steel structures - WELDED CONNECTIONS

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2. Maximum Size of Fillet Welds
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3. Minimum Size of Fillet Welds
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Smaller size weld is economical than large one.

4. Weld Specifications
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Effective length of
weld = overall
length – 2x size of
weld.
Provide end
returns for joints
subjected to
eccentricity,
stress reversals or
impact loads.

5. Effective Throat Dimensions
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Groove Welds
Fillet Welds

6. Fillet Welds at Varying
Angles to the Load
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Effective throat
thickness = K x
size of weld

7. End Fillet Normal to Direction of
Force
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When the weld axis is
normal to the load vector,
the end fillet weld
develops a high strength
with less ductility.
Cl.10.5.8.5 requires that
throat thickness ≥ 0.5 t.
The thickness of the welds
should be negotiated at a
uniform slope.

8. Design of Groove Welds
 For tension or compression normal to effective
area or parallel to axis of weld
Tdw = fy Lw te / γmw ;
γmw =1.25 for shop welding and 1.5 for site
welding.
fy = Smaller of ultimate stress of weld and the
parent metal in MPa
te = Effective throat thickness of weld
 For shear on effective area
Vdw = Lw te fyw / (3 x γmw)
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9. Design of Groove Weld (cont.)
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Combined Bending, shear
and bearing
Clause(10.5.10.2.2)
Equivalent stress
fb = Stress due to bending
fbr = stress due to bearing
q = shear stress

10. Design of Fillet Weld
 As per IS: 800, design strength
 Pdw = Lw tt fwn βlw
or
 Pdw = Lw K s fwnβlw
s = size of the weld, fwn = fu / (√3 γmw)
 When subjected to combined stresses, the
equivalent stress, fe, should satisfy
fa = normal stress
q = stress due to shear force or tension.
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mw
u
a
e
f
q
f
f

3
)
3
( 2



Reduction factor for long Joints 0
.
1
150
2
.
0
2
.
1 


t
j
lw
t
l

)
,
min( up
uw
u f
f
f 

11. Design Strength of Fillet Welds
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12. Intermittent Fillet Welds
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Assume the size of weld and compute the total length of
weld.
Follow the minimum effective length and clear spacing
clauses of IS code.
At the ends, the longitudinal intermittent fillet weld should
be of length not less than the width of the member.

13. Balancing the Welds in
a Tension Member
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P1 = Ty / d – P2 / 2
P2 = Rw Lw2
P3 = T(1-y / d) – P2 / 2
Compute P2 , P1 and P3.
Compute Lw1 = P1 / Rw and Lw3 = P3 / Rw

14. Welds for Tension Connection
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Unsatisfactory Satisfactory

15. Welded Seat Angle Connection
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16. Design of Unstiffened Angle Seat
The steps in the design are:
 Select a seat angle having a length equal to width of the beam.
 Calculate the length of the outstanding leg of the seat
b = R / [tw(fyw / γmo)]; γmo = 1.10.
R = reaction of the beam
tw = thickness of web of beam
 Determine length of bearing on cleat b1 = b-(Tf + rb)
Tf , rb = Thickness & root radius of the beam flange
 Determine distance from end of bearing on cleat to root of angle
b2 = b + g – (ta + ra)
where g = erection clearance + tolerance
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17. Design of Unstiffened Angle Seat
(cont.)
 Calculate bending moment at critical section
Mu = R x (b2 / b1) x b2 / 2
 Equate it to the strength of angle leg, bent about its
weak axis, determine thickness of seat angle
 Determine the required weld size.
 Without taking eccentricity
Lw = R / (2 x Rw); Rw = strength of weld per mm
 When eccentricity is considered,
 Rres = R / (2 L2
w) √[L2
w + 20.25 (b2 / 2)2 ]
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18. Simple Shear-
Double Angle Connection
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Source :AISC

19. Eccentric Shear
in the Plane of the Web
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R [P / (2L )] (L 12.96e )N / mm
res
2 2
2
2
 

20. Flexible End Plate Shear
Connection
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The end plate is shop welded to the web of beam and
connected to column flanges/webs by HSFC Bolts.

21. End Plate Connections
 The welds may be designed for the resultant force
using the elastic vector analysis
 Resultant force =
≤ Design strength of weld
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(P / A) (My / Z)
2 2

Extended end plates

22. Types of Eccentric Loading
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23. Properties of Welds
Treated as Lines
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24. Ecc. Load Causing Twisting
Moment
Steps involved in checking the adequacy of the weld
 Calculate the centroid of the weld line
 Determine twisting moment and the forces at the centroid
 T = Px ex + Py ey
 Locate the critical weld points
 Determine The force components due to twisting moment
and maximum shear force for critical weld point
 Fx
T = Ty / Ip and Fy
T = Tx / Ip
 Fx
P = Px / Lw and Fy
P = Py / Lw
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25. Ecc. Load Causing Twisting
Moment (cont)
 Calculate the resultant shear force
 FR = [(Fx
P + Fx
T)2 + (Fy
P + Fy
T)2]0.5
 The maximum shear force should be less than the
capacity of weld
FR < Rw (weld strength)
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26. Eccentric Bracket Connection
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27. Loads Applied Eccentric
to the Plane of Weld
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28. Stresses in Weld Subjected
to Eccentric Load Causing B.M.
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29. Welded Stiffened Seat Connection
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30. Welded stiffened seat connection
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Welded
stiffened seat
connection
using the split I
section in a car
parking
structure in
Bethesda, USA

31. Beam-to- Column Connections
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(a) Beam flange directly welded to column flange (d) welded flange
plate connection to column web

32. Beam-to-Column Connections
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Directly welded Flanges
Beam bottom flange welding -a challenge
–Weld access hole, cope and backup bar required
–Un-fused interface at bottom of back-up bar
 Potential crack initiation of CJP weld

33. Beam-Column Joint Behaviour
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34. Required Design Checks
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35. Continuous Beam-to- Column
Connections
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36. Continuous Beam-to- Column
Connections (cont.)
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37. Welded Beam Splices
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38. Hybrid Beam Splice
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Cover Plates Shop welded & Site Bolted

39. Welded Column Splices
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40. Column Splice with Complete Joint
Penetration Grove Weld
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Source: AISC

41. Welded Column Splices (cont.)
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42. Welded Tubular Connections
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43. Basic Types of Tubular Joints
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44. Examples with Welded Tubes
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45. Seismic Failure of
Moment Connections
 The January 1994 Northridge earthquake in
California and Kobe earthquake in Japan in 1995–
Showed failure of beam-column connections.
 Failures included
 Fracture of bottom beam flange-to-column flange
CJP groove welds.
 Secondary cracking of the beam web shear plate
 Failure of the beam top flange weld.
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46. Design of Seismic Moment
Connections
 More than ten Years of Research resulted in the
following documents:
 AISC 341-05 (Seismic provisions for structural steel buildings,
American Institute of Steel Construction).
 AISC 358-10 (Pre-qualified connections for special and
intermediate steel moment frames for seismic applications
including Supplement No.1)
 Some of the Pre-qualified connections are
discussed in the next few slides.
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47. Pre-qualified Seismic
Moment Connections
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Reduced beam section (RBS) moment connection (a)
connection, (b) details of reduced beam flange

48. Pre-qualified Seismic
Moment Connections (cont.)
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Bolted unstiffened extended end-plate (BUEEP) and bolted
stiffened extended end-plate (BSEEP) moment connections

49. Pre-qualified Seismic
Moment Connections (cont.)
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Bolted flange plate (BFP) moment connection

50. Pre-qualified Seismic
Moment Connections (cont.)
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Welded unreinforced Flange –
welded Web (WUF-W) moment
connection (a) connection,
(b) Detailing of connection

51. Pre-qualified Seismic
Moment Connections (cont.)
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Kaiser bolted bracket (KBB) moment connections (a)
Beam welded to bracket, (b) beam bolted to bracket

52. Dr. N. Subramanian 52
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