Code of Practice For Design Loads (Other Than Earthquake) For Buildings And Structures, Part 5: Special Loads And Combinations
1987 Edition

IS 875 Part 5 mandates consideration of two primary temperature effects in structural design: the uniform change in mean temperature across sections, which causes overall expansion or contraction; and the temperature gradient through the section thickness, leading to differential expansion and bending stresses. These thermal influences affect both the stress distribution and deformations within structural members, and the baseline or reference temperature is typically the state at construction or when the structure is stress-free.

The code specifies that lateral earth pressures on walls must include the effective weight of submerged soil, calculated as soil weight minus buoyant forces, plus the full hydrostatic pressure from groundwater. Foundation slabs and footings exposed to water pressures need to resist uniform uplift equal to the hydrostatic pressure. Stability checks must incorporate the buoyant weight of foundations to assess overturning risk. For columns embedded in sloping soils, an effective width factor is applied based on actual member width, using prescribed ratios to compute lateral soil pressure accurately.

Vertical loads for air raid shelters, typically situated below ground level, depend on the number of stories above and construction type. The standard specifies 28 kN/m² for up to two-storey buildings, 34 kN/m² for three to four storeys, and 41 kN/m² for buildings exceeding four storeys. Particularly robust reinforced in-situ concrete structures are assigned 28 kN/m² regardless of height. These values apply when the floor imposed load does not exceed 5.0 kN/m². Additionally, a safety factor against sliding of at least 1.4 is required, considering only 0.9 times the dead load.

The standard treats accidental loads as infrequent but potentially severe events caused by human-related incidents such as collisions and explosions. It advocates a risk-based design framework where principal load-bearing components are engineered to withstand such loads, considering the likelihood and magnitude through risk assessment. Loads deemed highly improbable may be disregarded after evaluation. This approach balances safety with cost-effectiveness by focusing design efforts on critical structural elements.

IS 875 Part 5 provides guidance on combining loads such as dead, imposed, earthquake, wind, and temperature loads, emphasizing realistic scenarios that avoid simultaneous occurrence of maximum values for all loads. It recommends applying proper load factors and partial safety factors in line with other relevant codes like IS 1893. When snow load is present, it replaces imposed load in combinations. The standard also highlights that reduced imposed loads should not be combined with earthquake forces and that special or accidental loads require individual consideration to ensure safe and economical structural design.