connection design
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Slide: 1
DYB 654: ADVANCED STEEL STRUCTURES - II
Assoc.Prof.Bülent AKBAŞ
Department of Earthquake and Structural Engineering
Crown Hall at IIT CampusChicago . IllinoisChicago . IllinoisLudwig Mies van der Rohe
Connections in Steel Structures
(adapted from Shen, J., Steel Structures, Class Notes, IIT, Fall 2009. )
Introduction
General limit states in connections
Bolt related limit states
CONTENTS
Bolt related limit states and detailing
Weld related limit states and detailing
Commonly used simple/shear/framing connections
2
Commonly used Moment/rigid Connections
Column Connections
Slide: 2
How critical a connection in steel structures –safety, cost, and performance
Connections | Introduction
The structural designer leads the connection design, but should work with steel fabricators to optimize the total cost of the project
a) Block Shear Rupture b) Bolt Bearing c) Bolt Shear
Connections | General Limit states
d) Bolt Tension Fracture e) Concentrated Forcesf) Flexural Yielding g) Prying Action h) Shear Yielding and Shear Rupture i) Tension Rupture j) Whitmore Section Yielding / Buckling
Slide: 3
Limit states | (a) Block Shear Rupture
(Photo by J.A. Swanson and R. Leon, courtesy ofGeorgia Institute of Technology)
Limit states | (b) Bolt Bearing (against the bolt hole edge)
(Photo by J.A. Swanson and R. Leon, courtesy ofGeorgia Institute of Technology)
Slide: 4
Limit states | (c) Bolt Shear
(Photo by P.S. Green)
Limit states | (d) Bolt Tension Fracture
(Photo by J.A. Swanson and R. Leon, courtesy ofGeorgia Institute of Technology)
Slide: 5
Limit states | (e) Under Concentrated Forces
When forces are transferred from one member to another, some form of localized deformation (due to yielding or buckling) occurs, depending on types of connections, as illustrated in the following slides .
Limit states | Under Concentrated Forces (compression due to bending)
Flange Local Bending Limit State
(Beedle, L.S., Christopher, R., 1964)
Slide: 6
Limit states | Under Concentrated Forces (Shear force)
Web Crippling Limit State
(Photo by T. Murray, Virginia Tech)
Limit states | Under Concentrated Forces (Compression)
Web Local Buckling Limit State
(SAC Project)
Slide: 7
Limit states | (f) Flexural Yielding
Web Local Yielding Limit State
(SAC Project)
Limit states | (g) Prying Action
(Photo by J.A. Swanson and R. Leon,courtesy of Georgia Institute of Technology)
Slide: 8
Limit states | (h) Shear Yielding and Shear Rupture
(Astaneh, A. and Nader, M.N. 1989)
Module IContents: OverviewLimit states | (i) Tension Rupture
A plate behind this taped plate
(Photo by J.A. Swanson and R. Leon,courtesy of Georgia Institute of Technology)
Slide: 9
Module IContents: OverviewLimit states | (j) Whitmore Section Yielding /
Buckling in Gusset Plate
Gusset plate
P
(Beedle, L.S. and Christopher, R., 1964)
a) Commonly used boltb) Bolt types c) Bolt shear strength (LRFD/ASD) d) B lt h l d f il d
Module IContents: OverviewConnections | Bolt related limit states and
detailing
d) Bolt hole and failure modese) Bolt minimum spacing and edge distance
Slide: 10
Bolt | Commonly used bolts
Bolt| Commonly used bolts
A307 – machine bolts (unfinished bolts or common bolts: we do not account for the clamping force from tightening of thewe do not account for the clamping force from tightening of thebolt)
Fnt = 310 MPa (45 ksi)A325 – high strength bolts (can be pretensioned)
F nt = 620 MPa (90 ksi)A490 high strength boltsA490 – high strength bolts
F nt = 780 MPa (113 ksi)F nt : nominal tension strength (can be pretensioned)
Slide: 11
Bolt| Commonly used bolts (AISC 360-05)
Bolt| Bolt types: N, X, and SC
Types of Connections:yp(a) Bearing Type (A307, A325, A490)
N - threads iNcluded in shear planeX - threads eXcluded from shear plane
(b) Slip Critical (A325, A490)(b) Slip Critical (A325, A490)SC - slip critical
Ex: 19 mm (¾ in.) A325 - N
Slide: 12
Bolt| Bolt shear strength in bearing-type (N and X)
• Fnv = Nominal shear stress (AISC 360-05 Table J3.2)(AISC 360 05 Table J3.2)
• For Connection design (unless specified otherwise): φ = 0.75 (LRFD); φ ( );Ω = 2.00 (ASD)
Module IContents: OverviewBolt | nominal shear strength in bearing-type (N and X)
Slide: 13
Bolt | nominal shear strength in bearing-type (N and X)
• Nominal Shear Strength per bolt pershear plane:rn = Fnv x Ab , MPa, (Ab is nominal bolt area = π db
2 /4)
• Nominal Shear Strength of the connection:Rn = rn x Number of Bolts x Number of Shear n n
Planes (either 1.0 or 2.0)
Bolt | nominal shear strength in bearing-type (N and X)
• Design Shear Strength of the Connection:
LRFD : φRn = 0.75 Rn
ASD : ΩRn = Rn / 2.00 (AISC 360-05, J3.1)
Slide: 14
Module IContents: OverviewBolt | Bolt hole and failure modes
• For all hole related limit states except tear out, the effective hole diameter used in calculations is
d′h = dh + 2mm (AISC360-05, Table J3.3)
The additional 2mm accounts for damage.
• For tear out the actual hole diameter is used• For tear out, the actual hole diameter is used.
• For bearing, the bolt diameter is used.
Module IContents: OverviewBolt | Bolt hole and failure modes
T uBearing
Tear Out TuTear Out
Le Lc
Slide: 15
Module IContents: OverviewBolt | Bolt hole and failure modes
Bearing
Tear Out
Le Lc
Module IContents: OverviewBolt | Bolt hole and failure modes
Section J3.10 Bearing Strength at Bolt Holes
For standard, oversized, and short-slotted holesRn = 1.2 L ct Fu < 2.4 db t Fu
1.2 L ct Fu is the tear out strength2.4 db t Fu is the bearing strengthLc = clear distance
Slide: 16
Module IContents: OverviewBolt | Minimum Spacing and Edge Distance
e s
e
s
e
e
Section J3.3 Minimum Spacing:Preferred: S = 3d; and e = S/2Preferred: S = 3d; and e = S/2d = the nominal diameter of the bolt.(commonly S = 75mm and e =38mm)
a) Fillet weld strength b) Effective width in Fillet weld
Module IContents: OverviewConnections | Weld related limit states
and detailing
)c) Minimum size, t, of fillet weldsd) Base metal rupture strengthe) Example: Determine design strength Td for Welds
Slide: 17
Module IContents: OverviewWeld | Fillet weld strength
Nominal Strength Rn = Fw Aw (AISC360-05, Eq.J2-4)
Fw = 0.60 FEXX (1.0 + 0.50 sin1.5θ) (AISC360-05, Eq.J2-4)
Fw = nominal strength of the weld metal per unit area, MPa
FEXX = electrode strength, MPaθ = angle of loading measured from the weld longitudinal axis, degrees
A =effective area of weld (mm2)Aw=effective area of weld (mm2)
Tθ
Weld
Weld RuptureWeld | Fillet weld strength
Tθ T
θ = 0 °θ=90 °
θ = 00 Fw = 0.60 FEXX
θ = 900 Fw = 0.60 (1.5 FEXX)
Slide: 18
Weld | Effective width in Fillet weld
t
t = 0 707 t
t
t t
t
teff = 0.707 t (ASIC360-05, J2a)
t : leg dimension
teff : effective throat of a fillet weld
Weld | Minimum size, t, of fillet welds
Slide: 19
Weld | Minimum size, t, of fillet welds
Maximum Fillet Weld Size (AISC360-05, J2.b):
tp < 6mm tw = tp
tp > 6mm tw = tp – 2mm1/16 “
tp :thickness of the platetw :weld size
Weld | Base Metal Rupture Strength at weld
AISC 360-05 Section J4.2 Shear Rupture Strength
The design shear rupture strength for the g p glimit state of rupture along a shear failure path in the affected and connecting:
Rn = (0.6 Fu Anv)
Anv : welded area subjected to shear (the same for base metal rupture andweld rupture)
Slide: 20
Weld |Example: Determine design strength Td for Welds
E70XX¼”
PL 3/8" x 8"E70XX Electrod, Fexx = 485 MPaSTI (A36) steel Fu = 400 MPa
PL 10mm x 200mm
6mm
Td
PL 5/16" x 5"5"
Weld Rupture:Tn=(0.6x485MPa)(0.707x6mm) )(125mmx2)
= 308.6 kNBase Metal: Tn= (0.6 Fu Anw)
PL 8mm x 125mm125mm
= (0.6x400MPa)(8mm)(125mmx2) = 480 kNTn = 308.6 kN (weld rupture governs)
Td = (0.75)(308.6kN)=231.5 kN (LRFD) Td = (0.50)(308.6kN)= 154.3 kN (ASD)
a Double-Angle Connection
Module IContents: OverviewConnections | Commonly used
simple/shear/framing connections
a. Double Angle Connectionb. Single-Plate (Shear Tab) Connectionc. Shear End-Plate Connectiond. Un-stiffened Seated Connectione. Single-Angle Connectionf. Tee Shear Connection
Slide: 21
Module IContents: Overview
Shear Connections | Double-Angle ConnectionAll Bolted Double-Angle Connection
Girder B1
Beam B1B
Beam B1BGirder B1
Girder B1
Module IContents: Overview
Shear Connections | Double-Angle ConnectionAll Bolted Double-Angle Connection (continued from the previous slide)
Girder B1 supports Beam B1B by an all-bolted, double-angle connection.
These double-angles are field bolted to the supporting girder and shop bolted to the supported beam. This eliminates "knifed" erection. (Lowering the supported beam web into place between the angles).
The offset bolt rows between the in-plane and outstanding angle legs provide better entering and tightening clearances.
Since both of the members are the same depth, the beam is double coped to accommodate the flanges of the girder.
Slide: 22
Shear Connections | Double-Angle Connection
Limit States associated with All Bolted Double-Angle Connection
Nominal Strength of the connection, Rn in kN, from g , n ,each of the following limit states:
a) Block Shear Rupture b) Bolt Bearing c) Bolt Sheard) Shear Yielding e) Shear Rupture f) Flexural strength
The governing nominal strength of the connection, Rn is the smallest among all.
Module IContents: Overview
Shear Connections | Double-Angle ConnectionPossible limit States in a typical beam-to-girder connection
1 25
2L
a) Block Shear Rupture of the beam web (1-1) or the angles (2-2) b) Bolt Bearing of the beam web or angles (3)
1 23, 4
5
5
A A
b) Bolt Bearing of the beam web or angles (3)c) Bolt Shear (4)d) Flexural Yielding of the coped webe) Shear Yielding of the gross area of angles along 5-5f) Shear Rupture of the net area of angles along 5-5
Slide: 23
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Block-shear rupture
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Bolt Bearing
Rn = 1.2 L ct Fu < 2.4 db t Fu , kN1.2 L ct Fu : tear out strength2.4 db t Fu : bearing strength
Lc : clear distance
Le Lc
Slide: 24
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Bolt Shear
Rn = Fnv x Ab x Number of Bolts in the web x N b f Sh Pl ( 2 f d bl Number of Shear Planes ( = 2 for double
angle connections), kN
Ab = π db2 / 4,
db : bolt diameter. b
Module IContents: Overview
Shear Connections | Double-Angle Connection
• Shear Yielding: Rn = (0.6 Fy)Ag
• Shear Rupture: R = (0 6F ) A
Limit State | Shear yielding and rupture
Shear Rupture: Rn = (0.6Fu) An
Fy = yield stress; Fu = tensile strengthAg = gross area in shear; and An = net area of the angles
Slide: 25
Shear Connections | Double-Angle Connection
Limit State | Flexural Strength – Single Coped Beam
R or RRu or Ra
Shear Connections | Double-Angle Connection
Limit State | Flexural Strength – Double Coped Beam
Ru or Ra
Ru or Ra
Slide: 26
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – with Coped Beams ( Rupture and local buckling)
Required flexural strength:
LRFD: M = R e ASD: M = R e AISC St l C t ti M l 13th Editi )LRFD: Mu = Ru e ASD: Ma = Ra e AISC, Steel Construction Manuel, 13th Edition)
Ru or Ra = beam end reaction force, kN
Available Strength based on Flexural Rupture: Mn = Fu Snet (for single or double coped beam cases)
φb = 0.75, Ωb= 2.00Available Strength based on Flexural Local Web Buckling:
Mn = Fcr Snet
φb = 0.90, Ωb= 1.67
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – with Coped Beams ( Rupture and local buckling) (cont’d)
Snet = net section modulus, mm3 , tabulated in Table 9-2 in AISC 13th Edition Manual
Fcr = available local web buckling stress as given in the following slides
Slide: 27
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – local web buckling stress Fcr with only top flange coped
Limitations: c < 2 d Ru or Ra
dc < d / 222
2012(1- )w
cr ytEF fk F
v hπ ⎛ ⎞
= ≤⎜ ⎟⎝ ⎠
⎧ 1.65h⎧ ⎛ ⎞
E = 29,000 ksi, 0.3ν =E=200,000 MPa, v=0.3
2 when 1.0
1 when >1.0
c cd df
c cd d
⎧ ≤⎪⎪= ⎨⎪ +⎪⎩
0
0
0
0
2.2 when 1.0
2.2 when >1.0
h cc hk
h cc h
⎧ ⎛ ⎞ ≤⎪ ⎜ ⎟⎪ ⎝ ⎠= ⎨⎪⎪⎩
f= plate buckling model adjustment factork=plate buckling coefficient
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – local web buckling stress Fcr with both top and bottom flanges coped
Limitations: c < 2 d
2
0.62 wcr d
tF E fch
π=
dct < 0.2 ddcb < 0.2 d
0ch
fd = 3.5 – 7.5 (dc / d) (adjustment factor)
dc = the larger of (dct , dcb)
Slide: 28
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – Example: Determine if adequate
75mm200mm
12mm
R u =180 kN W14x30
75mm
STII (A992 Steel)( )
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – Example: Determine if adequate
W14x30 STII (A992) Fy = 345 MPa Fu = 450 MPae = 212 mmc = 200 mmd = 351 mmtw = 6.86 mmdc = 75 mmh = 351 – 75 = 276 mmho = 351 – 75 = 276 mm.Snet = 137,160 mm3 from Table 9-2 AISC 13 Ed.
Manual
Slide: 29
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – Example: Determine if adequate
22
2012(1- )w
cr ytEF fk F
v hπ ⎛ ⎞
= ≤⎜ ⎟⎝ ⎠
c / d = 200 / 351 = 0 57 < 1 0
2
y cr
0.270 26,210 (1.16)(3.61)10.8
= 68.9 ksi>F 50 ksi, so F 50 ksi
⎛ ⎞= ⎜ ⎟⎝ ⎠
= = MPa345Fso,MPa345MPa12.476 cr =>=
)74.3)(14.1(276
86.6762,1802
⎟⎠⎞
⎜⎝⎛=
c / d 200 / 351 0.57 < 1.0So, f = 2 (c / d) = 2 x 0.57 = 1.14
c / ho = 200 / 276 = 0.72 < 1.0So, k = 2.2 (ho / c)1.65 = 2.2 (276 / 200)1.65 = 3.74
Module IContents: Overview
Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – Example: Determine if adequate
Use LRFD since Ru is given:
Required strength: Mu = Ru e = (180kN)(0.212m) = 38.16 kNm
Available Strength based on Flexural Rupture:
Mn = Fu Snet = (450)(137,160) = 61.72 kNm
φb Mn = (0.75)(61.72) = 46.29 kNm > Mu = 38.16 kNmAvailable Strength based on Flexural Local Web Buckling:
M F S (345)(137 160) 47 32 kNMn = Fcr Snet = (345)(137,160)= 47.32 kNmφbMn = Fcr Snet = (0.9) (47.32) = 42.59 kNm > Mu = 38.16 kNm
Slide: 30
References:
Shen, J., Advanced Steel Structures, Class Notes, Fall 2009.
American Institute of Steel Construction (AISC) Specification: AISC 360-05 Chapter J (included in the AISC Manual Part 16).
Design of Connections (Parts 9 through 13) of the AISC M lAISC Manual
AISC Documents on Teaching Steel Connections
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