ssc-392 probability based ship design

157 Pages·2004·0.89 MB·English

NTIS # PB97-109961

SSC-392

PROBABILITY BASED SHIP DESIGN:
IMPLEMENTATION OF DESIGN
GUIDELINES

This document has been approved
For public release and sale; its
Distribution is unlimited

SHIP STRUCTURE COMMITTEE
1996

CONVERSION FACTORS
(Approximate conversions to metric measures)
To convert from to Function Value
LENGTH
inches meters divide 39.3701
inches millimeters multiply by 25.4000
feet meters divide by 3.2808
VOLUME
cubic feet cubic meters divide by 35.3149
cubic inches cubic meters divide by 61,024
SECTION MODULUS
inches2 feet2 centimeters2 meters2 multiply by 1.9665
inches2 feet2 centimeters3 multiply by 196.6448
inches4 centimeters3 multiply by 16.3871
MOMENT OF INERTIA
inches2 feet2 centimeters2 meters divide by 1.6684
inches2 feet2 centimeters4 multiply by 5993.73
inches4 centimeters4 multiply by 41.623
FORCE OR MASS
long tons tonne multiply by 1.0160
long tons kilograms multiply by 1016.047
pounds tonnes divide by 2204.62
pounds kilograms divide by 2.2046
pounds Newtons multiply by 4.4482
PRESSURE OR STRESS
pounds/inch2 Newtons/meter2 (Pascals) multiply by 6894.757
kilo pounds/inch2 mega Newtons/meter2 multiply by 6.8947
(mega Pascals)
BENDING OR TORQUE
foot tons meter tons divide by 3.2291
foot pounds kilogram meters divide by 7.23285
foot pounds Newton meters multiply by 1.35582
ENERGY
foot pounds Joules multiply by 1.355826
STRESS INTENSITY
kilo pound/inch2 inch½(ksi(cid:214) in) mega Newton MNm3/2 multiply by 1.0998
J-INTEGRAL
kilo pound/inch Joules/mm2 multiply by 0.1753
kilo pound/inch kilo Joules/m2 multiply by 175.3
TABLE OF CONTENTS
LIST OF SYMBOLS.......................................................................................................vi
ACKNOWLEDGEMENT...............................................................................................xi
1. INTRODUCTION......................................................................................................1
1.1 Background .........................................................................................................1
1.2 Advantages of a Probability-Based Design Code...............................................1
1.3 Objectives of the Project.....................................................................................2
1.4 Organization of the Report..................................................................................3
2. PROTOTYPE CODE STATEMENT.........................................................................4
2.1 Forward to the Code Statements.........................................................................4
2.2 Planning...............................................................................................................5
2.3 Hull Girder..........................................................................................................6
2.4 Unstiffened Panel..............................................................................................10
2.5 Stiffened Panel..................................................................................................16
2.6 Fatigue...............................................................................................................23
APPENDICES
A LITERATURE REVIEW: STRUCTURAL RELIABILITY
AND CODE DEVELOPMENT...............................................................................36
B TARGET RELIABILITIES......................................................................................39
C PARTIAL SAFETY FACTORS (PSF) AND SAFETY
CHECK EXPRESSIONS.........................................................................................48
D COMMENTARY: LIMIT STATE FUNCTIONS FOR
HULL GIRDER COLLAPSE...................................................................................57
E COMMENTARY: LIMIT STATE FUNCTIONS FOR
BUCKLING OF PLATES BETWEEN STIFFENERS............................................61
F COMMENTARY: LIMIT STATE FUNCTIONS FOR
STIFFENED PLATES..............................................................................................93
G COMMENTARY: LIMIT STATE FUNCTIONS FOR
FATIGUE...............................................................................................................119
REFERENCES.............................................................................................................142
LIST OF SYMBOLS
A = the sectional area of the longitudinal plate-stiffener combination
A = sectional area of the longitudinal stiffener only
S
A = transformed area of the longitudinal plate-stiffener combination
tr
= bT + A
S
m
A = fatigue strength coefficient (NS = A ); defines design curve
0 0
a = length or span of plate; the length or span of the panel between transverse webs; the
length of the longitudinal stiffener
a/b = aspect ratio of plate
B = plate slenderness ratio
B = breadth of the panel
P
b = distance between longitudinal stiffeners
b = stiffener flange breadth
f
C = panel stiffness parameter
C = factor by which plate rotational restraint is reduced due to web bending
r
C = coefficient of variation of stress; includes modeling error and inherent stress
S
uncertainty; equivalent to C in Appendix G
B
c = buckling knock-down factor
c f z = ultimate moment capacity of the hull
y
D = fatigue damage; plate flexural rigidity,
= Et3/12(1-n 2)
d = stiffener web depth
w
E = modulus of elasticity (Young’s modulus)
F = ultimate tensile strength; ultimate strength of plate under uniaxial compressive
u
stress
f = stress
f = Euler’s buckling stress for the plate-stiffener combination
E
f = Euler’s buckling stress for the transformed section
E,tr
f = frequency of wave loading in the ith sea-state
i
f = proportional limit stress for the stiffener in compression
p
f = stress due to stillwater pressure
S
LIST OF SYMBOLS - continued
f = stress due to wave pressure
W
f = factored extreme axial in-plane compressive stress from hull girder bending
X
f = transformed in-plane compressive stress
X,tr
f = the elastic tripping stress for the beam-column
x,T
f = yield strength
y
f = yield strength of plate
yp
f = average compressive yield stress of the stiffener
ys
f = the average frequency of stress cycles over the service life, N
0 S
f = stress in the flange of the stiffener
1
f = stress in the plate flange of the stiffener
2
G = shear modulus
g = limit state or performance function
I ,I = the moment of inertia of the effective plating (alone) about the neutral axis of the
px py
combined plate and stiffener, in the longitudinal & transverse directions,
respectively
I = polar moment of inertia of stiffener about center of rotation
sp
I = moment of inertia of the stiffener only about an axis through the centroid of the
sz
stiffener and parallel to the web
I , = the moment of inertia of the plate-stiffener combination, longitudinal
x
I ,I = the moment of inertia of the combined plate and stiffener, longitudinal & transverse
x y
I = the moment of inertia of the transformed longitudinal plate-stiffener combination
tr
J = St. Venant’s torsional constant
k = buckling coefficient for a simply-supported plate under uniaxial in-plane load
k = load combination factor that accounts for phase angle for dynamic loads
D
k = load combination factor that accounts for phase angle for wave loads
W
k ,k = load combination factors
w d
LIST OF SYMBOLS - continued
k ,k = coefficients that depend on the aspect ratio a/b
1 2
M = extreme dynamic (slamming or springing induced) hull girder bending moment
d
(nominal)
M = plastic moment of longitudinal stiffener at center
l
M = stillwater hull girder bending moment (nominal)
s
M = plastic moment of transverse stiffener at center
t
M = ultimate moment capacity
u
= c f z
y
M = extreme wave induced hull girder bending moment (nominal)
w
M = max bending moment in a simply-supported beam under a uniform lateral load
0
m
m = negative reciprocal slope of the S-N curve; fatigue strength exponent (NS = A );
0
number of longitudinal stiffeners; number of longitudinal half-waves for stiffener
tripping
N = number of longitudinal sub-panels in overall (or gross) panel
N = fatigue stress cycles experienced during intended service life of ship
S
N ,N = ultimate longitudinal and transverse in-plane load from the stillwater hull girder
SX SY
bending moment, respectively
N ,N = ultimate longitudinal and transverse in-plane load from the wave hull girder
WX WY
bending moment, respectively
n = number of transverse stiffeners
P = pressure
P = stillwater hydrostatic pressure
S
P = extreme lateral pressure due to stillwater condition
s
P = wave hydrostatic pressure
W
P = extreme lateral pressure due to wave action
w
P = factored lateral pressure applied to the stiffened panel (Mode I)
1
P = factored lateral pressure applied to the stiffened panel
2
p = probability of failure
f
R = strength of plate under lateral pressure
LIST OF SYMBOLS - continued
S = equivalent constant amplitude stress (Miner’s stress); nominal stress at a detail
e
S = maximum allowable stress peak to satisfy fatigue requirement
m
S = design stress; stress peak which is exceeded, on the average, once during N cycles
p S
(S = S /2)
p 0
S = stress range which is exceeded, on the average, once during N cycles
0 S
T = transformation factor based on secant modulus concept
t = plate thickness
t = stiffener flange thickness
f
t = stiffener web thickness
w
y = distance from the centroidal axis of the cross-section to the mid-thickness of the
f
stiffener flange
y = distance from the centroidal axis of the transformed cross section to the mid-
p,tr
thickness of the plating
Z = hull girder section modulus to the location of interest
z = section modulus; section modulus at the compression flange (at deck in sagging or
at bottom in hogging condition)
a = plate aspect ratio
b = safety index (reliability index)
b = target safety index
0
D = the initial eccentricity of the beam-column, typically taken as a/750
D = eccentricity of load due to use of transformed section
p
D = target damage level, maximum allowable value of D
0
d = length of the transferse stiffener
d = the central deflection of a simply-supported beam under a uniform lateral load
0
G = gamma function, G (x) = (x - 1)!. (Note that non-integer factorials can be computed
from many electronic calculators)
F = cumulative distribution function for standard normal; magnification factor for in-
plane compressive loading
f = partial safety factor for strength