Iccgs 2013 presentation - Benson, Syrigou, Dow
-
Upload
simon-benson -
Category
Technology
-
view
891 -
download
0
Transcript of Iccgs 2013 presentation - Benson, Syrigou, Dow
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
2
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
4
• 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
6
7
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
9
Parameters
10
Models
Small Box Girder (5 bays of 1800mm each)
11
9000 mm
1800 mm
Models
Large Box Girder (7 bays of 1800mm each)
12
1800 mm
12600 mm
NLFEM Modelling
13
NLFEM Modelling
Assumptions:
• Boundary conditions: one side clamped / other side constrained
• Load: vertical rotation of the constrained end
• Solver: Static-implicit (Riks arc length)
14
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
15
Intact Condition Results – Small Box
• Comparison with and without residual stresses (NLFEM)
• Small box demonstrated interframe mode of collapse
16
Intact Condition Results – Large Box
• Comparison of interframe and compartment analyses (ProColl)
• Large box demonstrated overall mode of collapse
17
Damage Condition Results – Small Box
18
Transverse Damage Extent
• Constant longitudinal extent
1440mm
• Symmetrical damage
• Cut-out
Results
19
Damage Condition Results – Small Box
NLFEM Results with different
transverse cut-out extents
ProColl-Interframe Results with
different transverse cut-out extents
20
Damage Condition Results – Small Box
Ultimate strength as a function of damage width
21
Damage Condition Results – Small Box
Longitudinal damage extent
• Constant transverse extent
1440mm
• Symmetrical damage
• Cut-out
22
Damage Condition Results – Small Box
NLFEM and ProColl Results with different longitudinal cut-out extents
23
Damage Condition Results – Large Box
Transverse damage extent
• Similar pattern of damage
scenarios
• Initial “strength drop” in NLFEM
• Overall collapse mode is
predicted throughout
24
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
25
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
26
Questions?
Thank you