Tacking rivets for plates exposed to weather: what is the maximum permitted pitch along a line, expressed as a multiple of the outside plate thickness t?

Introduction / Context:
Tacking rivets (or bolts) are auxiliary fasteners used to keep built-up elements together between primary connections. Exposure to weather demands closer spacing to control plate separation and corrosion-induced issues.

Given Data / Assumptions:

• Plates are in compression and exposed to weather.
• t = thickness of the outside plate.
• Pitch refers to spacing of tacking rivets along a line.

Concept / Approach:
Legacy steel design practice and many exam standards limit the tacking pitch to the lesser of an absolute distance and a multiple of t. For weather-exposed plates, a conservative multiple of 16 t is adopted to avoid plate opening and local buckling.

Step-by-Step Solution:

Verification / Alternative check:
Compare to non-exposed guidance where larger multiples (e.g., 32 t) are allowed; exposure necessitates tighter spacing.

Why Other Options Are Wrong:
Values like 24 t or 32 t are too large for weather-exposed conditions; 8 t is overly conservative beyond common practice; 48 t is unsafe for exposed plates.

Common Pitfalls:
Using non-exposed limits on exposed work; neglecting the smaller governing absolute distance when 16 t is large in millimeters.

Final Answer:
16 t