Structural Information for Building Design in Canada: 1965: Supplement No. 3 to the National Building Code of Canada

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STRUCTURAL INFORMATION

FOR BUILDING DESIGN IN CANADA

1965

SUPPLEMENT No. 3 TO

THE NATIONAL BUILDING CODE

OF CANADA

Issued

by

the

ASSOCIATE COMMITTEE ON THE NATIONAL BUILDING CODE

NATIONAL RESEARCH COUNCIL

OnAWA, CANADA

Printed in Canada

NRC No. 8331

Price: SO cents

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ASSOCIATE COMMITTEE ON THE

NATIONAL BUILDING CODE

1964-1965

H. F. Legget (Chairman) E. A. Allcut D. C. Beam A. E. Bl'idge~ A. J. Cameron S. D. C. Chulter A. F. ()ufTus J. J. DU!'lsauh H. Eldel' J. H. Jenkins J. S. Johannson S. D. La!'lh G. C. Lount J. P. Lupien *Deceased July 1965. H.H.G.Moody G. S. Mooney* A. T. Muir J. H. Palmason B. Pelletier R. B. Rolland S. A. Sasso A. Tubby

A. E. Berry (ex officio) R. E. Bolton (ex officio) J. L. Davies (ex officio) C. G. E. Downing (ex officio)

D. T. Wright (ex officio) J. M. Robertson (Secretary)

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STRUCTURAL INFORMATION FOR BUILDING DESIGN IN CANADA

SUPPLEMENT NO. 3 TO

THE NATIONAL BUILDING CODE OF

CANADA

THE NATIONAL BUILDING CODE OF CANADA

PREFACE

Supplement No. 3 was first published with the 1960 edition of the National Building Code under the title "Handbook of Pressure Coefficients for Wind Loads", A broadening of the subject matter covered by this Supplement has been introduced with the publicatioil of the 1965 edition of the Code. The content is based on the recommendations of the Revision Committee on Structural Loads and Procedures with a new title: "Structural Infonnation for Building Design in Canada".

The purpose of this Supplement to the Code is to transfer certain design

infor-mation from the Code to a separate document where it can be treated in detail. The

current edition includes information on loads due to wind, snow, earthquake as well as information on stability under compressive stress, Future editions will probably

contain even more information covering perhaps other aspects that can be more

properly dealt with in a Supplement than in the Code itself .

It should be noted that the provisions of this Supplement are recommended and

not mandatory. Because the information provided in this Supplement cannot possibly cover all conditions that occur in practice, and also because new information may become available in the future, every designer should try to obtain the latest and most appropriate design information available, For unusual types of structures it may

be necessary to resort to special information such as theoretical studies, model tests,

wind tunnel experiments, to provide adequate design values.

Comments and suggestions on this Supplement are welcome and should be

ad-dressed to the Secretary of the Associate Committee on the National Building Code, National Research Council, Ottawa,

TABLE OF CONTENTS

Page

Chapter 1-Pressure and Force Coefficients for Wind Loads ... 2

Chapter 2-Coefficients for Snow Loads on Roofs ... . ... ... 23

Chapter 3-Note on Earthquake Resistant Design... . . ... ... ... .... ... 37

Chapter 4-Stability Under Compressive Stress . . . . .. ... 40

Chapter 5-Biley Pile Formula ... :... 45

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CHAPTER I

PRESSURE AND FORCE COEFFICIENTS

for

WIND LOADS

By W. R. Schriever* and W. A. Dalgliesh*

1.

EXTRACT FROM NATIONAL BUILDING CODE OF CANADA 1965

2. PRESSURE AND FORCE COEFFICIENT TABLES

Table Pap

Shoplifted Table for Building with Average

Heiglt.t: Wid th :Length Ratio A 4

Effect on Pre88t.U'e Coefficients of Varying Roof Slopes for Selected h1b:1 Ratios

h:b:l

=

1 :8:20 Bl 4

h:b:l=I:4:10 B2 4

h::bd=I:2:5 B3 5

h.:b:I-2:2:5 B4 5

h:b:l=4:2:5 B5 5

Effect of Building Proportion on Wind Force

·Coefficient for Building as a Whole C 6

Skyseraper, Flat Roof. D 8

Low Square Building Gable, Roof 0_3° • 1 8

Medium-high Square Building, Gable Roof 0_10° 2 8

High SqWU"e Building, Gable Roof 0-15° 3 8

Low Building, Roof Slope 30° 4 9

Average Building, Gable Roof 0_10° 5 9

Average Building, Gable Roof 30° 6 9

Average Building, Gable Roof 50° 7 9

High Building, Gable Roof 30° . 8 10

Long Building with Single Roof Slope • 9 10

Long Building with Single Shed Roof

.

10 10

Building with Multiple Shed Roof. 11 10

Clipped Flat Roof . 12 11

Building with Roof Vent . 13 11

Building Open on One Side 14 11

Building Open on Two Sides • . 15 11

Grand Stand, Open on Three Sides. 16 12

Roof Without Walls, Slope 30° . 17 12

Roof Without Walls, Slope 10°. . • 18 12

Roof Without Walls, Inverted Slope 10°. 19 12

Closed Connecting Passage-way 20 13

Free Standing Plates, Walls, Bill-boards 21 13

Cylindrical Stacks and Tanks, Spheres • 22 13

Hangar with Curved Roof 23 14

Vertical Poles and Cylinders

.

.

.

.

24 14

Spherical Roof on Smooth Cylindrical Tank 25 14

Wires and Cables. . . . • • . 26 14

Structural Members and Assembled Sections 27 15

Plane Trusses from Sharp-edged Sections 28 15

Shielding Factors .

.

.

.

29 16

Truss and Plate Girder Bridges. 30 16

Three-dimensional Trusses 31 16

3. APPENDIX: Explanation of Pressure and Force Coefficient Tables

Introduction. . . • 17

Effect of Shape of Structure • • • . • • 17

Pressure Coefficients for National Building Code, 1965 • 19

Explanations on the Use of Pressure Coefficients 19

References and Acknowledgement • 22

.Research Officers with Building Structures Section, Division of Building Research, National Research Counell.

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Extract from

National Building Code of Canada, 1965

Section 4.1- Structural Loads and Procedures: Loads Due to Wind

Wind loads

4.1.3.11.(1) The minimum design load, due to the pressure of wind on a surface is ... *psf applied normal to the surface, decreased or increased as may be provided for in Sentence (2) and Article 4.1.3.12.

·Recommended design wind pressures and other climatic information for building design in Canada are published in Supplement No. I to the National Building Code and can be obtained from the Secretary of the Associate Committee on the National Building Code, National Research Council, Ottawa.

Variation with height

(2) Where a surface or part of a surface is located within any of the height increments listed in Column I of Table 4.1.3.D, the minimum design load on that surface or part of a surface is that provided for in Sentence (1) multiplied by the appropriate factor in Column 2.

Table 4.1.3.D

Forming part of Sentence 4.1.3.11.(2)

Height, (ft.) Factor

o

to 40 1.0 Over 40 to 60 1.1 Over 60 to 90 1.2 Over 90 to 130 1.3 Over 130 to 190 1.4 Over 190 to 270 1.5 Over 270 to 420 1.6 Over 420 to 740 1.8 I Over 740 to 1200 2.0 Column 1 Column 2

Alternatively, the minimum design load may be calculated as a continuous function of the height as follows:

qh

=

q30

(~O)

lIs

where qh is the minimum design load at height h, q30 is the minimum design load as

provided for in Sentence (1) and h is the height of the load under consideration

expressed in feet.

Variation with shape

4.1.3.12. The minimum design load on a surface is that provided for in 4.1.3.11 multiplied by the algebraic difference of the pressure coefficients * * for the two sides of the surface.

Dynamic effects

4.1.3.13. Structures that may be subject to oscillation due to the wind shall be investigated by theoretical and possible experimental methods for the danger of dynamic overloading and vibration at critical frequencies. This is the case particularly for: high slender buildings, church steeples, high chimneys, sightseeing and other towers, etc.

• .Recommended Pressure Coefficients for wind loads applicable to many elements and surfaces and other structural information for building design in Canada are published in Supplement No. 3 to the National Building Code and can be obtained from the Secretary of the Associate Committee on the National Building Code, National Research Council, Ottawa.

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A

SIMPLIFtEP TASLE..

\VALLS

0<:.

~OOF~

VALID ONLY IF I. Stress due to wind

250/0 total stress 2. 2/3 h/b < 3/2

#r

h

Cpe: EXT. PRESS. COEFF. 3. 2/5 < lib < 5/2

slopull E.... F 4. Int. Press. Coefi. 0"_20" -1. 0 -0.7

rf

0

0

r±l~

~Arn~

zo·-50-+d;-o (5 ex-200) -0. 7

and local maxima (Tables 1-13) are used.

D 50"_90" +~ -0. 7

Effect on Pressure Coefficients of Varying

Roof Slopes for Selected h:b:l Ratios

LOW BUILOIHG See Table 4 for internal press. coeff. Cpi Local suction maximllnl on area m (drawn to scale) for roof slopes

o -5·

Cpe*" = -1.0

82

ROOF SLOPE VARIABLE

h: b : l = 2: 8 : 20

!c~rt~t

TtO

D See Table 4 for internal press. coeff. Cpi Local suction maximum on area m (drawn to scale) for roof slopes

o 10·

• Cpe* -1.5

FOR WIND DIRECTION ¢ :0 0 :!" 15°

Q,I + I· 0 r----,-...,...-..,.--.---,-...

8'

+ ·8 1:::----1---.,"l ~ +·6 ~

+.4-8

+·2 ~ 0 J:zl -·2 a; Ilt -.4-~ ·6

2

-·8 ~ - 1 . 0 +----''---'---'---'---'-.... ><: 0 to '20 30 40 50 60·

J:zl ROOF SLOPE

ex:

FOR WIND DIRECTION

P

0 ~ 15"

+ I· 0 t---,---r-,..-,....--,--t + . 8 "=-~__:~---.;--=---":1 8. + ·6 u + .4-~ ~ T ·2 J:zl o 0 u _ ''2 ~ - . 4 r . - - - - . o - J ' ... ~ -·6 -1''2 -1·4 -1·6+-__ ~___'_ _ _'_ _ _ ' _ _ _ _ _ ' ' _ _ _ + o 10 20 30 40 .50 boa ROOF SLOPE oC

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83

MEO LOW BUILDING ROOF SLOPE VARIABLE

h; b : l = 4: II : 20

hIO

See Table 4

for internal

~

press. coef!.

Cpi

C

Local suction

~HE8

maximum on area

m (drawn to scale) for roof slopes

L EF _{0 15"}

Cpe* -1. 8 D

MEO. HT. BUILDING

84 ROOF SLOPE VARIABLE

h: b: l = 11:11:20

hIO

See Table 4

for inte rnal press. coeff.

Cpi

~

C

~IrnB

Local suction maximum on area m (drawn to scale) for roof slopes

l EF _{o -ZO°} Cpe* = -Z.O D

{o

See Table 4 for internal press. coef!. Cpi

~

C

om

Local suction ::,... , ~ _{maximum on area} ~ 'A m (drawn to scale)

~I-

iGI1 B

L I E.F for roof slopes _{0 Z5"}

1-

Cpe* = -Z. 1

D

FOR WIND DIRECTION ~ '" 0

t

15° + I· 0 1 " - - - r -... -r---r-...,-; + '8 ~ +·6 u t.4-~ _{+ -'2} IJ:. III ₀ -0 U _--2 Vi III -.4-III --6 0:: 0.. _--8 ...l ~-I'O ~ -1-2 ~ -1,4-III -1-6 0 10 20 30 40 50 00° ROOF SLOPE 0(

FOR WIND DIRECTION r/J '" 0 ~ 15°

IV + ,·0 8'+ '8 _A ~+ '6 ~+ ·4

8

+ '2 vi 0 13 - ·2 ~ -.4-...l-·o < Z --8 0:: 1Il-I'O t-< x-1·2 III -1·4-0 10 20 60° ROOF SLOPE 0(

FOR WIND DIRECTION ¢ '" 0 ! 15° +

'·0

<v + ·8

_LA

Il. U + .6 ~ +·4 ~ +-·2

8

0 -vi _-·2 III III _-·4 0:: 0.. _·6 ...l < -·6 ~-

'·0

~-I·Z x_ 1.4 III 0 ROOF SLOPE 0(.

₅

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6

TABLE., C

en

r·4

-:5--- \.

\\"-/ '

".\.\.~

o

0'5 '-0 I"

'2·0

'2-,

3.

0

3'5

•

DEPTH RATIO SOURCE:

. {lib

if b < h

For depth ratIO use· l/h if b > h Reference No.

Effects of slendernes s and depth on the resultant force coefficient for buildings with flat roofs. en gives the combined effect of pressure on windward and suction on leeward sides; only wind direction normal to one face considered.

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EXAMPLE SHEET: EFFECT OF BUILDING PROPORTIONS ON WIND FORCE. (For Table C)

T

_h

₌₁₀

1

~H

b=O.5

T

_h

₌₁₀

1

~L.l

b=1

T

_h

₁₀

~"Jl=O.5

b=l

7

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8

SKYSCRAPER

1

D

ROOF SLOPE O·

1-_ _ h_:_b_:_l_8_:_'_:I _ _ ---1 Cpe: EXTERNAL PRESSURE COEFFICIENTS

h LOW SQUARE BLDG

I

GABLE ROOF 0- 30 h:b:t , 1:4:4

~.h~S-k

m • n

~

F: 5

nl 0 S!/API:P AREA'S TO

SCALE-MED. HT. SOUARE BLDG

2

GABLE ROOF 0-100 h:b:L

.':':1

~

o-,o~~

ti~jft

c!~

I!

B n D

SIiADUl AREAS TO '5eALL

HIGH SQUARE SLOG

3

GABLE ROOF 0-150 h:h:l. 2·5:':1

O-'5~[l

'0 h b

o.T~)1rrsn

n

D

5J1AD£O AREAS TO SCAI..£.

I

¢ A I B I C ' D I E i F : G 1 H

o· +0.8-0.61-0.71-0.71-0 61-0.61-0.6!-0.6 4S' +0 sl-o s'+o.51-0 sl-o 61-0.sl-o.5l-0.4 0° At Edge "0" (sides C and D) Cpe'"' = -1.5

Cpi: Internal Pressure Coefficients See Table 3

Cpe: EXTERNAL PRESSURE COEFFICIENTS

¢ A B

I

C

I

D I E F

J

G H

o· +0.9 -0.31_{-0.41-0.41 -0.8 -0 81 ·0 3 -0. 3}

15° +0.8 -0.31- 01 1- 05 1-0.7 -0. 8-r -0 2 -0. 3 4S· +0. 5 -0.41+0.Si-0.4! -0 9 -0 6l -0 6 -0.3 ISO For section "0 (Side C) C

.*--:

-0 8

4S' For section "m" Cn p>; ·2 0 ~'n" Cnp~'= -1.0

C_pi: INTERNAL PRESSURE COEFFICIENTS

OPENINGS ¢ =O'~ =IS~~ =4S'

~rml~stributed '0.2 :'0.2 1+ 0.2 Predominating on side "A" + 0.8 +0.7 i+v.4 Predominating on side "B" - 0.2 -0.31-0.4 Predominating on side "C" - O. 3 -0.2 1+0.4

11C;e:

EXTERNAL PRESSURE COEFFICIENTS

F

1

A B C D E G H

0° +0.9 -0. S -0.6 -0.6 -0.7 -0.7 i -0. S -0. S 15' +0.8 -0. 5 -0.7 -0.5 -0.7 -0.6 i -0. 5 -0.6 4So +O.S -0, S +0.5 -0. S -0,8 -0.51-0.s -0.4 4So For section "m" Cn ... *= -1.2 "nil Cn .. *::: -0.8 C pi: INTERNAL PRESSURE COEFFICIENTS

OPENINGS ¢ =0· ¢ :::1 So ¢:::4S'

~ly distributed ':!:'0.2 '::0.2 '::0.2

IPredominatin2 on side "A" + O. 8 + O. 7 + O. 4 IPr edominatin2 on side "B" 1-0.41-0.4 - 0, 4 IPredominatin2 on side "C" - O. S - 0, b +0.4

I

C pe: EXTERNAL PRESSURE COEFFICIENTS

¢ A B C D E F G H

O· +0, 9 -0.6 -0,7 -0.7 -0,8 -0,8 -0.8 -0.8 15' +0,8 -0, S -0,9 -0.6 -0,8 -0,8 -0.7 -0,7 45' +0.5 -0.5 +0.5 -0.5 -0.8 -0,7 -0.7 -0,5 4S' For section "m" C._ *::: -1. 0 "n" C_~ *= -0,8

O· At edqe "0" (sides C and D) C~A * = -I, S Cpi: INTERNAL PRESSURE COEFFICIENTS

OPENINGS

'" =0' 1¢=15° ¢=4So Uniformly distributed f:-0.2 ;to. 2 ~O,2 Predominating on side "A" 0,8 +0.7 +0,4 Predominating on side "B" - 0.5 - 0.5 - O. 4 Predominating on side "e" -0.6 - 0.8 + 0.4

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LOW BUILDING

I

C_pe: EXTERNAL PRESSURE COEFFICIENTS

4

GABLE ROOF 30°

;

h:b:l'I:II:16 A B C D E F G H

•

m~

45' 1+0.5 -0.5 +0.4 -0.3 +0. 0'1+0.8 -0.5 -0.5 -0.5 +0.2 +0.2 -0.6 -0.6 1 -0. 1 -0.8 -0.5 3 I

-fh

90' -0.3 -0.3 +0.9 -0.3 -0. 5 -0. 1 -0.5 -0. 1

~~~

IO~9C For sections "m" C ne*= -1.0

O~

<:1

C

oi: INTERNAL PRESSURE COEFFICIENTS

OPENINGS f =0· (J =45· ;=90·

Uniformly distributed :!:.0.2 :!:'0.2 !'0.2

Predominating on side "A" + O. 7 + 0.4 - 0.2 D Jpredominatina on side "B" - O. 4 - 0.4 - O. 2

SHAPED AlUM. TO 'SCALE..- IPredominatina on side "C" 1-O. 4 + 0.3 + 0.8

MEDIUM HT. BLDG

I

Cpe: EXTERNAL PRESSURE COEFFICIENTS

5

GABLE ROOF 0 -'0° B 1 h:b:l '2·5:2:5 ¢ A C D E F G H ~ O· +0.9 -0.5-0.7 -0.7 -0.6 -0.6 -0.5 -0.5

o~~a:}

45· +0.6 -0.51+0.4 -0. 5 -0.9 -0.7 -0.6 -0.7 90· -0.5 -0.51+0.9 -0.4 -0.8 -0.2 -0.8 -0.2

-~IJ

C pi: INTERNAL PRESSURE COEFFICIENTS 45· For section "m" Cne -1. 5

OPENINGS ¢=O· ;=45· [1=90·

UniformlY distributed +0.2 1!.0.2 !.0.2

IPredolninating on side "A" + 0.. 8 + 0.5 -0.4

IPredominatin(lon side liB" -0.4 - 0.4 -0.4

D

!Predominating on side "C"

SJlADI!.D AI?I!.Af/ TO 5t:.41..E.-- - O. 6 + 0.3 + O. 8

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MEDIUM HT. BLDG GABLE ROOF 30°

_I

'pe EXTERNAL PRESSURE COEFFICIENTS

h:b:L , 2· 5: 2 : 5 ¢ A B C D 1 E F G

1

H

3d~

O· +0.9 -0.5 -0.7 -0. 71 -0. 6 -0.6 1-0.5-0.5 45· +0.6 -0.5 +0.4 -0.41_{-0.4 -0.5 1-0.61-0.7} b h 90· -0.5 -0. 5 +0.9 -0.41-0.7 -0.2 -0.71-0.2

/ 45' For section "m" Cue'" -1. 2

[;1

d

- A E G

:1

·pi INTERNAL PRESSURE COEFFICIENTS

OPENINGS ; ,,0·

r!

,,45· ¢ =90· F H . Uniformly distributed

r:

0 . 2 .!.0.2 + 0.2

IPredominating on side "A" +0.8 +0. 5 -0.4

D IPredominating: on side "B" -0.4 -0.4

SHAO£t:J AREA5 TO SCA/'E- _{Jpredominating on side "C" -0.6 +0.8}

MEDIUM HT. BLDG

I

7

GABLE ROOF 50° _'pe EXTERNAL PRESSURE COEFFICIENTS

h:b:l ' 2-5: 2 5 A I B C I D I E

1

5~

¢ o·

_~O5

-0.81 -0.81 +0. 31 +0. 3 -0.6 -0.6 F G H f -+0.4 -0.41 +0.3 -0. 1 ~ O. 5 -0.5 -0.6 90· -0. 5 -0. 5 +0.91 -0.41 -0.

Sf

-0.2 -0.8 -0.2 75' For section "m" CD~?' -1. 2

em

:-<:

~1

C

pi: INTERNAL PRESSURE COEFFICIENTS

OPENINGS ¢ =0· ¢ =45· ¢ =90·

Uniformly distributed + O. 2 + O. 2 + O. Z

PredominatinJl: on side "A" + 0.8 + 0.5 !-0.4

D Predominatin" on side "B" - 0.4 - 0 4 - 0 4

SHA()ED A/HiA TO 5CALE- Predominatinll' on side "c" - O. 7 + 0.3 + O. 8

9

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10

IIIGII BUILDING

I

8

GABLE ROOF :sO·

h: b:l • 2.: I: 2

~-

-....l:-

h

o~C;I~

D

SHADE-V ARE.A TO

SCAi.E-LONG BUILDING

I

9

SINGLE SLOPE ROOF

h:b:l , 1:2·4: 1'2.

~O'

J?m;~~Uh

C

t]11L

c!

-A "

F1TfU

D

SHAD£O A~£A TO

5C;Ai.E-10

II

LONG BUILDING SINGLE SHED ROOF

h:b:l • I: I: 5

lOW BUILDING "'UlTIPLE SHED ROOF

h: b: l = I: 4: is EFGI-IJK L.M

'7~/h

_;;~)JI

n _{C n m} ~{ I ~

!

m m A ~ ~Db-l

SHIH)E" A.<i!l!AS TO 'f$;CAl~

I

C : EXTERNAL PRESSURE COEFFICIENTS

pe ¢ A I B C D lE F I G H 0'+0,91-0,5 -0,8 -0,81-1.0 -1. 01 -0,5 -0,5 45' ~O,5 +0,4 -0.4 -0.3 -0,41 -0.5 -0.6 --0,41 -0.7 -0.51 -0.7 90' 0.6 +0.9 -0.5

o· For section "m" C_ne* -1. 2

C '

pi' INTERNAL PRESSURE COEFFICIENTS

OPENINGS ¢ =0'; =45' ;=90'

~Y distributed + 0,2 + 0.2 + 0,2

Predominating on side "A" + 0,8 + 0.5 ,- O. 5 Predominating on side "B" - 0.4 - 0, 4 1- 0, 5 Predominatin£ on side "C" - 0,7 + 0.3 + 0, 8

C EXTERNAL PRESSURE COEFFICIENTS

pe ¢J A B C D ! E I F G H O' +0.9 -0.5 -0,6 -0.6 -0.51 -0.5 -0,5 -0.5 45' +0.5 -0,6 +0,4 I -0.4 -1.2-0,7 -1. I -0,7 90' -0,4 -0. 3 +0,9 I~-O. 2 -0.31 0 -0. 3 0 180' -0,4 +0.8 -0.7 ' -0.7 +0.11 +0. I +0.2 +0.2

45' For section "m" Cpe *= -I. 4 C '

pi' INTERNAL PRESSURE COEFFICIENTS

OPENINGS ¢ =0' ¢=45'1¢ =90' ¢=180

Uniformly distributed :!:.0.2 :!:.0.2 :!:.0.2 :!:.O,2 Pr edominating on side "A" + 0,8 +0.41-0.2 - O. 3 Predominating on side "B" - 0.4 - 0.5

i -

O. I 1+ 0,7 Predominating on side "C" - 0,5 + O. 3 • + O. 8 - O. 6

• C EXTERNAL PRESSURE COEFFICIENTS

.1~.e ¢ A B C I D , E F G H O· +0.9 -0.5 -0.6 ' -0,61 +0.6 +0.6 -0. 5 -0. 5 45' +0 5 -0 8 +0 41:0 51 -t 0 2 -0 1 .. ~~

~

90' -0.4 -0,4 +0.91 -0,3 -0.4 0 180' -0.5 +0.9 -0.61 -0.61 -0.5 -0. 5 -0.1 -0, 1 45' For section "m" C ne '" -I. 3

C .: INTERNAL PRESSURE COEFFICIENTS

Pl

:!:.o,

Predominati=n~~~~~-+~~+-~~~~~_0~.~4~

Predominatin + O. 8

Pr ec.oul111atin 0.8 0.5

Cpe : EXTERNAL PRESSURE COEFFICIENTS

¢

l

A B I C ! D E F I G H I J I K 0'1+0,9 -0, 3 ·0 4 1-0 4 to 6 ·0 6 1-0. 6 1-0 5 1-0 5 1-0.4 45"+0.5 -0.4 ftO. 5-0, 3 to. 2 ·0 8 1-0 5 -0.4-0.2-0.4 9 0°1-0 ,4 -0.4 ftO.9 i-0.3 -0.3 ·0 4 ,-0 4 -0,4 1-0 4 1-0 4 L M 0, 3 ~O, 3 0.2 ~O. 5 ,0,4 LO,3

~6G,.3 +0. 9 -0. 3 ,~,O 3 -0 2 ,-0 3 1-0 3 i-o 4 1-0 4 1-0 6 ,0 6 rO.1 ectlon "m" C ne '= -1.3 Section "n" C ne *= -2.0

C

pi: INTERNAL PRESSURE COEFFICIENTS

OPENINGS ¢ =0' ¢=45'1 ¢ =90 cl¢= 180 0

Uniformly distributed :!:.0.2 :!:.O. 2:!:.0. 2 I:.:..~~

Predominat~side "A"

-

1+ 0.8 +0.41-0.3 1_-0.2 Predominating on side "B" - O. 2 -0.31-0.31+ 0 . 8 Predominating on side "C" - 0.3 +0.41+ 0 . 8 I O. 2

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LOW BUILDlljG

I

12 CLIPPED FLAT ROOF

EXTERNAL PRESSURE COEFFICIENTS

n' b: l • I: 3: 4 'pe

L

Q·35h

l

¢ A B C D E F I G H

I

J K 1 M o - - \ , ; ; 0' -0.6 -0.6 -0.8 -0.81-0.4 -0.4-1. 0 -0.4 -0.5 -0. 5 30< A B hi 45' +0.5 -0.5 +0.5 -0.4 -0.6 -0.5 -0. 5 -0.5 1-0.5 -0.5 -0.5 -0. 5 -1>:-41-0.8 -0.4 1-0.4

m,

C 90' -0.5 -0.5 1+0.9 -0.4 -0.8 -0.4 -1. 0 -0.4

~

!d'+9d For section "m" Cue "'= -1. 1 Section "n" Cae *= -1. 5

1

;

A

rftf

C:=

E. G Cpi ' INTERNAL PRESSURE COEFFICIENTS

K

¢ =0' ¢=45' Ll=<Lo'

F H OPENINGS

r;

..--"

~niformly distributed + O. l. :'0. l. :'0. l.

~g--J

predominating on side "A" + O. 8 + 0.4 - O. 4 l>redominatinll on side "B" - O. 4 - O. 4 - 0.4

5J./AD£D AAEA$ TO 'SeAL£.- l>redominating on side "C" - 0.5 + O. 4 + O. 8

BLDG WITH ROOF VEljT

I

13 ROOFS 200 _C

pe: EXTERNAL PRESSURE COEFFICIENTS

h. b: l • I: 4: 8 G~H , ¢ A B C D E F G H J I K E F~;:1i ~-J K h.O·5h

;;;;(!5d0J?

0' +0.8 -0.5 -0.7 -0.7 -0. l. +0.6 -1. 0 -0. (, -0.51-0.6 +0.4 -0.51+0.4 -0.5 -0.3 +0. l. -1. 3 -1. 4 -1. ~ 45' C _{- 90' -0.4 -0.41+0.8 -0.3 -0.4 -O.l. -0.3 -0.3-0.2}

!~

tn 0° 0°445 For section " m " Cn p " : -1.l. Section "n" C" .... : -l..4

45

-,

n _l

Cpi : INTERNAL PRESSURE COEFFICIENTS

145

~m

- '

o

--X

B~ OPENINGS ¢ =0' ¢=45' ¢ =90'

45' 0

b~ ~ Vents at F and J closed + 0.2 + O. 2 + 0.2

me

~ents at F and J open - O. l. - 0.5 - O. 3

D - ~ents at F only open + 0.5 + O. 1 - O. l.

!iliA!)£-!) A~l!A5 TO SeAL.£..- Vents at J only open - O. 4 -'0.9 -0.2

BLDG OPEIj OljE SIDE

I

14 ROOF 30°

Cp ' PRESSURE COEFFICIENTS, LONG WALL OPEN

h; b: l ' I: 2; 4 ¢ A B C D E F G H J K

~TB

0' +0.8 -0.5 -0.7 +0.8 +0.8 -0.7 -0.3 +0.8 -0.4 +0.8 45' +0.7 -0.6 +0.4

1'0.1.:

-0.4 -0 I ~ _ +0.7 60' +0. 3 -0.7 +0.7 -0.4 -0.3 +O.l. -0.6 +O.l. C _{180' -0.5 +0.9 -0.8} -0,8 -0.4 -0.5 .n 7 _{.n "}

~Ttj

C

p: PRESSURE COEFFICIENTS, END WALL OPEN

0° L ¢ A B C D

~F

G H J K E-A jA 'B f:....C D 0' +0.9 -0.7 -0.7 -0.4 -0.7 -0.4 -0.7 45' +0.5 +0.7 +0.8 -0.5 +0. -0.4 -0.3 +0.7 -0.6 +0.8 F F 60" +0.1 +0.9 +0.9 -0.6 +0.9 -0.4 -0.31+0.9 -0.7 +0.9 90' -0.5 +0.8 +0.8 -0.5 1+0,8 -0.3 -0.4 +0.8 -0.4 +0.8 15 ROOF 30°

BLDG OPEIj Olj TWO SlOE!

h:b'l • I' 2; 4 CpO PRESSURE COEFFICIENTS, LONG ~~~~S

¢ C D E F G H J K

~~

0' -0. l. -0.7 -0.7 -0.2- 0.4 -0.9 -0. 5 -0. B

H J(

lh

.

45' +0.5 -0.4 +0.5 -0.4 0 -0.3 -0,6 0 60' +0. 7 -0.6 +0.5 -0.4 -0.3 -0. 1 -0.7 -0.3 C

~I8

C: PRESSURE COEFFICIENTS, END WALLS

P OPEN 00 I t b _¢ A B C D G H J K I b l A B CD 0' +0.9 -0.7 -0.7 -0.4 -0. Z -0.7 -0.4 -0.7

IE1

e 45' +0 5 -0.4 1-0. 1 -0. B -0.3 -0.4 -0.8 -0.3

===r

-f- _{60' +0. 3 -0. Z +0.1 -0.5 -0.3 -0.1 -0. B +0.1}

60' Gable sect. c=+O. 7, d= -0.6 Gable Bect. !~~~: ~ _II

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GRA"'D STA"'DS OPE'"

I 6

THREE SIDES ROOF - 5·

h:b:L. o·a:I:!·!

I

C: PRESSURE COEFFICIENTS FOR TOP AND p FRONT AND BACK

BOTTOM OF ROOF OF WALL

AC lEG

;

A B C D E F G H

;

J K L

h[2~4h

0 -1. 0 +0. <) -1. 0 11-0.9 -0.7 +0.9 -0.7 +0.9 O· +0. 9 -0.5 0.9 L. 45 -1. 0 +0.7 -0.7 11-0.4 -0,5 +0,8 -0.5 +0 3 45' 1+0.8 -0.6 0.4 0.4 n

JL:;W

135 -0.4 -1. 1 -0.7 -1. 0 -0.9 -1. 1 -0.9 -1. 0 135" -1. 1 +0.6 -1. 0 0.4 ISO -0.6 -0.3 -0.6 -0.3 -0.6 -0.3 -0.6 -0.3 ISO· -0.3 +0.9 -0.3 0.9 45 "mR" Cn· Top -2.0 60' Hmw' Cn K -1. 0

~~g~

~-1 ~~!~

o

C G: 45 tfInRH _{Co Bottom} = +1.0 60' "mW" Cll J = + 1. 0 1 r, )_: M i..I M

rh:,

5f1API.D ... .ell.... TO !feAt.#.

17

18

ROOFS WITHOUT WALLS ROOF JO·

h:b:l • 0·5:1:5

ROOF WITHOUT WALLS ROOF '0· h:b:l?O 0'5:1:5 ~

hr)~'n;~»n

~~I]~b

~!B

5HAOE.17 AIlEA TO

SCALE-I

C : PRESSURE COEFF. FOR

P TOP AND BOTTOM OF

n()('\"j;' ¢ A B C D O· +0.6 -1. 0 -0.5 -0.9 45· +0. I -0.3 -0.6 -0.3 90· -0.31-0.4 -0. 3 -0.4 45' " m " CD" Top = -1. 0 45· "m"Cn Bottom = -0.2 C: PRESSURE COEFF. P FOR TOP AND

BOTTOM OF ROOF

;

A B C D O· -1. 0 +0.3 -0.5 +0.2 45' -0.3 +0.1 -0. 3 +0. I 90' -0.3 0 -0.3 0 O· " m " Cn* Top:: -1.0 o· "m" C n" Bottonl =+0.4

I

C : PRESSURE COEFF.

1---'

p FOR TOP AND BOTTOM OF ROOF

19 ROOF WITHOUT WALLS ROOF -10·

h:b:l • 0·5 I;!S

¢ A B C D

O· +0.3 -0.7 ~0.2 -0.9 45' 0 -0.2 k-O. 1 -0. 3 90' -0.1 +0.1 -0.1 floO. 1 O· "m" Co'" Top:: +0.4

O· "m" Co'" Bottom =-1. 5

C : FOR GABLE ENDS P

} I

¢

I ,I

K

I

L

I ..

r 90~1 +0. sl-o. 6l+0. 3 ~O. 4

Note: At; :: 90· Coeff. for A - D apply only to length ~ = b,

at ¢ = O· and 45·to l=5b

Note: At ¢ -=90' Coef£. for A - ,D apply only to length t::: b,

(It; =0' and 45· to L .. 5b

These coef£. are valid only for relatively smooth underside B ~ D 12~

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CLOUD PASSAGE

I

20

eETWUN LARGE: WALLS

C EXTERNAL PRESSURE h:p;l ' 1:1=10 : pe COEFFICIENTS

I

¢

1+:8

!-l~ll-l\ 1_1~51

"1br-

I- l

-,

O·

--v-~::::f::g

Ami

C .: INTERNAL PRESSURE

::s:-4

f _2h pl

COEFFICIENTS

OPENINGS ;=0·

Uniformly distributed -0. 5 Predominating on side "A" +0.7 Predominating on side HBH -1. 1 Predominating on side "C" -1. 3

FREE STANI>ING

I

Fn=Cn·q·h·l

21

PLATES, WALLS

ANI> BILLBOARDS C - FORCE COEFF. FOR

n

WALLS ABOVE GROUND

t--Li

Ci.~~ ~i'~:

10

J

h

t

I l / h = 10 I

E

_{;gl/hat l/h 10+00 _{10 1}

l

fl_

l _~ I

_I

_{¢ -0·} fndwJl$} _l.O

Fnt_

0.

"I

,

Fn~

;Fn;"

a 5L 1.3 1. 15 f

I

~

¢ =40· 1.6 ¢ :00

~

~

a =. 3L ¢ ;50· 1.8 ¢ a =. 4l

C - FORCE COEFF. FOR

n

t)lt> \~A\'L" WALLS ON THE GROUND

( l/h ·10·"

11:'

l/h. 10 ~ l/h 10+00 h h L/h:l 10 1

"~#w

l

>"~,,

d:v""

l Md>' , l ' End vAIls) , =0· 1.l I.l 1.1 Fn I I Fn 1

l±l

a =. sL

l~~

I

al-

p

=40· 1.S

I

I

a =. 3L

p=oo~

.

~ ~

~

P

=50· 1.S a 4L

22

CYLIIIDERS, CHIMNEYS, TANKS TOTAL FORCE F = C n' q . Ch• A where A = d. h hjd=25 hid. 7 hftj.l /

C n' FORCE COEFFICIENT FOR d (Cj>2.;

Slenderness hid _____ l5 7 1

Cross sect. and roughness

o

lvioderately smooth, (metal, timber,concrete)

o

Rough surface (rounded ribs h l%d)

o

Very rough surface (sharp ribs h = 8'fod)

O

Smooth and rough surface sharp edges

en en en 0.S5 O. 5 0.4S 0.9 O. 8 0.7 I . l 1.0 0.8 1.4 1.2 1.0 C

re: J:.:XTERNAL PRESS. COEFF. FOR d.pr> 2.5 and moderately smooth surface

hid l idioc= l5 50

i

C pe H IC 'pe Z I epe A P = Pi - Pe O· IS· + 1. 0 +0.8 ·d.O 'to.8 ·d.O +O.H Pi _{C pi ' q} Pe'" Cpe ' q 30· 4S' 60· 7S· 90· 105· IlO· +0.1 -0.9 -1. 9 -l.5 -l.6 -1. 9 -0.9 +0.1 -0.8 -I. 7 -l. l -2.l -1. 7 -0.8 +0.1 -0.7 -1. 2 -1. 6 -1. 7 -1. l -0.7

Stack fully operating Cpi +0. 1 Stack throttled Cpi -0.8

135" 150· 165· 180· -0.7 -0.6 0.6 0.6 -0.6 -0. S O. 5 0.5 -0.5 -0.4 0.4 0.4

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14

23

SPHERfI TOTAL FORCE F = C

n. q ,Ch'A; A=

rtj.'Z

for d.['q> 12 and moderately smooth surface

C : FORCE COEFFICIENT n

C = O. Z n

p Pi for closed tanks = working press.

C

pe EXTERNAL PRESSURE COEFF. for

Pe = _{Cpe '} q

d{q> 1'2 and moderately smooth surface

24

MOO. SNOOTH SURFACE HANGAR, CURVED ROOF

I

r .... C_.: EXTERNAL PRESSURE COEFFICIENTS "i·e;;..., _ _ ,..._-r---r--,.--..,....-...,...---r~-~-..,.--~

RAD. r_%b h:b:l.I:I'1:12 ¢ A B C

DEI

F G H J K

:'0.2 + -0. Z :'0. Z

+ O. 4 + 0.7 oJ.O

, ,If,b 0·+0.7 -0.2. -0.3 -0.3 -0.11-0.5 -0.8 -0.8 -0.4 -0.1

1..

\.

T Glij

J-kQ.

30· +0.6 -0.3 +0.2. -0.4 -0.ll-0.4 -0.7 -0.9 -0.7 -0.4

htm~;~,~J

¢ 'A B C D L I M N 0 P Q

Y.~~':t:r41~' ;~: ~~~:iO~O;'~';~:e

.-0. =1

~~'!lt~Oc:e ::i~. -O~

3_;,0

5

1

-0.1

¢ ,I C

pi: INTERNAL PRESSURE COEFFICIENTS

d

A

~~

'. BL OPENINGS ¢ =0· rp =30·1.@=90 Uniformly distributed

Window Y open on side itA"

D All doors open on side HC" - 0.1 + O. LJ .,. O.!:!

O'lly door X open on side "C" - 1 5 + O. I , 0.4

ROOF LOAD ON SMOOT"

I

25

CLOSED TANK T F )

h:d:r" 1:(:!'5 otal force on roof _{n " (Pi - P e A} Pi working pressure in p. s. f.

C external pressure pe coefficient -1. 0

26 POLES. RODS ljd > a 100 WIRES

I

C n : FORCE COEFFICIENTS

d.fq

Total force F n = C n' q. _{Ch· A}

<

2.5 >2.5

~nooth wires, rods, pipes 0 _{1.2. O. 5}

A d . l

Mod. SI1100th wires and rods 0 1.2. 0.7

Fine wire cables

•

1.2 0.9 Thick wir" cables

•

1. 3 1. 1

«

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STRUCTURAL MEMBERS

I

21

SINGLE B ASSEMBLED SECTIONS L = Length of member A = h· l = Area

For wind normal to axis of member: Normal force F n = k. C

noo 'q,'Ch' A Tangential force F

t = k . Ct _ ' 'l,Ch' A C

noo and Ctoo : Force coefficients for an infinitely long member

o +1.9 +0.95 +1.8 +1.8 +1.75+0.1 +1.6 0 +2.0 0 +2.05 0 45 +1.8 +0,8 +2.1 +1.8 +0.85+0.8~+1.5 -0.1 +1.2 +0.9+1.85 +0.6 90' H.O +1. 7 -1. 9 -1. 0 +0. I +1. 7~ -0.95 +0. 7 -1. 6 H. I 0 +0.6 35' -1. 8 -0. I -2.0 +0.3 -0.75 +0. 7~ -0.5 +1. 05 -1. I H.4 -1. 6 +0.4 BO' -l.O +0. I -1. 4 -1. 4 -1. 75 -0. I -1. 5 0 -1. 7 ..:!2. I -1. 8 o ex: C C C C C C C C C C C C

nco to<> n_ too nco too nco too 1100 too noo too

O· +1.4 o H.05 0 +1.6 0 +l.O o +l.l 0 H.O 0

45"+1.l +1.6 +1.95+0.6 +1.5 +1.5f+1.8 +0.1 +1.4 +0.7 +1.5:+1.55 90· 0 +l. l ..:!0.5 +0.9 0 +1.9 0 +0.1 o ftO.75 0 H.O

For slenderness, F

res k: Reduction factor for members of finite length and slendernes s

hOC is to be used: ~t F

DO~

/ /

Fn

I.

l

.I;;r;

llhoc 5 10 lO 35 50 100 00

k 0.600.650.750.850.900.951.0

PLANE TRUSSES

I

A = Section area

28

MADE FROM 9

SHARP-EDGED SECTIONS A = h t . L A/A Fullness ratio

For wind normal to surface A: Normal force F = k • C . q' Ch' AS

n nco

IM~

~l§2JI~t

#F

_{li n}

I.

l

./

0

C : Force coeff. for an infinitely 1<: Reduction factor for trusses of noo

long truss, 0 ~ A / A ' 1 finite length and slenderness

A~I 0 10.110.151 0.ll°if.~OI0.9511.0 I

~

0.25 0.5 0.9 0.95 1.0 Cnoo

I

2.0 11. 9 11. 8

I

1. 711. 611. 8

I

l. 0

I

5 0.96 0.9 0.8 0.77 0.6C 20 0.98 0.9 O. 9~ 0.89 O. 7~ 50 0.99 0.91 0.9 0.95 O. <)(J 0 0 _{1.0 1.0 1.0 1.0 1.0}

15

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16 k SHIELDING FACTOR x PLANE OF MEMBER I PLANE OF MEMBER II ~O.l P.2 P.3 0.410.5 0.6 0.81.0 0.5 O. 93~. 75 0.56 o. 3~lo. 19 0 0 0 1 O. 99p. 810.650.480.32 O. l ' 0.1" O. I" 2 1. OO~. 87 0.730.590.44 O. 3() O. 3() O. 30 4 1.00P.90 0.780.650.52 0.4CO.4()0.40

~rt~<t

htL...:..

j.

~

1. 0 0 ~. 93 O. 83 O. no. 61 O. 5C O. 5~ O. 50

30

~~~::R A;~I:~;~E La Length of bridge

k. C • A • k from tables 28 and 29 nCllO S x

CASE I WITHOUT VEHICLES

Windward girder FI :: k C

noo . q' As

I-

X .. , Leeward girder FII k C . k q' A noo x s 1~ D«khod>, loadF h '1.0, q d'lB

~ h F d ]I Deck vert. load F :: 0.6 . q' b . LB

t vert." ~ l Length of vehicle; A h l ; ver~ v 1 vI v b A ₂ =h _v2 · l _v Windward girder FI :: k C noo . q' A 8 ~ WITH VEHICLES Leeward girde't" FII:: k Cnoo' kxq· As

Deck horiz. load F h 1 . 2 · q · d ·

J1

- " - "

~-I"

~

~{1V2~ ~

31

.~~.

F"ett b THREl - DIMENSIONAl "TRUSSES AsIA ~ 0·3 B Deck vert. load F

vert. ::: 0.8 . q. b· L B Traffic load F C q·A

vI n 1 F ::: C . 2/3q·

v2 n A2

Height and force coefficients h C

n v Railway vehicle 12.5' 1.5 Highway vehicle 10.0' 1.2 Pedestrian 5.6' 1.0 A:: d . L or h . l

L true length of member

~ :: angle formed by wind direction and the normal to member axis

k x - a function of A/A and x/b TOTAL LOAD IN WIND DIRECTION F

r.

F

Codf. Cod£.

(3

O· 15· 30· 45· 60" 1. 00 0.98 0.93 0.88 0.80

k"

See See table table 27 29 m F FORCE ON MEMBER m F m :: k· C_~ . q' Ch' Acos

f>

(Shielded member F k·

CC>Q~

.mkxq ·

Ch·Ac.os~)

1. 20 0.6 1. 16 See See 0.58 0.9 0.95 1. 04 table table 0.53 for _al!tant 0.85 27 29 0.42 ¥d=Z 5 0.60 0.28

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APPENDIX

EXPLANATION OF PRESSURE COEFFICIENT TABLES

By W. R. Schriever and W. A. Dalgliesh

INTRODUCTION

The calculation of wind loads on structures is based on the "stagnation pressure" which is the pressure the wind exerts when its kinetic energy is converted to pressure

on a surface obstructing flow of air. If p is the mass density of the air and v is the

wind velocity, then the stagnation or velocity pressure developed on an infinitely

large, flat plate perpendicular to the velocity is q = ~pv2. For an air density

cor-responding to 15°C. at 760 mm of mercury and the velocity v expressed in miles per

hour, the velocity pressure in psf. (pounds per square foot) is q = 0.00256 v2. In

Canada, because of lower temperatures, the coefficient 0.00256 frequently used else-where, has been increased to 0.0027.

Maximum wind velocities vary according to climate and geographic location. In Canada, :values of the maximum gust velocity pressures for design purposes are avail-able, as explained later, in a handbook of climatic information issued as a supplement

to the National Building Code, (Ref.

(1».

The values given are pressures which are

likely to be exceeded on the average once in thirty years.

In determining the design wind loads for a given building or structure, two other factors have to be considered, namely, the height above ground and the effect of the shape of the building itself.

Since wind velocity usually increases with height above the ground, the design pressure obtained from the climate handbook must be multiplied by a coefficient appro-priate to the height of the structure using a suitable velocity-height relationship. The coefficients used in the National Building Code are based on the assumption that gust

velocity varies as the 1 /lOth power of the height, (Ref. (1) ). Although it is known that

changes in "ground roughness" affect this relationship (Ref. (2», which is fairly conservative, no allowance for such variations has been made at the moment by the Revision Committee because present information is not considered adequate for this refinement, quite apart from the difficulties in predicting any changes in shelter con-dition for the life of a given structure.

The final step in obtaining actual pressures on a structure or building is the selection of appropriate shape factors or pressure coeffiCIents. The purpose of this Appendix is to present a brief discussion of the selection of pressure coefficients which may be used with the National Building Code, 1965. Other pressure coefficients, when known to be more applicable in a particular case or the results of special model tests, may be used in lieu of those given in this Handbook.

EFFECT OF SHAPE OF STRUCTURE

The relation between velocity pressure and actual pressures on a building, as a result of wind, cannot be expressed by a simple general rule or a mathematical equation. The variables are so many and the resulting relations so complex that the best approach developed so far has been to determine empirical constants for various situations by testing models in wind tunnels. Tests have also been made on full scale structures in natural wind, but these are so few as to serve to check model results rather than to replace them. Fortunately, for most sharp-edged structures, the results of wind tunnel tests on small models can be applied to full scale structures with reasonable confidence.

It is well known that suctions as well as pressures result from wind action on

structures. Both model tests and full scale observations indicate that very high suctions can occur over small areas and also that overall uplift can be great enough to remove

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inadequately anchored lightweight roofs. When suctions are indicated in model tests,

a:.!,

negative coefficients are applied to the velocity pressure. In general, the pressure dis- . ,

tribution (negative or positive) is nonuniform even over a single plane surface of a building and an average value is used for the pressure coefficient to simplify the design; local high pressures and suctions, however, should be so noted in the design rules that local damage can be prevented by proper design of fastenings, anchorages, etc. (Ref. (2), (3), (4) ).

In addition to external pressure, internal pressure must also be considered since air leakage due to openings such as windows and doors and even small cracks will give rise to a net internal pressure or suction depending on whether the openings are chiefly on the windward or leeward side. Such internal pressures and suctions must be con-sidered by using appropriate total pressure effects. On the other hand, it is agreed that in most cases, frictional forces acting tangentially are small and can be neglected; in other words, forces acting only at right angles to surfaces are usually considered.

Over the years, pressure coefficients have become increasingly extensive and accurate as more and different structures have been tested. Strict attention must be paid to the limitations and proper application of these coefficients, precisely because they are empirical and subject to so many variations. Some of the variables affecting shape coefficients not fully realized in early wind tunnel model tests (Ref. (2), (4), (5) ) are as follows:

(a) Orientation of building to wind direction.

(b) Ratios of length and height to breadth of building. (c) Variations in wind velocity profile found in nature. (d) Small scale turbulence present in nature.

(e) Shielding from nearby structures.

Orientation and length:height:breadth ratio of the building, taken together, can cause great variations in pressures, especially with regard to local suctions on the roof pressures near windward corners. For example, a diagonally oriented wind on a long building can cause local suctions up to five times the velocity pressure, whereas, for a wind norma1 to the eaves (in which case 1ength has little effect), the maximum suction coefficient may not exceed 1.0, (Ref. (4) ).

The wind velocity used in earlier model tests was constant over the height of the mode1 and the variations in pressure over the height of an actual building was assumed to follow the square of the velocity according to a specified profile. More recent model tests, carried out with a simulated velocity profile and also some observations on full-scale structures, have shown that the effect is practically equivalent to a uniform pressure over the whole projected height.

Some research has been done to include small scale turbulence in model tests and also to compare laminar flow model tests with natural wind on full scale structures. The results of various investigators appear somewhat contradictory but they agree in that small scale turbulence, hitherto ignored, has significant effects on pressure co-efficients, (Ref. (2) ).

Shielding from nearby structures has important effects and, again, the relationships are complicated. The difficu1ties of making general observations and establishing design rules are obvious, but it might be said that suction over the whole roof section is frequently an undesirable aspect of a shielded location (Ref. (2) ).

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PRESSURE COEFFICIENTS FOR THE NATIONAL

BUILDING CODE, 1965

The pressure coefficient tables in this Supplement are essentially the same as those in the 1961 edition of Supplement No.3 for use with the 1960 National Building Code except for some additional tables, a few corrections and a rearrangement. The simplified Table "0" is now Table A. The graphs of the new Tables Bl through B5 have been

added to show the effect of various roof slopes on pressure coefficients so that interpola~

tion of values will be easier. The graph of new Table C illustrates the influence of building slenderness on the overall force coefficient, and is of particular interest for tall, slablike buildings. The new Table D contains pressure coefficients for a typical high-rise building.

The S.I.A. Standards make some provision for variations in wind direction and variable length:width:height ratios, and include many special types of structures, with specific information on rounded shapes. (Ref. (7) ) The information on internal pressures is more thoroughly treated than in any other Code, and differs considerably from that in the 1953 National Building Code. The coefficients for gable roofs of different slopes differ substantial1y from those for the windward slope of the 1953 National Building Code but, on the other hand, values of the American Standards Association Code (Ref. (3» and some recent model tests agree closely with the S.I.A. Standards. The 1953 National Building Code coefficients for internal spans of a multiple shed roof differ from both the S.I.A. and A.S.A. Codes by a large factor but, as one would expect, recent model tests support the more recent codes.

These facts, coupled with the extensive coverage of pressure coefficients in the S.LA. Standards, in 1961 led the authors to the conclusion that the S.I.A. tables formed the best available basis for preparing shape factors for the National Building Code. This was in line with the opinions of others. notably T. W. Singell, (Ref. (6) ) who stated on p. 1710-4, "The S.lA. data is the latest and best data that could be found". Natural-ly, the S.I.A. Standards do not satisfy all of the design questions that will occur in practice. Some of the gaps have been filled by adding the new tables mentioned above, based on information submitted by Prof. J. Ackeret, Prof. D. Baines (see Acknowledge-ments) and the work of Prof. R. Pris(Ref. (8». Naturally. however, not even the present tables will permit coverage of all shapes and conditions that might occur in practice. Because of this and also in view of new information that might become available in the future, every designer should try to obtain the latest and most appropriate pressure coefficients for each case. For unusual types of structures, it may be necessary to resort to special wind tunnel experiments on scale models to obtain adequate design values.

EXPLANATIONS ON THE USE OF PRESSURE COEFFICIENTS

The pressure Coefficients Cp , shown in the Tables, give average pressures over the

building surfaces to which they refer except in the cases of spheres and cylinders, where the pressure varies too much from point to point. Since calculation of total force on spheres and cyJinders using such coefficients would require a laborious

sum-mation process, additional coefficients Cn are given, which can be used to calculate total

force on the projected area.

The total force F, on a surface such as a wall, roof, or other element, is the product

of the basic design pressure q (given in Article 4.1.2.12, Sentence (1) ), the height

factor Ch (given in Table 4.1.2.F), the total effect of external and internal pressure

coefficients Cpe and Cpj, and area A of the surface considered.

F = q • Ch • Cp • A

The various pressure coefficients are designated as follows:

Cpe -external' pressure coefficient.

Cpj -internal pressure coefficient.

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Cpt'· -local pressure coefficient, maximum, referring to a shaded area drawn to

scale in the sketches (not to be used for total forces). In two cases, at

t',

edges "0" in Tables D and 3, small crosses are shown instead of a shaded area. The crosses indicate that large suctions are more likely to occur there than elsewhere, but little information is presently available on the width of the area affected.

Cn -pressure coefficient supplied for spheres, and cylinders referring to the

total force on the projected area, and for bill-boards and free-standing walls referring to the total force (front and back).

Cnco -pressure coefficients for total forces in the "normal" and "tangential"

Ctco direction (see Table 27) acting on structural members of infinite length or slenderness. For members of finite length or slenderness, a reduction factor k is introduced into the expression.

C co{3 -Pressure coefficients for total forces of structural members in three dimen-sional truss constructions where the wind is not normal to the member

axis, but acts at an angle

fJ

from the normal. For members of finite length

or slenderness, a reduction factor k is again introduced.

Since the pressures developed can be positive or negative (pressure or suction), they are to be considered as differential pressures with regard to ambient atmospheric

pressure. A positive sign in the value of CPt' or Cpl indicates pressure, a negative

sign suction on the surface considered. To obtain the total effect, the total differential pressure has to be calculated. For example, if, for the windward wall of a building CPt' =

+

0.9 and Cpi = ± 0.2, then the maximum total differential effect is C p

=

1.1.

However, if the same building has a large opening on the windward side, then Cpl==

+0.8 and the total coefficient is +0.1 (inward force), whereas for a flat roof on this

building CPt' might be -0.7 so that, with Cpl= +0.8, the total coefficient is I.S

(up-ward force).

In the Tables, the structures are classified according to height:breadth:length ratio (designated h:b:l) with different pressure coefficients for different ratios where appropriate. The horizontal angle of wind direction, measured from the normal to one

side of a structure is designated by qJ.

TABLE A

For ordinary small buildings of average height: breadth: length ratios (h:b:l), the

external pressure coefficients Cpt' can be taken from the simplified Table subject to the

following conditions:

(a) The stress at any point in the building due to wind loads must not exceed

2S per cent of the total stress at that point.

(b) The height:breadth ratio must be in the range 2/3 < h/b< 3/2. (c) The length:breadth ratio must be in the range 2/S < l/b< S/2.

(d) The table applies to sharp-edged closed structures only and, in the approxima-tion, the wind has been assumed perpendicular to the eaves. Internal pressure coefficients and local pressure coefficient maxima must be obtained from the appropriate detailed Tables 1-13.

TABLE 1-21

For other than ordinary small buildings with average h: b:l ratios, information will

be found for many cases (see Table of Contents and Tables 1-21 which are considered

self-explanatory).

TABLE C

Table C shows the effects of building proportions on the overall force of the wind on the building. Coefficient Ch is the algebraic difference of the average pressure

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coefficients appropriate to the front and back of the building in the direction of the. wind. The net horizontal force exerted by the wind on the building is given by

Fh=Ch • h • b • q • Ch. Note that no information is provided about average pressure

coefficients for individual sides or about local maxima, and that only the wind direction normal to the width is considered.

ROUNDED STRUCTURES

For rounded structures (in contrast to sharp-edged structures) the pressures vary with the wind velocity, depending on Reynold's number. For practical purposes, this number can be expressed by dy'q where d is the diameter of the sphere or cylinder

in feet and q is the velocity pressure in pounds per square foot. Tables 22, 23 and 26

contain appropriate limitations.

The roughness of rounded structures may be of considerable importance. Common well laid brickwork without parging can be considered as having a "rough" surface (Table 22). Surfaces with ribs projecting more than 2 per cent of the diameter are

considered as "very rough". In case of doubt, it is recommended to use those Cn values

which result in the greater forces. For cylindrical and spherical objects with sub-stantial stiffening ribs, supports and attached structural members, the pressure co-efficients depend on the type, location and relative magnitude of these roughnesses.

ICING

In locations where the strongest winds and icing may occur simultaneously, struc-tural members, cables and ropes must be calculated assuming an ice covering based on climatic and local experience. Values of C for a "rough" surface shall be used for the iced condition according to Table 26.

STRUCTURAL MEMBERS, TRUSSES,

etc.

In Tables 27, 28, 30 and 31 pressure coefficients with subscripts co are used to

indicate that they apply to structural members of infinite lengths and this is multiplied by a reduction factor k for finite lengths of members. If a member projects from a large plate or wall, the reduction factor k shall be calculated for a slenderness based on twice the actual length. If a member terminates with both ends in large plates or walls, the reduction factors for infinite length shall be used.

SHIELDING

For members which are located behind each other in the direction of the wind the shielding effect may be taken into account. The windward member and those parts of the leeward member which are not shielded shall be designed with the full pressure

q, whereas the shielded parts of the leeward member shall be designed with the reduced

pressure qx according to Table 29.

For constructions made from circular sections with dy'q <2.5 and AsIA ~ 0.3,

the shielding factors can be taken by approxilIlQtion from Table 29. If dv'q

>

2.5,

the shielding effect is small and for a fullness ratios AsIA ~ 0.3, it can be taken into

account by a constant shielding factor kx=0.9S.

HIGH BUILDINGS

In high buildings, the walls near comers may be subjected to high local suctions. Allowance for this has been made in Table C and 3 by indicating a local maximum. High suctions near corners may be particularly critical in high buildings with light walls such as curtain walls. Another factor to be considered, particularly in high buildings with light curtain walls, is that of excessive lateral deflection of the building as a whole under wind loads. Whereas in the past, massive and rather rigid walls provided much additional stiffness, preventing even moderate deflection, many of the more recent high-rise buildings derive little bracing from their walls and rely to a much greater degree on the stiffness provided by the structural bracing of the frame. Designers are, there-fore, cautioned to pay increased attention to this problem of deflection in their designs.

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VIBRATIONS

Structures which may be subject to vibration due to the wind must be investigated Ii.~

by theoretical and possibly experimental methods for the danger of dynamic over-

W,

loading and vibration of critical frequencies. This is the case particularly for: church steeples and sightseeing towers, high chimneys, high buildings, antenna towers, power lines, aerial conveyors, cranes, etc. As a rough guide, it may be said that caution should be used if the period for a full cycle is more than one second.

CONSTRUCTION STAGES

It should also be noted that the shape of a structure may change during erection.

The wind loads, therefore, may be temporarily higher during erection than after

com-pletion of the structure. These increased wind loads shall be taken into account using

the appropriate coefficients from the Tables.

REFERENCES

(1) "National Building Code of Canada 1960," National Research Council, Associate

Committee on the National Building Code, Ottawa-NRC 5800.

(2) "Wind Loads on Structures," by A. G. Davenport, National Research Council, Division of Building Research (NRC 5576) March 1960.

(3) "American Standard Building Code Requirements for Minimum Design Loads in Buildings and Other Structures," A 58.1-1955, American Standards Association, New York, N.Y. 1955.

(4) "Wind Effects on Roofs," Great Britain, D.S.I.R., Building Research Station, Digest No. 122, Garston, May 1959.

(5) "The Use of Wind-Tunnel Models for Determining the Wind Pressure on Build-ings," by J. D. Haddon Civil Engineering and Public Works Review, Vol. 55, No. 645, April 1960.

(6) "Wind Forces on Structures, Forces on Enclosed Structures," by T. W. Singell, American Society of. Civil Engineers Proceedings, Vol. 84, No. ST 4, Paper 1710, July 1958.

(7) "Normen flir die Belastungsannahmen, die Inbetriebnahme und die Uberwachung der Bauten." (Standards for Load Assumptions, Acceptance and Inspection of Structures). Schweizerischer Ingenieur und Architekten Verein (Swiss Association of Engineers and Architects). No. 160, Zurich, Switzerland 19S6.

(8) R. Pris, annales de I'Institut technique du Batiment et des Travaux publics No. 181, Volume 16, page 1261-76, Paris, January 1963.

ACKNOWLEDGEMENTS

The permission of Prof. Dr. J. Ackeret of the Institute for Aerodynamics, Swiss Federal Institute of Technology, Zurich, for use of the Pressure Coefficient Tables of the S.I.A. Standards in this Handbook is gratefully acknowledged. The continued assistance of Prof. D. Baines of the University of Toronto and Prof. A. G. Davenport of the University of Western Ontario in the development and improvement of the wind load provisions of the National Building Code is also aCknowledged with gratitude.

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CHAPTER 2

COEFFICIENTS FOR SNOW LOADS ON ROOFS

By W. R. Schriever· and B. G. W. Peter·

TABLE OF CONTENTS

EXTRACT FROM NATIONAL BUILDING CODE OF CANADA, 1965

(Loads due to Snow, 4.1.3.7 to 4.1.3.10)

COEFFICIENTS FOR SNOW LOADS ON ROOFS

- Simple Flat and Shed Roofs - Simple Gable and Hip Roofs - Simple Arch and Curved Roofs

-Valley Areas of Two-span and MU,lti-span Sloped and

Curved Roofs. . • • • • . • . .

-Lower Level of Multi-level Roofs (when upper part of the same building or an adjacent building not more than 15 feet away)

-Lower of Multi-level Roofs with Upper Roof Sloped Towards Lower Roof

-Roof Areas Adjacent to Projections and Obstructions

on Roofs .

-Example Sheet 1. Snow Load Coefficients for Uniform and Unbalanced Load Conditions on Gable and Hip Roofs with Varying Slopes .

-Example Sheet 2. Design Snow Loads in psf for Various Differences in Roof Elevations for Multi-level Roofs with Three Typical Ground Snow Loads .

Fig. 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9

APPENDIX: EXPLANATION OF COEFFICIENTS FOR

SNOW LOADS

I V ARIATIONS OF SNOW LOADS ON THE GROUND AND ON ROOFS .

Climate Variations

Local Variations. Mountain Areas . Specific Gravity of the Snow

Effect of Wind on Snow Accumulation on Roofs Solar Radiation and Heat Loss

Redistribution of Load from Melting Snow II DESIGN SNOW LOADS IN THE

NATIONAL BUILDING CODE. . -.

Historiclll Notes

Changes in the 1965 National Building Code

III DETER~IINATION OF DESIGN SNOW WADS ON ROOFS.

Basic Snow Load Coefficients •

Influences that Modify the Basic Coefficients Reduction of Snow Loads for Exposed Roofs

Alternating Strip Loading (with FuJI and Half Load)

IV DETAILED EXPLANATIONS OF FIGt:RES 2-1 to 2-9

Page 25 25 25 26 26 27 27 28 29 30 30 30 30 31 31 32 32 32 32 32 33 33 34 34 34

-Research Officers in the Building Structures Section, Division of Building Research. National Research

Council-23

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