ASCE 7-10 SNOW LOADS-2010 Snow Loads guide to the Snow Load Provisions of ASCE 7-10《雪载荷 ASCE 7-10雪载荷规定指南》.pdf

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1、Snow Loads Michael ORourke, Ph.D., P .E. Guide to the Snow Load Provisions of ASCE 7-10Snow LoadsOther Titles of Interest Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-10. (ASCE Standard, 2010). Provides requirements for general structural design and includes means for determin

2、ing dead, live, soil, ood, wind, snow, rain, atmospheric ice, and earthquake loads and their combinations that are suitable for inclusion in building codes and other documents. A detailed com- mentary of explanatory and supplementary information is included. (ISBN 978-0-7844-1085-1) Signi cant Chang

3、es to the Wind Load Provisions of ASCE 7-10: An Illus- trated Guide, by T. Eric Stafford, P.E. (ASCE Press, 2010). Focuses on revi- sions to the wind load requirements set forth in the latest edition of the ASCE Standard for minimum design loads. (ISBN 978-0-7844-1116-2) Signi cant Changes to the Se

4、ismic Load Provisions of ASCE 7-10: An Illustrated Guide, by S. K. Ghosh, Susan Dowty, and Prabuddha Dasgupta. (ASCE Press, 2010). Focuses on revisions to the seismic load requirements set forth in the latest edition of the ASCE Standard for minimum design loads. (ISBN 978-0-7844-1117-9) Seismic Loa

5、ds: Guide to the Seismic Load Provisions of ASCE 7-05, by Finley A. Charney, Ph.D., P .E. (ASCE Press, 2010). Presents a detailed, authoritative interpretation of the seismic load provisions of ASCE 7-05 by a respected engineering professional. (ISBN 978-0-7844-1076-9) Wind Loads: Guide to the Wind

6、Load Provisions of ASCE 7-05, by Kishor C. Mehta, Ph.D., P .E., and William Coulbourne, P .E. (ASCE Press, 2010). Presents a detailed, authoritative interpretation of the wind load provisions of ASCE 7-05 by respected engineering professionals. (ISBN 978-0-7844-0858-2)Snow Loads Guide to the Snow Lo

7、ad Provisions of ASCE 7-10 Michael ORourke, Ph.D., P.E.Library of Congress Cataloging-in-Publication Data ORourke, Michael J.Snow loads : guide to the snow load provisions of ASCE 7-10 / Michael ORourke.p. cm.Includes bibliographical references and index.ISBN 978-0-7844-1111-71. Snow loads. 2. Struc

8、tural engineeringStandardsUnited States. I. American Society of Civil Engineers. II. Title.TA654.4.O762 2010624.172dc222010017955 Published by American Society of Civil Engineers 1801 Alexander Bell Drive Reston, Virginia 20191 www.pubs.asce.org Any statements expressed in these materials are those

9、of the individual authors and do not necessarily represent the views of ASCE, which takes no responsibility for any statement made herein. No reference made in this publication to any speci c method, product, process, or service constitutes or implies an endorsement, recommendation, or warranty ther

10、eof by ASCE. The materials are for general information only and do not represent a standard of ASCE, nor are they intended as a reference in purchase speci cations, contracts, regulations, statutes, or any other legal document. ASCE makes no representation or warranty of any kind, whether express or

11、 implied, concerning the accuracy, completeness, suitability, or utility of any information, apparatus, product, or process discussed in this publication, and assumes no liability therefor. This information should not be used without rst securing competent advice with respect to its suitability for

12、any general or speci c application. Anyone utilizing this information assumes all liability arising from such use, including but not limited to infringement of any patent or patents. ASCE and American Society of Civil EngineersRegistered in U.S. Patent and Trade- mark Of ce. Photocopies and reprints

13、. Y ou can obtain instant permission to photocopy ASCE pub- lications by using ASCEs online permission service (http:/pubs.asce.org/permissions/ requests/). Requests for 100 copies or more should be submitted to the Reprints Department, Publications Division, ASCE (address above); e-mail: permission

14、sasce. org. A reprint order form can be found at http:/pubs.asce.org/support/reprints/. Copyright 2010 by the American Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-1111-7 Manufactured in the United States of America. 18 17 16 15 14 13 12 11 10 1 2 3 4 5 Snow Loads: Guide to the S

15、now Load Provisions of ASCE 7-10 v v Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Unit Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix 1. Introduction . . . . . . . . .

16、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. Ground Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1 In uence of Latitude, Elevation, and Coastlines . . . . . . . . . . . . 62.2 Site-Speci c Case Studies . . . . . . . . . . . . .

17、 . . . . . . . . . . . . . . . . 7Example 2-1: Ground Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3. Flat Roof Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.1 Measured Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . 113

18、.2 Flat Roof Snow Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.3 Exposure Factor (C e ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.4 Thermal Factor (C t ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.5 Importance Factor (I s ) .

19、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.6 Minimum Snow Loads for Low-Sloped Roofs . . . . . . . . . . . . 21Example 3-1: Roof Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 4. Sloped Roof Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . .

20、 . . . . . . 254.1 Snow Sliding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.2 Balanced Roof Snow Load for Common New Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Example 4-1: Uniform Roof Snow Load, Monoslope Roof (1 on 12) . .

21、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Example 4-2: Uniform Roof Snow Load, Monoslope Roof (4 on 12). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Example 4-3: Uniform Roof Snow Load, Wide Gable Roof . . . . . . . 31 5. Partial Loads . . . . . . .

22、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335.1 Continuous-Beam Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 335.2 Other Structural Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Example 5-1: Uniform and Partial Snow Loads, Monoslope Ro

23、of with Overhang . . . . . . . . . . . . . . . . 37Example 5-2: Partial Snow Load, Continuous Purlins in Gable Roof (1 on 12) . . . . . . . . . . . . . . . . . . . . . . . 39Example 5-3: Partial Snow Load, Continuous Purlins in Gable Roof (3 on 12) . . . . . . . . . . . . . . . . . . . . . . . 40Exa

24、mple 5-4: Partial Snow Load, Cantilevered Roof Girder System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 6. Unbalanced Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.1 Hip and Gable Roofs . . . . . . . . . . . . . . . . . . . . . . . . . .

25、. . . . . 456.2 Curved Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496.3 Sawtooth-Type Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506.4 Domes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51vi Snow Loa

26、ds: Guide to the Snow Load Provisions of ASCE 7-10Example 6-1: Unbalanced Snow Load, Narrow Gable Roof . . . . . . . 51Example 6-2: Unbalanced Snow Load, Wide Gable Roof . . . . . . . . . 52Example 6-3: Unbalanced Snow Load, Asymmetric Gable Roof . . . . 53Example 6-4: Balanced and Unbalanced Snow L

27、oad, Curved Roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Example 6-5: Unbalanced Snow Load, Sawtooth Roof . . . . . . . . . . 56 7. Drifts on Lower Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597.1 Leeward Drift . . . . . . . . . . . . . . .

28、. . . . . . . . . . . . . . . . . . . . . . 607.2 Windward Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677.3 Adjacent Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Example 7-1: Roof Step Drift Load . . . . . . . . . . . . . . . . . .

29、. . . . . . . 69Example 7-2: Roof Step Drift, Limited Height . . . . . . . . . . . . . . . . . 71Example 7-3: Roof Step Drift, Low Ground Snow Load . . . . . . . . . 72Example 7-4: Roof Step Drift, Adjacent Structure . . . . . . . . . . . . . . 74 8. Roof Projections . . . . . . . . . . . . . . . .

30、. . . . . . . . . . . . . . . . . . . . . . . . 77Example 8-1: Parapet Wall Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Example 8-2: Rooftop Unit (RTU) Drift . . . . . . . . . . . . . . . . . . . . . . 81Example 8-3: Parapet Wall Drift, Low Ground Snow Load . . . . . . . 82 9. Slid

31、ing Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859.1 Adjacent Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859.2 Separated Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Example 9-1: Sliding Sno

32、w Load, Residential Gable Roof (4 on 12). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Example 9-2: Sliding Snow Load, Commercial Gable Roof (1 on 12). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90Example 9-3: Sliding Snow Load, Separated Roof . . .

33、. . . . . . . . . . . 91 10. Rain-on-Snow Surcharge Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Example 10-1: Uniform Design Snow Load, Monoslope Roof ( on 12) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Example 10-2: Uniform Design Snow Load, Gable Roof (

34、 on 12) . . . . 97 11. Ponding Instability and Existing Roofs . . . . . . . . . . . . . . . . . . . . . . . 9911.1 Ponding Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9911.2 Existing Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 12.

35、 Design Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Design Example 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Design Example 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Design Exampl

36、e 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 13. Frequently Asked Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Appendix . .

37、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

38、 . . . . 165 Snow Loads: Guide to the Snow Load Provisions of ASCE 7-10 vii Preface This guide provides practicing structural engineers with a detailed description of the snow load provisions of ASCE/SEI Standard 7-10, Minimum Design Loads for Buildings and Other Structures, published by the America

39、n Society of Civil Engineers (ASCE). The intent of this guide is to present the research and philosophy that underpins the provisions and to illustrate the application of the provisions through numerous examples. Readers and users of this guide will know how to use the provisions and also know the r

40、easoning behind the provisions. In this fashion, users may be able to address nonroutine snow loading issues that are not explicitly covered in ASCE 7-10. Every effort has been made to make the illustrative example problems in this guide correct and accurate. The author welcomes comments regarding i

41、naccuracies, errors, or different interpretations. The views expressed and the interpretation of the snow load provisions made in this guide are those of the author and not of the ASCE 7 Standards Committee or the ASCE organization. Acknowledgments The author would like to acknowledge the past and p

42、resent members of the Snow and Rain Loads Committee of ASCE 7. Without their comments, ques- tions, and discussions, the development of Section 7 in ASCE/SEI Standard 7-10, and subsequently this guide, would not have been possible. As with any document of this type, many individuals have contributed

43、 their hard work and effort. The author acknowledges the work and effort extended by the administrative staff of the Department of Civil and Environ- mental Engineering at Rensselaer Polytechnic Institute, who assisted in the word processing and preparation of the narrative. The author also would li

44、ke to acknowledge the sketch work prepared by Christopher Keado, AIA, who graciously contributed the hand-drawn illustrations associated with each chapter. Snow Loads: Guide to the Snow Load Provisions of ASCE 7-10 ix Unit Conversions Measurement S.I. Units Customary units Abbreviations m = meter (S

45、.I. base unit of length) yd = yard cm = centimeter in. = inch km = kilometer mi = mile ha = hectare acre L = liter (S.I. base unit of volume) gal = gallon mL = milliliters qt = quart kg = kilogram (S.I. base unit of mass) lb = pound g = gram oz = ounce N = Newton (mkgs 2 ) lbf = pound-force Pa = Pas

46、cal (N/m 2 ) psi = pounds per square inch kPa = kilopascals atm = atmosphere J = Joule ftlbf = feet times pound-force W = watt Btu = British thermal unit kW = kilowatt hp = horsepower s = second (S.I. base unit of time) s = second min = minute min = minute h = hour h = hour day day C = degrees Celsi

47、us F = degrees Fahrenheit ppm = parts per million ppm = parts per million Length 1 m = 3.2808 ft = 1.0936 yd 1 ft = 1/3 yd = 0.3048 m 1 cm = 0.3937 in. 1 in. = 2.54 cm 1 km = 0.6214 mile 1 mile = 0.869 nautical mile = 1.6093 km Area 1 m 2= 10.7643 ft 21 ft 2= 0.0929 m 21 km 2= 0.3861 mi 2 1 mi 2= 2.

48、59 km 2 1 ha = 2.4710 acre 1 acre = 43,560 ft 2= 0.4047 ha Volume 1 L = 0.2642 gal 1 gal = 4 qt = 3.7854 L 1 ml = 1 cm 3 1 ft 3= 7.481 gal = 28.32 L Mass 1 g = 0.0353 oz 1 oz = 28.3495 g 1 kg = 2.2046 lb 1 lb = 0.4536 kg Force 1 N = 0.2248 lb/ft 1 lbf = 4.4482 N Density 1 kg/m 2 = 0.2048 lb/ft 2 1 l

49、b/ft 2= 4.882 kg/m 2 1 kg/m 3= 6.2427 lb/ft 3 1 lb/ft 3= 16.018 kg/m 3 Pressure 1 kPa = 0.145 psi 1 psi = 6.8948 kPa 1 atm = 14.7 psi = 101.35 kPa Energy and Power 1 J = 1.00 Ws = 0.7376 ftlbf 1 ftlbf = 1.3558 J 1 kJ = 0.2778 Wh = 0.948 Btu 1 Btu = 1.0551 kJ 1 W = 0.7376 ftlbf/s = 3.4122 Btu/h 1 ftlbf/s = 1.3558 W 1 kW = 1.3410 hp 1 hp = 550 ftlb/s = 0.7457 kW Flow 1 L/s = 15.85 gal/min = 2.119 ft 3 /min 1 gal/min = 0.1337 ft 3 /min = 0.0631 L/s Concentration mg/L = ppm (in dilute solutions) Temperature C = (F 32) 5/9 F = (C 9/5) + 32 Fundame