Tension members – net area of double-angle section: For double angles in tension placed back-to-back and connected to either side of a gusset plate, the effective sectional area for design equals which of the following?

Introduction / Context:
In steel design, the tensile capacity of a member is governed by its net section across the line of fasteners. For built-up members like back-to-back double angles on either side of a gusset, the connection layout determines how much area is deducted for holes.

Given Data / Assumptions:

• Two equal angles, placed back-to-back.
• Connected on either side of a single gusset plate.
• Rivet/bolt holes occur in the connected legs only.

Concept / Approach:
Net area = gross area − sum of hole areas along the critical section. Since the load is transferred through the connected legs, holes in those legs reduce the area resisting tension. Unconnected legs do not have hole deductions along the critical section through the connection.

Step-by-Step Solution:
Determine gross area: sum of both angles’ areas.Locate critical section: through the line(s) of holes in the connected legs.Compute net area by subtracting hole areas from the gross area.

Verification / Alternative check:
Design standards consistently define tensile strength using net section accounting for fastener holes; detailing rules ensure shear lag and block shear checks are also satisfied.

Why Other Options Are Wrong:

• Gross area (no deductions) overestimates capacity.
• Adding hole area is non-physical.
• Multiplying gross area by hole area is meaningless dimensionally.

Common Pitfalls:

• Forgetting to consider stagger (use of pitch and gauge) when holes are staggered.
• Ignoring block shear which may govern instead of simple net area.

Final Answer:
the gross area minus area of rivet (bolt) holes