DAVIT ARM

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)

1.1  Load on davit

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

Outside Radius, a

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

Allowable load on weld,f

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)

4.1 Radial Load for Shell attachment

Half side vertical attachment, Cx =d/2

Half side horizontal attachment, Cø =b/2

Mean Radius, Rm

Shell thickness,t

Cx/Rm

Cø/Rm

Load on attachment, F

Kx from fig 5.13

Køfrom fig 5.13

Calculation Reference

Davit Arm Design

Hoisting and Lifting

Crane Design