Prying Forces

[SALTRAM4567777]

Are prying forces only a concern for HSFG Bolts?
I read somewhere it is only for Pretension bolts.
Also I want to ask how these forces are generared.I have read lot of books but still I am not able to understand propeely.

 

[jimstructures]

Sammy345,

Please give us some information to help understand what your problem is.

Where are you located?

What is the building and material code being used?

What are the loads on your connection?

What is the physical layout of your connections?

Please give us some details of what you are doing?

Nobody is going to write down a graduate level seminar on prying action until you give us some help on what you need or you going to get a smart a** reply of retake your science of material course and you connection course for whatever material and detail you are using.

Give us something.

Jim

 

[SALTRAM4567777]

I was just asking for improving my knowledge.As I was going through Design Guide 16 I read that Prying forces are a convern for Thin Plates onlyi.e Flexible Plates. So I started searching about the same and somewhere I read that Prying Forces are only a concern for Pretension Bolts.
So my question was will prying forces be generated when the bolts are snug tight only.If Yes how ?

 

[HTURKAK]

The answer is YES... The prying forces will develop in the bolts mainly due to the flexibility of connected plates . When only the
ends of the flanges are in contact due to the external load , prying force will develop , as shown in picture below:

The snap from the book ; Steel Structures Design and Practice (by N. SUBRAMANIAN )

 

[SALTRAM4567777]

But how it happens in bolts with no pre load. In case of pre tension bolts the plates are squeezed to maintain equilobrium.As tge load is applied the contaact between the plates becomes less which results in increase in force at tge ends of the flange to maintain equilibrium.But in bolts with no preload there is no contact force between the plates so how prying is generated

 

[MegaStructures]

First of all there is virtually always some pretension in bolts, even a "snug tight" connection adds significant pretension to the bolt. Second of all even if the plates aren't pulled into contact by pretension they can still behave as shown by HTURKAK. Plates start flat, yes? They can also be bent at the "middle" and act like a lever prying the bolt from their holes regardless of an initial force on the bolts. The bolt will tend to not want to stretch from it's initial position, which holds the outside of the plate flat, while the middle flexes, creating the same action shown above.

Great that you are coming here to understand the action better.

 

[HTURKAK]

Look figure 10.12 , the bolt with no preload. Eventually the graph of bolt with preload and and no preload are matching...

 

[SALTRAM4567777]

Yes I saw the figure . I still don't understand how it is possible when the bolts are only snug tight.

 

[HTURKAK]

Snug -tight or (spanner-tight) , when the tightness is attained by a person using a spanner.The prying force may develop for snug tight, finger tight or preloaded bolts mainly depending on the rigidity of connected plates.

If you imagine the deformed shape of the connected plates, see picture below,
the bolt will experience prying force Q .

 

[SALTRAM4567777]

What is the reason for this Q to be generated in flexible plates?
I thought that in case of pretension bolts the plates develop comlressive stress which makes them squeezed.As we apply load on the bolt and tye plate being flexile it loses its contact at the middle.Tbus to maintain equilibrium as Force is inverservely proportional to area .So as area of contact decreases between tge plates the force will have to increase . But for snug tight bolts this ia not the case .

 

[r13]

Sammy,

Preload or no preload, when the tension force introduce a moment in exceed the moment capacity of the flange, the flange will deform, as well as the bolt, and the prying force is the result, which is similar to a lever with fulcrum in the middle and a lift load on the upper end.