结构作用 - 第3部分：雪和冰作用

CONTENTS

Page

SECTION 1 SCOPE AND GENERAL
1.1 SCOPE	5
1.2 APPLICATION	5
1.3 NORMATIVE DOCUMENTS	5
1.4 DETERMINATION OF DESIGN ACTIONS	6
1.5 DEFINITIONS	6
1.6 UNITS	7
1.7 NOTATION	7
SECTION 2 SNOW REGIONS
2.1 GENERAL	9
2.2 AUSTRALIA	9
2.3 NEW ZEALAND	9
SECTION 3 ICE ACTION
3.1 GENERAL	12
3.2 DETERMINATION OF FORCES	12
3.3 ICE DENSITY	12
3.4 ICE THICKNESS	12
SECTION 4 SNOW ACTION
4.1 GENERAL	13
4.2 DESIGN SNOW LOADS	13
SECTION 5 GROUND SNOW LOAD
5.1 GENERAL	16
5.2 PROBABILITY FACTOR	16
5.3 GROUND SNOW LOADS FOR ALPINE REGIONS	16
5.4 GROUND SNOW LOADS FOR SUB-ALPINE REGIONS	17
SECTION 6 SHAPE COEFFICIENTS FOR ALPINE REGIONS
6.1 GENERAL	25
6.2 BALANCED SNOW LOAD	25
6.3 MONO-PITCHED ROOFS	25
6.4 DUO-PITCHED ROOFS	26
6.5 MULTI-PITCHED ROOFS	27
6.6 DRIFTING CAUSED BY OBSTRUCTIONS HIGHER THAN THE ROOF	27
6.7 DRIFTING AT PROJECTIONS AND OBSTRUCTIONS	29
6.8 CYLINDRICAL ROOFS	30
SECTION 7 SHAPE COEFFICIENTS FOR SUB-ALPINE REGIONS
7.1 GENERAL	31
7.2 SHAPE COEFFICIENTS AS FOR ALPINE REGIONS	31
7.3 OBSTRUCTED ROOFS	31
7.4 DRIFTING ON LOWER ROOFS	32
7.5 CURVED ROOFS	33
APPENDIX A BIBLIOGRAPHY	34

6

AS/NZS 1170.3:2003

This Joint Australian/New Zealand Standard was prepared by Joint Technical Committee BD-006, General Design Requirements and Loading on Structures. It was approved on behalf of the Council of Standards Australia on 1 November 2002 and on behalf of the Council of Standards New Zealand on 13 December 2002. This Standard was published on 16 January 2003.

---

The following are represented on Committee BD-006:

Association of Consulting Engineers Australia

Australian Building Codes Board

Australian Institute of Steel

Building Research Association of New Zealand

Cement Concrete and Aggregate Australia-Cement

Concrete Masonry Association of Australia Limited

Engineers Australia

Housing Industry Association

Institution of Professional Engineers New Zealand

James Cook University

Master Builders Australia

New Zealand Heavy Engineering Research Association

Property council of Australia

Steel Reinforcement Institute of Australia

Timber Development Association

University of Canterbury New Zealand

University of Melbourne

University of Newcastle

---

Keeping Standards up-to-date

Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased.

Detailed information about joint Australian/New Zealand Standards can be found by visiting the Standards Web Shop at www.standards.com.au or Standards New Zealand web site at www.standards.co.nz and looking up the relevant Standard in the on-line catalogue.

Alternatively, both organizations publish an annual printed Catalogue with full details of all current Standards. For more frequent listings or notification of revisions, amendments and withdrawals, Standards Australia and Standards New Zealand offer a number of update options. For information about these services, users should contact their respective national Standards organization.

We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Please address your comments to the Chief Executive of either Standards Australia or Standards New Zealand at the address shown on the back cover.

---

This Standard was issued in draft form for comment as DR 05368.

---

2

Structural design actions

AS/NZS 1170.3:2003

(Incorporating Amendment No. 1)

Australian/New Zealand Standard™

Part 3: Snow and ice actions

Originated in Australia as AS 1170.3—1990.

Originated in New Zealand as part of NZSS 95 Part IV:1939.

Previous New Zealand edition NZS 4203:1992.

AS 1170.3—1990 and NZS 4203:1992 jointly revised, amalgamated and redesignated as AS/NZS 1170.3:2003.

Reissued incorporating Amendment No. 1 (April 2007).

COPYRIGHT

© Standards Australia/Standards New Zealand

All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher.

Jointly published by Standards Australia, GPO Box 476, Sydney, NSW 2001 and Standards New Zealand, Private Bag 2439, Wellington 6020

ISBN 0 7337 4914 3

3

PREFACE

This Standard was prepared by the Joint Standards Australia/Standards New Zealand Committee BD-006, General Design Requirements and Loading on Structures, to supersede AS 1170.3—1990, Minimum design loads on structures, Part 3: Snow loads and, in part, NZS 4203:1992, Code of Practice for General Structural Design and Design Loadings for Buildings.

This Standard incorporates Amendment No. 1 (April 2007). The changes required by the Amendment are indicated in the text by a marginal bar and amendment number against the clause, note, table, figure or part thereof affected.

This Standard is published as a joint Standard and it is intended for use in New Zealand as well as Australia; however, NZS 4203, General structural design and design loadings for buildings, remains current in New Zealand until the publication of all parts (including Part 4: Earthquake action) and for a transition period afterwards.

The objective of this Standard is to provide designers of structures with values for snow and ice actions for use in the limit states design of structures subject to such actions.

This Standard is Part 3 of the AS/NZS 1170 series, Structural design actions, which comprises the following parts, each of which has an accompanying Commentary published as a Supplement:

AS/NZS

1170.0	Part 0:	General principles
1170.1	Part 1:	Permanent, imposed and other actions
1170.2	Part 2:	Wind actions
1170.3	Part 3:	Snow and ice actions

AS

1170.4

Part 4:

Earthquake actions

NZS

1170.5

Part 5:

Earthquake actions—New Zealand

The Commentary to this Standard is AS/NZS 1170.3 Supp 1, Structural design actions—Snow and ice actions—Commentary (Supplement to AS/NZS 1170.3:2003).

The Commentary gives background to the Clauses of the Standard. It also gives worked examples and information on issues such as siting of buildings, placing of doors, chimneys and similar and detailing of guttering, valleys, ridges, protrusions and cladding.

This Standard is not equivalent to ISO 4355:1998, Bases for design of structures—Determination of snow loads on roofs; however, ISO 4355 is drafted only as a guide to preparation of national Standards and the format given in ISO 4355 has been adopted in principle. A number of other Standards were consulted, including ENV 1991-2-3:1995, Basis of design and actions on structures, Part 2.3: Actions on structures—Snow loads.

This Standard is not equivalent to ISO 12494:2001, Atmospheric icing of structures. The adoption of this ISO Standard would have involved the collection of data on ice accumulation in Australia or New Zealand, which were not available at the time of publication.

Major changes from the previous editions of this Standard include the following:

(a) Amalgamation of Australian and New Zealand Standards.

(b) ISO 4355 has been adopted, where possible.

4

• (c) Incorporating changes resulting from the use of annual probabilities of exceedance (found for Australia in the Building Code of Australia and for New Zealand in AS/NZS 1170.0). (An amendment will accompany the publication of this Standard to change AS/NZS 1170.0, to remove the Appendix E, which provided adjustment of the 1990 edition of AS 1170.3.)
• (d) Reassessment of snow loads and factors for varying probability of exceedance of load have been included to bring the Standard into accordance with AS/NZS 1170.0.
• (e) Changing the factor for combinations involving snow (given in AS/NZS 1170.0) has been changed to 1.0 from 1.5 and 1.2 (Australia and New Zealand respectively) due to the introduction of annual probability of exceedance (see Clause 5.2).
• (f) For New Zealand, introduction of alpine and sub-alpine regions.

Notes to the text contain information and guidance and are not considered to be an integral part of the Standard.

A1 AS/NZS 1170.3 is independent of the design requirement specified—thus becoming a purely technical document. It may be used to calculate snow depths and roof loads given any annual probability of exceedance. The annual probability of exceedance (P) defines the snow or ice event (in which pressures and forces occur). Thus a high accumulation of snow with an annual probability of exceedance in the range of 1/200 to 1/2000 is used for ultimate limit states, while a much more frequent event (say of 1/20 or 1/25) might be used for serviceability limit states.

In AS/NZS 1170.3, Section 5 gives the ground snow loads factored for selected annual probabilities of exceedance using the probability factor kP and Section 4 sets out the determination of the snow actions (roof loads) that are appropriate for the annual probability specified.

The annual probability of exceedance is not defined in AS/NZS 1170.3, but is set out in AS/NZS 1170.0 [and by further reference for ultimate limit states in the BCA (Table of annual probabilities of exceedance) and in the Guide to the BCA (examples of structures for importance levels)]. AS/NZS 1170.0 gives requirements for New Zealand structures and for Australian structures not covered by the BCA. Guidance for serviceability events and associated limits is given in an informative Appendix of AS/NZS 1170.0 for loads associated with an appropriate annual probability of exceedance (P) for serviceability.

5

CONTENTS

Page

SECTION 1 SCOPE AND GENERAL
1.1 SCOPE	5
1.2 APPLICATION	5
1.3 NORMATIVE DOCUMENTS	5
1.4 DETERMINATION OF DESIGN ACTIONS	6
1.5 DEFINITIONS	6
1.6 UNITS	7
1.7 NOTATION	7
SECTION 2 SNOW REGIONS
2.1 GENERAL	9
2.2 AUSTRALIA	9
2.3 NEW ZEALAND	9
SECTION 3 ICE ACTION
3.1 GENERAL	12
3.2 DETERMINATION OF FORCES	12
3.3 ICE DENSITY	12
3.4 ICE THICKNESS	12
SECTION 4 SNOW ACTION
4.1 GENERAL	13
4.2 DESIGN SNOW LOADS	13
SECTION 5 GROUND SNOW LOAD
5.1 GENERAL	16
5.2 PROBABILITY FACTOR	16
5.3 GROUND SNOW LOADS FOR ALPINE REGIONS	16
5.4 GROUND SNOW LOADS FOR SUB-ALPINE REGIONS	17
SECTION 6 SHAPE COEFFICIENTS FOR ALPINE REGIONS
6.1 GENERAL	25
6.2 BALANCED SNOW LOAD	25
6.3 MONO-PITCHED ROOFS	25
6.4 DUO-PITCHED ROOFS	26
6.5 MULTI-PITCHED ROOFS	27
6.6 DRIFTING CAUSED BY OBSTRUCTIONS HIGHER THAN THE ROOF	27
6.7 DRIFTING AT PROJECTIONS AND OBSTRUCTIONS	29
6.8 CYLINDRICAL ROOFS	30
SECTION 7 SHAPE COEFFICIENTS FOR SUB-ALPINE REGIONS
7.1 GENERAL	31
7.2 SHAPE COEFFICIENTS AS FOR ALPINE REGIONS	31
7.3 OBSTRUCTED ROOFS	31
7.4 DRIFTING ON LOWER ROOFS	32
7.5 CURVED ROOFS	33
APPENDIX A BIBLIOGRAPHY	34

6