Improving earthquake resistance of earthen buildings - Guidelines
1993 Edition

Overview of IS 13827: Scope & Essential Definitions

Scope (Clause 3.0)

• Establishes terminology associated with seismic strengthening of earthen buildings.
• Emphasizes seismic zones, coefficients, and design parameters pertinent to retrofitting.

Key Terminology:

• Seismic Zone & Coefficient (Clause 3.5):

  • Classifies regions by seismic risk levels.
  • The seismic coefficient (Ah) is utilized for calculating lateral seismic forces.

• Zone Factor (Z) (Clause 3.6):

  • Indicates the level of seismic hazard.
  • Serves to develop the design response spectrum.
  • Values vary depending on geographic seismic zones (e.g., 0.10, 0.16, 0.24, etc.).

Foundation Requirements (Clause 10.3)

• Specifies foundation criteria for retrofitted buildings.
• Ensures foundations withstand seismic forces transmitted from the superstructure.

Formula to Determine Seismic Coefficient (Ah):

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

Where:

• Z = Zone factor (from seismic zoning maps)
• I = Importance factor (based on building function)
• R = Response reduction factor (dependent on structural system)

Typical Seismic Zone Factors:

flowchart LR
    A[Identify Seismic Zone] --> B[Determine Zone Factor (Z)]
    B --> C[Calculate Seismic Coefficient (Ah)]
    C --> D[Develop Design Spectrum]
    D --> E[Apply to Structural and Foundation Design]

This framework supports seismic retrofitting as outlined in IS 13827.

IS 13827: Key General Considerations

1. Horizontal Seismic Coefficient Calculation (Clause 3.4.2.3)

   • Computed following IS 1893:1984, considering soil-structure interaction 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 Design (Clause 10.3)

   • Must resist seismic forces transferred from above structure.
   • Soil-structure interaction effects must be accounted for accurate seismic response.

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

   • Symmetric and regular layouts with uniform stiffness and mass distribution are advised.
   • Avoid re-entrant corners, soft stories, and torsional irregularities.
   • Fig. 8 illustrates ideal configurations for seismic zones IV and V.

4. Seismic Reinforcement (Clause 12)

   • Includes wall anchorage, banding, and corner strengthening to improve seismic resilience.

Parameter Summary for Horizontal Seismic Coefficient

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

This summary guides seismic design considerations.

IS 13827: Seismic Zone Classifications and Their Application

Seismic Zones According to IS 1893 Part 1

• India is segmented into five seismic zones (I to V) based on earthquake hazard.
• Zone Factors (Z) represent fundamental seismic design coefficients.

(Zone I is deemed to have negligible seismic risk; Z = 0)

Applicability Criteria (IS 13827 Clause 3.5)

• Applies to buildings located in seismic zones II through V.
• Zone factors are adopted from IS 1893 (Part 1).
• Design lateral forces and base shear are computed using these zone coefficients.

Core Formula for Basic Seismic Coefficient

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

Where:

• (A_h) = Horizontal seismic coefficient
• (Z) = Zone factor (per IS 1893)
• (I) = Importance factor (based on building purpose)
• (S_a) = Soil spectral acceleration coefficient
• (R) = Response reduction factor (ductility related)

flowchart LR
    A[Seismic Zones I to V]
    A --> B[Zone Factors (Z) as per IS 1893]
    B --> C[Application in IS 13827 for Retrofit Design]
    C --> D[Seismic Coefficient Calculation \(A_h\)]
    D --> E[Base Shear and Load Design]

Summary: Use seismic zone factors from IS 1893, along with importance and soil factors, to determine seismic forces for retrofitting under IS 13827.

IS 13827: Design Advice for Seismic Risk Areas

Highlights from Clause 10.5 (Building Configuration)

• Advocates simple and symmetrical layouts (see Fig. 8) for earthen buildings in zones IV and V.
• Regularity in plan and elevation minimizes torsional forces and stress concentrations.
• Re-entrant corners, large openings, and irregular shapes should be avoided.

Seismic Reinforcement Measures (Clause 12)

• Employ horizontal bands at plinth, lintel, and roof levels to enhance ductility.
• Introduce vertical buttresses or reinforcements to bolster wall stability.
• Incorporate straw mixed into soil (up to 25% by volume) to control cracking (Clause 9.5).

Seismic Coefficient (Clause 3.5)

• Depends on seismic zone.
• Utilize appropriate zone factors (Z) from IS 1893.

Summary Table: Earthquake Resistance Features

Formula for Seismic Base Shear (IS 1893)

[ V_b = Z \times I \times S_a \times \frac{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 building
• (R) = Response reduction factor

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

In brief: Employ simple symmetrical plans with horizontal banding and controlled straw content to improve seismic resistance in earthen constructions as per IS 13827.

IS 13827: Key Points on Earthen Wall Construction

Types of Earthen Walls (Clause 5.0)

• Clay mud walls
• Adobe block walls
• Vertical reinforcement with cane or bamboo
• Horizontal reinforcement with crushed cane or split bamboo every fourth adobe layer

Reinforcement Specifications (Clause 12.2)

• Spacing (S): Approximately 400 mm between cane/bamboo reinforcements
• Diameter (d): Around 20 mm for cane or bamboo
• Reinforcement Patterns:
  • Clay mud walls reinforced vertically with cane/bamboo
  • Adobe walls reinforced horizontally every fourth layer

Rammed Earth Construction (Clause 9.1)

• Soil with lower clay content than adobe soil is preferred
• Moisture near Optimum Moisture Content determined by Proctor Test (IS 2740 Part 7:1980)
• Soil compacted in long wooden molds to achieve density

Recommended Building Shape for Seismic Resistance (Clause 4.6)

• Simple rectangular, symmetrical floor plan
• Continuous load-bearing walls in both directions
• Avoid L or T shapes; internal courtyards recommended for ventilation and drainage

Reinforcement Summary Table

graph TD
A[Clay Mud Wall] --> B[Vertical Cane/Bamboo Reinforcement]
C[Adobe Wall] --> D[Horizontal Cane/Bamboo Every 4th Layer]
E[Rammed Earth] --> F[Compacted Soil in Wooden Forms]
G[Building Shape] --> H[Rectangular and Symmetrical]
H --> I[Continuous Load-Bearing Walls]

These practices ensure structural soundness and improved seismic resistance.

IS 13827: Material Properties and Testing for Seismic-Resistant Adobe Construction

Critical Tests & Specifications:

• Fissure Control Test (Clause 6.2):

  • Prepare eight folded specimens with varying soil-to-sand volume ratios (1:0 up to 1:3).
  • After 48 hours, select the mix with the minimum sand content that exhibits no visible cracks in mortar.
  • This ratio determines the optimal soil-sand mixture for strength and durability.

• Compressive Strength Test (Clause 6.4):

  • Test 100 mm cubic samples of dried clay units.
  • Desired minimum compressive strength is 1.2 N/mm² for adobe blocks.

Minimum Dimensions for Wood Frame Components (Clause 3.3, Table A-3):

Summary:

• Adopt soil:sand ratios from 1:0 to 1:3; choose mix with no fissures after 48 hours.
• Ensure adobe blocks have compressive strength ≥ 1.2 N/mm².
• Adhere to minimum wood frame member sizes for effective retrofitting.

flowchart TD
    A[Prepare Soil-Sand Mixtures] --> B{Fissure Test After 48h}
    B -- No fissures --> C[Optimal Mix Selection]
    B -- Fissures Present --> D[Adjust Sand Content]
    C --> E[Adobe Block Production]
    E --> F[100 mm Cube Compressive Strength Test]
    F --> G{Strength ≥ 1.2 N/mm²?}
    G -- Yes --> H[Material Approved]
    G -- No --> I[Modify Mix and Retest]

This ensures materials meet standards for earthquake-resistant adobe construction.

IS 13827: Key Guidelines for Hand-Laid Layered Construction

1. Compressive Strength Testing (Clause 6.4)

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

2. Layering Method (Clauses 7.3 & 9.3)

• Each layer approximately 100 mm thick.
• Before placing the next layer, moisten the lower layer thoroughly to reduce horizontal cracks.
• Compact each layer completely.
• Sprinkle water on compacted layer prior to the next.
• Typical adobe block dimensions:
  • Length: 380 mm
  • Width: 250 mm
  • Thickness: 110 mm

3. Construction Recommendations

• Layer height before starting a new block ranges from 500 to 800 mm.
• Ensure strong bonding by wetting the completed layer before adding subsequent layers.

Summary Table

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

This approach promotes strong layer adhesion and minimizes crack formation.

IS 13827: Specifications for Adobe and Block Construction

Block Dimensions (Clause 8.2)

• Rectangular blocks: 380 mm × 250 mm × 110 mm with approximately 125 mm overlap.
• Square blocks: 380 mm × 380 mm × 110 mm with roughly 190 mm overlap.

Layering and Compaction (Clause 9.3)

• Soil layers of roughly 100 mm thickness, compacted fully.
• Water sprinkled over each compacted layer before adding the next.
• Total block layer height between 500 and 800 mm.
• Prior to placing a new block layer, wet the completed layer to ensure proper bonding.

Compressive Strength (Clause 6.4)

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

Construction Practice (Clause 7.3)

• Moisten the lower layer adequately before placing the next to reduce horizontal fissures.

Adobe Block Size Summary

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

This ensures adequate bonding and structural strength in adobe masonry.

IS 13827: Essential Guidelines for Rammed Earth Construction

Soil and Moisture Requirements

• Use soil with lower clay content compared to adobe soil.
• Maintain moisture content close to Optimum Moisture Content (OMC) as determined by Proctor Test (IS 2740 Part 7:1980).

Construction Procedure (Clause 9.1)

• Soil is deposited into long wooden molds.
• Compaction is carried out manually or mechanically to achieve desired density.
• After compaction, forms are removed.

Masonry Bonding Principles (Clause 8.4)

• Courses should be laid level.
• Vertical joints must be staggered with appropriate overlap.
• Mortar joints should be fully filled.
• Avoid continuous vertical joints at wall intersections.

Reference for Proctor Test

• Determines Optimum Moisture Content and maximum dry density.
• Ensures soil compaction quality and consistency.

Typical Specifications

flowchart LR
    A[Select Suitable Soil] --> B[Adjust Moisture to OMC]
    B --> C[Place Soil in Wooden Forms]
    C --> D[Compact Soil (Manual/Mechanical)]
    D --> E[Remove Forms]
    E --> F[Cure and Finish Walls]

Refer to IS 2740 (Part 7) for Proctor test methodology and IS 13827 clauses 8.4 & 9 for bonding and construction.

IS 13827: Key Recommendations for Construction in Seismic Zones

1. Seismic Zoning and Coefficients (Clause 3.5)

• Seismic zones I to V defined; zones IV and V represent high seismic hazard.
• Seismic coefficient (Ah) varies with zone and soil type; used for calculating lateral seismic forces.

2. Appropriate Building Configuration (Clause 10.5)

• Promote simple, symmetrical plans (see Fig. 8) for earthen structures.
• Avoid irregularities in plan and elevation to minimize torsional effects.
• Ensure continuous load paths for seismic force transmission.
• Provide sufficient wall lengths and thickness for lateral stability.

3. Site Selection Criteria (Clause 10.2.1)

• Avoid sites with:
  • Loose sandy soils
  • Poorly compacted clays
  • Fill materials prone to settlement
  • High groundwater tables
• Especially important for zones IV and V.

4. Seismic Strengthening Measures (Clause 11)

• Incorporate straw in soil-water mix up to 25% volume to control fissures in bearing walls.

Seismic Zone vs Coefficient Table (Typical Values)

flowchart TD
    A[Site Selection] --> B{Soil Quality}
    B -->|Suitable| C[Proceed with Construction]
    B -->|Loose Sand, Poor Clay, Fill| D[Avoid Site]
    A --> E[Groundwater Level]
    E -->|High| D
    E -->|Low| C
    C --> F[Adopt Adequate Building Configuration]
    F --> G[Ensure Symmetry and Structural Continuity]
    F --> H[Maintain Proper Wall Thickness]
    G & H --> I[Implement Seismic Reinforcement]

Note: For detailed design, consult IS 13827 Fig. 8 and Clause 12.

IS 13827: Guidelines for Seismic Strengthening of Load-Bearing Walls

Essential Provisions

• Clause 10.5 (Building Configuration):

  • Follow the layout in Fig. 8 for zones IV and V.
  • Includes symmetrical plan, uniform wall distribution, and proper anchorage of floors and roofs.

• Clause 11 (Strengthening Measures):

  • Add reinforced concrete (RC) bands at plinth, lintel, and roof levels.
  • Provide vertical RC or masonry columns at wall corners and junctions.
  • Insert steel or RC anchors to connect walls with floor and roof structures.
  • Repair masonry cracks with suitable mortar.

Typical Strengthening Specifications:

Important Considerations:

• Maintain a continuous load path from roof to foundation.
• Avoid adding excessive mass without corresponding strength.
• Refer to Fig. 8 in IS 13827 for layout and band placement.

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

This structural system enhances ductility and load distribution critical for seismic resistance.

IS 13827: Integration of Wood and Cane Frameworks in Earthen Walls

Structural System (Clause 12.1)

• Framework consists of vertical posts and horizontal blocking members made from wood, large cane, or bamboo.
• Wall panels filled with cane, bamboo, or reed matting, plastered on both sides with mud.
• Construction can be performed in situ or using prefabricated panels (see Fig. 12).

Reinforcement Practices in High Seismic Zone V (Clause 11.1)

• Implement mesh reinforcement using canes or bamboo throughout the walls.
• Employ collar beams fashioned from cane or bamboo.
• Vertically oriented canes are tied to horizontal members, collar beams (lintel), and roof beams (eaves).

Essential Parameters (Clause 12.2)

• Cane/bamboo diameter approximately 20 mm.
• Horizontal crushed cane or split bamboo reinforcement every fourth adobe layer.
• Spacing between canes around 400 mm.
• Reinforcement patterns shown in Fig. 11 for clay mud and adobe walls.

Parameter Summary

Simplified Structural Diagram

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

This configuration provides ductility, seismic resilience, and durability to earthen walls reinforced with wood or cane frameworks.

IS 13827: Important Guidelines on Plastering and Painting

Objectives (Clause 13.0)

• Enhance protection and longevity of walls and thatch roofing.
• Improve aesthetic appearance.

Plaster Application (Clause 13.1)

• Employ two-layer plastering in dry regions:
  • First layer: 12-15 mm thick; composed of mud mixed with straw (1:1 by volume) and a natural additive like cow dung for moisture resistance.
  • Second layer: Fine mud finish, polished with small, hard, rounded pebbles after drying.

Painting and Finishing (Clause 13.4)

• Use water-insoluble paints or apply washes of:
  • Lime solution
  • Cement solution
  • Gypsum solution
• Apply on external walls and treated thatch roofs.

Bracing for Plaster Support (Clause 12.3)

• Diagonal bracing using cane or bamboo nailed to framing before plastering.
• Ensures seismic resistance, especially in zones IV and V.

Summary Table:

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

This process ensures durable, moisture-resistant, and earthquake-resilient plaster finishes.

IS 13827: Internal Bracing Techniques for Earthen Houses (Clause 12.3 & Annex A)

Overview:

• Purpose: Provide seismic stability in zones IV and V via internal diagonal bracing within walls and horizontal bracing at wall tops.
• Materials: Use cane, bamboo, or wood nailed to framing members prior to plastering.
• Bracing Details:
  • Diagonal braces anchored at ends and intersections (see Fig. 13).
  • Mud plaster applied over cane or bamboo mesh.

Internal Bracing System Types (Annex A):

Holdfasts for Walls:

• Applicable for earthen walls up to 400 mm thick.
• Employ Z-shaped steel holdfasts screwed to wooden posts and embedded into earthen walls to improve anchorage and stability.

Summary Diagram:

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

This system enhances seismic safety by reinforcing wall integrity and frame stability using readily available local materials.

IS 13827: Committee Members Overview (Annex B)

The Earthquake Engineering Sectional Committee, CED 39, was responsible for drafting IS 13827. It comprises experts from a broad spectrum of organizations to ensure thorough coverage of earthquake-resistant construction methods.

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 Headquarters, Structural Engineering Research Centre, CPWD, and BIS.
• Alternate members nominated for most organizations.
• Member Secretary: Shri Y. R. Taneja, Director (Civil Engineering), BIS.

Purpose:

• To incorporate national expertise and facilitate international coordination.
• To align standards with Indian construction practices.

Additional Seismic Design Note (Clause 10.1.7):

• Maximum allowable total width of openings in walls:
  • Zone V: ≤ 33% of wall length
  • Zones IV & III: ≤ 40% of wall length

This multidisciplinary committee ensures comprehensive input for robust earthquake-resistant construction standards.