Earthquake and wind loads in building design

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Engineering Journal, 46, 9, pp. 27-35, 1963-10-01

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Earthquake and wind loads in building design

Cherry, S.; Ward, H. S.; Dalgliesh, W. A.

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Ser

TH].

t[2].t2

no. L52

e . Z

BTDC

NATIONAL RESEARCH

CANADA

DIVISION OF BUILDING

COUNCIL

RESEARCH

EARTHQUAKE

AND WIND LOADS

IN BUILDING

DESIGN

5. Cherry, ru.r.t.c.

D e p q r t m e n t o f C i v i l E n g i n e e r i n g U n i v e r s i t y o f B r i t i s h C o l u m b i o

H . S . W q r d ,

B u i l d i n g P h y s i c s S e c i i o n D i v i s i o n o f B u i l d i n g R e s e o r c h N o l i o n q l R e s e q r c h C o u n c i l Oitowq

W. A. Dolgliesh, A.M.r.r.c.

B u i l d i n g S l r u c t u r e s S e c t i o n D i v i s i o n o f B u i l d i n g R e s e o r c h N o t i o n o l R e s e o r c h C o u n c i l Ollowo

.4. it

REPRINTED FROM

THE ENGINEERING

_JOURNAL

46, NO. 9, SEPTEMBER 1963, P. 27-35.

iscussion.

YoI. 46, No. 9, 1963, p. 48.

Published jointly by the

National Research Council o{ Canada

and the

University of British Columbia

i-s?s?

TECHNICAL PAPER NO. 162

OF THE

DIVISION OF BLTILDING

RESEARCH

OTTAWA

OCTOBER

T963

NRC 765]

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o f t h e o r i g i n o l p u b l i s h e r . T h e D i v i s i o n w o u l d b e g l o d t o b e o f o s s i s i o n c e i n o b t o i n i n g s u c h

p e r m i s s i o n ,

P u b l i c o t i o n s o f t h e D i v i s i o n o f B u i l d i n g R e s e o r c h m o y b e o b t o i n e d b y m o i l i n g t h e o p

p r o p r i o t e r e m i l t o n c e , ( o B o n k , E x p r e s s , o r P o s t O f f i c e M o n e y O r d e r o r o c h e q u e m o d e p o y

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t o t h e N o t i o n o l R e s e o r c h C o u n c i l , O t t o w o . S t o m p s o r e n o l o c c e p t o b l e .

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o f o l l N o t i o n o l R e s e o r c h C o u n c i l p u b l i c o t i o n s i n c l u d i n g s p e c i f i c o t i o n s o f t h e C o n q d i o n G o v

-e r n m -e n t S p -e c i f i c o t i o n s B o q r d .

I

EARTHQUAKE

AND WIND LOADS

IN BUILDING

DESIGN

S. Cherry, ttt.r.t.c.

Deportment of Civil Engineering University of British Columbio

H. 5. Word

Building Physics Section D i v i s i o n o f B u i l d i n g R e s e q r c h N o t i o n q l R e s e o r c h C o u n c i l Ottowo

W. A. Dolgliesh, A.M.E.r.c.

B u i l d i n g S i r u c f u r e s S e c t i o n D i v i s i o n o f B u i l d i n g R e s e o r c h N o t i o n o l R e s e q r c h C o u n c i l Ottqwo

qEISMOLOGISTS

AGREE that no

LJ area is immune from the possibility

of earthquake damage; but t-here are

certain areas of recognized seismic

ac-tivity for which there is a substantial

probability

of future

strong-motion

earthquakes. Two such region;in

Can-ada are the St. Lawrence Valley and

the coastal area of British Columbia.

This is amply demonstrated by recent

publications of the Dominion

Obser-vatoryl, which show the locations and

magnitudes of the known earthquakes

in these regions. (Magnitude-term

used to define the instrumental

mea-surement of an earthquake and related

to the amount of energy it releases.

Structural damage at the epicentre

normally begins at a magnitude of

about 5.6. The epicentre is the point

on the earth's surface directly above

the origin of an earthquake.)

Ilodgson2

has reported that,

al-though Canada has had fewer

de-structive earthquakes than, say

Cali-folnia, the magnitudes of those that

have occurred are about as severe

as those of California. Damage

esti-mates of some of the more recent

disfurbances in Eastern Canada are

as follows: Cornwall-Massena,

1944,

magnitude 5.9, damage $2 million;

Temiskaming, Quebec, 1935,

magni-tude 6.3, damage $20,000; St.

Law-rence Valley, 1925, magnitude 7.0,

damage $f00,000. Along the Pacific

Northwest, major earthquakes have

been reported with epicentres in the

Queen Charlotte Islands 1949,

mag-nitude 8.0; off the British Columbia

Coast 7946, magnitude 7.3;

Van-couver Island 1918, magnitude 7.0

and 1957 magnitude 6.0. Fortunately,

except for the Cornwall earthquake,

the property damage resulting from

these tremors was slight since the

immediate epicentral areas were very

sparsely settled. The effects of a few

earthquakes in settled areas make an

interesting comparison: Seattle 1949,

magnitude 7.7, damage $20 millions;

Long Beach, California 1933,

magni-trrde 6.2 (less than that of

Temis-kaming) damage $50 million; and the

great San Francisco earthquake of

1906, magnitrde 8.2, damage $400

million.

Thus, although the record of

dam-age and disaster in Canada has

forfu-nately been relatively low, this fact

should not lead one to believe that

serious earthquakes are never likely

o

to occur in our country. Centres such

as Quebec, Montreal, Ottawa,

Van-couver and Victoria are all in

seis-mically active regions. Due to

popula-tion increase, industrial expansion and

development of urban areas, and the

associated demands for taller, heavier

structures and major engineering

pro-jects, the hazard from possible

earth-quakes has become much more acute

in recent years.

What can and should be done about

earthquake

hazard?

Attempts

to

answer this question have led to the

development of the specialized field

of earthquake engineering. Although

much of the research activity has been

in California and Japan, scientists and

engineers in many other countries are

concerned as well, with the result

that, following

two world

confer-ences,s' a an International Association

for Earthquake Engineering has now

been formed. Canada has

member-ship in the Association, and a

Na-tional Committee is being organized

under the auspices of the National

Research Council.

Earthquake

engineering

is

con-cerned with the sfudy of the

struc-tural stresses induced by earthquakes

and the development ol design

pro-cedures suitable for structural design

use. A major Canadian task, as in the

past, will

be to evaluate current

knowledge in the field and to decide

how to apply it to Canadian needs.

The purpose of this paper is to

survey the present state of

under-standing of earthquake forces and the

response of buildings to such forces.

The first section deals in a

funda-mental way with the dynamics of

buildings. This will be followed by

an examination of the way certain

building

codes attempt

to protect

against earthquake damage. This will

include, in particular, a discussion of

the current provisions of the National

Building Code of Canada.5 Finally,

a comparison will be made of the

earthquake provisions and the

some-what overlapping provisions for wind

Ioads in the National Buildine Code.

BEHAVIOUR

OF STRUCTURES

DUR.ING

EARTHQUAKES

The rational design and

construc-tion of earthquake-resistant structures

requires a knowledge of the lateral

forces developed in the structure by

the earthquake. These forces can be

evaluated theoretically by subjecting

the base of a damped system of many

degrees of freedom (the structure) to

transient erratic motion (the

earth-quake) and determining the response

of the system. Although

amenable

to mathematics,

this represents a

complex dynamic problem, the

essen-tial features of which will be

exam-ined here. The presentation is

in-tended as an introduction

to the

subject of earthquake engineering and

is based largely on the publications

E t ! / n d ' l ' v

3 . 0

2 . 0

r . 0

0

Fig 2-Velociry speclrum for Toft Eorthquoke, July 21,1952 (from Reference 6).

0 . 5

r . 0

1 . 5

2 . O

2 . 5

S E C

4

B A S E S H E A R

Fig. l-Schernotic represenlolion of

one-storey flexible slructure.

of Housner,6 CIough,T Blume and

others.8

Single-storey Slructu res

Figure 1 is a schematic

representa-tion of the deformed shape assumed

by an idealized one-storey structure

whose rigid foundation undergoes a

displacement equal to the earthquake

motion, x, of the ground. Due to the

flexibility

of the structure and the

inertia of its mass, m, the columns

deform thereby permitting

the mass

to displace relative to the ground by

the amount u :

y_x,

where y is

the displacement of the mass from

its original position. These

displace-ments are a function of time, t, and

the structure is therefore excited into

motion which is opposed by the shear

sti{fness, k, of the colunms and the

inherent friction of the structure,

nor-mally referred to as the damping. For

a linear elastic system the shear or

lateral

force,

V,

exerted

by

the

columns on the mass and on the

ground may be expressed as

V : l r u

( 1 )

z V

The friction of a struchrre can be

described satisfactorily by the

condi-tion of viscous or linear damping.

Linear damping results in damping

forces directly propottional and

op-posed to the velocity; the

proportio-nality constant, c, is known as the

damping coefficient. When motion is

restricted to translation in one

direc-tion only (as represented by u), the

differential equation governing the

response of the flexible structure may

be written as

d"u ,

md'.!t

nd:(.r + u)

, d t t t u : a t r : d .

-or

mu + cu t ku : -mli,

(2)

where i is the horizontal acceleration

of the base or ground which is

identi-cal with that recorded by a

stlong-motion accelerometer during an

earth-quake.

If, as is normally encountered in

building structures, the damping is

small, the solution of equation (2) for

the response u, at arty time f, is given

by the Duhamel integrals as

/ , \ T l ' . . , , - F 1 r o r l 1 3 . , 1 u \ r ) : 2 T J o l \ r ) e

,-snlf (t - r) dr

(B)

where T = natural undamped period

of vibration of the structure

. / i

: r "

_{U n}

B :

fraction of critical damping

The critical damping c" is the

mini-mum value of c resulting in a

non-oscillating response.

It should be noted from equation

(3) that the dynamic response u of

the structure is dependent on the

character of the structure, defined

by its natural period of vibration (a

function of its stiffness and weight)

and its damping, and on the

charac-tel of the ground acceleration.

The character of the glound

ac-celeration is exhibited by the integral

appearing in equation (3) namely

,*

X s i n l ' f t - r ) d r

'I

A )

If the displacement a(f) equation

(3) is differentiated, the velocity z(t)

will be obtained and the maximum

value of z(/) is found to equal the

maximum value of S(l). For a

partic-o

UJ U)

c c

cc

z\/ hm

I t

s ( t ) : I i ( 7 ) p ' F ' z ' r t ' r - "

J o

l

il

_I,t

V

ilJ

ll

l]

P = o '

'.*

F = o ' 2

U N D A M P E D

N A T U R A L

P E R I O D ,

3 . 0

ular ground acceleration input record,

and for a particular F andT, the

inte-gral defining S(t) can be evaluated

and the maximum value, S,, observed.

The plot of such maxima for a range

of shuctural periods T yields a graph

or influence line of maximum velocity

response known as the velocity

re-sponSe spectrum. A family of such

spectrum curves can be obtained

cor-responding to different B values.

The computation required for the

evaluation of the response spectrum

is extremely great and is best done

by analogue or digital

computers.

Velocity response spectra for the Taft,

California

earthquake

_{of Jrrly 2I,}

1952,6 are presented in Fig. 2. The

effectiveness of small amounts of

damping in modifying

the response

is seen to be very marked.

The dynamic response of a

struc-ture to

any given

earthquake

is

directly obtainable from the velocity

spectrum of that earthquake. When

this spectrum is lcnown, the maximum

base shear transmitted into the

struc-ture from the ground may simply be

written as

V e : k u , , ^ * : f # t ,

or, alternatively

/ o - c \

v " : l + ! l w

: c t v ( b )

\ T s /

where W denotes the weight of the

structure and g is the acceleration

of gravity. C, known as the seismic

coefficient, is seen to depend on the

period of the structure and on the

spectral velocity.

Although the exact nature of future

earthquake ground motions is not

known, average response spectra may

be predicted as shown by Housner.B

These average spectra were developed

from numerous strong-motion records

of past disturbances.

Multi-storey Structures

Multi-storey structures have several

characteristic or normal modes of

vi-bration that are transiently excited by

earthquakes. It is possible to describe

the actual response of a structure by

a superposition of its normal mode

components.

By modal superposition principles,lo

the actual multi-degree of freedom

structure may be represented by an

equivalent set of one-mass systems.

Each system responds to the

earth-quake excitation independently and

in its own mode. Then the actual

re-sponse of a linearly elastic multi-storey

structure with small linear damping

can be expressed as the sum of the

responses of the independent modes.

The spectrum concept is applicable

to each mode separately. The base

shear eontribution made by each

in-dividual mode is therefore determined

from equation (5), using for the nth

normal mode its corresponding period

T^ and an effective weight W*

given by

w- : E'@zw')t'

_{" " -}

/A\

> 6 , , 7 w "

( o /

where ar" represents the weight of the

zth floor whose displacement in the

nth mode is {rr. There are as many

values of n as there are degrebs of

freedom. $"n and T^ are

characteris-tics of the structure and can be

evaluated by standard means.8

On the basis of the spectrum

con-cept, the total maximum base shear,

V B, transmitted into the structure

from the ground is therefore

V n : 2 " V s "

( 7 \

where, from equation (5),

/ \

l e o

I

r o , : \ ) w " l s u ^ .

r r

" 9

/

It should be noted that the result

represented by equation (7) is only

approximate. V6 is actually greater

than the true maximum base shear

sinc'e the individual modal maxima

are not achieved concurrently. The

error arising from the superposition

of the spectral maxima can be

over-come, in part, by assuming that the

total maximum response is given by

the square root of the sum of the

tqrrur"i of the modal maxima.lo

The resolution of the base shear

into equivalent lateral seismic forces,

F, acting on the masses at each floor

level is also effected by modal

super-position principles. Due to the nth

mode contribution, the maximum

value of this force at the ath level is

T - l

I Q " " u ' | , ^ ,

r "" : v enl>6--"1

(8)

and, using response spectrum

pro-cedures, the total marimum seismic

force at this level may be

approxi-mated by

t-

-t

r,: IF,. : I v'""1ffi) tvl

Again, F, is greater than the true

maximum value.

Influence of lnelqstic Behqviour

The preceding account of structural

behaviour is based on the assumption

of a purely elastic response. During

an earthqtiake, strucfures may

under-go inelastic deformations of relatively

large magnitudes before failure

oc-curs. The energy absorbed in this

plastic

deformation prevents an

energy build-up to the levels

re-quired for achieving maximum

spec-trum velocities. This has the effect

of reducing the response of the system

and limiting the lateral forces

de-veloped in the structure.

Recent studies8,11,1z,13

have shown

quantitatively the importance. of

in-Fig. 3-Volues of seismic coefficient C, occording to Notionol Building Code of Conodo, 1960.

0 . 1 4

0 . t 2

0 . r 0

0 . 0 8

0 . 0 6

0 ' 0 4

0 ' 0 2

0

l 0 1 5 2 0 2 5 3 0 N O . O F S T O R I E S A B O V E L E V E L B E I N G C O N S I D E R E D

H O U

S N E

R ' S

V E L O C I T Y

\

S P E C T

R U [ I

t . .

C U R V E

S O F T

G R O U N D

z . s \ k = s . o

t . r

r . 0

0

r . 0

2 . 0

3 . 0

F U N O A M E N T A L P E R I O O , S E C

Fig 4-Typicol volues of seismic coeff icient, K?, from Rumoniqn 66s1s.16 (Broken line, typicol velocity spectrum for "cveroge" eorthquoke.6)

elastic deformations in limiting

dy-namic stluctural response. In this

re-gard, the structural framing system

has a significant

influence

on the

over-all ductility

and

energy-absorb-ing capacity of the structure.

Effects of Orher Foclors

The theoretical principles outlined

above focus attention on important

parameters influencing the behaviour

of structures during earthquakes. It

should be recognized that additional

factors may play a significant role in

determining dynamic structural

re-sponse. Among these are: soil

con-ditions

at the site, building

and

ground interaction, and alterations to

earthquake motions due to

interfer-ence from the structure itself

(feed-back). Many of these problems are

complex and have not been

com-pletely investigated or are not yet

fully understood.

BUITDING

CODE APPROACHES

TO EARTHQUAKE

DESIGN

In the several countries that have

earthquake load requirements in their

building codes, a number of different

approaches are used. The provisions

of five building

codes are outlined

to illustrate

the principal

feafures,

and to show how these provisons are

related to the principles described in

the preceding section. Attention will

be confined to buildings,

although

may of the codes also consider special

structures such as dams and bridees.

C o n o d o

In the National Building Code of

Canada 1960,5 earthquake loads are

dealt with in Part 4, Section

4.I.2.-15(1). The shear force, V. In the

Cana-dian Code the symbol F is used) at

any level in a structure is given by:

v : cl,v,

(10)

where W is the total load above this

level and consists of the design dead

load plus the design stored load and

service equipment loads. The seismic

coefficient, C, is computed from:

The present Canadian Code (1960)

follows closely the treatment given in

the (U.S.) Uniform

Building

Code,

1958.14 One difference is the

pro-vision in the Canadian Code for a

complete dynamic analysis by a

per-son competent in this field.

Jopon

The Japanese code, Standards of

Aseismic Civil Engineering

Construc-tions,l5 uses a formula similar to

equa-tion (10). The chief distincequa-tion is that

a high seismic coefficient is chosen,

but on the other hand the allowable

working stresses are also high (e.g.

steel: 15.3 tons/sq. in.). Implicitly

this approach considers a large

earth-quake, with low probability of

occur-rence, but still permits an economical

design on account of the high

work-ing stresses,

The seismic coefficient is a

func-tion of building height, type of

con-struction, type of foundation material

and the seismicity of the region, thus

C : ABCI,

where ,48 > 0.5

(12)

In equation (f2) A is a variable

which depends on the type of the

construction and foundation;

typical

values of A are shown in Table L

These values are based on the

rela-tionship between the expected

fre-quency content of a particular ground

motion, and the frequency response

of a given type of construction. For

example, wood construction tends to

be flexible and is not as adversely

affected by a high frequency

ex-citation as is the more rigid masonly

constnrctionl high

frequency

ex-citation is associated with the

ealth-quake

motion

of

hard

grounds.

Table I, then, indicates the possible

occurrence of resonance for different

types of structure-foundation

condi-tions.

The values of B may be I.0, 0.9

or 0.8, depending on the seismic risk

of a region. Co is the basic seismic

coefficient and its value varies with

building height; for buildings up to

16 metres high C" is 0.20 and for

every additional 4 metres C. is

in-Wood

Steel

ReinJorceil

Cm,crete Masomry

I a U 6

2-0

ts-L o F O J

=

f x

=

0 . 2

r 1

r ' \

where l/ is the number of stories

above the level under consideration

and K is the integer 1,2 or 4,

repre-senting the seismic risk associated

with a region. Values of C for

differ-ent values of N and K are plotted

in Fig. 1). Values of K are obtained

from a seismic regionalization map,

based on information

from the

De-partment of Mines and Technical

Sur-veys. The St. Lawrence Valley and

the lVest Coast are regarded as

re-gions of high seismicity, for which K

has the value 4. Recently a Seismic

Regionalization Committee was

form-ed in the Department of Mines and

Technical Surveys to re-appraise

seis-mic activity in Canada.

FoundaLion Material

^

_-

K(0.15)

N + 4 . 5

TABLE I.

Typical Values of Coefficient A in Equation (I2) C on str u cti. on aL M at erinl : ? o o O

< t s

T e r t i a r y R o c k . . . . .

Gravel ].

. .

Alluvium

Very Soft Soil

0 6

0 . 8

1 0

1 . 5

0 . 8

0 . 9

1 . 0

1 . 0

1 . 0

1 . 0

1 . 0

1 . 0

0 6

0 . 8

1 0

1 . 0

VERY HARD GROUND

N L

- o

creased by 5%. Heights of buildings

are restricted in regions with the

highest seismic risk, as shown in

Table II.

R u m q n i a

The Rumanian Building

specifies that the total base

Vu, be calculated from:

r - , : I v u " : K * E t t - , r ,

Code16

shear,

( 1 3 )

where K represents the seismicity of

a region. In Rumania there are four

seismic zones for which the values of

K are 1.0, I.7, 2.9 and 5.0. The

parameter y is a function of the

foundation soil and the period of

vi-bration of the structure. Typical

curves for the product Ky are shorrnn

in Fig. 4, and these show a

re-semblance to the velocity spectrum

curves obtained by Housner.6 g is a

damping function whose value

de-pends on the type of construction:

for steel construction g :

I.6 and

for reinforced concrete rp : 1.2.

When the base shear has been

cal-culated the lateral load at the zth

storey is calculated from equation (9).

u.s.s.R.

The latest Soviet Building Codstz

concerned with

earthouake loads

states that the total design seismic

tot-ce, F", at the ath storey is

deter-m i r r e d

f r o m t h e f o r m u l a :

r, : T F.. : KD u"r.,"n" (14)

where K = a regional seismic

co-efficient, the value of which may be

0.025, 0.05 or 0.10. A certain amount

of flexibility is allowed in the use of

this coefficient; if a careful survey is

made within a region with a

speci-fied K value then this value can be

modified if it is justified by the

sur-vey. Important

structures, such as

powel stations and government

build-ings, within a given region are

de-signed on the assumption that they

are in a region with a higher seismic

risk.

The coefficient 8 is a function of

the period of free vibrations of the

structure. The coefficient is plotted

in Fig. 5 and again the resulting

curve is seen to resemble the velocity

spectrum curve of an idealized

earth-TABLE II.

Height Variations in Seisrnic

Areas in Japan

Height Restriction,

Type of Builfling

metres

Steel .

Reinforced Concrete.

r . 0

2 ' o

P E R I O D , S E C

Fig. S-Volue of coefficient $, vs period of free vibralion of slruclure,

quake. The coefficienl rlrn is a

func-tion of the deforrnafunc-tion curve

result-ing from free vibrations of the

struc-ture:

n ^ : o ^ 8 t v , 6 , "

(15)

E*'ri"

where N is the total number of

stories.

If a complex structure is being

designed the following substitution is

allowed:

o , : h "

( 1 6 )

where h, is the vertical distance from

the base to the zth storey. This

ap-proximation can only be applied for

the fundamental mode of vibration.

The weight of the lth storey, Wi, is

taken as the dead load plus 80 per

cent of the live load. Equati,on (14)

computes the actual load at the ath

storey, not the shear force, and its

use demands a dynamic analysis of

the system.

u . s . A .

Many of the large cities on the

west coast of the U.S.A. have their

own building codes, but perhaps the

most significant American document

is the 1961 edition of the Uniform

Building Code.ra The base shear, Vs,

is calculated from

il

V B : K E C > , \ ' I t i

( 1 7 )

In equation tffl f

t

"pr"sents

the

seismicity of a region, and its value

can be 0.25, 0.5 or L0. E represents'

the capability of a structure to

dis-sipate energy and its values are given

in Table III. The Code requires that

all buildings over 160 feet high must

be constructed of completely

moment-resisting frames.

The coefficient C in equation (17)

is a functidn of the fundamental

period of vibration T, thus

^

0 . 0 5

m \

C :

W,

? ) 0.1 see. (18)

The base shear is distributed along

the height of the structure by the

following formula:

F , :

w " h " . v "

( 1 9 )

I'/

ltv,n,

i-l

In this equation h1 is the height to

the ith storey, and Fn is the lateral

load, not the shear force, at the ath

storey.

The overturning moment, M,

act-ing on a structure is calculated from

il

M : J LF"h,

(20)

where J is an empirical factor that

indirectly takes account of the

dimin-ishing importance of higher order

modes:

0 . 5

J :

d,

(0.33 <

"r < l)

(21)

Discussion of the Building Code

Requiremenls

The building codes described in

this paper express in different forms,

the action of an earthquake upon a

building, but they have certain

fea-tures in common. All the codes

con-tain a factor which defines the

avail-able knowledge concerning a region's

seismic activity.

Each of the building codes takes

into account, explicitly or otherwise,

the response of a building to an

earthquake. The Uniform Building

Code, and Rumanian and Soviet

Codes explicitly use the free periods

of vibration of the strucfure as the

parameter determining building

re-sponse; this is also loosely implied

in the Canadian Building Code,

in-sofar as it is possible to relate the

height of a building to its

funda-mental period. A plot of height

ver-sus period for a number of buildings

indicates an approximate linear

re-Iation of the form H/f

-

767,

TABLE III.

Values of Coefficient E in Equation (17) Type or Arrangement of

Resi.sting Elements E

Buildings with a moment-resisting

space frame, capable of resisting

l0OTo of the total lateral load. . 0 . 67

Buildings with a complete

hori-zontal bracing system capable of

resisting aII lateral loads,

includ-ing a moment-resistinclud-ing space

frame, which by itself can resist

a minimum of 257o of this load. .

Other tvpes of framine svstems. . .

Buildin!'with a box slst'em; this is

defined as a complete vertical

load-carrying spacd frame while

the lateral loads are resisted bv

shear walls.

. . . .

Other structures.

0 . 8 0

1 . 0 0

30

1 6

20

1 . 3 3

1 . 5 0

Wood

^ 1 0

b< F z U a o & d -r U @ ^ A S S U M P T I O N S : S T O R Y H E I G H T . 1 2 F T ! = t o t , T r s F U N D A M E N T A LP E R I O D , H I S B U I L D I N G H E I G H T 'n

Y-Y.

{!trs6y1

_{K , I ,} E . I

-{ea;

where I1 is building height in feet

and ? is the fundamental period in

seconds. This makes it possible to

compare the base shear coefficients

of the Canadian Code and the U.B.C.

as shown in Fig. 6.

The Japanese and Rumanian codes

take account of different foundation

materials in earthquake design. The

two

variables

considered

in

this

aspect of the problem are the degree

of consolidation

of the foundation

material and the period of vibration

of the structure. An expression for

the damping action of structures is

formulated

in the Rumanian code,

and is implied in the factors C and

8 of the U.B.C. and Soviet codes

re-spectively. It is worth noting,

how-ever, that the damping values used

are arbitrarily

related to building

types rather than being based on

actual measurements.

In an attempt to obtain some

com-parison between the National

Build-ing Code, the Uniform BuildBuild-ing Code

and the Soviet Building

Code, two

buildings were designed according to

these different codes. The two

com-parative designs are shown in Figs.

7 and 8. Fisure

7 illustrates the

300

0 2 4

L A T E R A L

S H E A R

x IO - , 2

K I P S

Fig. 7-Compcrison of ecrlhquoke designs for o lS-storey building (Alexonder Building, Son Francisco). Zone 3 assumed.

200

_{2 0 0}

0

0 . 2

0 ' 4

0 . 6

0 . 8

t . 0

t . z

t - 4

F U N D A M E N T A L

P E R I O D .

S E C

Fig. 6-Comparison of seismic coefficients of Notionol Building Code (Conodo, 1960)

U n i f o r m B u i l d i n g C o d e ( U . S . , l 9 5 l ) .

W E I G H T

D J S T R I B U T I O N ,

K I P S

r 0 0

2 0 0

L A T E R A L

L O A D , K I P S

F r UJ

u-I tiJ ul I O

z

)

r n n

o t v v (9 t! F T t! T F t! t! tL I r! t ! -J o z = r n n o r v v E U

=

UJ

-T O -T A L

W E I G H T

O F E U I L O I N G

t 4 , 6 1 9

K r P S

F U N O A M E N T A L

P E R I O D

O F B U I L D I N G t . 2 5 S E C

r N A T I O N A L B U I L D I N G C O D E O U B C , ^ S O V I E T C O D E ! o A

l t t

i ? f

! i i

JJ/

'l I

I I

d a

t l

O A

I I

o A

t l

o N A T I 0 N A L B U I L D I N G C O D E O U B . C ^ S O V I E T C O D E

EUILDING

CODE

B A S E

S H E A R ,

K I P S

E F F E C T I V E S E I S M I C C O E F F I C I E N T

O V E R T U R N I N G

M O M E N T ,

K I P F T

C A N A D I A N I 9 6 O

4 7 5 . 1

3. ?5 '/"

7 3 , t 9 3 .

U. B.

c o D E i 9 5 |

4 5 3 . 9

3 . 2 0 ./ "

2 6 , 9 4 4 .

s 0 v rE

T t 9 5

7

8 r 6 . 8

5'7 6 '/o

1 t 2 , 4 9 6

W E I G H T

D / S T R I B U T I O N .

K I P S

. NAT, BLDG. CODE

O U.B.

C O D E

^ S O V I E T

C O D E

5 t 0

L A T E R A L

L O A D ,

K I P S

80

z.

.=

9 r - o u

. ^ U - u J LrJ (

o i ' r u

9 u r

. trJ = J ^ ^

(,

trJ T

8 0

z.

=

o . b u - u t-.t L O ' a v

< ;

F J . ^ (, Lv u T

0

. NAT.

BLDG.

CODE

o u.8. coDE

S O V I E T

C O D E

2 0

3 0

S H E A R ,

K I P S

r5

o L

- 0

L ATERAL

T O T A L W E I G H T O F E U I L D I N G 3 7 t . 4 K I P S F U N D A M E N T A L P E R I O D O F B U I L D I N GU ' T Z b J L L

Fig. 8-comporison _{of eorthquoke designs for o four-slorey building. Zone 3 ossumed,}

fact that the Canadian and Uniform

Building

Codes give similar values

for the base shear of high rise

build-ings; because of the / factor eiven

equation (16) has been used in the

calculations for the Soviet code and

so the values given in Figs. 7 and 8

are not fully repr-esentative of this

design method. Fig. 8 illustrates the

fact that the Uniform Building Code,

when compared with the other two

codes, favours smaller buildinss with

a relatively high fundamental

-period.

Of the three methods based on

dynamic

principles,

the

Uniform

Building Code is the easiest to apply.

When the fundamental period of the

structure

_{has been evaluated, the}

base shear and overturning moment

can be calculated. fiilizing

equation

(20) for the latter. The Rumanian

and Soviet codes are based on a

complete free vibrational analvsis of

the structure

RETATIVE IMPORTANCE OF WIND

AND EARTHQUAKE I.OADING

The fact that winds, as well as

earthquakes, exert lateral forces on

buildings

invites a comparison

be-tween the two. A detailed discussion

of wind loads will not be included

in this paper as a comprehensive

re-view of wind loads has already been

provided by Davenport.le Suffice it

to say that although winds and

earth-quakes produce dynamic forces with

distinctly

different

characteristics,

both are approximated by static

load-ings in the simplified

approaches

usually adopted in building codes.

It is generally recognized that the

two forces need not be considered

simultaneously; it is therefore

neces-sary to ascertain r,vhich of the two

lateral load provisions will govern in

any given design problem where both

apply. A comparison of this sort,

however, is valid only for one

par-ticular set of conditions and may fail

to reveal the effects of certain

im-portant variables (e.g., geographic

lo-cation) on the relative importance of

wind and earthquake on a

country-wide basis.

Fig. 9-Vclues of F. ond F- used in

Equo-tions (28) qnd (29).

c 0 2 0 3 0 4 0 5 0

N N U M B E R O F S T O f l ! E S

In the following

discussion, the

relevant variables have been arranged

in a compact form to allow some

general

observations

to

be made

about their effects on a

wind-earth-quake comparison. It is hoped that

the ratios developed

will

aid in

placing the code provisions for the

two lateral forces in their proper

per-spective.

Bosis for Comporison

For the cornparison, equations for

shear and moment due to wind and

due to earthquake weie developed

using the Iateral force provisions of

the National Building Code (1960).

The only adjustment made to the

techniques laid down in the Code

was to replace the wind height

fac-tors (Table 4.1.2.F) by the following:

Gust pressure at height r,

f ,1'''

r" : cro

_frl

where q3o is the basic gust pressure

given in the Climate Supplement to

the Code.18

Ratios of wind shear to earthquake

shear and of wind moment to

earth-quake moment for a selected class of

buildings

which

includes

most of

those being built today were formed

from the equations for wind

and

earthquake loadings. The shears and

moments considered in the ratios act

just above the foundation and the

basement slab and occur only at this

point; a general indication of their

variation

along the height of the

building will be given later.

B U I L D I N G C O O E E A S E SHEAR. i(IPS EFFECTIVE S E I S M I C C O E F F I C I E N TO V E R T U R N I N G M O M E N T , K I P F T C A N A D I A N I 9 6 O

29.7 I

8'0 o/o

t 2 7 8 . 9

u I CODE

196

|

l 3 ' 8 0

3 . 7 %

3 7 5 . 2

S O V I E T

I 9 5 7

? 6 .

ve

vw

I

I

I

(n 40

lr, E

Pro

U) F

Izo

L!

o

E l o

LrJ @

=

= 0

z.

/ ' "

/,/r*

0

1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 0

2 5 0 5 0 0 7 5 0 1 0 0 0

B A S E

S H E A R ,

K t p S

E A S E

M O M E N T ,

F T K I P S

X I O - 3

---sidered, and the mean depth, defined

as the plan area divided by the

width.

Rqtios of Wind to Eorthquoke

The equations of wind shear and

moment and earthquake shear and

moment used to form the ratios are:

Wind shear

V, : 0.2949'he/,ul{et7 Q2)

Wind moment

14. : q' he'7

whlo.2g4l{et7

+ 0.166N16/7

l

(23)

Earthquake shear

V " : 0 . l \ K p d w

2 N + 9

(24)

Earthquake moment

M" :O.l1Kpdwh

,1t

2n -1 9

] uu,

where

q' - basic gust pressure ge6 (30

ft. ht.) multiplied by a total

pressure coefficient of 1.5,

p.s.f.

o : width of building as defined

earlier, ft.

d - depth of building as defined

earlier, ft.

h : storey height, ft.

pt = average unit weight of top

storey, p,s.f.

r -

ratio of increase in unit

wt./storey: p1

n = number of storeys down

from top (n, for roof = 0)

N : total number of storeys (not

incl. basement)

K = seismic zone tactor (7,2 or 4)

The ratios V*/Vu and M*/Mu can

be simplified by separating the parts

of the formulae which are functions

of N from the other factors as

fol-lows:

o.2g4Ne'7

eN + 9)

r r o r r D t r v /

:

0 1 5 t 4 +rA-2T(2 _ rW

(26)

4 0

? n

2 0

r0

4 i ' r N 2 + ( 2 - r ) N

4 l r n 2 * ( 2 - r ) n

E A R T H Q U A K E

_ Z O N E

I I

W I N D

_ G U S T

P R E S S U R E

The buildings considered have a

uniform plan area for all stories (no

setbacks), and all storey heights

in-cluding the single basement storey

are the same. Storey weights are

either uniform or else increase

uni-formly from t}le top storey

down-wards. Service machinery is located

in a penthouse on the roof, and the

combined weight of the roof

struc-ture, penthouse and contents is twice

the weight of the top storey. Only

two plan dimensions are used

regard-less of the shape (rectangular,

U-shaped, L-U-shaped, etc.): the over-all

widths normal to the forces

con-' r 1 = , 2 1 ,

]

' . , H A L T F A X

B U I L D I N G

W E T G H T

t 5 0 p S F / S T O R y ,

f = l o l o , D T M E N S T O N S

l 2 o '

x l 8 o '

Fig. l0-Comporison of wind and earlhquoke designs for o common rype of building Holifax region,

f o.zs+Nn''

a n d 1 ' ' - ( f l )

'l

-t

+ 0.1661116'

Fig. ll-Comporison of wind ond eorthquoke designs for o common rype of building in tvlontreql region,

0

1 0 0 0

2 0 0 0 3 0 0 0 4 0 0 0 0

B A S E

S H E A R ,

K I P S

250 500 750 1000

B A S E

M O M E N T ,

F T K t P S

X t 0 - 3

0 . 1 5

^ r

a

r l

? " + , e I

? - o L 4 + r n 2

l ( 2 - r ) n )

e7)

Then the ratios are:

r l ^ ' r - 9 1 7

! : t :l:-.F,(N)

( 2 8 )

V"

Kptd

-M.

_{q'hr,, . ,}

* " : 6 n ' 1 - ( N )

( 2 e )

F,(N)

and F^(N)

are plotted

against N for four different values

of "r" in Fig. 9.

D T S C U S S t O N

Geographic location determines the

wind gust pressure g and the seismic

factor K. The considerable influence

that location has on the design forces

can be shown by Figs. 10 and 11,

where the same structure has been

a 4 0

y!

E

P 3 0

U) F

!zo

LL

o

E l o

trl CD

= 0

z

4 0

Y,;,

30

2 0

r0

E A R T H Q U A K E

- Z O N E

] I I ( K =

W

I N D

_ G U S T

P R E S S U R E

1 5

M O N T R E A L

B U I L D t N G

W E I G H T

l 5 0 P S F / S T O R Y ,

( = l o l o , D I M E N S I 0 N S

t 2 o '

x t 8 0 '

,ol,

J '''

v e l

I

VW

V

7

o

sl (\l il (\I F (\t

2 O S T O R Y

B U I L D I N G

S H E A R

MOMENT

0

t 0 0 0 2 0 0 0

S H E A R ,

K I P S

M O M E N T ,

F T K I P S

X I O

- 5

E A R T H Q U A K E

_ Z O N E

t r ( K = 2 )

W I N D

_ G U S T

P R E S S U R E

2 I P S F

B U I L D I N G

W E I G H T

3 B , 7 O O

T O N S

- D I M E N S I O N S

I 2 0 , X

I 8 0 ,

Fig. l2-Sheor ond moment distribution whh heighr for o 2O-storey building (comporison of wind cnd eorthquoke loods).

analyzed for two different areas, one

with high wind loads and the other

with a high earthquake factor. Shear

and moment are plotted against

building height, and although the

shapes of the curves remain the same,

the relations between those for wind

and those for earthquake vary

con-siderably from one region to t}e

other.

Other factori bei.rg constant, the

higher the building, the more

prob-able it is that wind effects will

ex-ceed earthquake effects. Earthquake

effects, on the other hand, exceed

those due to wind for all buildings

below a certain height and, as shown

in Fig. 11, this critical height may

well be as high as 30 storeys (360 ft.)

or even more.

Weight distribution is expressed by

four paramete$, p1, d, w and r. For

relatively low buildings, an average

storey weight, Wayq, can be

substi-tuted as follows:

' ' 9 / 7 Q W n

Ratio :

fW*.F(.V\

(30)

as Fig. 9 demonstrates that the

weight distribution assumed is not

critical for buildings up to l0 storeys

in height. For taller buildings, the

ratios are more sensitive to

'7',

in-dicating the need for a more careful

assessment

of the weight distribution

and/or a more liberal allowance for

error in the result.

Distribution of wind and

earth-quake forces along the height of a

firical building is shown in Fig. 12.

It may be observed that when

earth-quake governs at the base, then it

governs all the way to the roof; on

the other hand, even though wind

may govern at the base, earthquake

invariably

takes over at and above

some upper level of the building.

coNcr.usroNs

Evidence

of seismic activity

in

Canada demonstrates the need for

earthquake protection in certain

re-glons.

In the light of present-day

knowl-edge it appears that the National

Building Code of Canada does not

adequately account for all the

vari-ables involved

in the problem

of

earthquake design. There are strong

arguments for considering the

funda-mental period of vibration of a

struc-ture as a basic design parameter and

also for considering the relations

be-tween type of structure and type of

soil. Nevertheless for many typical

structures the National Building Code

specifies values of base shear that do

not deviate far from the values

cal-culated according to the regulations

of other countries.

In comparison with wind,

earth-quake requirements govenr the

de-sign of buildings lower than a

cer-tain

critical

height,

which

varies

from below five to more than 30

storeys, depending on the building

and its location. Wind requirements

dominate for the lower part of

build-ings which

are over this critical

height, although a substantial upper

part may still be governed by

earth-quake.

REFERENCES

l(o). Milne, W. G. qnd K. A. Lucos. Seismic Activiry in Western Cqnodo 1955 to 1959 incl. Publicotions of ihe Dominion O b s e r v o t o r y , O t t o w o , V o l . 2 6 , N o . l , I 9 6 1 .

(b). Smith, W. E. T. Eorthquokes of Eost ern Conodo and Adiacent Areos 153& 1927. Publicotions of the Dominion Ob-servqtory, Ottqwd, Yol.26, No. 5, 1962. 2. Hodgson, J. H. A Seismic Probobility

Mcp for Cqnsdq. Cqnodiqn Underwriter, Vof. 23, No. 7, April, 1956. 4p. 3, Proceedings of the World Conference

on Ecrthqocke Engineering, June 1956. Eorthquoke Engineering Reseorch Insti-fute, Sqn Froncisco 4, Colit.

4, Proceedings of the Second World Con-ference on Eorthquoke Engineering, July 1960. Vols. l-3, Associqtion for Science Documents Informolion, Tokyo, Jopon. 5. Nsrionql Building Code of Conodc, 1960. Associqte Commiitee on the Notionol Building Code, Nofionol Reseorch Coun-cil, Ottowo.

6, Housner, W. G. Behoviour of Slructures During Eorfhquokes. Proc. Amer. Soc. Civil Engineers, Vol. 85, No. EM4, Octo-b e r , 1 9 5 9 .

7. Clough, R. W. Dynomic Effects of Eorth-quokes, Trons. Amer. Soc. Civil Engi-neers, Vof. 126, Pt ll, 1961,

8 . B l u m e , J . A . , N , M . N e w m o r k o n d [ . H. Corning. Design of Multistorey Reinforced Concrete Buildings for Earfhquoke Mo-fions, Portlond Cemenl Associotion, 1961, 9. Timoshenko, S. Vibrqrion Problems in

Engineering. 2nd Ed. Von Nostrqnd. 10. Clough, R. W. Eorthqucke Anolysis by

Response Spectrum Superposition. Bulletin Seismologicol Society of Americo, Vol. 52, No. 3, 1962.

ll, Penzien, J. Dynomic Response of Elosto-plcslic Fromes. Proc. Amer. Soc. Civil Engineers, Vol. 86, No. ST7, Jvly 196O. 12. Blvme, J. Structurol Dynomics in

Eorth-qucke Resistonl Design. Proc. Amer. Soc. Civif Engineers, Yol. 84, No. ST4, July I 958.

1 3 . V e l e f s o s , A . S . o n d N . M. Newmqrk, Effects of lnelosfic Behqviour on the Response of Simple Systems to Eorth-quoke Motions. 2nd World Conference on Eorthquoke Engineering, Vol. ll, Tokyo, 1960.

14. Uniform Building Code, issued by the Inlernqiionol Conference of Building Officiqls.

15. Stondqrds of Aseismic Civil Engineering Constructions in Jopon. Building Sfcnd-ord Low Enforcemenl Order, Ministry of C o n s t r u c t i o n , N o t i f i c o t i o n N o . 1 O 7 4 . 1 6 . T i t o r u , E . o n d A . Cismigiu. On rhe Rumonion Generql Design Specificcrions for Civil ond Industriot Buildings in Seismic Areos. Proceedings of the Sec-ond World Conference on Eorlhquoke

E n g i n e e r i n g , J o p o n I 9 6 0 , V o l . l l t , p . 2177-2192.

17, Stqndqrds ond Regulotions for Building in Seismic Regions (SN-8-52). The Build-ing ond Archifecturol Acodemy of the U.S.S.R. ond ihe Seismology Council of lhe Acodemy of Sciences. In lronslofioris in Eorthquoke Engineering, Eorthquoke Engineering Reseorch Instifute, 1950, p. 77-I45. Son Froncisco, Cqlifornio. 18. Climof ic lnformotion for Buitding

De-s i g n i n C a n c d q . 1 9 5 1 . S u p p l e m e n t N o . I fo the Nqiionol Building Code of Ccnodo, Nofionol Reseorch Council, As-sociole Committee on the Notionol-Building Code, Otiowo, Cqnodo. NRC 6453.

19. Dovenport, A. G. Wind Loods on Struc-lures. Noiionol Reseqrch Council, Divi-sion of Building Reseorch, Ottowo, Mqrch 1960. NRC 5576. _E-tT

0

t 0 0 2 0 0

V

7

EARTHQUAKE

AND WIND TOADS

IN BUITDING DESIGN

5. Cherry, M.r.t.c.

Deporlmenl of Civil Engineering

University of British Columbiq

H . 5 . W q r d

Building ond Physics

Section

Division of Building Reseqrch

Nqfionql Reseorch

Council, Ottqwq

W. A. Dolgliesh, r.M.r.t.c.

Building Slruclures Section

Division of Building Reseqrch

Nqtionql Reseorch Council, Ottqwo

T h e E n g i n e e r i n g J o u r n o l , S e p t e m

-ber, 1963, page 27

Discussion

by R. E. Dovid

Messrs. Cherry, Ward and Dalgliesh have presented a very interesting contribution to the new science of earthquake engineering, which is still in its infancy because of the extreme complexity of sudden seismic vibra-tions which seem to emanate from all directions. Up to last year, too few strong rnotion seismographs existed. Therefore, scientists and engineers lacked very im-portant data concerning the amplitude of the vibratioirs to which a structure had been subjected.

The authors are, unfortunately, right in reminding the structural engineer of the over-present danger. Hundreds of millions of dollars have been spent for all types of structures designed without the neces-sary precautions against earthquakes in the seismic zones of Canada.

The authors have provided a useful guide to the structural engineer who is at a loss, most of the time, when trying to select the right formula for evaluating earthquake loads. Single-storey structures are studied; so are multi-storey structures, which are mo(e susceptible to the yibratory effects. It would have been of interest if the authors had elaborated on the differ-ence of behaviour between 80 ft. and 300 ft. buildings.

Because the formulas given in this paper include a damping co-efficient, it is felt that it should be explained in detail. Damp-ing results frorn a number of causes such as: friction between the foundations and supporting soil, friction between building components. A more detailed study of this subject would have provided precious in-formation to the designer.

Discussion

It should be noted that the formulas specified in different codes deal only with the horizontal component of the seismic wave and not the vertical component. The horizontal component tends to overturn the building and, consequently, increases the vertical load on the columns. Never-theless, vertical components. of the wave are very seldom considered due to the fact that buildings are always well proportioned to resist vertical loads. Facts have nroved that vertical stresses are often greater than expected,

The earthquake which occurred in Aca-pulco in 1957 did very little damage. But the second earthquake of the equivalent magnitude which occurred in May, 1962, produced intense vertical vibrations with resulting serious damage.

The authors have also mentioned briefly that there is a definite relationship between the soil conditions and the extent of the damages. This fact has been emphasized recently following close studies of disaster areas. Therefo(e, structural engineers are advised to investigate the soil conditions in seismic zones. The study of soil con-ditions has given birth to a new science, "soil rnechanics applied to earthquake re-gions", which differs from "soil mechanics based on static tests."

Although we can assume that earthquake damage to certain materials is cumulative, it has been found that column failures were mainly responsible for the damages. For this reason dynamic formulas are much more realistic than the static formulas provided by the different building codes. The static formulas might be misleading because the designer might forget that he is facing a dynamic problem.

The study and comparison of the differ-ent codes and the derived examples, as pre-sented by the authors, are very inforn ative. They show the discrepancy between the different concepts which lead to the de-termination of the formulas.

Aulhors' reply:

The authors are grateful for the pertinent discussi6n of Monsieur R. E. David.

He is correct in pointing out that one of the major difficulties of an engineer faced with the design of a structure to withstand an earthquake is the lack of data regarding the amplitudes and periods of vibration to which typical structures can be subjected. This is mainly because relatively few strong-motion seismographs have been placed in

--rrF

structures that are within known earthquake zones, The United States of America in 1932, and Japan in 1951 inaugurated strong-motion seismograph programs: a similar

pro-gram is being initiated in Canada this year. The design engineers and owners of impor-tant structures within the earthquake zones of Canada could actively assist this program by installing strong-motion seismographs in their buildings.

At the present time there is very little information available concerning the damp-ing forces introduced durdamp-ing the vibration of buildings. In theoretical calculations vis-cous damping is usually assumed, but this is probably an oversimplification. Other damping mechanisms have been investi-gated,l but this information generally applies to small structural elements rather than large structures.

Observation has shown that soil condi-tions are an important factor in earthquake design. A certain amount of fundamental work has been published2,s'4 on the vibra-tion of foundavibra-tions, but again the engineer is confronted with a lack of quantitative information regarding the behaviour of actual foundations.

These three factors are the major im-ponderables in earthquake engineering. Some building codes do attempt to allow for them in utilizing the scanty information now available. but these details will almost cer-tainly be revised folowing further engineer-ing sttrdies of earthquakes. In the

mean-time the existing provisions of the National Building Code of Canada provide a good first-order measure of protection.

REFERENCES

l . S t r u c t u r a l D o m p i n g . A Colloquium on Structurol Domping Held ot the ASME A n n u o l M e e t i n g i n A i l o n t i c C i f y , N . J . , Dec. 1959.

2. Arnold, R. N., G. N. Bycrofi ond G. B. Worburton. Forced Vibrdfions of o Body on qn Infinite Elqsric Solid. Journol of Applied Mechonics, Sepi. 1955, p. 39I-100.

3. Richort, F. E. Foundoiion Vibrciions. Trons. ASCE 127 Pt. 1, 1962, p. 863-925. 4. Eostwood, W. The Foctors which Affect

fhe Nqturol Frequency of Foundolions, qnd the Effect of Vibrotions on the Beoring Power qnd Settlenent of Foun-d q i i o n s o n S o n Foun-d . T h e S l r u c t u r o l E n g i n e e r , V o l . 3 l ( 3 ) , p . 8 2 - 9 8 , M o r c h 1 9 5 3 .

A l i s t o f o l l p u b l i c o t i o n s o f i h e D i v i s i o n o f B u i l d i n g R e s e o r c h i s o v o i l o b l e o n d m o y

b e o b t o i n e d f r o m t h e P u b l i c o t i o n s S e c t i o n , D i v i s i o n o f B u i l d i n g R e s e o r c h , N o t i o n o l R e s e o r c h

C o u n c i l , O t t o w o , C o n o d o .

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