Connections 1

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1

FUNDAMENTALS OF

CONNECTION DESIGN FOR

STRUCTURAL STEEL

BUILDINGS



2

OUTLINE

Session 1 Connection Types/Classification/Load Paths/Limit States

Session 2 Direct Loaded Connections/Prying Forces/Bolt and Weld

Eccentricity

Session 3 Framing Connections



3

OUTLINE

Session 4 Framing Connections Continued

Session 5 Moment Connections

Session 6 End-Plate Moment Connections/

Bracing Connections



4

Session 1

TYPESCLASSIFICATION

LOAD PATHSLIMIT STATES



5

CONNECTION TYPES

• TENSION CONNECTIONS

TrussHanger

Light and Heavy Bracing



6

CONNECTION TYPES

• COMPRESSION CONNECTIONS

Column SpliceBeam Bearing Plate

Column Base Plate



7



8

CONNECTION TYPES

• FRAMING (SHEAR) CONNECTIONSDouble Angles

Single AngleShear Tab

Shear End-Plate

Tee Connections

Seated



9

Double Angles



10

Single Angle



11

Shear Tab



12

Shear End-Plate





14

CONNECTION TYPES

• MOMENT CONNECTIONSFlange Welded

Flange Plate Welded

Flange Plate Bolted

Tee-Stub

Flange Angle

Moment End-Plate



15

Flange Welded



16

Flange PlateBolted



17

Tee-Stub



18

Flange Angle



19

Moment

End-Plate



20

CLASSIFICATION OFBEAM-TO COLUMN

CONNECTIONS

• Fully Restrained - FR

Flange Welded

Flange Plate Welded or Bolted

Tee-Stub

Moment End-Plate



21

CLASSIFICATION OFBEAM-TO COLUMN

CONNECTIONS•Partially Restrained/Pinned - PR

Double Angles

Single Angle

Shear TabShear End-Plate

Seated



22

CLASSIFICATION OFBEAM-TO-COLUMN

CONNECTIONS

Classification: Depends on member length

and moment diagram andmagnitude of moment.

Example: Beam Line/Connection Curve



23

MOMENT ROTATION CURVES

Rotation, θ

M

o m e n t , M

M = 0.9M

Typical Beam Line

Type I, FR Moment Connection

PR Moment Connection

PR Simple Shear

Connection

F

M = 0.5M F

M = 0.2M F



24

SPECIFICATION

PROVISIONS

1999 LRFD Specification, Chapter J

Connection, Joints and Fasteners

1999 LRFD Specification, Chapter K Flanges and Webs with Concentrated Forces

LRFD Manual of Steel Construction3rd Edition: Parts 7 to 15



25

LIMITS STATES IN THE

LOAD PATH

Example: Tension Connection

5/16

5/8" PL2L 4 x 3 1/2 x 1/4 LLBB

Tu

3/4" Dia.

A325 Bolts, Typ

A

ASection A-A



26

LIMITS STATES IN THELOAD PATH

1. Angle Yielding

2. Angle Net Section Fracture (including Shear

Lag effects)3. Bolt Bearing/Tear Out in Angles

4. Angle Block Shear

A

A

Tu

1

1

2

2

3,4

4



27

LIMITS STATES IN THELOAD PATH

5. Bolt Shear Fracture

6. Bearing / Tear Out in Plate

7. Plate Block Shear

8. Plate Fracture

9. Plate Yield10. Weld Fracture

5

7

6,7

8

8

9

9

10



28

LRFD

Basic Requirement: R u < φφφφR n

Where

R u = required resistance from

factored loads

φφφφR n = design strength

φφφφ = resistance factorR n = nominal strength



29

LRFD

Tension Yielding: φφφφTn = 0.9 Fy Ag

Fracture: φφφφTn = 0.75 Fu Ae

Shear Yielding: φφφφVn = 0.9 (0.6 Fy)Ag

Fracture: φφφφVn = 0.75 (0.6Fu) An

Fy = yield stress Fu = tensile strength

Ag = gross area Ae = effective net area

An = net area



30

STEEL STRENGTHS

A36 (Generally plate and angle material)

Fy = 36 ksi

Fu = 58 ksi

A992 (Generally beam and column material)

Fy = 50 ksiFu = 65 ksi



31

BASIC BOLT RELATED

LIMIT STATES

AND

DETAILING



32

Bolt Types

A307 – machine boltsFu = 60 ksi

A325 – high strength bolts

Fu = 120 ksi

A490 – high strength bolts

Fu = 150 ksi



33

3/4 in. Dia.

7/8 in. Dia.

1 1/4 in. Dia.

A325 and A490 Bolts



34

Bolt Tension Strength

(LRFD Table J3.2)

Design tension strength of one Bolt, φφφφrt :φφφφ = 0.75

rt = Ft Ab

Ab = nominal bolt area

Ft = nominal strength from Table J3.2

φφφφrt = 0.75 Ft Ab = design tension strength

Note: reduced area through threads is

accounted for in Ft

.



35



36

Bolt Tension Strength

Example

Compute design tension strength for 3/4"A325 Bolt

φφφφrt = 0.75 Ft Ab

Ab = ππππ(.75"/2)2 = 0.442 in2

Ft = 90 ksi (Table J3.2)φφφφrt = 0.75 ×××× 90 ksi ×××× .442 in2 = 29.8 kips

(see also Table 7-14; p7-35)



37

Bolts in Shear:

Connection Types

Types of Connections:(a) Bearing Type

N - threads included in shear plane

X - threads excluded from shear plane

(b) Slip Critical

SC - slip critical

Ex: ¾ in. A325 - N

B lt Sh St th



38

Bolt Shear Strength

(LRFD Table J3.2)Design shear strength of one Bolt, φφφφrv :

φφφφ = 0.75

rv = nFv Ab

n = number of shear planesAb = nominal bolt area

Fv = nominal strength from Table J3.2

φφφφrv = 0.75 nFv Ab = design strength

Note: reduced area through threads and uneven

distribution of bolt forces included in Fv.



39



40

Table J3.2 Continued



41

Bolt Shear Strength Example

Pu

Pu/2

Pu/2

Compute design shear strength for

3/4" A325-N Bolt in Double Shear

B lt Sh St th E l



42

Bolt Shear Strength Example

(cont)

φφφφrv = 0.75 nFv Ab

n = 2

Ab = ππππ(.75"/2)2 = 0.442 in2

Fv = 48 ksi (Table J3.2)

φφφφrv = 0.75 ×××× 2 ×××× 48 ksi ×××× .442 in2 = 31.8 kips

(see also Table 7-10; p7-33)



43

Bolts: Connection Length Effect

Table J3.2 Footnote [e]

When bearing-type connections used to

splice tension members have a fastener

pattern whose length, measured parallel to

the line of force, exceeds 50 in., tabulated

values shall be reduced by 20 percent.



44

Slip Critical (-SC) Connections

• In Slip-Critical (SC) connections, slip isconsidered to be a limit state (serviceability or

strength)

• Slip checked using either factored load (slip isstrength limit state) or service loads (slip is

serviceability limit state)

• Slip-critical connections require pretensionedbolts and control of faying surface



45

Slip Critical ConnectionsSection J3.8a. Slip-Critical Connections

Designed at Factored Loads

Pu

Pu/2

Pu/2



46

Slip Critical ConnectionsSection J3.8a. Slip-Critical Connections

Designed at Factored Loads

φφφφrstr = φφφφ 1.13 µµµµTb Ns

µµµµ = mean slip coefficient (0.33-0.50)

Tb= minimum fastener pretension, Table J3.1Ns= number of slip planes

φφφφ Depends on the type of hole (0.60 to 1.0)



47

Slip Critical ConnectionsAppendix J3.8b. Slip-Critical Connections

Designed at Service Loads

φφφφrv = 1.0 Fv Ab

Fv from Table A-J3.6

Pservice

Pservice/2

Pservice/2

Bolts: Combined Shear and



48

Bolts: Combined Shear and

Tension Strength

f t

f v

Ft

Fv



49

Note: Shear stress, f v, not to exceed Fv.



50

Bolt HolesHole Types and Dimensions (Table J3.3):

• Standard (Std.) db + 1/16 in.

• Oversized (OVS)

• Short Slots (SS)

• Long Slots (LS)

(Standard Hole is default for these notes)



51



52

Bolt Holes in Calculations• For all hole related limit states except

bearing-tear out, the effective hole diameterused in calculations is

d′′′′h = dh + 1/16 in.

The additional 1/16 in. accounts for damagedue to hole making process.

• For bearing-tear out, the actual holediameter is used.



53

Bolts: Bearing Strength

Pu

Lc Lc

Pu

Excessive HoleElongation

Tear Out



54



55

Bolts: Bearing StrengthSection J3.10 Bearing Strength at Bolt Holes

φφφφ = 0.75

For standard, oversized, and short-slotted holes

R n = 1.2 L ct Fu < 2.4 db t Fu

1.2 Lc

t Fu

is based on tear out

2.4 db t Fu is based on excessive holeelongation

Lc = clear distance

Lc Lc

Pu

Example: Bearing Design Strength



56

Interior Bolts:

Lc

= 3 in – 13/16 in = 2.19 in

2.4dbtFu = 2.4 x 0.75 x 0.5 x 58 = 52.2 k (controls)

1.2LctFu = 1.2 x 2.19 x 0.5 x 58 = 76.2 k

φφφφR n = 0.75 x 52.2 = 39.2 k

3"112"

4"

112"

112"

PL 1/2" x 7"

A36, Fu = 58 ksi

3/4" A325-N Bolts

Std. Holes

Example: Bearing Design Strength (cont)



57

p g g g ( )

Edge Bolts:

Lc= 1.5 – 13/32 = 1.09 in.

2.4dbtFu = 2.4 x 0.75 x 0.5 x 58 = 52.2 k 1.2LctFu = 1.2 x 1.09 x 0.5 x 58 = 37.9 k (controls)

φφφφR n = 0.75 x 37.9 = 28.4 k

3"1

1

2"

4"

112"

112"

PL 1/2" x 7"

A36, Fu = 58 ksi

3/4" A325-N Bolts

Std. Holes

Bolts: Minimum Spacing and



58

Bolts: Minimum Spacing and

Edge Distance

Section J3.3 Minimum Spacing The distance between centers of standard,

oversized, or slotted holes, shall not be less

than 2 2/3 times the nominal diameter of

the fastener; a distance 3d is preferred .

Tu

e s

s

e

e



59Note: Sheared plates require larger edge distance.



60

BASIC WELD RELATED

LIMIT STATES

AND

DETAILING



61

Weld FractureWelds J2.4. Design Strength

Design Strength = φφφφ R n

= φφφφ Fw

Aw.

For Fillet Welds

φ = 0.75Fw = 0.60 FEXX

FEXX

= electrode tensile strength, ksi



62

Weld Fracture: Effective Areas

FCAW, GMAW, SMAW SAW

t e f f

t

t t e f f

t

t

teff = 0.707 t for t < 3/8” teff = t

for t > 3/8” teff = t + 0.11”

Weld Fracture



63

φφφφR n = 0.75 (0.6x70)(0.707x 1/16) = 1.392 k/in/1/16

Example:

Let D = no. of 1/16’s

φφφφR n = 1.392 D Lweld= 1.392 x 4 x 5 = 27.84 k

Weld Fracture

Example: E701/16

5"E70

1/4



64

Minimum Fillet Weld Sizes



65

Maximum Fillet Weld Size

Maximum Fillet Weld Size:

tp < ¼ in. tw = tp

tp > ¼ in. tw = tp – 1/16 in.

1/16"



66

Base Metal Strength at Weld

Section J4.1 Shear Rupture StrengthThe design rupture strength for the limit

state of rupture along a shear failure path

in the affected elements of connectedmembers shall be taken as

φφφφR n = 0.75 (0.6 Fu Anw)

E ample: Determine φφφφP for Welds



67

Example: Determine φφφφPn

for Welds

A36

Fu = 58 ksi

Weld Rupture:

φφφφPn.= (1.392x4) (5x2) = 55.7 k

Base Metal:

φφφφPn.= 0.75 (0.6 Fu Anw)= 0.75 (0.6x58) (5/16) (5x2) = 81.6 k

φφφφPn.= 55.7 k

φPn

E701/4

PL 5/16" x 5"

PL 3/8" x 8"

5"

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Connections 1