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FIGURE 6.33 Arc spot weld — single thickness of sheet.

FIGURE 6.35 Fillet welds. Copyright 2005 by CRC Press
FIGURE 6.36 Flare groove welds: (a, b) flare bevel groove weld and (c) flare V-groove weld.

6.7.1.1 Arc Welds

According to the AISI Specification, the nominal strengths of arc welds can be determined from the equations given in Table 6.7. The design strengths can then be computed by using the factor of safety or resistance factor provided in Table 6.1.

6.7.1.2 Resistance Welds

The nominal shear strengths of resistance spot welds are provided in the AISI Specification [7] according to the thickness of the thinnest outside sheet and the unit used for the nominal shear strength. They are applicable for all structural grades of low-carbon steel, uncoated or galvanized with 0.9 oz/ft2 of sheet or less, and medium carbon and low-alloy steels.

6.7.2 Bolted Connections

Due to the thinness of the connected parts, the design of bolted connections in cold-formed steel construction is somewhat different from that in hot-rolled heavy construction. The AISI design provisions are applicable only to cold-formed members or elements less than 16 in. (4.76 mm) in thickness. For materials not less than 16 in. (4.76 mm), the bolted connection should be designed in accordance with the AISC Specifications (42,43).

In the AISI Specification, five types of bolts (A307, A325, A354, A449, and A490) are used for connections in cold-formed steel construction, in which A449 and A354 bolts should be used as

TABLE 6.7 Nominal Strength Equations for Arc Welds

Type of weld

Type of strength

Nominal strength, Pn

Groove welds (Figure 6.32)

Arc spot welds (Figure 6.33)

Arc seam welds (Figure 6.34)

Fillet welds (Figure 6.35)

Flare groove welds (Figure 6.36)

Tension or compression

Shear strength of weld

Shear strength of connected part

Shear strength Strength of weld Strength of connected part

Shear strength of connected part based on end distance Tensile strength Strength of weld Strength of connected part

Shear strength Strength of connected part

Shear strength of weld (for t > 0.10 in.) Strength of connected part

1. Longitudinal loading L/t < 25

2. Transverse loading

Shear strength of weld (for t> 0.10 in.) Strength of connected part

1. Transverse loading

2. Longitudinal loading

For t < tw < 2t or if lip height < L For tw > 2t and lip height > L

Lte(0.6Fxx)

Lte(Fy /V3) 0.589decFxx 2.20tdaFu

0.785decFxx 0.8 (Fu/Fy)ctdaFu

0.75twLFxx

0.75tLFu tLFu

0.75twLFxx

0.833tLFu

0.75tLFu 1.50 tLFu

Note: d is the visible diameter of outer surface of arc spot weld, da is the average diameter of the arc spot weld at midthickness of t, da = (d — t) for single sheet or multiple sheets not more than four sheets, de is the effective diameter of fused area at the plane of maximum shear transfer, de = 0.7d — 1.5t < 0.55d, e is the distance measured in the line of force from the centerline of a weld to the nearest edge of an adjacent weld or to the end of the connected part toward which the force is directed, Fu is the tensile strength of the connected part, Fy is the yield point of steel, Fxx is the filler metal strength designation in AWS electrode classification, L is the length of the weld, Pn is the nominal strength of the weld, t is the thickness ofthe connected sheet, te is the effective throat dimension for groove weld, tw is the effective throat for fillet welds or flare groove weld not filled flush to surface, t„ = 0.707w1 or 0.707w2, whichever is smaller, and w1 and w2 are the leg of the weld, respectively.

equivalents of A325 and A490 bolts, respectively, whenever a diameter smaller than 1 in. (12.7 mm) is required.

On the basis of the failure modes occurring in the tests of bolted connections, the AISI criteria deal with three major design considerations for the connected parts: (1) longitudinal shear failure, (2) tensile failure, and (3) bearing failure. The nominal strength equations are given in Table 6.8.

In addition, design strength equations are provided for shear and tension in bolts. Accordingly, the AISI nominal strength for shear and tension in bolts can be determined as follows:

where Ab is the gross cross-sectional area of bolt and Fn is the nominal shear or tensile stress given in Table 6.9 for ASD and LRFD. For the LSD method, see appendix B of the North American Specification [7].

TABLE 6.8 Nominal Strength Equations for Bolted Connections (ASD and LRFD)a

Type of strength

Nominal strength, Pn

Shear strength based on spacing and edge distance Tensile strength in net section (shear lag)

1. Flat sheet connections not having staggered holes

With washers under bolt head and nut Single bolt in the line of force Multiple bolts in the line of force Without washers under bolt head or nut Single bolt in the line of force Multiple bolt in the line of force

2. Flat sheet connections having staggered hole (see AISI Specification for the modified An)

3. Other than flat sheet (see AISI Specification for the effective net area Ae)

Bearing strength

1. Without consideration of bolt hole deformation (see AISI Specification for bearing factor, C, and modification factor, mf)

2. With consideration of bolt hole deformation (see AISI Specification for coefficient a)

teK,

Same as item (1), except for An

(4.64at + 1.53)dtFu a For the LSD method, see appendix B of the AISI North American Specification [7] for shear strength based on spacing and edge distance and for tensile strength in net section.

Note: An is the net area of the connected part, d is the nominal diameter of bolt, Fu is the tensile strength of the connected part, s is the sheet width divided by the number of bolt holes in cross-section being analyzed, and t is the thickness of the thinnest connected part.

TABLE 6.9 Nominal Tensile and Shear Stresses for Bolts (ASD and LRFD)a

Nominal tensile stress, Nominal shear stress,

TABLE 6.9 Nominal Tensile and Shear Stresses for Bolts (ASD and LRFD)a

Nominal tensile stress, Nominal shear stress,

Description of bolts

Fnt (ksi)

Fnv (ksi)

A307 bolts, Grade A,1 in. < d < 2 in.

0 0

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