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.”
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.
Herb, you will be better off with a grade 8.
October 23, 2009 at 10:18 amThere 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.
August 19, 2008 at 2:48 pmThanks 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.
July 11, 2008 at 9:55 amI found this, which might help.
http://www.rockcrawler.com/techreports/fasteners/index.asp
July 11, 2008 at 7:30 am@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.
April 24, 2008 at 7:50 amWhen 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.
April 24, 2008 at 4:58 am