3- IS 1905 1987 Masonry Code.pptx

Masonry

1. Code of practice for structural use of unreinforced masonry IS1905:1987

2. GENERAL This code gives the recommendations for structural design aspects of unreinforced load bearing and non load bearing walls, constructed with solid and perforated burnt clay bricks, sand lime bricks, stone, concrete blocks in regard to the material to be used and maximum permissible stresses and method of design Recommendations of the code do not apply to walls constructed in mud mortars

3. Important terminology Bed block :- A block bedded on a wall, column or pier to disperse a concentrated load on a masonry unit Bond :- Arrangement of masonry units in successive courses to tie the masonry together both longitudinally and transversely Column :- An isolated vertical load bearing member, width of which does not exceed four times the thickness Pier :- A thickened section forming integral part of wall placed at regular interval along the wall, to increase the stiffness of wall

4. Buttress :- A pier of masonry built as an integral part of wall and projecting from both the surfaces, and decreasing in cross section area from base to bottom Cross section area of masonry units :- Net cross section area of masonry unit shall be taken as gross c/s area minus area of cellular space Curtain wall :- A non load bearing wall subjected to lateral loads and it may be laterally supported by vertical or horizontal structural members Important terminology

5. Hollow unit :- A masonry unit of which net cross sectional area in any plane parallel to the bearing surface is less than 75% of its gross cross sectional area measured in the same plane Grout :- Mortar of pourable consistency Panel wall :- An exterior non load bearing wall in framed construction , wholly supported at each storey but subjected to lateral loads Shear wall :- A wall designed to carry horizontal forces acting in its plane with or without vertical imposed loads Partition wall :- An interior non load bearing wall, one storey or part storey in height Important terminology

6. Veneered wall :- A wall in which facing is attached to backing but not so bonded as to result in a common action under load Cavity wall:- A wall comprising two leaves, each leaf being built of masonry units and metal ties or bonding units to ensure that two leaves act as one structural unit Faced wall :- A wall in which facing and backing of two different material bonded together to ensure common action under load TYPES OF WALL

7. Design considerations Masonry structures gain stability from the support offered by cross walls, floors, roofs and other elements such as piers, buttress Load bearing walls are structurally more efficient when the load is uniformly distributed and structure is so planned that eccentricity of loading on members as small as possible Avoidance of eccentric loading by providing adequate bearing of floor and roof on walls providing adequate stiffness in slab and avoiding fixity at support is especially important in load bearing wall in multistory buildings

8. Lateral support Lateral support for a masonry element is intended to Reduce the possibility of buckling of member due to vertical loads To resist the horizontal component of forces to ensure the stability against overturning Lateral support may be in both horizontal and vertical direction

9. In case of a wall, where slenderness ratio is based on effective height, any of the following constructions are provided RCC floor/roof slab irrespective of the direction of span, bears on supported wall as well as cross wall to extent of at least 9 cm RCC floor/roof slab not bearing on the supported wall or cross wall is anchored to it with non corrodible metals ties of 60 cm length and of section not less than 6mm x 30mm and at intervals not exceeding 2m Lateral support

10. If precast RCC units are used for floors and roofs, it is necessary to interconnect them and suitably anchor them to the cross walls For small houses up to two storeys , stiffening effect of partition wall or cross walls should be such that metal anchors are not necessary in case of timber floor/roof and precast RCC floor/roof units Lateral support

11. Lateral support Anchoring of RCC Slab with Masonry wall

12. Lateral support Joist Right angle to wall Joist Parallel to wall Anchoring of Joisted floor with Masonry wall

13. Lateral support Joist Right angle to wall Anchoring of timber floors with cavity wall

14. Lateral support Joist Parallel to wall Anchoring of timber floors with cavity wall

15. In case of wall when slenderness ratio is based on the effective length of wall A cross wall/pier/buttress of thickness equal to or more than half the thickness of supported wall or 90mm whichever is more and length equal to or more than one fifth of the height of wall is built at right angle to wall Lateral support

16. Lateral support Dimension for Masonry Wall or Buttress providing effective lateral support

17. Lateral support Lateral support by buttress

18. Lateral support Lateral support by pier/ cross walls

19. In case of column, RCC beam forms part of beam and slab construction and is supported on column, and slab adequately bears on stiffening walls This construction will provide lateral support to column in the direction of both the horizontal axis In case of column, RCC or timber beam is supported on the column In this case the column will not be deemed to be laterally supported In the direction right angle to it Lateral support

20. Lateral support RCC Slab giving lateral support at top RCC Beam giving support to column in direction of t RCC Beam giving support to column in direction of both t and b

21. A trussed roofing may not‘ provide lateral support, unless special measures are adopted to brace and anchor the roofing Residential and similar buildings of conventional design with trussed roofing having cross walls, the stability requirements are assumed to be met with by the cross walls Lateral support

22. stability A wall or a column subjected to vertical and lateral loads may be considered to be provided with adequate lateral support from consideration of stability, if the construction providing the support is capable of resisting the following forces:- Simple static reaction at the point of lateral support to all the lateral loads; plus 2.5% of total vertical load that the wall and column is designed to carry at the point of lateral support

23. Stability requirement for load bearing buildings up to 4 storeys may deemed to have met if Height to width ratio of building does not exceed 2; Cross wall acting as stiffening walls continuous from outer wall to outer wall or to a load bearing inner and of thickness and spacing given in following table is provided If the walls that are in line are interrupted by opening, length of solid wall shall be at least one fifth of height of opening stability

24. stability Thickness and Spacing of Stiffening Walls

25. stability Location of Opening in Stiffening Wall

26. Floors and roof bear on cross walls such that all lateral loads are safely transmitted to those walls and through them to foundation Cross walls are built jointly with the bearing walls or the two interconnected by toothing Alternatively cross wall may be anchored to walls to be supported by ties of non corrodible metal of minimum section 6x35mm and length of 60 cm with ends bent up at least 5cm; maximum vertical spacing to ties being 1.2 If hall length exceeds 8 m, then safety and lateral support shall be checked by analysis stability

27. stability Anchoring of Stiffening Wall with Supported Wall

28. Capacity of cross wall (shear wall) to take horizontal loads and consequent bending moments, increases when parts of bearing of walls act as flange to the cross wall Maximum overhanging length of bearing wall which could effectively function as flange should be taken as Lesser of 12t or H/6 (for T/I shaped walls) Lesser of 6t or H/16 (for L/U shaped walls) t = thickness of bearing wall H = total height of wall stability

29. stability

30. stability

31. External wall of basement and plinth Stability requirements may be deemed to have been met if, Bricks used in basement and plinth have a minimum crushing strength of 5 N/mm 2 and mortar used in masonry is of grade M1 or better Clear height of ceiling in basement does not exceed does not exceed 2.6 In the zone of action of soil pressure on basement walls, traffic load excluding any surcharge due to adjoining building does not exceed 5 kN /M 2 and terrain does not rise

32. External wall of basement and plinth Minimum Thickness of Basement Walls

33. Walls mainly subjected to lateral loads Free standing wall:- Compound/parapet wall is acted upon by a wind force which tend to overturn it This tendency of overturning is resisted by gravity force due to self weight and also by flexural moment of resistance on account of tensile strength of masonry Stability of free standing wall shall be ensured such that stability moment of wall due to self weight equals or exceed 1.5 times the overturning moment

34. Retaining wall:- Stability for retaining wall shall normally be achieved through gravity action but flexural moment of resistance could also be taken advantage of under special circumstances at discretion of designer Walls mainly subjected to lateral loads

35. EFFECTIVE HEIGHT OF WALLS

36. EFFECTIVE HEIGHT OF WALLS

37. EFFECTIVE HEIGHT OF WALLS

38. EFFECTIVE HEIGHT OF WALLS

39. EFFECTIVE HEIGHT OF WALLS

40. EFFECTIVE HEIGHT OF WALLS

41. Effective height of column In case of column ,the effective height is taken as actual height for the direction it is laterally supported and as twice of the actual height for the direction it is not supported laterally

42. Effective height for openings Effective height of columns formed by openings in a wall is calculated for two cases When wall as full restraint at top and bottom When wall has partial restraint at top and bottom

43. Effective height for openings

44. Effective height for openings Restraint to the wall/column is considered in two ways RCC Slab bearing on wall provides full restraint to wall Timber floor comprising of timber joints and planking provides partial restraint

45. Effective height for openings Wall having full restraint

46. Effective height for openings Wall having Partial restraint

47. Effective length of wall

48. Effective length of wall

49. Effective length of wall

50. Effective length of wall

51. Effective length of wall If opening height > 0.5H, ends at opening are free

52. Effective length of wall If, opening is closer than 1/8 of height of wall from cross wall

53. Effective thickness to be used for calculation of slenderness ratio of a wall or column shall be taken as For solid walls/faced walls/column effective thickness shall be the actual thickness For solid walls adequately bonded into piers and buttresses effective thickness for determining slenderness ratio based on effective height shall be actual thickness of wall multiplied by stiffening coefficient Effective THICKNESSS of wall

54. Effective THICKNESSS of wall Stiffening coefficient for walls stiffened by piers/ buttresses/ cross walls S p = c/c spacing of pier, t w = actual thickness of wall t p = thickness of pier, w p = width of pier in direction of wall

55. No modification done when slenderness ratio is based on effective length of wall For solid walls or faced walls stiffened by cross wall, stiffening coefficient is determined assuming cross walls equivalent to piers of width equal to thickness of cross wall and of length equal to three times the thickness of stiffening wall For cavity walls with both leaves of uniform thickness, effective thickness shall be taken as two third the sum of the actual thickness of two leaves Effective THICKNESSS of wall

56. Section of a wall with tendency to buckle around horizontal axis under vertical load Buckling pattern of walls

57. Plan of a wall with tendency to buckle around vertical axis under vertical load Buckling pattern of walls

58. Slenderness ratio For walls slenderness ratio shall be effective height divided by effective thickness or effective length divided by the effective thickness, whichever is less In case of load bearing wall, slenderness ratio shall not exceed as

59. For column the slenderness ratio shall be taken to be the greater of ratio of effective heights to the respective effective thickness in the two principle directions Slenderness ratio for a load bearing column shall not exceed 12 Slenderness ratio

60. Structural design The building shall be analyzed to ensure safe and proper functioning in service of its component parts Design loads :- Loads considered for design of masonry components of a structure are dead load of walls, columns, floors and roofs Live/imposed loads over floors and roofs seismic forces on the structure wind load on vertical and sloping parts of structure

61. Permissible stresses Mortar Type 3.5 5.0 7.5 10 12.5 15 17.5 20 H1 0..35 0.50 0.75 1.00 1.16 1.31 1.45 1.59 H2 0.35 0.50 0.74 0.96 1.09 1.19 1.30 1.41 M1 0.35 0.50 0.74 0.96 1.06 1.13 1.20 1.27 M2 0.35 0.44 0.59 0.81 0.94 1.03 1.10 1.17 M3 0.25 0.41 0.56 0.75 0.87 0.95 1.02 1.10 L1 0.25 0.36 0.53 0.67 0.76 0.83 0.90 0.97 L2 0.25 0.31 0.42 0.53 0.58 0.61 0.65 0.69 28 day Basic Compressive Stress ( f b , N/mm 2 ) of Masonry for crushing strength & mortar type

62. Permissible stresses Basic compressive stress can be obtained for crushing strength of masonry units and grade of mortar f b valid for slenderness ratio up to 6, zero eccentricity and height to width ratio of masonry units up to 0.75 fb for RR masonry shall be 75% of stress for coarsed walling of similar material Linear interpolation is permissible Strength of ashlar masonry is related to stone strength and higher f b is allowed as/designer

63. Permissible stresses Which mortar mix to use? Relationship between strength of brickwork and strength of masonry for medium strength brick

64. Permissible stresses Which mortar mix to use? Effect of mortar mix on strength of brickwork

65. Permissible stresses Which mortar mix to use? Optimum mortar mix for maximum masonry strength

66. Permissible COMP. stress Permissible compressive stress of masonry wall is based on basic compressive stress ( f b ) f b is multiplied with stress reduction factor (SRF) and area reduction factor (ARF) and shape modification factor (SMF) to get permissible compressive stress

67. Permissible COMP. stress Stress reduction factor:- Accounts for the slenderness ratio of element and eccentricity of loading

68. Permissible COMP. stress Linear interpolation is to be carried out for intermediate values Slenderness ratio of a member for sections within 1/8 of height of the member above or below a lateral support may be taken to be 6 SRF value shall vary linearly between 1.0 and 0.2 for slenderness ratio of 6 and 20, respectively when eccentricity of loading is between 1 / 3 and 1 / 2 of the thickness of member

69. Permissible COMP. stress Area reduction factor:- Accounts for the smallness of sectional area of the element Applicable only when the sectional area of the element is less than 0.2 m 2 Area reduction factor (K s ) for cross sectional area of the member of A m 2 is given as K s = 0.7+1.5 A ARF is based on the concept that there is statistically greater probability of failure of a small section due to substandard units as compared to a large element

70. Permissible COMP. stress Area reduction factor:- Accounts for the smallness of sectional area of the element Necessity for ARF arise if there is appreciable variation in strength of individual units Strength of masonry units manufactured in India can appreciably vary Area/ Region Brick Strength (N/mm 2 ) Area/ Region Brick Strength (N/mm 2 ) Delhi & Punjab 7 to 10 Madhya Pradesh 3.5 to 5 Uttar Pradesh 10 to 20 Gujarat 3 to 10 Maharashtra 5 Rajasthan & AP 3 West Bengal 10 to 20 Assam 3.5

71. Permissible COMP. stress Shape modification factor ( k p ):- Accounts for shape of the units, (height to width ratio) Applicable for units of crushing strength up to 15 N/mm 2 Shape Modification Factor for Masonry Units

72. Permissible COMP. stress Increase in permissible stresses:- In members subjected to eccentric/lateral loads , increase in permissible compressive stress is allowed 1/24 < Eccentricity ratio < 1/6, 25% increase in permissible compressive stress is allowed 1/6 < Eccentricity ratio, 25% increase in permissible compressive stress is allowed but the area of the section under tension shall be disregarded for computing the load carrying capacity of the member

73. Permissible COMP. stress Increase in permissible stresses:- In members subjected to concentrated loads , increase in permissible compressive stress is Concentrated load (area of supporting wall > 3 x bearing area) and is concentric, bearing stress in masonry may exceed the permissible compressive by 50 percent, if load bears on central strip of wall up to half the wall thickness bearing stress in masonry may exceed the permissible compressive by 25 percent, if load bears on full wall thickness Interpolation required if bearing is between half to full wall thickness

74. Permissible COMP. stress Increase in permissible stresses:- In members subjected to concentrated loads (area of supporting wall > 3 x bearing area), increase in permissible compressive stress is Concentrated load For concentrated load from lintel, increase of 50 percent in permissible stress (if supporting area is not less than 3 times the bearing area) Maximum spread of concentrated load on wall shall be lesser of b + 4 t (width of bearing + 4 x wall thickness) stretch of wall supporting load center to center distance between loads

75. Permissible tensile stress Masonry shall be designed assuming masonry is not capable of taking any tension Flexural tensile stresses may be permitted in design of masonry For M1 or better mortar 0.07 N/mm 2 for bending in vertical direction where tension developed is normal to bed joints (0.1 N/mm 2 for boundary walls) 0.14 N/mm 2 for bending in longitudinal direction where tension developed is parallel to bed joints (for crushing strength of units > 10 N/mm 2 )

76. Permissible tensile stress For M2 mortar 0.05 N/mm 2 for bending in vertical direction where tension developed is normal to bed joints (0.07 N/mm 2 for boundary walls) 0.10 N/mm 2 for bending in longitudinal direction where tension developed is parallel to bed joints (for crushing strength of units > 7.5 N/mm 2 ) For water retaining structures, no tensile stress is permitted in masonry For earth retaining structures, no tensile stress is permitted in masonry as water may be present at the back of such walls

77. Permissible shear stress Wall built in M1 or richer mortar and resisting horizontal forces in the plane of wall, permissible shear stress shall not exceed F g = 0.1+f d /6 f d : compressive stress due to dead loads in N/mm 2 Permissible shear stress is calculated on the area of bed joints

78. Walls and column subjected to vertical load shall be designed on the basis of permissible compressive stress For designing walls, thickness is calculated for given wall length For designing column, cross-section is calculated Strength of masonry units and grade of mortar to be used is to be fixed Slenderness ratio, eccentricity, area of section, workmanship and quality of supervision are also to be considered Design thickness/cross section

79. Solid walls:- Thickness used for design calculation shall be actual thicknesses of masonry computed as sum of average dimensions of masonry units, together with the specified joint thickness In masonry with raked joints, thickness shall be reduced by depth of raking of joint for plastering/pointing Design thickness/cross section

80. Cavity walls:- Min. t hickness of each leaf shall be 7.5 cm When outer leaf thickness is half masonry unit, its uninterrupted height and length, shall be limited to avoid undue loosening of ties due to differential movement (outer leaf supported at least at every third storey or at every 10 meter of height, whichever is less) Use slenderness ratio from effective thickness of wall for calculating permissible stress when load carried by both leaves of wall Eccentricity of load shall be considered with respect to CG of cross section of wall Design thickness/cross section

81. Cavity walls:- If load is carried by one leaf only, permissible stress shall be greater of the two values as calculated below SR is based on effective thickness of wall and eccentricity with respect to CG of cross section of whole wall (when load carried by both leaves) SR is based on effective thickness of loaded leaf only and eccentricity of load with respect to CG of loaded leaf only. In either case, actual thickness of load bearing leaf shall be used in arriving at the cross section area resisting the load Design thickness/cross section

82. Faced walls:- The permissible load per unit length of wall shall be taken as the product of total thickness of wall and permissible stress in weaker of the two materials The permissible stress shall be calculated by using the total thickness of wall when calculating the slenderness ratio Design thickness/cross section

83. Veneered walls:- The facing shall be entirely ignored in calculations of the strength and stability The permissible stress shall be calculated by using the thickness of backing only when calculating the slenderness ratio Design thickness/cross section

84. Walls/columns mainly subjected to lateral loads Free Standing Walls: Walls subjected to wind pressure or seismic forces, shall be designed on the basis of permissible tensile stress in masonry or stability Retaining Walls : Masonry of retaining walls shall be designed for zero-tension and permissible compressive stress . However , if retaining walls support horizontal thrust from dry materials , these may be designed on the basis of permissible tensile stress Design thickness/cross section

85. Walls/columns subjected vertical and lateral loads For walls and columns , stresses worked out separately for vertical loads and lateral loads shall be combined and elements designed on the basis of permissible stresses. Design thickness/cross section

86. Walls subjected to in-plane bending and vertical loads Walls subjected to in-plane bending and vertical loads (shear walls) shall be designed on the basis of no-tension , permissible shear stress and permissible compressive stress Design thickness/cross section

87. Non-load bearing walls Non-load bearing walls , such as panel walls, curtain walls and partition walls which are mainly subjected to lateral loads, according to present state of art , are not capable of precise design and only approximate methods based on some tests are available Design thickness/cross section

88. Choice of masonry units is generally made from the considerations of local availability, compressive strength, durability , cost , ease of construction Choice of masonry units

89. Load carrying capacity of masonry member is governed by its slenderness ratio Masonry member may fail due to excessive stress or due to buckling If SR < 30, load carrying capacity at ultimate load is limited by stress If SR > 30, failure is initiated by buckling Short members (h/t < 4) fail through shear Vertical tensile splitting if h/t > 4 Lime mortar is more liable to bucking than cement mortar Load carrying capacity

90. Lime mortar (low limiting SR value) more liable to bucking than cement mortar due to low strength Maximum SR is less for taller buildings due to possible imperfections in workmanship Limiting SR is low for columns than walls as column can buckle around either of two horizontal axis Short members (h/t < 4) fail through shear Vertical tensile splitting if h/t > 4 Limiting slenderness ratio

91. Brick masonry easy construction requires less labour for laying thinner than stone masonry suitable soil may not be available in hills cost of fuel for burning may be high Stone masonry locally available practical limitation in dressing to shape and size extra cost due to thicker cross sections Choice of masonry units

92. Concrete block masonry suitable when brick/stone is uneconomical number of storeys is more than 2 Sand-lime brick masonry if good quality sand-lime available For simple residential buildings with one brick thick walls and medium size rooms Choice of masonry units Strength (N/mm 2 ) 3 to 3.5 7 10 15 No. of storeys 1-2 2-3 3-4 4-5

93. Requirements of good mortar for masonry high strength good workability good water retentivity low drying shrinkage early initial set strength gain within reasonable period cement/ lime/ cement-lime mortars may be used Choice of Mortar

94. Eccentricity Due to loading Due to slenderness Combined eccentricity

95. Eccentricity Eccentricity of vertical loading on a masonry element increases its tendency to buckle and reduces its load carrying capacity Effect of eccentricity is similar to slenderness Eccentricity by vertical load is maximum at point of loading ( top of member ), reduces linearly to zero at bottom ( just above the bottom lateral support) Eccentricity on account of slenderness is zero at the two supports and is maximum at the middle Combined effect of slenderness and eccentricity is taken into consideration slenderness Combined effect of eccentricity is at 0.6 H from base

96. Design concepts of load bearing masonry structures Building is subjected to vertical loads of dead loads of materials used in construction, plus live loads due to occupancy lateral loads due to wind and seismic forces All walls can take vertical loads Ability of a wall to take lateral load depends on direction of lateral load in relation to wall

97. Design concepts of load bearing masonry structures Lateral loads acting on the face of a building are transmitted through floors

98. Design concepts of load bearing masonry structures Stress pattern in cross wall acting as shear wall Wind load on shaded area is resisted by the cross wall Stress diagram

99. Design concepts of load bearing masonry structures Compressive stress increases on leeward side and reduces on windward side due to lateral loads Walls designed for no tension and permissible compressive stress What will you prefer? Lightly loaded or heavily loaded wall!

100. Design concepts of load bearing masonry structures What will you prefer? Cross wall construction!

101. Design concepts of load bearing masonry structures What will you prefer? Cellular/ box type construction!

102. Design concepts of load bearing masonry structures Size, shape and openings location (external walls) considerably influence stability and magnitude of stresses due to lateral loads

103. Design concepts of load bearing masonry structures If openings in longitudinal walls are so located that portions of these walls act as flanges to cross walls, the strength of the cross walls get considerably increased and structure becomes much more stable

104. Design concepts of load bearing masonry structures Load-bearing masonry structure is designed for permissible compressive and shear stresses (with no tension ) as a vertical cantilever No moment transfer is allowed for, at floor to wall connections Lateral forces are assumed to be resisted by diaphragm action of floor and roof slabs, which acting as horizontal beams, transmit lateral forces to cross walls in proportion to their relative stiffness (moment of inertia )

105. Design concepts of load bearing masonry structures Floor-wise calculation of stresses in various walls carrying greater loads Computations for vertical loads and lateral loads are made separately Results from the two computations are superimposed for net value of stresses In any particular floor, quality of bricks and mix of mortar is kept the same throughout In the vertical direction change in thickness of walls is made only at floor levels

106. Various modes of failure of Masonry Under vertical compressive loads Design thickness/cross section Tensile splitting Buckling

107. Various modes of failure of Masonry Cross-wall under lateral loads Design thickness/cross section Shear Failure Crushing @ toe

108. Load dispersion Angle of dispersion of vertical load on walls shall be taken as 30 degree from vertical Part of load over opening in wall transferred to sides of opening by arching action Masonry units should have good shear strength and should be laid in proper masonry bond using a good quality mortar for good arching action

109. Load dispersion Long wall portions on both sides of opening to serve as effective abutments for arched masonry above opening. Required to resist horizontal thrust by shear resistance of the masonry at the springing level on both sides of the opening For opening too close to the end of a wall , shear stress in masonry at springing level of imaginary arch may be excessive and no advantage of arching action can be taken in masonry for design of lintels

110. Load dispersion Arching effect on design of lintels & masonry stress

111. Load dispersion Arching effect on design of lintels & masonry stress Load from lintel gets uniformly distributed over supports Load of floor and masonry above equilateral triangle get transferred to sides of wall over stretches of masonry CD and EF at the soffit level of lintel (limited in length to L/2) over the stretches GH and JK at the floor level (limited in length to lesser of L or (L+H)/2)

112. Load dispersion How to design this building?

113. Load dispersion Simplified approach Stress in masonry at plinth level is assumed to be uniformly distributed in different stretches of masonry No deduction in weight of masonry at openings Extra stresses due to extra masonry compensates for concentrations of stresses due to openings In multi- storeyed load-bearing structure intervening floor slabs disperse the upper storey loads more or less uniformly on the inter-opening spaces below the slabs

114. Load dispersion Simplified approach

115. Load dispersion: lintel design If length of wall on sides of opening ≥ Span of lintel

116. Load dispersion: lintel design Lintels supporting masonry shall be designed to carry load of masonry and load received from any other parts of structure Length of bearing of lintel at each end shall not be less than 9cm or one tenth of the span whichever is more Area of bearing shall be sufficient to ensure that stresses in masonry do not exceed the permissible stresses

117. Load dispersion: lintel design If length of wall on one or both sides of opening < Span of lintel

118. Load dispersion: lintel design If length of wall on sides of opening ≥ Span of lintel and floor/roof slab within loading triangle but no other opening

119. Load dispersion: lintel design If length of wall on sides of opening ≥ Span of lintel and floor/roof slab within loading triangle with other opening

120. Load dispersion: lintel design If length of wall on sides of opening ≥ Span of lintel and other load between lintel and HP 25 cm above the apex of the triangle over the lintel