What is Load?
Definition :1
In civil engineering, load is the force or weight acting on a structure. Buildings, bridges, towers, and other structures are designed to safely withstand various types of loads throughout their service life.
Definition :2
In civil engineering, a load is any force, deformation, or acceleration applied to structural components (such as beams, columns, footings, or slabs). The primary objective of structural engineering is to ensure that a structure can safely resist all anticipated loads throughout its operational lifespan without collapse, excessive deflection, or structural damage.
Types of Loads
1. Dead Load
Dead Load (DL): The permanent, static weight of all structural and non-structural components. It never changes in magnitude or position over time.
Examples: Reinforced concrete slabs, steel columns, masonry walls, beams, floor finishes, and fixed utility pipes.
Standard Formula
Dead Load per Meter Run
DL (kN/m) = Cross-sectional Area × Unit Weight
or
DL = Width × Depth × Unit Weight
Where:
- Width (m)
- Depth (m)
- Unit Weight of RCC = 25 kN/m³
2. Live Load
Live Load / Imposed Load (LL): The temporary or moving weight produced by the occupancy, use, and contents of a building.
Examples: Human occupants, furniture, vehicles on bridges, movable machinery, and stored goods.
Formula
For a Beam Supporting a Slab
Live Load (kN/m) = Live Load on Slab (kN/m²) × Tributary Width (m)
Where:
- Live Load = kN/m²
- Tributary Width = Width of slab carried by the beam (m)
Standard Live Loads (IS 875 Part 2)
| Building Type | Live Load (kN/m²) |
|---|---|
| Residential Room | 2.0 |
| Bedroom | 2.0 |
| Kitchen | 2.0 |
| Office | 3.0 |
| Classroom | 3.0 |
| Corridor | 4.0 |
| Staircase | 5.0 |
| Hospital Ward | 3.0 |
| Library Reading Room | 4.0 |
| Library Stack Room | 6.0 |
| Shopping Mall | 4.0–5.0 |
| Roof (Accessible) | 1.5 |
| Parking Area | 2.5–5.0 |
Example – Residential Beam
Given
- Live Load = 2 kN/m²
- Tributary Width = 3 m
Calculation
LL = 2 × 3
LL = 6 kN/m
Answer: Live Load = 6 kN/m
Formula
For a Beam Supporting a Slab
Live Load (kN/m) = Live Load on Slab (kN/m²) × Tributary Width (m)
Where:
- Live Load = kN/m²
- Tributary Width = Width of slab carried by the beam (m)
Standard Live Loads (IS 875 Part 2)
| Building Type | Live Load (kN/m²) |
|---|---|
| Residential Room | 2.0 |
| Bedroom | 2.0 |
| Kitchen | 2.0 |
| Office | 3.0 |
| Classroom | 3.0 |
| Corridor | 4.0 |
| Staircase | 5.0 |
| Hospital Ward | 3.0 |
| Library Reading Room | 4.0 |
| Library Stack Room | 6.0 |
| Shopping Mall | 4.0–5.0 |
| Roof (Accessible) | 1.5 |
| Parking Area | 2.5–5.0 |
Example – Residential Beam
Given
- Live Load = 2 kN/m²
- Tributary Width = 3 m
Calculation
LL = 2 × 3
LL = 6 kN/m
Answer: Live Load = 6 kN/m
3. Wind Load
Wind Load (WL): The horizontal pressure exerted by air currents blowing against the exposed surface of a building. It increases significantly with structural height. Force exerted by wind on a structure.
4. Earthquake Load
Seismic / Earthquake Load (EL): Inertial forces generated on a structure due to rapid ground motion during an earthquake. Calculated based on seismic zones and structural ductility. Forces generated during seismic activity.
5. Snow Load
Snow / Ice Load: The vertical accumulation of snow or ice on roofs, highly critical in cold climate regions. Weight of accumulated snow on roofs.
6. Hydrostatic & Earth
Hydrostatic & Earth Pressure: Horizontal forces exerted by groundwater or surrounding soil against basement retaining walls and foundations. Sudden loads caused by moving objects or machinery.
Classification by Manner of Application
Engineers categorize how loads physically contact structural members to calculate internal bending moments and shear forces:
| Load Application Type | Description | Common Engineering Example |
| Point / Concentrated Load | A force acting over a small, isolated point on a member. | A heavy machine standing on a single beam location. |
| Uniformly Distributed Load (UDL) | A force spread evenly across the entire length or surface area. | The self-weight of a slab or floor finish on a beam. |
| Uniformly Varying Load (UVL) | A force that increases or decreases at a uniform rate along a length. | Water pressure against a triangular dam wall. |
Importance of Load Calculation
Importance of Load Calculations in Engineering
Ensures Structural Safety: Prevents catastrophic failures, structural buckling, and excessive cracking by keeping stresses within allowable limits.
Optimizes Construction Costs: Accurate load estimations allow engineers to design optimal rebar percentages and member sizes, avoiding wasteful over-design.
Determines Foundation Size: Dictates the depth, width, and surface area required for footings to safely transfer forces without exceeding soil bearing capacity.
Compliance with Building Codes: Guarantees that designs adhere to standard design codes (such as IS 875 / IS 1893 in India or ASCE 7 / IBC internationally).
Prevents structural failure
Improves durability
Helps in economical design
Maintains stability
Load Transfer Path
Load → Slab → Beam → Column → Foundation → Soil
Focus Keywords
- Load Definition
- Types of Loads
- Structural Loads
- Dead Load and Live Load
- Load on Structure
- Civil Engineering Basics
Image Ideas
- Load transfer diagram
- Building load illustration
- Dead load vs live load chart
- Structural load path diagram
Frequently Asked Questions (FAQ)
What is Dead Load (DL)?
Dead Load is the permanent weight of a structure and its fixed components.
What is the unit of Dead Load per Meter Run?
The standard unit is kN/m.
What is the unit weight of RCC?
The commonly used value is 25 kN/m³.
Why is Dead Load important?
It is essential for designing safe beams, slabs, columns, and foundations.
Is furniture included in Dead Load?
No. Furniture is considered a Live Load (LL) because it can change over time.
Conclusion
Loads are one of the most important considerations in structural engineering. Proper identification and calculation of loads help engineers design safe, durable, and efficient structures.
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