Download General - Pillar Connections/Cross Ties connection

General - Stiffener/web connection
Size of welding gun compared to
typical stiffener height
Continuous welding
difficult
Start and stop defects
50mm
Approval Centre Sydney
General - Stiffener/web
connection
Difficult to weld
Small shear
capacity
Bracket or flat bar added
Not too difficult to weld
General - Stiffener/web
connection
Cover plate will
improve shear
capacity and improve
force distribution
If possible avoid scallops, snipe corner of collar
plate to allow space for longitudinal weld and then
weld continuously around collar plate
Approval Centre Sydney
General - Brackets
Edge Stiffening Requirements
General - Tipping Brackets
Approval Centre Sydney
General - Termination of Sniped
Stiffeners
30 degrees
Sniping allowed when:
•buckling stiffeners
•dynamic loads/vibrations
of minor importance
D<25mm
General - Pillar Connections to
Deck
Should not be
applied if
tension through
pillar may occur
Approval Centre Sydney
General - Pillar Connections/Cross
Ties connection
Applicable to pillars/cross ties that may
be under compression and tension
General - Alignment in Way of
Section Joints
Bulkhead or Deck
Section Joint
Easier to get acceptable alignment when a
continuous member is penetrating the
bulkhead or deck structure
General - Longitudinals through
Web Frames
Approval Centre Sydney
Longitudinals at Watertight Bulkhead
Longitudinal continuous
through bulkhead
Longitudinal terminated at
bulkhead with soft-nose
brackets
Approval Centre Sydney
Edge Support of Cut-Outs
Edge support when length of free edge exceed 50t or D50t
Cut-outs to be kept well clear of end of brackets and
locations where shear stresses are high
Hard Chine / Knuckle
Problem: Cracking due to unfavourable detail design.
Possible Cause: The knuckle represents an elastic
element in the plate, the effective flange will be
reduced and the stresses will increase locally in way of
the web / bulkhead, in addition large dynamic
pressures act on the planing strip / spray rail.
Integral spray rail
Cracks
External spray rail
Cracks in web
and shell plating
Hard Chine / Knuckle
Solution:
CHINE SUPPORT
KNUCKLE SUPPORT
Pillar Connections/Cross Ties
connection
Problem:
Cracking and
buckling of frame
webs and ties.
Possible Cause:
Unfavourable
detail design.
Buckling and tripping of frame
Position
Cracks
Pillar Connections/Cross Ties
connection
Solution:
Additional tripping brackets
should be fitted to support
cross tie or pillar.
Soft toe brackets to be fitted
Soft toe brackets
Add tripping brackets
Transverse Frames - Buckling
Problem : Buckling and
tripping of frame in
way of sharp radius.
Position
Buckled web and tripped flange
Transverse Frames Buckling
Solution: as illustrated below, or
various combinations to increase
buckling capability
Additional
buckling stiffener
Additional bracket
Tripping brackets
Tripping brackets
SKEGS FOR DIRECTIONAL STABILITY
Problem:
Cracks in various locations
starting from weld to
bottom plating, edges and
slot welds
Bottom Pl.
Possible Cause:
Unfavourable detail
design.
Insufficient stiffening
Unfavourable weld
method
Cracks
SKEGS FOR DIRECTIONAL STABILITY
Solution:
Introduce additional
stiffening.
Improve weld connections
by using double sided
fillet welds or full
penetration with backing
bar where access is
difficult.
Avoid scallop welds,
replace with continuous
welds against permanent
backing
Additional Stiffening / Continuous Welding
SCALLOPS AND CHAIN WELDS
Problem:
Cracks originating from end of chain
weld propagating into stiffener.
Cracks originating from scallops
propagating into web or shell
plating, along HAZ of weld
Possible Cause:
Vibrations from machinery or high
dynamic sealoads. Unfavourable
detail design for area.
Unfavourable weld execution at
starts and stops of chain welds and
at ends/terminations of scallops
Crack
Cracks in web along HAZ of weld,
crack in bottom plating
SCALLOPS
AND
CHAIN
WELDS
Solution:
Longitudinal
stiffeners in area
should be welded
with double
continuous welds.
Scallops should be
avoided, necessary
drain holes may be
cut in web above weld
to bottom plating
Re-weld with continuous
welding
Scallops avoided, necessary
drain holes cut above weld.
Thrust Bearing, Shaft Bearing and
Engine Foundations
Problem:
Cracks in various parts of
foundations originating from
weld toes at ends of brackets,
stiffeners and scallops, ends of
sniped flanges, or at ends of
buttwelds in flanges in way of
thickness transitions.
Possible Cause:
Unfavourable detail design,
weld execution at ends, in way
of scallops and at buttwelds of
thickness transitions.
Insufficient thickness of critical
parts.
Cracks in bracket supports starting
from bracket ends and scallops
a
a
a:a
Cracks in foundation flanges in way
of thickness transitions
Thrust Bearing, Shaft Bearing and
Engine Foundations
Solution:
Improve detail design, by avoiding
brackets and stiffening with
unfavourable details as indicated
New thicker transverse webs cut from
one piece welded without scallops and
previously.
Increase thickness in certain locations. with weld toes ground. Reposition girder
webs inside line of gear bed bolting.
Improve position and profile of
transitions between thick and thinner
parts.
Improve structural continuity by adding
a
a
brackets or new flange pieces replacing
sniped flanges.
a:a
Careful grinding of critical welds and
rounding of edges of foundations,
Reposition weld in relation to
flanges and transitions will improve
supports and increase taper
fatigue life.
Thrust Bearing, Shaft Bearing and
Engine Foundations
 Foundations supporting oscillatory equipment will be
exposed to varying degrees of vibrations at high
frequency.
 Fatigue failure must therefore be taken into
consideration.
 Typical details that may give rise to high stress
concentrations and for which it is difficult to obtain a
good surface finish are scallops, cutouts, sniped flanges
etc.
 It is therefore very important to maintain structural
continuity, avoid scallops and sniped flanges whenever
possible and improve details by grinding smooth
surfaces at critical locations.
FOIL AND APPENDAGE FOUNDATION
Problem:
Cracks in various parts of
foundations originating from
weld toes at ends of
brackets, stiffeners and
scallops, or at ends of
buttwelds in flanges in way
of thickness transitions.
Possible Causes:
Unfavourable detail design.
Poor execution of welds.
Insufficient dimensions of
critical parts. Lack of
structural continuity
Foil internal
supporting
structure
Cracks in various of the flange
junctions and bracket end connections
FOIL AND APPENDAGE FOUNDATION
Solution
Improving detail design
by ensuring soft
transitions at cruciform
joints, positioning of
buttwelds outside areas
of stress concentrations,
avoiding scallops or
ensuring proper weld
finishing at the scallop
toes, fitting of soft toe
brackets at ends of
girders.
Approval Centre Sydney
Use proper soft transitions
between girder flanges
and soft toe brackets at
girder ends
BULKHEAD STIFFENING ARRANGEMENT
Problem: Cracks in brackets or stiffener at ends or
cracks in bulkhead plating in way of unsupported
stiffener ends
Possible Cause: Unfavourable detail design. Fatigue
cracking from sloshing of liquid in tanks or varying sea
pressure
Cracks
Cracks
Typical cracks at unsupported
ends of vertical stiffeners
BULKHEAD STIFFENING ARRANGEMENT
Solution
Soft toe brackets
Provide full shear connection of webs
Provide end support to unsupported
stiffeners.
End connection of bulkhead stiffeners
Soft toe brackets,
stiffener
webs welded
continuously to
bulkhead.
BRACKET CONNECTIONS
Problem
Cracks in brackets and
longitudinal stiffener, cracks
originating from weld toes in
various locations propagating into
plating or along HAZ of weld.
Possible Causes
Vibrations from machinery or high
dynamic sealoads. Unfavourable
detail design for the area.
Unfavourable workmanship.
Insufficient scantlings.
Cracks
Intermittent welding
Approval Centre Sydney
BRACKET CONNECTIONS(cont)
Solution
Connect webs of
longitudinals to
bulkheads or frames
with continuous welds,
avoid scallops and weld
start / stops in critical
positions. Fit soft toe
brackets. Toe height
should be limited refer soft toe bracket
detail
Soft bracket possibly of
increased size.
Webs welded continuously.
TRANSVERSE FRAMES
Problem
Cracking in plate buttweld
in knuckle. Cracking in
webs and bulkheads in way
of knuckle.
Possible Causes
Unfavourable detail design.
The knuckle represents an
elastic element in the plate,
the effective flange will be
reduced and the stresses
will increase locally in way
of the web / bulkhead.
Cracks in webs and along
shell plating butt weld
Crack in longitudinal
butt weld in shell
Cracks in webs from scallop
TRANSVERSE FRAMES
Solution
Knuckles should be
supported with brackets
which are properly
connected to stiffeners on
bulkheads or flanges of
web frames.
For knuckles with small
change of direction, a
plate insert made from a
bent plate may be
introduced to move butt
weld out of the knuckle
area.
Insert bent plate
Add brackets to support knuckle
Alt. 1, on both
sides of frame
Alt. 2, on one
side of frame
STRUCTURAL DESIGN - POINTS TO
REMEMBER
1. Bottom slamming will be
dimensioning to all structures in this
area. Shear area requirement to
longitudinal stiffener may be severe.
2. Chines and knuckles have to be
supported
3. Side plating (L>50m) may need
increased thickness for shear
buckling.
4. Vertical pillars to be positioned
correctly first time.
5. Transverse deck girders will often
have long spans which need
appropriate section properties.
6. Deck plates of catamarans need to
be checked for buckling due to
transverse bending moment.
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