IS 875 Part 2 — Code of Practice for Design Loads (Other Than Earthquake) For Buildings And Structures, Part 2: Imposed Loads

Detailed content not available.

IS 875 Part 2 - Scope & Key Specifications

IS 875 (Part 2): Imposed Loads for Buildings — covers imposed (live) loads on floors, roofs, stairs, balconies, etc.

1. Scope

• Specifies imposed loads for various occupancies and structural elements.
• Includes loads due to human occupancy, furniture, movable partitions, and maintenance activities.
• Covers flat, sloping, and curved roofs with slope adjustments.
• Provides horizontal imposed loads on parapets, balustrades, stairs.

2. Key Formulas & Load Values

• Roof Loads (Clause 4.1, Table 2):

• Horizontal Loads on Parapets (Clause 5.1, Table 3):

• Imposed Floor Loads (Table 1):

IS 875 Part 2 - Terminology & Imposed Loads Summary

This part defines imposed floor loads for various occupancies, crucial for structural design.

Key Terminology & Load Specifications:

Notes:

• Concentrated loads on balconies are applied 1.5 kN/m run at the outer edge.
• Some rooms require calculated loads but not less than specified minimums (e.g., vaults, boiler rooms).
• Corridors/staircases loads depend on usage and may increase for wheeled loads.

Application Formula for Design Load:

[ \text{Design load} = \text{Imposed load} \times \text{Load factor} ]

Where load factors depend on safety requirements (typically 1.5 for imposed loads).

Visual Summary (Mermaid Diagram):

flow

Detailed content not available.

IS 875 Part 2: Imposed Loads — Key Formulas & Tables

1. Imposed Loads on Roofs (Clause 4.1, Table 2)

• Where:
  • y = h / l
  • h = height from springing to highest point
  • l = chord length of roof segment

2. Horizontal Loads on Parapets & Balustrades (Clause 5.1, Table 3)

3. Impact and Vibration Effects (Clause 1.9)

• Roof slab: 1.9 kN/m width uniformly distributed
• Beams/trusses/walls: 4.5 kN uniformly distributed
• Roof membrane sheets/purlins: start at 0.75 kN/m², reduce by **0

IS 875 Part 2: Key Load Application Formulas & Tables

1. Imposed Loads on Roofs (Clause 4.1, Table 2)

2. Load Application (Clause 3.1.1)

• Uniformly distributed loads applied as static loads over full or partial floor areas to produce critical effects.
• Concentrated loads:
  • For bending/shear: act at a point.
  • For local effects (crushing/punching): act over 0.3 m × 0.3 m area.

3. Horizontal Loads on Parapets (Clause 5.1, Table 3)

4. Impact & Vibration (Clause 1.9)

IS 875 Part 2: Loads Due to Partitions (Clause 3.1.2)

• For light partitions in offices or similar buildings, where exact loads are unknown during planning, design floors and supporting members to carry a uniformly distributed load (UDL) of not less than 0.34 kN/m² (i.e., 339% of some base value, typically 0.1 kN/m² as per IS context).

• This load is in addition to other imposed loads.

Key Specifications for Partitions:

Additional Related Loads (Clause 1.9):

• Impact and vibration effects:
  • Roof slab: 1.9 kN/m² over 1 m width
  • Beams/trusses/walls: 4.5 kN/m uniformly distributed

Design Notes:

• For sloping roofs >10°, reduce load on roof membranes by 0.02 kN/m² per degree increase over 10°, minimum 0.4 kN/m².

• For curved roofs, use formula:

  [ \text{Load} = (0.75 - 0.52 y^2) \text{ kN/m}^2 ]

  where ( y = \frac{h}{l} ), ( h ) = height from springing to crown, ( l ) = chord length.

Summary:

• Design partition loads as 0.34 kN/m² UDL if actual loads unknown.
• Add this load to other imposed loads per IS 875 Part 2.
• Consider impact, vibration, and roof slope effects separately.

flowchart TD
    A[Start Design] --> B{Are partition loads known?}
    B -- No --> C[Use 0.34 kN/m² UDL for light partitions]
    B -- Yes --> D[Use actual partition loads]
    C --> E[Add to other imposed loads]
    D --> E
    E --> F[Check roof slope &

IS 875 Part 2: Reduction in Imposed Loads on Floors (Clause 3.2)

1. Reduction for Floor Supporting Structural Members (Clause 3.2.1)

• Note (3.2.1.1): If reduced load on a lower floor is less than that on an upper floor, adopt the upper floor's reduced load.

2. Reduction for Beams, Girders, or Trusses (Clause 3.2.2)

• For a single span supporting ≥ 50 m² floor area:
  • Reduce imposed load by 5% per 50 m², max 25% reduction.
• Exclusions: No reduction for
  • Moving loads,
  • Machinery or concentrated loads,
  • Partition wall loads,
  • Impact or vibration loads,
  • Roof loads (no reduction applies).

Summary Formula for Floor Load Reduction on Columns:

[ \text{Reduced Load} = \text{Imposed Load} \times \left(1 - \text{Reduction % from table}\right) ]

flowchart TD
    A[Number of Floors] --> B{Reduction \%}
    B -->|1| C[0% reduction]
    B -->|2| D[10% reduction]
    B -->|3| E[20% reduction]
    B -->|4| F[30% reduction]
    B -->|5-10| G[40% reduction]
    B -->|>10| H[50% reduction]

This approach optimizes design by considering realistic load sharing across floors.

IS 875 Part 2 - Imposed Loads on Roofs (Clause 4.1 & Table 2)

Key Specifications for Imposed Loads on Roofs

• h: height from springing to crown
• l: chord length (shorter side if doubly curved)

Notes:

• Loads exclude snow, rain, dust; design for greater of imposed or snow/rain load.
• For curved roofs, divide into 6 segments; apply load per segment slope.
• For roofs used as promenades or assembly, use imposed floor loads from Table 1.

Formula for Curved Roof Imposed Load:

[ q = 0.75 - 0.52 \left(\frac{h}{l}\right)^2 \quad \text{kN/m}^2 ]

Summary Diagram:

graph TD
    A[Roof Type] --> B{Slope ≤ 10°}
    A --> C{Slope > 10°}
    B --> D[Access Provided: 1.5 kN/m²]
    B --> E[Access Not Provided: 0.75 kN/m²]
    C --> F[Sloping Roof: 0.75 - 0.02(slope-10), min 0.4 kN/m²]
    C -->

IS 875 Part 2: Loads on Members Supporting Roof Coverings

Key Specifications (Clause 4.5 & related)

• Members directly supporting roof coverings must be designed for the more severe load from:
  • Imposed loads on roofs (Clause 4.1, Table 2)
  • Concentrated loads for maintenance (Clause 4.2)
  • Other loads as applicable

Imposed Loads on Roofs (Clause 4.1, Table 2)

Where:

• ( y = \frac{h}{l} )
• ( h ) = height of highest point from springing
• ( l ) = chord length of roof

Concentrated Load for Maintenance (Clause 4.2)

• All roof coverings (except glass/fiber glass) must carry:
  0.90 kN concentrated load on 12.5 cm² area
• Load placement should produce maximum stress
• Reduction possible with Engineer-in-Charge approval

Summary Formula for Curved Roof Load

[ q = (0.75 - 0.52 y^2) \text{ kN/m}^2, \quad y = \frac{h}{l} ]

Design Approach

• Use greater of uniform imposed load or concentrated load effects
• For curved roofs,

IS 875 (Part 2) - Concentrated Imposed Loads with Impact and Vibration

Key Specifications:

• Impact factor for machinery loads: Minimum 20% (Clause 6.2).
• Impact allowance varies with machinery type, e.g., 100% increase for lifts and hoists foundations.

Imposed Loads on Roofs (Clause 4.1 & Table 2):

Concentrated Loads with Impact:

• Consider impact factor ≥ 20% for light machinery.
• For heavy machinery or lifts, impact allowance can be 100% or more.
• Design loads should consider impact + vibration effects.

Horizontal Loads on Parapets (Clause 5.1):

Formula for Curved Roof Load:

[ q = 0.75 - 0.52 \left(\frac{h}{l}\right)^2 \quad \text{kN/m

IS 875 (Part 2) - Equipment Loads Summary

1. Imposed Loads on Roofs (Clause 4.1 & 1.9)

2. Horizontal Loads on Parapets & Balustrades (Table 3, Clause 5.1)

3. Impact & Vibration (Clause 1.9 & 6.2.1)

• Allow 1.9 kN/m width on roof slabs and 4.5 kN on beams/trusses for equipment loads.
• Provision for concentrated equipment loads during installation/maintenance must be made.
• Impact allowance can be up to 100% increase for machinery foundations and lifts.

Key Formula for Curved Roof Load:

[ q = 0.75 - 0.52 \left(\frac{h}{l}\right)^2 \quad \text{kN/m}^2 ]

where:

• (h) = height from springing to highest point
• (l)

IS 875 Part 2: Crane Load Combinations (Clause 6.4)

Key Specifications:

• Vertical Loads (6.4.1):

  • Two adjacent cranes in tandem:
    Design for both cranes fully loaded with overloading factor as per Clause 6.3(a).
  • Long span gantries with multiple cranes:
    Design girder for:
    • One crane fully loaded with overloading (6.3(a))
    • Plus additional cranes fully loaded without overloading to maximize effect.

• Loads to consider (6.0):

  • Vertical loads
  • Eccentricity effects from vertical loads
  • Impact factors
  • Lateral braking forces (across rails)
  • Longitudinal braking forces (along rails)

Overloading factor (Clause 6.3(a)):

Typically, 1.25 times the rated crane load.

Typical Load Combination Formula for Vertical Loads:

[ \text{Design Load} = 1.25 \times \text{Rated Load (for one crane)} + \sum \text{Rated Loads of other cranes (without overloading)} ]

Summary Table:

Where:

• (L) = Rated crane load
• (n) = Number of additional cranes on span

flowchart LR
    A[Crane Load Combinations] --> B[Two Adjacent Cranes]
    A --> C[Long Span Gantry]
    B --> D[Both cranes fully loaded with overload (1.25×L)]
    C --> E[One crane with overload (1.25×L)]
    C --> F[Other cranes without overload (L each)]

For lateral and longitudinal forces, refer to Clause 6.0 and IS 875 Part 5 for combined special load cases.

IS 875 Part 2: Special Loads & Load Combinations Summary

1. Special Loads & Load Combinations

• Refer IS 875 Part 5 (1988) for special loads like earthquake, crane, etc.
• Earthquake design criteria per IS 1893 (Fourth Revision).
• Crane load combinations per Clause 6.4 of IS 875 Part 5.

2. Imposed Loads on Roofs (Clause 1.9)

• Divide curved roofs into ≥6 segments; calculate load per segment slope.
• Consider snow, rain, dust loads separately if greater.
• Account for moisture absorption in permeable roof materials.

3. Horizontal Loads on Parapets & Balustrades (Table 3, Clause 5.1)

4. Impact Allowances for Machinery & Lifts

• Impact allowance minimum 100% for lifts, hoists, foundations, and machinery supports.

Load Combination Guidance

• Use IS 875 Part 5 for combining imposed, wind, earthquake, and crane loads.
• Typical combinations include:
  • 1.5 (Dead Load + Imposed

IS 875 Part 2: Reduction of Imposed Loads in Multi-storeyed Buildings (Clause 3.2.1.2, Appendix A)

Key Concept:

• Imposed loads on columns reduce with increasing tributary floors due to load diversity.
• Reduction factors are applied cumulatively to the sum of imposed loads from roof to the floor considered.

Formula for Reduced Imposed Load at Floor n:

[ P_{reduced} = \left(\sum_{i=1}^n P_i\right) \times (1 - r_n) ]

Where:

• (P_i) = imposed load at floor (i)
• (r_n) = reduction factor at floor (n) (increasing with number of floors)

Typical Reduction Factors (r_n) (Illustrative from IS 875 Part 2 Appendix A):

Example Calculation (Floor 4):

• Loads (kN): 30 (Roof) + 40 + 50 + 50 = 170 kN
• Reduction factor (r_4 = 0.3)
• Reduced load = (170 \times (1 - 0.3) = 119 , kN)

Important Note:

• If reduced load at a lower floor is less than that on the floor above, adopt the higher load for design (monotonic non-decreasing load pattern).

Summary Table (Excerpt):