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Bolt Shear Strength Considerations

Question: What is the shear strength of carbon steel bolts?

Answer: First, unlike tensile and yield strengths, there are no published shear strength values or requirements for ASTM specifications. The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8) states that shear strength is approximately 60% of the minimum tensile strength.

“As an empirical guide, shear strengths of carbon steel fasteners may be assumed to be approximately 60 percent of their specified minimum tensile strengths. For example, an SAE grade 5 hex cap screw has a specified minimum tensile strength of 120,000 psi. Therefore, for design purposes, its shear strength could be reasonably assumed to be 70,000 psi.”

Quick Tip: For instructions on how to calculate the strength for your bolt, see Calculating Yield and Tensile Strength.

It is important to understand that some imported fasteners, like lag screws, are typically ungraded. Since they are not manufactured to any specific grade, it is impossible to determine any strength characteristics associated with them unless you have them strength tested at a laboratory. For applications where shear will occur in the unthreaded portion the nominal diameter should be used to calculate the value. Whereas, if the shear area is in the threaded section the minor diameter should be used.

AISC provides published values for ASTM A325 and A490 structural bolts listed in Specifications for Structural Steel Buildings under Table J3.2 (16.1-104).

Although, the Strength by Grade Chart has no shear strength information, it shows the strength requirements of common ASTM and SAE grade construction fastener specifications.

Posted by Greg Lindsay

Phone: (800) 599-0565 Email: greg@portlandbolt.com
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The below content is submitted by readers and has not been researched or checked for accuracy. It is not endorsed in any way by Portland Bolt.

10 Responses to “Bolt Shear Strength Considerations”

  1. Dane McKinnon says:

    @MarkSeavey – We do have tensile and yield mechanicals for stainless steels made per ASTM A193 on our website. We do not list shear, but it is typically 60% of tensile. For other grades of stainless I’d be happy to give you what I have if you let me know what grade/specification you are working with.

  2. Mark Seavey says:

    Please advise, where can I get a chart for bolt Shear/tinsel strength for stainless steel bolts.

  3. matt says:

    if you are using a bolt in a high movement/lateral stress area and it keeps breaking

    you might try using either lots of washers or thick spacers. so you end up with a longer bolt.

    examples of this can be found on exhaust manifolds on cars.

    the longer bolt means when the items flexs the angle is less than that of a shorter bolt. sometimes a super tight bolt hole can cause you more problems than benefits. but obviously this is job specific.

  4. Gilbert says:

    It is true that grade 8 bolts are more brittle than grade 5. In general (although not always the case), steels that have a higher strength are less ductile. Grade 8 bolts have a higher strength and, therefore, would require fewer bolts in a joint than grade 5. This may be of benefit in joints that are tight for space. However, depending on the application, it may be preferable to use the weaker and more ductile grade grade 5 bolts. The statement that grade 8 bolts are better than grade 5 cannot be generalized. Consult with an engineer (structural or mechanical) about your particular application.

    The shear strength of bolts is taken as approximately 60% of the tensile strength. This is not a rule of thumb. A large number of tests on high strength bolts tested in shear has indicated that the shear strength is about 62% of the tensile strength. A purely theoretical relationship between shear strength and tensile strength indicates that the shear strength is 58% of the tensile strength. In practice we use 60% as a good approximation of test results and theory.

  5. ben says:

    Herb, you will be better off with a grade 8.

  6. David Benyon says:

    There is a UK company called Bolt Science who have computer programs on bolt tensile strengths (there used to be a free time limited demo as well!) There is also a rule of thumb that puts shear strength as 60% of tensile strength. Put the two together and voila! Note however that antique solid mounted diesel engines can wreak havoc on their mounting frames and won’t be the least impressed with ones clever calculations! Salt can also give unexpected results as tests done a great many years ago on chains showed that they were weaker when immersed in seawater. Ideally the bolts should only be loaded to about 10% of their failure load, possibly 20% on a rough job.

  7. Adam Oakley says:

    Thanks for adding the helpful link, Eric. Even though this is from an automotive standpoint, it looks like there is some good information for industrial and construction applications.

  8. Eric says:

    I found this, which might help.

    http://www.rockcrawler.com/techreports/fasteners/index.asp

  9. Greg Lindsay says:

    @Herb: Due to liability issues and given the fact that Portland Bolt does not have any engineers on staff, we are not in a position to answer questions regarding the use of specific quantities, sizes and grades of fasteners for a specific application. Please consider consulting a structural engineer for assistance with this question. Sorry we couldn’t be of more assistance.

  10. Herb says:

    When a bolt is used in a sheer load is it better to use grade 5 or grade 8? I’ve heard that grade 8 bolts are harder and therfore more brittle. Assuming a good fit with no slop in the assembly or a slightly loose fit – say 25-30 thousandths.

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