Yu W., LaBoube R.A. Cold-Formed Steel Design

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BOLTED CONNECTIONS 285

Cornell University in the 1950s to study the type of failure

caused by shearing of the bolt.

8.37,8.38

It was found that

the shear–tension strength ratio is independent of the bolt

diameter, and the ratios are equal to about 0.62 and 0.72

for double-shear and single-shear tests, respectively. In

view of the fact that the failure by shearing of the bolt

is more sudden than that in the sheets being connected,

a conservative shear-to-tension ratio of 0.6 has been used

in the past for both double- and single-shear conditions

in the development of design provisions, even though the

extremes of test values ranged from 0.52 to 1.0; that

is, the type of failure by shearing of the bolt occurs

at a strength equal to 0.6 times the tensile strength of

the bolt.

8.4.2 AISI Design Criteria for Bolted Connections

Based upon the results of tests summarized in Section 8.4.1

and past design experience, Section E3 and Appendix A of

the 2007 edition of the AISI North American Speciﬁcation

includes a number of requirements for the design of bolted

connections in the United States and Mexico and are

summarized herein. Section E3 and Appendix B contain

the provisions for Canada.

8.4.2.1 Thickness Limitations On the basis of the same

reasons discussed in Section 8.3.2.1 for the design of

welded connections, Section E3 of the Speciﬁcation is

applicable only to the design of bolted connections for cold-

formed steel members that are less than

in. (4.8 mm) in

thickness. For materials not less than

in. (4.8 mm), the

AISC speciﬁcation

1.411

should be used for the design of

bolted connections in cold-formed steel structures.

8.4.2.2 M aterials Prior to 1980, the AISI design provi-

sions concerning the allowable shear stresses for mechan-

ical fasteners were limited to A307 and A325 bolts. Because

the maximum thickness for cold-formed steel members was

increased in 1977 from

in. (12.7 mm) to 1 in. (25.4 mm),

other high-strength bolts, such as A354, A449, and A490

bolts, were added to the 1980 speciﬁcation for bolted

connections.

In view of the fact that A325 and A490 bolts are available

only for a diameter of

in. (12.7 mm) and larger, whenever

smaller bolts [less than

in. (12.7 mm) in diameter] are

required in a design, A449 and A354 Grade BD bolts

should be used as equivalents of A325 and A490 bolts,

respectively.

For other types of fasteners, which are not listed in

Section E3 of the AISI North American Speciﬁcation, draw-

ings should indicate clearly the type and size of fasteners

to be employed and the design force.

8.4.2.3 Bolt Installation The requirement for bolt instal-

lation was added to the AISI Speciﬁcation since 1980

to ensure that bolts are properly tightened according to

acceptable practice. Because the required pretension in bolts

usually varies with the types of connected part, fasteners,

applied loads, and applications, no speciﬁc provisions are

provided in the AISI North American Speciﬁcation for

installation.

The effect of torques on the strength of bolted connec-

tions has been studied in the past and was reported in

Ref. 8.45.

8.4.2.4 Maximum Sizes of Bolt Holes The 1986 and

the 1996 editions of the AISI Speciﬁcation include the

maximum sizes of standard holes, oversized holes, short-

slotted holes, and long-slotted holes, as shown in Table 8.4.

Standard holes should be used in bolted connections, except

that oversized and slotted holes may be used as approved

by the designer. Additional requirements are given in the

AISI North American Speciﬁcation for the use of oversized

and slotted holes.

8.4.2.5 Shear, Spacing, and Edge Distance in Line of

Stress According to Section E3.1 of the AISI North

American Speciﬁcation, the nominal shear strength, P

,of

the connected part as affected by spacing and edge distance

in the direction of applied force shall be calculated as

follows:

= teF

(8.51)

(a) When F

≥ 1.08:

 = 2.0 (ASD)

φ = 0.70 (LRFD)

(b) When F

< 1.08

 = 2.22 (ASD)

φ = 0.60 (LRFD)

where P

= nominal resistance per bolt

e = distance measured in line of force from

center of standard hole to nearest edge of

adjacent hole or to end of connected part

t = thickness of thinnest connected part

= tensile strength of connected part

= yield stress of connected part

Equation (8.51) was derived from Eq. (8.45) in Section

8.4.1.1. The above design equation is the same as that used

in previous editions of the AISI speciﬁcation, except that

the limiting F

ratio was reduced in 1996 from 1.15

286 8 CONNECTIONS

to 1.08 for the consistency with the ductility requirement

prescribed in Section A3.3.1 of the Speciﬁcation.

In addition to the above requirements, Section E3.1 of

the AISI North American Speciﬁcation also includes the

following requirements concerning minimum spacing and

edge distance in the line of stress:

1. The minimum distance between centers of bolt holes

should not be less than 3d.

2. The distance from the center of any standard hole to

the end or other boundary of the connecting member

should not be less than 1

3. For oversized and slotted holes, the distance between

edges of two adjacent holes and the distance measured

from the edge of the hole to the end or other boundary

of the connecting member in the line of stress should

not be less than the value of e − 0.5d

,inwhiche is

the required distance computed from Eq. (8.51) using

the applicable safety factor for ASD and resistance

factor for LRFD, and d

is the diameter of a standard

hole deﬁned in Table 8.4. Also, the clear distance

between edges of two adjacent holes should not be

less than 2d and the distance between the edge of the

hole and the end of the member should not be less

than d.

8.4.2.6 Tensile Strength of Connected Parts at

Connection Prior to 1999, the tensile strength on

the net section of connected parts was determined in

accordance with Speciﬁcation Section E3.2 in addition to

the requirements of Speciﬁcation Section C2. In Section

E3.2, the nominal tensile strength on the net section of the

bolt connected parts was determined by the tensile strength

of steel F

and the ratios r and d/s. These design equations

represent the shear lag effect on the tensile capacity of ﬂat

sheets with due consideration given to the use of washers

and the type of joints, either a single-shear lap joint or a

double-shear butt joint.

During recent years, research work has been conducted

by Holcomb, LaBoube, and Yu at the University of

Missouri-Rolla to study the effect of shear lag on the

tensile capacity of angles and channels as well as ﬂat steel

sheets.

6.24,6.25

The same project included a limited study of

the behavior of bolted connections having staggered hole

patterns. It was found that when a staggered hole pattern

is involved the net area can be determined by a design

equation using the well-known parameter s

2

/4g.

Based on the research ﬁndings, the 2007 edition of the

AISI North American Speciﬁcation includes the following

Speciﬁcation Section E3.2 to deal with the determination of

the nominal tensile strength for (a) ﬂat sheet connections not

having staggered hole patterns, (b) ﬂat sheet connections

having staggered hole patterns, and (c) structural shapes

including angles and channels.

E3.2 Rupture in Net Section (Shear Lag)

The nominal tensile strength of a bolted member shall be

determined in accordance with Section C2. For rupture in the

effective net section of the connected part, the nominal tensile

strength, P

, shall be determined as follows:

1. For ﬂat sheet connections not having staggered hole

patterns:

= A

(8.52)

a. When washers are provided under both the bolt head

and the nut:



1.0 +



≤ F

(8.53a)

For multiple bolts in the line parallel to the force

= F

(8.53b)

For double shear

 = 2.0 (ASD)

φ = 0.65 (LRFD)

For single shear

 = 2.22 (ASD)

φ = 0.55 (LRFD)

b. When either washers are not provided under the bolt

head and the nut or only one washer is provided under

Table 8.4 Maximum Sizes of Bolt Holes

Nominal Standard Oversized Short-Slotted Long-Slotted

Bolt Hole Hole Hole Hole

Diameter, d Diameter, d Diameter, d Dimensions Dimensions

(in.) (in.) (in.) (in.) (in.)

d +

(d +

) by (d +

)(d+

) by (2

≥

d +

(d +

) by (d +

)(d+

) by (2

Note: 1in. = 25.4 mm.

BOLTED CONNECTIONS 287

either the bolt head or the nut:

= (2.5rd/s)F

≤ F

(8.54a)

For multiple bolts in the line parallel to the force

= F

(8.54b)

 = 2.22 (ASD)

φ = 0.65 (LRFD)

where A

= net area of the connected part

s = sheet width divided by the number of bolt

holes in cross section being analyzed

= tensile strength of the connected part as

speciﬁed in Section A3.1 or A3.3.2

and d is deﬁned in Section E3.1.

2. For ﬂat sheet connections having staggered hole patterns:

= A

[Eq. (8.52)]

 = 2.22 (ASD)

φ = 0.65 (LRFD)

where F

is determined by Eqs. (8.47) and (8.48) and

= 0.90



− n

t +





s





(8.55)

Where A

= gross area of member

s = sheet width divided by number of bolt

holes in cross section being analyzed

(when evaluating F

)



= longitudinal center-to-center spacing of

any two consecutive holes

g = transverse center-to-center spacing between

fastener gage lines

= number of bolt holes in cross section being

analyzed

= diameter of standard hole

and t is deﬁned in Section E3.1.

3. For other than a ﬂat sheet:

= A

(8.56)

 = 2.22 (ASD)

φ = 0.65 (LRFD)

where F

is the tensile strength of the connected part

as speciﬁed in Section A3.1 or A3.3.2 and A

= A

is the effective net area with U = 1.0 for members

when the load is transmitted directly to all of the cross-

sectional elements. Otherwise, the reduction coefﬁcient

U is determined as follows:

a. For angle members having two or more bolts in the

line of force:

U = 1.0 −

1.20 ¯x

< 0.9 (8.57a)

but U shall not be less than 0.4.

b. For channel members having two or more bolts in the

line of force:

U = 1.0 −

0.36 ¯x

< 0.9 (8.57b)

but U shall not be less than 0.5

where ¯x = distance from shear plane to centroid of

cross section (Fig. 8.29)

L = length of connection (Fig. 8.29)

The speciﬁcation Eqs. (8.53) and (8.54) were

derived from Eqs. (8.48) and (8.50), respectively. See

Section 8.4.1.3 in this volume.

8.4.2.7 Bearing Strength between Bolts and Connected

Parts

a. Deformation Around the Bolt Holes Is Not a Design

Consideration. The nominal bearing strength (resistance)

of the connected sheet for each loaded bolt is given in

Section E3.3.1 of the Speciﬁcation as

= Cm

dtF

(8.58)

 = 2.50 (ASD)

φ =



0.60 (LRFD)

0.50 (LSD)

Figure 8.29 Determination of ¯x for sections using bolted connections.

1.346

288 8 CONNECTIONS

where C = bearing factor, determined in accordance

with Table 8.2

= modiﬁcation factor for type of bearing

connection determined in accordance with

Table 8.3

d = nominal bolt diameter

t = uncoated sheet thickness

= tensile strength of sheet

b. Deformation Around the Bolt Holes Is a Design Consid-

eration. When the movement of the connection is critical

and the deformation around bolt holes is a design consid-

eration, nominal bearing strength should also be limited

by Eq. (8.47) according to Section E3.3.2 of the the 2007

edition of the Speciﬁcation. For using Eqs. (8.47a) and

(8.47b),  = 2.22 (for ASD), φ = 0.65 (for LRFD), and

φ = 0.55 (for LRFD). See Section 8.4.1.2 for additional

discussion.

8.4.2.8 Shear and Tension in Bolts Section E3.4 of

the AISI North American speciﬁcation speciﬁes that the

nominal bolt strength P

resulting from shear, tension, or

a combination of shear and tension shall be calculated as

follows:

= A

F (8.59)

where A

is the gross cross-sectional area of the bolt.

When bolts are subject to shear or tension, the nominal

stress F

is given in Table 8.5 by F

for shear or F

for

tension. The applicable values of  and φ are also given

in the same table. When bolt tension is involved, the pull-

over strength of the connected sheet at the bolt head, nut,

or washer shall be considered. See Section 8.5.1.

When bolts are subject to a combination of shear and

tension,



⎧

⎪

⎨

⎪

⎩

1.3F

−

F

≤ F

(for ASD method) (8.60a)

1.3F

−

φF

≤ F

(for LRFD method) (8.60b)

Table 8.5 Nominal Tensile and Shear Strength for Bolts

1.345

Tensile Strength Shear Strength

Factor Nominal Factor Nominal

of Safety Resistance Stress of Safety Resistance Stress

 Factor φF

Description of Bolts (ASD) (LRFD) ksi MPa (ASD) (LRFD) ksi MPa

A307 bolts, Grade A,

in. (6.4 mm) ≤ d <

in. (12.7 mm)

2.25 0.75 40.5 279 2.4 0.65 24.0 165

A307 bolts, Grade A, d ≥

in. 2.25 45.0 310 27.0 186

A325 bolts, when threads are not excluded

from shear planes

2.0 90.0 621 54.0 372

A325 bolts, when threads are excluded from

shear planes

90.0 621 72.0 496

A354 Grade BD bolts,

in. ≤ d <

in., when

threads are not excluded from shear planes

101.0 696 59.0 407

A354 Grade BD bolts,

in. ≤ d <

in., when

threads are excluded from shear planes

101.0 696 90.0 621

A449 bolts,

in. ≤ d <

in., when threads

are not excluded from shear planes

81.0 558 47.0 324

A449 bolts,

in. ≤ d <

in., when threads

are excluded from shear planes

81.0 558 72.0 496

A490 bolts, when threads are not excluded

from shear planes

112.5 776 67.5 465

A490 bolts, when threads are excluded from

shear planes

112.5 776 90.0 621

Applies to bolts in holes as limited by Table 8.6. Washers or back-up plates shall be installed over long-slotted holes and the capacity

of connections using long slotted holes shall be determined by load tests in accordance with Chapter F.

BOLTED CONNECTIONS 289

where F

= nominal tensile stress from Table 8.5

= nominal shear stress from Table 8.5

= required shear stress

and  and φ are also from Table 8.5. In addition, the

required shear stress shall not exceed the allowable shear

stress F

/ (ASD) or the design shear stress φF

(LRFD)

of the fastener.

In Table 8.5, the allowable shear and tension stresses

speciﬁed for A307, A325, and A490 bolts are approx-

imately the same as those permitted by the AISC

1.411

and the Research Council on Structural Connections for

bearing-type connections.

8.108

Slightly smaller allowable

shear stresses are used for A449 and A354 Grade BD bolts

with threads in the shear planes as compared with A325

and A490 bolts, respectively. Such smaller shear stresses

are used because the average ratio of the root area to the

gross area of the

- in. (6.4-mm) and

- in. (9.5-mm)

diameter bolts is 0.585, which is smaller than the average

ratio of 0.670 for the

- in. (12.7-mm) and 1-in. (25.4-mm)

diameter bolts. According to Ref. 1.159, these design values

provide safety factors ranging from 2.25 to 2.52 against the

shear failure of bolts.

Example 8.4 Determine the allowable load for the bolted

connection shown in Fig. 8.30. Use four

-in.-diameter

A307 bolts with washers under the bolt head and nut. The

steel sheets are A570 Grade 33 steel (F

= 33 ksi and

= 52 ksi). Use ASD and LRFD methods. Assume that

the dead load–live load ratio is

and that the deformation

around bolt holes is not a design consideration.

SOLUTION

A. ASD Method

In the determination of the allowable load, consideration

should be given to the following items:

•

Shear, spacing, and edge distance in line of stress

(Section 8.4.2.5)

•

Tensile strength of connected parts at connection

(Section 8.4.2.6)

•

Bearing strength between bolts and connected parts

(Section 8.4.2.7)

•

Shear strength in bolts (Section 8.4.2.8)

1. Shear, Spacing, and Edge Distance in Line of Stress.

The distance from the center of a standard hole to the

nearest edge of an adjacent hole is

= 2 −

(d + 1/16) =2 −

(1/2 + 1/16)

= 1.72in.

Figure 8.30 Example 8.4.

The distance from the center of a standard hole to the

end of the plate in the line of stress is

= 1in.

Since e

, the allowable load should be deter-

mined by e

Because F

= 52/33 = 1.58 > 1.08, according

to Eq. (8.51), the allowable shear strength of the

connected sheet using four bolts can be computed as



4(te

)

2.0

4(0.105 × 1 × 52)

2.0

= 10.92 kips

In addition, some other AISI requirements should be

checked on the basis of Section E3.1 of the AISI

North American Speciﬁcation or Section 8.4.2.5 in

this volume as follows:

a. Distance between centers of bolt holes:

2in.>(3d = 1.5in.) OK

b. Distance from center of any standard hole to end

of plate:

1in.>(1

d = 0.75 in.) OK

2. Tensile Strength of Steel Sheets. Based on the AISI

design criteria, the allowable tensile strength of the

steel sheet can be determined under the following

considerations:

Based on Section C2 of the 2007 edition of the AISI

North American speciﬁcation, the allowable tensile

strength can be computed as follows:

(i) For yielding [Eq. (6.2)],



1.67

(4.0 × 0.105)(33)

1.67

= 8.30 kips

290 8 CONNECTIONS

(ii) For fracture away from the connection [Eq.

(6.3)],



2.00

(4.0 × 0.105)(52)

2.00

= 10.92 kips

Use T

= 8.30 kips for the requirement of

Section C2 of the speciﬁcation.

According to Sec. E.3.2(1) of the 2007 edition of

the speciﬁcation for bolts with washers under the

bolt head and nut and for a single-shear connection

( = 2.22), the allowable tensile strength should

be determined by Eq. (8.52) as follows:

= P

/ = A

/

where

= [4 −2(1/2 + 1/16)](0.105) = 0.30 in.

= F

= 52 ksi

(0.30)(52)

2.22

= 7.03 kips

Since P

,use(P

)

= 7.03 kips for section

a–a.

3. Bearing Strength between Bolts and Steel Sheets.

According to Section E3.3.1 of the 2007 edition of

the Speciﬁcation, the allowable bearing strength per

bolt is



2.50

= 4.76

Therefore C = 3.0 (Table 8.2) and m

= 1.0

(Table 8.3).

= (3)(1.0)(52)(

)(0.105) = 8.19 kips

8.19

2.50

= 3.27 kips

The allowable bearing strength for four bolts is

= 4 × 3.27 = 13.10 kips

4. Shear Strength in Bolts. From Table 8.5, the nominal

shear stress for the

-in.-diameter A307 bolts is

27 ksi and the gross area of the bolt is 0.196 in.

Therefore, the allowable shear strength for four bolts

4(A

)



4(0.196)(27)

2.4

= 8.82 kips

Comparing P

, P

,andP

, the allowable load

for the given bolted connection is 7.03 kips, which is

governed by the tensile strength of sheet A at section

a–a.

B. LRFD Method

For the LRFD method, the design considerations are the

same as for the ASD method. The design strength can be

calculated by applying some of the values used for the ASD

method.

1. Shear, Spacing, and Edge Distance in Line of Stress.

Using Eq. (8.51) for F

> 1.08, the design shear

strength of a connected sheet using four bolts is

(φP

)

= 4(0.70)(te

) = 4(0.70)(0.105)(1)(52)

= 15.288 kips

2. Tensile Strength of Steel Sheets

Based on Section C2 of the 2007 edition of the speci-

ﬁcation, the design tensile strength of the connected

sheet is:

i. For yielding [Eq. (6.2)],

= (φ

)(A

) = (0.90)(4 ×0.105)(33)

= 12.474 kips

ii. For fracture away from the connection [Eq.

(6.3)],

= φ

) = (0.75)(4 ×0.105)(52)

= 16.38 kips

Use φ

= 12.474 kips for the requirement of

Section C2 of the speciﬁcation.

On the basis of Section E3.2(1) of 2007 edition

of the speciﬁcation, the design tensile strength on

the net section of sheet A at section a–a can be

computed from Eq. (8.52) as follows:

φP

= φ(A

)

From the ASD method, A

= 0.30 in.

and F

52 ksi. Therefore,

φP

= (0.55)(0.30)(52) = 8.580 kips

Since φP

<φ

,use(φP

)

= 8.580 kips.

3. Bearing Strength between Bolts and Steel Sheets. The

nominal bearing strength per bolt is the same as calcu-

lated for the ASD method, that is, P

= 8.19 kips.

The design bearing strength between four bolts and

the steel sheet is

(φP

)

= 4(0.60)(8.19) = 19.656 kips

BOLTED CONNECTIONS 291

4. Shear Strength in Bolts. Based on Table 8.9, the design

shear strength of four bolts is

φ(P

)

= 4(0.65)(A

) = 4(0.65)(0.196)(27)

= 13.759 kips

Comparing the values of (φP

)

,(φP

)

,(φP

)

and (φP

)

, the controlling design strength is 8.580

kips, which is governed by the tensile strength of

sheet A at section a-a.

The required strength can be computed from Eqs.

(3.5a) and (3.5b) for the dead load–live load ratio

From Eq. (3.5a),

)

= 1.4P

+ P

= 1.4P

+ 5P

= 6.4P

From Eq. (3.5b),

)

=l.2P

+ 1.6P

=1.2P

+ 1.6(5P

) = 9.2P

and 9.2P

controls.

The dead load P

can be computed as follows:

9.2P

= 8.580 kips

= 0.932 kip

= 5P

= 4.663 kips

The total allowable load based on the LRFD method

is P

= P

+ P

= 5.595 kips. It can be seen that

the LRFD method is more conservative than the ASD

method due to the use of a relatively low resistance

factor.

Example 8.5 Check the adequacy of the bearing-type

connection as shown in Fig. 8.31. Use four

-in.-diameter

A325 bolts and A606 Grade 50 steel sheets (F

= 50 ksi

and F

= 70 ksi). Assume that washers are used under the

bolt head and nut and that threads are not excluded from

shear planes. Use standard holes and the ASD method. The

deformation around bolt holes is not a design consideration.

SOLUTION

1. Shear, Spacing, and Edge Distance in Line of Stress.

Since the inside sheet is thicker than the sum of

the thickness of both outside sheets and the distance

from the center of the hole to the end of the plate

is the same for inside and outside sheets, the outside

sheets will govern the design. For F

= 70/50 =

1.4 > 1.08, the safety factor to be used for determining

the allowable shear strength of the outside sheets is

2.0 according to Section 8.4.2.5.

Using Eq. (8.51), the allowable design shear

strength of the outside sheet can be computed as

follows:



teF

2.0

(0.105)(1)(70)

2.0

= 3.675 kips/bolt >

= 2.25 kips/bolt OK

In addition, the following requirements should also be

checked:

a. Distance from center of hole to edge of adjacent

hole:

2 −

(

1/2 + 1/16

)

= 1.72 in.

>(e = 1.0in.) OK

b. Distance between centers of bolt holes:

2in.>(3d = 1.5in.) OK

c. Distance from center of the hole to end of plate:

1in.>(1

d = 0.75 in.) OK

2. Tensile Strength of Steel Sheets

Based on Section C2 of the 2007 edition of the

speciﬁcation, the allowable tensile strength of the

Figure 8.31 Example 8.5.

292 8 CONNECTIONS

outside sheet can be computed as follows:

(i) For yielding [Eq. (6.2)],

1.67

(4.0 ×0.105)(50)

1.67

= 12.57 kips > 9kips OK

(ii) For fracture away from the connection [Eq.

(6.3)],

2.00

As in Example 8.4, A

= 0.30 in.

,and

(0.30)(70)

2.00

= 10.5kips> 9kips OK

Based on Section 8.4.2.6, the allowable tensile

strength of the outside steel sheet for double shear

can be calculated from Eq. (8.52) with a safety

factor of 2.0:



2.0

= 70 ksi

(0.30)(70)

2.0

= 10.50 kips > 9kips OK

By inspection, it is not necessary to check the inside

sheet for tensile strength because it is thicker than

the sum of the thicknesses of both outside sheets.

3. Bearing Strength between Bolts and Steel Sheets. The

allowable bearing strength can be obtained using

Section 8.4.2.7 for the inside sheet and the outside

sheets which are used in a double-shear connection:

a. For the inside sheet, the allowable bearing strength



(3.0)(1.33)(70)(0.5)(0.25)

2.50

= 13.96 kips/bolt >(

= 4.5 kips/bolt) OK

b. For the outside sheets, the allowable bearing

strength is



(3)(1.0)(70)(0.5)(0.105)

2.50

= 4.41 kips/bolt <(

= 4.5 kips/bolt) NG

4. Shear Strength in Bolts. When threads are not

excluded from shear planes, the nominal shear stress

for A325 bolts can be obtained from Table 8.5

that is,

= 54 ksi

The allowable shear strength for the double shear

condition is

(2)(A

)



(2)(0.196)(54)

2.4

= 8.82 kips/bolts >(

= 4.5 kips/bolt) OK

On the basis of the above calculations for the ASD

method, it can be concluded that the given connection

is not adequate for the applied load of 18 kips. The

same design considerations should be used for the

LRFD method.

8.4.3 Additional Design Information on Bolted

Connections

The research work reviewed at the beginning of Section

8.4 dealt mainly with the previous studies conducted in the

United States. The design criteria discussed in Section 8.4.2

were based on the 2007 edition of the AISI North American

speciﬁcation.

1.345

Additional research work on bolted connections has

been conducted by Baehre and Berggren,

1.25,8.4

Stark

and Toma,

8.5,8.49,8.50

Marsh,

8.51

LaBoube,

8.52

Zadanfar-

rokh and Bryan,

8.71

Carril, Holcomb, LaBoube, and

Yu,

6.23–6.25

Seleim and LaBoube,

8.72

Kulak and Wu,

8.73

Wheeler, Clarke, Hancock, and Murray,

8.74

Rogers and

Hancock,

2.55–2.61

and other researchers.

1.362–1.366

The

criteria for the bolted connections and the additional

information on mechanical fasteners have been published

in Refs. 8.4, 8.7, 8.8, and 8.53. See also other design

speciﬁcations mentioned in Chapter 1.

8.5 SCREW CONNECTIONS

Screws can provide a rapid and effective means to fasten

sheet metal siding and rooﬁng to framing members and to

make joints in siding and rooﬁng, as shown in Fig. 8.32.

They can also be used in steel framing systems and roof

trusses and to fasten gypsum sheathing to metal studs and

tracks.

Figure 8.33 shows some types of self-tapping screws

generally used in building construction.

8.2

Self-drilling

tapping screws are to be in compliance with ASTM

C1513.

8.109

Guidance for selection of screws can be found

in the publication of the Cold-Formed Steel Engineers

Institute.

8.110

8.5.1 AISI Design Criteria

The AISI design provisions for screw connections were

developed in 1993.

8.83

The background information on the

AISI design criteria is summarized by Pekoz in Ref. 8.54.

SCREW CONNECTIONS 293

Figure 8.32 Application of self-tapping screws.

8.1

Based on the ECCS Recommendations and the British Stan-

dard with the results of over 3500 tests from the United

States, Canada, Sweden, United Kingdom, and the Nether-

lands, the following requirements were developed as given

in Section E4 of the 1996 edition of the AISI Speciﬁcation

for the design of screw connections and were essentially

unchanged in the 2007 edition of the Speciﬁcation:

E4 Screw Connections

The following notation applies to this section of the Speciﬁca-

tion:

d = nominal screw diameter

 = 3.00 (ASD)

φ = 0.50 (LRFD)

= 0.40 (LSD)

= nominal shear strength [resistance] per screw

= nominal shear strength [resistance] of the screw

= nominal tension strength [resistance] per screw

= nominal shear strength [resistance] of the screw

not

= nominal pull-out strength [resistance] per screw

nov

= nominal pull-over strength [resistance] per screw

= thickness of member in contact with screw head or

washer (Figs. 8.35 and 8.36)

= thickness of member not in contact with screw head

or washer (Figs. 8.35 and 8.36)

= tensile strength of member in contact with screw head

or washer

= tensile strength of member not in contact with screw

head or washer

All E4 requirements shall apply to screws with 0.08 in. (2.03

mm) ≤ d ≤ 0.25 in. (6.35 mm). The screws shall be thread

forming or thread cutting, with or without a self-drilling point.

Alternatively, design values for a particular application shall

be permitted to be based on tests according to Chapter F. For

diaphragm applications, Section D5 shall be used.

Screws shall be installed and tightened in accordance with

the manufacturer’s recommendations.

The nominal screw connection strengths [resistances] shall

also be limited by Section C2.

E4.1 Minimum Spacing

The distance between the centers of fasteners shall not be less

than 3d .

E4.2 Minimum Edge and End Distance

The distance from the center of a fastener to the edge of

any part shall not be less than 1.5d. If the end distance is

parallel to the force on the fastener, the nominal shear strength

[resistance] per screw, P

, shall be limited by Section E4.3.2.

E4.3 Shear

E4.3.1 Connection Shear Limited by Tilting and Bearing

The nominal shear strength [resistance] per screw, P

,shall

be determined as follows: For t

< 1.0, P

shall be taken

Figure 8.33 Types of self-tapping screws.

8.3

(Courtesy of Parker-Kalon Corporation.)

294 8 CONNECTIONS

Figure 8.34 Comparison of tilting and bearing.

1.310,1.346

Figure 8.35 Design equations for t

 2.5.

Figure 8.36 Design equations for t

 1.0.

as the smallest of

= 4.2(t

1/2

(8.61)

= 2.7t

(8.62)

= 2.7t

(8.63)

For t

≥ 2.5, P

shall be taken as the smaller of

= 2.7t

[Eq. (8.62)]

= 2.7t

[Eq. (8.63)]

For 1.0 <t

< 2.5, P

shall be determined by linear inter-

polation between the above two cases.

E4.3.2 Connection Shear Limited by End Distance

The nominal strength shear strength per screw, P

, shall not

exceed

= teF

(8.64)

where t = thickness of part in which the end distance is

measured

e = distance measured in line of force from center of

a standard hole to nearest end of connected part.

E4.3.3 Shear in Screws

The nominal strength [resistance] of the screw shall be P

reported by the manufacturer or determined by independent

laboratory testing. In lieu of the value provided in Section E4,

the safety factor or resistance factor shall be permitted to be

determined in accordance with Section F1 and shall be taken

as 1.25 ≤ 3.0 (ASD), φ/1.25 ≥ 0.5 (LRFD),or φ/1.25 ≥ 0.4

(LSD).

E4.4 Tension

For screws which carry tension, the head of the screw or

washer, if a washer is provided, shall have a diameter d

not less than

in. (7.94 mm). Washers shall be at least

0.050 in. (1.27 mm) thick.

E4.4.1 Pull-Out

The nominal pull-out strength [resistance], P

not

, shall be calcu-

lated as follows:

not

= 0.85t

(8.65)

where t

is the lesser of the depth of the penetration and the

thickness, t

E4.4.2 Pull-Over

The nominal pull-over strength [resistance], P

nov

, shall be

calculated as follows:

nov

= 1.5t

(8.66)

where d



is the pull-over diameter determined in accordance

with (a), (b), or (c) as follows:

(a) For a round head, a hex head (Fig. 8.37), or hex washer

head (Figure 8.37) screw with an independent and solid

steel washer beneath the screw head,



= d

+ 2t

+ t

≤ d

(8.67)

where d

= screw head diameter or hex washer head

integral washer diameter

= steel washer thickness

= steel washer diameter

(b) For a round head, a hex head, or a hex washer head screw

without an independent washer beneath the screw head:



= d

but not larger than

in. (12.7mm)

the screw head (Fig. 8.37), it is permissible to use d



calculated in Eq. (8.67) with d

, t

,andt

,asdeﬁnedin

Fig. 8.37. In the equation, d



cannot exceed

in. (16 mm).

Alternatively, pull-over design values for domed washers,

including the safety factor, , and the resistance factor, φ,

shall be permitted to be determined by test in accordance

with Chapter F.

E4.4.3 Tension in Screws

The nominal strength [resistance] of the screw shall be P

reported by the manufacturer or determined by independent

laboratory testing. In lieu of the value provided in Section E4,