Wind load Calculations

IS 875 (Part 3): 2015 Structural Design Example

Detailed Verification & Calculation Analysis for Cladding & Structural Elements

Project Type G+3 Commercial Building

Location New Delhi, India

Design Standard IS 875 (Part 3): 2015

Reference Height (z) 12.0 Meters

1. Structural Parameters & Inputs

The calculation considers a standard 4-story commercial structure situated in New Delhi. Parameters used within the automated script execution model are detailed below:

Parameter Description	Code Symbol	Selected Value	Reference / Remarks
Basic Wind Speed	Vb	44.0 m/s	New Delhi (Appendix A, Table 1)
Risk Coefficient (Design Life)	k1	1.00	Class B structure (50-year design life)
Terrain Category & Structure Size	—	Cat 3, Size B	Suburban area; medium building dimension
Terrain & Height Factor	k2	1.1030	Interpolated at z = 12.0m (Table 2)
Topography Factor	k3	1.00	Flat ground (Slope ≤ 3°)
Importance Factor (Cyclonic)	k4	1.00	Non-cyclonic industrial zone
External Pressure Coeff.	Cpe	-1.30	Typical overall cladding/façade suction
Internal Pressure Coeff.	Cpi	-0.20	Normal building envelope (Closed)
Tributary / Panel Area	A	2.00 m²	Design window glass frame element

2. Step-by-Step Mathematical Derivation

Step 2.1: Design Wind Speed (V_z)

The design wind speed at height z is calculated by modifying basic wind speed with environmental factors:

V_z = V_b × k₁ × k₂ × k₃ × k₄
V_z = 44.0 × 1.00 × 1.1030 × 1.00 × 1.00 = 48.532 m/s

Step 2.2: Design Wind Pressure (p_z)

The basic design velocity pressure at height z is determined from kinetic energy equations defined in Clause 7.2:

p_z = 0.6 × (V_z)²
p_z = 0.6 × (48.532)² = 0.6 × 2355.355 = 1413.213 N/m² (1.413 kN/m²)

Step 2.3: Net Pressure Combinations (p_net)

Net surface pressure action depends on internal and external differential air pressure profiles:

Case A (Cumulative Internal Action):
p_net,A = p_z × (C_pe + C_pi) = 1413.213 × (-1.30 + (-0.20)) = -2119.820 N/m²

Case B (Opposing Internal Action):
p_net,B = p_z × (C_pe - C_pi) = 1413.213 × (-1.30 - (-0.20)) = -1554.534 N/m²

Step 2.4: Total Design Force on Panel (F)

Total localized suction force applied across the 2.0 m² tributary element surface:

F_A = p_net,A × A = -2119.820 N/m² × 2.0 m² = -4239.640 N (-4.24 kN)
F_B = p_net,B × A = -1554.534 N/m² × 2.0 m² = -3109.068 N (-3.11 kN)

3. Calculation Summary & Verification Output

Governing Computational Results

Design Speed (V_z)

48.532 m/s

Wind Pressure (p_z)

1.413 kN/m²

Max Suction (p_net)

-2.120 kN/m²

Design Panel Load (F)

-4.240 kN

Engineering Verification Note: The mathematical outcome calculated in this report precisely matches the JS function outputs executed via wc_example(). The negative signs indicate outward suction pressure on the building face, which governs the structural design of exterior wall brackets, mullion anchors, and glazing structural silicon seams as per IS 875 (Part 3): 2015 limits.

Yogendra Gopal Borse

Civil Engineer | Assistant Engineer Grade-I, Maharashtra PWD

B.Tech (Civil) from VJTI Mumbai. Experienced in bridge design, road works, estimation, project monitoring and digital engineering tools. Creator of YogiPWD – practical technical resources for civil engineers.

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