Connection DesignConnection Design

Bolted Steel Connections Bolted Steel Connections

Bolts in tension

Bolts in shear

6 x 200 =1200 kN

Failure modes of bolts in shearFailure modes of bolts in shear

Hole tearout

Bolt shear

Hole bearing

Bolts in Bolts in shearshear

Hole bearing

Br = 3 φ t d n Fu

e

d

d + 2 mm

t

φ = 0.67; n = number of bolts; m = number of shear planes

Bolt shear

Vr = 0.6 φ n m Ab Fu

A325M bolts: Fu = 830 MPaA490M bolts: Fu = 1040 MPa

Hole tearout

Br = φ t n e Fu

350W steel: Fu = 450 MPa

Bolts in tensionBolts in tension

d

Tensile strengthTr = 0.75 φ n Ab Fu=0.75(0.67)(1)(314)(830) N = 131 kN

threads shank

A325M 20 mm dia

Bolts in tension and shearBolts in tension and shear

Bolts in combined shear and Bolts in combined shear and tensiontension

( )2222

2

56.0 ubbff FAT

mV

βϕβ ≤+

Where β = an interaction factor derived from test results= 0.69 for A325 bolts, shear plane through shank= 0.41 for A325 bolts, shear plane through threads= 0.56 for A490 bolts, shear plane through shank= 0.30 for A490 bolts, shear plane through threads

Interaction FormulaInteraction Formula• A simpler version:

( )( )

( )0.1

56.0

2

22

2

75.0

2222

2

2

2

≤+

≤+

r

f

V

r

f

FA

ubbff

TT

TmV

FATmV

r

ubb

β

βϕβφβ

Vf/Vr

Tf/Tr

1.0

1.0

ExampleExample

Hole bearing

Br = 3 φ t d n Fu= (3)(0.67)(12)(20)(3)(450)= 651 x 103 N = 651 kN

e = 45mm

d = 20mm

d + 2 mm = 22 mm

t = 12mm

Bolt shear

Vr = 0.6 φ n m Ab Fu= 0.6(0.67)(3)(2)(314)(830) N= 630 kN

A325M bolt: Fu = 830 MPa

Hole tear-outBr = φ t n e Fu= (0.67)(12)(3)(45)(450)= 487 x 103 N = 487 kN

350W steel: Fu = 450 MPa

Ab= πd2/4=314 mm2

To avoid hole tear-oute > 3d

SlipSlip--critical connectionscritical connections• When slippage of a connection during normal

service conditions (under unfactored loads) is undesirable

• Bolts are pretensioned to at least 70% of their ultimate strength

Vs = c1 ks m n (0.7)(0.75) AbFu

where ks = slip coefficient and c1 = coefficient that relates the specific initial tension and mean slip to a 5% probability of slip for bolts installed by the turn-of-the-nut method

Values of cValues of c11 and and kkss

c1Contact surface of bolted parts

ksA325 and A325M bolts

A490 and A490M bolts

Clean mill scale, or blast-cleaned with class A coatings 0.33 0.82 0.78

Blast-cleaned or blast-cleaned with class B coatings 0.50 0.89 0.85

Hot-dipped galvanized with wire brushed surfaces 0.40 0.90 0.85

SlipSlip--critical connections in critical connections in combined shear and tensioncombined shear and tension

0.19.1 ≤+ubs FnA

TVV

Welded connectionsWelded connections

4 Times Square, NYC

Welded connectionsWelded connections

Types of welds:

Welded truss connectionsWelded truss connections

Welded beam connectionsWelded beam connections

Bolted connection for web

Full penetration groove weld

Backing bar

Moment connectionSimple

connection

Strength of welded connectionStrength of welded connection

Shear

Base metal: Vr = 0.67 φw Am Fu

Weld metal: Vr = 0.67 φw Aw Xu

Tension

Base metal: Tr = φ Ag Fy

Weld metal: Tr = φw An Xu

φw = 0.67

Fillet weld Fillet weld strengthsstrengths

0.707b

b

Am = b LAw = 0.707 b L

Base metal: Vr = 0.67 φw Am Fu

Weld metal: Vr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)

θ = 90o

θ = 0o

L

P

P

Electrode strengths, Electrode strengths, XXuu

Steel grades (G40.21-M)Matching electrode strength Xu [MPa]

260 300 350 380 400 480 700

410 X X

480 X X X X

550 X

620 X

820 X

Fillet weld exampleFillet weld example

0.707b = 4.2 mm

b = 6 mm

Am = b LAw = 0.707 b L

Weld strength:

Base metal: Pr = 0.67 φw Am Fu

= 0.67(0.67)(6)L(450) N= 1.2 L = 1.2 (550) = 660 kN

Weld metal: Pr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)

= 0.67(0.67)(0.707)(6)L(480)(…..) N= 0.914 [400 + 1.5(150)]= 571 kN

6 mm fillet

6 mm fillet20

0 mm

P

P

150 mm

Base metal: Vr = 0.67 φw Am Fu

Weld metal: Vr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)

Example Example

150 mm

200 mm

C

Tr = 2 x571= 1142 kN

1000 kN

400 kN

1000 kN

400 kN1142 kN

800 kN

Lreq = [800 / 0.9] / 2= 444 mm

6 mm fillet

Example Example

16 mm

150 mm

450

mm

Mr= Tr (0.45) kNm= 756 (0.45)= 340 kNm

Tr = φ A Fy= 0.9 (16) (150) (350) N= 756 kN Vr = 210/2 x 10

= 1050 kN

Vr

A325 20 mm dia