CFS Joint Design & Load Calculations 2 — Questions and Answers
Question 1: In a bolted joint under eccentric loading, the fastener farthest from the centroid of the bolt group experiences:
- The smallest shear force
- The largest shear force (Correct answer)
- Zero shear force
- Equal shear force to all others
Correct answer: The largest shear force
Fasteners farthest from the centroid carry the greatest shear because the eccentric moment creates forces proportional to the distance from the centroid.
Question 2: The 'joint stiffness ratio' (Ck) in a bolted connection is defined as the ratio of:
- Bolt stiffness to grip length
- Bolt stiffness to clamped material stiffness (Correct answer)
- Clamping force to bolt tension
- Preload to proof load
Correct answer: Bolt stiffness to clamped material stiffness
Ck = Kb / Km, where Kb is bolt stiffness and Km is the stiffness of the clamped members, and it determines how external load is shared.
Question 3: When calculating the tensile stress area of a threaded fastener, which diameter is used?
- Major diameter
- Minor (root) diameter
- Pitch diameter
- A diameter between pitch and minor diameters (Correct answer)
Correct answer: A diameter between pitch and minor diameters
The tensile stress area uses an effective diameter between the pitch and minor diameters, defined by ASME/ASTM standards as approximately (d_pitch + d_minor)/2.
Question 4: A joint under combined shear and tension loading should be checked against:
- The von Mises (distortion energy) criterion (Correct answer)
- The maximum normal stress theory only
- Pure tensile capacity only
- The shear capacity multiplied by 1.5
Correct answer: The von Mises (distortion energy) criterion
The von Mises criterion accounts for the interaction of shear and tensile stresses to predict yielding under combined loading.
Question 5: Which factor does NOT directly affect the clamp load developed when tightening a fastener to a specified torque?
- Thread friction coefficient
- Under-head bearing friction coefficient
- Fastener material tensile strength (Correct answer)
- Thread pitch
Correct answer: Fastener material tensile strength
Clamp load from applied torque is governed by friction coefficients and thread geometry (pitch/lead angle), not by the tensile strength of the fastener material.
Question 6: In a lap joint loaded in shear, bearing stress is calculated as:
- Load divided by fastener cross-sectional area
- Load divided by (fastener diameter × plate thickness) (Correct answer)
- Load divided by net tensile area of the plate
- Load divided by contact area between plates
Correct answer: Load divided by (fastener diameter × plate thickness)
Bearing stress = P / (d × t), where d is fastener diameter and t is the thinner plate thickness, representing the force per unit contact area on the hole wall.
Question 7: For a bolted flange under internal pressure, the required bolt load must overcome:
- Only the pressure end force
- Only the gasket seating force
- Both the hydrostatic end force and the force needed to maintain gasket seating (Correct answer)
- Only the weight of the fluid
Correct answer: Both the hydrostatic end force and the force needed to maintain gasket seating
ASME flange design requires bolts to simultaneously resist the hydrostatic end force from pressure and maintain sufficient compressive stress on the gasket to prevent leakage.
CFS Joint Design & Load Calculations 2
In a bolted joint under eccentric loading, the fastener farthest from the centroid of the bolt group experiences: