Structural engineering is a complex field that requires a thorough understanding of the various forces and loads that act on buildings. The careful consideration of these loads is essential to ensure the safety and economic viability of a prefabricated steel building.
For everyone who is planning to put their hard-earned money into a custom steel building, it’s important to learn about the different types of structural loads. Engineers must take into account during the design and construction of buildings.
Before moving ahead, let’s understand what structural load is.
Structural loads refer to the forces, deformations, or accelerations applied to a metal structure or its components. The assessment of these loads is crucial in preventing structural failure. Excessive loads can lead to deformations or even the collapse of a building if not properly considered during the design phase.
Different Types of Structural Loads
1. Dead Loads (DL)
Type of Load: Vertical Load
Dead loads are permanent or stationary loads that act on a structure throughout its lifespan. These loads are primarily due to the self-weight of structural members, permanent partition walls, fixed equipment, and the weight of different materials used in construction. Major components contributing to dead loads include roofs, beams, walls, and columns.
Calculating Dead Loads:
The dead loads of each structure are calculated by determining the volume of each section and multiplying it by the unit weight of the material. Here are some unit weights for common construction materials:
|
Material |
Unit Weight (lb/ft³) |
Unit Weight (kN/m³) |
|
Reinforced concrete |
150 |
23.60 |
|
Plain concrete |
145 |
22.60 |
|
Structural steel |
490 |
77.00 |
|
Aluminium |
165 |
25.90 |
|
Brick |
120 |
18.90 |
|
Concrete masonry unit |
135 |
21.20 |
|
Wood (Douglas fir larch) |
34 |
5.30 |
|
Engineered wood (plywood) |
36 |
5.70 |
2. Imposed Loads (IL) or Live Loads (LL)
Type of Load: Vertical Load
Imposed loads, also known as live loads, introduce dynamic vertical forces to a steel building. They encompass movable or moving loads, such as vehicle traffic, occupants, and furniture.
Unlike dead loads, live loads are variable and can change over time. Their consideration is vital in designing structures that can accommodate the fluctuating weights associated with daily activities within a building.
From office spaces to residential buildings, engineers must carefully estimate and allocate the appropriate live load capacities to ensure the safety and longevity of the structure.
3. Snow Loads (SL)
Type of Load: Vertical Load
Snow loads come into play in regions prone to snowfall, where the accumulation of significant snow quantities can impact a structure’s integrity. The shape of the roof becomes crucial in determining the magnitude of the snow load.
Different locations have specified ground snow loads, with values varying based on geographical considerations. Engineers must account for these loads during the design phase to implement proper structural measures, ensuring the building can withstand the weight imposed by snow accumulation.
The shape of the roof plays a crucial role in determining the magnitude of the snow load. Different locations have specified ground snow loads, as indicated in ASCE 7-16.
4. Wind Loads
Type of Load: Horizontal Load
Wind loads, acting horizontally, result from the movement of air relative to the earth. While not critical for low-rise buildings, they become increasingly significant for taller structures. Calculating wind loads involves considering the wind velocity and the size of the building.
Engineers determine a building’s design wind speed using historical records and extreme value theory, predicting future unusual wind speeds. Addressing wind loads is essential for designing structures that can resist lateral forces and remain stable under varying wind conditions.
5. Earthquake Loads (EL)
Type of Load: Vertical & Horizontal Load
Earthquake loads encompass both vertical and horizontal forces generated by the total vibration during an earthquake. While the vertical movement does not significantly affect the superstructure, horizontal movement is a critical consideration in the design process. Factors affecting earthquake loads:
- Seismic hazard
- Structural parameters
- Gravity load
Engineers must carefully analyze these factors to develop earthquake-resistant designs, ensuring structures can withstand the dynamic forces imposed during seismic events.
6. Thermal Load
Temperature changes induce thermal loads as all materials expand or contract. These loads can exert significant forces on a structure, necessitating the incorporation of expansion joints at various points.
Expansion joints accommodate the structural movements resulting from temperature fluctuations, preventing potential damage. Considering thermal loads is crucial in designing structures that can endure temperature variations without compromising their stability and integrity.
Other Loads and Effects
Aside from the main loads mentioned above, other forces and effects acting on structures include:
- Foundation movement
- Elastic axial shortening
- Soil and fluid pressure
- Vibration
- Flood load
- Fatigue
- Impact
- Erection loads
- Stress concentration effect due to point load
The intricate landscape of structural engineering demands a comprehensive understanding of the diverse loads that act on buildings. Engineers must navigate the complexities of dead loads, live loads, snow loads, wind loads, earthquake loads, and thermal loads while also considering a myriad of other forces and effects.
Through meticulous analysis and calculation, structural engineers can craft designs that prioritize safety, stability, and resilience, ensuring buildings stand the test of time in the face of varying environmental and operational conditions.