# Connection Design.

## Presentation on theme: "Connection Design."— Presentation transcript:

Connection Design

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…

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

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.

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

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.

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.

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.

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

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.

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

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

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

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

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