Steel design and detailing: What is the minimum number of rivets required to connect a member to a gusset plate so that a safe, non-rotational connection is achieved in civil/structural engineering practice?

Introduction / Context:
In steel structures, members such as truss bars, bracing angles, or plates are commonly connected to a gusset plate using rivets (or bolts in modern practice). The minimum fastener count is a fundamental detailing rule because it governs the connection’s ability to resist rotation and carry axial force safely.

Given Data / Assumptions:

• The connection is between a structural member and a gusset plate.
• Only riveted (or similarly behaving bolted) shear connections are considered.
• Connection must be safe against unintended rotation and slip under service actions.

Concept / Approach:
A single fastener provides a point support, which does not prevent rotation of the connected member about the fastener’s center. To prevent this free rotation and to provide a statically reliable transfer of axial force, at least two fasteners are placed with spacing. Two fasteners create a couple arm that resists rotational tendencies and improves redundancy and slip resistance.

Step-by-Step Solution:
Connection with 1 rivet: allows rotation about the rivet center, which is undesirable and unsafe for axial members.Connection with 2 rivets: provides a line of action with spacing, enabling resistance to rotation and ensuring a determinate transfer path.Codes and standard practice: traditional riveted/bolted detailing guides require a minimum of two fasteners for primary member-to-gusset connections.

Verification / Alternative check:
Review of free-body diagrams shows that a single fastener connection cannot equilibrate an axial force without allowing rotation. Two fasteners separated by a pitch distance provide moment resistance against rotation via couple action under small slips.

Why Other Options Are Wrong:
'1': rotationally unstable and non-redundant.'3' or '4': acceptable but not the minimum; the question asks for the minimum number.

Common Pitfalls:
Confusing temporary erection pins with permanent fasteners; assuming a single fastener is acceptable because the member is laterally braced elsewhere; neglecting torsional effects in truss joints.

Final Answer:
2