Design of Steel Tension Connections

8/13/2019 Design of Steel Tension Connections

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Advantages of Bolts

Does not require as highly skilled workers

Requires less equipment

Reduced risk of fire Better quality control


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Types of Connections by Bolt Action


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Bolt Holes(Sizes in Table J3.3) p. 16.1-62

Standard

Oversized

Short-slotted

Long-slotted

Connection types

Bearing

Slip-critical


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Spacing, Edge and End Distances

Maximums

Center to Center (pitch) 24 x thickness

of thinner part 12 Edge distance 12 x thickness of part 6


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Bolt Shear Strength

J3.6FnAb Table J3.2

FnTable J3.2

AbArea of bolt

Tabulated on page 7-33, Table 7-10


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Bearing Strength at Bolt Holes

J3.10 Rn 0.75

Rngiven by equations J3-2

Tabulated on page 7-34,35


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Analysis of Tension Connection

Example (p. 15 notes)

Two A36 steel plate tension membershave been connected with a lap spliceusing diameter A307 bolts,arranged as shown. Find theallowable service live load. Also findrequired distances a and b. Assume

service live load is two times deadload. Plate edges are likely to besheared.


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Analysis of Tension Connection

Example (p. 15 notes)

P P

a a3 in.

10 in.

P

P

3/8 in.

3/8 in.

b

b


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Bolt Design Example p. 16 notes

Design a pair of splice plates to

connect the two parts of the channel

tension member shown. The forcesin the member are 110 kips live load

and 69.7 kips dead load. The bolts in

the surrounding joints are 1diameterA325N. All steel is A36. Slip is not

critical.


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Bolt Design Example p. 16 notes


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Block Shear Rupture

J4.3Equations J4-3a and J4-3b


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Welded Tension Connections

Two primary types of welds:


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LRFD Specification for Welds

p. 16.1-52

Effective throat thickness = 0.707 x

Where = weld size or leg size


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Limitations on Fillet Welds

Minimum weld sizeTable J2.4

Maximum weld size:

along edge of material < thick= thickness of material

along edge of material > thick= material thickness - 1/16

Minimum length Greater than 4 x weld size and,

If longitudinal filet welds are used alone in endconnections of flat bar tension members length perpendicular distance between them (p. 16.1-234)


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Limitations on Fillet Welds

Intermittent fillet weld segments must be atleast 4 times the weld size and 1

Lap joints require a lap of at least 5 times

the thickness of the thinner part joined, butnot less than 1 in. (p. 16.1-235)

Returns are required when practicable at

the ends of fillet welds. The must be atleast 2 times the weld size and usually notmore than 4 times the weld size.


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Design Strength of WeldsTable J2.5 p. 16.1-57

Fillet welds (shear on effective area):

Where:

Aw= Area of weld = throat thickness x length

FEXX=Weld metal designation(FE70 = 70 ksi)

Welded connection design procedure p. 22 notes

))(60.0)(75.0( wEXXww AFAF


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Weld Design Example p. 22 notes

An L 6 x 4x is stressed in tension by a 50

kip live load and a 40 kip dead load. At

the truss panel point the angle member is

attached to a 5/8thick gusset plate. The4 leg of the angle is outstanding. Check

the angle for tension strength and design

the welded connection of the angle to theplate. Assume all material is A36 steel

and that the loading will be static.


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Weld Design Example p. 22 notes

Design of Steel Tension Connections

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