1.6. Codes and Loads types and categories

1.6.1 Codes:

• The design loading for structures is often specified in codes such as:

  • Minimum Design Loads for Buildings and Other Structures ASCE 7-16
  • International Building Code – 2018 (IBC-2018)

• Design codes provide detailed technical standards used to establish actual structural design. Some Examples:

  • Building Code Requirements for Reinforced Concrete by American Concrete Institute (ACI)
  • Steel Construction Manual, by American Institute of Steel Construction (AISC)
  • British Standards (BS)
  • EURO Code (European Code)

This chunk introduces the concept of codes in structural engineering. Codes are essential guidelines that dictate the minimum design standards required when constructing buildings. For example, the ASCE 7-16 code provides specific loading requirements that must be met to ensure safety and structural integrity. The International Building Code (IBC-2018) is another widely used standard. Various organizations, like the American Concrete Institute (ACI) and the American Institute of Steel Construction (AISC), develop these codes to ensure that materials and structures meet specific performance criteria. Overall, understanding these codes is crucial for engineers to create safe and effective structures.

Think of building codes like traffic laws. Just as road signs and regulations keep drivers safe and guide them on how to navigate roads, building codes ensure that structures are built safely and functionally. For instance, just like there are speed limits to prevent accidents, there are codes that specify the maximum load a building can handle to prevent collapses.

1.6.2 Load Types:

• Concentrated loads:

  • Applied over relatively small area
  • Examples: Column loads, Vehicular wheel load

• Line loads:

  • Distributed along a narrow strip of the structure
  • Examples: Beam self-weight, weight of wall or partition

• Surface loads:

  • Distributed over an area of the structure
  • Examples: floor and roof loads

This chunk describes the different types of loads that structures must support. Concentrated loads are significant forces acting on a specific point, such as the weight of a column or a parked vehicle. Line loads are forces distributed over a narrow area, like the weight of a wall resting on a beam. Surface loads, on the other hand, are spread out over a broader area, such as the weight of floors and roofs. Being aware of these load types allows engineers to design structures that can withstand the various forces they will encounter.

Imagine a dining table. If you place a heavy vase (concentrated load) in the center, the table must support that specific weight right there. Now, think about a long buffet table (line load) that needs to support the weight of plates and food along its length. Finally, picture the entire area of the table (surface load) covered with a tablecloth and plates; the weight is distributed over the whole surface rather than concentrated in one spot.

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.
  • For a building, dead loads include weight of:
    • Roof Slab
    • Walls
    • Floor Slab
    • Windows
    • Beams
    • Plumbing
    • Girders
    • Electrical Fixtures
    • Columns
    • Ducts
  • 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.
  • For loads associated with service equipment, they can be obtained from the manufactures.
  • They are usually small for small structures and errors can be neglected. Yet, for multistory structures the error is high and cannot be ignored.

• Live Loads:

  • Vertical loads due to human occupancy, snow, rain ponding, furniture, partition walls and moveable equipment.
  • Horizontal (lateral) loads due to wind, earthquake, water pressure, blast/explosion, collision, etc.
  • Loads produced through construction or occupancy of the structure.
  • They can be caused by weights of objects temporarily placed on a structure, moving vehicles, or natural forces.
  • 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.
  • Codes have established its data based on studying the history of such loads.
  • Types of live loads:
    • Building Loads
    • Snow Load
    • Highway Bridge Loads
    • Earthquake Loads
    • Railroad Bridge Loads
    • Hydrostatic Pressure
    • Impact Loads
    • Soil Pressure
    • Wind Loads
    • Other Environmental Loads
  • Floors are assumed to be under uniform live loads which depend on the purpose for which the building is designed.
  • These loads are usually tabulated in adapted code.
  • These values include some protection against overloading, emergency situations, construction loads, and serviceability requirements due to vibration.
  • 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
      • Depends on:
        • Wind speed
        • Mass density of the air
        • Location of the structure
        • Geometry of the structure
        • Vibrational characteristics of the system
    • 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
      • Creates horizontal shear forces and deflections
      • Depends on:
        • Nature of the ground movement
        • The inertia response of the structure

This chunk distinguishes between different load categories that structural engineers must consider. Dead loads refer to the permanent weight of the structure and everything attached, like beams and walls. Calculating these loads involves knowing the density and dimensions of materials. On the other hand, live loads are dynamic and vary over time, coming from people, furniture, and environmental factors like snow or wind. Live loads can lead to more considerable structural effects due to their changeability. Attributes like occupancy loads and traffic loads also figure into this category. Environmental loads, which include snow, rain, and earthquake forces, play a critical role in determining how a structure will perform during debates and how it needs to be designed to sustain durability and safety.

Consider a bookshelf as a representation of dead and live loads. The weight of the bookshelf itself, along with any books that are permanently placed on it, represents the dead load. If you take off all the books temporarily, the load is effectively reduced, similar to live loads that change based on occupancy or use. If you were to shake the bookshelf (replicating an earthquake), that dynamic force represents environmental load acting on the structure, showing how it can impact stability.

--