Brick Masonry Walls Book PDF
Brick Masonry Walls Book PDF
Brick Masonry Walls Book PDF
0
:: IITK-GSDMA-EQ19-V2.0
::IITK-GSDMA-EQ25-V2.0
Final Report :: A - Earthquake Codes
IITK-GSDMA Project on Building Codes
by
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Code &Commentary IS:1905
CONTENTS
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Code &Commentary IS:1905
CONTENTS
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Code &Commentary IS:1905
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Code &Commentary IS:1905
PROVISIONS COMMENTARY
0. – Foreword C0. – Foreword
0.1 –
This Indian Standard (Third Revision) was
adopted by the Bureau of Indian Standards on
30 August 1987, after the draft finalized by the
Structural Safety Sectional Committee had
been approved by the Civil Engineering
Division Council.
This draft revision of IS: 1905 is prepared as a
project entitled “Review of building codes and
Handbook” awarded to IIT Kanpur by GSDMA,
Gandhinagar through World Bank Finances.
0.2 –
Structural adequacy of masonry walls depends
upon a number of factors, among which
mention may be made of quality and strength
of masonry units and mortars, workmanship,
methods of bonding, unsupported height of
walls, eccentricity in the loading, position and
size of openings in walls: location of cross
walls and the combination of various external
loads to which walls are subjected.
0.3 –
This code was first published in 1961. In its
revision in 1969, basic compressive stresses
and stress factors for slenderness were
modified resulting in increased permissible
stresses in load bearing brick and block walls.
Subsequently two more revisions were
published in 1980 & 1987. The following major
changes were made in its second revision:
a) Use of stones (in regular sized units),
concrete blocks, lime based blocks and
hollow blocks were included as masonry
units;
b) Mix proportions and compressive strengths
of mortars used in masonry were revised;
c) Optimum mortar mixes for maximum
strength of masonry for units of various
strengths were indicated;
d) Provisions for lateral supports to walls had
been amplified so as to include stability
requirements;
e) Conditions of support for calculation of
effective height of masonry walls and
columns, and effective length of masonry
walls were spelt out more clearly;
f) Maximum allowable slenderness ratio for
load bearing walls was increased;
g) In case of free-standing walls, height to
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Code &Commentary IS:1905
PROVISIONS COMMENTARY
thickness ratios were indicated for different
wind pressures, based upon requirements
for stability;
h) Basic compressive stresses for masonry
members were modified so that strength of
masonry units correspond to revised values
of brick crushing strength specified in
IS:1077-1986*;
i) Formula for calculating area reduction
factor was modified;
j) Angle of dispersion of concentrated loads,
from the direction of such loads was
changed from 45° to 30°;
k) Provisions relating to shape modification
factors for masonry units other than
common bricks were amplified;
l) Values of permissible shear stress was
related to the actual compressive stresses
in masonry due to dead loads;
m) Provisions on ‘corbelling’ were amplified.
0.4 –
The present revision is intended to further
modify certain provisions as a result of
experience gained with the use of the second
revision of the standard. The following major
changes have been made in this revision.
(i) The requirements of a masonry element for
stability have been modified.
(ii) In the design of a free standing wall,
provision has been made for taking
advantage of the tensile resistance in
masonry under certain conditions.
(iii)Provision regarding effective height of a
masonry wall between openings has been
modified.
(iv)Method of working out effective height of a
wall with a membrane type DPC has been
modified,
(v)Criteria for working out effective length of
wall having openings have been modified.
(vi)Some general guidelines have been given
for dealing with concentrated loads for
design of walls.
(vii)Provisions regarding cutting and chases in
walls have been amplified.
(viii)The title has been changed for the sake of
greater clarity.
0.5 – C0.5 -
The following major changes have been Unlike previous versions of this code, this new
introduced in the present fourth revision : version addresses both unreinforced and
(a) Permissible stresses in masonry reinforced masonry.
whenever applicable have been
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PROVISIONS COMMENTARY
expressed in terms of compressive
strength of masonry.
(b) Permissible strength in shear has been
modified to include shear strength
corresponding to all likely failure modes.
(c) Some new definitions have been added
and ‘pier’ and ‘pillaster’ have been re-
defined.
(d) Some general guidelines for the proper
selection of the mortar have been given.
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PROVISIONS COMMENTARY
America, 1969.
n) Masonry Designer’s Guide (Third Edition),
The Masonry Society.
0.7 –
It is assumed in this code that design of
masonry work is done by qualified engineer
and that execution is carried out (according to
the recommendations of this code read with
other relevant codes) under the directions of
an experienced supervisor.
0.8 –
For the purpose of deciding whether a
particular requirement of this standard is
complied with, the final value, observed or
calculated, expressing the result of a test or
analysis, shall be rounded off in accordance
with IS: 2-1960*. The number of significant
places retained in the rounded off value should
be the same as that of the specified value in
this standard
*Rules for rounding off numerical values
(Revised).
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PROVISIONS COMMENTARY
1. – Scope C1. – Scope
1.1 – C1.1 –
This code gives recommendations for BIS did not formulate any Code of practice for
structural design aspect of un-reinforced and design and construction of reinforced masonry in
reinforced load bearing and non-load bearing the past since it considered the quality of bricks
walls, constructed with solid or perforated generally available in the country were not suitable
burnt clay bricks, sand-lime bricks, stones, for use in reinforced masonry. Despite this
concrete blocks, lime based blocks or burnt reinforcement has been widely used in masonry
clay hollow blocks in regard to the materials to construction and strongly encouraged for the
be used, maximum permissible stresses and earthquake resistance by certain BIS Codes of
methods of design. practices. Presently available masonry materials
certainly can be used for reinforced masonry, if
proper care is exercised about the quality of
construction and use of non-corroding
reinforcement.
1.2 – C1.2 –
The recommendations of the code do not Mud mortar for masonry as bonding material is
apply to walls constructed in mud mortars. normally not used in the present day construction
because of its poor bonding quality. Mud mortar
does attain some strength on drying, but it readily
absorbs moisture on coming in contact with
moisture or rain and loses its strength when wet.
For temporary and low cost single storeyed houses,
however, it is sometimes used particularly in rural
areas, when economy in cost is the main
consideration.
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PROVISIONS COMMENTARY
2. – Terminology C2. – Terminology
For the purpose of this code, the definitions
For the consistent use of this code, various terms
given in IS: 2212-1962* and the following shall
are assumed to have certain meaning in this code.
apply.
Many terms as defined in this commentary not
*Code of practice for brickwork.
always correspond to their meaning in ordinary
usage.
Some of the terms defined in this clause are
illustrated further to clarify their meaning.
Some of the terms defined in this clause are
illustrated in Fig. C-l to C-8.
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PROVISIONS COMMENTARY
stresses in the brick by interface bond whilst
maintaining the bed-joint mortar in compression.
Greater the height to length ratio of the wall, higher
the value of horizontal tensile stresses at the
vertical joints and, therefore, weaker the wall
against vertical splitting under load.
Since a column has greater height to length ratio in
comparison to a wall, it has a lower permissible
stress under a vertical load.
A masonry column has been defined as a vertical
member the width of which does not exceed 4
times the thickness. However, a limiting value of 3
times the thickness for width of the column has
also been used by some codes.
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PROVISIONS COMMENTARY
(a) Brick more than 75% solid. Net area equals gross
area
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PROVISIONS COMMENTARY
surface is less than 75 percent of its gross bricks but for perforation areas up to 35 percent of
cross-sectional area measured in the same the cross-section, the bricks have been found to
plane (see 2.4 and 2.18). behave as if solid.
2.10 – Grout
A mixture of cement, sand and water of
pourable consistency for filling small voids.
Door Jamb
Head joints
Collar joints
Bed joints
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PROVISIONS COMMENTARY
2.13.2 – Cross (Head) Joint
A vertical joint, normal to the face of the wall.
2.14 – Leaf
Inner or outer section of a cavity wall.
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2.17 – Masonry
An assemblage of masonry units properly
bonded together with mortar.
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but subjected to lateral loads in out plane
direction such as wind loads.
2.22 – Prism
An assemblage of masonry units bonded by
mortar with or without grout used as a test
specimen for determining properties of
masonry.
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PROVISIONS COMMENTARY
cavity and tied together with metal ties or
bonding units to ensure that the two leaves act
as one structural unit, the space between the
leaves being either left as continuous cavity or
filled with a non-load bearing insulating and
waterproofing material.
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PROVISIONS COMMENTARY
2.29 – Wythe
A continuous vertical tie of masonry one unit in
thickness. Plinth Band, Lintel band
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PROVISIONS COMMENTARY
3. – Materials C3. – Materials
3.1 – Masonry Units C3.1 – Masonry Units
Masonry units used in construction shall Choice of masonry units is generally made from
comply with the following standards: the consideration of: (a) local availability, (b)
compressive strength, (c) durability, (d) cost, and
IS : 1077-1986* or (e) ease of construction. Brick has the advantage
Burnt Clay Building
IS : 2180-1985 or over stone that it lends itself to easy construction
bricks
IS : 2222-1979 and requires less labour for laying. Stone masonry,
Stones (in regular IS : 3316-1874§ or because of practical limitations of dressing to shape
sized units) IS : 3620-1979** and size, usually has to be thicker and results in
Sand lime bricks IS : 4139-1976∂ unnecessary extra cost. Thus, the first choice for a
IS:2185(Part 1)- building at any place would be brick, if it is
Concrete blocks 1979¥ or available at reasonable cost with requisite strength
(Solid & hollow) IS:2185(Part 2)- and good quality. In hills as well as in certain
1983€ plains where soil suitable for making bricks is not
Lime based blocks IS : 31151978;± available or cost of fuel for burning bricks is very
Burnt clay hollow high and stone is locally available, the choice
IS : 3952-19785║ would be stone. If type and quality of stone
blocks
Gypsum partition available is such that it cannot be easily dressed to
IS : 2849-1983╫ shape and size, or if the cost of dressing is too high,
blocks
Autoclaved cellular IS:2185 (Part 3)- use of concrete blocks may prove to be more
concrete blocks 1984╤ economical, particularly when construction is to be
more than two storeys, since thickness of walls can
NOTE 1 -Gypsum partition blocks are used be kept within economical limits by using concrete
only for construction of non-load bearing blocks. In areas where bricks and stone of suitable
partition walls. quality are not available and concrete blocks cannot
NOTE 2 - Use of other masonry units, such as be manufactured at reasonable cost, and lime and
precast stone blocks, not covered by the sand of good quality are available, masonry units
above specifications, can also be permitted could be of sand-lime bricks. However, for
based on test results. manufacture of sand-lime bricks, special equipment
is required, and thus use of sand-lime bricks is not
* Specification for common burnt clay building common in India as yet.
bricks (Fourth revision)
Specification for heavy-duty burnt clay
building bricks(second revision)
Specification for burnt clay perforated
building bricks(second revision)
§ Specification for structural granite (First
revision).
** Specification for late rite stone block for
masonry (First revision).
∂ Specification for sand lime bricks (First
revision).
¥ Specification for concrete masonry units:
Part 1
Hollow and solid concrete blocks (second
revision).
€ Specification for concrete masonry units :
Part 2
Hollow and solid lightweight concrete blocks
(First revision).
± Specification for lime based blocks (First
revision).
║ Specification for burnt clay hollow blocks for
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PROVISIONS COMMENTARY
walls and partitions (First revision ).
╫ Specification for non-load bearing gypsum
partition blocks (solid and hollow types)
(First revision )
╤ Specification for concrete masonry units :
Part 3
Autoclaved cellular (aerated) concrete
blocks (First revision).
3.1.1 – C3.1.1 –
Masonry units that have been previously used Bond between mortar and masonry units is largely
shall not be reused in brickwork or block work influenced by suction rate (initial rate of water
construction, unless they have been absorption) of masonry units. Masonry units, which
thoroughly cleaned and conform to the code have been previously used in masonry would not
for similar new masonry units. possess adequate suction rate and as a result may
not develop normal bond and compressive
strengths when reused. It is therefore not advisable
to reuse such units in locations where requirement
of masonry strength is critical.
3.1.2 – C3.1.2 –
The shape and dimension of masonry units, As a general rule, apart from strength of masonry
construction practices, including methods of units and grade of mortar, strength of masonry
positioning of reinforcement, placing and depends on surface characteristics and uniformity
compacting of grout, as well as design and of size and shape of units as well as certain
detailing should be such as to promote properties of mortar. Units which are true in shape
homogeneity of structural members. and size, can be laid with comparatively thinner
joints, thereby resulting in higher strength. For this
reason, use of A grade bricks gives masonry of
higher strength as compared to that with B grade
bricks, even though crushing strength of bricks of
the two grades may be same. For similar reasons
ashlar stone masonry which uses accurately dressed
and shaped stones is much stronger than ordinary
coursed stone masonry.
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Table C1: Effect of Mortar Mix on Strength of
Brickwork
[using clay brick of strength 32.7 MPa ]
Mortar mix Mortar Brickwork Ratio
(Cement: Compressive compressive
Lime: Strength (28 strength (28
Sand) days) days)
X Y Y/X
(1) (2) (3) (4)
MPa MPa
1:¼:3 17.8 8.9 0.5
1:½:4½ 10.8 9.3 0.86
1:1:6 4.7 8.5 1.82
1:2:9 1.7 4.6 2.69
NOTE: Lime used was in the form of well matured
putty
3.2.1 – C3.2.1 –
Mix proportions and compressive strengths of
Mortars are intimate mixtures of some cementing
some of the commonly used mortars are given
materials, such as cement, lime and fine aggregate
in Table 1.
(such as sand, burnt clay/surkhi, cinder, etc). When
Table 1: Mix Proportion and Strength of Mortars for only fat lime is used, which sets very slowly
Masonry ( Clause 3.2.1 )
through the process of carbonation, it becomes
Mix Proportions ( By Loose Minimum
S Volume ) Compressi necessary, for the sake of better strength, to use
Grade some pozzolanic material, such as burnt clay/surkhi
L Lime Pozz ve
of
N Cem Pozzo- o- Sand Strength at or cinder. Plasticizers are used in plain cement-
Mortar Lime
o -ent lana lana 28 Days In sand mortars to improve workability. Mortars
Mixture MPa
¼ C or
could be broadly classified as cement mortars, lime
1 H1 1 0 0 3 10 mortars and cement-lime mortars. Main
B
¼ C or characteristics and properties of these three
2(a) H2 1 0 0 4 7.5
B categories of mortars are as under:
½ C or a) Cement mortars: These consist of cement and
2(b) H2 1 0 0 4½ 6.0
B
3(a) M1 1 0 0 5 5.0 sand, varying in proportion from 1:8 to 1:3,
3(b) M1 1 1 C or B 0 0 6 3.0 strength and workability improving with the
1(LP- increase in the proportion of cement. Mortars richer
3(c) M1 0 0 0 1½ 3.0
40) than 1:3 are not used in masonry because these
4(a) M2 1 0 0 0 6 3.0
cause high shrinkage and do not increase in
4(b) M2 1 2B 0 0 9 2.0
4(c) M2 0 1A 0 0 2 2.0 strength of masonry. Mortars leaner than 1:5 tend
4(d) M2 0 1B 0 1 1 2.0 to become harsh and unworkable and are prone to
4(e) M2 0 1 C or B 0 2 0 2.0 segregation. Cement mortars set early and gain
1(LP- strength quickly. Setting action of mortar is on
4(f) M2 0 0 0 1¾ 2.0
40) account of chemical changes in cement in
5(a) M3 1 0 0 0 7 1.5
5(b) M3 1 3B 0 0 12 1.5 combination with water, and thus these mortars can
5(c) M3 0 1A 0 0 3 1.5 set and harden in wet locations. In case of lean
5(d) M3 0 1B 0 2 1 1.5 mortars, voids in sand are not fully filled, and
5(e) M3 0 1 C or B 0 3 0 1.5 therefore, these are not impervious. Rich mortars
M3 0 1(LP- 0 2 1.5 though having good strength have high shrinkage
5(f) 0
40)
6(a) L1 1 0 0 0 8 0.7
and are thus more liable to cracking.
6(b) L1 0 1B 0 1 2 0.7 b) Lime mortars: These consist of intimate
6(c) L1 0 1 C or B 0 2 1 0.7 mixtures of lime as binder and sand, burnt
L1 0 1(LP- 0 1½ 0.7 clay/surkhi, cinder as fine aggregate in the
6(d) 0
40) proportion 1:2 to 1:3. As a general rule, lime
L1 0 1(LP- 0 2½ 0.7
6(e) 0 mortars gain strength slowly and have low ultimate
20)
7(a) L2 0 1B 0 0 3 0.5 strength. Mortars using hydraulic lime attain
7(b) L2 0 1C or B 0 1 2 0.5 somewhat better strength than those using fat lime.
7(c) L2 0 0 1(LP-7) 0 1½ 0.5 In fact, lime mortars using fat lime do not harden at
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PROVISIONS COMMENTARY
all in wet locations. Properties of mortar using
semi-hydraulic lime are intermediate between those
of hydraulic and fat lime mortars. When using fat
lime, it is necessary to use some pozzolanic
material such as burnt clay/surkhi or cinder to
improve strength of the mortar. The main
advantage of lime mortar lies in its good
workability, good water retentivity and low
shrinkage. Masonry in lime mortar has, thus, better
resistance against rain penetration and is less liable
to cracking, though strength is much less than that
of masonry in cement mortar .
c) Cement/lime mortars: These mortars have the
good qualities of cement as well as lime mortars,
that is, medium strength along with good
workability, good water retentivity, freedom from
cracks and good resistance against rain penetration.
Commonly adopted proportions of the mortar
(cement: lime: sand) are 1:1:6, 1:2:9 and 1:3:12.
When mix proportion of binder (cement and lime)
to sand is kept as 1:3, it gives a very dense mortar
since voids of sand are fully filled.
NOTE 1 - Sand for making mortar should be
well graded. In case sand is not well graded,
its proportion shall be reduced in order to
achieve the minimum specified strength.
NOTE 2 - For mixes in SI No. 1 and 2, use of
lime is not essential from consideration of
strength as it does not result in increase in
strength. However, its use is highly
recommended since it improves workability.
NOTE 3- For mixes in SI No. 3(a), 4(a), 5(a)
and 6(a), either lime C or B to the extent of l/4
part of cement (by volume) or some plasticizer
should be added for improving workability.
NOTE 4- For mixes in Sl No. 4(b) and 5(b),
lime and sand should first be ground in mortar
mill and then cement added to coarse stuff.
NOTE 5 - It is essential that mixes in Sl No.
4(c), 4(d), 4(e), 5(d), 5(e), 6(b), 6(c), 7(a) and
7(b) are prepared by grinding in a mortar mill.
NOTE 6 - Mix in Sl No. 2(b) has been
classified to be of same grade as that of Sl No.
2(a), mixes in SI No. 3(b) and 3(c) same as
that in Sl No. 3(a) and mixes in SI No. 4(b) to
4(f) same as that in SI No. 4(a), even though
their compressive strength is less. This is from
consideration of strength of masonry using
different mix proportions.
NOTE 7 - A, B and C denote eminently
hydraulic lime, semi-hydraulic lime and fat lime
respectively as specified in relevant Indian
Standards.
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Code &Commentary IS:1905
PROVISIONS COMMENTARY
that cement-lime mortars are much better than
cement mortars for masonry work in most of the
structures.
3.2.2.1 – C3.2.2.1 –
Requirements of a good masonry for masonry Requirements of a good mortar for masonry are
structures are workability, flow, water strength, workability, water retentivity and low
retentivity in the plastic state and bond, drying shrinkage. A strong mortar will have
extensibility, compressive strength, and adequate crushing strength as well as adequate
durability in the hardened state. Compressive tensile and shear strength. It is necessary that
strength of mortar, in general, should not be mortar should attain initial set early enough to
greater than masonry unit. enable work to proceed at. a reasonable pace. At
the same time it should gain strength within
reasonable period so that masonry is in a position
to take load early. A workable mortar will hang
from the trowel and will spread easily. A mortar
with good water retentivity will not readily lose
water and stiffen on coming in contact with
masonry units, and will remain plastic long enough
to be easily adjusted in line and level. This property
of good water retentivity will enable the mortar to
develop good bond with masonry units and fill the
voids, so that masonry has adequate resistance
against rain-penetration.
3.2.2.2 – C3.2.2.2 –
For commonly-used mortars conforming to Optimum mortar mixes from consideration of
Table 1, the optimum mortar mixes from the maximum strength of brickwork for various brick
unit strength consideration only are given in strengths based on Madras Detailed Standard
Table 2: Specification – 1956 (Reprint 1964), (Second
Series).
Table 2: Unit Strength of Mortar
(Clause 3.2.3.2)
Mortar Masonry unit strength
type (MPa)
M2 Below 5
M1 5-14.9
H2 15-24.9
H1 >25
3.2.2.3 – C3.2.2.3 –
Compressive strength shall not be sole-
An unnecessarily strong mortar concentrates the
criterion for the selection of mortar. Bond
effect of any differential movement of masonry in
strength, in general, is more important, as is
fewer and wider cracks while a weak mortar
good workability and water retentivity, which
(mortar having more of lime and less of cement)
are required for maximum bond. Lime-based
will accommodate movements, and cracking will
mortars of Table 1 should be preferred for it is
be distributed as thin hair cracks which are less
desirable to sacrifice some compressive
noticeable. Also stresses due to expansion of
strength of the mortar in favour of improved
masonry units are reduced, if a weak mortar is
bond. A set of preferred mortar mixes are
used. Lean mortars of cement alone are harsh,
given in Table 3.
pervious and less workable. Thus when strong
mortars are not required from considerations of
strength or for working under frosty conditions or
for work in wet locations, it is preferable to use
composite mortars of cement, lime and sand, in
appropriate proportions. Figure C9 based on
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PROVISIONS COMMENTARY
Madras Detailed Standard Specification – 1956
Table 3: Mortar Mix Composition (Reprint 1964) illustrates the relation between
(Clause 3.2.3.3) strength of mortar and brickwork for a number of
Mortar Preferred mix mortar mixes when bricks of medium strength (20
type Cement Lime Sand to 35 MPa according to British Standards) are used.
H1 1 ¼ 3 As the proportion of lime in mortar is increased,
H2 1 ½ 4½ though mortar loses strength, reduction in strength
M1 1 1 6 of brickwork is not much.
M2 1 2 9
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Data at very low stress (below 0.05 fm) usually
include the deformations of seating if
measurements are made on the testing machine
loading platens. As shown in Figure C10 the elastic
modulus of the masonry is taken as chord modulus
of stress-strain curve obtained during a prism test
between stress levels of 0.05 and 0.33 times fm.
Compressive strength
Δ Stress
Em =
Stress
Δ Strain
0.33×Compressive strength
∆ Stress
0.05×Compressive strength
∆ Strain
Strain
Figure C10: Chord modulus of elasticity
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4. – DESIGN C4. – DESIGN
CONSIDERATIONS CONSIDERATIONS
4.1 – General C4.1 – General
Masonry structures gain stability from the In order to ensure uniformity of loading, openings
support offered by cross walls, floors, roof and in walls should not be too large. and these should
other elements such as piers and buttresses be of 'hole in wall' type as far as possible; Bearings
Load bearing walls are structurally more for lintels and bed blocks under beams should be
efficient when the load is uniformly distributed liberal in sizes; heavy concentration of loads should
and the structure is so planned that be avoided by judicious planning and sections of
eccentricity of loading on the members is as load bearing members should be varied where
small as possible. Avoidance of eccentric feasible with the loadings so as to obtain more or
loading by providing adequate bearing of less uniform stress in adjoining parts of members.
floor/roof on the walls providing adequate One of the commonly occurring causes of cracks in
stiffness in slabs and avoiding fixity at the masonry is wide variation in stress in masonry in
supports, etc, is especially important in load adjoining parts.
bearing walls in multistorey structures. These
matters should receive careful consideration NOTE- A 'hole in wall' type opening is defined as
during the planning stage of masonry an opening where total width or height of solid
structures. masonry around the opening is equal to or greater
than the corresponding window dimension.
a1
a2
b1 b
w
b1 + b2 ≥ w
a1 + a2 ≥ h
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4.2.1.1 –
Lateral support may be in the vertical or
horizontal direction, the former consisting of
floor/roof bearing on the wall ‘or properly
anchored to the same and latter consisting of
cross walls, piers or buttresses.
4.2.1.2 –
Requirements of 4.2.1 (a) from consideration
of slenderness may be deemed to have been
met with if:
a) In case of a wall, where slenderness ratio
is based on effective height, any of the
following constructions are provided:
1) RCC floor/roof slab ( or beams and
slab), irrespective of the direction of
span, bears on the supported wall as
well as cross walls to the extent of at
least 9 cm;
2) RCC floor/roof slab not bearing on the
supported wall or cross wall is
anchored to it with non-corrodible
metal ties of 60 cm length and of
section not less than 6 x 30 mm, and
at intervals not exceeding 2 m as
shown in Fig. 5; and
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(i)
Concrete, min
Length 30 cm
(i)
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Code &Commentary IS:1905
PROVISIONS COMMENTARY
Metal anchor
fixed to joist
(ii)
Mild steel dowel
(i)
Topping
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PROVISIONS COMMENTARY
In case of a wall, when slenderness ratio is
based on its effective length; a cross
wall/pier/buttress of thickness equal to or more
than half the thickness of the supported wall or
90 mm, whichever is more, and length equal to
or more than one-fifth of the height of wall is
built at right angle to the wall (see Figure 78)
and bonded to it according to provision of
4.2.2.2 (d);
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supports. Further it should be kept in view that
horizontal force of 2.5 percent of vertical loads
need not be considered for elements of construction
that provide lateral stability to the structure as a
whole.
4.2.2.1 –
For the purpose specified in 4.2.2, if the lateral
supports are in the vertical direction, these
should meet the requirements given in 4.2.1.2
(a) and should also be capable of acting as
horizontal girders duly anchored to the cross
wall so as to transmit the lateral loads to the
foundations without exceeding the permissible
stresses in the cross walls.
4.2.2.2 – C4.2.2.2 –
In case of load bearing unreinforced buildings Provision in sub-clause (a) of height to width ratio
up to four storeys, stability requirements of of building for stability has been a traditional
4.2.2 may be deemed to have been met with requirement.
if:
a) Height to width ratio of building does A cross wall acting as a stiffening wall provides
not exceed 2; stability to the wall at its junction with the cross
wall thereby resisting movement of wall at
b) Cross walls acting as stiffening walls horizontal intervals and sharing a part of the lateral
continuous from outer wall to outer load. Further in conjunction with the diaphragm
wall or outer wall to a load bearing supported on the wall, it resists horizontal
inner wall, and of thickness and movement of the top of the wall. For the first mode
spacing as given in Table 2 4 are of stiffening, it is necessary that cross wall is built
provided. If stiffening wall or walls jointly with the load bearing wall or is adequately
that are in a line, are interrupted by anchored to it and there should be opening in the
openings, length of solid wall or walls cross wall close to its junction with the main wall
in the zone of the wall that is to be (refer clause 4.2.2.2(b) of the code); for the second
stiffened shall be at least one-fifth of mode, the diaphragm should be capable of acting as
height of the opening as shown in a horizontal girder and also the diaphragm should
Figure 9; be so connected to the cross walls that lateral forces
c) Floors and roof either bear on cross are transmitted to function the cross walls through
walls or are anchored to those walls shear resistance between diaphragm and cross
as in 4.2.1.2 such that all lateral loads walls.
are safely transmitted to those walls
and through them to the foundation; When bricks of old size that is, 23 X 11.5 X 7.7 cm
are used, Table C-3 may be used in place of Table
d) And cross walls are built jointly with 4 of the Code for buildings up to 3 storeys.
the bearing walls and are jointly
mortared, or the two interconnected Table C3: Thickness and Spacing of stiffening
by toothing. Alternatively, cross walls walls (Brick Size 23 X 11.5 X 7.7 cm)
may be anchored to walls to be
Sl. Thickness of Height Stiffening wall
supported by ties of non-corrodible
no. load bearing of Minimum Maximum
metal of minimum section 6 x 35 mm
wall to be storey thickness spacing
and length 60 cm with ends bent up
stiffened (cm) (m) (cm) (cm)
at least 5 cm; maximum vertical
spacing of ties being 1.2 m (see (1) (2) (3) (4) (5)
Figure 910). 1 11.5 3.25 11.5 4.50
2 23 3.25 11.5 6.00
3 34.5 and 5.00 11.5 8.00
above
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Table 4:Thickness and spacing of
stiffening walls [Clause 4.2.2.2 (b)]
Thickness Height* Stiffening Wall*
of load of storey Thickness
No. bearing not to not less than Maximum
wall to be exceed 1 to 3 4 spacing
stiffened storey storey
cm m cm cm cm
1 10 3.2 10 - 4.5
2 20 3.2 10 20 6.0
3 30 3.4 10 20 8.0
4 Above 30 5.0 10 20 8.0
4.2.2.3 – C4.2.2.3 –
In case of halls exceeding 8.0 m in length, Cross walls in conjunction with floors and roof
safety and adequacy of lateral supports shall diaphragms in a building provide stability to the
always be checked by structural analysis. structure against the effect of lateral loads. In case
of large rooms, halls, etc, we have only end walls
and there are no intermediate cross walls. If hall is
longer than 8.0 m, the end walls may not be able to
provide adequate stability (depending upon the
extent of lateral loads) and therefore, it is necessary
to check stability and stresses by structural
analysis.
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and if found necessary, stiffeners to be provided.
Also end walls will be subjected to shear and
bending and should be designed for permissible
shear and no-tension in case of unreinforced
masonry. It is necessary that diaphragms must bear
on the end walls so that lateral load is transmitted
to these walls through shear resistance.
4.2.2.4 – C4.2.2.4 –
A trussed roofing may not provide lateral When a hall or a large industrial building is
support, unless special measures are adopted provided with trussed roofing the longitudinal
to brace and anchor the roofing. However, in walls cannot be deemed to be laterally supported at
case of residential and similar buildings of the top unless trusses are braced at the tie beam
conventional design with trussed roofing level as shown in Figure C12. With braced trusses
having cross walls, it may be assumed that as lateral supports, longitudinal walls will act as
stability requirements are met with by the propped cantilevers and should be designed
cross walls and structural analysis for stability accordingly.
may be dispensed with.
Tie of roof
Tie runners trusses fixed to
walls
4.2.2.5 –
Capacity of a cross wall and shear wall to take
horizontal loads and consequent bending
moments, increases when parts of bearing
walls act as flanges to the cross wall.
Maximum overhanging length of bearing wall
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which could effectively function as a flange
should be taken as 12 t or H/6, whichever is
less, in case of T or I shaped walls and 6 t or
H/6, whichever is less, in case of L or U
shaped walls, where t is the thickness of
bearing wall and H is the total height of wall
above the level being considered as shown in
Fig. 11.
Bearing Wall
4.2.2.6 –
In case of external walls of basement and
plinth stability requirements of 4.2.2 may be
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deemed to have been met with if:
a) bricks used in basement and plinth have a
minimum crushing strength of 5 MPa and
mortar used in masonry is of Grade Ml or
better;
b) clear height of ceiling in basement does
not exceed 2.6 m;
c) walls are stiffened according to provisions
of 4.2.2.1;
d) in the zone of action of soil pressure on
basement walls, traffic load excluding any
surcharge due to adjoining buildings does
not exceed 5 kN/m2 and terrain does not
rise; and
e) Minimum thickness of basement walls is
in accordance with Table 5.
cm m m
1 40 2.50 2.00
2 30 1.75 1.40
4.2.2.7 – Walls Mainly Subjected to Lateral C4.2.2.7 – Walls Mainly Subjected to Lateral
Loads Loads
A free standing wall has no cross walls to give it
a) Free-standing wall - A free-standing wall
stability against overturning due to lateral loads
such as compound wall or parapet wall is
that is, wind or seismic loads. It thus acts like a
acted upon by wind force which tends to
cantilever fixed at the base and free at the top.
overturn it. This tendency to overturning is
resisted by gravity force due to self weight
of wall, and also by flexural moment of
resistance on account of tensile strength of
masonry. Free-standing walls shall thus be
designed as in 5.10.2.1. If mortar used for
masonry can not be relied upon for taking
flexural tension (see 5.7.1), stability of free-
standing wall shall be ensured such that
stabilizing moment of wall due to self weight
equals or exceeds 1.5 times the overturning
moment.
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b) Retaining wall - Stability for retaining walls If a wall is intended to retain some dry material and
shall normally be achieved through gravity there is no likelihood of any hydrostatic pressure,
action to ensure that the entire cross- the design of wall could be based on permissible
section is in compression but flexural tension in masonry. A retaining wall intended to
moment of resistance could also be taken support earth should be designed as a gravity
advantage of under special circumstances structure, placing no reliance on flexural moment
at the discretion of the designer (see 5.8) of resistance, since water can get access to the back
of the wall and impose pressure through tensile
cracks if any and endanger the structure.
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wall and pilasters are supporting a distributed load,
we would get the advantage of stiffening effect of
pilasters as in 4.5.2 of the Code.
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NOTE 1 A roof truss or beam supported on a
column meeting the requirements of 4.2.2.1 is
deemed to provide lateral support to the
column only in the direction of the beam/truss.
NOTE 2 - When floor or roof consisting of
RCC beams and slabs is supported on
columns, the columns would be deemed to be
laterally supported in both directions
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rotational restraint).
Lateral as well as rotational
restraint (that is, full restraint)
at one end and only lateral
restraint (that is, partial
restraint) at the other. For
2 example, RCC floor/roof at one 0.85 H
end spanning or adequately
bearing on the wall and timber
floor/roof not spanning on wall,
but adequately anchored to it,
on the other end.
Lateral restraint, without
rotational restraint (that is,
partial restraint) on both ends.
3 For example, timber floor/roof, 1.00 H
not spanning on the wall but
adequately anchored to it on
both ends of the wall, that is,
top and bottom.
Lateral restraint as well as
rotational restraint at bottom
but have no restraint at the top.
For example, parapet walls, on
4 1.50 H
RCC roof with slab having
adequate bearing on the lower
wall, or a compound wall with
proper foundation on the soil.
Strictly speaking actual height of a wall for the
NOTE 1 -H is the height of wall between purpose of working out its effective height should
centers of support in case of RCC slabs and be taken to be the clear distance between the
timber floors. In case of footings or foundation supports. However, in the Code it has been given
block, height (H) is measured from top of as the height between centres of supports, which is
footing or foundation block. In case of roof in accordance with the provisions of other masonry
truss, height (H) is measured up to bottom of codes. Since thickness of floors is generally very
the tie beam. In case of beam and slab small as compared to height of floors, this method
construction, height should be measured from of reckoning actual height will not make any
centre of bottom slab to centre of top beam. All appreciable difference in the end results. One
these cases are illustrated by means of could, therefore, take actual height as given in the
examples shown in Figure 12. Code or clear distance between supports as may be
found convenient to use in calculations.
NOTE 2 - For working out effective height, it is
assumed that concrete DPC, when properly
bonded with masonry, does not cause
discontinuity in the wall.
NOTE 3 - Where membrane type damp-proof
course or termite shield causes a discontinuity
in bond, the effective height of wall may be
taken to be greater of the two values
calculated as follows:
a) Consider H from top of footing ignoring
DPC and take effective height as 0.75H
b) Consider H from top of DPC and take
effective height as 0.85H.
NOTE 4 - When assessing effective height of
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walls, floors not adequately anchored to walls
shall not be considered as providing lateral
support to such walls.
NOTE 5 - when thickness of a wall bonded to Implication of this note is that when wall thickness
a pier pilaster is at least two-thirds the is not less than 2/3 of the thickness of the pilaster, a
thickness of the pier pilaster measured in the concentrated load on the pilaster, will be borne by
same direction, the wall and pier pilaster may the pilaster as well as the wall. In this case we may
be deemed to act as one structural element. design the element just as a wall supporting a
concentrated load, taking advantage of the increase
in the supporting area due to the pilaster projection.
In case thickness of wall is less than 2/3 of the
thickness of pilaster, we have to design the pilaster
just like a column, for which permissible stress is
less because of greater effective height and further
supporting area will be only that of the pilaster that
is, without getting any benefit in design of the
adjoining walls on either side. However in case, the
wall and pilasters are supporting a distributed load,
we would get the advantage of stiffening effect of
pilaster as in 4.5.2 of the Code.
L1
y
L2 x
H H
x< , y≥
8 6
l = 1.5L2
y x x
H H
x≥ , y≥
8 6
l=L
L
x y
H H
x< , y≥
8 6
l = 2L
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x L
H
x<
8
Slenderness determined by height
x x y
H H
x≥ , y≥
8 6
l = 0 .9 L
L
x y
H H
x≥ , y≥
8 6
l = 1.3L
L
y x x y
H H
x≥ , y≥
8 6
l = 0.8 L
Figure 14: Effective Length of the Wall
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Where a wall is supported by
a cross wall at one end and
continuous with cross wall at
other end
OR
2 0.9 L
Where a wall is supported by
a pier pilaster /buttress at one
end and continuous with pier
pilaster /buttress at other end
conforming to 4.2.1.2 (b)
Where a wall is supported at
each end by cross wall
OR
3 Where a wall is supported at 1.0 L
each
end by a pier pilaster /buttress
conforming to 4.2.1.2 (b)
Where a wall is free at one
end and is continuous with a
cross wall at the other end
OR
4 Where a wall is free at one 1.5 L
end and continuous with a
pier pilaster /buttress at the
other end conforming to
4.2.1.2 (b)
Where a wall is free at one
end and supported at the
other end by a cross wall
OR
5 Where a wall is free at one 2.0 L
end and supported at the
other end by a pier pilaster /
buttress conforming to 4.2.1.2
(b)
NOTE -In case there is an opening taller than
0.5 H in a wall, ends of the wall at the opening
shall be considered as free
4.5.1 – C4.5.1 –
For solid walls, faced walls or columns, In case of masonry using modular bricks, actual
effective thickness shall be the actual thickness of a one-brick wall for design calculation
thickness is taken as 190 mm, though nominal thickness is
200 mm. Similarly in case of brick masonry with
bricks of old size (FPS System) actual thickness of
one-brick wall would be taken as 220 mm though
nominal size of brick is 230 mm.
4.5.2 – C4.5.2 –
For solid walls adequately bonded into piers When the ratio tp/tw is 1.5 or less and the wall is
pilaster /buttresses, effective thickness for having distributed load, Note 4 of Table 6 would be
determining slenderness ratio based on
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effective height shall be the actual thickness applicable. It follows from this that interpolation of
of wall multiplied by stiffening coefficient as values in Table 6 are valid only when tp/tw exceeds
given in Table 8. No modification in effective 1.5.
thickness, however, shall be made when
slenderness ratio is to be based on effective
length of walls
4.5.3 –
For solid walls or faced walls stiffened by
cross walls, appropriate stiffening coefficient
may be determined from Table 8 on the
assumption that walls are equivalent to piers
pilaster of width equal to the thickness of the
cross wall and of thickness equal to three
times the thickness of stiffened wall.
4.5.4 – C4.5.4 –
For cavity walls with both leaves of uniform It has been observed from tests that a cavity wall is
thickness throughout, effective thickness 30 percent weaker than a solid wall of the same
should be taken as two-thirds the sum of the thickness as the combined thickness of two leaves
actual thickness of the two leaves. of the cavity wall, because bonding action of ties
cannot be as good as that of normal bond in a solid
wall. That explains why effective thickness of a
cavity wall is taken as two-thirds of the sum of the
actual thickness of two leaves.
4.5.5 – C4.5.5 –
For cavity walls with one or both leaves In this type of wall either one leaf (inner) or both
adequately bonded into piers, buttresses or leaves could be load bearing. In the former case,
cross walls at intervals, the effective thickness effective thickness will be two-thirds the sum of
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of the cavity wall shall be two-thirds the sum of the two leaves or the actual thickness of the loaded
the effective thickness of each of the two leaf whichever is more. In the latter case effective
leaves; the effective thickness of each leaf thickness will be two-thirds of the sum of thickness
being calculated using 4.5.1 or 4.5.2 as of both the leaves, or the actual thickness of the
appropriate. stronger leaf, whichever is more.
4.6.2 – C4.6.2 –
Effective span of a cantilever shall be taken as
a) distance between the end of cantilever In case, it forms the end of a continuous beam, the
and the center of it’s support length to the center of support should be taken.
b) distance between the end of cantilever
and the face of support plus half it’s
effective depth whichever is greater.
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Not 27 20 ignoring strengthening effect of other supports.
exceeding
2
Exceeding 27 13
2
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and height shall not exceed 3 times the
thickness. The parapet wall shall not be
thinner than the wall below.
4.8.3 – C4.8.3 –
Minimum dimension shall be 200 mm.
Due to the structural importance of columns and
Slenderness ratio shall not exceed 20.
their vulnerability as isolated members, many
codes specify a 200 mm nominal minimum
dimension.
4.9 – C4.9 –
4.9.1 – Eccentricity C4.9.1 – Eccentricity
Eccentricity of vertical loading at a particular Eccentricity of vertical loading on a masonry
junction in a masonry wall shall depend on element increases its tendency to buckling and
factors, such as extent of bearing, magnitude reduces its load carrying capacity; its effect is thus
of loads, stiffness of slab or beam, fixity at the similar to that of slenderness of the member. Thus
support and constructional details at junctions. combined effect of slenderness and eccentricity is
Exact calculations are not possible to make taken into consideration in design calculations by
accurate assessment of eccentricity. Extent of the factor known as Stress reduction factor (ks) as
eccentricity under any particular given in Table 11 of the Code.
circumstances has, therefore, to be decided
according to the best judgment of the Eccentricity caused by an eccentric vertical load is
designer. Some guidelines for assessment of maximum at the top of a member, that is, at the
eccentricity are given in Appendix A. point of loading and it is assumed to reduce
linearly to zero at the bottom of the member that is,
just above the bottom lateral support, while
eccentricity on account of slenderness of a member
is zero at the two supports and is maximum at the
middle. Taking the combined effect of eccentricity
of loading and slenderness critical stress in
masonry occurs at a section 0.6H above the bottom
support as shown in Figure C16.
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4.9.2 – C4.9.2 –
Columns shall be designed for a minimum
Columns are generally not subjected to perfectly
eccentricity of 10% of side dimension for each
concentric axial loads. Eccentricity due to
axis in addition to applied loads.
imperfections, lateral loads, and eccentrically
applied axial loads occur almost always and they
must be considered in design. Hence many
masonry codes require a minimum eccentricity of
10% of side dimension.
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5. – STRUCTURAL C5. – STRUCTURAL
DESIGN DESIGN
5.1 – General C5.1 – General
The building as a whole shall be analyzed by Some general guidance on the design concept of
accepted principles of mechanics to ensure load bearing masonry structures is given in the
safe and proper functioning in service of its following paragraphs.
component parts in relation to the whole
building. All component parts of the structure i) A building is basically subjected to two types of
shall be capable of sustaining the most loads, namely:
adverse combinations of loads, which the a) vertical loads on account of dead loads of
building may be reasonably expected to be materials used in construction, plus live loads due
subjected to during and after construction. to occupancy; and
b) lateral loads due to wind and seismic forces.
While all walls in general can take vertical loads,
ability of a wall to take lateral loads depends on
its disposition in relation to the direction of
lateral load. This could be best explained with the
help of an illustration.
In Figure C17, the wall A has good resistance
against a lateral load, while wall B offers very
little resistance to such load. The lateral loads
acting on the face of a building are transmitted
through floors (which act as horizontal beams) to
cross walls which act as shear walls. From cross
walls, loads are transmitted to the foundation.
This action is illustrated in Fig. C18. Stress
pattern in cross walls due to lateral loads is
illustrated in Fig. C19.
Iinplane
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x x
y
y
x-y
x+y
Cross wall
b
d
x+y
x-y
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ii)As a result of lateral load, in the cross walls there
will be an increase of compressive stress on the
leeward side, and decrease of compressive stress
on the wind-ward side. These walls should be
designed for 'no tension' and permissible
compressive stress. It will be of interest to note
that a wall which is carrying greater vertical
loads will be in a better position to resist lateral
loads than the one which is lightly loaded in the
vertical direction. This point should be kept in
view while planning the structure so as to
achieve economy in structural design.
Elevation
Plan
Figure C20-A Cross wall construction-unstable
in longitudinal direction
Plan
Figure C20-B Cellular or box type construction
stable in both directions
Figure C20: Stability of cross wall and cellular
(box type) construction
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iv) Size, shape and location of openings in the
external walls have considerable influence on
stability and magnitude of stresses due to lateral
loads. This has been illustrated in Figure C21.
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Cracking through masonry
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consideration according to the best judgement
of the designer.
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loads are considered along with normal loads. some criticism, it is permitted by the code in the
absence of more reliable information.
As an alternative of using an increased permissible
stress value when checking safety of structural
components, one can use a 25% reduced load for
load combinations involving wind or earthquake
forces and compare with full permissible stress
values. Thus, the modified load combinations b, c
and d will be:
b) 0.75 [DL + IL + (WL or EL)]
c) 0.75 [DL + WL]
d) 0.75 [0.9DL +EL]
W = Concentrated load
w = Distributed load after dispersal at depth h from
plane of application of concentrated load
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supported on lintels and beams, in accordance opening in the wall gets transferred to the sides of
with established practice. Increased axial the opening. For good arching action masonry
stresses in the masonry associated with units should have good shear strength and these
arching action in this way, shall not exceed the should be laid in proper masonry bond using a
permissible stresses given in section 5.6. good quality mortar. Further, portions of the wall
on both sides of the opening should be long
enough (see C-6.3.3) to serve as effective
abutments for the arched masonry above the
opening since horizontal thrust for the arch is to
be provided by the shear resistance of the
masonry at the springing level on both sides of
the opening. If an opening is too close to the end
of a wall, shear stress in masonry at springing
level of imaginary arch may be excessive and
thus no advantage can be taken of arching in
masonry for design of lintels.
Masonry Load
On Lintel
R
P Q
C F
D E
L
L/2 Effective L/2
Span
Floor
A G H Level J K B
x x
X= L or (L+H)/2, whichever is less
Figure C25: Arching action in masonry
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level, limited in length to L or (L-H)/2
whichever is less, H being the height of top of
the opening from the floor level.
In case some other opening occurs between the
lintel and horizontal plane 25 cm above the apex
R of the triangle, arching action gets interrupted
because of inadequate depth of masonry above
the triangle to function as an effective arching
ring. Also if there is some other load between
the lintel and horizontal plane 25 cm above the
apex R of the triangle, loading on the lintel gets
affected.
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applicable) and loads received from any other practice to assume that length of walls on both
part of the structure. Length of bearing of lintel sides of an opening should be at least half the
at each end shall not be less than 9 cm or effective span of the opening for transfer of load
one-tenth of the span, whichever is more, and to sides by arch action. In case it is less, lintel
area of the bearing shall be sufficient to should be designed for full load over the opening
ensure that stresses in the masonry regardless of the height of the floor slab as
(combination of wall stresses, stresses due to shown in Figure C27-A.
arching action and bearing stresses from the
lintel) do not exceed the stresses permitted in
5.6 (see AppendixC).
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OPENING
h > 250
Floor
Load On
Masonry Load
On Lintel
L1 L L2
(Effective
Span)
Load of Floor B
Load of and Masonry
Storey B Floor A Load of Storey
Masonry B on Lintel
Load of
Storey B
Floor A
Masonry
Load of
Storey A
on Lintel
Storey A
L1 L L2
L1 or L2 > L/2
Figure C27-D: Effective load when L1 and L2 ≥
L/2 and equilateral triangle above the lintel is
within 25 cm (vertically) of another opening in
the upper storey.
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lintel and horizontal plane 25 cm above the apex
of the equilateral triangle over the lintel, the
latter is designed for the loads as shown in Fig.
C-27-E.
Another load within 25 cm from the horizontal plan
Additional masonry load on the lintel on
account of the influence of the other
Masonry
<250 load of
equilateral
triangle
over the
lintel
60°
Load from the
other Load
within the
Influence of
L1 L L2 the
Equilateral
triangle over
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of diaphragm rigidity and of horizontal walls, it can be considered rigid and lateral loads
torsion due to eccentricity of wind and are distributed in various lateral load resisting wall
seismic loads resulting from non-uniform elements in proportion to their relative stiffness.
distribution of mass. Horizontal torsion developed due to eccentricity of
the applied lateral load with the plan centre of the
rigidity can cause forces in the wall parallel and
perpendicular to load direction. In-plane rigidities
are considered in the analysis, which includes both
shearing and flexural deformations. Generally
rigidities of transverse walls in direction
perpendicular to the direction of lateral force, is
usually disregarded. However, stiffening effect of
certain portion of such walls as permitted by the
Code in section 4.2.2.5 can be considered, if the
method of connection between the intersecting
walls and between walls and diaphragms is
adequate for the expected load transfer.
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detailed in 5.4.1.1 to 5.4.1.3.given below:
(a) Prism not tested/Unit Strength
Method:
Values of basic compressive stress given
in Table 10 which are based on the
crushing strength of masonry unit and
grades of mortar, and hold good for values
of SR not exceeding 6, zero eccentricity
and masonry unit having height to width
ratio ( as laid ) equal to 0.75 or less.
(b) Prisms tested :
The basic compressive stress can be
obtained by multiplying the specified
compressive strength obtained from
prism test with 0.25
Sl. Mortar Table 10: Basic compressive strength in MPa corresponding to masonry
no Type units of which height to width ratio does not exceed 0.75 and crushing
strength in MPa is not less than
3.5 5.0 7.5 10 12.5 15 17.5 20 25 30 35 40
1 H1 0.35 0.50 0.75 1.00 1.16 1.31 1.45 1.59 1.91 2.21 2.50 3.05
2 H2 0.35 0.50 0.74 0.96 1.09 1.19 1.30 1.41 1.62 1.85 2.10 2.50
3 M1 0.35 0.50 0.74 0.96 1.06 1.13 1.20 1.27 1.47 1.69 1.90 2.20
4 M2 0.35 0.44 0.59 0.81 0.94 1.03 1.10 1.17 1.34 1.51 1.65 1.90
5 M3 0.25 0.41 0.56 0.75 0.87 0.95 1.02 1.10 1.25 1.41 1.55 1.78
6 L1 0.25 0.36 0.53 0.67 0.76 0.83 0.90 0.97 1.11 1.26 1.40 1.06
7 L2 0.25 0.31 0.42 0.53 0.58 0.61 0.65 0.69 0.73 0.78 0.85 0.95
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particular storey height, generally stress is worked
Table 11: Stress reduction factor for out at the section just above the bottom support
slenderness ratio and assuming it to be maximum at that section.
eccentricity(Clause 5.6.2.1) Theoretically critical section in a storey occurs at a
Slende Eccentricity of loading divided by the height 0.6 H above the bottom support as explained
rness thickness of the member in C-4.8. Thus provisions of the Code and the
Ratio 0 1/24 1/12 1/6 1/4 1/3 design procedure in question as commonly
(1) (2) (3) (4) (5) (6) (7) followed, is an approximation that errs on the safe
6 1.00 1.00 1.00 1.00 1.00 1.00 side.
8 0.95 0.95 0.94 0.93 0.92 0.91 Advantage of Note 3 under Table 11 of the Code is
10 0.89 0.88 0.87 0.85 0.83 0.81 taken when considering bearing stress under a
12 0.84 0.83 0.81 0.78 0.75 0.72 concentrated load from a beam. Bearing stress is
14 0.78 0.76 0.74 0.70 0.66 0.66 worked out immediately below the beam and this
16 0.73 0.71 0.68 0.63 0.58 0.53 should not exceed the permissible compressive
18 0.67 0.64 0.61 0.55 0.49 0.43 stress of masonry. Also stress in masonry is
20 0.62 0.59 0.55 0.48 0.41 0.34
worked out at a depth of H/8 from the bottom of
22 0.56 0.52 0.48 0.40 0.32 0.24
24 0.51 0.47 0.42 0.33 0.24 - the beam. This should not exceed the permissible
26 0.45 0.40 0.35 0.25 - - compressive stress in masonry. If actual stress
27 0.43 0.38 0.33 0.22 - - exceeds allowable stress in either case, a concrete
bed block is provided below the beam.
NOTE 1 - Linear interpolation between values
is permitted. In accordance with 5.6.2.5 of the Code, some
increase in permissible compressive stress is
NOTE 2 - Where, in special cases, the allowed for concentrated loads which are
eccentricity of loading lies between 1/3 and 1/2 concentric. For checking bearing stress under such
of the thickness of the member, the stress a load, however, some authorities on masonry
reduction factor should vary linearly between recommend a conservative approach-that is, either
unity and 0.20 for slenderness ratio of 6 and to take advantage of Note 3 of Table 11 of the
20 respectively. Code or to take advantage of provisions of 5.6.2.5
NOTE 3 -Slenderness ratio of a member for of the Code but do not apply both the provisions of
sections within 1/8 of the height of the member the code at the same time.
above or below a lateral support may be taken
to be 6.
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5.6.2.3 – Shape Modification Factor C5.6.2.3 – Shape Modification Factor
This factor takes into consideration the shape Shape modification factor is based on the general
of the unit, that is, height to width ratio (as laid) principle that lesser the number of horizontal joints
and is given in Table 12. This factor is in masonry, greater its strength or load carrying
applicable for units of crushing strength up to capacity. It has, however, been found from
15 MPa. experimental studies that for units stronger than
15 MPa, extent of joints in masonry does not have
Table 12: Shape Modification Factor For any significant effect on strength of masonry
Masonry Units (Clause 5.6.2.3 ) because of use of the comparatively high strength
Height to Shape modification factor (kp) for mortar that normally goes with high-strength units.
width ratio units having crushing strength in
of units(as MPa
laid) 5.0 7.5 10.0 15.0
(1) (2) (3) (4) (5)
Up to 0.75 1.0 1.0 1.0 1.0
1.0 1.2 1.1 1.1 1.0
1.5 1.5 1.3 1.2 1.1
2.0 to 4.0 1.8 1.5 1.3 1.2
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approach for various ranges of eccentricity ratios
namely (a) eccentricity ratio of 1/24 or less; (b)
eccentricity ratio exceeding 1/24 but not
exceeding 1/6, and (c) eccentricity ratio
exceeding 1/6. Basis of this design approach is
explained below.
C=0
t/2 W = Fat
t
Fa Fa
Figure C28-A
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W
e
e = t/24
t/2 f1 = 1.25Fa
f2 = 0.75Fa
W = Fat
f2 f1
Figure C28-B
PROVISIONS COMMENTARY
e
t 24 < e < t 26
f1 = 1.25 Fa
=
W ⎛ 1 + 6e ⎞
⎜ ⎟
t ⎝ t ⎠
t 1.25 Fa t
W =
6e
f1 1+
t
f2
Figure C28-C
t W
e=
6 t
e=
t 6
6 2W
f1 = = 1.25 Fa
t
t 1.25 Fa × t
W=
2
f1
Zero
Stress
Figure C28-D
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f1 + 0 f1
f av = =
2 2
Since f1 has to be limited to 1.25Fa
1.25 Fa
f av =
2
The Total allowable load W in this case will be
equal to average compressive stress multiplied
by length ab of the stress triangle abc. Since for
equilibrium, the load must pass through the
W = average stress × ab
1.25 × Fa t centroid of the
= × 3( − e)
2 2
stress triangle abc and the load is at a distance of
t/2- e from the compressive face, we get
ab t ⎛t ⎞
= − e and ab = 3 ⎜ − e ⎟
3 2 ⎝2 ⎠
Thus Total allowable load,
W = average stress × ab
1.25 × Fa t
= × 3( − e)
2 2
From the above equation we can see that
theoretically design load W is zero when e= t/2.
However for practical considerations e should be
limited to t/3.
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f A fB stresses between axial and flexure loads, which can
+ ≤1 be extended for the biaxial bending, by using the
Fa Fb bending stress quotients for both axes. In this
Where, interaction formula, the secondary effect of
fa= Calculated compressive stresses due to moment magnification for flexure term due to axial
axial load only loads is not included, which is an error on the
fb= Calculated Compressive stresses due to unsafe side. However, this error for practical size
flexure only of walls will be relatively small and large overall
Fa = Allowable axial compressive stress safety factor of about 4 is adequate to account for
Fb = Allowable flexural compressive stress this amplification of flexure term.
= 1.25 Fa The code allows 25% increase in allowable axial
compressive stress, if it is due to flexure. The
permissible flexural compressive stress can be
expressed as a function of masonry prism strength
as follows:
Fb = 1.25 Fa = 1.25 x 0.25 fm = 0.31 fm
.
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NOTE 2- Allowable tensile stress in bending in In accordance with Note 2 of the clause tensile
the vertical direction may be increased to 0.1 stress up to 0.1 MPa and 0.07 MPa in the masonry
MPa for M1 mortar and 0.07 MPa for M2 of boundary/compound walls is permitted when
mortar in case of boundary walls. mortar used in masonry is of M1 and M2 grade
respectively or better. This relaxation has been
made to effect economy in the design of the
boundary/compound walls since there is not much
risk to life and property in the event of failure of
such walls.
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0.6
0.5 MPa or fm ≥ 16 MPa
0.3
0.1
0
0 0.5 1 1.5 2 2.5 3
Stress due to dead loads, MPa
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with mortar of M1 grade or stronger, raking
thickness can be ignored.
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of the wall and the permissible stress in the
weaker of the two materials. The permissible
stress shall be found by using the total
thickness of the wall when calculating the
slenderness ratio.
5.10.2 – Walls and Columns Mainly C5.10.2 – Walls and Columns Mainly
Subjected to Lateral Loads Subjected to Lateral Loads
5.10.2.1 – Free-Standing Walls C5.10.2.1 – Free-Standing Walls
1980 version of the Code provided for design of a
a) Free-standing walls, subjected to wind
free-standing wall as gravity structure that is,
pressure or seismic forces, shall be
without placing reliance on the flexural moment of
designed on the basis of permissible
resistance of the wall due to tensile strength of
tensile stress in masonry or stability as in
masonry. It was seen that this approach to design
4.2.2.4. However, in seismic zone II,
resulted in fairly thick walls and maximum height
freestanding walls may be apportioned
of an unplastered 230 mm thick wall (one-brick
without making any design calculations
thick of conventional size) could be only about
with the help of Table 14, provided the
0.86 m while it has been a common practice since
mortar used is of grade not leaner than
long to build such walls to heights much greater
M1.
than 0.86 m. From a study of practices being
followed in some other countries in this regard, it is
evident that, for design of free-standing walls, it is
appropriate to take into consideration flexural
moment of resistance of masonry according to the
grade of mortar used for the masonry.
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M1 mortar can be 1.5 m for a straight wall, 3.2 m
for a staggered wall and 4.0 m for a diaphragm
wall.
b) If there is a horizontal damp-proof course
near the base of the wall that is not
capable of developing tension vertically,
the minimum wall thickness should be the
greater of that calculated from either:
1. the appropriate height to thickness
ratio given in Table 14 reduced by 25
percent, reckoning the height from
the level of the damp-proof course; or
2. the appropriate height to thickness
ratio given in Table 14 reckoning the
height from the lower level at which
the wall is restrained laterally.
Retaining walls shall be designed on
the basis of zero-tension, and
permissible compressive stress.
However, in case of retaining walls
for supporting horizontal thrust from
dry materials, retaining walls may be
designed on the basis of permissible
tensile stress at the discretion of the
designers.
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5.10.3 – Walls and Columns C5.10.3 – Walls and Columns Subjected
Subjected to Vertical as Well to Vertical as Well as Lateral
as Lateral Loads Loads
For walls and columns, stresses worked out Longitudinal walls of tall single storey wide span
separately for vertical loads as in 5.8.1 and buildings with trussed roofs such as industrial
lateral loads as in 5.8.2, shall be combined buildings, godowns, sports halls, gymnasia, etc,
and elements designed on the basis of which do not have any intermediate cross walls
permissible stresses. other than gable walls, tend to be very thick and
uneconomical if designed as solid walls, since
vertical load is not much and the lateral load due to
wind/earthquake predominates. This would be
particularly so when the trusses are not adequately
braced at the tie beam level so as to be able to act
as horizontal girders for transmitting the lateral
loads to the gable walls. In this case, the walls act
as simple cantilevers and flexural stress at the base
will be quite high. When, however, trusses are
adequately braced to provide girder action and are
suitably anchored to the gable walls, longitudinal
walls would function as propped cantilevers, thus
resulting in considerable reduction in bending
moments on the long walls as shown in Figure
C32.
Truss not
braced
P
p
PH/2
Truss braced
Prop
3H/8
+ 9PH/128
P
p
5H/8
PH/8
(max)
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steel I-joist that is, placing more material at places
where stresses are more. As a result section
modulus to area ratio of a diaphragm wall is much
higher than that of a solid wall, thereby resulting in
economy.
Ribs
Course A
Alternate courses
¼ Bricks Course B
149.5
5.10.5 – Non Load Bearing Walls C5.10.5 – Non Load Bearing Walls
Non-load bearing walls, such as panel walls, Non-load bearing panel and curtain walls if not
curtain walls and partition walls which are designed on the basis of guidelines given in
mainly subjected to lateral loads, according to Appendix D of the Code may be apportioned with
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present state of the art, are not capable of the help of Table C-5 which is extracted from
precise design and only approximate methods Recommended Practices for Engineered Brick
based on some tests are available. Guidelines Masonry. The table is based on the assumption that
for approximate design of these walls are wall is simply supported only in one direction
given in Appendix D. either vertically or horizontally without any
opening or other interruptions. Where the wall is
supported in both directions, the allowable distance
between lateral supports may be increased such that
the sum of the horizontal and vertical spans
between supports does not exceed three times the
permissible distance permitted for supporting in the
vertical direction.
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6. – GENERAL C6. – GENERAL
REQUIREMENTS REQUIREMENTS
6.1 – Methods of Construction
6.1.1 – General
Brickwork IS : 2212-1962*
Stone masonry IS : 1597 ( Part 1 )-1967
IS : 1597 ( Part 2 )-1967
Hollow concrete IS : 2572-1963
block masonry
Autoclaved cellular IS : 6041-1985
concrete block
masonry
Lightweight concrete IS : 6042-19697
block masonry
Gypsum partition IS : 2849-1983**
blocks
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diaphragms to create a box-like system for lateral
loads.
Preferably buildings located in high seismic
regions IV and V shall be designed for forces in IS:
1893 and provisions of reinforced masonry as per
IITK-GSDMA Guidelines (available at
www.nicee.org)
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external walls for reducing outdoor air-borne
noise.
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Table C-10 Suitability of Walls for Different
Exposures (R-Recommended and NR- Not
Recommended)
Sl Particulars of wall Type of Exposure
No Shel Mod Seve
. tered erate re
1 Brick mas onry-burnt clay or
sand-Iime
a)1 brick wall – not R NR NR
plastered
b)1 brick wall – plastered R R NR
both sides
c)1½ brick wall – not R R NR
plastered
d) 1½ brick wall – R R R
plastered both sides
2 Stone masonry
a) Minimum thickness R R NR
35cm – not plastered
b)Minimum thickness 35cm R R R
– plastered both sides
Stone blocks – 20 cm
4 minimum thickness
a)Not plastered R NR NR
b)Plastered both sides R R NR
Cavity wall of 25 cm
5 minimum thickness R R R
NOTES:
1 Use of cement-lime or lime mortar in place of
cement mortar appreciably improves the resistance
of a wall to rain. It is also important that joints in
masonry are fully filled with mortar.
2 Sheltered conditions’ are those where wall is
protected by overhangs or adjoining buildings or
rainfall is low (less than 750 mm per year and is
generally not accompanied by strong winds.
'Severe conditions' occur when wall is subjected to
strong winds and persistent rain and there is no
sheltering action of overhangs or adjoining
buildings, or rain fall is heavy (exceeding 1000
mm). 'Moderate condition' obtains when exposure
conditions are between 'Sheltered' and 'Severe'
conditions.
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workmanship with reasonable degree of d) Unduly thick bed joints;
supervision. If the work is inadequately e) Uneven or deeply furrowed bed joints;
supervised, strength should be reduced to f) Voids in perpend (head) joints; and
three-fourths g) Disturbance of bricks after laying.
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mortar from the bed joints on pressing into
position. This practice should be avoided.
6.3.3 – Bond
Cross-joints in any course of one brick thick
masonry wall shall be not less than one-fourth
of a masonry unit in horizontal direction from
the cross-joints in the course below. In
masonry walls more than one brick in
thickness, bonding through the thickness of
wall shall be provided by either header units or
by other equivalent means conforming to the
requirements of IS : 2212-1962*.
*Code of practice for brickwork.
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perpends shall not exceed one-fifth of
the specified thickness.
NOTE - These tolerances have been specified
from point of view of their effect on the
strength of masonry. The permissible stresses
recommended in section 5.3 may be
considered applicable only if these tolerances
are adhered to.
6.5.2 –
In masonry, designed by structural analysis, all
chases, recesses and holes shall be
considered in structural design and detailed in
building plans.
6.5.3 –
When chases, recesses and holes have not
been considered in structural design are not
shown in drawings, these may be provided
subject to the constraints and precautions
specified in 6.5.3 to 6.5.13.
6.5.4 –
As far as possible, services should be planned
with the help of vertical chases and use of
horizontal chases should be avoided.
6.5.5 –
For load bearing walls, depth of vertical and
horizontal chases shall not exceed one-third
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and one-sixth of the wall thickness
respectively.
6.5.6 –
Vertical chases shall not be closer than 2 m in
any stretch of wall and shall not be located
within 34.5 cm of an opening or within 23 cm
of a cross wall that serves as a stiffening wall
for stability. Width of a vertical chase shall not
exceed thickness of wall in which it occurs.
6.5.7 –
When unavoidable horizontal chases of width
not exceeding 6 cm in a wall having
slenderness ratio not exceeding 15 may be
provided. These shall be located in the upper
or lower middle third height of wall at a
distance not less than 60 cm from a lateral
support. No horizontal chase shall exceed one
meter in length and there shall not be more
than 2 chases in any one wall. Horizontal
chases shall have minimum mutual separation
distance of 50 cm. Sum of lengths of all
chases and recesses in any horizontal plane
shall not exceed one-fourth the length of the
wall.
6.5.8 –
Holes for supporting put-logs of scaffolding
shall be kept away from bearings of beams,
lintels and other concentrated loads. If
unavoidable, stresses in the affected area
shall be checked to ensure that these are
within safe limits.
6.5.9 –
No chase, recess or hole shall be provided in
any stretch of a masonry wall, the length of
which is less than four times the thickness of
wall, except when found safe by structural
analysis.
6.5.10 –
Masonry directly above a recess or a hole, if
wider than 30 cm, shall be supported on a
lintel. No lintel, however, is necessary in case
of a circular recess or a hole exceeding 30 cm
in diameter provided upper half of the recess
or hole is built as a semi-circular arch of
adequate thickness and there is adequate
length of masonry on the sides of openings to
resist the horizontal thrust.
6.5.11 –
As far as possible, chases, recesses and
holes in masonry should be left (inserting
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sleeves, where necessary) at the time of
construction of masonry so as to obviate
subsequent cutting. If cutting is unavoidable, it
should be done without damage to the
surrounding or residual masonry. It is
desirable to use such tools for cutting which
depend upon rotary and not on heavy impact
for cutting action.
6.5.12 –
No chase, recess or hole shall be provided in
half-brick load bearing wall, excepting the
minimum number of holes needed for
scaffolding.
6.5.13 –
Chases, recesses or holes shall not be cut into
walls made of hollow or perforated units, after
the units have been incorporated in masonry.
h
x≤
2
t
x≤
3
d
x≤
3
θ = tan −1 h / x
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6.6.2 –
The load per unit length on a corbel shall not
be greater than half of the load per unit length
on the wall above the corbel. The load on the
wall above the corbel together with four times
the load on the corbel shall not cause the
average stress in the supporting wall or leaf to
exceed the permissible stresses given in 6.6.
6.6.3 –
It is preferable to adopt header courses in the
corbelled portion of masonry from
considerations of economy and stability.
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7. – NOTATIONS AND C7. – NOTATIONS AND
SYMBOLS SYMBOLS
7.1 –
The various notations and letter symbols used
in the text of the standard shall have the
meaning as given in Appendix E.
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Appendix A
(Clause 4.8)
SOME GUIDELINES FOR ASSESSMENT OF ECCENTRICITY OF LOADING ON WALLS
A1. –
Where a reinforced concrete roof and floor slab of normal span (not exceeding 30 times the
thickness of wall) bear on external masonry walls, the point of application of the vertical loading
shall be taken to be at the centre of the bearing on the wall. When the span is more than 30 times
the thickness of wall, the point of application of the load shall be considered to be displaced from
the centre of bearing towards the span of the floor to, in extent of one-sixth the bearing width.
A2. –
In case of a reinforced concrete slab of normal span (that is, less than 30 times the thickness of
the wall), which does not bear on the full width of the wall and 'cover tiles or bricks' are provided on
the external face, there is some eccentricity of load. The eccentricity may be assumed to be one-
twelfth of the thickness of the wall.
A3. –
Eccentricity of load from the roof/floor increases with the increase in flexibility and thus deflection
of the slabs. Also, eccentricity of loading increases with the increase in fixity of slabs/beams at
supports. Precast RCC slabs are better than in-situ slabs in this regard because of very little fixity.
If supports are released before further construction on top, fixity is reduced.
A4. –
Interior walls carrying continuous floors are assumed to be axially loaded except when carrying
very flexible floor or roof systems. The assumption is valid also for interior walls carrying
independent slabs spanning from both sides, provided the span of the floor on one side does not
exceed that on the other by more than 15 percent. Where the difference is greater, the
displacement of the point of application of each floor load shall be taken as one-sixth of its bearing
width on the wall and the resultant eccentricity calculated there from.
A5. –
For timber and other lightweight floors, even for full width bearing on Wall, an eccentricity of about
one-sixth may be assumed due to deflection. For timber floors with larger spans, that is, more than
30 times the thickness of the wall, eccentricity of one-third the thickness of the wall may be
assumed.
A6. –
In multi-storeyed buildings, fixity and eccentricity have normally purely local effect and are not
cumulative. They just form a constant ripple on the downward increasing axial stress. If the ripple
is large, it is likely to be more serious at upper levels where it can cause cracking of walls than
lower down where it may or may not cause local over-stressing.
Note-The resultant eccentricity of the total loads on a wall at any level may be calculated on the
assumption that immediately above a horizontal lateral support, the resultant eccentricity of all the
vertical loads above that level is zero.
A7. –
For a wall corbel to support some load, the point of application of the load shall be assumed to be
at the centre of the bearing on the corbel.
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Appendix B
( Clause 6.6.1)
CALCULATION OF BASIC COMPRESSIVE STRESS OF MASONRY BY PRISM TEST
Prisms shall be tested after 28 days between sheets of nominal 4 mm plywood, slightly longer than
the bed area of the prism, in a testing machine, the upper platform of which is spherically seated.
The load shall be evenly distributed over the whole top and bottom surfaces of the specimen and
shall be applied at the rate of 350 to 700 kN/m. The load at failure should be recorded.
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Appendix C
(Clauses 5.3.3 and 5.6.2.5)
GUIDELINES FOR DESIGN OF MASONRY SUBJECTED TO CONCENTRATED LOADS
C2.2 –
If the load bears on full thickness of wall and is concentric, 25 percent increase in stress may be
allowed.
C2.3 –
For loading on central strip wider than half the thickness of the wall but less than full thickness,
increase in stress may be worked out by interpolation between values of increase in stresses as
given in C-2.1 and C-2.2.
C2.4 –
In case concentrated load is from a lintel over an opening, an increase of 50 percent in permissible
stress may be taken, provided the supporting area is not less than 3 times the bearing area.
C3.2 –
When any section of masonry wall is subjected to concentrated as well as uniformly distributed
load and resultant stress, computed by making due allowance for increase in stress on account of
concentrated load, exceeds the permissible stress in masonry, a concrete bed block ( of M-15
Grade ) should be provided under the load in order to relieve stress in masonry. In concrete, angle
of dispersion of concentrated load is taken to be 45° to the vertical.
C3.3 –
In case of cantilevers and long span beams supported on masonry walls, indeterminate but very
high edge stresses occur at the supports and in such cases it is necessary to relieve stress on
masonry by providing concrete bed block of M-15 Grade concrete. Similarly when a wall is
subjected to a concentrated load from a beam which is not sensibly rigid ( for example, a timber
beam or an RS joist), a concrete bed block should be provided below the beam in order to avoid
high edge stress in the wall because of excessive deflection of the beam.
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Code &Commentary IS:1905
Appendix D
(Clause 5.8.5)
GUIDELINES FOR APPROXIMATE DESIGN OF NON-LOAD BEARING WALL
Bending
PL/25 PL/18 PL/14 PL/12 PL/11 PL/10. PL/10
moment
5
Note - For H/L ratio less than 0.30, the panel should be designed as a free-standing wall and for
H/L ratio exceeding 1.75, it should be designed as a horizontally spanning member for a bending
moment value of PL/8.
c) When either there are no window openings or windows are of ‘hole-in-wall' type, the panel is
considered to be simply supported on all four edges. In this case also, amount of maximum
bending moment depends on height to length ratio of panel and ratio (μ) of flexural strength of
masonry in vertical direction to that in the horizontal direction. Approximate values for maximum
bending moment in the horizontal direction for masonry with μ = 0.50, are given in Table 17.
Bending
moment PL/72 PL/36 PL/24 PL/18 PL/15 PL/13 PL/12
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Code &Commentary IS:1905
view of smaller lateral loads, ordinarily these could be apportioned empirically as follows:
a) Walls with adequate lateral restraint at both ends but not at the top:
1) The panel may be of any height, provided the length does not exceed 40 times the
thickness; or
2) The panel may be of any length, provided the height does not exceed 15 times the
thickness (that is, it may be considered as a free-standing wall); or
3) Where the length of the panel is over 40 times and less than 60 times the thickness, the
height plus twice the length may not exceed 135 times the thickness;
b) Walls with adequate lateral restraint at both ends and at the top:
1) The panel may be of any height, provided the length does not exceed 40 times the
thickness; or
2) The panel may be of any length, provided the height does not exceed 30 times the
thickness; or
3) Where the length of the panel is over 40 times and less than 110 times the thickness, the
length plus three times the height should not exceed 200 times the thickness; and
c) When walls have adequate lateral restraint at the top but not at the ends, the panel may be of
any length, provided the height does not exceed 30 times the thickness.
D3.2 –
Strength of bricks used in partition walls should not be less than 3.5 MPa or the strength of
masonry units used in adjoining masonry, whichever is less. Grade of mortar should not be leaner
than M2.
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Code &Commentary IS:1905
APPENDIX E
(Clause 8.1)
NOTATIONS, SYMBOLS AND ABBREVIATIONS
E-1. The following notations, letter symbols and abbreviations shall have the meaning indicated
against each, unless otherwise specified in the text of the standard:
A Area of a section
An Net area
Ast Area of steel
Av,min Minimum area of shear reinforcement
b Width of bearing
d Effective depth
db Nominal diameter of bar (mm)
DPC Damp proof course
e Resultant eccentricity
Em Elastic modulus of clay and concrete masonry
Es Elastic modulus of steel reinforcement
fA Calculated axial compressive stress
fB Calculated bending stress
fb Basic compressive stress
fd Compressive stress due to dead loads
fm Compressive strength of masonry ( in prism test)
Fa Allowable axial compressive stress
Fb Allowable bending compressive stress
Fs Permissible tensile/compressive stress in steel (MPa)
Fv Permissible shear stress
GL Ground level
H Actual height between lateral supports
H’ Height of opening
H1, H2 High strength mortars
h Effective height between lateral supports
ka Area factor
kp Shape modification factor
ks Stress reduction factor
L Actual length of wall
Ld Development length
L1, L2 Lower strength mortars
M1, M2 Medium strength mortars
P Total horizontal load
Po Permissible compressive force for Reinforced Masonry
PL Plinth level
RCC Reinforced cement concrete
RS Rolled steel
s Spacing of shear reinforcement
Sp Spacing of piers/buttresses/cross walls
SR Slenderness ratio
t Actual thickness
tp Thickness of pier
tw Thickness of wall
V Total applied shear force
W Resultant load
W1 Axial load
W2 Eccentric load
wp Width of piers/buttresses/ Cross walls
μ Ratio of flexural strength of wall in the vertical direction to that in
the horizontal direction.
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Code &Commentary IS:1905
Acknowledgement
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Explanatory Examples for Structural Use of Unreinforced Masonry
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Explanatory Examples for Structural Use of Unreinforced Masonry
10.0
1.25
1.50 Wall ‘a’ W
W
2.50 b
4m
1.50 W W
2.50 b b
1.50 D 20.0
Wall ‘b’ N
W W
b b
Wall ‘c’ W
D
Solution:
Height of plinth above foundation footing = 0.7 m
Design Data/Assumptions:
Clear height of hall, h=5.5 m
Roof consists of RCC T-beams 400 mm×800 mm
with RCC slab 120 mm thick, beams being at c/c spacing of beams, sb=4.0 m
4.0 m centers. Roof covered with lime concrete Wind pressure, fw = 1200 N/m2
terrace of 150 mm average thickness.
Hall Dimension Length, L = 20 m
Modular bricks are used of the nominal size of 20
cm × 10 cm × 10 cm Width, B = 10 m
Height of parapet hp = 200 mm above slab level Size of T-beam: Width, b = 400 mm
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Explanatory Examples for Structural Use of Masonry
RCC slab
and beam
Prop
3/8 H
9
p PH
P 218
H
5/8 H
PH/8
Fixed
B M Diagram
Sectional view
Figure 1.2: Bending moment diagram of wall
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Explanatory Examples for Structural Use of Unreinforced Masonry
Moment of inertia about neutral axis is given by: Compressive stress due to dead loads (i.e. due to
self weight and load from slab)
Ic = I0 +I1
0.29 × 10 3 fd =
(
0.75 × 61.1 × 103 + 6 × 103 × 2 ) = 0.19 MPa
where, I 0 = = 24 m4 0.29 × 1000
12
Permissible shear stress (Fv) is the least of the
2 × (0.45 + 0.29 ) × 0.29 × 5.15 2
I1 = = 0.9 m4 following:
12
i) 0.5 MPa
Ic = 24+0.9 = 24.9 m4
ii) 0.1 + 0.2fd = 0.14 MPa
Check for Combined Stress: iii) 0.125 √ fm= 0.395MPa
ymax = 5+0.29 = 5.29 m (Assuming crushing strength of masonry as
Bending stresses at extreme fibers, 10 MPa )
M c × y max 280.8 × 5.29 Hence, the permissible shear stress is 0.14 MPa.
f cb = = = 0.06 MPa Actual stress being only 0.04 MPa, the wall is
Ic 24.9
safe in shear. Thus both cross walls are safe in
Combined stresses in cross walls shear and tension. Use M2 grade mortar.
= axial stress + bending stress Masonry for walls:
In case of cross wall ‘a’ combined stresses are:
Long Wall
fca1 = fcaa + fcb = 0.22+0.06 = 0.28 MPa
Masonry of cross wall should be designed for
fca2 = fcaa - fcb = 0.22-0.06 = 0.16 MPa maximum compressive stress i.e., 1.21 MPa
(both compressive) Slenderness ratio is given by:
In case of cross wall ‘b’ combined stresses are: 0.75 × (0.7 + 5.5 + 0.4)
SR = = 19
fcb1 = fcab + fcb = 0.25+0.06 = 0.31 MPa 0.26
As per Table 11, Draft code IS: 1905, Stress
Explanatory Examples for Structural Use of Unreinforced Masonry
Solutions:
Design wind speed, Vz = k1×k2×Vb
Design Data/ Assumptions:
= 0.73×0.91×47
Grade of Mortar = M1
= 31.2 m/s
Actual Size of Bricks, lb = 0.22 m,
Wind pressure, pz = 0.6Vz2
bb = 0.105 m,
= 0.6(31.2)2
tb = 0.077 m
= 584.9 N/m2
Wind Velocity, Vb = 47 m/s
Risk Coefficient factor, k1 = 0.73 Calculation of Moment of Inertia:
(for boundary wall)
Consider the diaphragm unit of length B and
Terrain & Height factor, k2 = 0.91 height H
Topography factor, k3 = 1.00 Length of diaphragm unit,
Permissible tension in masonry with M1 mortar, 10.5
B = 5.25 × 22 + +6
ft = 70000 N/m2 2
Unit weight of masonry, w = 20000 N/m3 B = 1.27 m
Overall width of unit, D = 22×2 + 10.5 + 2
Calculation of Wind Pressure:
D = 0.565 m
According to IS: 875 (Part 3): 1987,
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Explanatory Examples for Structural Use of Unreinforced Masonry
= − = 6982H2 – 20000H
12 12 Transposing and simplifying,
4
= 0.015 m (Refer to Fig 2.1) 698.2H2 - 2000H - 7000 = 0
y = D/2 = 0.282 m H2-2.86H-10=0
In accordance with the code, permissible tension Solving the quadratic equation we get
in masonry with mortar M1 is
0.07 N/mm2 = 70000 N/m2 2.86 + (2.86)2 + 4 × 1 × 10
H= = 4.9 m
and w = 20000 N/m3 2 ×1
= 5.0 m (say)
Calculating Height of Wall:
Hence, the wall can be built to a height of 5 m
Bending moment, with M1 mortar.
pz × B × H 2
M=
2
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Explanatory Examples for Structural Use of Unreinforced Masonry
D
b W a
Solution:
From Figure 3.1 it is observed that portion ‘b’ of Live load, LL= 1.5 kN/m2
wall will have the maximum stress. We will,
Unit weight of lime terrace, γlt = 20 kN/m3
however, for the sake of comparison and
illustration, work out stress at plinth level in Calculation of Loads:
portion ‘a’ of the wall as well. Since there are no
openings below PL, load disperses below plinth Parapet load, Ppt = (0.19+0.03)×0.8×20×103
and corresponding stresses get reduced = 3.5 kN/m
notwithstanding the increase in self-load of
masonry. Roof load:
Roof slab, Psl = 0.1×25×103 = 2.5 kN/m2
Given Data:
Lime terrace of 120 mm thick,
Wall thickness = 0.2 m
Plt = 0.12×20×103 = 2.4 kN/m2
Plinth height = 1.2 m
Total roof load, Pt = 1.5+2.5+2.4 = 6.4 kN/m2
Floor to ceiling height = 2.8 m
Effective Span of slab,
Clear span of RCC slab = 3.0 m
leff = ls + 0.1 =3.0+0.1 = 3.1 m
Thickness of slab = 0.1 m
Parapet Details: Roof load on wall,
Height of parapet above roof slab = 0.8 m Prw = 0.5×6.4×3.1 = 9.92 kN/m
Thickness of parapet = 0.1 m Self weight of wall,
Plaster thickness = 0.03 m Psw = (0.19+0.03)×2.8×20×103 = 12.32 kN/m
Unit weight of masonry, γm = 20 kN/m3 Portion “a” of wall:
Unit weight of concrete, γc = 25 kN/m3 Length of wall (up to centre of cross wall)
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Explanatory Examples for Structural Use of Unreinforced Masonry
from Table 12 of Draft Code IS:1905, the shape may be possible to effect economy in cost by
modification factor is given by kp = 1.1. using a lower grade masonry for walls which do
not have large openings and to use the masonry
Basic compressive stress of required masonry,
we have calculated only for the portion of wall ‘b’
f bcb which has openings in both sides. For that
fb = = 0.846 MPa
kp purpose stresses on other walls should also be
calculated and masonry design accordingly. It
So, the grade of mortar for the masonry to be used should however be kept in view that if in one
is M1 (Refer to Table 10). storey of a building, bricks and mortar of different
strength/grades are to be used a very close
Remarks: supervision is required in order to avoid mistakes.
It may be mentioned that if there is only a small
portion of wall which is carrying high stress, it
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Explanatory Examples for Structural Use of Unreinforced Masonry
GENERAL PLAN
Center Line of Bays
5.0 A A
2.5
Solution:
Thickness of external wall = 0.23 m
Design Data:
Thickness of internal corridor wall = 0.115 m
Number of stories = 3
Centre to centre height of a wall, h = 3.0 m
Number of bays = 6
Roof and floor load = 7 kN/m2
Width of building =18.5 m
Wind pressure = 1.32 kN/m2
Thickness of cross wall = 0.23 m
Unit weight of masonry = 20×103 N/m3
Bay length = 30 m
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Explanatory Examples for Structural Use of Unreinforced Masonry
Bending moment borne by one inner cross wall Referring to Table 10 of IS Code IS:1905, bricks
should be 10 MPa and M1 mortar.
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Explanatory Examples for Structural Use of Unreinforced Masonry
Control Joints
27.0
1 2 3 4 5
6.0 5.5
Solution:
Load Combinations: Load Combination 0.75(D+W):
The loading on pier 1 is shown in the figure 5.2. It Assume one brick wall with raked joints to a
is assumed that there is no gravity roof load depth of 1cm on both sides is used with unit
applied to this wall pier. Only two load weight of 20 kN/m3. Nominal thickness of wall is
combinations i.e. (i) 0.75(D+W) and (ii) 200 mm and effective wall thickness is 190 mm.
0.75(D+E) are checked, for illustration.
At the base of wall per meter length:
4.9 Factored axial load is given by
Seismic= 30 kN
P = 0.75×20×6×0.19×4.9 kN = 83.79 kN
Wind = 10 kN Factored bending moment is given by
Pier 1 M = 0.75×10×5.5 kN = 41.25 kN
6.0
5.5
Check for Tension
Area of wall is given by
A = 4.9×0.19 m2 = 0.931 m2
V
Section modulus is given by
M P 0.19 × 4.92 3
S= m = 0.76 m3
6
Figure 5.2: Loading on pier 1
In-plane flexural considerations:
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