TI-CHNIC~L
I N S T R U C T I O N N O - 1 QF 1 9 - S r 2
0.Zntroduc t i o n
Load
w o r k is not new
but
suitably
walls/brickwork is of
comparatively r e c e n t
origin.
The
f i r s t I n d i a n S t a n d a r d Code w a s i s s u e d in 1961
and subsequently r e v i s e d i n 1969-and I S E ) O , : I S 1905 of 1980- ' C o d e o f P r a c t i c e
f o r structural s a f e t y o f b u i l d i n g s Masonry walls'. I n t h e p a s t
twenty
years
there has
been emergence o f
modern
structural
masonry
for
multistareyed c o n s t r u c t i o n in many c o u n t r i e s . T h e development has been
based on application a f s t r u c t u r a l engineering p r i n c i p l e s t o design o f
masonry s t r u c t u r e s , thus overcoming the limitations a f ' R u l e of thumb'
0.1
designed
b e a r i n g masonry walls/brick
load
bearing
procedures.
Basic advantage o f masonry c o n s t r u c t i o n lies i n the f a c t t h a t in
load bearing c o n s t r u c t i o n masonry p e r f o r m s a v a r i e t y o f f u n c t i o n s v i r ;
supparting loads, s u b - d i v i d i n g s p a c e , providing thermal and accoustic
insulation, fire a n d w e a t h e r p r o t e c t i o n e t c . ,
which
In
framed
b u i l d i n g s h a v e t o be p r o v i d e d f a r s e p a r a t e l y .
0.2
0.3
In
Western
c o u n t r i e s 12 t o 20
s t o r e y e d well designed
load
bearing
masonry buildings have been c o n s t r u c t e d h a v i n g o n l y 20 t o
40
cm
thick
walls.
In I n d i a quality o f b r i c k s m a n u f a c t u r e d
are
c o m p a r a t i v e l y poor 2nd m a x i m u m c r u s h i n g strength g e n e r a l l y is o f o r d e r
of
70 to 150 kg/crn
In many Western c o u n t r i e s b i c k s o f e v e n medium
q u a l i t y have c r u s h i n g s t r e n g t h 400 to 600 k q / c m
fi
few
mechanisrd
brick
p l a n t s have s i n c e bsen set u p at f e w p l a c e r in our c o u n t r y
and
b r i c k s o f 150 t o 250 k g / c m
s t r e n g t h are b e i n g m a n u f a c t u r e d . I t should
naw
be possible in some p a r t s o f India to g o i n for 5 to 6
storeyed
load
bearing structures at c o s t s 15 to 20% less than RCC +ramed
construction.
.
1.
5.
S t r u c t u r a l Considerations
1.1
The
structural adequacy o f masonry walls depends upon a
o f f a t t o r s as u n d e r :-
masonry u n i t b r i c k s o r b l o c k s
(a)
S t r e n g t h of
(b)
S t r e n g t h o f mortar
c
W o r k m a n s h i p and method of bonding
(dl
Location of
(e>
Position and size of openings i n the walls
f
U n s u p p o r t e d h e i g h t and l e n g t h o f
(g)
Eccentricity i n t h e loading
(
C o m b i n a t i o n o+ various loads ta which walls a r e subjected
1
number
longitudinal and c r o s s walls,
walls and s l e n d e r n e s s r a t i o
2.
Hasrmry Units
2.1
These a r e generally o f the following t y p e s :
(a)
Common b u r n t clay bricks-Specifications a r e laid down i n I S 1077
o f 1976- 'Specifications f o r common b u r n t clay b u i l d i n g b r i c k s ' { t h i r d
revision).
B r i c k s a r e classified as class 3 5 , 5 0 , 7 5 , 1 0 0 , 1 2 5 , 1 5 0 , 1 7 5 ,
200,250,300
and
350
a c c o r d i n g ta average c o m p r e s s i v e s t r e n g t h
in
.
2
kg/cm
These
are
f u r t h e r subclassified as o f sub-class A
or
rubc iass B. Brick of s u b - c l a s s A h a v e s m o o t h rectangular f a c e s w i t h sharp
edges a n d corners and u n i f o r m i t y o f colour, B r i c k s 0 5 sub-class B h a v e
s l i g h t distortion.
(b)
t i n re&gular s i z e s u n i t s > - D e t a i l e d
IS 1597 o + 1967 Part I t 1 1 - ' C o d e o f
Stoncs
given
in
true tion o f
s t o n e masonry'
.
specifications a r e
for cons-
Practice
I S 4 1 3 9 of 1976- 'Sperifi c a t i n n s f o r sand 1 i m e
a s class 7S,100,L50, and 200 a c c o r d i n g
to
their
a v e r a g e compressiv& s t r e n g t h as f o r common b u r n t c l a y bricks.
Sand l i m e b r i c k s -
( c )
brick'
classified
M i n i m m average compressive s t r e n g t h s p e c i . f i e d
2185 o f 1967- 'Speci+ications f o r hollow c e m e n t
c o n c r e t e b l o c k ' . The IS Code i s however, under r e v i s i o n and t h e blocks
are
being
p r o p o s e d to be d i v i d e d i n t o v a r i o u s g r a d e s
depending
on
their
compressive
s t r e n g t h v a r y i n g f r o m 20 to 70 k g / c m Z
for
Hol low
C a n c r e t e Blocks.
(d)
blocks5 te
as per IS
Corrcr
is 5 0 kg/cm
te)
P r e c a s t stun? masonry block-Specifications a r e l a i d down i n CBRI
Data S h e e t No. B o f b u i l d i n g t e c h n i q u e series Sep 1977 and CBRI
infarmatian Note 1 o f Sep 1978. S t o n e m a s o n r y b l o c k s o f
30~20x15 cm
nominal s i z e using spalls o f 12 crn size and lean cement c o n c r e t e m i x
of
1:5:8 a r e m a d e
The block should be compacted d u r i n g casting by
using p l a t e v i b r a t o r . T h e nominal length and h e i g h t o f the b l o *
is
kept
30 rrn a n d 15 c m respectively b u t t h e b r e a d t h m a y b e 20 c m , 15cm
or
10 cm a c c o r d i n g to thickness o f wall. T h e 29 d a y s compressive
s t r e n g t h o f blocks w i t h the above m i x is 70 kg/cm
T h e concrete
mix
proportion
is to b e
suitably a d j u s t e d w i t h locally
available
materials
t~ m e e t t h e required s t r e n g t h .
This
masonry
black
construction
is economical inwareas where s t o n e s a r e available in
abundance
and at economical c o s t . M e t h o d o f p r o d u c t i o n of b l o c k s
and
special p r e c a u t i o n s t o be t a k e n and details o f masonry c o n s t r u c t i o n
a r e given in the aforesaid data sheet n o . B and information n o t e
No, 1
i s s u e d b y C e n t r a 1 Bui l d i n q Research I n s t i t u t s , Roorkee.
.
.
3.1
Requirements o f qand mortar f a r masonry a r e s t r e n g t h ,
worka b i l i t y , w a t e r r e t e n t i v i t y and low d r y i n g shrinkage. M o r t a r s could
be
broadly
classified a s cement mortars, lime m o r t a r s and cement-lime
mortars. Main characteristics a r e a s under:
(a)
Cement
mortarsThese consist: o f c e m e r i t a n d
sand v a r y i n g I n
proportions
-From 1 : b t o 1:3. M o r t a r s l e a n e r than 1 ; 6 tend
to become
harsh and
u n w o r k a b l e and a r e prone to s e g g r e g a t i o n .
R i c h mortars
though
having
gaod strength h a v e h i g h s h r i n k a g e and thus
liable to
cracking.
L i m e m o r t a r s - These c o n s i s t o f lime, sand and b u r n t c l a y / s u r k h i
proportion 1:2:3. The m a i n a d v a n t a g e o f limc m o r t a r
lies i n
their
qood w o r k a b i l i t y , low s h r i n k a g e and b e t t e r
resistance against
rain penetration. Hawever s t r e n g t h is much less than t h a t o f
cement
{ b)
in
the
mortar.
(c)
well
qood
C a m e n t : L i m e m o r t a r s - These h a v e gaod qualities o f b o t h c e m e n t as
as lirnk mortars i.e. qood s t r e n g t h alongwith good workability,
.water
retentivity,
Sreedom f r o m
cracks
and
good
a g a i n s t r a i n penetration. C o m m o n l y a d o p t e d m i x e s a r e 1:1;6,
1 : 3 : 12.
3.2
'Code
resistance
1:2:9
and
1965
Detail6 o f mortars f o r masonry a r e contained in IS 2250 o f
0 4 Practice f o r p r e p a r a t i o n and use o f masonry m o r t a r s ' and
IS
162s o f
mortars'.
lime
1971- ' C o d e Of ~ r s c t i r af o r p r e p a r a t i o n and use o f
Strength o f v a r i w o mortars are g i v e n in T a b l e 1 below:
TfiBLE 1
- COMPRESSIVE
STRENGTH OF MASONRY HORTRRS
. ..:.r
Mix
M i x compressive
&trength i n k g / c m2
(28 days)
( Cemen t
Surkhi/Putzolona
Limr
Sand !
-
to 15
to 20
to 30
ta 30
to 50
to 5 0
,,
,,
,,
,,
,,
,,
and above
and above
3-3
Mortar
masonry u n i t .
s t r e n g t h shall in general be n o t g r e a t e r
than
that
of
1
s
a g e n e r a l r u l e , a p a r t from strength o f masonry units and
grade PC m o r t a r , s t r e n g t h o f masonry depends on t h e uniformity o f s i z e
and shape o f u n i t s . U n i t s w h i c h a r e t r u e i n shape and s i z e can be l a i d
with r a r n p a r a t i v ~ l ~thinner j o i n t s ,
thereby
resulting i n
higher
s t r e n g t h . For t h i s reason, use o f ' f i ' grade b r i c k s g i v e s masonry of
h i g h e r s t r e n g t h a s camparcd to that w i t h B grade b r i c k s even though
c r u s h i n g s t r e n g t h af B g r a d e b r i c k s may be same as thase o f A grade.
F o r similar reasons a s h l a r stone masonry w h i c h uses accurately d r e s s e d
and shaped s t o n e b l o c k s is much stranger (nearly d o u b l e ) t h a n
coursed
s t o n e m a s n p r y . Increase in thickness a/ bod j o i n t s from 1Omm ta l b m m
r e d u c e s t r e n g t h bf masonry by approximately 25%. For brick masonry
work
p r o v i s i o n s a# I S 2212 04 19&2 ' C ~ d cof P r a c t i c e f o r brick
work'
are to be
fallowed. Details of band, b e d d i n g and j o i n t i n g a r e l a i d
down in this code. Poor warkmanship may seriously i m p a i r
the strength
oi
brick
work
and
intraduce weakness w h i c h may
permit
moisture
penetration and o t h e r d e f e c t s . The main d e f e c t s i n workmianship w h i c h
impair the strength of masonry a r e as under :4.1
(a) Use
of
dry
b r i c k s n o t p r o p e r l y s o a k e d i n water
( b l Bed joints o f r+nccssive thickness
( c J Failure to f i l l
bed j o i n t s
( d l Deviation from vertical Plane o r a l i g n m e n t i - e . o u t o f
plumb
masonry
(el Unfavourable
c u r i n g conditions
Tolerances permissible in t h e masonry arc given in table 2 belawt
TABLE 2-MAXIMUM
PERHISSSBLE TOLERANCES I N MASONRY
I tern
S.No.
Tolerance
1.
Deviatioq f r o m the position shown on
plan o f any b r i c k w o r k more than o n e
etnrey i n h e i g h t
2.
Deviation from vertical w i t h i n a storey
b mm per 3 m h e i g h t
3.
Deviation f r o m vertical i n t h e total
12.5 m m
height of building
I
4.
Relative displacement between load
bearing w b l 1s in adjacent storeys
intended to be in v e r t i c a l alignment
5,
Deviation f r o m line in plan
{ a ) i n any l e n g t h u p t o 1 2 m
I b ) i n any l e n g t h o v e r 1 2 m
6
Deviation o f bed j o i n t f r o m horizontal :
la) i n any length u p t o 12 m
I b ) i n any length aver 12 m
7.
T h i c k n e s s o f bed joints, c r a s s j o i n t s
o r p e r p e n d i c u l a r joints.
6 mm
12.3 mm total
g m m an t h i c k n e s s
specified
These
tolerances have been specified f r o m p o i n t o f view o f
effect
on t h e s t r e n g t h o f masonry.
The
permissible
stresses
recommended in t h i s Technica 1 I n s t r u r tion may be c o n s i d e r e d a p p l i c a b le
o n l y i f the tolerance g i v e n i n tabla 2 a r e c o m p l i e d w i t h .
Note:their
5.
Location a+ Longitudinal and Cross Walls
5.1
A building
is basically s u b j e c t e d to two types of loads, viz:
( a ) V e r t i c a l loads on a c c o u n t o f dead loads o f materials used in
canetruction, plus live loads due to occupancy; and
( b ) lateral
loads d u e to wind and seismic
farces.
While a l l
w a l l s i n general can t a k e vertical loads, a b i l i t y o f a w a l l
to t a k e
l a t e r a l loads depends on i t s d i s p o s i t i o n in relation to t h e direction
o+ lateral load. T h i s could be best explained with help a+ an
illustration, see f i g 1 .
In f i g . 1 , the wall A has v e r y good r e s i s t a n c e against a lateral
load, w h i l e wall 8 , offers little r e s i s t a n c e to laad a c t i n g i n
the
longitudinal direction o f t h e wall. T h e de+arrnatians in t h e t w o cases
a r e shown by dotted lines. T h e lateral loads a c t i n g on the f a c a d e o f a
building a r e transmitted t h r o u g h floors { w h i c h act as h o r i z o n t a l
beams)
to
cross walls, w h i c h act as s h e a r w a l l s . From c r b s s w a l l s ,
loads a r e transmitted to t h e foundation. T h i s action is illustrated in
Fig. 2 & 3.
5.2
As a
result a + lateral load, t h e r e w i l l
be
an i n c r e a s e o f
compressive s t r e s s on the leeward s i d e , and d e c r e a s e o f
compressive
s t r e s s on
t h e wind-ward aide. T h e c r o s s wall is
designed
for
zero
t e n s i o n , and p e r m i s s i b l e c o m p r e s s i v e s t r e s s . I t will b e o f i n t e r e s t to
n o t e t h a t a wall w h i c h is c a r r y i n g g r e a t e r v e r t i c a l l o a d , will b e in a
better
position
to
resist lateral load than one w h i c h is lightly
5.3
l o a d e d in the v e r t i c a l d i r e c t i o n . T h i s f e a t u r e should be k e p t j ; :
w h i l e p l a n n i n g the structure so as to obtain an ecanomical desA::c
-,~ew
5.4
A
structure
should have adequate stability along
buth
the
p r i n c i p a l a x e s . T h e 50 cal led ' c r o s s wall,' construction would ria,,: ;:ave
much
lateral resistance in the longitudinal direction,
Zn I
?
of
h i g h - r i s ~ buildings, i t - - i - s
desirable to adopt 'cellular' or ' 1 0 h :,:.pe'
c o n s t r u c t i o n as illustrated in F i g . 4 .
t.
Openinqs i n
Walls
6.1
Size, shape and l o c a t i a n o f o p e n i n g s i n t h e e x t e r n a l htrl ;- . . . , A v P
considerable influence on stability and m a g n i t u d e of s t r e s s e s d:.,.-~ to
lateral laads. T h i s ,has b e e n illustrated i n Fig.5.
I f t h e o p e n i n g in l o n g i t u d i n a l w a l l s a r e so located and par t i ms
of
these
walls a c t as flanges ta c r o s s walls, t h e s t r e n g t h o i
:.he
c r o s s walls g e t considerably i n c r e a s e d a n d s t r u c t u r e becomes much ~ n ; - r e
s t a b l e , as will b e seen from Fig. 6 .
6.2
6.3
I n a load b e a r i n g wall the l e n g t h o f o p e n i n g s should be m i r - ! . . r , v ~ m
possible to allow m o r e wall length to c a r r y t h e laads. The m a r e
l lie
openings,
t h e less will be t h e e f f e c t i v e wall area and t h e more i . l r i l P
be
the i n d u c e d - s t r e s s . A e a g e n e r a l rule the length o f o p e n i n g s 11-1 a
load bearing wall should not exceed SOX of t h e total length o f wa;i
7.
Slenderness R a t i o
( a ) Walls- ~ l s n d e r n e a sratio far a; wall shall b e t h e e f f e l z t i g e
height d i v i d e d b y the ef+ertive t h i c k n e s s or e f f e c t i v e l e n g t h d l d l n : ! e d
by the effective t h i c k n e s s , whichever is less.
Ib)
effective
(thickness
values is
direction.
Column-
Slenderness r a t i o o r a column shall be t h e
divided
by
t h e corresponding
lateral
dimension
or
w i d t h ) , For the purpose o f design, higher o f
the t w o
taken into account since the column c a n b u c k l e in any
heipht
tc)
M a x i m u m slenderness raticr- For walls built i n cement m o r t a r
& c e m e n t lime m o r t a r , it shall not e x c e e d 27. When l i m e mortar is used
limits of
slenderness r a t i o shall be 13 and 20 f o r dewellings
exceeding t w o s t o r e y e and n o t exceeding t w o s t o r e y s r e s p e c t i v e l y .
For
non-laad bearing walls like panel walls, c u r t a i n walls and p a r a p e t
wallsl slenderness ratio shall n o t exceed 30. P a r a p e t w a l l s shall
however
be d e s i g n e d t o be s t r o n g enough to w i t h s t a n d
lateral
forces
and ather loads. For c o l u m n s slenderness r a t i o shall n o t e x c ~ e d12.
T h e effective h e i g h t a f a wall or column shall b e
the actual
multiplied
by
an a p p r o p r i a t e f a c t o r depending upon
end
c o n d i t i o n s a s g i v e n in t a b l e 3 ( F i g 7 ) . Similarly a f f e c t i v e length of
a wall shall be actual length multiplied by a p p r o p r i a t e f a c t o r as per
table 4. Please r e f e r Fig 7 & 8
:
.
Note:height
TABLE 3
Fig 7
EFFECTIVE HEIGHT
S . No.
C o n d i t i o n o f support
Wall e f f e c t i v e
height
1.
adequate
lateral s u p p a r t and partial rotational
restraint
at t a p and bottom-where t h e floor
o r
roof)
0.75 H
. ; -: +,~ c i o n o f span at r i g h t a n q l g ? to t h e wall,
50
tha .
.?e r e a c t i o n to t h e load o f the :f l.QQv o r
roof
is
pro6 ::?:-d by t h e walls
o r w h e r e the c o " = r b t e f l o o r 5 have
a b s . j r i n q on walls, irrespective of
the' direction o f
.,*
hls.:
sp;.-,:
.
2.
Adequate
lateral s u p p o r t and partial
rotational
r e s ~ . - z l n tat e i t h e r t o p or bottom, and lateral r e s t r a i n t
a'k r ; - h ~ end.
r
Fully b r a c e d construction w h i c h is itself
ade;tlately supported and i n c o r p o r a t e s ( a ) t i m b e r floors
imn,~,llately
below o r above a r e i n f o r c e d c o n c r e t e
floor,
(b!
rauf
trusses above a r e i n f o r c e d c o n c r e t e f l o o r
or
the ~ l k e .
Adequate lateral s u p p o r t at t o p
and
bottom-where
t h e floors (or r o o f s )
have a direction o f span parallel
with
the wall, t o p and bottom, a n d do n o t bear an it:
o r f u l ly b r a c e d c o n s t r u c t i o n w h i c h i s itself
adequately
supported and which i n c o r p o r a t e s r o o f t r u s s e r and t i m b e r
upper s t o r e y floors.
3.
4.
Adequate
lateral s u p p o r t and partial
ratatibnal
restraint a t - b o t t o m and no lateral support or rotational
r e s t r a i n t at the t o p w h e r e the wall has no lateral
s u p p o r t at ,top (construction not fully a n c h o r e d or not
fully braced).
5.
Free standing non-lnad
b e a r i n q members.
TABLE 4
t
Fig
E F F E C T I V E LENDTH OF THE WALLS
S.Na.
Conditions
of
B
E f f e c t i v e Length
Suppart
1.
Where a wall is continuous and supported by
cross
walls o f b u t t r e s s e s and there is na opening w i t h i n oneeiqht o+ the wall h e i g h t , h or H ( w h i c h e v e r is less)
f r o m t h e face o f supporting walls, o r pier or b u t t r e s s .
0.8 L
2.
Where a
wall is s u p p o r t e d b y a buttress o r c r a s s
wall at one end continuous w i t h buttress of c r o s s wall
supparts at other e n d .
1.0 L
3.
Where
a wall is supported to
buttress a r a c r o s s wall.
each
end
4.
Where the wall is f r e e at one end supported
other end by a b u t t r e s s o r c r o s s wall.
by
a
at t h e
Where
L = the l e n g t h o f wall
cross walls,
H = the
of
f r o m or between c e n t r e s of
p i e r s o r buttresses.
actual
height of wall between c e n t r e s
lateral supports, and
,
h = the rfSective h e i g h t o f
adequate
the wall.
\
8.
E c c e n t r i c Loads
8.1
Eccentric loading a f f e c t s the uniformity o f s t r e s s distribution
in t h e wall, and s t r e s s on one side became5 more than t h a t on t h e
othrr
side, When eccentricity r a t i o reaches 1/6 ( f a r n rectangular
section) s t r e s s an one side b e c o m e s z e r o and on t h e a t h e r s i d e
compressive stress becomes twice the average v a l u e i . e .
the stress
distribution block is a triangle.
If eccentricity ratio e x c e e d s 1 / 6 *
tension i s developed i n one s i d e .
S i n c e masonry is h o t e x p e c t e d to
take any tension a p a r t o f thickness o f masonry m e m b e r becomes
ineffective.
For econamical
design, t h e r e f o r e ,
ecrentritity
OC
loading shouli be the least possible if n o t completely avoided.
Allowable compressive s t r e s s in t h e
eccentric Inads.
9.
masonry
also
reduced
with
Design Considerations
Ganara l -Load b e a r i n g w a l Is a r e s t r u c t u r a 1 1y more e f f ic ian t
when
load is uniformly d i s t r i b u t e d and when the eccentricity of loading
on t h e wall
is as small a s pnssible, k r ensuring u n i f o r m i t y o f
loading, openings in walls should not be t o o
large,
bearings f o r
lintels and bed b l o c k s u n d e r beams should b e liberal in s i z e ,
heavy
concentration o f
loads should be a v o i d C d .
One o+ t h e cbmnonly
o c c u r i n q causes o f c r a c k s in masonry is w i d e variation i n s t r e s s
in
masonry
i n adjoining parts.
Eccentricity o f loading on walls should
be reduced by providing f u l l b e a r i n g o f f l o o r s t r o o f an the walls.
9.1
the
9.2
Design Procedure
7 . 2 . 1 The building a s a w h o l e shall be analysed by a c c e p t e d principles
of
mechanics.
A l l component p a r t s of t h e s t r u c t u r e shall be c a p a b l e
of
sustaining
the most
a d v e r s e combinaticrns o f
l o a d s which t h e
building may be reasonably e x p e c t e d to be s u b j e c t e d to d u r i n g o r a f t e r
erection.
During construction
the e f f e c t s o f w i n d , back filling
b e h i n d walls, o r o t h e r e r e c t i o n conditions shall be so controlled that
no adverse o r unsafe conditions occur In t h e m a s o n r y .
9.3
Thickness o S Wall
9 . 3 . 1 The t h i c k n k s o+ a load b e a r i n g wall shall be sufficient at a l l
p o i n t s to ensure t h a t t h e stresses due to w o r s t conditions of
loading
are within
the l i m i t s p r e s c r i b e d f o r t h a t particular t y p e
wall.
The
thickness used #or design calculatians shall be t h e actual
thickness
o+ the m a s o n r y , n o t t h e nominal t h i c k n e s s . See F i g . 9 .
In
masonry w i t h r a k c d j o i n t s , t h e t h i c k n e s s s h a 1 l " b e r e d u c e d by t h e d e p t h
of the r a k i n g o u t . See F i g . 10.
7 . 3 . 2 However,
if
jaints
a r e r a k e d to
p r o v i d e k e y f o r subsequent
plastering,
r a k i n g could be i g n a r e d .
I f any +ace o f a wall is to be
p o i n t e d , it is d e s i r a b ' h to d o raking and p o i n t i n g while the m a r t a r is
green
to avoid a n y loss of s t r e n g t h d u e to r a k i n g .
For
solid walls
adequately bonded i n t o piers o r b u t t r e s s e s at intervals, the effective
t h i - c k n e s s shall be the actual thickness o f solid wall
multiplied
by
t h e a p p r o p r i a t e stiffening coefqicicnt g i v e n i n t a b l e 5 g i v e n
below.
For
c a v i t y walIs t h e effective thickness shall b e t w o - t h i r d s
of
the
s u m o f the a c t u a l t h i c k n e s s o f t h e t w o leaves.
STIFFENING
COEFFlCIENT
TABLE 5
FOR WALLS STIFFENED
BY
PIERS
BUTTRESSES/QR
I N T E R S E C T I N G WALLS
STIFFENING COEFFICIENT
Ratio,
sp/wp
tp/tw
= 1
tp/tw
= 2
tp/tw
= 3 o r more
-
b
8
1 .O
10
15
20 o r m a r e
where
sp =
tp =
t w =
wp =
2.0
1.7
1 .O
1.4
1.3
1.2
1.0
1.d
1.1
1 .O
1.2
1.0
1.4
1.0
c e n t r e to r e n t r e s p a c i n g o f t h e p i e r or intersecting wall
the thickness o f p i e r
actual t h i c k n e s s o f wall p r o p e r ; and
w i d t h o f t h e p i e r in the d i r e c t i o n o f the wall
or
t h e actual
thickness o f t h e intersecting wall.
Note:-Linear
interpolation between t h e values g i v e n in this table
permissible b u t not extrapolation outside t h e l i m i t given.
is
In case o f veneered walls, v e n e e r shall n o t b e considered to
part o f t h e wall when computing the s t r e n g t h o r r e q u i r e d thickness
t h e wall.
be
of
Permissible Compressive Stress
10.
10.1
T h e permissible compressive stress in m a s o n r y depends
following f a c t o r s :
(a>
(b)
Ic)
Id)
(el
(f)
upon
the
S t r e n g t h o f masonry u n i t s
Mix of mortar
Slenderness ratio o f m a s o n r y element
E c c e n t r i c i t y o f loading
Cross-section a r e a of masonry
Shape and size o f t h e masonry u n i t
E f f e c t o f these f a c t o r s is explained in s u b - p a r a s
10.2 a n d
10.4
below.
-
b
~ e r r n i s s i 6 l es t r e s s shall b e related to b a s i c s t k e s s as g i v e n
in
table 6
d e p e n d i n g upon t h e c r u s h i n g s t r e n g t h o f masonry unit and
mix
10.2
o f m o r t a r used.
10.3 For s l e n d e r n e s s r a t i o a r e d u c t i o n oS f a c t o r g i v e n
in t a b l e 7
below is to be applied.
S i m i l a r l y , far w a l l s o r column s u b j e c t e d to
eccentric
loads o r vertical loads plus lateral
loads, a r e d u c t i o n
factor
is to be a p p l i e d given i n the Table 7 b e l o w . F a r e c c e n t r i c
loads p l e a s e r e f e r f i g 12.
1 0 . 4 .Where
there
a r e a d d i t i o n a l s t r e s s e s d u e ta e c c e n t r i c i t y
of
loading and lateral f o r c e s , t h e m a x i m u m resultant stress may exceed
t h e a l l o w a b l e s t r e s s by n o t more than 25% provided that such e x c e s s is
s o l e l y d u e t o eccentricity o f loading.
Case 1-- f i x i a l load o n l y
Permissible s t r e s s = a p p r o p r i a t e b a s i c s t r e s s f r o m t a b l e 6 m u l t l p l l e d
(axial 1
by
appropriate
stress f a c t o r
for s l e n d e r n ~ s
ratio w i t h z e r o eccentricity f r o m t a b l e 7 .
TABLE b
B f i S I C COMPRESSIVE STRESSES FOR MASONRY MEMBERS ( A T AND AFTER THE STATED TIMES)
.
C
.Nn.Descriptim
of =tar
Maxinun (Parts by Volume)
e to
Harrlming
Basic
Stress in
kg /cm2
correspondin
s t m g t h of
time after u n i t s whose c r u s h i n g s t r e n g t h in k g / c m
1s
m
t L i n ~Lime Pozzo- Pozzolana Sand mrtar at
cmpletim
c
28 days kg/cmZ of wgrk
land M i x t u r e (see note 3 )
(see note 3 )
note 4)
(see note 5 )
Days
E 70 10S 1 4 0 i 5 210 280 2EQ 440
tanpressive
,
Cement
1
Cement
brmt lime
1
Cwrrent lime
Cwrrent
1
1
1
Lime pozzolana -
mixture
I
Hydraulic lime Lime pozzolana -Cwnent lime
3 Lime
-
The table is valid for slenderness ratio 6 and the loading w i t h zero eccentricity.
Linear interpolation is permissible for units wfrose crushing strengths are intermediate k b e m those g i v m in the table.
~te--3 Lime shall c m f o r m to IS:712-1964
'Spcifiraticn for building limes'. A,B and C denote the classes of limes as i n IS:712964. Pozzolana shall con-form to IS: 1334-19bEI 'Specificatim for burnt clay pozzolana ( F i r s t revision)' or 1S:JBlZ (Part 1)-19&
Specification for fly ash:Part I f o r use a5 pozzalana'.
D~E--4 For mortar in Serial No. & lime pazzalana m i x t u r e shall k of G r a d e I
F 40 conforming to IS :*I967
'Spetification f o r lime
~zzolanam i x t u r e '
~te-5 Mortar strmgth values are for information m l y and have been reprduced f run I S : m 1 9 & ' M e o+ practice for preparatim
1
~te--2
.
rd use of masjanry rrrortar'.
ute-& I t i s advisable to use plastic ire^ for cement mortars in order to improve proprties of t k mortar !ach as flow and w a t e r
e t e n t i v i t y . Plasticizers sharld be u d according to manufacturer's instructims.
o*-7
M a m r j c m t -tars
a m a l s advisable and shall be used according to manufacturer's instrurtims. The mix proprtims of
axlnry cmnmt:sand shall be w c h as to give cunparable mortars crushing s t r e n g t h w i t h the cement:sand mortar of the particular grade.
* ~ k s e periods shaJld be increased by the full amunt of any time during which tk air tRnperature remains below 4.5'
half t k amatnt of any time during which the temperature is be4.5' C and 10" C
The inclusion of lime in c e m n t martars is optional.
(47)
.
C
plus
Case I [ - -
E c c e n t r i c load
Permissible compressive stress(axia1 = appropriate b a s i c s t r e s s multiand
b e n d i n p compressian)
plied
by
stress
factor
for
s l e n d e r n e s s r a t i o and e c c r n t r i -
c i t y multiplied by 1.25
Mate:-ln n o case shall the s t r e s s d u e to a x i a l load alone e x c e e d
values given in t a b l e 6 & 7.
the
REDUCTION FACTORS FOR SLENDERNESS R A T I O AND ECCENTHICITY OF LOADING
REDUCTION FUCTOR
Slenderness
Ratio
Equivalent
0
Note:-1
0.04
eccentricity o f loadlng
thickness o f the member
0.1
0.2
0.3
divided
0.33
by
the
0.55
L i n e a r interpolation b e t w e e n values f o r the s t r e s s f a c t o r s
is
permissible.
Note:-2
of
For u n r e i n f a r c e d masonry,
interpolation nnl y .
10.5
t h e values in cal 8 a r e f o r purposes
A r e a Qedurtion F a c t o r
1025.1 Where cross,section a r e a of wall o r column does n o t e x c e e d 3000
the b a s i c s t r e s s shall be m u l t i p l i e d by a r e d u c t i o n f a c t o r equal
to (0.7S+A/l200) w h e r e R is a r e a (in sq c m ) o f t h e horizontal c r o s s section
of
the
wall o r column.
The area limit o f 3000 sq c m
15,
however,
Iikely to be r e v i s e d ta 1500 sq tin, k e e p i n g in view
the
provisions o f the B r i t i s h Code.
cm
10.6
fillonance for Shape Factor
units
of crushing s t r e n g t h n o t
greater
than
55
h e i g h t to t h i c k n e s s ( a 5 laid) g r e a t e r
than
0.75 b u t n o t g r e a t e r than 3 , t h e b a s i c s t r e s s m a y be m o d i f i e d b y
the
f a c t o r specified as under i n table 8 .
10.6.3
kqt'cm
For
masonry
and with a r a t i o o f
MODIFICATION FACTOR F O R SHWE O F MASONRY UNIT
h t to thickness
o f brick o r b l a c k
R a t i o of
Factor
,-lo.7
0.75
1.0
1.5
2.0 t o 3.0
1.0
3 m2
1.6
2.0
Member Subjer ted to Concentrated Loads
stresses
of
a
p u r e l y local
n a t u r e as
a t girder
column bases, lintels or ather concentrated loads shall
be
calculated and
t h e m a x i m u m s t r e s s resulting f r o m a combination
of
local
stresses
w i t h other s t r e s s e s s h a l l
not e n c e e d
the
.these
permissible s t r e s s by more than 50% when the loading is transmitted
through m a s o n r y .
T h a angle o f dispersion o f t h e
loading shall
be
t a k e n a 5 n o t m o r e than 45. f r o m t h e d i r e c t i o n o f s u c h loading.
Addition
10.7.1
bearings,
'
,
Please r e f e r to f i g 13.
It.
Tensile Stresses in Hasonry
11.1
I n general no reliance s h a u l d b e placed on t h e tensile s t r e n g t h
of b r i c k w o r k i n t h e raculatians.
The p a r t a+ t h e section i n tensions
will
be
assumed
to be i n a c t i v e a n d , t h e remainder will
carry
romprassive
stress o n l y .
In some t y p c s ' o f wall tensile s t r e s s e s i n
bending may be t a k e n i n t o a c c o u n t .
For mortar n o t w e a k e r than
1:1:6
cement:lime:sand
m i x o r i t s equivale t, the permissible tensile s t r e s s
in b e n d i n g s h o u l d n o t exceed I kg/cm
9.
12.
P e r m i s s i b l ~Shear Stress
12.1
In t h e case o f w a l l s b u i l t i n m o r t a r n o t weaker than 1:l:b
cement:lime:sand
m i x and resisting horizontal f o r c e s i n t h e p l a n e
of
t h e wall, t h e p e r r n i s ~ i b l eshear s t r e s s , calculated in t h e a5ea o f
the
h a r i z a n t a l m o r t a r bed j o i n t , shauld n o t e x c e e d a s 1 . 5 k q / c m
.
13,
Thermal Movements and O t h e r M o v e m e n t s a f M a s o n r y
13.1
Thermal
expansion
and
contraction
of
masonry
shall
be
accommodated
b y vertical control j o i n t s ,
These control j o i n t s
shall
also accommodated m o v e m e n t s d u e to d r y i n g shrinkage o f
masonry.
Vertical
contral joints shall b e located in all c o n t i n u o u s e x t e r n a l
and
internal load b e a r i n g as w e l l as non-load bearing masonry walls.
for p u r p o s e o f
general g u i d a n c e ,
it is recommended t h a t walls
exceeding
45 m i n l e n g t h shall be d i v i d e d by o n e o r more expansion
jo~ntc.
These
may
be provided at closer
spacing
when
there
are
apenings o r r e t u r n s . i n masonry.
Vertical c o n t r o l j o i n t s shall n o t be
less than
10 mm w i d e and shall
provide
a continuaus vertical
s e p a r a t i o n through t h e f u l l thickness o+ t h e m a s o n r y w ~ l lor leaf o f a
cavity wall
and
extending f r o m the t a p o f t h e wall to t h e t o p o f
concrete
foundations o r t h e t o p o f the grade beam o v e r piles where
provided.
. The rule $ o r s p a c i n g clf expansion/vertical c o n t r o l
joints
and
t h e i r w i d t h will generally depend m a i n l y on
local
experience
gained
fram
observation o f s t r u c turps earlier r o n 5 t r u c ted.
The
precise d e t e r m i n a t i o n oS t h e amount o f m o v e m e n t o c c u r i n g in b u i l d i n g
ta
ascertain
t h e s p a c i n g and w i d t h o f j o i n t s is v e r y
complicated
owing to numerous factors i n v o l v e d an.d m a y n o t be n e c e s s a r y i n normal
circumstances.
Genera 1-1y t h e ' sp,ating':#or expansion j a i n t s
shall
be
a c c o r d i n g to recommendations; ' g i v e n l i n + a b l e 9 b e l o w .
*.
(49)
HE COPlMENDAf f O N 5 F-'LJH SF'AC I NG DC
E XF'RNS 1 IIN
-
--
J (-1 I
N T tii
S . No.
(1)
1.
Walls
1
L-aad b e a r i n q w a l l s w l t t l c r o s s w a l l s
a1
intervals.
' I ' r a d i t i u n a l type of
one-brick
thick o r m o r e
SOm ~ n t e r v a l s
(2)
W a l l s o + warehouse t y p e c o r ~ s t r u c t l o n
E x p a n s i o n .jalnts
i n walls at 3 0 m
t w l thout c r o s 5 - . - w a l l s )
m a x i m u m intervals.
( I f the walls
are
p a n r l walls between
columns at n o t more
than
c? m c e n t r e s
no
j o i n t s are neces5ary)
Cnntrol
j o ~ r i t s over
centre
of
apenings
may b e g l v e n at
half
the
spacing
of
expansion joints.
il.
Chajjas,
i i i . Roofs
balconies and p a r a p e t s
bm to 1 2 m intervals
/ - ,
( 1 ) O r d i n a r y roof s l a b s o f RCC
protected
by
layers o f m u d
phuska
or
other insulating
m e d l a i n u n + r a m a d construc t inn
20 to 3 0 m
intervals,
and a t
changes
in
directinns
as
in
L.,T,I-i
and V
shaped
stlruc t u r e s
( 2 ) T h i n u n p r o t e c t e d slabs
iv,
Frames
Joint i n ~ t r u c t u r - ethr-ough ~ l a b z i , ~
Corners af L,tJ, T
columns, e t c dividlng the
building i n t o t w o independent
shaped s t r u c t u r e s and
at 3 0 m i n t e r v a l s i n
l o n g uniform
structures
beams,
structural units
and
Corresponding to j o i n t s i n the r o o f 5lahs
14.
Strengthening firrangements f a r Earthquake H e ~ i s t a n tDesign
14.1
A s e p a r a t e t e c h n i c a l i n s t r u c t i o n has been i s s u e d i n T I
of
1/75
g i v l n g details f o r the earthquake r e s i s t a n t d e 5 i q n .
H c w ~ v e r briefl)
t h e s t r e n g t h e n i n g measures a r e g i v e n b e l o w ta b e a d o p t e d f o r b u i l d i n g s
upto
f o u r st.orey5. Fur b l d g s m o r e than f o u r storeys s ~ i s r n l c f o r c e c
shoul;d b e specifically p r o v i d e d f o r in t h p s t r u c t u r a l analysis.
14.2 A l l b u i l d i n g s to b e c o n s t r u c t e d a f mssonry shall b e s t r ~ n g t h e n e c
by t h e methods as specified in t a b l e 4 o f T I No. 1 o f 1979.
14.3 L i n t e l band a s p e r s p e c i f i c a t i o n in s u b p a r a 14.6 b e l a w shall b~
provided
a t lintel level on all longitudinal a n d c r o s s walls e x c e p i
panel a n d p a r t i t i o n walls.
14.4
Roof band as p e r 5 p e c i f 1 c a t i o n i n sub p a r a 1 4 . 6 b e l o w
shall
he
provided
belaw
t h e r o o f o r floors ( e x c e p t a t p l l n t h l e v e l ) .
Such
a
band n e e d n o t be p r o v i d e d u n d e r n e a t h r e i n f o r c e d c o n r r e t - e o r b r ' i c k w a r k
slabs r e s t i n g on b e a r i n g walls p r o v i d e d t h a t t h e s l a b s a r e
continuous
over
p a r t 5 between c r u m p l e sections, 1-i a n y , and c o v e r t h e w i d t t i
of
walls f u l l y .
1
G a b l e band is to be p r o v i d e d a t the t n p o f g a b l e
masonry
below
the
p u r l i n s as specified i n s u b p a r a 14.6 b e l o w . T h l s b a n d
shall
be
made continuous with t h e r o o f b a n d a t t i e level.
T h e band shall be made o f r e i n f o r c e d c o n r r e t e g r a d e
not
leaner
H
1 0 or r e i n f o r c e d b r i c k w o r k in cement m o r t a r not
leaner
than
1 : 4 . T h p band shall be to t h e full w i d t h o f t h e wall and n o t less than
7.5 c m i n d e p t h a n d shall b e r e i n f o r c e d w i t h steel as indicated
In
t a b l e 7 of ;TI No. 1 o f 1 9 7 9 .
14.6
than
14.7
V e r t i c a l steel at c o r n e r s a n d j u n c t i o n s o f walls w h i c h a r e u p t o
1-1/2
brick
t h i c k s h a l l b e p r o v i d e d either of MS o r
high
strength
deformed
b a r s a s g i v e n in table 8 of T I N o . 1/79. F o r t h i c k e r walls,
t h e area o f b a r s s h a l l bp p r o p o r t i o n a l l y increased. The r e i n f o r c e m e n t
shall b e p r o p o r t i o n a l l y i n c r e a s e d . The r e i n f o r c e m e n t shall b e p r n p e r l y
embedded
i n the
p l i n t h masonry o f . f o u n d a t i o n s a n d r a a f slab o r
roof
band so a s to develop its tensile s t r e n g t h i n bond and passing t h r o u g h
the
lintel
bands i n all s t o r e y s . B a r s i n d l + f e r e n t
5 t o r ~ y s may
b~
w e ) d e d ar sui t a b 1 y l a p p e d ..
O p e n i n g s i n b e a r i n g walls s h a l l be s t r e n g t h e n ~ d where
necessary
p r o v ~ d l n g rei,n#orced c o n c r c t e m e m b e r s or reinforcing
brick
work
a r o u n d t h e m w i t h B mrn b a r s , o n e f a r e v e r y half b r i c k t h i c k n e s s o f wall.
14.0
by
14.9 The o p e n i n g s s h a l l p r e f e r a b l y b e l o c a t e d away f r o m t h e c o r n e r by
a c l e a r d i s t a n c e equal ta at least 1 / B o f t h e h e i g h t o f o p e n i n g
where
seismlc
capfficient
is less t h a n .OR a n d 1 / 4 o f
the
height
where
seismic coefficient 1s . O R o r m o r e . Where o p e n l n g s d o n o t c o m p l y w i t h
this requirement
t h ~ y s h a l l b e s t r e n g t h e n e d as p e r
sub
para
14.8
above. F o r o t h e r details o f spacing o f o p e n i n g s T I N o . 1 o f 1979 m a y be
ref e r r e d .
15.
15.1
Uuality Control
b r i c k w o r k 1s d e s i g n e d a s an engineering m a t e r i a l and
c o n f o r m t o the s t r i c t requirements o f such
norms
of
c o n s t r u c t i a n ~ . S i t e and L a b o r a t o r y c o n t r o l m u s t b e accepted as a
s t a n d a r d p r a c t i c e f o r calculated l o a d bearing w o r k c o n s t r u c t i o n .
m u s t
Structural
therefore
The a v e r a g e e x i s t i n g s t r e n g t h o f b r i c k s s h o u l d b e d e t e r m i n e d
as
IS:3435
( P a r t 1 ta I V ) o f 1976 ' M e t h o d o f t e s t
for
burnt
clay
b u i l d i n g s bricks.'
T h i s is i m p o r t a n t as t h e s t r e n g t h o f
masonry
1s
d i r e c t l y a f f e c t e d by the c r u s h i n g s t r e n g t h o f m a s o n r y u n i t s .
fidequate
arrangements
at
s i t e should
be
ensured
fur
snaking
of
brlcks,
preparation o f m a r t a r and p r o p e r c u r i n g . o f m a s o n r y a s i t also a f f e c t s
the
strength o f masonry. O t h e r p o i n t s about b o n d , t r u e p l u m b a n d b e d
J o l n t s be assured by a d e q u a t e s u p e r v ~ s i o n .
15.2
per
1.
2.
3.
4.
5.
Bricks
their
proper,tles
and
use
by
the
Brick
Development
Association E n g l a n d .
Elements o f toad b e a r i n g B r i c k w o r k b y [)avid L e n e t e r ( U K ) .
E x p l a n a t o r y Hand book an M a s o n r y b y I n d i a n St.-lndard - 1 n s t i t u t l u n .
I n d i a n S t a n d a r d s a s q u o t e d in t h e 7 1 .
CBRI
Data S h e ~ t N o . 8
of
Buildirg
I - e c h n i ~ u e series
ar\d
l n f a r m a t l o n N o t e No. 1 on p r e c a s t stont. M a s o n r y B l t ~ c l c .
HIM
PLAN
CROSS
WALL
-
C O N S T R U C T lOM
U N S T A B L E IN
DIRECTION
L O H G l f UDINAL
-
-
- El El
d
CC
T H I S BRICKWCRL ~ 1 1 . N1O T RESIST
LATERAL LOADING kS SUCCEgFUttY AS
El El
u
sD'
W U [ 2 ) A S IT TENUS TO
SEPARATE SHORT
T H A B on&.
A C T AS THREE
LENGTHS R A T HER
<
l ,
d
_
I
C
fn e
In
P7
-w-
-c-
--L
-
&ALL
WILL T E k D TO A C T
OHE
L o1.1G FORTlON OF BXlc#>'~Ciw
AND WILL
BE M O R E RE515 T A N T
To L A T E R A L L O A D I N G .
TkilS
AS
r l
r~ a
rl El
2
--
EFFECT O,F OPENINGS ON SHEAR '
STR,ENGTH O F WALLS
FIG*5
7.1No: IoFig&
O N E A N D A H A L F BRlCK H A S NOMINAL
'
OF 34 c h AND ACTUALTHICKMESS
I S 1 9 t l t 9 = 2 9 cm. I T I S THE L A T T E R WWKW -,*
IS T A K E N l M T 0 A C C O U N T I H M A $ o N R Y D L $ ~ G N
THlCYNESS
FIG- 9 THICKNESS OF WALL
c
IU
THIS
SloE
-
A
RAkEO
EF F E C T i V . E
THUS
19
SKETCH
t
= CB
JOINT3
O
N
DEPTH o f
cm.
T H I L K N E4 5
O F WALL r
70
A
cm,
JOINT R A K E D
F I G . 10
.*
EFFECTI\E.
ONE
THICKNESS