connection design

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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

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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

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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)


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Limit states | (c) Bolt Shear

(Photo by P.S. Green)

Limit states | (d) Bolt Tension Fracture


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)

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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)

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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)

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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

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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)

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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

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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)

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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)

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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.


T uBearing

Tear Out TuTear Out

Le Lc

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Bearing

Tear Out

Le Lc


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

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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

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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)

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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

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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)

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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

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Module IContents: Overview

Shear Connections | Double-Angle ConnectionAll Bolted Double-Angle Connection

Girder B1

Beam B1B

Beam B1BGirder B1

Girder B1


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.

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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.


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

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Shear Connections | Double-Angle ConnectionLimit State | Block-shear rupture


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

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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



• 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

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Limit State | Flexural Strength – Single Coped Beam

R or RRu or Ra


Limit State | Flexural Strength – Double Coped Beam

Ru or Ra

Ru or Ra

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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


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

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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


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)

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Shear Connections | Double-Angle ConnectionLimit State | Flexural Strength – Example: Determine if adequate

75mm200mm

12mm

R u =180 kN W14x30

75mm

STII (A992 Steel)( )



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

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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



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

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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

connection design

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