scholarly journals Snow on two-level flat roofs — measured vs. 1990 NBC loads

1992 ◽  
Vol 19 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Donald A. Taylor
Keyword(s):  
Average Density ◽  
Research Needs ◽  
Snow Density ◽  
Limit States ◽  
Snow Load ◽  
Load Factors ◽  
Multi Level ◽  
Snow Loads ◽  
Upper Level ◽  
Flat Roofs

Between 1967 and 1982, depths and specific gravities of snow were recorded on 44 single- and multi-level flat-roofed buildings between Halifax and Edmonton. The average density of snow in the drifts where the roofs change elevation was about 3.0 kN/m3, the value used consequently in the 1990 National Building Code of Canada (NBC). This is some 25% higher than the value used in the 1985 NBC. Data on drift geometry and maximum loads in the drifts are presented and compared with provisions in the 1990 NBC. As well, the paper presents measured values of average and maximum roof-to-ground load ratios for upper level roofs and for lower roofs away from the drifts. These compare favourably with those recommended in the 1985 and 1990 NBC. The statistical variabilities of snow loads and densities are given, since these are required to establish load factors used for limit states design in the NBC. Further research needs are identified. Key words: snow loads, snow drifts, uniform snow, flat roofs, snow density, snow load variability, snow load survey.

Load factor calibration for the proposed 2005 edition of the National Building Code of Canada: Companion-action load combinations

2003 ◽  
Vol 30 (2) ◽  
pp. 440-448 ◽  
Author(s):  
F M Bartlett ◽  
H P Hong ◽  
W Zhou
Keyword(s):  
Companion Paper ◽  
Building Code ◽  
Wind Loads ◽  
Load Factor ◽  
Live Load ◽  
Dead Load ◽  
Limit States ◽  
Snow Load ◽  
Load Factors ◽  
Snow Loads

The 2005 edition of the National Building Code of Canada (NBCC) will adopt a companion-action format for load combinations and specify wind and snow loads based on their 50 year return period values. This paper presents the calibration of these factors, based on statistics for dead load, live load due to use and occupancy, snow load, and wind load, which are summarized in a companion paper. A target reliability index of approximately 3 for a design life of 50 years was adopted for consistency with the 1995 NBCC. The load combinations and load factors for strength and stability checks recommended for the 2005 NBCC were based on preliminary values from reliability analysis that were subsequently revised slightly to address major inconsistencies with past practice. The recommended load combinations and factors generally give factored load effects similar to those in the 1995 NBCC, but are up to 10% more severe for the combination of dead load plus snow load and are generally less severe for the combination of dead load, snow load, and live load due to use and occupancy. Load factors less than one are recommended for checking serviceability limit states involving specified snow and wind loads. Importance factors for various classifications of structure are also presented. Revisions to the commentaries of the NBCC are recommended that will provide guidance on dead load allowances for architectural and mechanical superimposed dead loads and cast-in-place cover slabs and toppings.Key words: buildings, code calibration, companion action, dead loads, live loads, load combinations, load factors, reliability, safety, snow loads, wind loads.

Revised ground snow loads for the 1990 National Building Code of Canada

1989 ◽  
Vol 16 (3) ◽  
pp. 267-278 ◽  
Author(s):  
M. J. Newark ◽  
L. E. Welsh ◽  
R. J. Morris ◽  
W. V. Dnes
Keyword(s):  
Method Of Moments ◽  
Snow Depth ◽  
Extreme Value Distribution ◽  
Building Code ◽  
Snow Pack ◽  
Snow Density ◽  
Snow Load ◽  
The Mean ◽  
Snow Loads ◽  
Made In

The last systematic recalculation of ground snow loads in the Supplement to the National Building Code of Canada was made in 1977 and used data up to 1975. Data from three times as many stations are now available and there is also an additional 10 years of record. Using this expanded data base, ground snow loads have been recalculated for the 1990 Supplement.Several changes in methods have been utilized, the most significant of which is the use of an objective technique to estimate ground snow loads at Code (or other) locations. It explicitly incorporates an assumed dependence of the snow load on topographical elevation, and accounts for the magnitude of errors at snow depth observation sites. Other differences include (a) the use of the method of moments to fit the Gumbel extreme value distribution for the purpose of estimating the 30-year return period snow depth; (b) the use of geographically varying snow pack densities; and (c) using probabilistic rain components of the total snow load and estimating this component by use of a snow pack model.Results show an average national decrease of 6.6% in the 1990 loads compared with those in the 1985 Supplement. A regional exception is in the Northwest Territories where the use of a greater snow density has led to an average increase of about 16% in the loads. A reduction in the standard deviation about the mean load suggests a more spatially consistent set of values for the 1990 Supplement. Key words: snow, loads, building, code.

scholarly journals Effects of roof size, heat transfer, and climate on snow loads: studies for the 1995 NBC

1995 ◽  
Vol 22 (4) ◽  
pp. 770-784 ◽  
Author(s):  
P. A. Irwin ◽  
S. L. Gamble ◽  
D. A. Taylor
Keyword(s):  
Heat Transfer ◽  
Size Effect ◽  
Heat Loss ◽  
Large Area ◽  
Finite Area ◽  
Area Element ◽  
Snow Load ◽  
Snow Loads ◽  
Flat Roofs ◽  
Element Method

As roof sizes increase, the ability of the wind to reduce the uniform snow loads is diminished, thus resulting in higher uniform loads. Results of recent research into this size effect and the influence of heat loss through roofs in four Canadian cities (St. John's, Montreal, Saskatoon, and Edmonton) using the finite area element method are described and snow load formulae for uniform loads on large roofs are proposed. Also, the drift loading on lower roofs adjacent to large area upper roofs has been studied using similar techniques, and revised formulae for the peak loading in the drift at the step are put forward taking into account the size of the upper roof and the presence of parapets. The snow load provisions developed in this paper have been proposed for the 1995 edition of the National Building Code. Key words: snow loads, drift loads, uniform loads, large flat roofs, size effect, heat loss, finite area element method, computational fluid dynamics.

scholarly journals Snow loads in a changing climate: new risks?

2008 ◽  
Vol 8 (1) ◽  
pp. 1-8 ◽  
Author(s):  
U. Strasser
Keyword(s):  
Snow Cover ◽  
Freezing Point ◽  
Warning System ◽  
Winter Precipitation ◽  
Snow Load ◽  
Time Period ◽  
Sudden Rise ◽  
Trigger Event ◽  
Snow Loads ◽  
Modelling Data

Abstract. In January/February 2006, heavy snowfalls in Bavaria (Germany) lead to a series of infrastructural damage of catastrophic nature. Since on many collapsed roofs the total snow load was not exceptional, serious engineering deficiencies in roof construction and a sudden rise in the total snow load were considered to be the trigger of the events. An analysis of the then meteorological conditions reveals, that the early winter of 2005/2006 was characterised by an exceptional continuous snow cover, temperatures remained around the freezing point and no significant snowmelt was evident. The frequent freezing/thawing cycles were followed by a general compaction of the snow load. This resulted in a re-distribution and a new concentration of the snow load on specific locations on roofs. With respect to climate change, the question arises as to whether the risks relating to snow loads will increase. The future probability of a continuous snow cover occurrence with frequent freezing/thawing cycles will probably decline due to predicted higher temperatures. However, where temperatures remain low, an increase in winter precipitation will result in increased snow loads. Furthermore, the variability of extremes is predicted to increase. If heavy snowfall events are more frequent, the risk of a trigger event will likely increase. Finally, an attempt will be made here in this paper to outline a concept for an operational warning system for the Bavarian region. This system envisages to predict the development and risk of critical snow loads for a 3-day time period, utilising a combination of climate and snow modelling data and using this together with a snow pillow device (located on roofs) and the results of which.

A Probabilistic Approach to the Prediction of Snow Loads

1974 ◽  
Vol 1 (1) ◽  
pp. 28-49 ◽  
Author(s):  
N. Isyumov ◽  
A. G. Davenport
Keyword(s):  
Formation Process ◽  
Extreme Values ◽  
Meteorological Data ◽  
Digital Simulation ◽  
Probabilistic Approach ◽  
Snow Accumulation ◽  
Meteorological Variables ◽  
Snow Load ◽  
Design Values ◽  
Snow Loads

The magnitudes of loads imposed by snow depend upon a number of climatological and meteorological variables and as a result exhibit marked variations geographically, due to local effects within a particular region, and with time. The snowload formation process, which depends both on the macro- and microclimates of such meteorological variables as the depth of the snowfall, the snowfall density, wind speed, air temperature etc., as well as, the size and geometry of particular roofs and the influence of their immediate environment, is discussed.A model of the snow load formation process based on a mass balance approach, which takes into account the deposition of snow by individual snowfalls and the depletion of the snow load by wind action and thermal effects, is introduced. The use of this approach requires the establishment of statistical descriptions of the various meteorological variables, as well as a knowledge of the physical process of snow accumulation and depletion for a particular roof. The statistical properties of some of the more important meteorological variables are discussed. Also presented are some model derived data of snow accumulation and depletion for particular roofs located in different terrain.It is shown that even relatively simple statistical descriptions of the relevant meteorological data and snow accumulation and depletion mechanisms can lead to realistic predictions of roof snow loads. Snow loads on a flat roof are generated by a digital simulation technique and compared with full scale observations. Annual extreme values of the simulated snow load process are presented and compared with currently specified design values. Comments are made regarding the practicability of this approach.

Safety factors and limit states analysis in geotechnical engineering

1984 ◽  
Vol 21 (1) ◽  
pp. 1-7 ◽  
Author(s):  
G. G. Meyerhof
Keyword(s):  
Geotechnical Engineering ◽  
Stability Conditions ◽  
Safety Factors ◽  
Limit States ◽  
Resistance Factors ◽  
Performance Factors ◽  
Load Factors ◽  
Partial Safety Factors ◽  
And Performance ◽  
Earth Retaining Structures

This paper outlines the ultimate and serviceability limit states in geotechnical engineering analyses. The magnitude of customary total and suggested partial safety factors in earthworks, earth retaining structures, excavations, and foundations is discussed. On the basis of comparisons between these safety factors and using recommended load factors on various types of loading, including water pressures, common resistance factors on cohesion and friction of soils and performance factors can be established together with some additional modification factors for particular stability conditions. The serviceability limit states of foundations and structures are briefly discussed.

scholarly journals Prerequisites for accounting of fiber reinforcement when calculating normal sections of fibrorubcon beams

2019 ◽  
Vol 7 (1) ◽  
pp. 66-69
Author(s):  
Алексей Поликутин ◽  
Aleksey Polikutin ◽  
Юрий Потапов ◽  
Yuriy Potapov ◽  
Артем Левченко ◽  
...  
Keyword(s):  
Fiber Reinforcement ◽  
High Strength ◽  
Polymer Concrete ◽  
Pure Bending ◽  
Limit States ◽  
A Value ◽  
Methods Of Calculation ◽  
Steel Cord ◽  
Multi Level ◽  
Rubber Concrete

Develop recommendations for the use of polymer-concrete bending structures is impossible without the creation or optimization of existing methods of calculation, this is especially true for bending elements that use multi-level reinforcement. Для применения (especially under the influence of aggressive environment) for use as a material for the manufacture of bending structures, we offer rubber concrete. – polymer-concrete, which is characterized by high strength characteristics. It is important to note that the composition of fibrorubcon used industrial waste such as fly ash and steel cord. Beams made from cauton and fibrocahuton were tested for pure bending - the most characteristic form of loading in the study of such elements. As a result of the theoretical studies of polymer concrete beams, the prerequisites were established for the calculation of the first group of limit states of rubcon beams and the method for calculating fibrorubcon beams was optimized. It was determined that fiber reinforcement with a percentage of reinforcement by mass of the rubcon element equal to 2.5% corresponds to the work of rod longitudinal reinforcement with a value of μ = 0.34%.

scholarly journals Accounting for Non-stationarity in Extreme Snow Loads: a Comparison with Building Standards in the French Alps

2020 ◽  
Author(s):  
Erwan Le Roux ◽  
Guillaume Evin ◽  
Nicolas Eckert ◽  
Juliette Blanchet ◽  
Samuel Morin
Keyword(s):  
Climate Change ◽  
Snow Depth ◽  
Return Level ◽  
Snow Density ◽  
French Alps ◽  
Return Levels ◽  
Ground Snow Load ◽  
Snow Loads ◽  
Building Standards ◽  
Current Standards

Abstract. In a context of climate change, trends in extreme snow loads need to be determined to minimize the risk of structure collapse.We study trends in annual maxima of ground snow load (GSL) using non-stationary extreme value models. Trends in return levels of GSL are assessed at a mountain massif scale from GSL data, provided for the French Alps from 1959 to 2019 by a meteorological reanalysis and a snowpack model. Our results indicate a temporal decrease in 50-year return levels from 900 m to 4200 m, significant in the Northwest of the French Alps until 2100 m. Despite this decrease, in half of the massifs, the return level in 2019 at 1800 m exceeds the return level designed for French building standards under a stationary assumption. We believe that this high number of exceedances is due to questionable assumptions concerning the computation of current standards. For example, these were devised with GSL, estimated from snow depth and constant snow density set to 150 kg m−3, which underestimate typical GSL values for the full snowpack.

scholarly journals Injury Severity of Bus–Pedestrian Crashes in South Korea Considering the Effects of Regional and Company Factors

2019 ◽  
Vol 11 (11) ◽  
pp. 3169 ◽  
Author(s):  
Ho-Chul Park ◽  
Yang-Jun Joo ◽  
Seung-Young Kho ◽  
Dong-Kyu Kim ◽  
Byung-Jung Park
Keyword(s):  
South Korea ◽  
Injury Severity ◽  
The Elderly ◽  
Type I ◽  
Severe Injuries ◽  
Crash Data ◽  
Level Model ◽  
Multi Level ◽  
Pedestrian Crashes ◽  
Upper Level

Bus–pedestrian crashes typically result in more severe injuries and deaths than any other type of bus crash. Thus, it is important to screen and improve the risk factors that affect bus–pedestrian crashes. However, bus–pedestrian crashes that are affected by a company’s and regional characteristics have a cross-classified hierarchical structure, which is difficult to address properly using a single-level model or even a two-level multi-level model. In this study, we used a cross-classified, multi-level model to consider simultaneously the unobserved heterogeneities at these two distinct levels. Using bus–pedestrian crash data in South Korea from 2011 through to 2015, in this study, we investigated the factors related to the injury severity of the crashes, including crash level, regional and company level factors. The results indicate that the company and regional effects are 16.8% and 5.1%, respectively, which justified the use of a multi-level model. We confirm that type I errors may arise when the effects of upper-level groups are ignored. We also identified the factors that are statistically significant, including three regional-level factors, i.e., the elderly ratio, the ratio of the transportation infrastructure budget, and the number of doctors, and 13 crash-level factors. This study provides useful insights concerning bus–pedestrian crashes, and a safety policy is suggested to enhance bus–pedestrian safety.

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