Improving earthquake resistance of earthen buildings - Guidelines

IS 13827: Scope & Key Specifications

Scope (Clause 3.0)

• Defines terms related to seismic strengthening of buildings.
• Focus on seismic zones, coefficients, and design parameters for retrofitting.

Key Definitions:

• Seismic Zone & Seismic Coefficient (Clause 3.5):

  • Seismic zones classify regions by earthquake risk.
  • Seismic coefficient (Ah) is used to calculate lateral forces.

• Zone Factor (Z) (Clause 3.6):

  • Represents seismic hazard level.
  • Used to derive design response spectrum.
  • Values depend on geographic seismic zones (e.g., 0.10, 0.16, 0.24, etc.).

Foundation (Clause 10.3)

• Specifies foundation requirements for retrofitted structures.
• Ensures foundation can resist seismic forces transmitted from superstructure.

Important Formula for Seismic Coefficient (Ah):

[ A_h = \frac{Z}{2} \times \frac{I}{R} ]

Where:

• Z = Zone factor (from seismic zone map)
• I = Importance factor (based on building use)
• R = Response reduction factor (based on structural system)

Seismic Zone Factors (Typical Values):

flowchart LR
    A[Seismic Zone] --> B[Zone Factor (Z)]
    B --> C[Calculate Seismic Coefficient (Ah)]
    C --> D[Design Spectrum]
    D --> E[Structural Design & Foundation]

This framework guides seismic retrofitting as per IS 13827.

IS 13827: General Considerations - Key Points

1. Horizontal Seismic Coefficient (Clause 3.4.2.3)

   • Calculated per IS 1893:1984, factoring soil-foundation system and importance factor (I).
   • Formula:
     [ C_s = \frac{Z I S_a}{2 R g} ]
     where:
     • (Z) = Zone factor (from IS 1893)
     • (I) = Importance factor
     • (S_a) = Soil amplification factor
     • (R) = Response reduction factor
     • (g) = Acceleration due to gravity

2. Foundation (Clause 10.3)

   • Foundations must be designed to resist seismic forces transmitted by the superstructure.
   • Soil-structure interaction should be considered for accurate seismic response.

3. Adequate Configuration (Clause 10.5 & Fig. 8)

   • Symmetrical, regular layouts with uniform stiffness and mass distribution are recommended.
   • Avoid re-entrant corners, soft stories, and torsional irregularities.
   • Fig. 8 (not shown here) illustrates an ideal configuration for seismic zones IV and V.

4. Seismic Strengthening (Clause 12)

   • Additional measures like wall anchorage, banding, and corner reinforcement enhance seismic performance.

Summary Table: Key Parameters for Horizontal Seismic Coefficient

graph TD
A[Seismic Load] --> B[Soil-Foundation System]
B --> C[Horizontal Seismic Coefficient (C_s)]
C --> D[Structural Design]
D --> E[Foundation Design]
D --> F[Superstructure Configuration]

This concise

IS 13827: Seismic Zones and Applicability

Seismic Zones (as per IS 1893 Part 1)

• India is divided into five seismic zones (I to V) based on seismic risk.
• Zone Factors (Z) represent basic seismic coefficients for design.

(Zone I is considered negligible seismic risk; Z = 0)

Applicability (IS 13827 Clause 3.5)

• The code applies to buildings in seismic zones II to V.
• The seismic coefficient (Z) is adopted from IS 1893 (Part 1).
• Design base shear and lateral forces are calculated using these zone factors.

Key Formula: Basic Seismic Coefficient

[ A_h = Z \times I \times \frac{S_a}{2R} ]

Where:

• (A_h) = Horizontal seismic coefficient
• (Z) = Zone factor (from IS 1893)
• (I) = Importance factor (building usage)
• (S_a) = Spectral acceleration coefficient (soil type dependent)
• (R) = Response reduction factor (ductility)

flowchart LR
    A[Seismic Zones I to V]
    A --> B[Zone Factors (Z) from IS 1893]
    B --> C[Apply in IS 13827 for retrofit design]
    C --> D[Calculate Seismic Coefficient \(A_h\)]
    D --> E[Design Base Shear and Forces]

Summary: Use seismic zone factor (Z) from IS 1893 Table 2, apply importance and soil factors, and calculate seismic coefficients for retrofit design as per IS 13827 Clause 3.5.

IS 13827: Design Recommendations for Seismic Areas

Key Points from Clause 10.5 (Adequate Configuration)

• The standard recommends a simple, regular configuration (see Fig. 8 in IS 13827) for earthen buildings in seismic zones IV and V.
• Regularity in plan and elevation reduces torsion and stress concentrations.
• Avoid re-entrant corners, large openings, and irregular shapes.

Seismic Strengthening Features (Clause 12)

• Use of horizontal bands (plinth, lintel, and roof bands) to improve ductility.
• Vertical reinforcement or buttresses to enhance wall stability.
• Use of straw mixed in soil (max 25% by volume) for crack control (Clause 9.5).

Seismic Coefficient (Clause 3.5)

• Seismic coefficient depends on the seismic zone.
• Use appropriate zone factor (Z) from IS 1893 for design.

Summary Table: Earthquake Resistance Features

Basic Formula for Seismic Base Shear (from IS 1893)

[ V_b = Z \times I \times S_a \times W / R ]

Where:

• (V_b) = design base shear
• (Z) = seismic zone factor
• (I) = importance factor
• (S_a) = spectral acceleration coefficient
• (W) = seismic weight of the structure
• (R) = response reduction factor

graph TD
A[Regular Plan] --> B[Reduced Torsion]
B --> C[Improved Seismic Performance]
A --> D[Horizontal Bands]
D --> C
A --> E[Straw Reinforcement]
E --> C

In summary: Follow simple, regular configurations with horizontal bands and controlled straw content for seismic resistance in earthen buildings per IS 13827. Use seismic coefficients as per IS 1893 for design loads.

IS 13827: Construction of Earthen Walls – Key Points

Types of Earthen Walls (Clause 5.0)

• Clay mud walls
• Adobe walls
• Vertical cane/bamboo reinforcement
• Horizontal crushed canes/split bamboo every 4th adobe layer

Reinforcement Details (Clause 12.2)

• Spacing (S): ~400 mm between canes/bamboo
• Diameter (d): ~20 mm for cane/bamboo
• Patterns:
  • Clay mud walls: vertical cane/bamboo reinforcement
  • Adobe walls: horizontal crushed canes/split bamboo reinforcement every 4th layer

Rammed Earth Construction (Clause 9.1)

• Use soil with less clay content than adobe soil
• Moisture content near optimum moisture content from Proctor Compaction Test (IS 2740 Part 7:1980)
• Soil compacted in long wooden forms to achieve density

Building Shape for Earthquake Resistance (Clause 4.6)

• Simple rectangular, symmetrical plan
• Continuous load-bearing walls in both directions
• Avoid L, T shapes; prefer inner courtyard for ventilation and drainage

Summary Table: Reinforcement in Earthen Walls

graph TD
A[Clay Mud Wall] --> B[Vertical Cane/Bamboo @ 400mm spacing]
C[Adobe Wall] --> D[Horizontal Cane/Bamboo every 4th layer]
E[Rammed Earth] --> F[Compacted soil in wooden forms]
G[Building Shape] --> H[Rectangular, symmetrical]
H --> I[Continuous load bearing walls]

This ensures structural integrity and seismic resistance as per IS 13827.

IS 13827: Material Properties & Testing for Earthquake-Resistant Adobe Construction

Key Specifications & Tests:

• Fissure Control Test (Clause 6.2):

  • Prepare 8 folded units with varying soil:sand ratios (1:0 to 1:3 by volume).
  • After 48 hours, select the mix with the least sand that shows no visible fissures in mortar.
  • This ratio indicates optimal soil-sand mix for strength and durability.

• Compressive Strength Test (Clause 6.4):

  • Test 100 mm cubes of dried clay units.
  • Minimum compressive strength: 1.2 N/mm² desirable for adobe blocks.

Material Dimensions for Braced Wood Frames (Clause 3.3, Table A-3):

Summary:

• Use soil:sand ~1:0 to 1:3; select mix with no fissures after 48h.
• Ensure adobe blocks have ≥1.2 N/mm² compressive strength.
• Follow wood frame minimum dimensions for retrofitting adobe walls.

flowchart TD
    A[Soil-Sand Mix Preparation] --> B{Fissure Test after 48h}
    B -- No fissures --> C[Optimal Mix Ratio]
    B -- Fissures --> D[Adjust Sand Content]
    C --> E[Use for Adobe Block Production]
    E --> F[100 mm Cube Compression Test]
    F --> G{Strength ≥ 1.2 N/mm²?}
    G -- Yes --> H[Approved Material]
    G -- No --> I[Modify Mix & Ret

IS 13827: Hand-formed Layered Construction Key Points

1. Compressive Strength (Clause 6.4)

• Test 100 mm clay cubes after complete drying.
• Minimum compressive strength: 1.2 N/mm² desirable.

2. Layering Technique (Clauses 7.3 & 9.3)

• Layer thickness: ~100 mm per layer.
• Preparation:
  • Moisten the lower layer well before adding the next to minimize horizontal fissures.
  • Fully compact each layer.
  • Sprinkle water on the compacted layer before placing the next.
• Block dimensions (typical adobe block):
  • Length: 380 mm
  • Width: 250 mm
  • Thickness: 110 mm

3. Construction Tips

• Total block height per layer: 500 to 800 mm before starting a new block.
• Ensure good bonding by wetting the completed layer before adding the next.

Summary Table

flowchart TD
    A[Prepare Lower Layer] --> B[Moisten Lower Layer]
    B --> C[Place 100 mm Mud Layer]
    C --> D[Compact Layer Fully]
    D --> E[Sprinkle Water on Layer]
    E --> F[Repeat for Next Layer]
    F --> G[Build up to 500-800 mm Height]
    G --> H[Start New Block]

This ensures strong bonding and minimal fissures in hand-formed layered adobe walls.

IS 13827: Key Specifications for Block/Adobe Construction

Block Dimensions (Clause 8.2)

• Rectangular block: 380 mm × 250 mm × 110 mm
  • Overlap: ~125 mm
• Square block: 380 mm × 380 mm × 110 mm
  • Overlap: ~190 mm

Layering & Compaction (Clause 9.3)

• Soil placed in layers of 100 mm thickness, fully compacted.
• Water sprinkled on each compacted layer before next layer placement.
• Total height of block layers: 500 to 800 mm.
• Before starting a new block, pour sufficient water on the completed layer to ensure bonding.

Compressive Strength (Clause 6.4)

• Test 100 mm clay cubes after drying.
• Minimum compressive strength: 1.2 N/mm².

Construction Practice (Clause 7.3)

• Moisten the lower layer well before adding a new one to avoid horizontal fissures.

Summary Table: Adobe Block Sizes

flowchart TD
    A[Prepare Soil] --> B[Place 100 mm Layer]
    B --> C[Compact Layer Fully]
    C --> D[Sprinkle Water]
    D --> E{Height < 500-800 mm?}
    E -- Yes --> B
    E -- No --> F[Pour Water on Completed Layer]
    F --> G[Start New Block Layer]

This ensures good bonding and structural integrity in adobe walls.

IS 13827: Rammed Earth Construction Key Points

Soil & Moisture

• Soil should have less clay than adobe soil.
• Moisture content near Optimum Moisture Content (OMC) from Proctor Test (IS 2740 Part 7:1980).

Construction Method (Clause 9.1)

• Soil is poured in long wooden forms.
• Compacted manually or mechanically to achieve desired density.
• Forms removed after compaction.

Masonry Bonding Principles (Clause 8.4)

• Courses laid level.
• Vertical joints staggered with overlap.
• Joints fully filled with mortar.
• Avoid through vertical joints at wall intersections.

Proctor Compaction Test Reference

• Determines OMC and maximum dry density.
• Ensures soil compaction quality.

Typical Specification Summary

flowchart LR
    A[Soil Selection] --> B[Moisture Adjustment to OMC]
    B --> C[Fill Soil in Wooden Forms]
    C --> D[Compaction (Manual/Mechanical)]
    D --> E[Remove Forms]
    E --> F[Wall Curing & Finishing]

Note: Refer IS 2740 (Part 7) for Proctor Test details and IS 13827 clauses 8.4 & 9 for bonding and construction specifics.

IS 13827 Key Recommendations for Seismic Areas

1. Seismic Zones & Coefficient (Clause 3.5)

• Seismic zones are classified I to V; Zones IV & V are high seismic risk.
• Seismic coefficient (Ah) depends on zone and soil type; used for design lateral forces.

2. Adequate Configuration (Clause 10.5)

• Buildings should have simple, symmetric layouts (see Fig. 8 in IS 13827).
• Avoid irregularities in plan and elevation to reduce torsion.
• Use continuous load paths for seismic forces.
• Provide adequate wall lengths and thickness for lateral stability.

3. Site Selection (Clause 10.2.1)

• Avoid:
  • Sandy loose soils
  • Poorly compacted clays
  • Fill materials prone to settlement
  • High water table sites
• Especially critical for Zones IV & V.

4. Seismic Strengthening (Clause 11)

• Use small amount of straw (≤ 25% volume of soil-water mix) for fissure control in bearing wall construction.

Summary Table: Seismic Zone vs Seismic Coefficient (Typical values)

flowchart TD
    A[Site Selection] --> B{Soil Type}
    B -->|Good| C[Proceed]
    B -->|Loose Sand, Poor Clay, Fill| D[Avoid Site]
    A --> E[Water Table]
    E -->|High| D
    E -->|Low| C
    C --> F[Adequate Building Configuration]
    F --> G[Symmetry & Continuity]
    F --> H[Proper Wall Thickness]
    G & H --> I[Seismic Strengthening]

Note: For detailed design, refer to IS 13827 Fig. 8 and Clause 12 for additional strengthening features.

IS 13827: Seismic Strengthening of Bearing Wall Buildings

Key Specifications & Guidelines

• Clause 10.5 (Adequate Configuration):

  • Follow the configuration shown in Fig. 8 of IS 13827 for general adequacy in seismic zones IV & V.
  • This includes symmetrical plan, uniform wall distribution, and proper anchorage of floors and roofs.

• Clause 11 (Seismic Strengthening Features):

  • Strengthening may include:
    • Adding reinforced concrete (RC) bands at plinth, lintel, and roof levels.
    • Providing vertical RC or masonry columns at wall junctions and corners.
    • Inserting steel or RC anchors to improve wall-to-floor/roof connections.
    • Repairing and repointing masonry cracks with suitable mortar.

Typical Strengthening Details (from IS 13827 & related guidelines):

Important Notes:

• Ensure continuous load path from roof to foundation.
• Avoid heavy modifications that increase mass without strength.
• Refer to IS 13827 Fig. 8 for layout and band positioning.

graph TD
    A[Roof Slab] -->|Anchored to| B[RC Lintel Band]
    B --> C[Wall]
    C --> D[RC Plinth Band]
    D --> E[Foundation]
    C --> F[Vertical RC Columns at Corners/Junctions]
    F --> E

This configuration improves ductility and load distribution, critical for seismic resistance.

IS 13827 – Earthen Constructions with Wood or Cane Structures: Key Points

Structural Scheme (Clause 12.1)

• Framework: Vertical posts + horizontal blocking members (wood, large cane, bamboo).
• Panels: Filled with cane, bamboo, or reed matting plastered with mud on both sides.
• Construction: In situ or prefabricated panels (Fig. 12).

Reinforcement in Seismic Zone V (Clause 11.1)

• Use mesh form reinforcement of canes/bamboos throughout walls.
• Collar beams made of cane/bamboo.
• Vertical canes tied to horizontal canes, collar beams (lintel), and roof beams (eave).

Fundamental Rules (Clause 12.2)

• Cane/bamboo diameter d ≈ 20 mm.
• Horizontal crushed canes/split bamboo every 4th adobe layer.
• Spacing S ≈ 400 mm between canes.
• Patterns shown in Fig. 11 for clay mud and adobe walls.

Summary Table of Key Parameters

Conceptual Diagram (Simplified)

graph TD
    A[Vertical Posts (Wood/Cane)] --> B[Horizontal Blocking Members]
    B --> C[Panels: Cane/Bamboo/Reed Matting]
    C --> D[Mud Plaster Both Sides]
    B --> E[Collar Beams (Cane/Bamboo)]
    E --> F[Roof Beam at Eave]
    C --> G[Mesh Reinforcement in Seismic Zone V]

This ensures ductility, seismic resistance, and durability of earthen walls with wood/cane frameworks as per IS 13827.

IS 13827: Key Points on Plastering and Painting

Purpose (Clause 13.0)

• Protection and durability of walls and thatch roofs.
• Aesthetic improvement.

Plastering Specifications (Clause 13.1)

• Two-layer plaster in dry areas:
  • First layer: 12-15 mm thick; mud + straw (1:1 volume) + natural additive (e.g., cow dung) for moisture resistance.
  • Second layer: Fine mud, rubbed with small, hard, rounded pebbles after drying.

Painting & Finishing (Clause 13.4)

• Use water-insoluble paint or wash with:
  • Lime solution
  • Cement solution
  • Gypsum solution
• Applied on exterior walls and treated thatch roofs.

Bracing for Plaster Support (Clause 12.3)

• Diagonal bracing with cane/bamboo nailed to framing before plastering.
• Ensures seismic resistance in Zones IV & V.

Summary Table:

flowchart TD
    A[Wall Framing] --> B[Diagonal Bracing (Cane/Bamboo)]
    B --> C[Panel Mesh Fixing]
    C --> D[First Plaster Layer (Mud+Straw+Cowdung)]
    D --> E[Second Plaster Layer (Fine Mud + Pebble Rub)]
    E --> F[Painting / Lime-Cement-Gypsum Wash]

This ensures durable, moisture-resistant, and seismic-safe plastered walls with proper finishing.

IS 13827 - Internal Bracing Systems in Earthen Houses (Clause 12.3 & Annex A)

Key Points:

• Purpose: Provide seismic resistance in Zones IV & V by internal diagonal bracing in walls and horizontal bracing at wall tops.
• Materials: Canes, bamboos, or wood nailed to framing members before plastering.
• Bracing Details:
  • Diagonal braces tied at ends and intersections (see Fig. 13).
  • Mud plaster applied over cane/bamboo matting.

Internal Bracing Systems (Annex A):

Holdfasts to Walls:

• Earthen walls ≤ 400 mm thick.
• Use Z-shaped steel holdfasts screwed to wooden posts, embedded in earthen walls for improved stability.

Summary Diagram:

graph TD
    A[Wooden Frame] --> B[Diagonal Bracing (Cane/Bamboo)]
    B --> C[Mud Plaster on Matting]
    A --> D[Z-shaped Steel Holdfasts]
    D --> E[Embedded in Earthen Walls ≤ 400mm]

This system enhances seismic safety by improving wall integrity and frame stability using simple, locally available materials.

IS 13827 - Committee Composition (Annex B Summary)

The Earthquake Engineering Sectional Committee, CED 39 prepared IS 13827. It includes experts from diverse organizations ensuring comprehensive coverage of earthquake-resistant construction.

Key Highlights:

• Chairman: Dr. A. S. Arya, Roorkee
• Members: Representatives from Indian Roads Congress, BHEL, CSIR-NGRI, University of Roorkee, IMD, North Eastern Council, IS Earthquake Technology, Central Water Commission, Railway Board, NHPC, DAE, NTPC, Tata Consulting Engineers, NBO, CBRI, Geological Survey of India, Engineers India Ltd, Nuclear Power Corporation, Army HQ, Structural Engineering Research Centre, CPWD, and BIS.
• Alternate members are nominated for most representatives.
• Member Secretary: Shri Y. R. Taneja, Director (Civil Engineering), BIS.

Purpose:

• To incorporate national expertise and international coordination.
• To relate standards with prevailing Indian practices.

Additional Note on Seismic Design (Clause 10.1.7):

• Maximum sum of opening widths in walls:
  • Seismic Zone V: ≤ 33% of wall length
  • Zones IV & III: ≤ 40% of wall length

This committee composition ensures multidisciplinary inputs for robust earthquake-resistant construction standards.