Connection 6

8/3/2019 Connection 6

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1

Basic principles of steel structures

Dr. Xianzhong ZHAO

[email protected]

www.sals.org.cn

Members + connections = system

transfer forces supportedby a member to others

ConnectionsOutlines

types of connections and their characteristics

butt weld connections: details and calculation

fillet weld connections: details and calculation

bolted connections: details and calculation

high-strength bolted connections: details andcalculation

Types of structural connectionsbasic types of connections

welded connections

molten parent metals are fused with each other being together

electric-arc/slag/resistance welding, gas welding

riveted connections

bolted connections

ordinary structural bolt/ high strength bolt

other connections

screw, glue

weld rivet bolt

Types of structural connectionswelded connections: types of welding

electric arc welding: molten weld metal (welding wire orelectrode) is fused with the base metal of the members beingconnected

shielded metal arc welding (SMAW)

Q235: E43 electrode / Q345: E50 / Q390, Q420: E55

electrode matches with lower yield strength steel

submerged arc welding (SAW) : auto-/ semi-automatic

H08 welding wire, with Mn flux

gas metal-arc welding (GMA): CO2

shielding gas (indoor weld)

Types of structural connectionswelded type: shielded metal arc welding


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Types of structural connectionswelded type: submerged arc welding

Types of structural connectionswelded type: gas metal-arc welding

Types of structural connectionswelded connections: types of welding

electric slag welding

molten slag + base metal + welding wire

electric resistance welding

Molten base metal + pressure

gas welding

Acetylene + oxygen + electrode

Types of structural connectionsclassification of welds

Types of joint used: position of base metals

butt, lap, tee, edge, corner

Types of weld made

butt weld: straight / bevel welds

fillet weld: end / side welds

Types of structural connectionsclassification of welds Types of weld made

Continuous weld

Intermittent weld

Welding position

Flat, horizontal, vertical, overhead

Types of structural connectionsadvantage and disadvantage of weld connections

Efficiency: material saving and time saving

Wider range of application

More rigid, most truly continuous structures

Residual stress: rigid, stability and fatigue

Weld deformation

HAZ: brittle failure

Crack: propagation to members

Qualified: skill dependent/ qualification of welding procedure

crack, blow hole, slag inclusion, undercut, overlap

incomplete penetration / fusion / filled groove


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Types of structural connectionsresidual stress

Self balance system

Not affect the static performance

Decrease the stiffness?

Decrease fatigue?

Decrease stability?

P

u

P/ yA f=

P=u=

0.6rt yf =

0.3rc yf =

0.4

yf =

0 .3 0 .4 0 .1 + =

0 .6 0 .4 1+ =

0.8 yf =

0.1

1

0 .4 3 / 2 0 .7+ =

y

f =

0.7

1

0 .2 3 / 2 1+ =

Types of structural connectionsweld deformation

Types of structural connectionsHAZ and weld crack

Butt weld connectionsdetailing

Backup strip, back gouging and weld mending

1:2.5

1:2.5

Grooves and welding symbols

Run-out plate

Transition of thickness and width

Butt weld connectionsdesign of butt welds

design resistance of butt welds

Quality grade I & II : equal to the design strength of base metal

Quality grade III : decrease to 85% design strength of base metal

how to classify the quality grade of butt weld

Quality grade III: visual inspection

Quality grade II: visual inspection + ultrasonic testing (20%)Quality grade I: visual inspection + ultrasonic + radiographic (100%)

cross-section of butt weld

(1) Area = thickness of plate (t) X effective length of weld (L)

(2) With run-out plate: L = length of weld

(3) Without run-out plate: L = length of weld 2t


design principle of butt welds

a. Butt weld subject to compressive force: NO NEED

b. Butt weld under repeated load: Quality grade I

c. Butt weld under tension load: Quality grade II + run-out plate

d. Set the butt weld in the vicinity of lower stress

Steps to design of butt weld

(1)Determine the internal force at the section to be checked

(2)Calculate the section properties of A, S, W, I

(3)Calculate the stress

(4)Check the strength of weld


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Typical problem using butt welds(1) butt-welded plates subject to axial load

(2) butt-welded plates subject to axial load (inclined welds)

(3) butt welds under shear force (plates and bracket)

(4) butt welds under combined shear and moment

equivalent stress

(5) butt welds under combined tensile, shear and moment

Fillet weld connectionsdetailing

Orthogonal fillet weld

Oblique (angle) fillet weld

End weld: transversely loaded fillet weld

Side weld: fillet weld loaded parallel to the welds axis

hf

hf hfhfhf

hf

hf

hf

hf

normal fillet weld concave fillet weldunequal leg fillet weld

Fillet weld connectionsdetailing

Leg size of fillet weld

Minimum: 1.5Xsqrt(tthick), prevent weld crack

Maximum: 1.2tthin, prevent burn through

Length of fillet weldMinimum: 8hf & 40mm, avoid mass imperfection

Maximum: 60hf ,, avoid uneven stress distribution

Distance between two longitudinal fillet welds: shear lag

Weld symbols

Fillet weld on one side / on both side

Fillet weld all around joint (L, 3 or 4 sides)

Fillet weld in the field

8

8

8

8

8

Fillet weld connectionsfailure mode

Stress distribution

End weld: tri-axial stress

(brittle failure)

Side weld: mainly shear stress

(ductile failure)

Failure plane (assumption)

Effective plane = failure plane

(45 degree through the throat)

Effective thickness = 0.7 leg size

(weld throat)


Failure plane and theoretical throat

Orthogonal fillet weld

Oblique-angle fillet weld


Failure plane and stress distribution (assumption)

Normal stress perpendicular to the throat plane

Shear stress (in the plane of the throat) perpendicular to the weld axis

Shear stress (in the plane of the throat) parallel to the weld axis

w

ff3)(32

//

22 =++

//

1)75.0()75.0()(

2

2

//

2

2

2

2

=++ w

u

w

u

w

u fff


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2 2 2 2 w w3 0.5 1.5 2 3 1.22f f + + = = =

Failure plane and stress distribution (assumption)

wff3)(3 2//22 =++

2 2 w w

//3 3 3 f = = =

// =

//

End weld: larger strength and rigid, less deformation ability

Side weld: 22% less than strength of end weldlarger deformation ability

Fillet weld connectionssimplified method

w

f

f3)(3 2

//

22 =++

simplified method for design resistance of fillet weld

amplification factor for weld strength perpendicular to the weld axis,taken as 1.22 for static loading and 1.0 for dynamic loading

w

f

2

f

2

f

f )( f+

f

w

ff design strength of fillet weld (same for shear, tension and compression)

For applied force N perpendicular to the weld axis

stress on the failure plane

f w e/ N l h =

f w e/V l h =

For applied force V parallel to the weld axis//

fN

fV

w f2l l h= e f0.7h h=

Fillet weld connectionsprocedure of fillet weld design

Focus on the distinguishing of stress perpendicular to the weld axis

and stress parallel to the weld axis

Calculation of weld section properties, A, S, I, W (weld length)

Centroid of welds coincides with that of members

Axial force, shear force or combined axial and shear force

Combined bending moment, axial and shear forces

Combined torsional moment, axial and shear forces

Stress calculation under single force

w

f

2

f

2

f

f )( f+

Analysis of internal forces at weld connection

Superposition of stress components at critical point, thencheck with practical equation

Fillet weld connectionstypical problem (1)

Axially loaded weld connections

w

f

2

f

2

f

f )( f+

N

(1) Internal force1N

V

sin1 NN =

cosNV =

(2) Weld stress

f

11f

A

N

lh

N

we

==

f

fA

V

lh

V

we

==

(3) Stress check

w

f

f

0,0 f

A

N=

w

ff

f

0 ,90 fA

N =


Axially loaded weld connections ( C & Angle)

(1) 3 sides around welds (cover plate of flange)

w

f

f 1 e1 2 f2 e22( )

Nf

l h l h h

+ 1l2l

2l

NN

(2) 2 sides welds

(4) L-shape welds (angle) ?

NN1 f1,l h

2 f2,l h

1e

2eb

1 2 1( / )N e b N k N = =Internal force

2 1 2( / )N e b N k N = =0.7

0.3 0.25

0.750.65

0.35

(root)

(toe)1k

2k

(3) 3 sides around welds (angle)

NN1 1 30.5 N k N N =

2 2 30.5 N k N N =

Internal force


, , ,N V N V M

N

fx

f

N

A =

V

fy

fw

V

A ==

weld connections subject to bending moment, axialand shear forces

(1) Internal force

(2) Weld stress

(3) Stress check

N

V

M

V

x

y

M

fx

fx

M y

I =

N M2 V 2 wfx fx

fy f

f

( ) ( ) f

++


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assumption

(1) The connected plate isperfectly rigid, thus the

welds are assumed to beperfectly elastic

(2)


weld connections subject to torsional moment, axialand shear forces

m

mr r

=

m

m

dF dA rdAr

= =

Resultant force for any micro-element

Torsional moment about weld centroidfor the micro-element

2m

m

dM rdF r dAr

= =

Total torsional moment for the weldconnection

m m fyf xf

m m

( )J

I Ir r

= + =

2mi i

m

M rdF r dAr

= =

2 2m

m

( ) x y dAr

= +

mmr

r

dA

x

y


weld connections subject to torsional moment, axialand shear forces

y

x

mmr

M

fx

M

M

fy

N

fx

V

fy

N

V

(1) Stress calculation for welds subject totorsional moment and axially force(taken Q point, how about S point?)

Q

M mfx m

f f

sin sin Mr My

J J = = =

M

fy

f

Mx

J =

N

fx

wi ei f

N N

l h A = =

V

fy

f

V

A =

V M

fy fy 2 N M 2 w

fx fx f

f

( ) ( ) f

+ +

S

(2) Stress check

critical point,S or Q?

Fillet weld connectionscomparison of butt weld with fillet weld

Butt weld

groove preparation

less filler metal, just afew run-out plate

computing method ofweld is similar with thatof base metal

design strength of weldequals to base metal

base metal-weld-basemetal connect smoothly,less stress concentration

Fillet weld

No groove

pretty much gussetplates

completely different instress calculationcompared to base metal

design strength of weldis less than base metal

performance is worsethan that of butt welds

Manufacture

Weldstrength

Dynamicperformance

Fasteners connectionscharacteristics

Characteristics

Machining

Position and hole machining: drill, punch

Surface treatment (for slip-resistant connection)

Assembly: snug-tight or pretensioned

Ease to erect on site ( less skill / facility dependent)

Fatigue resistance (for slip-resistant connection)

Easy to prevent the propagation of crack

Easy to realize the removable structures

Material and time waste

Strongly depend on the machining accuracy

Partially damnifying the base metal

Common-bolt connectionsintroduction

Types of bolt

Unfinished, ordinary or common bolt

High-strength bolt (pretensioned)

Bolt grade

Grade 4.6, 4.8: Q235BF (Grade C bolt)

Grade 5.6, 8.8: quality carbon steel (Grade A, B bolt)

heat-treatment

Hexagonal bolt Twist-ff bolt

Common-bolt connectionsintroduction

Drilled hole dimension

Hole dimension = bolt diameter + 1~1.5mm

Grade A, B bolt: hole quality, hole size deviation +0.25mm

Grade C bolt: relatively large tolerances in shank, thread dimensionsand holes, hole size deviation + 1mm

Load transfer

bolt loaded shear force

bolt loaded tension


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Common-bolt connectionsbolt for shear transfer

Behaviour mechanism (load transfer)

friction plate shear off the bolt and

the bolt push or bear against the hole

Failure mode

Shearing of the bolt (calc.)

Bearing of the bolt/hole (calc.)

Tension failure of plate (calc.)

Shearing out of part plate (calc. & detail)

Bending of bolt (detail) 5l d

Common-bolt connectionsbolt for shear transfer

Design resistance for individual bolt subjected to shear

b

v

2

v

b

v4

fdnN =

b

c

b

c fdtN =

},min{][ bcb

v

b

v NNN =

(1) Shear resistance (shear plane)

(2) Bearing resistance (thickness for bearing same-direction force)

F

F/2

F/2

F/2

F/2

F/2

F/2

(3) Design resistance for individual bolt

Common-bolt connectionsbolt for tension transfer


The two contact plates tend to expandand the bolt are tensioned

Prying action

How prying actionaffect the internalforce of the bolt?

F0. 5 F

0. 5 F

F0. 5 F P+

P

P

0. 5 F P+

Design resistance for individual bolt subjected to tension

b

t

2

e

b

t4

fdN =

Measure to reduceprying action

Tension increase in bolt decrease strength of bolt

Failure plane: effective section in thread

Common-bolt connectionsspacing and edge distance of bolts


Specification of spacing allowance (hole-size based)

requirement of capacity: cutting off and buckling

requirement of detail: anti-corrosion

requirement of construction: room for wrench

Pitch: the center-to-center distance of bolts in a direction parallel to the member axis

Gage: the center-to-center distance of bolt lines perpendicular to the member axisEdge distance: the distance from the center of bolt to the adjacent edge of a member

Net area for

regular and staggered spacing bolt

Common-bolt connectionstypical problem (1)

Uniformly shearing bolts

Long joint: uneven shear force in each bolt

Elastic and plastic period: uneven uniform

Procedure of design

(1) determine the shear force on the connect plane

(2) calculate the shear force of each bold endured

(3) ascertain the design resistance for individual bolt:

single shear, double shear or multiple shear?

shear resistance or bearing resistance?

long joint need to reduce resistance by a reduction factor?

1 01 .1 / 15 0l d = 1.0 =

0.7 =

1 0 / 15l d

b b

V V[ ] [ ]N N

1 015 / 60l d<

1 0 / 60l d

(4) check the capacity of net section


Bolted eccentric connection with torsional moment

x

y

M

xN

M

N

xN

N

V

V

yN

M

yN

assumption(1) The bolt is perfectly elastic and the connected plate is perfectly rigid

(2) The shear stress of a bolt at a centroidal distance d is proportional to d

M

x 2 2

i i( )

M yN

x y=

+M

y 2 2

i i( )

M xN

x y=

+ Procedure of design

Same as procedure mentioned before, andpay attention to the superposition of shearforce under torsion with that under axial load

b

V

M

y

M

x NNN ][)()(22 +


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Bolted connection subjected to tension

assumption(1) Location of neutral axis?(2) The tension force of a bolt at a centroid

distance d is proportional to d

Bolted connection subjected to bending moment

Capacity check: (maximum loaded bolt)

M b11 t2

i

MyN N

y=


Bolted connection subjected tocombined tension and bending moment

1ty

'

1y

The tension force of a bolt depends on the

location of the neutral axis.

(1) Assume the neutral axis locates the centroid ofbolt connection

M 1c1c 2

i

M yN

y=

N N

Nn

=

(2) If , the assumption is ok andthe critical tension force

M N

1c 0N N+

M b1t1 t2

i

M y N N N

y n= +

1

'

M b

1 t' 2

i

( ) M N e yN N

y

+=

M N

1c 0N N+


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high-strength bolt connectionsbolt for tension transfer

design resistance for individual slip-critical bolt subjected to tension

Q: why use 0.8 reduction? (for the sake of shear transfer)

design resistance for individual bearing-type bolt subjected to tension

PN 8.0b

t =

b

t

2

e

b

t4

fdN =

Q: why same as the common-bolt capacity?

High-strength bolt connectionstypical problem (1)

Uniformly shearing bolts

Slip-critical connection:

- shearing of bolt- capacity of net section:

Bearing-type connection: same as common bolt

Bolted connection subjected to combined shear andtension forces

N

1

' 5.0 nn

NNN =

1)()( 2b

t

t2

b

v

v +N

N

N

N

2.1/bcv NN

1b

t

t

b

v

v +N

N

N

N

)25.19.0 tfb

v NPnN =

(GB50017-2003)

(GBJ17-88)

For slip-critical connection: For bearing-type connection:

Q: why use 1.2 notas common-bolt?

High-strength bolt connectionstypical problem (2)

Bolted eccentric connection with torsional moment/shear

Internal force at each bolt is ascertained as common bolt

Check the capacity: slip-critical or bearing-type bolt?

Bolted connection subjected to bending moment

As subjected to bending moment

Test result: external force is smaller Tongjis is better; while larger, Chens better

Internal force at each bolt is as common bolt

Location of neutral axis:

- Tongji: at centroid,

max. tension in bolt less 0.8P, and the connected plateis always in compression

- Chen Shao-fan: as common bolt

Bolted connection subjected to bending moment & tension

Question:

Question:

T

P

P

N

0 d y R /( 3 ) / N b d t f f =

Connection 6

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