Bolted Connections MCQ with answer and solution

Concept

Property class designation of bolts in steel structures indicates ultimate tensile strength and yield-to-ultimate strength ratio.

Formula

f_u = X × 100 MPa f_y = (X × Y) × 10 MPa

Step-by-step solution

1. Identify the grade of the bolt as 6.8, where X = 6 and Y = 8. 2. Calculate ultimate tensile strength (f_u) = 6 × 100 = 600 MPa. 3. Calculate yield strength (f_y) = (6 × 8) × 10 = 480 MPa.

Explanation

For a bolt designated as 'grade X.Y' (such as 8.8 or 6.8), the first digit (X) represents 1/100th of the ultimate tensile strength in MPa, and the product of the two digits (X × Y) represents 1/10th of the yield strength in MPa. For grade 6.8, the ultimate strength is 6 × 100 = 600 MPa, and the yield strength is (6 × 8) × 10 = 480 MPa.

Why the other options are wrong

A: 400 is the yield strength for 4.6 or 8.8 incorrect product. C: 360 is incorrect. D: 800 and 600 correspond to grade 8.8 bolts.

Shortcut

First digit × 100 = Ultimate strength. Product of both digits × 10 = Yield strength.

Common mistake

Confusing the yield ratio (Y) as a direct percentage without multiplying by the first digit.