Basic Structural Steel Design

CE 3050

Connections

Rupen Goswami
Department of Civil Engineering
Indian Institute of Technology Madras
 Introduction
y Necessity of Connections
ƒ Limited length of members
• Rolling & Transportation constraints
ƒ Larger size of structures

y Importance of Connections
ƒ Structure is only as strong as the weakest link
ƒ Connection failure to be avoided before member failure
• The full strength of members is to be utilised
• Connection failure is usually brittle

2 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Introduction…

y Requirements of Connection Design

ƒ Strength, Stiffness & Ductility
ƒ Deflection control & Stability under Service Load
ƒ Large deflection & Ductility at Ultimate Load

y Connections
ƒ Are complex to Analyse & Design
ƒ Are most vulnerable component of a structure
ƒ Have greater potential for variability in strength and
response

• Connection failure often leads to failure of structure

3 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Introduction…

Beam-to-Column
Connection Region

Joint Panel Zone

Region

Beam

Joint Column

4 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Introduction…

y Complexity of Connections
ƒ Complex Geometry
• Highly indeterminate
• Non-linearity due to slip & local yielding
• Stress concentration
• Residual stresses & strains
• Geometric imperfections

5 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Introduction…

y Complexity of Connections…
ƒ Geometric Imperfections
• Bow in members (rolling tolerance)
• Gaps & tolerances in fabrication and erection
• Fabrication errors
• Lack of fit of bolts in clearance holes
• Welding distortions
• Member deflections

6 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Introduction…

y Types of Connections
ƒ Riveted Connection
• Mild steel
• High strength steel

ƒ Bolted Connection
• Bearing type (carbon steel, high strength steel)
• Friction Grip type (High strength steel - HSFG)

ƒ Welded Connections
• Fillet welded
• Groove welded

7 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Introduction…

y Connections in Buildings
ƒ 4 Types
Column
Column
Beam
Beam Splice
Splice
Splice
Splice

Beam
Beam ––
Column
Column
Column
Column
Base
Base

8 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
Design of Connections
 10.6 – Design of Connections

y Connections and adjacent regions of the

members shall be designed such that:

ƒ The design action effects distributed to various elements

shall be in equilibrium with the design action effects on the
connection

ƒ The required deformations in the elements of the

connections are within their deformations capacities

ƒ All elements in the connections and the adjacent areas of

members shall be capable of resisting the design action
effects acting on them

ƒ The connection elements shall remain stable under the

design action effects and deformations

10 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 10.7 – Minimum Design Action…
y Connections carrying design action effects
shall be designed to transmit the greater of:

ƒ a) The design action in the member, and

ƒ b) The minimum design action effects expressed either as

the value or the factor times the member design capacity
for the minimum size of member required by the strength
limit state, specified as follows:

11 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
10.7 – Minimum Design Action…

y b) The minimum design action effects expressed either

as the value or the factor times the member design
capacity for the minimum size of member required by
the strength limit state, specified as follows:
• 1) Connections in Rigid Construction:: A bending moment of at
least 0.5 times the member design moment capacity

• 2) Connections to Beam in Simple Construction:: A shear force

of at least 0.15 times the member design shear capacity or 40
kN, whichever is lesser

• 3) Connections at the ends of Tensile or Compression Member::

A force of at least 0.3 times the member design capacity

• 4) Splices in Members Subjected to Axial Tension:: A force of at

least 0.3 times the member design capacity in tension

12 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
10.7 – Minimum Design Action…

y b) The minimum design action effects expressed either

as the value or the factor times the member design
capacity for the minimum size of member required by
the strength limit state, specified as follows:
• 5) Splices in Members Subjected to Axial Compression –

for ends prepared for full contact:: Adequate fasteners to keep

line and transmit 0.15Pd
for ends not prepared for full contact:: Adequate fasteners to
keep line and transmit 0.3Pd and a moment of Pd L/1000 where
L = distance between lateral supports

• 6) Splices in Flexural Member:: A bending moment of 0.3 times

the member design capacity in bending unless designed to
transmit shear only

• 7) Splices in Members Subject to Combined Actions:: a splice in

a member subject to a combination of design axial tension or
design axial compression and design bending moment shall
satisfy requirements in (4), (5) and (6) above

13 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 Other Details
y 10.8 – Intersections
• At a joint, the member centroidal axes shall meet at a
point, otherwise the members shall be designed for the
bending moment arising due to eccentricity

y 10.9 – Choice of Fasteners

• Use HSFG, weld or fitted bolts to avoid slip in
serviceability. When ordinary bolts are subjected to
impact or vibration use locking devices

y 10.10 – Connection Components

• Cleats, gusset plates, brackets and the like shall have
their capacities assessed using the provisions of
Sections 5, 6, 7, 8 and 9 as applicable

14 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 General Issues
in
Connection Design
 Traditional Analysis
y Assumptions:

ƒ Connection elements are assumed to be rigid compared to

the connectors
ƒ Connector behaviour is assumed to be linearly elastic
ƒ Distribution of forces arrived at by assuming idealized load
paths
ƒ Provide stiffness according to the assumed behaviour
ƒ Ensure adequate ductility and rotation capacity
ƒ Provide adequate margin of safety

16 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 10.11 – Analysis of Bolt / Weld Group
y In-plane Loading:: The design force in a bolt/weld shall
be determined by
ƒ a) Considering the connection plates to be rigid and to rotate
relative to each other about a point known as the instantaneous
centre of rotation ICR of the group
ƒ b) In the case of a group subject to a pure couple only, the ICR
coincides with the group centroid. In the case of
in-plane shear force applied at the group centroid, the ICR is at
infinity and the design force is uniformly distributed throughout
the group.
In all other cases, either the results of independent analyses for a
pure couple alone and for an in-plane shear force applied at the
group centroid shall be superposed, or a recognized method of
analysis shall be used
ƒ c) The design force in a bolt or design force per unit length at any
point in the group shall be assumed to act at right angles to the
radius from that point to the instantaneous centre, and shall be
taken as proportional to that radius

17 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
10.11 – Analysis of Bolt / Weld Group…

y Combined In-plane Shear & Moment

ƒ Bolt shear due to Px and Py
• Rxi = Px / N; Ryi = Py / N

ƒ M = Px × y’ + Py × x’
• Rmi = k × ri
• Mi = k × ri2
• M = Σ(k × ri2) = k Σri2
ƒ Bolt shear due to M x’
Rmi= Mri / Σri2 Rmi
ƒ Combined Shear ri
y’
P
Ri = [(R xi + Rmi cos θ i )2 + (R yi + Rmi sin θ i )2 ]
⎧⎡ P My i ⎤
2
⎡ Py Mx i ⎤
2
⎫
⎪ x ⎪
Ri = ⎨⎢ + 2 ⎥
+⎢ + 2 ⎥ ⎬
⎪⎩⎢⎣ n ∑ i i ⎥⎦ ⎢⎣ n
( x 2
+ y ) ∑ i i ) ⎥⎦
( x 2
+ y ⎪⎭
Bolt
Bolt group
group
eccentrically
eccentrically loaded
loaded in
in shear
shear
18 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
10.11 – Analysis of Bolt / Weld Group…

y Out-of-plane Loading:: The design force in a bolt/weld

shall be determined by

ƒ a) The design force resulting from shear or axial force shall be

considered to be equally shared by all bolts or over the length
weld

ƒ b) The design force resulting from a bending moment shall be

considered to vary linearly with the distance from the centroidal
axes

ƒ c) Centroid & Second Moment of Area

• 1) In bearing type of bolt group, plates in the compression
side of the neutral axis and only bolts in the tension side may
be considered

• 2) In the friction grip bolt group only the bolts shall be

considered

• 3) The fillet weld group shall be considered in isolation from

the connected element; of the weld length

19 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
10.11 – Analysis of Bolt / Weld Group…

y Combined out-of-plane Shear & Moment

ƒ Bolt shear due to V
• Ri = V / N

ƒ Ti = k × l i
ƒ M = Σ (Ti × Li)
ƒ Ti = M×li / Σ (li × Li)

Ti

d li Li Li
NA
d/6 C C

ƒ Check for combined Bolt

Bolt group
group resisting
resisting shear
shear and
and
• Tension + Shear ( + Prying) out-of-plane
out-of-plane moment
moment
20 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 10.12 – Lug Angles

1.4Fo 1.2Fo
1.2Fo 1.1Fo
Fo Fo
Fc Fc

21 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 F2 – Beam Splice
y Rolled Section
ƒ Flange splice carries the moment
ƒ Web splice carries shear
y Plate (Deep) Girder
ƒ Flange splice & web splice carries moment
ƒ Web splice carries shear

V V V V
M M M M

Optional Inner Splice Plates Optional Stiffener Plate

22 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
F2 – Beam Splice…

y Bolt Group in Web Splice

ƒ Shall be designed for moment due to eccentricity in addition
to shear
y Flange Splice Area
ƒ 1.05 Flange Area

V V V V
M M M M

Optional Inner Splice Plates Optional Stiffener Plate

23 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 F3 – Column Splice
y Machined for Bearing in Compression
ƒ To hold the line
y Not Machined
ƒ Design to transmit ALL FORCES
y Centroidal Axis
ƒ Proportion to coincide
centroidal axes of both
splice and members

Column Splice
(Typical)

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Beam-to-Column Connections
 Standard Beam-Column Connections

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 Connection Behaviour

27 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 Connection Classification

28 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 Connection Classification Limits

Connection Type In terms of Strength In terms of Stiffness

Rigid m1 ≥ 0.7 m1 ≥ 2.5θ1

Semi-rigid 0.7 > m1 > 0.7 2.5θ1 > m1 > 2.5θ1

Flexible m1 ≤ 0.2 m1 ≤ 0.5θ1

29 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 Semi-Rigid Connection Model

y Moment – Curvature Relation

θr = C1(KM)1 + C2 (KM)3 + C3 (KM)5
‰ Frye-Morris polynomial model

30 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 F5 – Column Bases
y Base Plate Anchor Bolt Connection
ƒ Bolts ■ Base Plate
• Tension ● Bending
• Shear P
M

Column

Connection Element

Base Plate

T fmax
R
x/3
x
N
…will do in more details later!
31 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 Summary
y Connections
ƒ Critical component
ƒ Load transfer path
ƒ Conservative Design
ƒ Proper Detail
ƒ Various types
• Connection Classification
• Semi-rigid Connections

32 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 IS 800: 2007
y Section 10
• 10.6 Design of Connections
• 10.7 Minimum Design Action on Connection
• 10.8 Intersections
• 10.9 Choice of Fasteners
• 10.10 Connection Components
• 10.11 Analysis of a Bolt / Weld Group
• 10.12 Lug Angles

• Annex F Connections

33 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I
 Have a Wonderful Day!
34 CE3050:: Basic Strucural Steel Design / Rupen Goswami / IITM / 2009-2010 Semester I