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Connections
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1
Structural Steel ConnectionsStructural Steel Connections
Overview of Connections
Beam End ConnectionsBeam-to-GirderBeam-to-Column
Other Connection Types
Connection Basics: Bolt and weld strength, and other design issues
Design Example
Beam End ConnectionsBeam End Connections
End Fixity
Simple (Shear) Connections
Moment Connections- Fully Restrained (FR)- Partially Restrained (PR)
Primary Applications
Beam-to-Girder Connections- usually Simple connections
Beam-to-Column Connections- Simple or Moment (FR)- Moment (PR) rarely used
BeamBeam--toto--Girder ConnectionsGirder Connections
Double Angle: Bolted- Bolted
2
Double Angle: Welded - Bolted
Shear End Plate
3
Single Plate (Shear Tab)
4
BeamBeam--toto--Column ConnectionsColumn Connections
Simple ("Pinned") FramingSimple ("Pinned") Framing
5
2 Angles
Double Angle
2 Angles
Double Angle
6
Flange Seat Flange Seat
Single Plate
Single Plate (Shear Tab)
7
BeamBeam--toto--Column ConnectionsColumn Connections
Moment ConnectionsMoment Connections
8
Bolted Flange Plate
V M
Welded Flange
9
Moment End Plate
10
Other ConnectionsOther Connections
11
12
13
Specification References for Connection Design
2005 AISC Specification:Chapter J - Design of Connections
Additional References for Connections in Seismic-Resistant Steel Structures:
2005 AISC Seismic Provisions for Structural Steel Buildings.
Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications
2005 AISC Specification
Chapter J - Design of Connections
Connection Basics: Bolt and Weld Strength and other Design Issues
14
Bolt Strength
Three cases to consider:
1. Bolts loaded in tension
2. Bolts loaded in shear
3. Bolts loaded in shear + tension
For any loading case:
Limit State = Bolt Fracture
Examples:
Bolts loaded in tension
Examples: Bolts loaded in shear Examples: Bolts loaded in shear and tension
15
Bolt Strength Bolt Strength -- TensionTension
Tension Strength Requirement:
LRFD: Ru Rn = 0.75
ASD: Ra Rn / = 2.00
Nominal Strength in Tension:
Rn = Fnt AbAb = nominal area of bolt (area of unthreaded portion)
Fnt = nominal tensile stress = 0.75 Fu
Bolt Strength Bolt Strength -- TensionTension
Rn = Fnt AbFnt = nominal tensile stress = 0.75 Fu
A325 Bolt: Fu = 120 ksi Fnt = 0.75 x 120 ksi = 90 ksi
A490 Bolt: Fu = 150 ksi Fnt = 0.75 x 150 ksi = 113 ksi
Example:
Compute the Available Tension Strength of a 7/8" A325 Bolt
7/8 Bolt: Ab = (.875"/2)2 = 0.601 in2
Rn = Fnt Ab
A325: Fnt = 90 ksi
Rnt = 90 ksi x 0.601 in2 = 54.1 kips
LRFD: Rn = (0.75) (54.1 kips) = 40.6 kips
ASD: Rn / = 54.1 kips / 2.00 = 27.1 kips
16
Bolt Strength Bolt Strength -- ShearShear
Shear Strength Requirement:
LRFD: Ru Rn = 0.75
ASD: Ra Rn / = 2.00
Nominal Strength in Shear (per shear plane):
Rn = Fnv AbAb = nominal area of bolt (area of unthreaded portion)
Fnv = nominal shear stress
Nominal Strength in Shear (per shear plane):
Rn = Fnv AbAb = nominal area of bolt (area of unthreaded portion)
Fnv = nominal shear stress
Fnv = 0.40 Fu threads included in shear plane
Fnv = 0.50 Fu threads excluded from shear plane
A325-N Fnv = 0.40 x 120 ksi = 48 ksi
A325-X Fnv = 0.60 x 120 ksi = 60 ksi
A490-N Fnv = 0.40 x 150 ksi = 60 ksi
A490-X Fnv = 0.50 x 150 ksi = 75 ksi
17
Example:
Compute the Available Shear Strength of a 7/8" A325-N Bolt in Double Shear:
7/8 Bolt: Ab = (.875"/2)2 = 0.601 in2
Rn = Fnv Ab
A325-N: Fnv = 48 ksi
Rnt = 48 ksi x 0.601 in2 x 2 shear planes = 57.7 kips
LRFD: Rn = (0.75) (57.7 kips) = 43.3 kips
ASD: Rn / = 57.7 kips / 2.00 = 28.9 kips
Bolt Strength Bolt Strength -- Shear + TensionShear + Tension
Tension Strength Requirement:
LRFD: Ru Rn = 0.75
ASD: Ra Rn / = 2.00
Nominal Strength in Tension:
Rn = F'nt AbAb = nominal area of bolt (area of unthreaded portion)
F'nt = nominal tensile stress modified to include effects of shear
18
Bearing Strength at Bolt Holes
Limit States:
- Excessive elongation at bolts holes
- Tear-out at bolt holes
Bearing Strength at Bolt Holes
Excessive hole elongation
Tear-out
Bearing Strength at Bolt Holes
LcLc
Standard holes: Rn = lesser of2.4 d t Fu1.2 Lc t Fu
19
Welds
Fillet Weld
w = leg size
w
Welds
Groove weld: Complete joint penetration (CJP)
Groove weld: Partial joint penetration (PJP)
20
Welds
Plug Weld
Welds
Limit State for welds: Fracture
Welds
Available Strength:
LRFD: RnASD: Rn /
Rn = lesser ofFBM ABM Base metal
Fw Aw Weld metal
21
22
Other Connection Design IssuesOther Connection Design Issues
Connection Elements in Tension Connection Elements in Shear Block Shear Rupture
Connection Elements in Tension
P
Gusset Plate in Tension
Check yield of Gusset PlateRn = Ag Fy = 0.9 = 1.67
Pu Rn (LRFD)
Pa Rn / (ASD)
Connection Elements in Tension
P
Gusset Plate in Tension
Check fracture of Gusset PlateRn = Ae Fu = 0.75 = 2.00
Pu Rn (LRFD)
Pa Rn / (ASD)
Connection Elements in Tension
Whitmore Section
23
Vu
Connection Elements in Shear
Check shear yield of connection plateRn = Ag (0.6 Fy) = 0.9 = 1.67
Vu Rn (LRFD)
Va Rn / (ASD)
Vu
Connection Elements in Shear
Check shear fracture of connection plateRn = Ae (0.6 Fu) = 0.75 = 2.00
Vu Rn (LRFD)
Va Rn / (ASD)
Block Shear Rupture
P
Ubs Ant Fu + lesser ofRn = Anv (0.6 Fu)
Agv (0.6 Fy)
LRFD: = 0.75 Pu RnASD: = 2.00 Pa Rn /
Block Shear Rupture
P
Ubs Ant Fu + lesser ofRn = Anv (0.6 Fu)
Agv (0.6 Fy)
Ant = net area of tension surface of block
Agt = gross area of shear surface of block
Ant = net area of shear surface of block
tension surface of block
shear surface of block
24
Block Shear Rupture
P
Ubs Ant Fu + lesser ofRn = Anv (0.6 Fu)
Agv (0.6 Fy)
tension surface of block
shear surface of block
Ubs = 1 for uniform stress on tension surface
Ubs = 1 for non-uniform stress on tension surface
Example:Example: Beam to Column Shear Connection Beam to Column Shear Connection Single Plate ConnectionSingle Plate Connection
Ref: AISC Manual - Section 10
Two options:
Conventional Configuration
Extended Configuration
Single Plate Connection: Conventional ConfigurationSingle Plate Connection: Conventional ConfigurationLimitations
L T / 2
Single row of bolts.
2 n 12
a 3.5"
Standard or Short-Slotted Holes Permitted.
Leh 2 db for plate and for beam web.
Lev must satisfy Spec. Table J3.4
Plate or beam web must satisfy: t db/2 + 1/16".
25
L T / 2
Single Plate Connection: Conventional ConfigurationSingle Plate Connection: Conventional ConfigurationDesign
Check bolt shear and bearing.
Check plate for shear yielding, shear fracture, and block shear rupture.
For standard holes, ignore eccentricity on bolts forn 9
Size fillet weld with leg size of 5/8 tp (develops strenghtof either A36 or Gr. 50 plate)
Example: LRFDa=3"
Leh=1.75"
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
1/41/4
L = 1
5"
Bolts: 7/8" A325-N
Welds: E70
W24x76 (A992)
W10x112 (A992)
Vu
Compute Design Strength of this Single Plate Connection
26
Check Limitationsa=3"
Leh=1.75"
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
1/41/4
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
W10x112 (A992)
Vu
L T / 2W24x76: T = 20"L = 15"
OK
Single Row of Bolts OK
2 n 12 n=5 OK
Standard Holes OK
n 9 - ignore eccentricities OK
Check Limitationsa=3"
Leh=1.75"
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
1/41/4
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
W10x112 (A992)
Vu
Leh 2 dbLeh = 1.75"2 db = 1.75" OK
Lev must satisfy Spec. Table J3.4
Lev = 1.5"Per Table J3.4:Lev 1.25" OK
Check Limitationsa=3"
Leh=1.75"
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
1/41/4
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
W10x112 (A992)
Vu
Plate or beam web must satisfy: t db/2 + 1/16"
db/2 + 1/16" = 1/2"tp = 3/8" OK
Design Strength: Bolt Shear and Bearing
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
Vu
Bolt Shear
7/8" A325-N single shear:
rn = 21.6 kips / bolt
(Table 7-1)
27
Design Strength: Bolt Shear and Bearing
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
Vu
Bolt Bearing on 3/8" Plate
Top Bolt: rn = lesser of:
2.4 d t Fu =(0.75)(2.4) (7/8) (3/8) (58) =34.3 kips
OR
1.2 Lc t Fu =(0.75) (1.2) [1.5-(15/16/2)] (3/8) (58) =20. 2 kips controls
Design Strength: Bolt Shear and Bearing
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
Vu
Bolt Bearing on 3/8" Plate
Lower four bolts: rn = lesser of:
2.4 d t Fu =(0.75)(2.4) (7/8) (3/8) (58) =34.3 kips controls
OR
1.2 Lc t Fu =(0.75) (1.2) [3-15/16] (3/8) (58) =40.4 kips
Design Strength: Bolt Shear and Bearing
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
Vu
Bolt Bearing on W24x76 web
W24x76: tw = .44"
Bearing on beam web does not control by inspection
28
Design Strength: Bolt Shear and Bearing
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Bolts: 7/8" A325-N
Standard Holes
Welds: E70
W24x76 (A992)
Vu
Top bolt:Bearing in 3/8" Plate Controls rn = 20.2 kips
Remaining bolts:Bolt Shear Controls rn = 21.6 kips / bolt
Rn = 20.2k + 4 (21.6k) = 106.6 kips
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Vu
Design Strength: Shear Yield of Plate
Rn = (0.9) (Agross) (0.6Fy)
Agross = 3/8" x 15" = 5.625 in2
Rn = (0.9) (5.625) (0.6x36) =
109 kips
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
L = 1
5"
Vu
Design Strength: Shear Fracture of Plate
Rn = (0.75) (Anet) (0.6Fu)
Anet = 3/8" x (15" - 5x1") = 3.75 in2
Rn = (0.75) (3.75)x (0.6x58) =
97.9 kips
P 3/8 x 4 x 15 (A36)L
13.5"
1.75"
Design Strength: Block Shear Rupture of Plate
Anv (0.6 Fu)Agv (0.6 Fy)
Ubs Ant Fu + lesser of Rn = (0.75)
Anv (0.6 Fu) = (3.375) (0.6x58) = 117.5k
Agv (0.6 Fy) = (5.063) (0.6x36) = 109.4k controls
Rn = (0.75) [ (0.469) (58) + 109.4 ] = 102.5 kips
Ant = [ 1.75" - (1") ] (3/8") = 0.469 in2
Anv = [ 13.5" - 4(1") ] (3/8") = 3.375 in2
Agv = (13.5") (3/8") = 5.063 in2
Ubs = 1
29
a=3"Leh=1.75"
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
1/41/4
L = 1
5"
Bolts: 7/8" A325-N
Welds: E70
W24x76 (A992)
W10x112 (A992)
Vu
Design Strength: Weld Fracture
For Conventional Configuration:
Double sided fillet weld is adequate (weld stronger than plate) if: leg size 5/8 tp
5/8 tp = 5/8 x 3/8 = 0.23"
Fillet weld leg size = 1/4"
Weld OK for strength
Minimum weld size (Spec. Table J2.4): 3/16" OK
Weld: OK
Design Strength
Limit State Rn
Bolt shear and bearing
Shear yield of plate
Shear fracture of plate
Block shear rupture of plate
Weld fracture
106.6k
109k
97.9k
102.5k
OK
Controls
Example: LRFDa=3"
Leh=1.75"
4 @ 3"
= 12
"1.5
"1.5
" P 3/8 x 4 x 15 (A36)L
1/41/4
L = 1
5"
Bolts: 7/8" A325-N
Welds: E70
W24x76 (A992)
W10x112 (A992)
Vu
Compute Design Strength of this Single Plate Connection
Rn = 97.9 kips
Vu 97.9 kips
ASD:
Rn / = 97.9k / 1.5 = 65.3 kips
Va 65.3 kips
Rn = 97.9 kips
Rn / = 65.3 kips