коррозия элементов арок и фахвер­ковых стоек в приопорной зоне, а также сквозная коррозия элементов покрытия. Представлены результаты проверочных расчётов, которые показали, что прочность и устойчивость цеха («Шуховского пролёта») даже с учётом удаления из расчётной схемы сильно повреждённых узлов и участков эле­ментов конструкций здания цеха, достаточна для восприятия действующих на момент обследования нагрузок, а количество повреждённых конструкций листопрокатного цеха, требую­щих восстановления или замены, будет незначительным и не повлияет на культурно-историческую ценность здания. Для восприятия дополнительных усилий от снеговой нагрузки (в случае, если бы кровельное покрытие в настоящее время было сохранено) потребовалось бы заменить большую часть элементов каркаса цеха либо установить дополнительные опоры, что недопустимо при реставрации объекта культурного наследия. В статье приведены рекомендации по разборке, реставрации элементов перемещаемого в центральную часть города Выксы сооружения методом лазерной наплавки и последующей их сборке, которые позволят сохранить этот уникальный памятник архитектуры и инженерной мысли.

ІМОВІРНІСНЕ ПРЕДСТАВЛЕННЯ КОЕФІЦІЄНТА КРИТИЧНОГО ФАКТОРУ В ЗАДАЧАХ НАДІЙНОСТІ БУДІВЕЛЬНИХ КОНСТРУКЦІЙ

Стаття порушує актуальну проблему практичного розрахунку надійності для такого класу будівельних споруд, як сталеві ємності зберігання. Зокрема дослідження орієнтоване на визначення такого узагальненого коефіцієнта критичного фактору, як відношення узагальнених величин зусиль та міцності, представлених випадковими процесами. З огляду на використання методів теорії імовірності та математичної статистики, значення критичного фактору виражається через його статистичні характеристики, диференціальну та інтегральну функції розподілу. Визначення середньоквадратичного відхилення та коефіцієнту варіації проводилося шляхом лінеаризації нелінійної функції випадкових величин в околі її математичного очікування. При цьому була врахована поправка на нелінійність при обчисленні дисперсії. Щільність розподілу коефіцієнта критичного фактору визначалася при використанні нормального закону розподілу для випадкових величин узагальненої міцності. Стохастичний процес узагальненого зусилля схематизувався двома законами розподілу – нормальним, що використовують для опису тиску сипучого матеріалу на стінки корпусу ємності зберігання, та подвійним експоненціальним розподілом Гумбеля, що використовується для опису максимумів снігового та вітрового навантаження. Таким чином, на базі класичного підходу, було отримане кінцеве аналітичне рішення в двох варіантах. Інженерний розрахунок, відповідно до даного алгоритму, ускладнений і потребує застосування спеціальних математичних пакетів для обчислення інтегральнихвиразів. Для уникнення цієї процедури була обґрунтована можливість використання процедури імітаційного моделювання для вирішення задачі пошуку функції розподілу імовірностей в зоні значень аргументу при ординатах, близьких до одиниці. Запропоновано імовірнісні властивості коефіцієнта критичного фактору виражати властивостями іншої випадкової величини, на основі полігону та функції розподілу котрої підбираються апроксимуючі вирази для заданого діапазону зміни імовірностей. Отримані таким чином значення для критичного фактору дозволяють вирішити задачу імовірнісного розрахунку аналітично без застосування складних обчислювальних процедур.

LOAD-CARRYING CAPACITY INCREASE OF ARCH-TYPE TIMBER ROOF

Possibility to increase load-carrying capacity of arch-type timber roof of multifunctional public building with the span equal to 60 m was analysed. Three-hinged segment arches with the rectangular glued cross-sections are considered as the main load-carrying structures in the transversal direction. Freely supported purlins with the massive rectangular cross-sections are considered as the main load-carrying structures in the longitudinal direction. The dependences between height of the arches, it bays and distances between the bracing members strengthening top and bottom zone of the arches cross-sections so as relative materials consumption and specific load-carrying capacity of the arches were obtained as the second power polynomial equations. Height of the arches and it bay changes within the limits from 10 to 30 and from 2 to 9 m, correspondingly. The distances between the bracing members strengthening top and bottom zone of the arches changes within the limits from 2 till 10 and from 4 till 16 m, correspondingly. The arch-type timber roof was considered under the action of the load combination which include structural dead weight, drifted and undrifted snow loads and wind loads. The relative materials consumption of the arches was determined as a relation between the dead weight of the arch to it span and changes within the limits from 24 till 114 kg/m. Glued and solid timber with strength classes GL24h and C24 are considered as materials of arches and purlins, correspondingly. The specific load-carrying capacity of the arches was determined as a relation between load –carrying capacity of the arche and volume of structural materials. Specific load-carrying capacity of the arches changes within the limits from 0.23 till 0.83 kN/m/t in the case, if purlins are taken into account. It was shown, that the rational from the point of view of materials consumption and specific load-carrying capacity height of the arche, it bays so as the distances between the bracing members strengthening top and bottom zone of the arches are equal to 15, 7.5, 5 and 15 m, correspondingly. Corresponding values of relative materials consumption and specific load-carrying capacity are equal to 24 and 0.23 kN/m/t. The depth and width of the arche cross-section were equal to 1617 and 318 mm, correspondingly. It was shown, that strengthening of the arches cross-section by the steel bars of strength class B500 and carbon fibre reinforced plastic tape Sika Crbo Dur S512 enables to increase load-carrying capacity of the arche by 10.20 and 9.48%, correspondingly. But common use of the steel bars together with the carbon fibre reinforced plastic tapes enables to increase load-carrying capacity of the arche by 18.89%.

Design considerations for photovoltaic panel arrays made from aluminium: a case study

AbstractThis paper presents the design considerations for typical photovoltaic panel arrays having aluminium members. Section and member design checks are performed according to Eurocode 9 on the basis of the wind, snow and seismic loads of Eurocodes 1 and 8. Improvements to the design are then sought, starting by reducing the distance between the vertical posts and then by changing the thickness of specific sections. Following that, the effects of member imperfections and connection flexibility are studied using a reduced flexural rigidity and different rotational stiffness values respectively. The degree of dynamic coupling when the array is placed on the top floor of an existing building as well as the influence of founding the vertical posts on compliant ground are also evaluated.

Comparison of Simulations of Updraft Mass Fluxes and Their Response to Increasing Aerosol Concentration between a Bin Scheme and a Bulk Scheme in a Deep-Convective Cloud System

Key microphysical processes whose parameterizations have substantial impacts on the simulation of updraft mass fluxes and their response to aerosol are investigated in this study. For this investigation, comparisons of these parameterizations are made between a bin scheme and a bulk scheme. These comparisons show that the differences in the prediction of cloud droplet number concentration (CDNC) between the two schemes determine whether aerosol-induced invigoration of updrafts or convection occurs. While the CDNC prediction leads to aerosol-induced invigoration of updrafts and an associated 20% increase in the peak value of the updraft-mass-flux vertical profile in the bin scheme, it leads to aerosol-induced suppression of updrafts and an associated 7% decrease in the peak value in the bulk scheme. The comparison also shows that the differences in ice processes, in particular, in the snow loading lead to the different vertical patterns of the updraft-mass-flux profile, which is represented by the peak value and its altitude, between the schemes. Higher loading of snow leads to around 20–30% higher mean peak value and its around 40% higher altitude in the bin scheme than in the bulk scheme. When differences in the CDNC prediction and ice processes are removed, differences in the invigoration and the vertical pattern disappear between the schemes. However, despite this removal, differences in the magnitude of updraft mass fluxes still remain between the schemes. Associated with this, the peak value is around 10% different between the schemes. Also, after the removal, there are differences in the magnitude between cases with different aerosol concentrations for each scheme. Associated with this, the peak value is also around 10% different between those cases for each scheme. The differences between the cases with different aerosol concentrations for each scheme are generated by different evaporative cooling and different intensity of gust fronts between those cases. The remaining differences between the schemes are generated by different treatments of collection and sedimentation processes.

Detecting intercepted snow on mountain needleleaf forest canopies using satellite remote sensing

Snow interception in cold regions needleleaf forest canopies is a crucial process that controls local snow accumulation and redistribution over >20% of the Earth's land surface. Various ground-based methods exist to measure intercepted snow load, however all are based on single-tree measurements and are difficult to implement. No research has focussed on detecting large areal intercepted snow loads and no studies have assessed the use of satellite observations. In this study, four remote sensing indices (NDSI, NDVI, albedo, and land surface temperature (LST)) were retrieved from Landsat images to study their sensitivity to canopy intercepted snow and the possibility of using them to detect the presence of intercepted snow. The results indicate that presence of intercepted snow on canopy increased NDSI and albedo, but decreased NDVI. Intercepted snow presence also decreased the areal variability of NDSI and NDVI while increasing that of albedo. For these three indices, the differences between snow-free and snowcovered canopies were correlated to topography and forest canopy cover. Of these indices, NDSI changed the greatest. Intercepted snow noticeably decreased the LST difference between forest and open areas in springtime while the influence in wintertime was relatively smaller. An intercepted snow detection approach that uses both NDSI and NDVI to classify pixels into either snowcovered canopy or other (snow-free canopy and non-forest areas) is proposed here. A case study applying this approach compared remote sensing detection to simulations by the snow interception and sublimation model implemented in the Cold Regions Hydrological Modelling platform (CRHM). This used local meteorological observations from the pine, spruce and fir forest covered Marmot Creek Research Basin in the Canadian Rockies. The remote sensing detection of intercepted snow agreed well with CRHM simulations for continuous forests (83%) and less well for sparse forests (72%) and clearings with small trees (70%). Therefore, the approach is suitable for intercepted snow detection over continuous evergreen canopies. This technique provides a new capability for large-scale snow interception model validation and data assimilation to cold regions hydrological forecasting models.

Investigation of parameters of pre-stressed metal combined cable-stayed systems with hanging transport equipment

The previous tension in building structures allows the distribution of force between the elements of the structure so that in each of them, at least at one combination of loads, the actual stress is equal to or close to the calculated resistance of the material. Pre-stressed metallic combined cable-stayed systems with hanging transport equipment have been investigated. They have been calculated with optimization of distribution of forces and material according to the method and algorithm proposed by the author. Optimization has been done executed using linear programming. With the help of the computer program created by the author, calculations of metal constructions of combined cable-stayed coverings of industrial buildings with 60, 85 and 105 meters spans were performed on the permissible combinations of permanent, snow, wind and crane loads. Comparison of calculations results was carried out on maximum deformations and the actual weight of the structure, using the graphs made by the author, concerning dependence of construction coefficients of weight of the cables on their length. Recommendations are given for the calculation of such structures in accordance with the undeformed scheme, the dismemberment of the beam of rigidity on the panel, the method of coupling the beam of stiffness, pylons and risers, the number of suspension guy, the height of the pylons, the slope angle of the guy-wire, the choice of the material of the cables, The table and examples of graphs are presented, which illustrate some results for individual runs of the investigated constitutions.

PREDICTION OF UNEVEN DISTRIBUTION OF SNOW LOAD BASED ON GENERALIZED REGRESSION NEURAL NETWORK

At present, there are mainly three research ways on the distribution of snow load: field measurement, experimental simulation, and numerical simulation. They all need expensive equipment, specimen model used only once, and slight defective simulation software. Artificial Neural Networks (ANNs) rely on a large number of input functions to estimate unknown or known occurrences. This paper applies ANNs to predict the uneven distribution of snow loads. First, the snow load database is collected and set up, including all the data from field measurement and experimental simulation. Second, part of the data from the 1 m3 model is used as a training set to train Backpropagation Neural Networks (BPNN) and Generalized Regression Neural Networks (GRNN). The parameters of the two neural networks are determined (such as the smoothing factor in the GRNN), and the rest of the data is used to examine the model; the prediction and measurement results of the two models are compared. Finally, based on different wind direction angles and wind speed, a GRNN model is established to predict the uneven snow load distribution. Through comparative analysis, GRNN is more suitable for predicting the uneven distribution of snow loads, especially in predicting snow thickness. In particular, the prediction effect of the model on the snow load distribution trend is good, and the prediction ability of the neural network model is displayed.

An investigation of snow drifting on flat roofs: Wind tunnel tests and numerical simulations

In snowy areas, the accurate prediction of snow distributions on roofs plays an important role in designing structures. The process of snow accumulations on roofs is complicated due to the action of wind, which is related to the wind field conditions (e.g., wind velocity, turbulence intensity, and wind direction), the geometry of roofs, temperature, humidity, and the property of the snow. To systematically study the effect of the length-height ratio of the flat roof and approach flow velocity on the uneven accumulation of snow loads on 3D flat roofs, wind tunnel tests of snow drifting are carried out using silica sand to simulate snow particles. Four models are designed with length-height ratios of 1, 2, 3, and 4, and then four nominal wind velocities are taken into consideration, namely 5.0 m/s, 5.5 m/s, 6.0 m/s, and 6.5 m/s. Two newly added parameters, the snow residual rate η and the erosion rate λ, are set up to illustrate the snow redistribution on 3D flat roofs. Then the effects of wind velocity or roof length on the average transport rate and the mass flux of flat roofs are systematically analyzed. Furthermore, the flow characteristics around the flat roof are obtained by means of numerical simulation, and the relationships between the flow characteristics (vorticity magnitude and friction velocity) near the flat roof and the snow redistribution pattern are carefully discussed. The snow redistribution on flat roofs is obviously uneven due to erosion mainly on both sides where the vorticity magnitude and friction velocity are also larger than in other places. The quantitative analysis indicates that the transport rate of snowdrift on the whole flat roof is proportional to the 4.45 power of the approaching wind velocity, which is slightly larger than the 3.8 derived from the empirical formula from field measurements.

A study of snow drifting on a flat roof during snowfall based on simulations in a cryogenic wind tunnel

Wind tunnel simulation is a very important approach to studying snow drifting and predicting drift snow loads on roofs. A complete simulation of the full process of wind-induced snow accumulation on a roof should include snow drifting both during snowfall and after snowfall. However, in most of the previous studies, snow drifting phenomenon was only simulated without concurrence of snowfall. We herein describe simulations of snow drifting on a flat roof during snowfall, which were carried out in a cryogenic wind tunnel using artificial snow particles. Based on the results, we demonstrate the differences and similarities between snow drifting during snowfall and that without concurrent snowfall. The developments of snow transport before saturated state apparently follow the same rule, no matter whether there is concurrent snowfall or not. However, it seems that the required fetch distance for a saturated saltation state can be reduced by snowfall. A formula is proposed to more reasonably describe the development of snow transport rate. Based on test results and deductions, some discussions on similarity requirements for modelling snow drifting on roofs during snowfall will be presented. Finally, a prediction of the prototype fetch distances under different wind and snowfall conditions will also be presented, which can provide a guide for further research and engineering application.

Improved Snow Drift Relations

AbstractDrift loads on roofs are arguably the most important snow load from a structural engineering perspective in the US, as they are the governing load for most cases of snow related structural ...

Practical tasks of probability calculation of the elements of steel silos

Problem statement. The use of probability methods in engineering practice is currently insufficient. This is hindered by the need to use a specific area of knowledge, such as the theory of random processes, mathematical statistics, the theory of reliability of buildings and structures, etc. However, the quantitative calculation of reliability indicators is a necessary moment in the process of building any construction. The level of reliability should be substantiated in the regulatory documents and directly applied in the process of design activities. Considering this, the research focuses exclusively on obtaining a quantitative estimate of the probability of failure-free operation for separate elements of steel storage capacities. This was done in accordance with the author's methodology and the main features of probability calculation. At the same time, the model of reliability function completely corresponds to the probability nature of constant and technological loads. For elements of steel storage capacities representing a random value of generalized strength is realized by a normal distribution law. For snow and wind loads, which are described by the method of random processes, it is used a technique that allows to proceed from the study of the whole process to the consideration of only its maximums, which are described by the double exponential distribution of Humbel. The example of solving practical problems will provide visibility to the performed research and will help the ordinary specialist to approach to the mastering of probabilistic calculations. Purpose. To provide an analytically simple algorithm for determining the level of reliability of elements of steel storage capacities or for solving other related problems of probability calculation of the given type of structures. On the basis of practical examples to illustrate the procedure of solving problems of this type and acquaint the engineer with the elementary principles of calculating for reliability the elements of steel construction of the storage capacities. Conclusion. On the basis of the unified approach and using the approximating expressions and concise mathematical calculations, a generalized algorithm for analytic probability calculation of elements of steel storage capacities is represented. Accordingly to formulas, it was made a numerical calculation of the probability of a failure-free operation, the reliability of the circular stiffener of the cylindrical capacity and it was solved the practical problem of the selection of the cross-section radial stiffener, according to the given level of the normative probability of work.

НАПРЯЖЕННО-ДЕФОРМИРОВАННОЕ СОСТОЯНИЕ КОНСТРУКЦИЙ КАРКАСА ПРИ ВАРЬИРОВАНИИ СНЕГОВОЙ НАГРУЗКИ

The multi-variant loading of the large-span unique steel covering of the stadium under snow load is considered. The spatial finite element model is developed using LIRA software. The analysis of the existing schemes application of snow loading is carried out according to the codes. Four snow load cases on the stadium's covering are assumed for analysis. The analysis of the stress-strain state of the stadium structures, the selection and verification of sections of the steel covering are performed. The results show that it is necessary to simulate behaviour of a structure under all possible load cases.