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Safety Working Load Calculation Of Panama Chocks
Mar 16, 2018



According to Panama Canal Authority Rules Panama chock is a kind of mooring chock that designed and applied to marine ships for crossing Panama Canal. Compared to other chocks, the Panama chock has a slightly higher tensile strength and safety working load.

This article is conduced to show how to calculate SWL (safety working load) of Panama chocks.

 

1. Force analysis.

Force analysis of panama chocks 

    Horizontal load                                                 Vertical load

As the sketch shows above, F is 2 times mooring rope breaking load.

Following is a example calculation of AC310 model Panama chock. Dimensions of AC310 Panama chock please click here.

2. Calculation of horizontal load.

AC310 Panama chock mooring rope breaking load is 64 N.

F=2×64×9.8=1254.4N.

a. Bending moment from mooring rope to the bottom of marine chock.

M=2F×(130+180)=2×2×64×1000×310×9.8=777728000N·m.

Flexural modulus of the bottom of marine chock.

W=W1+W2

W1=(T×L42)/6=32×7082/6=2673408mm3.

W2=(T×L52)/6=32×6522/6=2267221mm3.

W=W1+W2=2673408+2267221=4940629mm3.

Bending stress.

α=M/W=777728000/4940629=157.4Mpa.

b. Shear stress from mooring rope to the bottom of marine chock.

Sectional area of marine chock bottom.

S=708×32+652×32+296×32×2=62464mm2.

Shear stress.

τ=2×F/S=2×2×64×1000×9.8/62454=40Mpa.

c. Synthetic stress.

αs=α/2+((α/2)22)1/2=78.7+88=166.7Mpa.

Permissible stress of marine chock’s material (ZG200-400).

[α]=0.85αm=0.85×200=170Mpa.

Result: αs < [α], horizontal load of Panama chock is satisfied.

3. Calculation of middle load.

Shear force from mooring rope to the middle of marine chock.

T=2×F=2×2×64×1000×9.8=2508800N.

Sectional area shows as below:

Sectional area of panama chock 

S=2×(9305+8239)=2×17544=35088mm2.

Shear stress.

τ=T/S=2508800/35088=70Mpa.

[τ]=0.6αm=0.6×200=120Mpa.

Result: τ < [τ], middle load of Panama chock is satisfied.

4. Calculation of vertical load.

Force detail of Panama chock bottom as below:

Force detail of Panama chock 

a. Tensile stress from mooring rope to the bottom of marine chock.

F1=2F×sin(70°/2)=2×1254.4×0.57=1438640N.

Resolve F1 to horizontal force F2 and vertical force F3.

Horizontal force F2=F1×cos55°=825170N.

Vertical force F3=F1×sin55°=1178465N.

Bending moment from horizontal force to the bottom of marine chock.

M=F2×440=825170×440=363074800N·mm.

Flexural modulus of the bottom of marine chock.

W1=(323×708/12)+(32×708×1642)/180=3396050mm3.

W2=(323×652/12)+(32×652×1642)/180=3127463mm3.

W=W1+W2=6523486mm3.

Tensile stress.

α1=M/W=363074800/6523486=55.6Mpa.

b. Vertical tensile stress to the bottom of marine chock.

Sectional area of marine chock bottom.

S=708×32+652×32+296×32×2=62464mm2.

Vertical tensile stress.

α2=F3/S=1178465/62464=18.8Mpa.

c. Synthetic stress.

α=α12=55.6+18.8=74.4Mpa.

Result: α < [α], vertical load of Panama chock is satisfied.

 

This calculation is a reference for designers who want to choose a suitable model of Panama chocks. More information please contact us.


A PDF document please click here.

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