Module 13
Connection and joint design
A joint is a chain of components in series. That one idea settles both questions it raises — the weakest component sets the resistance, and every component sets the stiffness — and they are almost never the same component.
What this module covers
- Recognise the T-stub in an end plate, a column flange and an angle cleat
- Derive the three T-stub failure modes and say which is ductile
- Explain prying as a consequence of the flange bending, not a code allowance
- Assemble components in series and say why the weakest and the softest differ
- Calculate a joint's moment resistance and initial stiffness
- Say when the initial stiffness is the wrong number to have used
Lessons
Almost every bolted joint contains a piece of plate that bends to deliver tension into a bolt. One model covers all of them, and its three failure modes are derivable.
Start lesson →Components in series. The weakest sets the resistance, every one sets the stiffness, and improving the wrong one is the most common wasted effort in joint design.
Start lesson →
Module checkpoint
Check what you have taken in
8 questions
Question 1
A T-stub has Mpl = 6.0 kNm and m = 50 mm. What is its mode 1 resistance in kN?
Question 2
The same T-stub has n = 40 mm and ΣFt,Rd = 400 kN. What is its mode 2 resistance in kN?
Question 3
Four components have k values of 5, 10, 20 and 40 mm. What is keq?
Question 4
In that group the k = 5 component is made rigid. What is the new keq?
Question 5
A joint's lever arm is increased from 350 mm to 450 mm with no other change. By what factor does Sj,ini increase?
Question 6
A bolt row develops 250 kN at a lever arm of 380 mm. What moment does it contribute, in kNm?
Question 7
Which T-stub mode gives the least warning before failure?
Question 8
Why must keq always be smaller than the smallest individual ki?