Minimum thickness requirements for structural steel members (Exposure and member category considerations.)
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AMembers exposed to weather and accessible for repainting: thickness not less than 6 mm.
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BMain members not directly exposed to weather: thickness not less than 6 mm.
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CSecondary members not directly exposed to weather: thickness not less than 4.5 mm.
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DAll of the above.
Answer
Correct Answer: All of the above.
Explanation
Introduction:Minimum thickness prescriptions in steel design reduce corrosion risk and ensure a practical maintenance interval. Requirements vary with exposure and whether a member is primary (main) or secondary.
Given Data / Assumptions:
- Exposure: weather-exposed vs not directly exposed.
- Accessibility for repainting.
- Member category: main vs secondary members.
Concept / Approach:Weather exposure accelerates corrosion; accessibility permits more frequent maintenance and allows slightly thinner minimums. Secondary members may have somewhat lower thickness requirements than primary load-carrying members when not exposed.
Step-by-Step Solution:1) For exposed but accessible members, minimum thickness is commonly taken as 6 mm.2) For main members not directly exposed, 6 mm minimum ensures durability.3) For secondary members not directly exposed, 4.5 mm minimum is acceptable.4) All three statements are therefore correct.
Verification / Alternative check:Comparative durability charts show faster section loss in exposure; minimum thicknesses are set accordingly to maintain structural capacity between maintenance cycles.
Why Other Options Are Wrong:Options A–C are each correct; hence the best choice is “All of the above”.
Common Pitfalls:Applying exposed-member minima to sheltered interiors; neglecting coating systems and detailing that improve durability (drip edges, sealants).
Final Answer:All of the above.