Code of practice for earthquake-resistant design and construction of buildings

IS 4326: Scope - Key Specifications & Tables

Scope (Clause 3.0):
Defines seismic resistance measures for buildings, focusing on strengthening floors/roofs with precast components and detailing openings in bearing walls, and separation gaps between adjoining structures.

1. Strengthening Measures for Floors/Roofs (Table 8, Clause 9.2.7)

Legend:

• a = Tie beam (9.2.3)
• b = Reinforcing bars tied to tie beam (9.2.4)
• c = Reinforced deck concrete (9.2.5)
• d = Reinforced deck concrete (9.2.6)
• e = Reinforcement bars in joints tied to tie beam (9.2.7)

2. Openings in Bearing Walls (Table 4, Clause 8.3.1)

IS 4326: Definitions & Key Specifications Summary

1. Definitions (Clause 3.0)

• Defines terms related to earthquake-resistant design and construction of masonry buildings.
• Includes terms such as tie beams, precast units, strengthening measures, and building categories (A to E).

2. Building Categories & Strengthening (Table 8, Clause 9.2.7)

Strengthening Codes:

• a = Tie beam (Clause 9.2.3)
• b = Reinforcing bars tied to tie beam (9.2.4)
• c = Reinforced deck concrete (9.2.5)
• d = Reinforced deck concrete (9.2.6)
• e = Reinforcement in joints (9.2.7)

3. Openings in Bearing Walls (Table 4, Clause 8.3.1)

IS 4326: General Principles for Earthquake Resistant Construction

Key Points from Clause 4.0 (General Principles):

• 4.1 to 4.9 outline essential principles for earthquake-resistant buildings.
• Emphasize simple, regular geometry to avoid torsion.
• Use strong, continuous load paths from roof to foundation.
• Ensure adequate foundation design to transfer seismic forces safely.

Foundations (Clauses 4.6, 5.3, 10.5):

• Foundations must be designed to resist seismic shear and uplift.
• Provide uniform bearing capacity to avoid differential settlement.
• Use reinforced concrete footings with adequate anchorage of columns.
• Avoid soft soils or improve them by compaction or grouting.

Important Formulas (Generalized):

• Base Shear, V = Ah × W

  Where:

  • Ah = Design horizontal seismic coefficient (from IS 1893)
  • W = Weight of the structure

• Overturning moment, M = V × h

  Where:

  • h = height of the center of mass above foundation

Summary Table: Foundation Design Parameters

flowchart TD
    A[Seismic Forces] --> B[Load Transfer in Structure]
    B --> C[Roof to Columns]
    C --> D[Columns to Footings]
    D --> E[Footings to Soil]
    E --> F[Soil Reaction]

Note: Always refer to IS 4326 clauses 4.1-4.9 for detailed principles and IS 1893 for seismic coefficients.

IS 4326: Seismic Zones and Coefficients

• Seismic Zones (Clause 3.4 & IS 1893:1984)
  India is divided into 5 seismic zones (I to V) based on seismic risk:

  Zone	Description	Basic Seismic Coefficient (Ah)
  I	Low seismicity	0.01
  II	Moderate seismicity	0.02
  III	Considerable	0.04
  IV	High	0.08
  V	Very High	0.16

• Design Seismic Coefficient (Clause 3.8 & IS 1893:1984 3.4.2.3(a))
  [ Ah = \frac{Z I S_a}{2 R g} ] Where:

  • (Z) = Zone factor (from above table)
  • (I) = Importance factor (1 to 1.5 depending on building use)
  • (S_a/g) = Soil amplification factor (from soil type)
  • (R) = Response reduction factor (depends on structural system)

• Seismic Resistance Measures (Clause 9.2)
  Include:

  • Proper foundation design
  • Adequate lateral load-resisting systems
  • Ductility and detailing as per IS 13920

flowchart LR
    A[Seismic Zone (Z)] --> B[Basic Seismic Coefficient (Ah)]
    B --> C[Multiply by Importance Factor (I)]
    C --> D[Multiply by Soil Factor (Sa/g)]
    D --> E[Divide by Response Reduction Factor (R)]
    E --> F[Design Seismic Coefficient (Ah)]

Summary: Use IS 1893 for zone factors and soil coefficients; apply importance and response factors to get design seismic coefficient for structural design as per IS 4326.

IS 4326: Separation and Crumple Sections

Key Definitions

• Separation Section: A deliberate gap between two structural parts to allow independent movement during an earthquake.
• Crumple Section: A separation section filled with material designed to deform (crumple/fracture) under seismic forces, absorbing energy (Clause 3.1.1).

Specifications (Clause 5.2 & 5.2.2)

• Separation or crumple sections must be detailed as per Fig. 3 of IS 4326.
• For alternative joint details, refer to IS 3414:1968.
• These sections prevent damage transfer between adjoining structures or additions (Clause 4.2.3).

Typical Design Considerations

• Width of Separation: Sufficient to accommodate expected relative displacement.
• Material in Crumple Section: Compressible or sacrificial materials (e.g., soft wood, foam, or special blocks).
• Joint Detailing: Ensure easy replacement after seismic events.

Summary Table (Conceptual)

flowchart LR
    A[Existing Structure] -->|Separation Gap| B[Crumple Section]
    B -->|Absorbs Energy| C[New Structure]
    style B fill:#f9f,stroke:#333,stroke-width:2px

Note: Always verify gap size and material choice based on site-specific seismic data and structural movement estimates.

IS 4326: Types of Construction

1. Types of Construction (Clause 6.1)

• Framed Construction (Clause 6.2): Structural frame carries vertical and lateral loads.
• Box Type Construction (Clause 6.3):
  • Walls along both axes act as load-bearing and shear walls.
  • Includes traditional masonry, prefabricated or in situ concrete/reinforced concrete walls.
  • Critical: Ensure shear transfer in panel connections for prefabricated walls.

2. Building Categories (Clause 7.1.1)

• Refer to Table 2 in IS 4326 for building categories based on occupancy, importance, and risk.

Key Notes:

• Box Type Construction is suitable for resisting horizontal loads from any direction.
• Prefabricated panels require robust connections to ensure shear force transfer.

Summary Table: Types of Construction

If you need specific formulas or design provisions for shear walls or framed structures, please specify!

IS 4326: Building Categories & Importance Factors Summary

Building Categories (Clause 7.1 & Table 2)

Buildings are classified into categories A to E based on:

• Seismic Zone (II to V)
• Importance Factor (I)

• Note: Category A is obsolete (Zone I no longer exists).

Importance Factor (I) (Clause 6.4.2 & IS 1893 Part 1 Table 6)

• Reflects building importance for seismic design.
• Typical values:
  • 1.0 for ordinary buildings
  • 1.5 for essential facilities (hospitals, emergency centers)

Application

• Importance factor I multiplies seismic forces:
  [ F = I \times Z \times S_a \times W / R ] where
  (F) = design seismic force,
  (Z) = zone factor,
  (S_a) = spectral acceleration,
  (W) = seismic weight,
  (R) = response reduction factor.

Reference:

• Masonry design per IS 1905:1987 and IS 2212:1991 (Clause 8.1).

IS 4326 - Masonry Construction with Rectangular Units

Key References:

• Design & Construction: Governed by IS 1905:1987 (Code of Practice for Structural Use of Unreinforced Masonry) and IS 2212:1991 (Code of Practice for Brickwork).
• Masonry Units: Rectangular units including brick, squared stone, stone block, or hollow concrete block masonry (per IS 1597 Part 2:1992).

Important Tables & Specifications:

Table 2: Building Categories for Earthquake Resistant Features (Clause 7.1.1)

• Note: Category A is obsolete; Zone I no longer exists.

Key Points for Rectangular Masonry Units:

• Use adequate strength units as per IS 1597 (Part 2):1992.
• Follow IS 1905 and IS 2212 for structural detailing and workmanship.
• Ensure proper mortar mix and curing to achieve design strength.
• Masonry walls should be designed considering seismic loads as per IS 1893.

Typical Masonry Strength Parameters (per IS 1905):

flowchart TD
    A[Masonry Construction] --> B[Rectangular Units]
    B --> C[Brick Masonry]
    B --> D[Stone Masonry]
    B --> E[Hollow Concrete Block]
    A --> F[Design Codes]
    F --> G[IS 1905:1987]
    F --> H[IS 2212:1991]
    F --> I[IS 1597 (Part 2):1992]

For detailed design, refer to IS 190

IS 4326: Floors and Roofs with Small Precast Components – Key Points

1. Types Covered (Clause 9.1)

• Channel/cored units
• R.C. planks and joists
• Brick panels and joists
• Precast waffle units

2. Strengthening Measures (Clause 9.2.1, Table 8)

Legend:

• a = Tie beam as per 9.2.3
• b = Reinforcing bars in precast unit tied to tie beam (9.2.4)
• c = Reinforced deck concrete (9.2.5)
• d = Reinforced deck concrete (9.2.6)
• e = Reinforcement bars in joints between waffle units tied to tie beam (9.2.7)

3. Reinforcement Details

• Tie beam reinforcement: Refer Table 6 of IS 4326.
• Typical reinforcement for connection (see Figures 26-30):
  • Ø6 mm MS bars @ 150 mm c/c both ways tied to tie beam.
  • For waffle units: 6 mm MS dowel bars @

IS 4326: Brick Nogged Timber Frame Construction (Clause 10.8)

Key Specifications:

• Frame Composition: Vertical members, columns, sills, wall plates, horizontal noggings, diagonal braces, and stretcher bond brick masonry infill (Clause 10.8.1).

1. Minimum Finished Sizes of Verticals (Table 11, Clause 10.8.2)

Grade I timber as per IS 883:1992 Table 5.

2. Minimum Sizes of Horizontal Nogging Members (Table 12, Clause 10.8.5)

3. Minimum Sizes of Diagonal Braces (Table 10, Clauses 10.7.4 & 10.8.4)

IS 4326: Horizontal & Vertical Reinforcement Detailing Summary

1. Vertical Reinforcement (Clause 8.4.8 & Table 7)

• Applies to walls ≤ 340 mm thick; thicker walls require proportional increase in steel area.
• No vertical steel in Category A buildings.
• Vertical bars are HSD bars; for mild steel, use equivalent diameters (see Table 6 Note 2).
• Bars embedded in M15 concrete/mortar pockets for corrosion protection and bonding.
• Vertical bars must pass through lintel bands, floor slabs, and be embedded in plinth masonry.
• Bars can be welded or lapped (per IS 2751 & IS 9417).

2. Horizontal Reinforcement - RC Bands (Clause 8.4.5 & Table 6)

• Bands width = wall thickness (min 200 mm).
• Cover = 20 mm.
• Vertical thickness: 75 mm (2 bars), 150 mm (4 bars).
• Concrete: M15 grade.
• Stirrups: 6 mm dia @ 150 mm c/c.
• Bars: HSD; mild steel equivalent diameters given below.

| Span (m) | Cat B (No., Dia mm) | Cat C | Cat D | Cat E | |

IS 4326 - Restrictions on Openings in Bearing Walls (Clause 8.3)

Openings in bearing walls reduce lateral load resistance; thus, their size and position are strictly regulated:

Key Specifications (Table 4, Clause 8.3.1)

Important Notes:

• Openings should be small and centrally located.
• Arches over openings are discouraged; if used, provide steel ties (Clause 8.3.6).
• Strengthen masonry around openings using toothed joints (Fig. 6) and proper reinforcement (Fig. 8).

Formula for total opening length ratio:

[ \frac{b_1 + b_2 + b_3}{l} \leq \text{max ratio (as per building category and storeys)} ]

Where (b_1, b_2, b_3) = lengths of openings; (l) = wall length (11 or 12 as per table).

graph TD
A[Inside Corner of Wall] -->|Min distance b5| B[Opening]
B -->|Pier width b4| C[Next Opening]
B -->|Vertical distance h3| D[Opening above]

This ensures structural integrity by limiting opening size and spacing per IS 4326 guidelines.

IS 4326: Foundation and Soil Considerations (Summary)

Key Points from IS 4326 (Clauses 5.3.1 to 5.3.3)

• Design Reference:
  Follow IS 1904:1986 (Foundation Design) along with IS 1893:1984 (Earthquake Resistant Design).

• Soil Uniformity:
  The subgrade beneath the entire building should preferably be uniform soil type. If not, provide a separation or crumple section to accommodate differential movement.

• Unsuitable Soils:
  Avoid loose fine sand, soft silt, expansive clays. If unavoidable:

  • Use rigid raft foundation or pile foundations reaching firm strata.
  • For light structures, improve soil by:
    • Sand piling
    • Soil stabilization

Typical Foundation Design Considerations (IS 1904)

Common Soil Improvement Techniques

• Sand Piling: Driving sand columns to increase bearing capacity and reduce settlement.
• Soil Stabilization: Using lime, cement, or other additives to improve soil strength.

Conceptual Diagram of Foundation Soil Interaction

graph TD
    A[Building Load] --> B[Foundation]
    B --> C[Uniform Soil]
    B --> D[Non-uniform Soil]
    D --> E[Separation/Crumple Section]
    C --> F[Good Bearing Capacity]
    E --> G[Settlement Accommodation]

References:

• IS 4326: 5.3
• IS 1904: Foundation design principles
• IS 1893: Earthquake resistant design integration

IS 4326: Strengthening & Repair of Buildings – Key Formulas, Tables & Specs

1. Strengthening Measures for Floors/Roofs with Small Precast Components (Table 8, Clause 9.2.7)

Legend:

• a = Tie beam (Clause 9.2.3)
• b = Reinforcing bars in precast unit tied to tie beam (9.2.4)
• c = Reinforced deck concrete (9.2.5)
• d = Reinforced deck concrete (9.2.6)
• e = Reinforcement bars in joint between waffle units tied to tie beam (9.2.7)

2. Tie Beam Reinforcement (Table 6 & Figures 26-30)

• Tie beam: Ø6 MS bars @ 150 mm c/c both ways tied to precast unit reinforcement.
• For precast units: Top reinforcement (2 no.) projected and tied to tie beam bars.
• Precast waffle units: Dowels Ø6 MS bars @ 150 mm c/c projected out of tie beam.
• Reinforcement in

IS 4326: Construction Practices & Quality Control - Key Points

1. Continuity of Construction (Clause 4.2)

• Ensure continuous construction without interruption to maintain structural integrity and avoid cold joints.

2. Mortar Specifications (Clause 8.1.2.1)

• Use mortars as per Table 3 or equivalent for masonry.
• Typical mortar mix for masonry:
  • Cement : Sand = 1:4 (for general purpose)
  • Use quality sand and water for consistent strength.

3. Masonry Construction Standards (Clause 8.1)

• Follow IS 1905:1987 and IS 2212:1991 for design and construction of masonry walls.

4. Strengthening Measures for Floors/Roofs (Clause 9.2.7, Table 8)

Legend:

• a = Tie beam (Clause 9.2.3)
• b = Reinforcing bars tied to tie beam (9.2.4)
• c = Reinforced deck concrete (9.2.5)
• d = Reinforced deck concrete (9.2.6)
• e = Reinforcement bars in joints tied to tie beam (9.2.7)

5. Tie Beam Reinforcement (Typical)

• Ø6 mm MS bars @ 150 mm c/c both ways tied to tie beam reinforcement.
• Precast units connected to tie beams with dowel bars and reinforcement as per figures 26-30.

Summary Diagram: Precast Floor Strengthening Concept

graph LR
A[Precast Unit] -->|Connected by|