1. Connection Design

2. Types of Connections Three forces: Axial, shear and moment
Many connections have 2 or more simultaneously.
Connections are usually classified according to the major load type carried.
Shear
Moment
Axial: splices, bracing, truss connectors, hangers…

3. Economic Considerations
Shear Connections:
Design for specified factored loads
Allow use of single-plate and single-angle shear connections
Do NOT specify full-depth connections or rely on AISC uniform load tables

4. Economic Considerations
Moment connections:
Design for specified factored moments and shears.
Provide a breakdown of the total moment
Gravity, seismic, wind are treated separately
This is needed for column web doubler plate calcs
If stiffeners are required, allow use of fillet welds instead of complete joint penetration welds
To avoid use of stiffeners, consider redesign with a heavier column to avoid them.

5. Economic Considerations
Bracing Connections
In addition to providing brace force, also provide beam shear and axial transfer force.
The transfer force is not necessarily the beam axial force obtained from FEA
Misunderstanding of the transfer force can lead ot uneconomic or unsafe connections

6. Strength Limit States: Tension
Either tension yielding or fracture govern. Design strength for yielding in the gross section is
F Rn = f sy Ag
Design strength for fracture in net section is
f Rn = f su An
f = 0.9 for yield, 0.75 for fracture
sy = yield strength; su = tensile strength; Ag = gross area; An = net area.

7. Tension
Sometimes entire gross area or net area cannot be considered effective.
For example, brace attaching to a large gusset: Gross area is based on the Whitmore section
Or, connecting elements, such as angles, where only one leg of the angle is connected, a shear lag factor must be included in the calculation of net area.

8. Shear
Either shear yielding or fracture govern. Design strength for yielding in the gross section is
F Rn = f 0.6 sy Ag
Design strength for fracture in net section is
f Rn = f 0.6 su An
Due to resistance provided by the flange, net shear fracture will govern capacity of flanged members only when BOTH flanges are coped.

9. Bending
Either tension yielding or fracture govern. Design strength for yielding in the gross section is
F Rn = f sy Zg
Design strength for fracture in net section is
f Rn = f su Zn

10. Bending: Plastic section
Zn = Zg (1 - dh/b)
Where dh = hole diameter and b = bolt spacing
This is exact for even number of rows, and slightly conservative for odd number.

11. Localized Limit States
Bearing at bolt holes
Bolt tear-out
Block shear
Local web yielding
Local web crippling
Local web compression buckling
Local flange bending
Axial yield line
Plate Plastification

12. Bearing at Bolt holes
Large compressive stresses can occur where the shank of the bolt bears on the connected material.
f Rn = f 2.4 db t su
Where f = 0.75, db = bolt diameter, t = thickness of material.
If deformation at the bolt hole under service loads is not a design consideration, the bearing strength can be determined as
f Rn = f 3.0 db t su

13. Bolt Tear-out
Shear fracture where bolt tears out through the material.
If deformation at bolt hole is a concern, use previous equation or this (whichever is smaller)
f Rn = f 1.2 Lc t su < f 2.4 db t su
if we don’t care about hole def,
Rn = f 1.5 Lc t su< f 3.0 db t su
where Lc = length of connector tearing out

14. Possible failures For each bolt, have to check Bolt shear
Bearing on main material at bolt
Bearing on connection material at bolt
Bolt tear out through main material
Bolt tear out through connection material

15. 7/8” A490X bolts
1.5” 3”
1.5” 3 1
3/8 PL (A36)
W8x15 4 2