Steel tension members — rivet hole allowances and net section calculation (Choose the correct combination based on steel design practice.)

Introduction:
Tension members in steel structures require careful deduction for fastener holes to obtain the net section. Rivet (or bolt) hole allowances vary with nominal diameter. This problem checks knowledge of net area calculation and standard hole clearances.

Given Data / Assumptions:

• A: Net area equals gross area minus deductions for holes.
• B: Hole allowance stated as +1.5 mm for holes greater than 25 mm.
• C: Hole allowance stated as +2.0 mm for holes greater than 25 mm.
• D: Total deduction equals thickness multiplied by sum of diameters of holes in any critical chain.

Concept / Approach:
Net section is found by subtracting material removed by holes along the critical section. Standard practice is to take the gross diameter of a hole as the nominal fastener diameter plus a clearance. For larger rivets (> 25 mm), the clearance adopted is typically larger (about +2.0 mm).

Step-by-Step Solution:
1) Statement A is fundamental and correct.2) Statement B conflicts with standard allowance for sizes greater than 25 mm; +1.5 mm is typical for smaller diameters, not larger.3) Statement C is correct for > 25 mm nominal size (about +2.0 mm).4) Statement D correctly describes deduction across a chain (critical path) through the section.

Verification / Alternative check:
Worked examples for net section in tension members consistently use the enlarged hole diameter (nominal + clearance) multiplied by thickness to compute deductions.

Why Other Options Are Wrong:
Option A (only A and C) omits D, which is correct. Option C misclassifies B and D. Option D claims all statements are correct, but B is not consistent with larger-hole allowances.

Common Pitfalls:
Using nominal diameter instead of hole diameter for deductions; forgetting stagger corrections when applicable; choosing the wrong critical chain across multiple rows of holes.

Final Answer:
A, C and D are correct; B is incorrect.