Improving earthquake resistance of low-strength masonry buildings - Guidelines

IS 13828: Scope & Key Specifications

IS 13828 covers seismic strengthening of low-strength masonry buildings, focusing on improving earthquake resistance.

Key Points from Scope & Relevant Clauses:

• Seismic Zones & Coefficients (Clause 3.6): Defines seismic zones and coefficients for design.

• Openings in Bearing Walls (Clause 8.4.1, Table 2): Limits on size and position of openings to maintain wall integrity.

• Strengthening Methods (Clause 8.5.1, Table 3): Recommended strengthening based on building category and storeys.

Notes:

• Strengthening codes (b, c, d, f, g) refer to specific methods detailed in the standard.
• Openings should be carefully designed to maintain seismic resistance.

Summary Diagram: Openings in Bearing Walls

flowchart TB
    A[Inside corner of outside wall]
    B[Opening 1]
    C[Opening 2]
    D[Pier between openings (ba)]
    E[Vertical distance between openings (hg)]

IS 13828: Key Definitions, Tables & Specifications

1. Definitions (Clause 3.0 & 3.6)

• Seismic Zone: Regions classified based on seismic hazard.
• Seismic Coefficient: A factor representing earthquake forces for design.
• Building categories are classified per seismic risk and importance.

2. Building Categories & Importance Factor (Table 7.1.1, Clause 7.1.1)

• Note: Category A is obsolete (Zone I no longer exists).
• Low strength masonry prohibited for Category F buildings.

3. Size & Position of Openings in Bearing Walls (Table 8.5, Clause 8.4.1)

Where:

• b1, b2, b3 = lengths of openings
• l1 = wall length

4. Strengthening Masonry Around Openings (Fig. 5)

• Provide lintels and vertical bars around openings.
• Maintain minimum thickness and reinforcement as per code.

flowchart LR
    A[Seismic Zone] --> B[Building Category]
    B --> C[Importance Factor]
    C --> D[Design Parameters]
    D --> E[Size & Position of Openings]
   

IS 13828: Seismic Zones & Design Coefficients Summary

• Applicable Zones: IS 13828 applies mainly to seismic zones III, IV, and V. Zones I & II require no special seismic provisions.

• Seismic Zones (I to V): Classified as per IS 1893 (Part 1).

• Basic Seismic Coefficient (Z): Defined in IS 1893 Table 2 for zones II to V.

• Usage:

  • Use Z from IS 1893 for calculating lateral seismic forces:
    [ F = Z \times I \times S_a \times W ]
    where:
    • (F) = design lateral force
    • (I) = importance factor
    • (S_a) = spectral acceleration coefficient
    • (W) = seismic weight of the structure

• Horizontal Tie (Clause 3.5): Use reinforced concrete, brick, or wooden runners horizontally in walls to provide horizontal bending strength and tie walls together.

flowchart LR
    A[Seismic Zones (I-V)] --> B[IS 1893 Zone Factors]
    B --> C{Zone Factor Z}
    C -->|Zone II| D[0.10]
    C -->|Zone III| E[0.16]
    C -->|Zone IV| F[0.24]
    C -->|Zone V| G[0.36]
    H[Design Force F] --> I[F = Z × I × S_a × W]

Note: Always refer to the latest IS 1893 for updated zone factors and spectral coefficients.

IS 13828: General Construction Requirements - Key Points

1. Continuity of Construction (Clause 4.2)

• Ensure structural continuity for seismic resistance.
• Avoid discontinuities or weak joints in masonry.

2. Types of Low Strength Masonry (Clause 8.1.1)

• Brick masonry with weak mortar
• Random rubble & half-dressed stone masonry with clay, mud lime-sand, or cement-sand mortar.

3. Building Categories for Earthquake Resistance (Clause 7, Table 1)

4. Openings in Bearing Walls (Clause 8.4.1, Table 2)

5. Important Notes

• Low strength masonry not permitted in Category E buildings.
• Strengthening around openings (lintels, vertical bars) is critical.

Diagram: Strengthening Masonry Around Openings

graph TD
  A[Wall Thickness (l)] --> B[Window Width (w)]
  B --> C[Lintel Thickness (l1)]
  C --> D[Vertical Reinforcement (v)]
  D --> E[Strengthening Mason

IS 13828: Special Construction Features - Key Points

1. Fire Safety (Clause 4.5)

• Buildings must be fire-resistant per relevant Indian Standards, as fire often follows earthquakes.

2. Seismic Strengthening Around Openings (Clause 8.4.1, Table 8.5)

• Maxt formula:
  [ M_{axt} = \frac{b_1 + b_2 + b_3}{l_1} \quad \text{or} \quad \frac{b_g + b_y}{l_2} ] where (b_i) = opening widths, (l_1), (l_2) = wall lengths (11 or 18 units).

3. Built-in Staircase (Clause 5.3.2)

• Staircase walls must extend full height and foundation for rigidity and damage protection.

4. Box Type Construction (Clause 6)

• Walls act as vertical load supports and shear walls.
• Prefabricated panels require strong shear transfer connections.

Diagram: Strengthening Masonry Around Openings

graph LR
A[Wall] --> B[Opening]
B --> C[Pier Width (ba)]
B --> D[Vertical Distance (hg)]
B --> E[Distance from Corner (bs)]

Summary:
Ensure fire resistance, maintain minimum pier widths and distances around openings, provide rigid stair enclosures, and ensure shear connections in box-type masonry for seismic safety.

IS 13828: Materials and Mortars for Low Strength Masonry

Mortar Types & Mix Ratios (Clauses 8.2.2, 8.3.2)

• Lime-Sand Mortar: 1:3 (lime : sand) — good quality lime and sand.
• Clay Mud Mortar: Good quality clay mud.
• Cement-Sand Mortar:
  • For horizontal steel reinforcement: 1:3 mix with 6 mm mortar cover above and below steel.
  • For vertical steel reinforcement: use 1:6 cement-sand mortar around steel bricks (brick size 1x1 or 1½x1½ depending on wall thickness).

Mortar Usage Guidelines

• Weak mortars (lime-sand 1:3, clay mud) are used in brickwork without steel.
• Cement-sand mortar (1:6) is preferred around vertical steel reinforcement.
• Horizontal steel requires stronger cement-sand mortar (1:3) for proper bonding and cover.

Building Categories for Earthquake Resistance (Table 1, Clause 7)

Note: Low-strength masonry is not permitted for Category E seismic zones.

Summary Table: Mortar Mixes and Applications

flowchart TD
    A[Brickwork] --> B{Steel Reinforcement?}
    B -- No -->

IS 13828: Building Categories for Earthquake Resistance

Key Points from Clause 7.1.1 & Table 1 (Building Categories)

Buildings are categorized A to E based on:

• Seismic Zone (II to V)
• Importance Factor (I) (from IS 1893 Part 1)
• Category A is defunct (Zone I no longer exists)
• Low strength masonry not allowed in Category F

Importance Factor (I)

• Refer IS 1893 (Part 1) Table 6 for values (typically 1.0 to 1.5 depending on building use)

Strengthening (Clause 8.5.1, Table 3)

For low strength masonry:

Strengthening codes (b, c, d, f, g) refer to specific methods like banding, corner reinforcement, etc. (See Clause 8.5.1)

Formula for Design Seismic Coefficient (Clause 7):

[ h = I \times d_o ]

• h = design seismic coefficient for the building
• I = Importance factor (from IS 1893)

IS 13828: Low Strength Masonry Construction Key Points

Types Covered (Clause 8.1.1)

• a) Brick construction with weak mortar (clay mud, weak cement-sand)
• b) Random rubble & half-dressed stone masonry with clay mud, lime-sand, or weak cement-sand mortars

Building Categories (Clause 7, Table 1)

Note: Low-strength masonry is prohibited in Category E zones (high seismic risk).

Definitions (Clause 3.1)

• Fired brick in clay mud mortar
• Random rubble or semi-dressed stone masonry in weak mortars (clay mud, lime-sand, cement-sand)

Important Specifications

• Follow IS 4326 (1993) for general seismic design principles.
• Special seismic detailing is mandatory to improve resistance.
• Low strength masonry is not engineered construction; it has limited resistance in severe seismic zones (VIII or IX).

Relevant IS Codes for Reference

• IS 1597 (Part 1): Stone masonry construction
• IS 1893: Earthquake resistant design criteria
• IS 1904: Foundation design in soils
• IS 4326: Earthquake resistant building design

Typical Seismic Design Considerations for Low Strength Masonry

• Use of seismic bands (horizontal and vertical reinforcement)
• Proper mortar mix to improve bonding
• Avoid use in high seismic zones (Category E)
• Limit building height and mass

flowchart TD
    A[Low Strength Masonry Types]
    A --> B[Brick + Weak Mortar]
    A --> C[Random Rubble Stone Masonry]
    B --> D[Clay Mud Mortar]
    B --> E[Weak Cement-Sand Mortar

IS 13828: Low Strength Masonry - Key Points

Types of Low Strength Masonry (Clause 8.1.1 & 3.1)

• a) Brick construction using weak mortar (e.g., clay mud mortar).
• b) Random rubble and half-dressed stone masonry with mortars like clay mud, lime-sand, cement-sand.

Building Categories & Restrictions (Table 1, Clause 7)

Note: Low strength masonry is prohibited in Category E seismic zones.

Specifications & Notes

• Low-strength masonry includes fired bricks in clay mud mortar, random rubble stone masonry in weak mortars.
• Not considered engineered construction; may not resist severe seismic intensities (VIII or IX) fully.
• Special seismic design features in IS 13828 improve resistance and reduce collapse risk.
• Refer to IS 4326 for general masonry provisions and IS 1597 (Part 1) for rubble stone masonry construction.

Summary Table: Mortar Types for Low Strength Masonry

flowchart TD
    A[Low Strength Masonry] --> B[Brickwork with weak mortar]
    A --> C[Random rubble / half-dressed stone masonry]
    C --> D[Clay mud mortar]
    C --> E[Lime-sand mortar]
    C --> F[Cement-sand mortar]

References:

• IS 13828 Clause 8.1.1, 3.1, Table 1 (Clause 7)
• IS 4326:1993 for seismic design principles
• IS 159

Masonry and Mortar Specifications (IS 13828)

Mortar Types & Mixes (Clause 8.2.2):

• Lime-sand mortar: 1:3 (lime : sand) — for general use.
• Clay mud mortar: Good quality, used in weak mortar masonry.
• Cement-sand mortar: 1:3 — mandatory where horizontal steel reinforcement is placed; ensure 6 mm mortar cover above and below steel.
• For vertical steel reinforcement, use surrounding brickwork with 1:6 cement-sand mortar in a 1x1 or 1½ x1½ brick size zone.

Low Strength Masonry (Clause 8.1.1 & 3.1):

• Includes brickwork in weak mortar (clay mud, lime-sand, cement-sand).
• Random rubble and half-dressed stone masonry with weak mortars.

Building Categories for Earthquake Resistance (Table 1, Clause 7):

Summary:

• Use lime-sand (1:3) or clay mud mortar for weak masonry.
• For steel reinforcement, use cement-sand mortar (1:3) with proper cover.
• Low-strength masonry is restricted in high seismic zones (Category E prohibited).
• Mortar thickness and brick size around vertical steel reinforcement must be carefully controlled.

flowchart LR
    A[Brickwork] --> B{Mortar Type}
    B --> C[Lime-Sand 1:3]
    B --> D[Clay Mud]
    B --> E[Cement-Sand 1:3]
    E --> F[Horizontal Steel: 6mm cover]
    E --> G[Vertical Steel: 1x1 brick zone with 1:6 cement-sand]
    A --> H[

IS 13828: Wall Construction and Detailing Key Points

1. Size and Position of Openings (Clause 8.4.1, Table 2)

• Openings should be small and centrally located to maintain lateral load resistance.

2. Wall Thickness and Bonding (Clause 8.3.3 & 8.3.6)

• Wall thickness t ≤ 450 mm, preferably ~350 mm.
• Stones in inner and outer wythes must interlock to prevent delamination and buckling.
• Use bonding elements (8-10 mm steel bars bent S-shape or hooked) with 25 mm cover instead of through stones.
• Alternative bonding: treated wood bars (38×38 mm) or concrete bars (50×50 mm) with central 8 mm rod.

3. Strengthening Around Openings

• Use lintels and vertical bars with thickness and reinforcement as per Fig. 5 (not shown here).
• Maintain minimum pier widths and vertical clearances as above.

Summary Diagram: Wall Opening Layout

graph TD
    A[Inside Corner] -->|bs| B[Opening 1]
    B -->|ba| C[Opening 2]
    B -->|hg| D[Opening Above]

Ensure compliance with these dimensions and detailing for seismic resistance and structural integrity.

IS 13828 - Openings in Bearing Walls (Clause 8.4)

Key Specifications from Table 2 (Clause 8.4.1)

• b1, b2, b3 = lengths of openings in one wall segment
• bg, by = lengths of openings in orthogonal directions

Strengthening (Clause 8.4.3)

• If openings exceed limits, provide R.C. lining around openings.
• Use 2 high strength deformed (HSD) bars of 8 mm dia in lintel and jambs.
• Refer to Fig. 5 for reinforcement detailing.

Summary Diagram of Strengthening Detail:

graph TD
    A[Wall] --> B[Opening]
    B --> C[RC Lintel with 2 HSD bars Ø8mm]
    B --> D[RC Jambs with 2 HSD bars Ø8mm]
    C & D --> E[Improved lateral strength]

Note: Keep openings small, centrally located to maintain lateral load resistance. Use provided ratios and distances to design safe openings in bearing walls.

IS 13828 - Seismic Strengthening Arrangements (Clause 8.5)

1. Strengthening Methods by Building Category (Table 3 - Clause 8.5.1)

Legend for strengthening methods (refer to IS 13828 for details):

• b: Vertical reinforcement at corners and junctions
• c: Horizontal bands (at plinth, lintel, and roof levels)
• d: Additional vertical bars at wall intersections
• f: Strengthening around openings
• g: Anchoring floors to walls

2. Openings in Bearing Walls (Table 2 - Clause 8.4.1)

Formulas for openings length ratio:
[ M_{axt} = \frac{b_1 + b_2 + b_3}{11} \quad \text{or} \quad \

IS 13828: Fire Safety Considerations & Related Structural Specifications

Fire Safety (Clause 4.5)

• Fire often follows earthquakes; buildings must be fire resistant per relevant Indian Standards (e.g., IS 1641, IS 1642).
• Use fire-resistant materials and detailing to prevent fire spread post-earthquake.

Key Specifications for Openings in Bearing Walls (Clause 8.4.1 & Table 2)

• Openings reduce lateral resistance; keep them small, central, and well spaced.
• Strengthen masonry around openings using lintels and vertical bars (see Fig. 5 in IS 13828).

Building Categories & Importance Factors (Clause 7.1.1)

• Higher importance factor → stricter fire and seismic resistance.

Summary Diagram: Openings in Bearing Walls

flowchart LR
  A[Inside Corner] -->|Distance bs| B(Openings)
  B -->|Pier width ba| C(Adjacent Opening)
  B -->|Vertical distance hg| D(Opening above)
  B -->|Lintel & vertical bars| E(Strengthening)

References:

• Fire resistance per IS 1641, IS 1642
• Opening size & position per IS 13828 Table 2
• Building importance & seismic zones per IS 13828 Table 1

IS 13828: References and Amendments - Key Points

1. Amendments:

• Third Reprint August 2008 includes Amendment Nos 1, 2 & 3.
• Clause 8.1.1 Table 1 has been deleted in this reprint.

2. References:

• IS 1893 (Criteria for earthquake resistant design of structures) for seismic zones and coefficients.
• IS 4326 (Earthquake resistant design and construction of buildings) for complementary guidelines.
• International Association for Earthquake Engineering's "Guidelines for earthquake resistant non-engineered construction" (Tokyo, 1986) referenced.

3. Committee Composition:

• Earthquake Engineering Sectional Committee CED 39 prepared the standard.
• Members from BIS, IIT Kanpur, BHEL, National Geophysical Research Institute, Central Water Commission, and other key organizations.

Important Tables from Amendments:

Table 2: Size and Position of Openings in Bearing Walls (Clause 8.4.1)

Table 4: Vertical Steel Reinforcement in Low Strength Masonry Walls (Clause 8.5.7)