A common question that we get here at Portland Bolt is in regards to the shear strength of bolts. The shear strength is the value at which the lateral stress on a bolt or screw causes it to fail. It is an important factor to take into consideration when designing structural steel or timber connections. Shear strength is also an easy value to roughly calculate when the ultimate tensile strength is known.
Below is a transcript of a recent live chat that we had on our website addressing shear strength. The chat was fielded by our very own Dane McKinnon and serves as a good example of what kind of response you can expect when you ask us a question. We’re substituting a generic name below for the customer to protect their privacy.
- Visitor: Henry
- Operator: Dane McKinnon
- Company: Portland Bolt
- Started: 26 Jan 2010 12:07:57
- Ended: 26 Jan 2010 12:22:18
Henry:
What is the shear strength of grade 8 bolts 1/4″ – 1″
Call accepted by Dane McKinnon. Currently in room: Dane McKinnon, Henry.
Dane McKinnon:
Good afternoon Henry. Shear strength is typically 60% of tensile strength, and the minimum tensile strength of a grade 8 bolt is 150,000 psi. We have an FAQ that addresses this question here: https://www.portlandbolt.com/technical/faqs/bolt-shear-strength-considerations
Henry:
How are all grade 8 bolts the same tensile strength?
Dane McKinnon:
They are all the same tensile strength per square inch. The larger ones have a larger cross section of material, and so are therefore stronger. To calculate the tensile strength of a particular size, you would multiply 150,000 psi by the tensile stress area, found here: https://www.portlandbolt.com/technical/thread-pitch-chart/
Henry:
Thank you
Henry is now off-line and may not reply. Currently in room: Dane McKinnon.
Dane McKinnon has left the conversation. Currently in room: room is empty.
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If a 5/8″x 12″ NC grade 8 bolt has a tensile strength of 150,000 psi. Then the shear strength is 90,000 psi, therefore what is the shear strength in lbs for this 5/8″ bolt?
@Bradley – for shear in the unthreaded shank, the value is 27,611lbf. For shear in the threads, the value is 16,380lbf.
I have 3 AR-500 steel gongs. A 3”, an 8” and a 10”.
I have suspended them from a 2x 12” lengths of chain.
Each Gong had 2x carriage bolts in them. At 50 yards I ripped the carriage bolt tops off and managed to pull the heads through the gong 3/8” square holes.
Would schedule 80 bolts hold up? Or should I mount the to a stationary base over a swinging chain?
Just a bit of info I shot them with a Mossin Nagant” 7.62x54R tulammo…
@Dan- Apologies, but we not able to offer any assistance on this.
@Ozgur Taner: Not true! Lots of bolted connections are designed for shear stresses, especially in designing trusses, mechanical applications such as automotive suspensions, cranes, etc. this is why, single shear and double shear tables are available for bolted connections.
I would like to make some comments about the shear strength questions asked to Dave, which he is answering very well already, but here it goes anyways:
When bolt joints are designed, the intention is not to work them under sustained shear stresses.
It is obviously important to know the shear strength as unintentionally shear stresses may occur due to “slippages” between surfaces may occur, especially when the clamping force weakens, this may be due to many reasons but as an example we can name one: loosened bolts.
The bolt joint designs typically intend is to keep the two overlapping surfaces together and not allow movements,”slippages”, in the direction that is parallel to the overlap surfaces. This is in fact achieved by the friction force which is related to the force applied in the normal direction and friction coefficient between two surfaces (making 90 deg. to overlap surface). Friction is generated by tightening the bolt. In some cases when joint is under dynamic loads, such as vibration and especially cyclic loads, a pre-tensioning is also done. This is mostly why engineers will give torque specs to be followed during assemblies.
If the shear stresses on the bolt cannot be avoided bushings should be used to have the tensile stresses carried by the bolts and the shear stresses carried by the bushing.
Thanks
Ozgur
Making a 20 ton press what grade bolt should I use for the fail point?
@Adam- We are sorry, but we since we do not have any engineers on staff, we are unable to make application specific recommendations. We are happy to talk you through available materials and sizes, but we can’t tell you which is best for this. Apologies.