Universiti Teknologi PETRONAS Civil Engineering Department Design of Steel Structures (VCB 3022) Connections with Bolts

Universiti Teknologi PETRONAS

Civil Engineering Department

Design of Steel Structures (VCB 3022)

Connections with Bolts

Lecture: Dr. Montasir O. Ahmed

Analyze and design STEEL connections

SUJECT TO COMPLEX LOADING (in-plane

and out-of-plane )

CLO3

Learning outcome

After the session the students will be able to:

Identify different classes of connections used in steel structure construction

Properties, advantage and drawbacks of commonly used connections.

Analysis and Design of Connections with bolts and pins using EC 3-1-8

Main classes of connection

1. Connection where a change of direction occurs.

e.g. beam-to-column connections, beam-to-beam connections and connections

between different members in trusses.

2. Connection which ensure manageable sizes of steel members for transportation and

erection

e.g. columns are normally spliced every two or three storeys.

3. Connections provided where there is a change of component

e.g. column bases, and connections beams or columns with walls, floors and roofs.

CONNECTIONS IN SIMPLE CONSTRUCTION

• The typical connections in braced multi-storey buildings of simple connection, single

storey buildings and portal frames are:

• Web cleat connections

• Flexible end plate connections (Header plate connection)

• Fin plate connections

• The connections using the above types are:

• Beam to column connection using web cleats

• Beam to beam connection using web cleats

• Beam to column using flexible end plates

• Beam to beam connection using flexible end plates

• Beam to column connection using fin plates

• Beam to beam connection using fin plates

Different configurations in simple joints

Joint about major axisJoint about the minor axis

Beam to column single sided joint configurations:

Beam to column double sided joint configurations:

Joint about major axis Joint about the minor axis

Uncoped beam supported

on beam web

Single Coped beam supported

on beam web

Double Coped beam

supported on beam web

Uncoped beam supported

on beam web

Single Coped beam

supported on beam web

Double Coped beam

supported on beam web

Splice joints

Beam splice joint

Column splice joint

Braced joint configuration

Web cleat connections

Connections photos source:

http://www.tatasteelconstruction.com/en/reference/teaching_resources/arc

hitectural_studio_reference/elements/connections/beam_to_column_conne

ctions/

Header plate connections

Fin plate connections

• “Connection” and “Joints” are often regarded as the same.

• EC3-1-8 defines them slightly differently.

• A connection is the location at which two or more elements

meet. For design purposes it is the assembly of the basic components required to

represent the behaviour during the transfer of relevant internal forces and moments

at the connection.

• The joint is the zone where two or more members are

connected.

Example: A beam–to–column joint consists of a web panel and either

one connection (single sided joint configuration) or two connections

(double sided joint configuration).

Eurocode EC3-1-8: Joints and Connections

General Requirement of a Joint:

EC3-1-8 states that all joints shall have design resistance such

that the structure satisfies all the design requirements of EC3-

1-8 and EC3-1-1.

Type

Resistance of bolts

Resistance of rivets

Resistance of welds

Resistance of plates in bearing

𝜸𝑴𝟐 1.25

Slip resistance at the ultimate limit state (category C) 𝜸𝑴𝟑 1.25

Slip resistance at the serviceability limit state (category B) 𝜸𝑴𝟑,𝒔𝒆𝒓 1.1

Bearing resistance of an injection bolt 𝜸𝑴𝟒 1.0

Resistance of joints in hollow section lattice girder 𝜸𝑴𝟓 1.0

Preload of high strength bolts 𝜸𝑴𝟕 1.1

Table: Recommended partial safety factors for joints

Common methods of connections:

• Welding

• Bolting

• Riveting (not often used nowadays)

• Clause 2.5 Analysis of connection and related assumptions

• Clause 2.6 recommends the type of joints

• Clause 2.7 gives guidance on how the effect of joint

eccentricity is considered in different types of structures.

Related code: EC3-1-8

“To be capable of safely transferring load from the supported

members to the supporting member”.

This implies that three properties of the connection need to be

considered: strength, stiffness, deformation capacity.

Requirements of a connection:

Beam-to-column connections:

• Very frequent connection

• Classified by their stiffness as nominally pinned, semi-rigid or rigid.

• Classified by their capability to transfer moments as nominally

pinned, partial-strength and full-strength connections.

Connections: Bolts, rivets and pins

Two types/classes of bolts are provided for use by EC3-1-8:

2005 (in Table 3.1) :

Ordinary bolts

High strength bolts.

• The rules in EC3-1-8 are valid for 7 bolt classes 4.6, 4.8, 5.6,

5.8, 6.8, 8.8 and 10.9.

• Ordinary bolts or ordinary grade bolts are put in bolt classes

4.6, 4.8, 5.6, 5.8 and 6.8

• High strength grip bolts or high strength bolts are put in

classes 8.8 and 10.9. They can be used for preloaded bolts which are

characterized by a slip-type resistance in shear.

Class 4.6 4.8 5.6 5.8 6.8 8.8 10.9

fybN/mm2 240 320 300 400 480 640 900

fub N/mm2 400 400 500 500 600 800 1000

EC3-1-8 provides bolt class and corresponding yield

strength (fyb) and ultimate tensile strength (fub ) which

may be used as characteristic values in design

Bolt Class

Table 3.1: Nominal values of the yield strength fyb and the ultimate tensile strength fub for

bolts

• Nominal diameters of bolts is given in mm.

• Bolts are designated as M12, M16, M20, M22, M24, M27,

M30 etc where 12, 16, etc are diameters in mm

Nominal SIZE bolt diameter in mm Nominal clearance

M12 12 1 mm

M16 to M24 16, 18, 20, 22, 24 2 mm

M27 , M30 and above 27, 30 3 mm

Bolt holes are usually drilled.

Bolt holes are larger than the bolt diameter to take care of

drilling tolerance

Common Drilling tolerance are summarised in table below:

Bolts

Symbols for spacing of fasteners (excerpted from EC 3-3-8)

d0 is the diameter of the hole

3D view of single riveted

lap joint Top view and sectional elevation

of single riveted lap joint

Top view and

sectional elevation of

double riveted lap

joint

Types of Bolted Joints based on geometry

When two members are overlapped and connected is called a Lap

joint

Rivet in single shear in a lap joint

Single cover butt jointSingle bolted single cover butt

joint

Double bolted double cover

butt joint

Single bolted double

cover butt jointDouble cover butt joint

Bolt in double shear in butt joint

When two members are placed end to end and connected using cover

plates, it is called a butt joint

Double bolted single cover butt joint

Double cover butt joints are preferred due to two

reasons.

1. The shear force transmitted by the members’ acts on two

planes whereas in lap joint it acts on only one plane.

Therefore the shear carrying capacity in double cover

butt joint is twice that in a lap joint.

2. Also in double cover butt joint, there is no eccentricity

of force and thus bending is eliminated.

Lap Joint Vs Butt Joints

Simple joints can be classified based on the nature of force

transfer as follows

Direct shear joints

Direct tension joints

Eccentric connections: There are two principal types of

eccentric loaded connections namely:

Bolt group in direct shear and torsion

Bolt group in shear and tension

Types of joints based on force transfer

A shear joint can fail in 5 modes:

1. Mode 1: By shear on the bolt shank

2. Mode 2: By bearing on the member or bolt

3. Mode 3: By shear at the end of the member

4. Mode 4: By tension in the member

5. Mode 5: By block shear.

prevented by providing sufficient number of

bolts of suitable diameter.

prevented by providing sufficient

end distance.

prevented by design tension members

for its effective area

failure is observed in a shear joint involving a

group of bolts. To prevent such failure check

the effective shear area as per the code

provisions.

The bolts are arranged to act in single or double shear.

Figure: A joint in which the bolt is in single shear.

Shearing strength

If the loads are large enough, the bolt may fail by shearing as shown

below:

The area resisting this failure is the circular area of the bolt shank. The

shear resistance per plane is calculated using equation given in table 3.4 of

BS EN 1993 -1-8.

Direct shear joints

2

,

M

ubv

Rdv

AfF

The shear resistance per plane:

Condition Value of

When the shear plane passes through the threaded portion

of the bolt (A is the tensile area of the bolt)For classes 4.6, 5.6, 8.8

αv =0.6

For classes 4.8, 5.8, 6.8 and

10.9

αv =0.5

When the shear plane passes through the unthreaded

portion of the bolt (A is the gross cross section of the bolt) αv =0.6

Value of αV

Bolt diameter

mm

Gross area

mm2

Tensile stress

area

At mm2

8 50 36

10 78 58

12 113 84

16 201 157

18 254 192

20 314 245

22 380 303

24 452 353

27 573 459

30 707 561

36 1017 817

Table: shows the gross areas and tensile areas of standard diameter

bolts.

2

,

M

ubv

Rdv

AfF

Bearing strength

• When relatively large diameter bolts are used to connect two thin steel

plates, then failure will take place by tearing of plates by bolt.

• This type of failure is known as bearing failure.

• The area of contact of bolt with the plates on one side is actually semi-cylindrical

(figure 7.8), but since the variation of stress around the perimeter of hole is

indeterminate, the strength of bolt in bearing is determined using equation in table

3.4 of EC3 -1-8

Where thicknesses of plates connected are not equal, the

thickness of the thinner plate is used.

Principal provisions of positioning of holes for bolts is

given in section 3.5 of BSEN 1993-1-8:2005

bearing failure

2

1

,

M

ub

Rdb

dtfakF

0

1

3d

ed

4

1

3 0

1 d

pd

For edge bolts:

For inner bolts:

Where ab is the smallest of αd ; 𝑓𝑢𝑏

𝑓𝑢or 1.0

αd is evaluated in the direction of load transfer separately for edge

bolts and inner bolts by following expressions:

k1 is evaluated perpendicular to the direction of load transfer

separately for edge bolts and inner bolts by following expressions:

For edge bolts: k1 is the smallest of or 2.5

For inner bolts: k1 is the smallest of or 2.5

Strength of bolt in bearing

• Block tearing or block shear is a potential failure mode in

bolted connections for tension members, coped beams and

gusset plates.

• Block tearing consists of failure in shear at the row of bolts

along the shear face of the hole group accompanied by tensile

rupture along the line of bolt holes on the tension face of the

bolt group.

• Typically this failure mode is characterised by tearing out of a

block of steel with a combination of tension and shear failures

through the bolt holes.

• Clause 3.10.2 provides the guidelines for design for block

tearing.

Design for block tearing/ block shear

(a) I-beam with no coping (b) I-beam with single coping

(c) I-beam with double coping (d) Plate under concentric loading

(e) Plate under concentric loading (f) Angle section

Figure: Block tearing

Figure shows different

cases of block tearing of

gusset plates (Figure d

and e)

Beam web shear of

connections with and

without coped I-beams

(Figure a,b and c)

Angles connected by

one leg (Figure 7.9f).

Figure a,b and c shows

bolt group subject to

eccentric loading.

02

,2,3

15.0

M

nvy

M

ntuRdeff

AfAfV

02

,1,3

1

M

nvy

M

ntu

Rdeff

AfAfV

Figure d and e shows symmetric bolt group subject to concentric

loading. The design block shearing resistance 𝑉𝑒𝑓𝑓,1,𝑅𝑑 is given by

Note that in the above expressions, for tension rupture net area is taken

whereas for shear yielding the gross area is used.

Figure a,b and c shows bolt group subject to eccentric loading.

The design block shearing resistance 𝑉𝑒𝑓𝑓,2,𝑅𝑑 is given by

Ant is net area subjected to tension;

Anv is net area subjected to shear.

The code has two categories for connections loaded in tension as per clause

3.4.2 BS EN 1993-1-8:

Category D: Non – preloaded: (clause 3.4.2(1) a)

Bolt classes 4.6 to 10.9 should be used. Where connections are subject to

variations in tensile loading, this type of connection is not to be used.

However, they can be used in connections subject to normal wind loads.

Category E: Preloaded: (clause 3.4.2(1) b)

Bolt classes 8.8 and 10.9 are used with controlled tightening as per reference

Standards 1.2.7: Group & to be applied.

Direct Tension joints

2

2

,

M

sub

Rdt

AfkF

2

,

6.0

M

upm

Rdp

ftdB

The design tension resistance is given by the expression:

k2 =0.63 for countersunk bolt; otherwise, 0.9

Table 3.2 provides the design checks to be carried out for tension

connections. The design punching shear resistance is given in Table 3.4:

Figure below shows a lap joint. Two 10 mm thick S275 plates

have been joined using a single bolt of 16 mm diameter and

grade 8.8. Determine the following:

Check on minimum and maximum edge and end distances.

Also the load capacity of the connection with respect to

• Bolt shear

• Bolt bearing

• Plate bearing

• Block shear

• Tension capacity of plates

Example 1

From EC3-1-1 Table 3.1, for grade S 275 steel, fy= 275 N/mm2

and fu = 430 N/mm2. From the figure it is seen that there is only

shear plane and the bolts are fully threaded.

The edge and end distances provided have to be compared with

minimum and maximum end and edge distances required as per

table 3.3 of EC 3-1-8

Solution

For 16 mm bolts, 2 mm clearance holes are provided.

Diameter of bolt hole = 16 + 2 = 18 mm diameter.

Minimum edge distance ≥ 1.2d0 = 1.2 x 18 = 21.6 mm

Maximum end/edge distance = 4t + 40 mm = 4 x10+ 40 = 80 mm

From the figure, Edge distance provided =25 mm

End distance provided = 25 mm. So, Minimum end and edge

distance provided are OK.

Often minimum edge distance + 5 mm is

provided to accommodate any enlargement

which may become necessary at the site.

2

,

M

ubv

Rdv

AfF

kNAf

FM

ubv

Rdv 288.6025.1

1578006.0

2

,

u

ub

f

f

86.1430

800

u

ub

f

f

46.0183

25

3 0

1

d

edd

(a) Bolt shearing:

Bolt shearing resistance,

For grade 8.8 bolts, fub = 800 N/mm2 and Area of bolt = At = 157 mm2

As per EC 3-1-8 clause 3.6.1 (10) single rivets should not be used in single lap joints.

However ignoring that;

or 1.0

> 40kN

in the direction of load transfer at end bolts:

Therefore, = 0.46

Bolts are adequate in shear

(b) Bolt bearing:

αb is the smallest of αd;

d

2

1,

M

ubRdb

dtfkF

Bolt bearing resistance

7.18.20

2 d

e

19.27.118

258.27.18.2

0

2 d

e

kNdtfk

FM

ub

Rdb 447.5525.1

101643046.019.2

2

1

,

For edge bolts k1 is the smallest of :or 2.5

Therefore bearing resistance is given by

>40kN

To determine k1:

Note that EC3 includes the bolt bearing and plate bearing in the same

equation.

(c) Plate bearing:

Discussed above

02

,2,3

5.0

M

nvy

M

ntu

Rdeff

AfAfV

1025ntA

1025nvA

430uf

275yf

kNV Rdeff 693.82693.394331

10)25(275

25.1

10)25(4305.0,2,

(d) Block shear:

Clause 3.10.2 of EC3-1-8

For a bolt group subject to eccentric loading, the design block shear

tearing resistance Veff,2,Rd is given by

>40kN

Plate is adequate with respect to block shear.

kNAf

NM

y

Rdpl 5.1370.1

2751050

0

,

kN

fAN

M

unet

Rdu 072.9925.1

4301018509.09.0

2

,

Plate tension capacity is taken as the smaller of :

(I) Design plastic resistance of the cross section

(ii) Design ultimate resistance of the net cross section at

holes for fasteners

(e) Plate tension capacity:

EC3-1-1 clause 6.2.3

>40kN

Plate is sufficient for the applied tensile force.

Considering (a), (b),(c),(d) and (e); the connection strength is

governed by the smallest value namely

(a) bolt shearing strength = 60.288kN

(b) & (c) bolt bearing strength = 55.447 kN

(d) block shearing = 82.69 kN

(e) Plate tension capacity = 99.072kN

Bolt bearing strength governs.

Maximum force that can be transmitted =55.447kN > 40 kN

OK.

Any questions?

Thank you