1.6.3. Load Categories

Dead Load:

• Weight of the various structural members and the weights of any objects that are permanently attached to the structures.

A dead load refers to the static weight of all permanent components of a structure. This includes not only the materials used in construction, such as beams and columns, but also anything that is permanently affixed to the structure, like plumbing and electrical fixtures. Understanding dead loads is crucial for engineers to calculate how much weight a structure will consistently carry.

Think of a dead load like the furniture in your home. Once you've bought your couch and placed it in your living room, it becomes a permanent part of the space, just like how beams and walls contribute to the dead weight of a building.

For a building, dead loads include weight of:

• Roof Slab
• Walls
• Floor Slab
• Windows
• Beams
• Plumbing
• Girders
• Electrical Fixtures
• Columns
• Ducts

Dead loads consist of various components. Each of these components, like the roof slab, walls, and beams, has a specific weight based on the material used. For example, concrete is heavier compared to wood, and knowing the weight of these components helps in structural calculations.

Consider a bookshelf you’ve built. The wood for the shelves and sides contributes to its overall weight—the same principle applies to building structures. The heavier the materials, the greater the dead load.

The dead loads can be calculated knowing the densities and dimensions of the structural components. The unit weights of typical building materials can be found in codes and standards.

To calculate dead loads accurately, you need both the dimensions and the density (or weight per unit volume) of each material. Construction codes often provide standard values for common materials, making it easier for engineers to determine the total dead load for their structures.

Imagine baking a cake – you need to know how much flour (a component) to measure. Similarly, engineers measure dimensions and densities to determine the total weight of materials used in construction.

They are usually small for small structures and errors can be neglected. Yet, for multistory structures the error is high and cannot be ignored.

In smaller buildings, the calculation of dead loads might not significantly affect structural integrity, as the weights are manageable. However, in tall buildings or complex structures, precise calculations are vital. A small error in estimating the dead load can lead to serious structural issues.

Think of how a single miscalculation in a large recipe can ruin the dish. Just like in baking, precise measurements are essential in construction, especially for high buildings where every kilogram counts.

Live Loads:

• Vertical loads due to human occupancy, snow, rain ponding, furniture, partition walls and moveable equipment.

Live loads refer to the loads that can change over time, such as people walking in a building, or furniture that can be moved around. These loads are dynamic and need to be considered during structural design to ensure the building can safely support them under varying conditions.

Think about a stadium – during events, thousands of people fill the stands, creating a massive live load. This load changes as people get up and move around, showing how live loads can fluctuate.

Can be categorized to:

• Occupancy loads of buildings (ASCE-7)
• Traffic loads for bridges (AASHTO)
• Impact loads
  • Applied over a very short period of time
  • Have greater effect on the structure
• Moving loads:
  • Dynamic significance.
  • Change over a period of time.

Live loads can be further classified into specific types based on their sources and impacts. For instance, occupancy loads are considered in living spaces, traffic loads are crucial for bridge design, and impact loads are relevant in cases such as a vehicle crashing into a structure. Understanding these classifications helps engineers design structures that can handle different scenarios effectively.

Consider a busy cafe versus a quiet reading room. The cafe must handle many people moving around (live loads) while the reading room might handle fewer people at any given time, illustrating how different environments influence load types.

Environmental loads:

• Snow and ice loads
• Rain loads
  • Accumulation of rainwater on flat roof (ponding)
  • Avoid by providing (2%) slope and design adequate drainage.
• Wind loads
  • Causes forces, vibrations, and (in some cases) instability.

Environmental loads include loads from natural phenomena like snow, rain, and wind. Snow can accumulate on roofs, while rain can create pooling if the drainage isn't adequate. Wind loads can impose lateral forces that may affect a building's stability. Proper design must account for these environmental factors to ensure the safety and integrity of structures.

Imagine a flat roof in winter – if not designed correctly, the weight of the snow can cause the roof to collapse. Engineers need to foresee these scenarios just like a homeowner has to clear snow off their roof to prevent damage.

Earthquake loads:

• It is the common dynamic loading associated with the ground movement.
• It affects the base of the structure.
• The rest of the structure is affected due to inertia.

Earthquake loads are dynamic loads that occur from the ground shaking during seismic events. This type of load exerts force on the structure, particularly at its base, and the entire building reacts due to inertia. Engineers design structures to withstand these forces to prevent collapse during earthquakes.

Think of standing in a subway train as it starts moving – you feel a force pushing you backward. Similarly, during an earthquake, a building experiences forces that can push it in various directions, which is why engineers must design for these dynamic loads.

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