Climatic Text C-1

Climatic Text C-1 - Division B Appendix G Climatic and...

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Unformatted text preview: Division B Appendix G Climatic and Seismic Information for Building Design in Canada Introduction The great diversity of climate in Canada has a considerable effect on the performance of buildings; consequently, building design must reflect this diversity. This Appendix briefly describes how climatic design values are computed and provides recommended design data for a number of cities, towns, and smaller populated locations. Through the use of such data, appropriate allowances can be made for climate variations in different localities of Canada and the National Building Code can be applied nationally. The climatic design data provided in this Appendix are based on weather observations collected by the Atmospheric Environment Service, Environment Canada. The climatic design data have been researched and analyzed for the Canadian Commission on Building and Fire Codes by Environment Canada, and appear at the end of this Appendix in Table C-2, Design Data for Selected Locations in Canada. As it is not practical to list values for all municipalities in Canada, recommended climatic design values for locations not listed can be obtained by contacting the Atmospheric Environment Service, Environment Canada, 4905 Dufferin Street, Downsview, Ontario M3H 5T4, (416) 739-4365. It should be noted, however, that these recommended values may differ from the legal requirements set by provincial, territorial or municipal building authorities. The information on seismic hazard in spectral format has been provided by the Geological Survey‘of Canada of Natural Resources Canada. Information for municipalities not listed may be obtained through the Natural Resources Canada Web site at www.EarthquakesCanada.ca, or by writing to the Geological Survey of Canada at 7 Observatory Crescent, Ottawa, Ontario K1A 0Y3, or at PO. Box 6000, Sidney, B.C. V8L 4B2. General The Choice of Climatic elements tabulated in this Appendix and the form in which they are expressed have been dictated largely by the requirements for specific values in several sections of the National Building Code of Canada 2005. These elements include the Ground Snow Loads, Wind Pressures, Design Temperatures, Heating Degree-Days, One-Day and 15-Minute Rainfalls, the Annual Total Precipitation values and Seismic Data. The following notes briefly explain the significance of these particular elements in building design, and indicate which weather observations were used and how they were analyzed to yield the required design values. In Table C-2, Design Data for Selected Locations in Canada (referred to in this Appendix as the Table), design weather recommendations and elevations are listed for over 600 locations, which have been chosen based on a variety of reasons. Many incorporated cities and towns with significant populations are included unless located close to larger cities. For sparsely populated areas, many smaller towns and villages are listed. Other locations have been added to the list when the demand for climatic design recommendations at these sites has been significant. The named locations refer to the specific latitude and longitude defined by the Gazetteer of Canada (Natural Resources Canada), available from Publishing and Depository Services Canada, Public Works and Government Services Canada, Ottawa, Ontario K1A 0S5. The elevations are given in metres and refer to heights above sea level. Almost all of the weather observations used in preparing the Table were, of necessity, observed at inhabited locations. To estimate design values for arbitrary locations, the observed or computed values for the weather stations were mapped and interpolated appropriately. Where possible, adjustments have been applied for the influence of elevation and known topographical effects. Such influences include the tendency of cold air to collect in depressions, for precipitation to increase with elevation, and for generally stronger winds near large bodies of water. Elevations have been added to the Table because of their potential to significantly influence climatic design values. This Appendix is included for explanatory purposes only and does not form part of the requirements. National Building Code of Canada 2005 Volume 2 Division B C-1 Appendix 0 Division B Since interpolation from the values in the Table to other locations may not be valid due to local and other effects, Environment Canada will provide climatic design element recommendations for locations not listed in the Table. Local effects are particularly significant in mountainous areas, where the values apply only to populated valleys and not to the mountain slopes and high passes, where very different conditions are known to exist. Changing and Variable Climates Climate is not static. At any location, weather and climatic conditions vary from season to season, year to year, and over longer time periods (climate cycles). This has always been the case. When estimating climatic design loads, this variability can be considered using appropriate statistical analysis, data records spanning sufficient periods, and meteorological judgement. The analysis generally assumes that the past climate will be representative of the future climate. Past and ongoing modifications to atmospheric chemistry (from greenhouse gas emissions and land use changes) are expected to alter most climatic regimes in the future. As a result, it can no longer be safely assumed that the climate of the past few decades will be a sufficient guide to the climate of the next few decades. While average climatic conditions may be changing, the frequency and magnitude of extreme climatic events may also be changing in unknown ways. Although consensus is emerging on the long-term trends for some climatic elements, there is no agreement as yet on the changes expected in climatic variability. January Design Temperatures A building and its heating system should be designed to maintain the inside temperature at some pre-determined level. To achieve this, it is necessary to know the most severe weather conditions under which the system will be expected to function satisfactorily. Failure to maintain the inside temperature at the pre-determined level will not usually be serious if the temperature drop is not great and if the duration is not long. The outside conditions should, therefore, not be the most severe in many years, but should be the somewhat less severe conditions that are occasionally but not greatly exceeded. The January design temperatures are based on an analysis of January air temperatures only. Wind and solar radiation also affect the inside temperature of most buildings and may need to be considered for energy-efficient design. The January design temperature is defined as the lowest temperature at or below which only a certain small percentage of the hourly outside air temperatures in January occur. In the past, a total of 158 stations with records from all or part of the period 1951-66 formed the basis for calculation of the 2.5 and 1% January temperatures. Where necessary, the data were adjusted for consistency. Since most of the temperatures were observed at airports, design values for the core areas of large cities could be 1 or 2°C milder, although the values for the fringe areas are probably about the same as for the airports. No adjustments were made for this urban heat island effect. The design values for the next 20 to 30 years probably will differ from these tabulated values due to year-to-year climate variability and global climate change resulting from human modifications to atmospheric chemistry. A review of the design temperatures was undertaken for the 1995 issue of this Appendix using hourly temperature observations from 265 stations for the length of record up to 1993. Where needed, hourly temperatures were supplemented with correlated record minimum temperatures from 1449 long-term stations. The results from the recent analysis indicated reasonable consistency with the previous recommendations. Consequently, the January design temperatures remain unchanged from previous issues of the Supplement to the National Building Code of Canada. The 2.5% January design temperature is the value ordinarily used in the design of heating systems. In special cases, when the control of inside temperature is more critical, the 1% value may be used. Other temperature-dependent climatic design parameters may be considered for future issues of this document. July Design Temperatures A building and its cooling and dehumidifying system should be designed to maintain the inside temperature and humidity at certain pre-determined levels. To achieve this, it is necessary to know the most severe weather conditions under which the system is expected to function satisfactorily. Failure to maintain the inside temperature and humidity at the pre-determined levels will usually not be serious if the increases in temperature and humidity are not great and the duration is not long. The outside conditions used for design should, therefore, not be the most severe in many years, but should be the somewhat less severe conditions that are occasionally but not greatly exceeded. C-2 Division B National Building Code of Canada 2005 Volume 2 Division B Appendix C The summer design temperatures in this Appendix are based on an analysis of July air temperatures and humidities. Wind and solar radiation also affect the inside temperature of most buildings and may, in some cases, be more important than the outside air temperature. More complete summer and winter design information can be obtained from Environment Canada. In the past, two datasets formed the basis for calculation of the July 25% dry-bulb temperatures. The first dataset was based on temperature frequency distributions for 33 stations and an empirical relationship between design temperatures and the mean annual maximum temperature. The second dataset consisted of hourly data summaries for 109 stations based on records from 1957 to 1966. Results from the two datasets were averaged and adjusted for consistency. The July 2.5% wet-bulb temperatures were obtained in a similar way, using the two datasets, but without the use of an empirical relationship for the first dataset. A review of the July design temperatures was undertaken for the 1995 issue of this Appendix. Design dry-bulb temperatures were analyzed using hourly temperature observations from 264 stations for the length of record up to 1993. Where needed, hourly dry—bulb temperatures were supplemented with correlated record maximum temperatures from 1450 long-term stations. The July 2.5% coincident wet-bulb temperatures were obtained by - averaging wet-bulb temperatures for all hours when the dry—bulb temperature was within 02°C of the July design dry-bulb temperature. A comparison of the results indicated reasonable consistency for design dry-bulb temperatures but some differences for design wet-bulb temperatures that will be investigated for future issues. The July design temperatures remain unchanged for this issue. Heating Degree-Days The rate of consumption of fuel or energy required to keep the interior of a small building at 21°C when the outside air temperature is below 18°C is roughly proportional to the difference between 18°C and the outside temperature. Wind speed, solar radiation, the extent to which the building is exposed to these elements and the internal heat sources also affect the heat required and may have to be considered for energy-efficient design. For average conditions of wind, radiation, exposure, and internal sources, however, the proportionality with the temperature difference generally still holds. Since the fuel required is also proportional to the duration of the cold weather, a convenient method of combining these elements of temperature and time is to add the differences between 18°C and the mean temperature for every day in the year when the mean temperature is below 18°C. It is assumed that no heat is required when the mean outside air temperature for the day is 18°C or higher. Although more sophisticated computer simulations using other forms of weather data have now almost completely replaced degree-day-based calculation methods for estimating annual heating energy consumption, degree—days remain a useful indicator of relative severity of climate and can form the basis for certain climate—related code requirements. The degree-days below 18°C have been computed day by day for 1030 stations for the length of record available from the period 1961 to 1990. The average annual degree-day values were then interpolated from analyzed maps. When observations with 20 years or more of record were available, recommendations for those locations were weighted towards the observed value. A difference of only one Celsius degree in the mean annual temperature will cause a difference of 250 to 350 in the Celsius degree-days. Since differences of 0.5 of a Celsius degree in the mean annual temperature are quite likely to occur between two stations in the same town, heating degree-days cannot be relied on to an accuracy of less than about 100 degree-days. Heating degree—day values for the core areas of larger cities can be 200 to 400 degree-days less (warmer) than for the surrounding fringe areas. The observed degree—days, which are based on daily temperature observations, are often most representative of rural settings or the fringe areas of cities. Snow Loads The roof of a building should be able to support the greatest weight of snow that is likely to accumulate on it in many years. Some observations of snow on roofs have been made in Canada, but not enough to form the basis for estimating roof snow loads throughout the country. Similarly, observations of the'weight, or water equivalent, of the snow on the ground have not been available in digital form in the past. The observations of roof loads and water equivalents are very useful, as noted below, but the measured depth of snow on the ground is used to provide the basic information for a consistent set of snow loads. The estimation of the design snow load on a roof from snow depth observations involves the following steps: 1. The depth of snow on the ground, which has an annual probability of exceedance of 1—in-50, is computed. National Building Code of Canada 2005 Volume 2 Division B C-3 Appendix 0 Division B The appropriate unit weight is selected and used to convert snow depth to loads, SS. The load, S, which is due to rain falling on the snow, is computed. Because the accumulation of snow on roofs is often different from that on the ground, adjustments are applied to the ground snow load to provide a design snow load on a roof. $.09!” The annual maximum depth of snow on the ground has been assembled for 1618 stations for which data has been recorded by the Atmospheric Environment Service (AES). The period of record used varied from station to station, ranging from 7 to 38 years. These data were analyzed using a Gumbel extreme value distribution fitted using the method of momentsm as reported by Newark et al.(2) The resulting values are the snow depths, which have a probability of 1-in—50 of being exceeded in any one year. The unit weight of old snow generally ranges from 2 to 5 kN / m3, and it is usually assumed in Canada that 1 kN/ m3 is the average for new snow. Average unit weights of the seasonal snow pack have been derived for different regions across the country(3) and an appropriate value has been assigned to each weather station. Typically, the values average 2.01 kN/m3 east of the continental divide (except for 2.94 kN/ m3 north of the treeline), and range from 2.55 to 4.21 kN/ m3 west of the divide. The product of the 1-in—50 snow depth and the average unit weight of the seasonal snow pack at a station is converted to the snow load (SL) in units of kilopascals (kPa). Except for the mountainous areas of western Canada, the values of the ground snow load at AES stations were normalized assuming a linear variation of the load above sea level in order to account for the effects of topography. They were then smoothed using an uncertainty-weighted moving-area average in order to minimize the uncertainty due to snow depth sampling errors and site-specific variations. Interpolation from analyzed maps of the smooth normalized values yielded a value for each location in the Table, which could then be converted to the listed code values (SS) by means of an equation in the form: SS 2 smooth normalized SL + bZ where b is the assumed rate of change of SL with elevation at the location and Z is the location’s elevation above mean sea level (MSL). Although they are listed in the Table of Design Data to the nearest tenth of a kilopascal, values of S5 typically have an uncertainty of about 20%. Areas of sparse data in northern Canada were an exception to this procedure. In these regions, an analysis was made of the basic SL values. The effects of topography, variations due to local climates, and smoothing were all subjectively assessed. The values derived in this fashion were used to modify those derived objectively. For the mountainous areas of British Columbia, Yukon, and the foothills area of Alberta, a more complex procedure was required to account for the variation of loads with terrain and elevation. Since the AES observational network often does not have sufficient coverage to detail this variability in mountainous areas, additional snow course observations were obtained from the provincial and territorial governments of British Columbia, Yukon, and Alberta. The additional data allowed detailed local analysis of ground snow loads on a valley-by-valley basis. Similar to other studies, the data indicated that snow loads above a critical or reference level increased according to either a linear or quadratic relation with elevation. The determination of whether the increase with elevation was linear or quadratic, the rate of the increase and the critical or reference elevation were found to be specific to the valley and mountain ranges considered. At valley levels below the critical elevation, the loads generally varied less significantly with elevation. Calculated valley- and range-specific regression relations were then used to describe the increase of load with elevation and to normalize the AES snow observations to a critical or reference level. These normalized values were smoothed using a weighted moving-average. Tabulated values cannot be expected to indicate all the local differences in SS. For this reason, especially in complex terrain areas, values should not be interpolated from the Table for unlisted locations. The values of S5 in the Table apply for the elevation and the latitude and longitude of the location, as defined by the Gazetteer of Canada. Values at other locations can be obtained from Environment Canada. The heaviest loads frequently occur when the snow is wetted by rain, thus the rain load, Sr, was estimated to the nearest 0.1 kPa and is provided in the Table. When values of Sr are added to S5, this provides a 1-in—50-year estimate of the combined ground snow and rain load. The values of Sr are based on an analysis of about 2100 weather station values of the 1-in-50-year one-day maximum rain amount. This return period is appropriate because the rain amounts correspond approximately to the joint frequency of occurrence of the one-day rain on maximum snow packs. For the purpose of estimating rain on snow, the individual observed one-day rain amounts were constrained to be less than or equal to the snow pack water equivalent, which was estimated by a snow pack accumulation model reported by Bruce and Clark.(4) C-4 Division B National Building Code of Canada 2005 Volume 2 Division B Appendix c The results from surveys of snow loads on roofs indicate that average roof loads are generally less than loads on the ground. The conditions under which the design snow load on the roof may be taken as a percentage of the ground snow load are given in Subsection 4.1.6. of the Code. The Code also permits further decreases in design snow loads for steeply sloping roofs, but requires substantial increases for roofs where snow accumulation may be more rapid due to such factors as drifting. Recommended adjustments are given in the User’s Guide — NBC 2005, Structural Commentaries (Part 4 of Division B). Annual Total Precipitation Total precipitation is the sum in millimetres of the measured depth of rainwater and the estimated or measured water equivalent of the snow (typically estimated as 0.1 of the measured depth of snow, since the average density of fresh snow is about 0.1 that of water). The average annual total precipitation amounts in the Table have been interpolated from an analysis of precipitation observations from 1379 stations for the 30-year period from 1961 to 1990. Annual Rainfall The total amount of rain that normally falls in one year is frequently used as a general indication of the wetness of a climate, and is therefore included in this Appendix. See also Moisture Index below. Rainfall Intensity Roof drainage systems are designed to carry off rainwater from the most intense rainfall that is likely to occur. A certain amount of time is required for the rainwater to flow across and down the roof before it enters the gutter or drainage system. This results in the smoothing out of the most rapid changes in rainfall intensity. The drainage system, therefore, need only cope with the flow of rainwater produced by the average rainfall intensity over a period of a few minutes, which can be called the concentration time. In Canada, it has been customary to use the 15-minute rainfall that will probably be exceeded on an average of once in 10 years. The concentration time for small roofs is much less than 15 minutes and hence the design intensity will be exceeded more frequently than once in 10 years. The safety factors in the National Plumbing Code of Canada 2005 will probably reduce the frequency to a reasonable value and, in addition, the occasional failure of a roof drainage system will not be particularly serious in most cases. The rainfall intensity values tabulated in previous editions of this information were based on measurements of the annual maximum 15-minute rainfalls at 139 stations with 7 or more years of record. They were the 15-minute rainfalls that would be exceeded once in 10 years on average, or the values that had 1 chance in 10 of being exceeded in any one year. The values were analyzed using a Gumbel extreme value distribution“) It is very difficult to estimate the pattern of rainfall intensity in mountainous areas, where precipitation is extremely variable and rainfall intensity can be much greater than in other types of areas. Many of the observations for these areas were taken at locations in valley bottoms or in extensive, fairly level areas. One-Day Rainfall If for any reason a roof drainage system becomes ineffective, the accumulation of rainwater may be great enough in some cases to cause a significant increase in the load on the roof. In previous editions of this information, it had been common practice to use the maximum one-day rainfall ever observed for estimating the additional load. Since the length of record for weather stations in Canada is quite variable, the maximum one-day rainfall amounts in previous editions often reflected the variable length of record at nearby stations as much as the climatology. As a result, the maximum values often differed greatly within relatively small areas where little difference should be expected. The current values have been standardized to represent the one-day rainfall amounts that have 1 chance in 50 of being exceeded in any one year or the 1-in-50-year return value one-day rainfalls. The one-day rainfall values in the Table were based on measurements of the annual maximum one-day rainfalls for 2051 stations with 10 years or more of record. These 1-in-50—year values were obtained using a Gumbel extreme value distribution fitted using the method of moments.(1) Rainfall frequency observations can vary considerably over time and space. This is especially true for mountainous areas, where elevation effects can be significant. In other areas, small scale intense storms or local influences can produce significant spatial variability in the data. As a result, the analysis incorporates some spatial smoothing. National Building Code of Canada 2005 Volume 2 Division B C-5 Appendix c Division B Moisture Index (Ml) Moisture index (MI) values were developed through the work of a consortium that included representatives from industry and researchers from the Institute for Research in Construction at NRC.10 The MI is an indicator of the moisture load imposed on a building by the climate and is used in Part 9 to define the minimum levels of protection from precipitation to be provided by cladding assemblies on exterior walls. It must be noted, in using MI values to determine the appropriate levels of protection from precipitation, that weather conditions can vary markedly within a relatively small geographical area. Although the values provided in the Table give a good indication of the average conditions within a particular region, some caution must be exercised when applying them to a locality that is outside the region where the weather station is located. MI is calculated from a wetting index (WI) and a drying index (DI). Wetting Index (WI) To define, quantitatively, the rainwater load on a wall, wind speed and wind direction have to be taken into consideration in addition to rainfall, along with factors that can affect exposure, such as nearby buildings, vegetation and topography. Quantitative determination of load, including wind speed and wind direction, can be done. However, due to limited weather data, it is not currently possible to provide this information for most of the locations identified in the Table. This lack of information, however, has been shown to be non-critical for the purpose of classifying locations in terms of severity of rain load. The results of the research indicated that simple annual rainfall is as good an indicator as any for describing rainwater load. That is to say, for Canadian locations, and especially once drying is accounted for, the additional sensitivity provided by hourly directional rainfall values does not have a significant effect on the order in which locations appear when listed from wet to dry. Consequently, the wetting index (WI) is based on annual rainfall and is normalized based on 1000 mm. Drying Index (DI) Temperature and relative humidity together define the drying capacity of ambient air. Based on simple psychrometrics, values were derived for the locations listed in the Table using annual average drying capacity normalized based on the drying capacity at Lytton, BC. The resultant values are referred to as drying indices (DI). Determination of Moisture Index (MI) The relationship between WI and DI to correctly define moisture loading on a wall is not known. The MI values provided in the Table are based on the root mean square values of WI and 1-DI, with those values equally weighted. This is illustrated in Figure C-1. The resultant MI values are sufficiently consistent with industry’s understanding of climate severity with respect to moisture loading as to allow limits to be identified for the purpose of specifying where additional protection from precipitation is required. C-6 Division B National Building Code of Canada 2005 Volume 2 Division B Appendix c MI > 1 1 3 2 __Z O é '5 (U D. (U 0 O) E 2‘ D .C .9 .C 0 low , high 1 Ram load: WIN EG02066A Figure 6-1 Derivation of moisture index (Ml) based on normalized values for wetting index (WI) and drying index (DI) Note to Figure 0-1: (1) MI equals the hypotenuse of the triangle defined by WIN and 1-DlN Driving Rain Wind Pressure (DRWP) The presence of rainwater on the face of a building, with or without wind, must be addressed in the design and construction of the building envelope so as to minimize the entry of water into the assembly. Wind pressure on the windward faces of a building will promote the flow of water through any open joints or cracks in the facade. Driving rain wind pressure (DRWP) is the wind load that is coincident with rain, measured or calculated at a height of 10 m. The values provided in the Table represent the loads for which there is 1 chance in 5 of being reached or exceeded in any one year, or a probability of 20% within any one year. Approximate adjustments for height can be made using the values for Ce given in Sentence 4.1.7.1.(5) as a multiplier. Because of inaccuracies in developing the DRWP values related to the averaging of extreme wind pressures, the actual heights of recording anemometers, and the use of estimated rather than measured rainfall values, the values are considered to be higher than actual loads(9) Thus the actual probability of reaching or exceeding the DRWP in a particular location is less than 20% per year and these values can be considered to be conservative. DRWP can be used to determine the height to which wind will drive rainwater up enclosed vertical conduits. This provides a conservative estimate of the height needed for fins in window extrusions and end dams on flashings to control water ingress. This height can be calculated as: height of water, mm : DRWP/10, Pa National Building Code of Canada 2005 Volume 2 Division B 0-7 Appendix 0 Division B Note that the pressure difference across the building envelope may be augmented by internal pressures induced in the building interior by the wind. These additional pressures can be estimated using the information provided in the Commentary entitled Wind Load and Effects of the User’s Guide — NBC 2005, Structural Commentaries (Part 4 of Division B). Wind Effects All structures need to be designed to ensure that the main structural system and all secondary components, such as cladding and appurtenances, will withstand the pressures and suctions caused by the strongest wind likely to blow at that location in many years. Some flexible structures, such as tall buildings, slender towers and bridges, also need to be designed to minimize excessive wind-induced oscillations or vibrations. At any time, the wind acting upon a structure can be treated as a mean or time-averaged component and as a gust or unsteady component. For a small structure, which is completely enveloped by wind gusts, it is only the peak gust velocity that needs to be considered. For a large structure, the wind gusts are not well correlated over its different parts and the effects of individual gusts become less significant. The User’s Guide — NBC 2005, Structural Commentaries (Part 4 of Division B) evaluates the mean pressure acting on a structure, provide appropriate adjustments for building height and exposure and for the influence of the surrounding terrain and topography (including wind speed-up for hills), and then incorporate the effects of wind gusts by means of the gust factor, which varies according to the type of structure and the size of the area over which the pressure acts. The wind speeds and corresponding velocity pressures used in the Code are regionally representative or reference values. The reference wind speeds are nominally one-hour averages of wind speeds representative of the 10 m height in flat open terrain corresponding to Exposure A or open terrain in the terminology of the User’s Guide — NBC 2005, Structural Commentaries (Part 4 of Division B). The reference wind speeds and wind velocity pressures are based on long-term wind records observed at a large number of weather stations across Canada. In the past, reference wind velocity pressures in the Code have been calculated from hourly averaged wind speed observations measuring the number of miles of wind passing a wind anemometer cup in one hour. The pressures derived from these measurements were representative of true hourly wind pressures. When wind pressures were last calculated in the early 19605, the hourly averaged wind speeds were the records most commonly available for statistical analysis. Since that time, the majority of the principal observation stations, including the major airports, have converted their observation programs to aviation-type wind speed measurements or spot readings of wind speed.(5) These one-minute averaged wind speeds (later converted to two—minute averages) were observed just before the hour. True one-hour averaged wind speed records from over 100 stations for periods from 10 to 22 years formed the basis for most of the wind pressures provided in the Table. The wind velocity pressures, q, were calculated in Pascals using the following equation: q = %pV2 where p is an average air density for the windy months of the year and V is wind speed in metres per second. While air density depends on both air temperature and atmospheric pressure, the density of dry air at 0°C and standard atmospheric pressure of 1.2929 kg/m3 was used as an average value for the wind pressure calculations. As explained by Boyd(6), this value is within 10% of the monthly average air densities for most of Canada in the windy part of the year. Hourly wind speeds that have 1 chance in 10 and 50‘ of being exceeded in any one year were analyzed using the Gumbel extreme value distribution fitted using the method of moments with correction for sample size. Values of the 1-in—30—year wind speeds for locations in the Table were estimated from a mapping analysis of wind speeds. The 1-in-10- and 1-in-50—year speeds were then computed from the 1-in-30-year speeds using a map of the dispersion parameter that occurs in the Gumbel analysis“) Table C-1 has been arranged to give pressures to the nearest one-hundredth of a kPa and their corresponding wind speeds. The value of q 1n kPa is assumed to be equal to 0.00064645 V2, where V is given in m/ s. n // * Wind speeds that have a one-in- n -year chance of being exceeded in any year can be computed from the one-in—lO and one—in—SO return values in the Table using the following equation: Vl/n : ' V 5 —V —0.0339 {V1/50 +0.4565 V1/10 + M 1 } 1.4565 1.1339 X 11111(1 — 1/11) C-8 Division B National Building Code of Canada 2005 Volume 2 § Division B Appendix c Table C-1 Wind Speeds q V q V G V q V kPa m/s kPa m/s kPa m/s kPa m/s 0.15 15.2 0.53 28.6 0.91 37.5 1.29 44.7 0.16 15.7 0.54 28.9 0.92 37.7 1.30 44.8 0.17 16.2 0.55 29.2 0.93 37.9 1.31 45.0 0.18 16.7 0.56 29.4 0.94 38.1 1.32 45.2 0.19 17.1 0.57 29.7 0.95 38.3 1.33 45.4 0.20 17.6 0.58 30.0 0.96 38.5 1.34 45.5 0.21 18.0 0.59 30.2 0.97 38.7 1.35 45.7 0.22 18.4 0.60 30.5 0.98 38.9 1.36 45.9 0.23 18.9 0.61 30.7 0.99 39.1 1.37 46.0 0.24 19.3 0.62 31.0 1.00 39.3 1.38 46.2 0.25 19.7 0.63 31.2 1.01 39.5 1.39 46.4 0.26 20.1 0.64 31.5 1.02 39.7 1.40 46.5 0.27 20.4 0.65 31.7 1.03 39.9 1.41 46.7 0.28 20.8 0.66 32.0 1.04 40.1 1.42 46.9 0.29 21.2 0.67 32.2 1.05 40.3 1.43 47.0 0.30 21.5 0.68 32.4 1.06 40.5 1.44 47.2 0.31 21.9 0.69 32.7 1.07 40.7 1.45 47.4 0.32 22.2 0.70 32.9 1.08 40.9 1.46 47.5 0.33 22.6 0.71 33.1 ' 1.09 41.1 1.47 47.7 0.34 22.9 0.72 33.4 1.10 41.3 1.48 47.8 0.35 23.3 0.73 33.6 1.11 41.4 1.49 48.0 0.36 23.6 0.74 33.8 1.12 41.6 1.50 48.2 0.37 23.9 0.75 34.1 1.13 41.8 1.51 48.3 0.38 24.2 0.76 34.3 1.14 42.0 1.52 48.5 0.39 24.6 0.77 34.5 1.15 42.2 1.53 48.6 0.40 24.9 0.78 34.7 1.16 42.4 1.54 48.8 0.41 25.2 0.79 35.0 1.17 42.5 1.55 49.0 0.42 25.5 0.80 35.2 1.18 42.7 1.56 49.1 0.43 25.8 0.81 35.4 1.19 42.9 1.57 49.3 0.44 26.1 0.82 35.6 1.20 43.1 1.58 49.4 0.45 26.4 0.83 35.8 1.21 43.3 1.59 49.6 0.46 26.7 0.84 36.0 1.22 43.4 1.60 49.7 0.47 27.0 0.85 36.3 1.23 43.6 1.61 49.9 0.48 27.2 0.86 36.5 1.24 43.8 1.62 50.1 0.49 27.5 0.87 36.7 1.25 44.0 1.63 50.2 0.50 27.8 0.88 36.9 1.26 44.1 1.64 50.4 0.51 28.1 0.89 37.1 1.27 44.3 1.65 50.5 0.52 28.4 0.90 37.3 1.28 44.5 1.66 50.7 National Building Code of Canada 2005 Volume 2 Division B C-9 Appendix 0 Division B Seismic Hazard The parameters used to represent seismic hazard for specific geographical locations are the 5%-damped horizontal spectral aCCeleration values for 0.2, 0.5, 1.0, and 2.0 second periods and the horizontal Peak Ground Acceleration value that have a 2% probability of being exceeded in 50 years. The four spectral parameters are deemed sufficient to define spectra closely matching the shape of the Uniform Hazard Spectra (UHS). Hazard values are 50th percentile (median) values based on a statistical analysis of the earthquakes that have been experienced in Canada and adjacent regions.(7)(3) The median was chosen over the mean because the mean is affected by the amount of epistemic uncertainty incorporated into the analysis. It is the view of the Geological Survey of Canada and the members of the Canadian National Committee on Earthquake Engineering that the estimation of the epistemic uncertainty is still too incomplete to adopt into the Code. Further details regarding the representation of seismic hazard can be found in the Commentary on Design for Seismic Effects in the User ’s Guide — NBC 2005, Structural Commentaries (Part 4 of Division B). References (1) Gumbel, E.]., Statistics of Extremes. Columbia University Press, New York, 1958. (2) Newark, M.]., Welsh, L.E., Morris, R.]., and Dnes, W.V., Revised Ground Snow Loads for the 1990 NBC of Canada. Can. I. Civ. Eng., Vol. 16, No. 3, June 1989. (3) Newark, M.]., A New Look at Ground Snow Loads in Canada. Proceedings, 41st Eastern Snow Conference, Washington, DC, Vol. 29, pp. 59—63, 1984. (4) Bruce, ].P and Clark, R.H., Introduction to Hydrometeorology. Pergamon Press, London, 1966. (5) Yip, TC. and Auld, H., Updating the 1995 National Building Code of Canada Wind Pressures. Proceedings, Electricity ’93 Engineering and Operating Conference, Montreal, paper 93-TR-148. (6) Boyd, D.W., Variations in Air Density over Canada. National Research Council of Canada, Division of Building Research, Technical Note No. 486, June 1967. (7) Basham, P.W. et al., New Probabilistic Strong Seismic Ground Motion Source Maps of Canada: a Compilation of Earthquake Source Zones, Methods and Results. Earth Physics Branch Open File Report 82-33, p. 205, 1982. (8) Heidebrecht, A.C. et al., Engineering Applications of New Probabilistic Seismic Ground—Motion Maps of Canada. Can. I. Civ. Eng., Vol. 10, No. 4, pp. 670—680, 1983. (9) Skerlj, PF. and Surry, D. A Critical Assessment of the DRWPs Used in CAN / CSA—A440-M90. Tenth International Conference on Wind Engineering, Wind Engineering into the 21st Century, Larsen, Larose & Livesay (eds), 1999 Balkema, Rotterdam, ISBBN 90 5809 059 0 (10) Cornick, 5., Chown, G.A., et a1. Committee Paper on Defining Climate Regions as a Basis for Specifying Requirements for Precipitation Protection for Walls. Institute for Research in Construction, National Research Council, Ottawa, April 2001. c-1o Division B National Building Code of Canada 2005 Volume 2 ...
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Climatic Text C-1 - Division B Appendix G Climatic and...

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