Design of Tension Circular Flange Joints in Tubular StructuresDescripción completa
Descripción completa
RESUMEN DE UN POZO TUBULAR
Full description
Multi storeyed building design
AC MembersFull description
Tubular Non Tubular
Description complète
Tubular Bells
Members of ACMAFull description
Desi gnofTubul arMemb mber s
Earthquake Engineering Research Centre Earthquake International Institute of Information Technology IIIT Hyderabad, Gachibowli, Hyderabad -
Tubular members: Tubular members are commonly used for jacket structures. Because these are resisting various forces. Following are the reasons:
Good dynamic properties (low d ! m"
Good resistance against hydro static pressure.
Good buoyancy to weight ratio
#niform property across section
$o torsional buckling
Good ultimate strength compared to others
Full moment connections
Tubular members: Following factors affect the strength of the member:
&aterial properties (' F y Ft"
)mperfections and residual stresses
,roduction method of tubular sections
Boundary conditions
-oading
Geometric properties (-/ /t"
(an*t be +ero".
(This is based on e0perience and code guidelines. Both parameters will play major role in design".
1tiffeners: circumferential or longitudinal (hoose stiffeners rather than increasing thickness of pipe. (a" #neconomical and (b" ,lates are already purchased".
Material properties of Steel:
/ensity: 3456 kgm2 or 34.5 k$m 2
Tensile stress (Ft": 786966 &pa
;ield stress (Fy": %569766 &pa
&odulus of 'lasticity ('": %669%<6 Gpa
1train in elastic range: 6.%=
,oisson*s ratio: 6.296.7
o.efficient of friction: 6.296.7
Imperfections: Following are some imperfections that need to be included
>ariation in cross section
>ariation in thickness (-arger the bending radius smaller the stresses. -arger the /t ratio strain will be smaller. ?eat induced stresses during welding
could be large due to restraint provided by the joining components". @educe yield stress by 5= as per /$>. @esidual stresses ,) @, % is silent on residual stresses
Aut9off roundnessstraightness
&isalignment of thicknesslength
Imperfections:
Aut9off straightness The tolerance shall be measured at all points along the length of member and the ma0imum shall be taken for consideration.
/$> code specifies a ma0imum limit of 6.66<5- or - as the limit. ,) specifies a ma0imum limit of -86 or 8.5 mm
The tolerance is important as this deviation will lead to eccentric load and corresponding moment.
Imperfections:
Aut9off roundness Aut of roundness is normally specified as δ D D max D min −
=
D
%
D mean
,) 1pec %B specifies that the above tolerance shall not e0ceed %= and /$> specifies that the tolerance shall not e0ceed <= /ma0 /mean
/min
Imperfections:
&isalignment of joints ()t includes additional eccentricity in a0ial loads and stresses".
,) allows an eccentricity Ce* of (a" 6.% t
/$> allows an eccentricity of 6.<5 t < or 7 mm whichever is less
-ocal ! global buckling
-ocal buckling is governed by /t ratio
Global buckling is governed by k-r ratio
Design Methods: /esign of structural member
1elect a suitable material with sufficient strength
1atisfy the functional reuirements with adeuate safety margin
/ivide the member into sections and calculate a0ial bending and shear forces in each section along the length. t least 2 sections shall be checked. 'stablish geometric properties such as sectional area moment of inertia effective length factors radius of gyration for each section. alculate the applied a0ial (f a" bending (f b0 f by" hoop (f h" and shear stresses (f s" using the geometry of the section and the applied a0ial bending hydrostatic and shear forces. 'stablish the slenderness ratio (k-r" and calculate the allowable a0ial stress (F a" and calculate the elastic buckling stress (F 0e" and inelastic buckling stress (F 0c". 'stablish the /t ratio and calculate the allowable bending stress (F b". The combined effect of loads is obtained using interaction of these loads in an appropriate manner using a0ial bending hoop and shear interaction formulae.
ASD Design 'rocedure: Applied Stresses Following method shall be used in calculation of applied stresses in members.
Axia$ Stress, f a
P =
A
#en!in" Stress, f %x Shear Stress, f s Hoop Stress, f h
=
Mxy I xx
f %y
=
V =
=
0.5A Ph D 2t
( Ph
=
γ h )
Myy I yy
ASD Design 'rocedure: Allowable Stresses Following method shall be used in calculation of allowable stresses in members. (Source: A'I R' +A ,SD cl- .-+) A/ial !ompression:
D0t 1 23
ASD Design 'rocedure: Allowable Stresses
For members with a /t K 6 substitute the critical local buckling stress (F0e or F0c whichever is smaller" for F y in determining c and Fa.
ASD Design 'rocedure: Allowable Stresses <. 'lastic local buckling stress
The elastic local buckling stress F 0e should be determined from
The theoretical value of is 6.. ?owever a reduced value of L 6.2 is recommended to account for the effect of initial geometric imperfections within ,) 1pec %B tolerance limits.
ASD Design 'rocedure: Allowable Stresses %. )nelastic local buckling stress
The inelastic local buckling stress F 0c should be determined from
For /t ratios greater than 266 refer to ,) Bulletin %#. &a0imum value is limited to 3-56 " &ost of the time we don*t permit /t beyond 6 for offshore structures. )t is mandatory because of local buckling effects.
ASD Design 'rocedure: Interaction of a/ial compression and bending
ylindrical
members
subjected
to
combined
compression and bending should be proportioned to satisfy following reuirements at all points along their length. For f aFa K 6.<5
For f aFa E 6.<5
General case
ASD Design 'rocedure: Interaction of a/ial compression and bending For asymmetric sections
ASD Design 'rocedure: Moment Reduction actor
&eLm&B
>alues of the reduction factor C m referred to in the above table are as follows (with terms as defined by )1":
e&
+2π 2 * =
( ' r ) 2
ASD Design 'rocedure: 7lastic hoop buc8ling stress The elastic hoop buckling stress determination is based on a linear stress9strain relationship from:
The critical hoop buckling coefficient h includes the effect of initial geometric imperfections within ,) 1pec %B tolerance limits.
ASD Design 'rocedure: !ritical 9oop 4uc8ling Stress The material yield strength relative to the elastic hoop buckling stress determines whether elastic or inelastic hoop buckling occurs and the critical hoop buckling stress F hc , in ksi (MPa) is defined by the appropriate formula.
ASD Design 'rocedure: Interaction euation for a/ial tension and h"drostatic pressure Jhen member longitudinal tensile stresses and hoop compressive stresses (collapse" occur simultaneously the following interaction euation should be satisfied:
ASD Design 'rocedure: Interaction euation for a/ial tension and h"drostatic pressure 1afety Factors
ASD Design 'rocedure: Interaction euation for a/ial compression and h"drostatic pressure Jhen longitudinal compressive stresses and hoop compressive stresses occur simultaneously the following euations should be satisfied:
The following euation should also be satisfied when f x > 6.5 F ha
Ring Design: ircumferential stiffening ring si+e may be selected on the following appro0imate basis
