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Connection Design

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….

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Connection Design

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  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 = fsu 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 = fsu 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 Local web compression buckling Local flange bending Axial yield line Plate Plastification • Bearing at bolt holes • Bolt tear-out • Block shear • Local web yielding • Local web crippling

  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

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