Handbook on Masonry Design and Construction

Scope - IS SP Part 20 (S&T) : 1991

Key Design Parameters:

Typical Thicknesses & Assumptions (Clause 3.2.3)

Summary

• Max span ranges from 3.6 m to 5.4 m depending on case.
• **Live

IS SP Part 20: Materials for Masonry - Key Specifications and Tables

1. Specifications

• Materials for masonry follow Indian Standards (IS) referenced in SP:21.
• Mortar retempering times (Clause 1.4.7.1):
  • Cement & cement-lime mortar: within 2 hours
  • Hydraulic lime mortar: within 4 hours
  • Semi-hydraulic lime mortar: within 8 hours
  • Non-hydraulic lime mortar: within 12 hours
  • Mud mortar: no time limit
• Mortar retempering allowed only once.

2. Recommended Mortar Mixes (Table 3 Summary)

Notes:

• Mort

Key Specifications and Formulas for Stone Masonry (IS SP Part 20)

1. Choice of Masonry Units (Clause 3.1)

• Stone masonry is selected based on:
  • Local availability
  • Compressive strength
  • Durability
  • Cost
  • Ease of construction
• Stone masonry walls are thicker due to difficulty in dressing stones.
• Preferred where bricks are unavailable or costly.
• Concrete blocks may be economical for multi-storey buildings due to thinner walls.

2. Compressive Strength of Bricks (Indicative for comparison)

Stone strength varies widely depending on type.

3. Mortar Mix Recommendations (Table Summary from SP 20)

• Retemper mortar within 2 hours for cement mortars (Clause 1.4.7.1).

4. Thickness and Strength Considerations

• Stone masonry walls typically thicker than brick masonry.
• Use compressive strength of stone and mortar to calculate allowable stresses.

Summary Formula for Compressive Strength of Stone Masonry:

[ f_m = K \times f_s ] Where:

• ( f_m ) = compressive strength

IS SP Part 20: Brick Masonry - Key Specifications & Tables

1. Masonry Units - Physical Characteristics (Clause 1.3.2 & Table 1.3.2)

2. Important Notes:

• Heavy Duty Bricks are also called Engineering Bricks.
• Water absorption limits ensure durability; lower absorption means better resistance.
• Dimensions are actual sizes for design and construction.
• Compressive strength varies widely depending on brick type and use.

3. Typical Design Formulae (General Masonry)

• Compressive Strength of Masonry (f_m):

[ f_m = 0.33 \times f_b^{0.7} \times f_m'^{0.3}

IS SP 20 (S&T) : 1991 — Special Masonry Structures (Domes, Retaining Walls)

1. Masonry Domes (Clause 5.5)

• Domes are treated as shell structures with compressive stresses.
• Key parameters:
  • ( W ) = Vertical load/weight
  • ( e ) = Eccentricity of load
  • ( \sigma_c ) = Compressive stress due to dead loads
  • Use shape modification factor (Table H-3.3.3) to adjust basic compressive stress.

2. Retaining Walls

• Consider lateral earth pressure and surcharge loads.
• Use effective height (h) and thickness (t) of wall.
• Stability checks: sliding, overturning, bearing capacity.
• Use stiffening coefficient and modulus of section for wall design.

3. Key Formulas

4. Load Tables (Excerpt from Table E-17)

5. **Design Notes

IS SP 20 (S&T) : 1991 — General Construction Requirements

Key Specifications & Tables

1. Shape Modification Factor (Clause 1.1)

• Basic masonry stress values are divided by shape modification factors:
  • Factors: 1.2, 1.1, 1.1, 1.0 (per Table 8)
• Adjusted basic stress = Basic stress / Shape modification factor

2. Unit Loads on Roof/Floor and Walls (Table E-17)

3. Wall Thickness & Plastering (Clause 3.2.9)

• Wall plaster thickness (both sides): 3 cm
• Parapet wall height: >1.0 m (refer Clause 3.2.3)

4. Slab and Flooring Thickness (Clauses H-3.2.4 to H-3.2.8)

IS SP 20 Part 20: Design Considerations & Load Calculations

Key Load Parameters (from Tables E-17 & E-13)

Design Parameters (Clause 3.1)

• Max Span (Short Span for 2-Way Slab): 3.6 m to 5.4 m
• Width of Corridor: 1.5 m to 2.1 m
• Clear Height of Storey: 3.0 m to 3.3 m
• Live Load on Floors: 250 or 400 kg/m² depending on case

Shape Modification Factor (Clause 1.1 & 5.4.1.3)

Basic Stress Calculation Steps

1. Calculate basic stress without shape modification factor.
2. Apply stress reduction factor.
3. Divide by shape modification factor to get requisite basic stress.
4. Refer to Table 8 for masonry requirements based on stress.

Summary Formula for Basic Stress:

[ \sigma_{required} = \frac{\sigma_{basic} \times \text{stress reduction factor}}{\text{shape modification factor}} ]

Masonry Bonds & Laying Techniques (IS SP Part 20)

Key Specifications:

• Bonding: Achieved by closely fitting stones/bricks, using a specified proportion of headers and bond stones.
• Joint Staggering: Vertical joints must be staggered by at least 1/4 brick length from the course below/above to ensure load sharing.
• Avoid Long Vertical Joints: Face stones/bricks should be laid to break vertical joints as much as possible.

Common Bonds (Clause 2.2):

Bonding Rule Formula:

• Minimum joint offset = 1/4 × brick length
  This ensures vertical joints do not align, improving structural integrity.

Laying Tips:

• Use proper mortar thickness (typically 10 mm).
• Ensure full mortar bedding for uniform load transfer.
• Maintain level courses and vertical alignment.

flowchart LR
    A[Start Laying] --> B[Place stretcher bricks]
    B --> C{Next course}
    C -->|English Bond| D[Alternate headers & stretchers]
    C -->|Flemish Bond| E[Headers & stretchers alternate in same course]
    C -->|Stretcher Bond| F[All stretchers]
    D --> G[Stagger vertical joints ≥ 1/4 brick length]
    E --> G
    F --> G
    G --> H[Ensure no long vertical joints]
    H --> I[Complete wall]

Summary: Use proper bond patterns with staggered vertical joints (≥ 1/4 brick length), maintain mortar thickness, and avoid continuous vertical joints for strong, durable masonry.

Mortar Mixes and Preparation — IS SP Part 20 (Summary)

1. Standard Mortar Mixes (Clause 1.4.5 & Table 2 of IS 2250:1981)

• Mortar mixes are based on cement:lime:sand ratios.
• Common mixes range from rich (1:0:4) to lean (1:2:9) depending on strength and exposure.

2. Recommended Mortar Mixes for Masonry (Table 3, Clause 1.4.6.2)

3. Mortar Compressive Strength vs. Mix Ratio (Clause 32.7)

4. Retempering Mortar (Clause 1.4.7.1)

• Mortar stiffened by moisture loss can be retempered once by adding water within:
  • 2 hours for cement/cement-lime mortars
  • 4 hours for hydraulic lime mortars
  • 8-12 hours for semi/non-hydraulic lime mortars
• Mud mortar has no time limit

Handling and Storage of Masonry Units (IS SP 20 - Handbook on Masonry Design and Construction)

Key Specifications:

• Storage Height: Stack masonry units to a maximum height of 1.5 m to avoid crushing.
• Surface: Store units on a clean, dry, and level surface to prevent contamination and moisture absorption.
• Protection: Cover stacks with waterproof sheets to protect from rain and moisture.
• Handling: Use mechanical means or manual handling carefully to avoid chipping or cracking.

Important Guidelines:

• Keep units off the ground using timber or pallets.
• Avoid stacking near edges or unstable surfaces.
• Separate different types or sizes of units to prevent mix-up.

Typical Table: Maximum Stack Height for Masonry Units

Formula for Safe Stacking Load:

[ P = A \times \sigma_c ] Where:

• (P) = Safe load on the unit (N)
• (A) = Cross-sectional area of the unit (m²)
• (\sigma_c) = Compressive strength of the masonry unit (N/m²)

flowchart TD
    A[Receive Masonry Units] --> B[Inspect for Damage]
    B --> C[Store on Level Surface]
    C --> D{Stack Height < 1.5 m?}
    D -- Yes --> E[Cover with Waterproof Sheet]
    D -- No --> F[Reduce Stack Height]
    E --> G[Ready for Use]

Summary: Proper handling and storage ensure durability and strength of masonry units by preventing damage and moisture absorption.

IS SP Part 20: Prevention of Cracks and Durability in Masonry

Key Points from Clause 6.10 & Related References

• Causes of Cracks:

  • Drying shrinkage
  • Thermal movements
  • Differential strains
  • Chemical actions
  • Settlement of soil/foundation

• Control Measures (Clause 6.4):

  • Provide control joints at regular intervals to accommodate deformation.
  • Use movement joints to isolate different parts of masonry.
  • Ensure proper construction joints to avoid random cracking.

• Reference Handbook:
  SP 25:1984 — Causes and Prevention of Cracks in Buildings provides detailed guidelines.

Important Specifications & Formulas

Recommendations for Durability

• Use well-burnt bricks with low water absorption (<20%).
• Use quality mortar (cement:sand = 1:6 or richer).
• Avoid excessive water in mortar to reduce shrinkage.
• Provide adequate curing for at least 7 days.
• Protect masonry from chemical exposure and moisture ingress.

flowchart LR
    A[Causes of Cracks] --> B[Drying Shrinkage]
    A --> C[Thermal Movement]
    A --> D[Differential Strain]
    A --> E[Chemical Action]
    A --> F[Foundation Settlement]
    B & C & D & E & F --> G[Control Joints & Movement Joints]
    G --> H[Reduced Cracking]
    H --> I[Improved Durability]

For detailed design and crack control, refer to SP 25:1984 and IS 1905 (Masonry Code).

Thermal and Moisture Protection: Key Points from IS SP Part 20

1. Thermal Insulation (Clause 6.2 iii)

• Wall thickness for thermal insulation in non-industrial buildings should be based on IS 3792:1978 considering local climatic conditions.
• No specific industrial building standard yet; IS 3792 data can guide wall thickness decisions.

2. Fire Resistance (Clause 6.2 ii)

• Refer to IS 1641 to IS 1648 and National Building Code Part IV (1983) for detailed fire resistance requirements.

3. Sound Insulation (Clause 6.2 iv)

• External walls' sound insulation values depend on building type and noise level (see Table E-6):

• Party/internal walls sound insulation values (Table E-7):

• Sound insulation increases with wall weight (Table E-8):

• Masonry walls plastered both sides (Table E-9):

| Thickness (cm) | Sound Insulation (dB) | |----------------

Seismic Considerations in Masonry (IS SP 20 Part 20)

Key Steps & Formulas:

1. Basic Stress Calculation (Clause 5.4.1.3)

   • Calculate basic stress after applying stress reduction factor (SRF) but before applying the shape modification factor (SMF).
   • Formula:
     [ \sigma_b = \frac{\text{Total load per unit length}}{\text{Effective cross-sectional area}} \times \text{SRF} ]

2. Shape Modification Factor (SMF) Application

   • From Table 8 of the Code, SMF values are typically:

     Storeys	SMF (Shape Modification Factor)
     Triple	1.2
     Double	1.1
     Single	1.0

   • Adjust basic stress:
     [ \sigma_{b, adj} = \frac{\sigma_b}{\text{SMF}} ]

3. Masonry Requirements (Table 8 Reference)

   • Determine brick strength and mortar type based on adjusted basic stress.
   • Example notation: 20-7-M2 means 20 cm thick wall, brick strength 7 N/mm², mortar type M2.

Load Tables Summary (kg/m or kg/m²):

Important Notes:

• No deductions for openings in walls; conservative design assumed.
• Live loads are not reduced.
• Stability against wind assumed; seismic loads govern.
• Floor numbering per IS 2332:1972.

flowchart TD
    A[Calculate Total Load] --> B[Apply Stress Reduction Factor (SRF)]
    B --> C

Use of Precast Stone Blocks (IS SP 20 Part 20)

Key Points from Clause 1.3.7:

• Precast stone blocks combine stone pieces with lean cement concrete.
• They allow thinner walls than traditional stone masonry, improving economy and space efficiency.
• No specific IS standard yet; refer to CBRI Research Note No. 7 for manufacturing, properties, and usage.

Specifications & References

Important Notes:

• Precast stone blocks improve thermal insulation and reduce wall thickness.
• Selection depends on load, climate, availability, and cost (Clause 4.1.1).
• Use standard concrete blocks as per IS 2185 for load-bearing/non-load-bearing walls.
• For detailed design and manufacturing, consult CBRI Research Note No. 7.

flowchart LR
    A[Stone Pieces + Lean Cement Concrete] --> B[Precast Stone Blocks]
    B --> C[Thinner Walls]
    B --> D[Improved Economy]
    B --> E[Better Space Efficiency]
    C --> F[Load Bearing Walls]
    D --> F
    E --> F
    F --> G[Refer CBRI Note No.7]

Summary: Precast stone blocks per IS SP 20 Part 20 are innovative masonry units combining stone and concrete for thinner, economical walls.

IS SP 20 Part 20: Key Design Formulas, Tables & Specifications

1. Design Parameters (Clauses 2.1 & 3.1)

2. Masonry Wall Notation (Clause 2.3.5)

• 20-7-M2 means:
  • 20 cm thick wall
  • Brick crushing strength = 7 N/mm²
  • Mortar Type M2 (refer IS SP 20 Table 1 for mortar mix ratios)

3. Design Considerations

• No deduction for openings in walls.
• Live loads are not reduced for openings.
• Stresses are calculated at floor 1 level (top of foundation to center of slab).
• Wind forces are not considered; overall building stability assumed.

4. Worked Examples & Annexes (Clause 6.6)

• ANNEX H-I: Design of Structural Masonry
• ANNEX H-2: Brick Masonry for Residential (up to 3 storeys)
• ANNEX H-3: Brick Masonry for Office Buildings (up to 3 storeys)
• ANNEX H-4: Notations & Symbols

5. Typical Design Formula for Masonry Wall Load

[ \sigma = \frac{P}{A} = \frac{W_{dead} + W_{live}}{t \times h} ]

Where:

• (\sigma) = Stress on masonry (N/mm²)
• (P) = Load on wall (N)
• (A) = Cross-sectional area (