Longitudinal Strength Assessment of

Damaged Box Girders

Simon Benson, Maria Syrigou and Robert S Dow

School of Marine Science and TechnologyNewcastle University

ICCGS 2013

• Research Motivation:– Introduction

– Damage Representation

– Progressive Collapse

• Case Study:– Finite Element Modelling

– Results

– Conclusions

Presentation Contents

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Research Motivation

• 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

Damage Representation Finite Element Method

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Damage Representation Progressive Collapse Method

Case Study

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

Models

Large Box Girder (7 bays of 1800mm each)

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1800 mm

12600 mm

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

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