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 The impact of snow depth, snow density and ice density on sea ice thickness retrieval from satellite radar altimetry: results from the ESA-CCI Sea Ice ECV Project Round Robin Exercise

2015 ◽  
Vol 9 (1) ◽  
pp. 37-52 ◽  
Author(s):  
S. Kern ◽  
K. Khvorostovsky ◽  
H. Skourup ◽  
E. Rinne ◽  
Z. S. Parsakhoo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Snow Depth ◽  
Ice Thickness ◽  
Data Sets ◽  
Snow Density ◽  
Radar Altimetry ◽  
Sea Ice Thickness ◽  
The Mean ◽  
Satellite Radar ◽  
Satellite Radar Altimetry

Abstract. We assess different methods and input parameters, namely snow depth, snow density and ice density, used in freeboard-to-thickness conversion of Arctic sea ice. This conversion is an important part of sea ice thickness retrieval from spaceborne altimetry. A data base is created comprising sea ice freeboard derived from satellite radar altimetry between 1993 and 2012 and co-locate observations of total (sea ice + snow) and sea ice freeboard from the Operation Ice Bridge (OIB) and CryoSat Validation Experiment (CryoVEx) airborne campaigns, of sea ice draft from moored and submarine upward looking sonar (ULS), and of snow depth from OIB campaigns, Advanced Microwave Scanning Radiometer (AMSR-E) and the Warren climatology (Warren et al., 1999). We compare the different data sets in spatiotemporal scales where satellite radar altimetry yields meaningful results. An inter-comparison of the snow depth data sets emphasizes the limited usefulness of Warren climatology snow depth for freeboard-to-thickness conversion under current Arctic Ocean conditions reported in other studies. We test different freeboard-to-thickness and freeboard-to-draft conversion approaches. The mean observed ULS sea ice draft agrees with the mean sea ice draft derived from radar altimetry within the uncertainty bounds of the data sets involved. However, none of the approaches are able to reproduce the seasonal cycle in sea ice draft observed by moored ULS. A sensitivity analysis of the freeboard-to-thickness conversion suggests that sea ice density is as important as snow depth.

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.

Extreme snow loads in Austria

2021 ◽  
Author(s):  
Michael Winkler ◽  
Harald Schellander
Keyword(s):  
Structural Design ◽  
Snow Depth ◽  
Generalized Additive Models ◽  
Value Theory ◽  
Additive Models ◽  
Snow Load ◽  
Snow Loads ◽  
Snow Model ◽  
European Standards ◽  
Smooth Map

<p>In the framework of European standards for structural design, acceptable snow loads on constructions and buildings are based on maps for s<sub>k,</sub> the “characteristic snow load on the ground” with an average reoccurrence time of 50 years. The Austrian snow load standard is built on a very detailed zoning map from 2006, but underlying snow data is from the 1980s.</p><p>An updated snow load map for Austria is presented. It is based on 870 snow depth records with at least 30 years of regular daily observations between 1960 and 2019. ΔSNOW, a novel snow model, was used to simulate respective snow loads. Extreme value theory and generalized additive models led to a smooth map of extreme snow loads at 50x50m resolution. The methods are transparently published, reproducible and, thus, applicable in other regions as well.</p><p>The map can reasonably assign s<sub>k</sub> values up to 2000m altitude, a significant advantage compared to actual standards which are only valid up to 1500m. New insights in the spatial picture of extreme snow loads are provided and the quadratic altitude-s<sub>k</sub>-relation, which is widely used in snow load standards, is evaluated. Validation with station data reveals a higher accuracy for the presented map than for the currently used snow load map. The number of outliers, i.d. stations with significantly higher or lower s<sub>k</sub> values than the snow load maps would suggest, could be decreased in comparison with the actual standard. However, some problematic places remain, mostly in topographically and climatologically highly complex areas. In case the presented map will become a new base for future Austrian standards, those places will have to be treated in a special way.</p>

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.

scholarly journals Non-stationary extreme value analysis of ground snow loads in the French Alps: a comparison with building standards

2020 ◽  
Vol 20 (11) ◽  
pp. 2961-2977
Author(s):  
Erwan Le Roux ◽  
Guillaume Evin ◽  
Nicolas Eckert ◽  
Juliette Blanchet ◽  
Samuel Morin
Keyword(s):  
Snow Depth ◽  
Extreme Value ◽  
Extreme Value Analysis ◽  
Snow Density ◽  
Value Analysis ◽  
French Alps ◽  
Return Levels ◽  
Snow Loads ◽  
Structure Collapse ◽  
Building 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 50-year return levels of ground snow load (GSL) using non-stationary extreme value models. These trends 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 to 4200 m, significant in the northwest of the French Alps up to 2100 m. We detect the most important decrease at 900 m with an average of −30 % for return levels between 1960 and 2010. Despite these decreases, in 2019 return levels still exceed return levels designed for French building standards under a stationary assumption. At worst (i.e. at 1800 m), return levels exceed standards by 15 % on average, and half of the massifs exceed standards. We believe that these exceedances are due to questionable assumptions concerning the computation of standards. For example, these were devised with GSL, estimated from snow depth maxima and constant snow density set to 150 kg m−3, which underestimate typical GSL values for the snowpack.

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.

Snow loads in the 1985 National Building Code of Canada: Curved roofs

1985 ◽  
Vol 12 (3) ◽  
pp. 427-438 ◽  
Author(s):  
Timothy H. R. Kennedy ◽  
D. J. Laurie Kennedy ◽  
James G. MacGregor ◽  
Donald A. Taylor
Keyword(s):  
Shear Force ◽  
Circular Cross Section ◽  
Bending Moment ◽  
Building Code ◽  
Bending Moments ◽  
Snow Load ◽  
Wide Range ◽  
Loading Case ◽  
Snow Loads ◽  
Load Intensity

In the 1985 edition of the National Building Code of Canada (NBCC) the intensity of the specified snow load at any location on a roof is obtained by multiplying the ground snow load for the building locale by a series of factors. These factors reflect the overall reduction in average snow loads on roofs as compared with that on the ground, the effect of exposure to wind, the effect of roof slope, and the effect of drifting, sliding, creep, and drainage.The four loading cases for the design of curved roofs suggested in the Commentary on snow loads accompanying the 1980 NBCC were examined by determining, for roofs of circular cross section, the variation across the span of load intensity, shear force, and bending moment for a wide range of spans, ground snow loads, and roof edge slopes. The purpose of the examination was to fully describe known inconsistencies arising from these loading cases.A new case for drift loading was developed (case III) that, when used with "full" or "uniform" loading and with the unbalanced loading developed for the 1977 NBCC (case II), eliminates or at least reduces the inconsistencies. With this new loading case and the derivation of a formula to define when to switch from loading case II to the new case III the designer now has to consider only one unbalanced loading condition rather than three as before.A simplified method for establishing specified load intensities, shear forces, and bending moments, suitable at least for preliminary design, is also presented. Key words: bending moments, curved roofs, drifts, load intensity, shear force, snow load factors, wind.

scholarly journals Estimating the snow water equivalent on a glacierized high elevation site (Forni Glacier, Italy)

2018 ◽  
Vol 12 (4) ◽  
pp. 1293-1306 ◽  
Author(s):  
Antonella Senese ◽  
Maurizio Maugeri ◽  
Eraldo Meraldi ◽  
Gian Pietro Verza ◽  
Roberto Sergio Azzoni ◽  
...  
Keyword(s):  
Snow Depth ◽  
Snow Water Equivalent ◽  
High Elevation ◽  
Average Density ◽  
Snow Density ◽  
Alpine Regions ◽  
Yearly Average ◽  
Snow Water ◽  
The Mean ◽  
Observation Period

Abstract. We present and compare 11 years of snow data (snow depth and snow water equivalent, SWE) measured by an automatic weather station (AWS) and corroborated by data from field campaigns on the Forni Glacier in Italy. The aim of the analysis is to estimate the SWE of new snowfall and the annual SWE peak based on the average density of the new snow at the site (corresponding to the snowfall during the standard observation period of 24 h) and automated snow depth measurements. The results indicate that the daily SR50 sonic ranger measurements and the available snow pit data can be used to estimate the mean new snow density value at the site, with an error of ±6 kg m−3. Once the new snow density is known, the sonic ranger makes it possible to derive SWE values with an RMSE of 45 mm water equivalent (if compared with snow pillow measurements), which turns out to be about 8 % of the total SWE yearly average. Therefore, the methodology we present is interesting for remote locations such as glaciers or high alpine regions, as it makes it possible to estimate the total SWE using a relatively inexpensive, low-power, low-maintenance, and reliable instrument such as the sonic ranger.

scholarly journals Expected Snow Loads on Structures from Incomplete Hydrological Data

1977 ◽  
Vol 19 (81) ◽  
pp. 185-195 ◽  
Author(s):  
J. Martinec
Keyword(s):  
Snow Cover ◽  
Frequency Analysis ◽  
Building Code ◽  
Return Periods ◽  
Snow Load ◽  
Hydrological Data ◽  
Regional Effects ◽  
Direct Measurements ◽  
Snow Loads

Abstract An assessment of snow loads in Switzerland was required for a revision of the building code. Settling curves of snow are used to compute water equivalents of snow if direct measurements are not available. Based on a frequency analysis, relations between the snow load and the altitude are given for various return periods. Problems of regional effects and of converting the snow-cover data to roof loads are outlined.

scholarly journals Expected Snow Loads on Structures from Incomplete Hydrological Data

1977 ◽  
Vol 19 (81) ◽  
pp. 185-195 ◽  
Author(s):  
J. Martinec
Keyword(s):  
Snow Cover ◽  
Frequency Analysis ◽  
Building Code ◽  
Return Periods ◽  
Snow Load ◽  
Hydrological Data ◽  
Regional Effects ◽  
Direct Measurements ◽  
Snow Loads

AbstractAn assessment of snow loads in Switzerland was required for a revision of the building code. Settling curves of snow are used to compute water equivalents of snow if direct measurements are not available. Based on a frequency analysis, relations between the snow load and the altitude are given for various return periods. Problems of regional effects and of converting the snow-cover data to roof loads are outlined.

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