Guidelines for Improving the Cyclonic Resistance of Low-Rise Houses and Other Buildings/Structures

IS 15498: Scope Summary

• Scope Definition: IS 15498 specifies requirements for structural elements or materials (specific scope depends on the full standard text, which is not provided here).

• Rounding Off Values:

  • Follow IS 2:1960 for rounding numerical results.
  • Retain the same number of significant figures as the specified values in IS 15498.

• Referenced Standards:

  • Annex A lists related standards incorporated by reference.
  • Users should verify and apply the latest editions of these standards.

Key Points for Compliance Check

If you need formulas or tables, please specify the structural element or material covered under IS 15498 for targeted data.

Cyclonic Wind Field - IS 15498 Key Points & Formulas

1. Wind Velocity Distribution (Clause 3.1 & 3.2):

• Radius of Maximum Wind (RMW): Distance from cyclone eye center to max tangential wind.
• Velocity inside RMW (interior region): Linear from zero at eye center to max at RMW.
• Velocity outside RMW:

[ V(r) = V_0 \left(\frac{r_0}{r}\right)^x ]

Where:

• (V(r)) = wind speed at radius (r)
• (V_0) = max wind speed at (r_0) (RMW)
• (r_0) = radius of maximum wind
• (x) = power law exponent (0.4 to 0.6)
• (r) = radial distance from eye center

2. Design Wind Speed for Cyclonic Regions (Clause 1.15):

[ V_a = f \times k_1 \times k_2 \times k_3 \times V_b ]

Where:

• (V_a) = design wind speed at height (z) (m/s)
• (f) = enhancement factor for cyclonic risk
  • Dwellings: 1.0
  • Industrial buildings: 1.15
  • Post-cyclone importance structures: 1.30
• (k_1) = probability factor (risk coefficient)
• (k_2) = terrain, height & structure size factor
• (k_3) = topography factor
• (V_b) = basic wind speed (from IS 875 Part 3)

3. Notes:

• (k_1, k_2, k_3, V_b) values as per IS 875 (Part 3).
• Special structures (chimneys, towers) require code-specific provisions.
• Wind speed varies with height (z).

flowchart LR
    A(Cyclone Eye) -->|Radius r| B(Radius of Max Wind \(r_0\))
    B -->|Max Wind Speed \(V_0\)| C(Wind Speed \(V(r)\

Cyclonic Wind Speed for Design (IS 15498)

The design cyclonic wind speed (V_a) at height (z) is calculated as:

[ \boxed{ V_a = f \times k_1 \times k_2 \times k_3 \times V_b } ]

Where:

Additional Notes:

• Velocity distribution inside the cyclone eye radius varies linearly from zero at the center (Clause 3.2).
• For special structures (chimneys, transmission towers), refer to their respective codes.
• Cyclonic winds have higher turbulence and risk, hence the enhancement factor (f).

Summary Flow of Wind Speed Calculation

flowchart LR
    Vb[Basic Wind Speed (Vb)]
    k1[Probability Factor (k1)]
    k2[Terrain, Height, Structure Factor (k2)]
    k3[Topography Factor (k3)]
    f[Enhancement Factor (f)]
    Va[Design Cyclonic Wind Speed (Va)]

    Vb --> Va
    k1 --> Va
    k2 --> Va
    k3 --> Va
    f --> Va

Use IS 875 (Part 3) for detailed values of (k_1, k_2, k_3, V_b).

Key Formulas & Specifications for Pressures and Forces (IS 15498)

1. Design Wind Speed (Clause 1.15):

[ V_a = f \times k_1 \times k_2 \times k_3 \times V_b ]

• ( f ) = Cyclonic risk enhancement factor
  • Dwellings: 1.0
  • Industrial buildings: 1.15
  • Post-cyclone importance structures: 1.30
• ( k_1 ) = Probability factor (risk coefficient)
• ( k_2 ) = Terrain, height & structure size factor
• ( k_3 ) = Topography factor
• ( V_b ) = Basic wind speed (from IS 875 Part 3)
• ( V_a ) = Design wind speed at height ( z )

2. Pressure and Force Calculation:

• Use wind pressure coefficients from IS 875 (Part 3) for global and local pressures.
• For buildings in clusters:
  • Corner buildings: multiply pressures by 1.5 (Clause 1.50 c)
  • Interior buildings: apply shielding factor 0.8 (Clause 1.50 d)
• Roof uplift forces must be safely transferred to foundations via strong connections (GI bolts, straps, etc.).

3. Structural Recommendations:

• Provide minimum 600 mm parapet for load-bearing masonry.
• Anchor roof slabs to continuous lintel bands with adequate ties.
• In cyclone-prone areas, use ductile detailing per IS 13920 even if wind governs design.
• Provide bracing at bottom chord level of trusses to prevent buckling (Fig. 13).
• Round off building corners to reduce drag forces.

Reference Table: Cyclonic Risk Enhancement Factor ( f )

Summary Flow of Wind Pressure Calculation

flowchart TD
    A[Start: Determine Basic Wind Speed \(V_b\)] --> B[Apply Cyclonic Risk Factor \(f\)]
    B --> C[Apply Probability Factor \(k_1

IS 15498: Guidelines for Planning Cyclone-Resistant Buildings

Key Planning Guidelines (Clause 6)

• Site & Foundation:

  • Build on good ground; avoid partial made-up ground foundations.
  • Avoid low-lying and ridge-top locations prone to flooding and high wind speeds.

• Plan Shape & Orientation:

  • Prefer regular, compact, symmetrical plans (circular/polygonal preferred).
  • Avoid re-entrant corners and zig-zag plans.
  • Orient building so smallest facade faces prevailing wind if known.

• Building Arrangement:

  • Prefer cluster arrangements over rows to reduce tunnel wind effects.
  • Provide cross walls or pilasters for walls >3.5 m length.

• Roof Design:

  • Use hipped roofs over gabled roofs for better wind resistance.
  • Avoid roof slopes less than 1:3 except for large span roofs.

• Openings & Walls:

  • Total openings ≤ 50% of wall width.
  • Openings in load-bearing walls should be at least h/6 from inner corners (h = storey height).

• Group Housing:

  • Inter-building spacing ≥ 2 × building width for wind shielding.

• Flood Protection:

  • Use raised mounds, stilts, or retaining walls in flood-prone coastal areas.

Important Tables & Figures Summary

Formula for Opening Location:

[ \text{Distance of openings from inner corner} \geq \frac{h}{6

IS 15498: Guidelines for Non-Engineered Construction

Key Specifications & Guidelines (Clause 3.5 & 7):

• Long Walls:
  Length > 3.5 m must have cross walls or integral pilasters to improve lateral stability.

• Building Location:
  Avoid low-lying flood-prone areas and ridges in hilly regions (due to high wind velocity).

• Roof Slope:
  Roof pitch should be ≥ 1:3 slope.
  Hipped roofs preferred over gabled roofs (peak suction pressure ~80% of gabled).

• Openings in Walls:
  Total opening < 50% of wall width.
  Openings must be ≥ h/6 from inner corners (h = storey height to eave).

• Inter-building Spacing:
  If spacing < 2× building width, interior buildings get shielding (pressure factor 0.8), corner buildings pressure factor 1.5.

• Flood Protection:
  Use raised earthen mounds or stilts with bracings; posts anchored ≥ 900 mm deep with minimum bearing area of 22,500 mm².

• Anchorage & Connections:
  Roof must be securely tied down (e.g., diagonal organic ropes replaced annually).
  Overhang ≤ 450 mm or tied back.
  Use cyclone bolts to anchor roofs to lintel bands.

Important Tables & Figures Summary:

Anchorage Detail (Fig. 3b):

• Anchor Poles: 4 per post, at two levels,

Key Guidelines & Formulas for Semi-Engineered Construction (IS 15498):

Anchorage to Masonry (Clause 1.5 j)

• Angle of dispersion: 2 vertical : 1 horizontal.
• Shear strength of masonry: Neglected.
• Effective masonry weight above anchorage = 1.5 × uplift force at anchorage.

Structural Elements & Connections

• Use 3 × 25 mm MS plates for longitudinal reinforcement at crown and eaves.
• Anchorage to foundations via GI/MS straps (30 mm × 24 gauge) and heavy wire turns (16 gauge).
• Triangular roof frames spaced max 2.0 m apart for sloped roofs.
• Connections must safely transfer uplift forces to foundations using metal straps, bolts, nuts, and steel flats.

Hollow Concrete Block Masonry (Clause 3.0 d)

• Reinforced pilasters through hollow blocks spaced ≤ 3.0 m.
• Pilasters anchored into foundations and integrated with lintel bands and bond beams.

Roof & Wall Connections (Clause 3.0 e,f)

• Strong connections among wooden roof and wall elements.
• Roof uplift forces transmitted safely to foundation.
• Cyclone bolts anchor roof to continuous lintel bands if walls are strong brick masonry.

Planning & Layout (Clause 3.5)

• Long walls > 3.5 m require cross walls or pilasters.
• Roof pitch preferably > 1:3 slope; hipped roofs preferred over gabled (80% suction of gabled).
• Openings in load-bearing walls < 50% width; openings ≥ h/6 from corners for lateral support.
• Buildings in clusters: corner buildings load factor = 1.5; interior buildings shielding factor = 0.8.

Summary Table: Anchorage Forces and Design

IS 15498: Guidelines for Engineered Construction - Key Points

1. Structural Reinforcement & Pilasters

• Hollow concrete block masonry walls: Reinforcements pass through blocks forming pilasters (Fig. 9).
• Maximum pilaster spacing: 3.0 m.
• Reinforcements anchored into foundation and integrated with lintel bands and bond beams (Fig. 10).

2. Roof Connections

• Roof uplift forces must be safely transmitted to foundations.
• Use strong connections among wooden roof/wall elements (Fig. 11 & 12).
• Roof anchorage to continuous lintel band via cyclone bolts if strong brick walls exist.

3. Load Enhancement/Shielding Factors for Building Clusters

• Corner buildings: Pressure load × 1.50.
• Interior buildings: Apply shielding factor 0.80.

4. Anchorage & Load Dispersion

• Anchorage reinforcement for roof into masonry assumes an angle of dispersion of 2 vertical : 1 horizontal.
• Neglect masonry shear strength; effective masonry weight above anchorage = 1.5 × uplift force.

5. Wind Bracing for Roof Trusses

• Provide bottom chord bracing to prevent buckling and distribute horizontal loads (Fig. 13).

Summary Table: Load Factors for Cluster Buildings

Typical Connection Details (Highlights)

• Use U-hook bolts with washers for sheet fixing (Fig. 8).
• GI/MS straps and metal brackets recommended for roof-to-wall connections.
• Pilasters and bond beams must be continuous and well tied.

flowchart TD
    A[Roof Uplift Forces] --> B[Strong Roof-Wall Connections]
    B --> C[Transmission to Foundation]
    C --> D[Anchorage Reinforcement]
    D --> E[Load Dispersion (2V:1H)]
    E --> F[Foundation & Bond Beams]

References: IS 875 (Part 3) for wind loads, IS 800 for steel construction, IS 13920 for ductile detailing in seismic zones.

For detailed figures and connection specifics, refer to IS 15498 Figs. 9

Key Specifications & Formulas for Roof and Wall Connections (IS 15498)

1. Anchorage of Roof into Masonry (Clause 1.5 j)

• Angle of dispersion: 2 vertical : 1 horizontal.
• Shear strength of masonry: Neglected.
• Effective weight of masonry above anchorage:
  [ W_{eff} = 1.5 \times \text{uplift force} ]
• Anchorage reinforcement must safely resist uplift forces.

2. Triangular Frames for Sloped Roofs (Clause 2.0 f, g)

• Maximum spacing: 2.0 m between triangular frames.
• Frames must be strong enough to hold cross runners.
• Connections via metal straps, bolts, nuts, steel flats.
• Triangular frames anchored to bond beams at eaves; bond beams connected to wall posts using U bolts.

3. Restraining Bands for Tiled Roofs (Clause 1.2 a)

• Spacing: 1.2 m to 1.5 m.
• Band size: approx. 100 mm × 50 mm with at least one 10 mm dia. bar inside.
• Hip, valley, ridge tiles embedded in continuous mortar band.
• Nails through tile holes into mortar serve as shear connectors.

4. Anchorage to Foundations (Fig. 5 & Clause 2.0 g)

• Use U bolts to connect bond beams to foundation.
• Holding down bolts designed with Factor of Safety = 2.0.

5. Connection Details (Figs. 4, 6, 11, 12)

• Use MS plates (3 × 25 mm), GI/MS straps (30 mm × 24 gauge), and heavy gauge wire ties.
• Ensure connections transfer uplift forces safely to foundation.
• For thatched buildings: wire turns and straps secure rafters, braces, posts.

Summary Table: Typical Connection Elements

IS 15498: Bracing and Anchorage Requirements - Key Points & Formulas

1. Bracing Spacing & Strength

• Triangular frames for sloped roofs spaced max 2.0 m apart (Clause 2.0 f).
• Frames must be strong enough to hold cross runners.
• Connections via metal straps, bolts, nuts, steel flats for structural integrity (see Fig. 4, 5, 6).

2. Anchorage Details

• Triangular frames anchored firmly to bond beams at eaves (Clause 2.0 g).
• Bond beams connected to main wall posts using U bolts.
• Anchorage reinforcement assumes an angle of dispersion 2 vertical : 1 horizontal (Clause 1.5 j).
• Neglect masonry shear strength; consider effective masonry weight = 1.5 × uplift force.

3. Typical Dimensions & Materials

• Bond beam size: approx. 100 mm × 50 mm with 10 mm dia. bar inside (Clause 1.2 a).
• Metal straps: 30 mm × 24 gauge GI/MS straps.
• MS plates: 3 × 25 mm for longitudinal connections.
• Holding down bolts designed with Factor of Safety = 2.0 (Clause 1.2 b).

4. Connection Guidelines

• Use U bolts for asbestos sheet roofs.
• For hollow concrete block walls, pilasters spaced max 3.0 m with reinforcement anchored to foundation (Clause 3.0 d).
• Roof uplift forces must be safely transferred to foundations via strong connections (Clause 3.0 e).

Summary Table: Anchorage & Bracing

IS 15498: Materials and Construction Practices – Key Points & Formulas

1. Anchorage to Masonry (Clause 1.5 j)

• Angle of dispersion: 2 vertical : 1 horizontal for anchorage reinforcement.
• Shear strength of masonry: Neglected in calculations.
• Effective weight of masonry above anchorage:
  [ W_{effective} = 1.5 \times \text{uplift force at anchorage} ]
• Use cyclone bolts to anchor roofs to continuous lintel bands in strong brick walls.

2. Typical Anchorage Details (Figs. 4-6)

• Use 3 × 25 mm MS plates longitudinally at crown and eaves.
• GI/MS straps: 30 mm × 24 gauge for connections.
• Wire ties: 2 turns (16 gauge) or 4 turns heavy wire for rafters, braces, posts.

3. Semi-Engineered Construction Guidelines (Clause 3.5)

• Long walls > 3.5 m must have cross walls or integral pilasters.
• Roof pitch: Prefer slope > 1:3 (avoid flatter roofs).
• Hipped roofs preferred over gabled roofs (peak suction pressure ~80% of gabled).
• Openings in load-bearing walls < 50% width; openings ≥ h/6 away from inner corners.
• Avoid low-lying/flood-prone sites; use raised mounds or stilts with bracing in surge zones.

4. Non-Engineered Construction (Clause 7)

• Roof overhang ≤ 450 mm; tie back if exceeded.
• Posts anchored minimum 900 mm deep with 4 anchor poles.
• Mud walls protected with stone/brick barrier and waterproof plaster.

Summary Table: Anchorage & Construction Practices

IS 15498: Multi-Hazard Considerations (Cyclone & Flood)

Key Specifications & Guidelines (Clause 3.5 & related):

• Long walls > 3.5 m: Provide cross walls or integral pilasters to reduce wind damage.
• Avoid low-lying areas prone to flooding and cyclone surges.
• Hilly regions: Avoid construction on ridges (high wind velocity); valleys are safer.
• Roof slope: Avoid slopes less than 1:3 except for large-span sloped roofs.
• Roof type: Prefer hipped roofs over gabled roofs; use 80% of gable suction pressures if detailed data unavailable.
• Openings: Total opening in frontal wall < 50% of wall width; openings in load-bearing walls must be > h/6 from corners (h = storey height).
• Inter-building spacing: If < 2× building width, interior buildings get shielding but outer rows face higher forces.
• Flood-prone/coastal areas: Use raised mounds, stilts (no masonry below surge level), and bracing for earthquake resistance.

Important Dimensions & Limits:

Aerodynamic & Structural Notes:

• Use diagonal rope patterns to hold down thatched roofs.
• Paint posts below ground with coal tar up to max flood level.
• Provide stone/brick revetments and waterproof plaster on mud walls.

References for Load Calculations:

• Use IS 875 (Part 3) for wind pressure coefficients.
• Apply 80% of gable roof suction for hipped roofs if detailed data unavailable.

flowchart TD
    A[Long Wall > 3.5m] --> B[Cross Walls or Pilasters]
    C[Roof Slope < 1:3] --> D[Avoid except large-span roofs]
    E[

IS 15498 references several other Indian Standards essential for design and testing of cyclone resistant structures. While the provided context doesn't list them explicitly, typical key references include:

Commonly Referenced IS Codes in IS 15498:

• IS 875 (Part 3): Code for wind loads on structures
• IS 456: Plain and reinforced concrete code
• IS 1893: Criteria for earthquake-resistant design
• IS 800: General construction in steel — code of practice
• IS 13827: Guidelines for improving earthquake resistance of low strength masonry buildings
• IS 2: Rules for rounding off numerical values

Important Specification:

• Rounding off (IS 2:1960): Final calculated or observed values must be rounded off to the same number of significant digits as specified in the standard.

Summary Table: Rounding Off Rules (IS 2)

If you need specific formulas or tables from IS 15498, please specify the clause or topic (e.g., wind load calculations, structural detailing).

Committee Composition - IS 15498 (Annex B)

The Cyclone Resistant Structures Sectional Committee, CED 57 was responsible for formulating IS 15498. Key details:

Summary:

• The committee includes experts from government departments, research institutes, academia, and industry.
• Chairmanship held by Dr. Prem Krishna.
• Members represent diverse fields ensuring multi-disciplinary inputs for cyclone-resistant design.

If you need wind loading formulas or design tables, IS 15498 refers to IS 875 (Part 3) for pressure coefficients and load calculations.

flowchart LR
    A[Committee Composition] --> B[Government Departments]
    A --> C[Research Institutes]
    A --> D[Academic Institutions]
    A --> E[Industry Representatives]
    A --> F[BIS Directorate]

This structure ensures comprehensive expertise for the standard's development.

Key Specifications, Tables & Figures from IS 15498 Annexes and Illustrative Figures

1. Wind Pressure Factors (Clause 1.50)

• Corner roof pressure factor: 1.50 (for outer rows in industrial sheds)
• Interior buildings shielding factor: 0.80 (for gabled roofs)

2. Roof & Wall Fixing Details

• Concrete strips: 30 mm x 24 gauge GI/MS strips for roof fixing
• Hook bolts: Use 8 mm dia GI 'U' hook bolts; 'J' hooks are ineffective
• Fixings per sheet: Corners - 4, Ridges - 3, Interior - 2

3. Structural Elements

• Pilasters & Bond Beams: Reinforced concrete masonry pilasters with continuous bond beams (Fig. 9)
• Wall-to-foundation tie-down: Use GI tie-down bolts (Fig. 10)
• Roof-to-wall framing: Galvanized straps or wood cleats (Figs. 11 & 12)
• Truss bracing: Bottom chord bracing mandatory; upper chord bracing desirable (Fig. 13)

4. Planning Guidelines (Table 6, Clause 3.5)

5. Flood & Multi-Hazard Provisions

• Raised ground or stilts in flood-prone areas
• Parapet height ≥ 600 mm for load-bearing masonry
• Ductile detailing per IS 13920 in seismic zones III and above

Illustrative Figures Summary

flowchart LR
A[Roof Fixing] --> B[Concrete Strips & Hook Bolts]
A --> C[Fixing Quantities per Sheet]
D[Wall Fixing] --> E[Pilasters & Bond Beams]
D --> F[Tie-down Bolts]
G