Assertion (A): High-strength friction grip (HSFG) bolts are preferred over bearing-type bolts in structures subjected to dynamic or reversal of loads. Reason (R): HSFG bolts transfer the load through friction between the interface of the connected plates rather than through shear or bearing on the bolt shank. Choose the correct answer:
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A)Correct
- BBoth (A) and (R) are correct, but (R) is not the correct explanation of (A)
- C(A) is correct but (R) is incorrect
- D(A) is incorrect but (R) is correct
Solution
Concept
High-Strength Friction Grip (HSFG) Bolts
Formula
Vnsf = µf × ne × Kh × Fo
Step-by-step solution
1. Analyze Assertion (A) regarding the preference for HSFG bolts under dynamic or reversal loads. 2. Understand Reason (R) and the formula for nominal shear capacity (Vnsf = µf × ne × Kh × Fo), which shows load transfer occurs via friction rather than bolt shear/bearing. 3. Conclude that both (A) and (R) are correct and (R) correctly explains (A), selecting Option (a) as the correct choice.
Explanation
HSFG bolts use high tension to clamp plates tightly together, so load is transferred purely through friction between the plate surfaces rather than by the bolt pressing against the hole edges. Because there is no slip or stress concentration, these bolts prevent joint loosening and fatigue failure, making them ideal for structures with dynamic or reversing loads. Thus, both statements are correct, and the reason perfectly explains the assertion.
Shortcut
To easily remember HSFG bolts under dynamic loads, use the rule "Friction Means Zero Slip": - Friction Transfer: HSFG bolts clamp plates tightly to transfer load by friction rather than bolt shear. - Dynamic/Reversal: Zero slip and no stress concentrations prevent fatigue and joint loosening under dynamic loads.
Common mistake
A common mistake is selecting option B by believing that Reason (R) is merely an independent statement about friction transfer, without realizing that load transfer via friction directly eliminates slip and stress concentrations, which is the exact reason HSFG bolts perform superiorly under dynamic or reversal loads. Another frequent error is selecting option C or D due to confusion between bearing-type bolts and friction-grip bolts, assuming HSFG bolts still transfer loads primarily through shear or bearing on the bolt shank.
Correct answer: A) Both (A) and (R) are correct and (R) is the correct explanation of (A)