Structural Load
A structural load is any force or collection of forces that acts on a structure, causing internal stresses, deformations, or displacements within the members. Loads are classified by their nature (static or dynamic), their source (gravity, wind, seismic), and their duration (permanent or transient). Accurate load estimation is the foundation of structural design, ensuring that every member can safely resist the demands placed on it throughout the life of the structure.
Common Structural Load Types and Their Characteristics
| Load Type | Source | Duration | Example | Design Code Reference |
|---|---|---|---|---|
| Dead Load | Self-weight of structure | Permanent | Concrete slab weight | IS 875 Part 1 |
| Live Load | Occupants and movable items | Variable | Office floor occupants | IS 875 Part 2 |
| Wind Load | Wind pressure | Transient | Cyclone on facade | IS 875 Part 3 |
| Seismic Load | Ground acceleration | Transient | Earthquake inertia force | IS 1893 |
| Snow Load | Accumulated snow | Seasonal | Roof in Shimla | IS 875 Part 4 |
| Thermal Load | Temperature change | Variable | Bridge expansion | IS 875 Part 5 |
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Related Terms
Dead Load
A dead load is the permanent, static weight of all structural and non-structural components of a building that do not change over time, including the self-weight of beams, slabs, columns, walls, flooring, and fixed mechanical equipment. Unlike live loads, dead loads act continuously throughout the life of the structure and can be calculated with reasonable accuracy from material densities and member dimensions. In Indian practice, dead loads are determined per IS 875 Part 1 and form the primary permanent load case in structural design.
Live Load
A live load is a variable, transient force applied to a structure by its occupants, furniture, vehicles, stored goods, or any other movable item that is not permanently fixed to the building. Live loads are characterised by their variability in magnitude, position, and duration, making them inherently probabilistic in nature. In Indian design practice, live loads for floors, roofs, and bridges are specified in IS 875 Part 2 and IRC codes, and they are combined with dead loads using appropriate load factors to achieve safe designs.
Factor of Safety
The factor of safety (FOS) is a dimensionless ratio of the ultimate capacity (strength) of a structural element to the actual load (or stress) it is designed to carry, providing a quantitative measure of the margin between safe performance and failure. A factor of safety greater than 1 indicates that the structure can withstand more than the design load, accounting for uncertainties in material properties, load estimation, construction quality, and analytical model assumptions. In structural and geotechnical engineering, typical FOS values range from 1.5 to 3.0 depending on the consequence of failure and the degree of uncertainty involved.
From Latin "structura" (a fitting together, building) and Old English "lad" (way, course), later Middle English "lode/lod" meaning a burden carried. The engineering sense of a force acting on a structure emerged in the 18th century alongside systematic mechanics.