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.
Have a bolt related question of your own? Try our live chat feature and get the answer you need quickly.
is bolt designed for carrying point load (horizontal load). If yes, then what will be the breaking and bending capacity of bolt and time period of breaking and bending?
@Saif- We are sorry, but we do not have any information regarding bending and breaking loads for bolts used in that way.
How is the shear strength of M16 bolt
@Kabir- We do not have the thread geometry table needed to properly calculate the shear strength for M16 bolts, but can tell you that shear is approximately 60% of tensile. If you know the grade of bolt you are using, you should be able to look up the tensile requirement and calculate the shear from that.
Bolting an attachment to 31,000lbs excavator. Lateral down psi on the bolts at the attachments four points are in question. The psi is created with the attachment placed on the ground and using it to push, pull or raise the excavator tracks off the ground to spin and turn. Front of tracks come off the ground 2’ placing the machines weight on the rear of the tracks. Your thoughts ?
@Steve- Apologies, but we are not able to follow along. What is your question?
would appreciate it if you can inform me of the breaking load of a grade 8 – 3/8 by 10″ bolt. This bolt will be inserted horizontally one on top of each another spaced 8″ apart. load will be in the center of bolt with 4″ of downward vertical pressure supported by 3″ on each end. Basically bolt is going thru 2- 2 by twelves on each end that equals 3″ on each end. A 2 by 4 -3-1/2″ is in between the 4- 2 by 12s. Sorry for my long question. I guess im asking what would it take to snap the bolt in half. Respectfully Robert
@Robert- The breaking load of your bolt can be measured in two ways – shear and tensile. For a 3/8 grade 8 bolt, the shear would be 6,975lbs and the tensile would be 11,625lbs. We don’t have a good way to measure the bending point nor can we account for all the variables at play, but the tensile and shear values should help.
Just yesterday I had a 3/4″ Grade 8 coarse thread bolt snap on me. We have 2 bolts in our distribution hitch for our camper, one is a Grade 5 and the other a grade 8 bolt. I stopped for gas and noticed half of the Grade 8 hanging out of the hitch. We were able to park and pull it all apart. The Grade 5 was bent as well. If the Grade 8 is a 30k lb shear strength, do you have any clue what might have caused this bolt to fail? Our camper is only 9k lbs with only about 1200lbs on the hitch. I can’t imagine anything in that system that would generate close to 30k lbs force.
@Matt- You are correct that the shear force of that grade 8 bolt is about 30k lbs. However, there are more factor at play than just shear. For example, fatigue, the constant loading and unloading of force, can also cause a fastener to fail, and at a lower load than expected. We can’t be certain that fatigue is what’s causing your issue, but something like that caused it to break. An engineer who specializes in fracture analysis could probably shed more light on the subject.