Slip critical connection 2

[Veer007]

Hey guys, for slip critical connection which bolts would be great A325N, A490N (hex head) or F1852, F2280 (twist off type)?

Is there any special mechanical properties for the bolt named as A325SC or A490SC? Can anyone assist me!!

Thanks in advance!!

 

[trustthemodel]

The AISC Steel Construction Manual would be a good starting reference.

Before doing that I would recommend you double check the application and figure out whether the slip critical bolts are really the way to go.

 

[DrZoidberWoop]

No. A325SC can be the same bolt as an A325N, but designed for a "slip critical" condition, which reduces the bolt's load capacity. The condition of the surfaces you want to bring into contact is a factor in this. The RCSC seems to be the go-to document for high-strength bolts

https://www.boltcouncil.org/files/2014RCSCSpecification-withErrata.pdf

 

[dauwerda]

Don't confuse bolt type with connection type.
There are essentially two types of connections, bearing connections and slip critical connections.

A bearing connection carries load by contact between the side of the bolt bearing against the bolt hole, putting the bolt in shear, see below:

The bolt used in a bearing connection can be designated to include the threads of the bolt in the shear plane (designated with "N") or to exclude the threads from the shear plane (designated with "X")

A slip critical connection has the bolts installed to a specified pretension which clamps the two surfaces together so that the load is transferred through friction between the two surfaces, not through direct bearing, see below:

A slip critical connection requires that the two surfaces be prepared in a certain manner to ensure the expected friction develops between them.


Now on to bolts, there are essentially two strength types used.

Bolts with a strength of 120 ksi which include A325 and F1852 for twist off type
and bolts with a strength of 150 ksi which include A490 and F2280 (again twist off)

As noted above, these bolts can be designated as N, X, or SC (or blank). If the bolt is designated as A325N, this is a bearing type connection in which the threads of the bolts may be included in the shear plane. If it is designated as A325X, this is a bearing type connection in which the threads must be excluded from the shear plane. Finally, if it is designated as A325SC, it is a slip critical connection in which the surfaces must be prepared properly and the bolt must be installed to a specific pretension.
If there is no letter designation the spec may specify what the connection needs to be, otherwise it is generally understood that no designation means "N".

 

[MotorCity]

A few things that need to be mentioned. First, slip critical bolts still need to be checked for bearing even though the connection may not be designed to go into bearing.
Second, SC, N, and X are used to define the type of connection and do not indicate the mechanical properties of the bolt. A A325N bolt has the same mechanical properties as a A325SC bolt.
However, as others have alluded to above, the DESIGN STRENGTH is different for A325N and A325SC bolts.

 

[Veer007]

Hey guys, thank u all for the valuable comments


Both the hex head and twist off type bolts has same strength as each other whereas the connection need to be slip critical?


Thanks in advance!!

 

[Veer007]

I fully agree, MotorCity!!

Thanks in advance!!

 

[Veer007]

Hi dauwerda, A325SC bolts to be pretensioned due to its connection type, but my question is, there is nothing change in the mechanical property/design strength for both A325N and A325SC?

Thanks in advance!!

 

[dauwerda]

Veer007, that is correct. the letters at the end only designate the connection type, both connections use the same A325 bolt.

 

[ingparada]

Los pernos grado A325 de una conexión estructural con asignación A325N y A325SC tienen iguales propiedades mecánicas, pero la diseño de la conexión tendrá un comportamiento diferente.

 

[Veer007]

Thank u all for the valuable comments!!! ifso A325TC and A325N bolts has same strength?

Thanks in advance!!

 

[ingparada]

Yes, but the connection will behave the same as the first case mentioned.