Riveted splice with packing (> 6 mm) – code-based increase in number of rivets According to IS 800:1971, in a splice plate where the calculated shear is transmitted through a packing thicker than 6 mm, the required number of rivets should be increased by 2.5% for every additional thickness of:

Introduction / Context:
When load in a riveted (or bolted) splice is transferred through a packing piece instead of direct plate-to-plate bearing, deformation and secondary effects can reduce the effectiveness of the fasteners. Older code provisions (IS 800:1971 working stress design) therefore specify an increase in the number of rivets as the packing thickness grows.

Given Data / Assumptions:

• Packing thickness exceeds 6 mm.
• Increase in rivet count is expressed as a percentage per unit thickness.
• Provision cited is specific to IS 800:1971 practice.

Concept / Approach:
Load path through a compressible packing introduces additional eccentricity/deformation. A small percentage increase in rivet count offsets this potential reduction in joint efficiency. The code quantifies this as 2.5% per mm of extra packing thickness over 6 mm.

Step-by-Step Solution:

Verification / Alternative check:
Historical steel design handbooks repeating IS 800:1971 guidance show the same 2.5% per mm increase where shear passes through packing.

Why Other Options Are Wrong:
1.5 mm, 2.0 mm, 2.5 mm, or 3.0 mm increments would misstate the prescribed rate, leading to unconservative or overly conservative designs.

Common Pitfalls:
Forgetting the rule applies only to thickness beyond 6 mm; applying the percentage to shear force instead of the number of rivets; ignoring that more modern limit-state codes handle such effects differently.

Final Answer:
1.0 mm of packing (beyond 6 mm)