Bolt/threaded rod strengths differ for Grade 8.8 in BS 4190 and BS 5950 1

[PJ.]

BS 4190 says the bolt/thread rod strength for Grade 8.8 is 640 MPa. BS 5950 says it's 560 MPa for the same material. Why the difference? There is no difference for Grade 4.6, but there is again a difference for Grade 10.9. Thanks.

 

[klaus.]

is BS 5950 still valid ??

 

[PJ.]

There are certain areas where the superseded codes may still need to be used, such as in the assessment of existing buildings. However, this is just something I had noticed and it's been bugging me. If anybody had come across this before and know of the reason, your help in answering the question above is appreciated.

 

[MGZmechanical]

Not sure about the reason but the reason but the ISO 898 says Rp0,2 for 8.8 is 640 MPa and Rm = 800 MPa

 

[kingnero]

What do the mill test certificates (if available) say?
If you're checking an existing structure, I'd be inclined to go with the lesser value. Otherwise, I see no reason not to use 80% of 800 MPa, as that's the whole idea of the denomination of the fasteners.

 

[RolMec]

Hello P.J.
i don't have that BS under my hand, nevertheless the effect is known from similar standards.
640 Mpa is the materials nominal yield strength (8x8* 10).
560 MPa is the permitted stress of that material under tension load.
The bolt shall not be tensioned to full yield strength, but instead to a lower value which then still allows for operational loads.
Pls. refer explanatory notes, for
- pretensioning
- allowed loading when thread is in shear plane / not in s. p.
- combined loading (tension and shear)
There's some threads on EngTips on this one, too.
Regards

Roland Heilmann

 

[PJ.]

Thanks Roland. That's an explanation I can accept.

Although there is no such difference for the Grade 4.6 bolt, I can accept that for such weaker bolts, the design strength (or allowable strength) for the Grade 4.6 bolt is very close to its material strength, such that the two codes had used a common value.

Also note that the description in BS 4190 is "Strength grade designations for steel bolts and screws", while that for BS 5950 is "Tensile strength of bolts". This difference matches your explanation for the discrepancy.

 

[sengr]

I thought about this and come up with this. I could install 2 anchor bolts, on the 8" vertical leg, shim up the 4" leg with shim plates. Then the contractor could inject epoxy grout or suitable grout under the 4" leg to fill the gaps. Those 2 rows of anchor bolts on the side would be able to hold the angle up, with the shim plates and the grout under the 4" leg. It should be sufficient to hold things up.

The application is to prevent further concrete spalling on the vertical edge of a wall supporting precast panels over a road crossing. If you have a better suggestion, let's hear them. Thank you guys for the feedback.