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Know It All Contest Solution

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Chainplate Design Load = 1.34 x shroud or stay breaking strength. This assumes a safety factor (SF) of 3 for the rigging

wire itself, which is standard and rec-

ommended. (Uppers may have an SF

of about 2.5) This is an SF of 4 over

the rigging loads (3.34 uppers.)

We have a 5/16” dia. (8 mm) 316

cap shroud and a 3/8” (9.52 mm)

stainless intermediate shroud. These

are both 1x19 316 stainless wire

rope. Breaking strengths are 10,300

lb. (4640 kg) and 14,500 lb. (6580

kg) respectively. Therefore:

Chainplate Design Load (CDL) =

(10,300 lb. + 14,500 lb.) x 1.34 =

33,232 lb.

Or

Chainplate Design Load (CDL) =

(4640 kg + 6580 kg) x 1.34 = 15035

kgf = 147443

15035 kgf x 9.806 n/kgf = 147433 N

To avoid weld distortion, the heaviest

weld you should use in ordinary situa-

tions is 1/16th inch (1.5 mm) smaller

than the

plate being welded.

Thus if you have a 1/4-in. plate being

welded to a 3/8-in. plate, the heavi-

est weld would be 3/16 in.; or if you

have a 6 mm plate being welded to a

10 mm plate, the heaviest weld you

could use would be 4.5 mm. Lighter

weld causes less distortion, so you

want to use somewhat lighter welds

where possible, assuming that you

can get enough total weld length.

The chainplate design load (CDL) is 33,232 lb. or 147433 Newtons (N). Our aluminum chainplate 3/4 in. (19 mm) thick.

The aluminum knee it is being welded to is 1/4 in. (6 mm). This means that the heaviest weld usable is 3/16 in. or 4.5

mm. How many inches of 3/16-in. or 4.5 mm weld do you need to equal the required CDL?

Weld strength in lb. per lineal inch = WF x leg length, in. x cos 45° x psi

Or

Weld strength in N per lineal mm = WF x leg length, mm x cos 45° x mPa

Where:

leg length = weld leg length, in. or mm

psi = shear strength of material in the as-welded condition (for aluminum this is shear strength in as-welded

)

mPa = shear strength of material in the as-welded condition (for alum. this is shear strength in as-welded yield)

WF = weld strength reduction factor = 0.75 for aluminum, 0.90 for bronze, 0.95 for steels

As-Welded Shear Strength

psi

mPa

Marine Aluminum*

9,000

62

A36 Steel

34,000

234

A242 Cor-Ten

38,000

262

316 Stainless Steel

46,000

317

Silicon Bronze

31,000

214

*For aluminum as-welded YIELD shear

June 2012 Page 26

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