Chapter 6General Requirements

6.1 Methods of Construction

6.2 Minimum Thickness of Walls from Consideration other than Structural

Thickness of walls determined from consideration of strength and stability may not always be adequate in respect of other requirements, such as resistance to fire, thermal insulation, sound insulation and resistance to damp penetration for which reference may be made to the appropriate Parts/Sections of the Code, and thickness suitably increased, where found necessary.

6.3.1 General

Workmanship has considerable effect on strength of

masonry and bad workmanship may reduce the strength of brick masonry to as low as half the intended strength. The basic compressive stress values for masonry as given in Table 9 holds good for commercially obtainable standards of workmanship with reasonable degree of supervision.

6.4 Joints to Control Deformation and Cracking

Special provision shall be made to control or isolate thermal and other movements so that damage to the fabric of the building is avoided and its structural sufficiency preserved. Design and installation of joints shall be done according to the appropriate

recommendations in accordance with good practice [6-4(6)].

6.6.1 Where corbelling is required for the support of some structural element, maximum projection of masonry unit should not exceed one-half of the height of the unit or one-half of the built-in part of the unit and the maximum horizontal projection of the corbel should not exceed one-third of the wall thickness.

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 5.4.

6.6.3 It is preferable to adopt header courses in the corbelled portion of masonry from considerations of economy and stability.

7 REINFORCED BRICK AND REINFORCED BRICK CONCRETE FLOORS AND ROOFS

The construction and design of reinforced brick and reinforced brick concrete floors and roof shall be in accordance with good practices [6-4(7)].

8 SPECIAL CONSIDERATION FROM EARTHQUAKE POINT OF VIEW

8.0 Special features of design and construction for earthquake resistant masonry buildings are given in 8.2 to 8.8.2. However, special features of design and construction for improving earthquake resistance of low strength masonry buildings is covered in 9.

8.1 For the purpose of 8 and 9, the definitions given below shall apply in addition to those given in 2.

8.1.1 Separation Section — A gap of specified width

between adjacent buildings or parts of the same building either left uncovered or covered suitably to permit movement in order to avoid pounding due to earthquake.

8.1.1.1 Crumple section — The separation gap filled with appropriate material that crumples or factures in the event of an earthquake.

8.1.2 Centre of Rigidity — The point in a structure where application of lateral force produces equal deflections of its components at any level in any particular direction.

8.1.3 Shear Wall — A wall designed to resist lateral force in the own plane. Braced frames, subjected primarily to axial stresses, shall be considered as shear walls for the purpose of this definition.

8.1.4 Space Frame — A three-dimensional structural system comprised of interconnected members, without shear or bearing walls, so that to function as a complete self-contained unit with or without the aid of horizontal diaphragms or floor bracing systems.

8.1.4.1 Vertical load carrying frame — A space frame designed to carry all the vertical loads, the horizontal loads being resisted by shear walls.

8.1.4.2 Moment resistant frame — A space frame capable of carrying all vertical and horizontal loads, by developing bending moments in the members and at joints.

8.1.4.3 Moment resistant frame with shear walls — A space frame with moment resistant joints and strengthened by shear walls to assist in carrying horizontal loads.

8.1.5 Box System — A bearing wall structure without a space frame, the horizontal forces being resisted by the walls that act as shear walls.

8.1.6 Band — A reinforced concrete or reinforced brick runner provided in the walls to tie them together and to impart horizontal bending strength in them.

NOTE — For low strength masonry buildings, wooden runners may also be used as runner.

8.1.7 Seismic Zone and Seismic Coefficient — The Seismic Zones II to IV as classified in 5 of Part 6 'Structural Design, Section 1 Loads, Forces and Effects' of the Code and corresponding basic seismic coefficient $\alpha_{\mathrm{o}}$ as specified in 3.4 of good practice [6-4(8)].

8.1.8 Design Horizontal Seismic Coefficient — The value of horizontal seismic coefficient $A_{h}$ computed taking into account the soil-foundation system and the importance factor as specified in 6.4 of good practice [6-4(9)].

8.1.9 Concrete Grades — 28 day compressive strength

of concrete cubes of $150\mathrm{mm}$ size, in MPa; for example, for Grade M20 as per good practice[6-4(10)], the characteristic compressive strength equals to $20\mathrm{MPa}$.

8.1.10 Zone Factor (Z) — It is a factor to obtain the design spectrum depending on the perceived maximum seismic risk characterized by maximum considered earthquake (MCE) in the zone in which the structure is located.

The general principles given in 8.2.1 to 8.2.9 shall be observed in construction of earthquake resistant buildings.

8.2.1 Lightness

Since the earthquake force is a function of mass, the weight of the building shall be as minimum as possible, consistent with structural safety and functional requirements. Roofs and upper storeys of buildings, in particular, should be designed as light as possible.

8.2.2 Continuity of Construction

8.2.2.1 As far as possible, the parts of the building should be tied together in such a manner that the building acts as one unit.

8.2.2.2 For parts of buildings between separation or crumple sections to expansion joints, floor slabs shall be continuous throughout as far as possible. Concrete slabs shall be rigidly connected or integrally cast with the support beams.

8.2.2.3 Additions to the structures shall be accompanied by the provision of separation or crumple sections between the new and the existing structures as far as possible, unless positive measures are taken to establish continuity between the existing and the new construction.

8.2.2.4 Alteration to the building structure shall be done by maintaining its structural stability by ensuring proper load path.

8.2.3 Projecting and Suspended Parts

8.2.3.1 Projecting parts shall be avoided as far as possible. If the projecting parts cannot be avoided, they shall be properly reinforced and firmly tied to the main structure, and their design shall be in accordance with good practice [6-4(8)].

8.2.3.2 Ceiling plaster shall preferably be avoided. When it is unavoidable, the plaster shall be as thin as possible.

8.2.3.3 Suspended ceiling shall be avoided as far as possible. Where provided they shall be light, adequately framed and secured to which electrical fixtures shall be fully secured.

8.2.4 Building Configuration

8.2.4.1 In order to minimise torsion and stress concentration, provisions given in 8.2.4.2 to 8.2.4.4 should be complied with as relevant.

8.2.4.2 The building should have a simple rectangular plan and be symmetrical both with respect to mass and rigidity so that the centre of mass and rigidity of the building coincide with each other in which case no separation sections other than expansion joints are necessary. For provision of expansion joints reference may be made to good practice [6-4(6)].

8.2.4.3 If symmetry of the structure is not possible in plan, elevation or mass, provision shall be made for torsional and other effects due to earthquake forces in the structural design or the parts of different rigidities may be separated through crumple sections. The length of such building between separation sections shall not preferably exceed three times the width.

NOTE — As an alternative to separation section to reduce torsional moments, the centre of rigidity of the building may be brought close or coincident to the centre of mass by adjusting the locations and/or sizes of columns and walls.

8.2.4.4 Buildings having plans with shapes like L, T, E and Y shall preferably be separated into rectangular parts by providing separation sections at appropriate places. Typical examples are shown in Fig. 15.

NOTES

1 The buildings with small lengths of projections forming L, T, E or Y shapes need not be provided with separation section. In each cases the length of the projection may not exceed 15 to 20 percent of the total dimension of the building in the direction of the projection (see Fig. 16).

2 For buildings with minor asymmetry in plan and elevation, separation sections may be omitted.

8.2.5 Strength in Various Directions

The structure shall be designed to have adequate strength against earthquake effects along both the horizontal axes. The design shall also be safe considering the reversible nature of earthquake forces.

8.2.6 Foundations

The structure shall not be founded on such soils which shall subside or liquefy during an earthquake, resulting in large differential settlements (see also 8.3.3.3).

8.2.7 Ductility

The main structural elements and their connection shall be designed to have a ductile failure. This shall enable the structure to absorb energy during earthquakes to avoid sudden collapse of the structure. Providing reinforcing steel in masonry at critical sections, as specified in this Section shall not only increase strength and stability but also ductility. The details for achieving ductility in reinforced concrete structures is given in good practice [6-4(11)].

L - SHAPE

T-SHAPE

Y-SHAPE

Y-SHAPE

E-SHAPE

FIG. 15 TYPICAL SHAPES OF BUILDING WITH SEPARATION SECTIONS

16B Vertical Irregularities

FIG. 16 PLAN AND VERTICAL IRREGULARITIES

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

8.2.8 Damage to Non-Structural Parts

Suitable details shall be worked out to connect the non-structural parts with the structural framing so that the deformation of the structural frame leads to minimum damage of the non-structural elements.

8.2.9 Fire Safety

Fire frequently follows an earthquake and therefore, buildings shall be constructed to make them fire resistant in accordance with the provisions of Part 4 ‘Fire and Life Safety’ of the Code for fire safety.

8.3.1 Separation of Adjoining Structures

8.3.1.1 Separation of adjoining structures or parts of the same structure is required for structures having different total heights or storey heights and different dynamic characteristics. This is to avoid collision during an earthquake.

8.3.1.2 Minimum width of separation gaps as mentioned in 8.3.1.1, shall be as specified in Table 13. The design seismic coefficient to be used shall be in accordance with 5 of Part 6 'Structural Design, Section 1 Loads, Forces and Effects' of the Code.

8.3.1.3 Where separation is necessary, a complete separation of the parts shall be made except below the plinth level. The plinth beams, foundation beams and footings may be continuous. Where separation sections

17A BRICK WALL

17C METAL SIDING INDUSTRIAL WORK

$^{1)}$ See Table 14.

NOTE — Minimum total gap shall be 25 mm. For any other value of $A_{h}$ the gap width shall be determined proportionately.

are provided in a long building, they shall take care of movement owing to temperature changes also.

8.3.2 Separation or Crumple Section

8.3.2.1 In case of framed construction, members shall be duplicated on either side of the separation or crumple section. As an alternative, in certain cases, such duplication may not be provided, if the portions on either side can act as cantilevers to take the weight of the building and other relevant loads.

8.3.2.2 Typical details of separation and crumple sections are shown in Fig. 17. For other types of joint details, reference may be made to good practice [6-4(6)].

17B CONCRETE WALLS

17D WOOD SHEATHING INDUSTRIAL WORK

FIG. 17 TYPICAL DETAILS OF SEPARATION OR CRUMPLE SECTION (CONTINUED)

17E RCC SLAB ON ROOF SURFACE

17F SEPARATION JOINT DETAILS AT ROOF

NOTE — Fragile cover may consist of asbestos cement sheet, particle board and like.

FIG. 17 TYPICAL DETAILS OF SEPARATION OR CRUMPLE SECTION

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

8.3.3 Foundations

8.3.3.1 For the design of foundations, the provisions of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ and Section 2 ‘Soils and Foundation’ of the Code shall generally be followed.

8.3.3.2 The subgrade below the entire area of the building shall preferably be of the same type of the soil. Wherever this is not possible, a suitably located separation or crumple section shall be provided.

8.3.3.3 Loose fine sand, soft silt and expansive clays should be avoided. If unavoidable, the building shall rest either on a rigid raft foundation or on piles taken to a firm stratum. However, for light constructions the following measures may be taken to improve the soil on which the foundation of the building may rest:

a) Sand piling, and

b) Soil stabilization.

8.3.4 Roofs and Floors

8.3.4.1 Flat roof or floor shall not preferably be made of tiles of ordinary bricks supported on steel, timber or reinforced concrete joists, nor they shall be of a type which in the event of an earthquake is likely to be loosened and parts or all of which may fall. If this type of construction cannot be avoided, the joists should be blocked at ends and bridged at intervals such that their spacing is not altered during an earthquake.

8.3.4.1.1 For pitched roofs, corrugated iron or asbestos sheets shall be used in preference to country, Allahabad or Mangalore tiles or other loose roofing units. All roofing materials shall be properly tied to the supporting members. Heavy roofing materials shall generally be avoided.

8.3.5 Staircases

8.3.5.1 The inter-connection of the stairs with the adjacent floors should be appropriately treated by providing sliding joints at the stairs to eliminate their bracing effect on the floors. Large stair halls shall preferably be separated from the rest of the building by means of separation or crumple sections.

8.3.5.2 Three types of stair construction may be adopted as described below:

a) Separated staircases — One end of the staircase rests on a wall and the other end is carried by columns and beams which have no

connection with the floors. The gap at the vertical joints between the floor and the staircase may be covered either with a tread plate attached to one side of the joint and sliding on the other side, or covered with some appropriate material which could crumple or fracture during an earthquake without causing structural damage. The supporting members, columns or walls, are isolated from the surrounding floors by means of separation or crumple sections. A typical example is shown in Fig. 18.

as mentioned in respect of separated staircases, shall not be necessary.

The two walls mentioned above, enclosing the staircase, shall extend through the entire height of the stairs and to the building foundations.

c) Staircases with sliding joints — In case it is not possible to provide rigid walls around stair openings for built-in staircase or to adopt the separated staircases, the staircases shall have sliding joints so that they shall not act as diagonal bracing.

b) Built-in staircase — When stairs are built monolithically with floors, they can be protected against damage by providing rigid walls at the stair opening. An arrangement, in which the staircase is enclosed by two walls, is given in Fig. 19. In such cases, the joints,

8.4.1 The types of construction usually adopted in buildings are as follows:

a) Framed construction; and

b) Box type construction.

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

8.4.2 Framed Construction

This type of construction is suitable for multi-storied and industrial buildings as described in 8.4.2.1 and 8.4.2.2.

8.4.3 Box Type Construction

This type of construction consists of prefabricated or in-situ masonry, concrete or reinforced concrete walls along both the axes of the building. The walls support vertical loads and also act as shear walls for horizontal loads acting in any direction. All traditional masonry construction falls under this category. In prefabricated construction attention shall be paid to the connection between wall panels so that transfer of shear between them is ensured.

8.5.1 For the purpose of specifying the earthquake resisting features in masonry and wooden buildings, the buildings have been categorized in four categories B to E based on the seismic zone and the importance of the building I,

where

$I =$ Importance factor applicable to the building {as per good practice [6-4(9)]}.

8.5.1.1 The building categories are given in Table 14.

NOTE — Category A is now defunct as Seismic Zone I does not exist any more.

8.6.1 The design and construction of masonry walls using rectangular masonry units in general shall be governed by 3 to 7 of this Section and good practice [6-4(5)].

8.6.1.1 Masonry units

8.6.1.1.1 Well burnt bricks conforming to accepted standard $[6-4(12)]$ or solid concrete blocks conforming to accepted standard $[6-4(13)]$ and having a crushing strength not less than 3.5 MPa shall be used. The strength of masonry unit required shall depend upon

number of storeys and thickness of walls (see 3 to 6).

8.6.1.1.2 Squared stone masonry, stone block masonry or hollow concrete block masonry, as specified in the good practice [6-4(14)] of adequate strength, may also be used.

8.6.1.2 Mortar

8.6.1.2.1 Mortars, such as those given in Table 15 or of equivalent specification, shall preferably be used for masonry construction for various categories of buildings.

8.6.1.2.2 Where steel reinforcing bars are provided in masonry, the bars shall be embedded with adequate cover in cement sand mortar not leaner than 1 : 3 (minimum clear cover 10 mm) or in cement concrete of grade M20 (minimum clear cover 15 mm or bar diameter whichever is more), so as to achieve good bond and corrosion resistance.

8.6.3.1 Door and window openings in walls reduce their lateral load resistance and hence, should preferably be small and more centrally located. The guidelines on the size and position of opening are given in Table 16 and Fig. 21.

8.6.3.2 Openings in any storey shall preferably have their top at the same level so that a continuous band could be provided over them, including the lintels throughout the building.

FIG. 21 RECOMMENDED DIMENSIONS OF OPENINGS AND PIERS (SEE TABLE 16)

2 — ROOF/FLOOR BAND 5 — WINDOW

8.6.3.3 Where openings do not comply with the guidelines of Table 15, they should be strengthened by providing reinforced concrete or reinforcing the brickwork, as shown in Fig. 22 with high strength deformed (HSD) bars of 8 mm diameter but the quantity of steel shall be increased at the jambs to comply with 8.6.4.9, if so required.

FIG. 22 STRENGTHENING MASONRY AROUND OPENINGS

8.6.3.4 If a window or ventilator is to be projected out, the projection shall be in reinforced masonry or concrete and well anchored.

8.6.3.5 If an opening is tall from bottom to almost top of a storey, thus dividing the wall into two portions, these portions shall be reinforced with horizontal reinforcement of 6 mm diameter bars at not more than 450 mm intervals, one on inner and one on outer face, properly tied to vertical steel at jambs, corners or junction of walls, where used.

8.6.3.6 The use of arches to span over the openings is a source of weakness and shall be avoided. Otherwise, steel ties should be provided.

8.6.4.1 All masonry buildings shall be strengthened by the methods, as specified for various categories of

buildings, as listed in Table 17, and detailed in subsequent clauses. Figures 23 and 24 show, schematically, the overall strengthening arrangements to be adopted for category D and E buildings which consist of horizontal bands of reinforcement at critical levels, vertical reinforcing bars at corners, junctions of walls and jambs of openings.

FIG. 23 OVERALL ARRANGEMENT OF REINFORCING LOW STRENGTH MASONRY BUILDINGS

6 — VERTICAL STEEL BAR

8 — HOLDING DOWN BOLT

a) PERSPECTIVE VIEW

b) DETAILS OF TRUSS CONNECTION WITH WALL

c) DETAIL OF INTEGRATING DOOR LINTEL WITH ROOF BAND

FIG. 24 OVERALL ARRANGEMENT OF REINFORCING LOW STRENGTH MASONRY BUILDING HAVING PITCHED ROOF

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

where

8.6.4.2 Lintel band is a band (see 8.1.6) provided at lintel level on all load bearing internal, external longitudinal and cross walls. The specifications of the band are given in 8.6.4.5.

NOTE — Lintel band, if provided in panel or partition walls also shall improve their stability during severe earthquake.

8.6.4.3 Roof band is a band (see 8.1.6) provided immediately below the roof or floors. The specifications

Table 17 Strengthening Arrangements Recommended for Masonry Buildings (Rectangular Masonry Units)

(Clause 8.6.4.1)

$^{1)}$ 4 $^{th}$ storey not allowed in category E.

a = masonry mortar (see 8.6.1.2);

b = lintel band (see 8.6.4.2);

c = roof band and gable band where necessary (see 8.6.4.3 and 8.6.4.4);

d = vertical steel at corners and junctions of walls (see 8.6.4.8);

e = vertical steel at jambs of openings (see 8.6.4.9);

f = bracing in plan at tie level of roofs (see 8.3.4.2.2);

g = plinth band where necessary (see 8.6.4.6); and

h = dowel bars (see 8.6.4.7).

NOTE — In case of four storey buildings of category B, the requirements of vertical steel may be checked through a seismic analysis using a design seismic co-efficient equal to four times the one given in 5 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ of the Code (this is because the brittle behaviour of masonry in the absence of a vertical steel results in much higher effective seismic force than that envisaged in the seismic coefficient, provided in the Code). If this analysis shows that vertical steel is not required the designer may take the decision accordingly.

NOTE — In coastal areas, the concrete grade shall be M30 concrete and the filling mortar of 1 : 3 (H1) (cement-sand with water proofing admixture).

of the band are given in 8.6.4.5. Such a band need not be provided underneath reinforced concrete or brickwork slabs resting on bearing walls, provided that the slabs are continuous over the intermediate wall up to the crumple sections, if any, and cover the width of end walls, fully or at least $\frac{3}{4}$ of the wall thickness.

8.6.4.4 Gable band is a band provided at the top of gable masonry below the purlins. The specifications of the band are given in 8.6.4.5. This band shall be made continuous with the roof band at the eaves level.

8.6.4.5 Section and reinforcement of band

The band shall be made of reinforced concrete of grade not leaner than M20 or reinforced brickwork in cement mortar not leaner than 1 : 3 (H1). The bands shall be of the full width of the wall not less than 75 mm in depth and reinforced with steel, as indicated in Table 18.

8.6.4.8 Vertical reinforcement

Vertical steel at corners and junctions of walls, which are up to 340 mm (1½ brick) thick, shall be provided as specified in Table 19. For walls thicker than 340 mm the area of the bars shall be proportionately increased. For earthquake resistant framed wall construction, see 8.6.5.

8.6.4.8.1 The vertical reinforcement shall be properly embedded in the plinth masonry of foundations and roof slab or roof band so as to develop its tensile strength in bond. It shall be passing through the lintel bands and floor slabs or floor level bands in all storeys.

Bars in different storeys may be welded {see good practices [6-4(15)] and [6-4(16)], as relevant} or suitably lapped.

NOTE — Typical details of providing vertical steel in brickwork masonry with rectangular solid units at corners and T-junctions are shown in Fig. 26.

8.6.4.9 Vertical reinforcement at jambs of window and door openings shall be provided as per Table 19. It

1 The diameters given above are for HSD bars.

2 The vertical bars shall be covered with concrete M20 or mortar 1:3 grade in suitably created pockets around the bars (see Fig. 26). This shall ensure their safety from corrosion and good bond with masonry.

Load bearing walls can be made thinner than 200 mm say 150 mm inclusive of plastering on both sides. Reinforced concrete framing columns and collar beams shall be necessary to be constructed to have full bond with the walls. Columns are to be located at all corners and junctions of walls and spaced not more than 1.5 m apart but so located as to frame up the doors and windows. The horizontal bands or ring beams are located at all floors, roof as well as lintel levels of the openings. The sequence of construction between walls and columns shall be first to build the wall up to 4 to 6 courses height leaving toothed gaps (tooth projection being about 40 mm only) for the

FIG. 27 FRAMING OF THIN LOAD-BEARING BRICK WALL

columns and second to pour M20 (1 : 1½ : 3) concrete to fill the columns against the walls using wood forms only on two sides. The columns steel should be accurately held in position all along. The band concrete should be cast on the wall masonry directly so as to develop full bond with it.

Such construction may be limited to only two storeys maximum in view of its vertical load carrying capacity. The horizontal length of walls between cross walls shall be restricted to 7 m and the storey height to 3 m.

The following details may be followed in placing the horizontal and vertical steel in hollow block masonry using cement-sand or cement-concrete blocks.

8.6.6.1 Horizontal band

U-shaped blocks may be used for construction of horizontal bands at various levels of the storeys as shown in Fig. 28, where the amount of horizontal reinforcement shall be taken 25 percent more than that given in Table 18 and provided by using four bars and 6 mm diameter stirrups. Other continuity details shall be followed, as shown in Fig. 25.

FIG. 28 U-BLOCKS FOR HORIZONTAL BANDS

8.6.6.2 Vertical reinforcement

Bars, as specified in Table 19 shall be located inside the cavities of the hollow blocks, one bar in each cavity (see Fig. 29). Where more than one bar is planned these can be located in two or three consecutive cavities. The cavities containing bars are to be filled by using micro-concrete 1:2:3 or cement coarse sand mortar 1:3, and properly rodded for compaction. The vertical bars should be spliced by welding or overlapping for developing full tensile strength. For proper bonding, the overlapped bars should be tied together by winding the binding wire over the lapped length. To reduce the number of overlaps, the blocks may be made U-shaped as shown in Fig. 29 which shall avoid lifting and threading of bars into the hollows.

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

NOTE—OVERLAPPING OF VERTICAL REINFORCEMENT = 50D, AND D = DIAMETER OF THE REINFORCEMENT.

FIG. 29 VERTICAL REINFORCEMENT IN CAVITIES

8.7.1 Types of Precast Floors/Roofs

Earthquake resistance measures for floors and roofs with small precast components, as covered in this Section, have been dealt with as typical examples.

8.7.2 Seismic Resistance Measures

8.7.2.1 All floors and roofs to be constructed with small precast components shall be strengthened as specified for various categories of buildings in Table 20. The strengthening measures are detailed in 8.7.2.3 and 8.7.2.8.

8.7.2.2 Vertical castellation, called shear keys, shall be provided on the longitudinal faces of the channel, cored and waffle units to enable them to transfer horizontal shear force from one unit to the adjacent unit through the in-situ concrete filled in the joints between the units. The minimum percentage of area of shear keys as calculated below, on each face of the unit, shall be 15.

Shear keys shall have a minimum width of 40 mm at its root with the body of the component and shall be to the full height of the component and preferably at uniform spacing. Percentage of area of shear keys shall be calculated as:

8.7.2.3 Tie beam (see Table 20) is a beam provided all round the floor or roof to bind together all the precast components to make it a diaphragm. The beams shall be to the full width of the supporting wall or beam less the bearing of the precast components. The depth of the beam shall be equal to the depth of the precast components plus the thickness of structural deck concrete, where used over the components. The beam shall be made of cement concrete of grade not leaner

8.8.1 Timber has higher strength per unit weight and is, therefore, very suitable for earthquake resistant construction. Materials, design and construction in timber shall generally conform to good practice [6-4(17)].

FIG. 40 CONNECTION OF PRECAST Cored/CHANNEL UNIT WITH TIE BEAM

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

All dimensions in millimetres.

FIG. 41 CONNECTION OF CHANNEL/CORED UNIT FLOOR/ROOF (WITH DECK CONCRETE) WITH TIE BEAM

FIG. 42 CONNECTION OF PRECAST REINFORCED CONCRETE PLANK AND PRECAST BRICK PANEL FLOOR/ROOF (WITH DECK CONCRETE) WITH TIE BEAM

8.8.2 Timber (with masonry in-fill) construction shall generally be restricted to two storeys with or without the attic floor.

8.8.3 In timber (with masonry in-fill) construction attention shall be paid to fire safety against electric short circuiting, kitchen fire, etc.

8.8.4 The superstructure of timber buildings shall be made rigid against deformations by adopting suitable construction details at the junctions of the framing members and in wall panels as given in 8.8.6 to 8.8.10

so that the construction as a whole behaves as one unit against earthquake forces.

8.8.5 Foundations

8.8.5.1 Timber construction shall preferably start above the plinth level, the portion below shall be in masonry or concrete.

8.8.5.2 The superstructure may be connected with the foundation in one of the two ways as given below:

a) The superstructure may simply rest on the

All dimensions in millimetres.

FIG. 43 CONNECTION OF PRECAST WAFFLE UNIT FLOOR/ROOF (WITH DECK CONCRETE) WITH TIE BEAM

FIG. 44 PROVISION OF REINFORCEMENT IN CONCRETE FLOOR FINISH

plinth masonry, or in the case of small buildings of one storey having plan area less than about $50 \, m^{2}$ , it may rest on firm plane ground so that the building is free to slide laterally during ground motion.

1 Past experience has shown that superstructure of the buildings not fixed with the foundation escaped collapse even in a severe earthquake although they were shifted sideways.

2 Where fittings for water supply or water borne sanitation from the house are to be installed, proper attention should be given to permit movement so as to avoid fracture of damage to pipes.

b) The superstructure may be rigidly fixed into

the plinth masonry or concrete foundation as given in Fig. 45 or in case of small building having plan area less than $50 \, m^{2}$ , it may be fixed to vertical poles embedded into the ground. In each case the building is likely to move along with its foundation. Therefore, the superstructure shall be designed to carry the resulting earthquake shears.

8.9 Confined Masonry Building Construction

For the provisions relating to confined masonry building construction (see Annex E).