10.1 General
This Section gives the recommendations for structural design aspect of reinforced load bearing and non-load bearing walls, constructed with solid or perforated burnt clay bricks, sand-lime bricks, stones, concrete blocks, lime based blocks or burnt clay hollow blocks in regard to the materials to be used, maximum permissible stresses and methods of design.
10.2 Terminology
For the purpose of 10, the definitions given below shall apply.
10.2.1 Cross-Sectional Area of Masonry Unit — Net cross-sectional area of a masonry unit shall be taken as the gross cross-sectional area minus the area of cellular space. Gross cross-sectional area of cored units shall be determined to the outside of the coring but cross-sectional area of grooves shall not be deducted from the gross cross-sectional area to obtain the net cross-sectional area
10.2.2 Grout — A mixture of cement, sand and water of pourable consistency for filling small voids.
10.2.3 Grouted Masonry
10.2.3.1 Grouted hollow-unit masonry — That form of grouted masonry construction in which certain designated cells of hollow units are continuously filled with grout.
10.2.3.2 Grouted multi-wythe masonry — That form of grouted masonry construction in which the space
between the wythes is solidly or periodically filled with grout.
10.2.4 Joint Reinforcement — A prefabricated reinforcement in the form of lattice truss which has been hot dip galvanized after fabrication and is to be laid in the mortar bed joint.
10.2.5 Pier — It is an isolated vertical member whose horizontal dimension measured at right angles to its thickness is not less than 4 times its thickness and whose height is less than 5 times its length.
10.2.6 Prism — An assemblage of masonry units bonded by mortar with or without grout used as a test specimen for determining properties of masonry.
10.2.7 Reinforced Masonry — Masonry which is reinforced to the minimum requirements of this Section and grouted so that the two materials act together in resisting forces.
10.2.8 Grouted Cavity Reinforced Masonry — Two parallel single leaf walls spaced at least 50 mm apart, effectively tied together with wall ties. The intervening cavity contains steel reinforcement and is filled with infill concrete so as to result in common action with masonry under load.
10.2.9 Pocket Type Reinforced Masonry — Masonry reinforced primarily to resist lateral loading where the main reinforcement is concentrated in vertical pockets formed in the tension face of the masonry and is surrounded by in situ concrete.
10.2.10 Quetta Bond Reinforced Masonry — Masonry at least one and half units thick in which vertical pockets containing reinforcement and mortar or concrete infill occur at intervals along its length.
10.2.11 Specified Compressive Strength of Masonry — Minimum Compressive strength, expressed as force per unit of net cross-section area, required of the masonry used in construction by the contract document, and upon the project design is based. Whenever the quantity is under the radical sign, the square root of numerical value only is intended and the result has units of MPa.
10.2.12 Wall Tie — A metal fastener which connects wythes of masonry to each other or to other materials.
10.2.13 Wythe — A continuous vertical tie of masonry one unit in thickness.
10.3 Materials
10.3.1 Masonry Units
10.3.1.1 Masonry units shall be bricks, blocks or stones conforming to relevant Indian Standards. Masonry units that have been previously used shall not be reused in brickwork or block work construction, unless they have
PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY
been thoroughly cleaned and conform to the code for similar new masonry units. The minimum compressive strength of masonry units used for reinforced masonry shall be 7 MPa.
10.3.1.2 The shape and dimension of masonry units, construction practices, including methods of positioning of reinforcement, placing and compacting of grout, as well as design and detailing should be such as to promote homogeneity of structural members, development of the bond of the grout to both reinforcement and masonry units and avoidance of corrosion of reinforcement.
10.3.2 Concrete
For reinforced masonry M20 grade of cement concrete (minimum cover 15 mm at top and bottom and 20 mm side cover) shall be used to ensure transfer of internal forces from steel reinforcement to masonry.
NOTE — In case cover is less or mortar is put in mortar bed, necessary precaution against corrosion shall be provided as per 10.5.10.2. High strength mortars (H1 and H2) shall be used in mortar bed.
10.3.3 Reinforcement
Steel reinforcement of grade Fe 415 or less only shall be used (see also Note under 10.5.2.1). Deformed bar shall be used.
10.3.4 Material Properties
10.3.4.1 General
Unless otherwise determined by test, the following modulus shall be used in determining the effects of elasticity.
10.3.4.2 Elastic modulus
For steel reinforcement, For clay masonry and concrete masonry, or the chord modulus of elasticity taken between 0.05 and 0.33 of the maximum compressive strength of each prism determined by test in accordance with Annex B.
10.3.4.3 Shear modulus
For clay and concrete masonry, the shear modulus is 0.4 times the elastic modulus.
10.4 Design Considerations
10.4.1 General
Design considerations shall be as per 4 along with the following provisions.
10.4.2 Structural Continuity
Intersecting structural elements intended to act as a unit shall be joined together to resist the design forces. Walls shall be joined together to all floors, roofs or other
elements which provide lateral support for the wall. Where floors or roofs are designed to transmit horizontal forces to walls, the anchorages to the walls shall be designed to resist the horizontal forces.
10.4.3 Effective Span
10.4.3.1 The effective span of simply supported/continuous members may be taken as the smaller of the following:
a) Distance between centres of supports.
b) Clear distance between supports plus an effective depth, .
10.4.3.2 Effective span of a cantilever shall be taken as,
a) distance between the end of cantilever and the centre of its support; and
b) distance between the end of cantilever and the face of support plus half its effective depth, whichever is greater.
10.4.4.1 Wall
Slenderness ratio (ratio of effective height to effective thickness ) should not exceed 27 for vertically loaded reinforced masonry walls in their plane.
For reinforced masonry members such as walls subjected to out-of-plane bending and for beams as a part of wall subjected to bending in the plane of the wall, the maximum effective span to effective depth shall be as given in Table 28.
| Sl No. | Boundary Conditions | Maximum Effective Span to Effective Depth ( ) or Effective Thickness Ratios ( ) | |
| Wall Subjected to Out-of-Plane Bending | Beam Part of Wall Subjected to In-Plane Bending | ||
| (1) | (2) | (3) | (4) |
| i) | Simply-supported | 35 | 20 |
| ii) | Continuous | 45 | 26 |
| iii) | Spanning in two directions | 45 | — |
| iv) | Cantilevered | 18 | 7 |
10.4.4.2 Columns
For a column, slenderness ratio shall be taken to be the greater of the ratios of effective heights to the respective effective thickness in the two principal directions. Slenderness ratio for a load bearing unreinforced
column shall not exceed 15 whereas for reinforced column the slenderness ratio should be limited to 20.
10.4.5 Minimum Design Dimensions
10.4.5.1 Minimum thickness of load bearing walls columns
The nominal thickness of masonry bearing walls in building shall not be less than .
10.4.5.2 Parapet wall
Parapet walls shall be at least 200 mm thick and height shall not exceed 3 times the thickness. The parapet wall shall not be thinner than the wall below.
10.4.6 Eccentricity in Columns
Columns shall be designed for a minimum eccentricity of 10 percent of side dimension for each axis in addition to applied loads.
10.5 Requirements Governing Reinforcement and Detailing
10.5.1 General
This section provides requirements for the working (allowable) stress design of masonry structure neglecting the contribution of tensile strength of masonry.
10.5.1.1 Members are designed for composite action, stresses shall be computed using transformed area concept of linear elastic analysis as follows:
where
= total transformed cross-sectional area of the member,
cross-sectional area of brick,
cross-sectional area of reinforcement, and
modular ratio of steel reinforcement and brick.
10.5.1.2 Stiffness calculation shall be based on uncracked section properties.
10.5.2 Steel Reinforcement-Allowable Stresses
10.5.2.1 Tension
Tensile stress in reinforcement shall not exceed the following:
a) MS bars confirming to accepted standard [6-4(18)]
b) HYSD bars confirming to accepted standard [6-4(19)]
NOTE — For high yield strength deformed bars of Grade Fe 500 the permissible stress shall be ; where characteristics strength of steel.
10.5.2.2 Compression
Compressive stress in reinforcement shall not exceed the following:
a) MS bars confirming to : 130 MPa confirming to accepted standard [6-4(18)]
b) HYSD bars confirming to : 190 MPa accepted standard [6-4(19)]
10.5.3 Size of Reinforcement
a) The maximum size of reinforcement used in masonry shall be 25 mm diameter bars and minimum size shall not be less than 8 mm.
b) The diameter of reinforcement shall not exceed one-half the least clear dimension of the cell, bond beam, or collar joint in which it is placed.
10.5.4 Spacing of Reinforcement
a) Clear distance between parallel bars shall not be less than the diameter of the bars, or less than 25 mm.
b) In columns and pilasters, clear distance between vertical bars shall not be less than 1.5 times the bar diameter, nor less than 35 mm.
10.5.5 Anchorage
10.5.5.1 Development length of bars
The development length for deformed bars conforming to accepted standard [6-4(19)] shall be given by the following equation but shall not be less than :
where
= nominal diameter of bar (mm), and
= permissible tensile/compressive stress in steel (MPa).
10.5.5.2 For MS bars and epoxy coated bars shall be increased by 60 percent.
10.5.5.3 Standard hooks
a) Standard hooks shall be formed by one of the following methods (see Fig. 53):
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turn plus extension of at least 4 bar diameters but not less than 64 mm at free end of bar.
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A 90° turn plus extension of at least 10 bar diameters at free end of bar.