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.ShearMomentAxial: splices, bracing, truss connectors, hangers…
3 Economic Considerations Shear Connections:Design for specified factored loadsAllow use of single-plate and single-angle shear connectionsDo 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 momentGravity, seismic, wind are treated separatelyThis is needed for column web doubler plate calcsIf stiffeners are required, allow use of fillet welds instead of complete joint penetration weldsTo avoid use of stiffeners, consider redesign with a heavier column to avoid them.
5 Economic Considerations Bracing ConnectionsIn 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 FEAMisunderstanding 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 isF Rn = f sy AgDesign strength for fracture in net section isf Rn = f su Anf = 0.9 for yield, 0.75 for fracturesy = yield strength; su = tensile strength; Ag = gross area; An = net area.
7 TensionSometimes 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 sectionOr, 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 ShearEither shear yielding or fracture govern. Design strength for yielding in the gross section isF Rn = f 0.6 sy AgDesign strength for fracture in net section isf Rn = f 0.6 su AnDue to resistance provided by the flange, net shear fracture will govern capacity of flanged members only when BOTH flanges are coped.
9 BendingEither tension yielding or fracture govern. Design strength for yielding in the gross section isF Rn = f sy ZgDesign strength for fracture in net section isf Rn = f su Zn
10 Bending: Plastic section Zn = Zg (1 - dh/b)Where dh = hole diameter and b = bolt spacingThis is exact for even number of rows, and slightly conservative for odd number.
11 Localized Limit States Bearing at bolt holesBolt tear-outBlock shearLocal web yieldingLocal web cripplingLocal web compression bucklingLocal flange bendingAxial yield linePlate Plastification
12 Bearing at Bolt holesLarge compressive stresses can occur where the shank of the bolt bears on the connected material.f Rn = f 2.4 db t suWhere 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 asf Rn = f 3.0 db t su
13 Bolt Tear-outShear 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 suif we don’t care about hole def,Rn = f 1.5 Lc t su< f 3.0 db t suwhere Lc = length of connector tearing out
14 Possible failures For each bolt, have to check Bolt shear Bearing on main material at boltBearing on connection material at boltBolt tear out through main materialBolt tear out through connection material