Built-up members – use of perforated cover plates: Perforated cover plates are particularly suitable for built-up compression/tension members made from which of the following component arrangements?

Introduction / Context:
Built-up members are frequently formed from rolled sections (angles, channels) connected together. Rather than using lacing bars, designers sometimes adopt cover plates to tie the components. Perforated cover plates offer structural connectivity while reducing wind area and self-weight compared with solid plates.

Given Data / Assumptions:

• Built-up section made from channels and/or angles.
• Cover plates provided in lieu of lacing.
• Perforations reduce drag and weight yet maintain overall connectivity.

Concept / Approach:
Perforated plates act as continuous ties between components, enhancing torsional stiffness and load sharing. They are applicable for back-to-back channels, toe-to-toe channels (forming a box-like section), and four-angle box sections. The perforations mitigate wind loading and facilitate inspection while preserving the required shear transfer between elements.

Step-by-Step Solution:
Identify component arrangement (channels or angles) and whether a box or open section results.Recognize the function of the cover plate: to connect the elements and provide lateral restraint.Note that perforations improve aerodynamics and reduce weight; hence, suitability spans all listed arrangements.

Verification / Alternative check:
Design guides list perforated plates as acceptable alternatives to lacing for open and box built-up members, provided plate thickness and fastener spacing meet shear flow requirements.

Why Other Options Are Wrong:

• Each of a–c is individually suitable; therefore, the most comprehensive correct choice is “all the above.”

Common Pitfalls:

• Using solid cover plates unnecessarily, increasing wind load and weight.
• Insufficient perforation edge distances or fastener spacing, compromising shear transfer.

Final Answer:
all the above