Week 9-Fatigue of Tubular Structures

Question 1

What type of connections work best under fatigue?

Answer 1

Bolted connections

Question 2

What causes fatigue?

Answer 2

Fluctuating loads/stresses which cause a microstructural change in material

Question 3

What type of loading is considered when carrying out fatigue checks on a structure?

Answer 3

Live and unfactored loads

Question 4

What type of loading is NOT considered when carrying out fatigue checks on a structure?

Answer 4

Dead loads (self weight included)
Factored loads

Question 5

Where do fatigue cracks begin on a welded HSS member?

Answer 5

At the toe of the weld connecting the web and chord

Question 6

How can fatigue failure be mitigated?

Answer 6

With regular inspections of the structure to observe cracks and fix them

Question 7

List 5 ways to improve fatigue resistance (fatigue life extension) of welded HSSs?

Answer 7

1- By weld improve techniques which reduces stress concentration factors (SCF)

2-Using HSS with equal width branch and chord members

3-Concrete filled chords
4-Cast steel nodes
5-Stiffened connections

Question 8

With what 3 methods can you determine fatigue resistance in welded HSSs?

Answer 8

1- the Hot Spot Stress approach (geometric stress)
2-the Detail Category approach (normal stress)
3-Fracture mechanics

Question 9

In reality, what type of amplitude loading exists to cause fatigue?

Answer 9

Variable amplitude loading

Question 10

What is the difference between constant amplitude loading and variable amplitude loading?

Answer 10

Constant amplitude loading is produced by ref same type of load eg the same type of lorry going over a bridge every day, every week every year (unrealistic)

Variable amplitude loading is produced by different types of load eg (more realistic) several cars, lorries and trucks going over a bridge constantly

Question 11

Which approach to determining the fatigue resistance of HSSs is more accurate?

Answer 11

The Hot Spot Stress approach

Question 12

What is the failure criteria for members which have failed under fatigue?

Answer 12

Crack depth

Question 13

In Round welded HSSs (CHS), where are the critical crack locations?

Answer 13

The crown and saddle

Question 14

In Square and Rectangular welded HSSs where are the critical crack locations?

Answer 14

The corner radius

Question 15

List 3 current High Frequency Hammer Peening of weld toe methods in use?

Answer 15

1-High Frequency Impact Treatment (HiFIT)
2-Pneumatic Impact Treatment (PIT)
3-Ultrasonic Impact Treatment (UIT)

Question 16

How do you avoid fatigue in bolted connections?

Answer 16

Use bolts in shear

Question 17

Which weld performs better in fatigue?

Fillet weld or groove weld?

Answer 17

Groove welds