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# Gr. 8.8 Bolt Strength

## Gr. 8.8 Bolt Strength

(OP)
Can someone tell mee the strength of Gr 8.8 bolts (BS 3692)?  I'm looking for ultimate, yield, and shear strength.

Thanks,

Chris

### RE: Gr. 8.8 Bolt Strength

Hi meca

The grade 8.8 tells you the yield strength and ultimate stress, it works like this:-

multiply 8*8 then * 10=640N/mm^2 yield stress

multiply 8.8 *100     = 880N/mm^2 tensile stress

regards desertfox

### RE: Gr. 8.8 Bolt Strength

Hi meca

Sorry the last equation should have been the first number 8
multiplied by 100 to give the ultimate tensile strength

ie:- 8*100= 800N/mm^2

Both these values are ie yield and ultimate tensile are minimum values.
In addition the yield stress is the stress at a permanent
set limit of 0.2%

regards desertfox

### RE: Gr. 8.8 Bolt Strength

(OP)
Thanks desertfox.  Do you know what is typically used for the allowable shear stress (single plane)?

### RE: Gr. 8.8 Bolt Strength

Hi meca

It is normal to assume about 70% of the ultimate tensile stress for the shear stress.

regards desertfox

### RE: Gr. 8.8 Bolt Strength

Desert Fox

Is the mm^2 the nominal bolt dia, or root dia of the thread

Regards
pat

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### RE: Gr. 8.8 Bolt Strength

Hi patprimmer

I haven't got the correct BS spec in front of me now, but
yes I think its based on the root diameter of the thread as
that would be conservative for design calculations.
In fact all the design calculations relating to tension that I have seen are based on minimum root diameter.

regards desertfox

### RE: Gr. 8.8 Bolt Strength

An 8.8 bolt has an ultimate tensile strength of 80 Kg/mm2 (785N/mm2) and a yield strength of 80% x 80Kg/mm2 = 64 Kg/mm2 (628N/mm2)

Surely an allowable shear stress of 70% x ultimate tensile stress is much too high. This 550 N/mm2.

Generally, the shear stress is equal to 60% x yield stress. This gives a shear stress of 375 N/mm2. This stress only applies to factored loads.

If using unfactored loads, I would use half this valus, 185 N/mm2.

Regards

### RE: Gr. 8.8 Bolt Strength

Hi meca
linslade is correct the value I quoted would be the ultimate shear stress not the normal working shear stress.

regards desertfox

### RE: Gr. 8.8 Bolt Strength

In general, twice the shear stress is equivalent to the stress intensity, though that definition might not be quite correct. The stress intensity is limited by the yield stress and hence most design codes limit the shear stress to half the yield stress. I'd check with a design standard on correct factors to apply.

corus

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