# DAVIT ARM

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### Description

PRELIMINARY DAVIT ARM CALCULATION

DAVIT ARM CALCULATION
ITEM :SAND  BAGGING

1.0 MOMENT AND FORCES IN DAVIT
(Ref:Pressure Vessel Design Manual 3rd Edition by Dennis R. Moss Page 291~295)

Est Lifted Weight of Sand,  WL
Weight of Davit (Boom + Brace),  W1
Axial Load, P = WL + W1

Vertical Impact Factor, Cv
Horizontal Impact Factor, Ch

Vertical Force, fv = Cv x P
Horizontal Force, fh = Ch x P

1.2 Bending Moment in Davit Mast, M1
Length of Boom, L1
Length of Davit, L2
Length L5

Moment, M1 = fvL1 + 0.5W1L1 + fhL2
2.0 STRESS IN DAVIT

2.1 Davit Arm Properties
Mast Material
Yield Stress, Fy
Allowable Axial Stress, Fa = 0.6Fy
Allowable Bending Stress, Fb = 0.66Fy
Outside Diameter, Do
Wall Thickness of Davit, tp
Inside Diameter, Di
Cross Sectional Area, A1 = π/4 x(Do2-Di2)
Section Modulus, Z1 = (π/32Do)x (Do4-Di4)
Moment Inertia, I = π/64 x(Do4-Di4)
Radius of Gyration, r = Sqrt(I/A)

Section Modulus of Stiffener
Combined Section Modulus of davit (Ztot = Z1 + Zstf)

Cross sectional Area stiffener
Combined Area of Davit (Atot = A1 + Astf)

Moment of Inertia of stiffener
Moment of Inertia of combined section of davit

Axial Stress at Davit, fa = P/Atot
Bending Stress at Davit, fb = Mtot/Ztot
Calculate Combined Stress,  ( fa/Fa + fb/Fb )

Since Calculate Combined Stress

2.2 Boom Properties
Boom Material
Boom Size
Yield Stress, Fy
Allowable Axial Stress, Fa = 0.6Fy
Allowable Bending Stress, Fb = 0.66Fy
Cross Sectional Area, A2
Section Modulus, Z2

Axial Stress at Boom, fa = P/A
Bending Stress at Boom, fb = (fv xL5)/Z2
Combined Stress, fa/Fa + fb/Fb
Calculate Combined Stress

Since Calculate Combined Stress
3.0 WELDED DESIGN JOINT
(Ref:Pressure Vessel Handbook 12th Edition by Eugene F. Megyesy Page 459)

3.1 Davit Arm Bracket

Vertical Shear, V
Bending Moment, M = lV

Horizontal Weld Length,b
Vertical Weld Length,d
Length of Weld, Aw
Fillet Weld Used

Section Modulus (Bending Moment),Sw

Vertical Shear Forces,Ws =V/Aw
Bending Forces, Wb = M/Sw

Resultant Force, W =(Wb2 + Ws2)1/2

Fillet Weld Leg Size,w =W/f

Since Calc. weld size> Weld used

4.0 DESIGN OF LOCAL STRESS IN CYLINDRICAL SHELL
(Ref:Pressure Vessel Design Manual 3rd Edition by Dennis R. Moss Page 255~290)

Half side vertical attachment, Cx =d/2
Half side horizontal attachment, Cø =b/2

Shell thickness,t

Cx/Rm
Cø/Rm

Kx from fig 5.13
Køfrom fig 5.13

Calculation Reference
Davit Arm Design
Hoisting and Lifting
Crane Design

17 Sep 2014
19 Sep 2014
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