Design and strength assessment of a welded connection of a plane frame

1
Design and strength assessment of a welded
connection of a plane frame
2
Structural connections

• Structural connections of a plane frame must be
  able to transfer
• 1) internal forces between beam and beam
• 2) internal forces between beam and column
• 3) reaction forces between column and ground

• These are typical permanent connections and can
  be riveted, bolted or welded
• The basic criterion in the design of connections
  include
• - assessment of their static strength and
  endurance
• - assessment of the right transfer of the
  internal forces
• The welded connection at point B must be designed
  

3
Reaction and Internal moments

• Reaction forces and internal moments can be
  evaluate
• using handbook formulae for a similar structure
  loaded with distributed load or concentrated
  load, and then applying the superposition
  principle.
• applying the Principle of Virtual Work
• by means FEM model of the frame
• The suggestion is to evaluate reaction forces and
  internal moments by means of handbook formulae
  and to compare results with results obtained
• by Principle of Virtual Work or FEM analysis

4
Moment for distributed load handbook formulae
Manuale for mechanical engineer, Hoepli edition
1994, (in italian).
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Moment for concentrated load handbook formulae
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Principle of virtual work for frames
For plane frame Mt0 and the deformations due to
the axial and the shear forces are negligible,
only the internal bending must be taken into
account
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The examined plane frame

• The plane frame is symmetric only half of the
  frame have to be considered

Q/2
Q/2
p
p
RE
B
B
E
E
ME
h
RE and ME hyperstatic unknown
A
A
l/2
The structure is two times hyperstatic The
internal moment M(x) on the real structure is
M(x)M0(x)REM1(x)MEM2(x)
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Internal moment M(x) on the real structure
Q/2
p
1
B
B
E
B
E
E
1
Auxiliary structure n. 2
Isostatic structure
Auxiliary structure n.1
RA
A
1
A
A
1
MA
1h
M2(x)
M1(x)
M0(x)
M(x)M0(x)REM1(x)MEM2(x)
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PVW for the auxiliary structure n. 1
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PVW for the auxiliary structure n. 2
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Hyperstatic unknown

• The system
• allows the calculation of RE and ME

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FEM Analysis
20000 N/m
20000 N
Constrains Point A U1U2UR30 Point E U1UR30
Deformed shape
Model
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Example of results
The same cross section IPE 330 has been used for
the beam and for the column
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The cross section of the beam and of the column

• Cross sections can be choose on the basis of the
  bending moment only
• On each cross section act the bending moment due
  to the distributed load constant and the bending
  moment due to the concentrated load Q varying
  sinusoidally with time

y
x
E
z
Maximum of Mb,p and Mb,Qsinwt
Mb,p Mb,Qsinwt
z
x
y
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Bending stress on the cross section at point E

• We consider the cross section at point E where
  both Mb,p and Mb,Qsinwt are maximum.
• The bending stresses result linearly varying with
  the distance from the neutral axis
• and sinusoidally varying with time

a
Aa a
a
a
a
A a
A a
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• It is maximum at the points that are most distant
  from the neutral axis of the section
• The condition
• where ? is the safety factor and slim can be
  obtained from the Haigh diagram of the material
• allows the calculation of Jxx of the beam
  section.

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Bending Haigh diagram
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Design of the structural node
M2

• The node between the column and the beam,
  realized with a double T section, must be
  designed in order to realize a clamped constrain.
• The aim is to transfer the boundary moment M1,
  from the transverse beam to the vertical column

ht
M1
hc
M3
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The welded connection

• The end of the horizontal beam, upper plate,
  lower plate and web are welded to the upper plate
  of the column
• The weld is a fillet weld type

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Moment transfer

• In the double T sections, if subjected to
  flexural moment in the plane of the web, the
  axial forces that originate from the flexural
  moment are transmitted by the upper and lower
  plate.
• As a consequence the upper plate of the column
  receives the normal forces of the flexural moment
  from the transverse beam, and deflects, except
  close to the web.

• An overview of the deformations of the node is
  given in the figure, as result of a finite
  element analysis.
• The level of deformation, in absence of any
  reinforcement, is quite high, and not acceptable.

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Reinforcements

• From the previous considerations, it is intuitive
  that local reinforcements are needed, to
  correctly transfer the flexural moment to the
  upper and lower plate of the column.

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Adopted solution

• In the adopted solution, the node is considered
  as a group of four beams, plus a diagonal member,
  all hinged at their ends.

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• Let M be the moment to be transmitted to the
  column.

• Axial load on the upper and lower plate of the
  beam, transferred to the reinforcement results
• Axial load on the upper and lower plate of the
  column

• On the diagonal AD acts the force
• If the contribution of the web of the column is
  take into account, by means of the coefficient h

24

• The comparison between the reinforced node (a)
  and the one without reinforcement (b) allow to
  visualize their different behavior.

(a)
(b)
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Verification of the beam-column welded joint

• In the following the verification of the welding
  is reported. Let the two profiles be a IPExxx for
  the beam and for the column.
• The reference sections of the fillet of the
  welding are place as shown in figure below.

TB
MB

• J is the moment of inertia of the resistant
  section of the welding
• MB and TB are the bending moment and the shear
  that must be transmitted by the welded joint

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• At the edges of the fillets welding along the
  web, where bending and shear are present, the
  stresses are

• So that the reference stress results
• The corresponding safety coefficients then
  results
• At point A (top of the horizontal fillet) only sT
  due to bending is present and he corresponding
  safety coefficients results