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.
Key Formula
W_DL = density × gravitational acceleration × volume
LaTeX: W_{DL} = \rho \cdot g \cdot V
| Symbol | Meaning | Unit |
|---|---|---|
| W_{DL} | Dead load force | kN |
| \rho | Material density | kg/m³ |
| g | Gravitational acceleration | m/s² |
| V | Volume of the structural member | m³ |
Worked Example
Problem
A reinforced concrete slab is 150 mm thick and covers a plan area of 6 m × 5 m. The density of reinforced concrete is 25 kN/m³. Calculate the total dead load of the slab.
Solution
Step 1: Volume of slab = length × width × thickness = 6 × 5 × 0.15 = 4.5 m³. Step 2: Dead load = density × volume = 25 kN/m³ × 4.5 m³ = 112.5 kN. Step 3: Dead load per unit area = 25 × 0.15 = 3.75 kN/m².
Answer
Total dead load = 112.5 kN; Dead load intensity = 3.75 kN/m²
Unit Weights of Common Construction Materials (IS 875 Part 1)
| Material | Unit Weight (kN/m³) | Typical Use | Notes |
|---|---|---|---|
| Plain Concrete | 24 | Footings, mass concrete | Without reinforcement |
| Reinforced Concrete | 25 | Slabs, beams, columns | Includes steel rebar |
| Structural Steel | 78.5 | Steel frames, trusses | All grades |
| Brick Masonry | 19–20 | Walls, partitions | Depends on density of bricks |
| Timber (hardwood) | 8–10 | Flooring, joists | Air-dry condition |
| Glass | 25 | Curtain walls, facades | Float glass |
Interactive Tools
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Related Terms
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.
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.
Structural Beam
A structural beam is a horizontal or inclined load-bearing member that resists transverse loads primarily through bending and shear, transferring forces from the loaded surface to the supports at its ends or along its length. Beams develop internal bending moments and shear forces that determine the distribution of tensile and compressive stresses across the cross-section, with the neutral axis experiencing zero direct stress. Beams are among the most fundamental structural elements and are constructed from steel, reinforced concrete, prestressed concrete, timber, or aluminium depending on the application.
The term "dead" contrasts with "live" loads, reflecting the idea that this weight is fixed and immovable — it does not "move" or change with use. The distinction appears in 19th-century railway engineering, where the dead weight of locomotives was separated from their live load payload.