iccgs 2013 presentation - benson, syrigou, dow
TRANSCRIPT
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Longitudinal Strength Assessment of
Damaged Box Girders
Simon Benson, Maria Syrigou and Robert S Dow
School of Marine Science and TechnologyNewcastle University
ICCGS 2013
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• Research Motivation:– Introduction
– Damage Representation
– Progressive Collapse
• Case Study:– Finite Element Modelling
– Results
– Conclusions
Presentation Contents
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Research Motivation
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• Office of Naval Research (ONR) supported project:
“Structural Performance of Lightweight Vessels”
• Development and extension of simplified hull girder progressive collapse analysis methodologies:
– Ultimate Strength Analysis
– Limit State Design
– Optimisation
– Reliability
– Damage Strength
– Recoverability
• Evaluation of longitudinal bending capacity of the hull girder
• Inclusion of multiple load combinations:– Longitudinal Bending
– Pressure
– Shear
– Torsion
Introduction
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• Hull girder progressive collapse methods have been established
primarily for STEEL ships with INTACT structural arrangements.
• How do we adapt these approaches for:
– lightweight ship structures?
– damaged ship structures?
• Two general approaches to the problem:
– Simplified analytical methods (e.g. progressive collapse):• Fast and efficient
• Simplifying assumptions
• Implicit characterisation of material and geometric imperfections
– Sophisticated nonlinear finite element methods (FEM):• Able to represent all relevant geometry and the interaction between different parts of the
structure
• Computationally expensive
• Requires explicit characterisation of all material and geometric properties in the FE
model
Progressive Collapse Methods
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Damage Representation Finite Element Method
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Damage Representation Progressive Collapse Method
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Case Study
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Motivation
• Investigate the strength of two box girder models with different
levels of ruptured damage applied
• The area and location of the damage is systematically investigated
to show:
– Effect of the transverse damage extent
– Effect of the longitudinal damage extent
• The girders are analysed and compared using:
– The progressive collapse method
– The nonlinear finite element method
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Parameters
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Models
Small Box Girder (5 bays of 1800mm each)
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9000 mm
1800 mm
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Models
Large Box Girder (7 bays of 1800mm each)
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1800 mm
12600 mm
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NLFEM Modelling
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NLFEM Modelling
Assumptions:
• Boundary conditions: one side clamped / other side constrained
• Load: vertical rotation of the constrained end
• Solver: Static-implicit (Riks arc length)
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ProColl Modelling
Assumptions:
• Geometric imperfections and welding residual stresses are taken into
consideration:
– “Average” levels
– Implicitly defined within ProColl
• Interframe and extended (compartment) progressive collapse analyses
were completed
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Intact Condition Results – Small Box
• Comparison with and without residual stresses (NLFEM)
• Small box demonstrated interframe mode of collapse
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Intact Condition Results – Large Box
• Comparison of interframe and compartment analyses (ProColl)
• Large box demonstrated overall mode of collapse
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Damage Condition Results – Small Box
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Transverse Damage Extent
• Constant longitudinal extent
1440mm
• Symmetrical damage
• Cut-out
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Results
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Damage Condition Results – Small Box
NLFEM Results with different
transverse cut-out extents
ProColl-Interframe Results with
different transverse cut-out extents
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Damage Condition Results – Small Box
Ultimate strength as a function of damage width
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Damage Condition Results – Small Box
Longitudinal damage extent
• Constant transverse extent
1440mm
• Symmetrical damage
• Cut-out
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Damage Condition Results – Small Box
NLFEM and ProColl Results with different longitudinal cut-out extents
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Damage Condition Results – Large Box
Transverse damage extent
• Similar pattern of damage
scenarios
• Initial “strength drop” in NLFEM
• Overall collapse mode is
predicted throughout
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Damage Condition Results – Large Box
Longitudinal damage extent
• Behaviour is similar for all
damage cases
• However, the strength is slightly
reduced for longer damage
extents
• Girder stiffness up to ultimate
strength is also reduced for longer
damage extents
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Conclusions
• Results of intact cases show good agreement
• Results of damage cases show similar relationship
except for the narrow damage extent along the centreline:
– Immediate drop in strength predicted by NLFEM
– Due to change in effective boundary conditions for the damaged panel
– Progressive collapse method cannot account for this mechanism
• Future Work:
– Further investigations of damage extent on hull girder case studies
– Investigate transition from interframe to overall collapse modes
– Representation of an actual damage scenario in NLFEM
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Questions?
Thank you