Chapter 16 Basic Connection Design Bolts and Nuts

Chapter 16 Basic Connection Design

Bolts and Nuts • Bolt – Threaded fastener • Head on one end – Designed to hold two or more parts together • Nut – Tightened on bolt – Available in flat or washer base

Bolts and Nuts (Cont’d)

Machine Screws • Thread fastener – General assembly of machine parts – Nominal diameter up to ½ inch – Length up to three inches – No chamfer

Machine Screws (Cont’d)

Cap Screws • • Fine-finished machine screws Used without a nut Nominal diameter up to four inches Chamfer to depth of first thread

Cap Screws (Cont’d)

Steel Connection Design • For Steel Design, the LRFD and ASD methods were discussed in previous chapters • For connection design we will first determine the capacity of the connection, Rn • The most basic column design requirement in the LRFD method is that design connection capacity, Rn must be greater or equal to the required strength, Ru

Steel Connection Design (Cont’d) • For ASD, the basic connection design requirement is that allowable capacity (Rn / ) is greater than the required capacity • Shear on the bolt is assumed to be evenly distributed to each bolt in a group with the design capacity of the bolt group in shear being calculated as: – Nominal strength x A x n

Bolted Connections • For Bolted Connections check the following: – Bolt Shear – Bearing – Tension on the Gross Area – Tension of the Effective Net Area • Each has to be checked • Bolt Shear is the most basic

Bolted Connections (Cont’d) • Shear on the bolt is assumed to be evenly distributed to each bolt in a group with the design capacity of the bolt group in shear being calculated as: – Nominal strength • Equation 16 -1 – Rn = Fn(Ab)N • Fn = nominal shear stress (see Figure 16 -9) • Ab = area of bolt • N = number of shear planes

Bolted Connections (Cont’d) • Bearing is checking for Bearing Type Connections. It is where the bolts would “slip” and actually make contact with the member. Needs to be checked so that crushing or tear out does not occur.

Bolted Connections (Cont’d) • Tension of the Gross Area – This area is the “full” cross-sectional area and is a connection capacity that is calculated against the potential failure of yielding – Its nominal capacity is • Equation 16 -3 – Pn = Fy(Ag)

Bolted Connections (Cont’d) • Tension of the Effective Net Area – This area is the cross-sectional area where the bolts are and its connection capacity is calculated against the potential failure of fracturing through these holes – Its nominal capacity is: • Equation 16 -4 – Pn = Fu(Ae)

Rivets • Metal pin • Fasten two or more materials together • Hammered, forged, or pressed into place • Classified by body diameter, length, and head type

Rivets (Cont’d)

Welding Definition • Process of joining two or more pieces • Heat material until softened or melted • Performed with or without pressure

Welding Definition (Cont’d) • Parts that are welded become one • Method of fastening – More permanent – Used in many manufacturing applications

Welded Connections • For welded connection design we will first determine the capacity of the connection, Rn • The most basic design requirement in the LRFD method is that design connection capacity, Rn must be greater or equal to the required strength, Ru • For ASD, the basic design requirement is that allowable capacity (Rn / ) is greater than the required capacity

Welded Connections (Cont’d) • For Welded Connections check the following: – Weld – Shear Yield in Base Metal – Tension on the Gross Area / Effective Net Area • Each has to be checked • Checking the weld is the most basic

Welded Connections (Cont’d) • Weld’s Nominal Strength – Equation 16 -5 • Rn = (Fw)(Aw) – Fw = nominal strength of the weld itself from Table 16 -2 – Aw = effective area of the weld (for fillet welds using the SMAW process this is (0. 707)(Leg)(Length of weld)

Welding Processes • Shielded metal arc welding – Stick electrode welding – Most traditionally used – Produces high-quality welds with excellent uniformity – Low-cost equipment and supplies – Flexible and portable

Welding Processes (Cont’d) • Oxygen gas welding – Oxyfuel or oxyacetylene welding – Performed with natural gas, propane, or propylene – Uses • Fabricate thin materials • Repair work and metal cutting – Less equipment and operating costs

Welding Processes (Cont’d) • Gas tungsten arc welding – TIG welding – Performed on a wide variety of materials – Produces clean, high-quality welds – Generally limited • Thin materials • High-integrity joints • Small parts – High cost

Welding Processes (Cont’d) • Gas metal arc welding – MIG welding – Welds thin material or heavy plate – Used in industries with automation and robotics – Rapidly made, high-quality welds – Popularity helps reduce costs

Types of Joints

Welding Symbols

Welding Symbols (Cont’d)

Welding Annotation

Fillet Weld • Formed in internal corner formed by two pieces of metal • Size is shown on same side as symbol – When size is same on both legs • Size shown once – When size is different • Vertical dimension precedes horizontal dimension

Square Groove Weld • Applied to a butt joint between two pieces of metal • Root opening – When two pieces are spaced apart – Specified dimension given if not standard

Bevel Groove Weld • Created when one piece is square and the other has a beveled surface • Annotation requirements – Bevel angle – Root opening

U Groove Weld • Created when groove between two parts is in a U-shape • Annotation requirements – Root – Weld size – Angle formed by sides of the “U”

J Groove Weld • Necessary when one piece is a square cut and the other is in a J-shaped groove • Annotation requirements – Angle – Root opening – Weld size

Plug Weld • Made in a hole in one piece of metal that is lapped over another piece of metal • Annotation requirements – Weld size – Angle – Depth – Pitch

Field Weld • Performed in the field and not the shop – Individual components may be easier to transport disassembled – Mounting procedure may require job site installation

Weld All Around • Welded connection performed all around a feature

Flush Contour Weld • For welds that cannot be raised above the surface of the part • Must be performed without finishing unless specified – – – C: chipping G: grinding M: machining R: rolling H: hammering

Spot Weld • Resistance welding – Base material clamped between two electrodes – Momentary electric current produces heat for welding • Associated with welding sheet metal lap seams