Dead loads in structural design: which statement is correct regarding their nature and treatment in sizing members?

Difficulty: Easy

Correct Answer: Dead load includes self-weight of the structure plus superimposed loads permanently attached

Explanation:


Introduction / Context:
Accurate characterization of loads is critical for safe and economical design. Dead loads represent permanent, stationary actions on a structure and are the first inputs estimated when sizing beams, columns, and foundations.


Given Data / Assumptions:

  • Dead load comprises self-weight and other permanently fixed items.
  • Dead load is typically constant in time and space for a given configuration.
  • Designers determine dead load early using unit weights of materials.


Concept / Approach:
Dead loads are permanent: structural self-weight, floor finishes, roofing, partitions that are fixed, cladding, and permanently attached equipment. They do not migrate spatially and their magnitude is predictable from quantities and densities. In contrast, live loads vary with occupancy and usage, both in magnitude and location.


Step-by-Step Solution:
List dead-load components (self-weight + fixed attachments).Use unit weights (e.g., concrete, steel, masonry) and dimensions to estimate magnitudes at the outset.Recognize that dead load classification excludes position-varying loads.


Verification / Alternative check:
Codes define dead loads as permanent, immovable loads; live loads are moveable and variable. Estimation tables confirm designers compute dead loads at concept stage to select preliminary sizes and then refine as detailing progresses.


Why Other Options Are Wrong:

  • Dead loads change position and vary: describes live loads, not dead.
  • Dead loads are known at the beginning: generally true, but option (a) is the clearer definition; the question asks for a correct statement, and (a) most directly captures the definition.
  • None: incorrect because (a) is correct.


Common Pitfalls:

  • Classifying removable partitions or equipment as dead load when they may be treated as live or superimposed variable load by code.


Final Answer:
Dead load includes self-weight of the structure plus superimposed loads permanently attached.

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