What is the shear strength of carbon steel bolts?
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, 13th Ed.) (16.1-120, 14th Ed.).
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.
ASTM is material standards. It is the process that defines the test for grading materials. The code which defines if a member fails or not is what you are referring to. For example AISC provides a formula for the ASTM A572 Steel member. The formula will wait her give you the design strength/limit state or the allowable/actual stress of the member. ASTM defines that the member is minimum 50ksi. The formula defines the actual stress or limit state loading.
There are a lot of considerations on bolts. thread form J type have a rounded radius root that lowers stress Concentrations. Stress Concentrations draw free Hydrogen and oxygen causing stress cracking.
In salt water I would use a 316 stainless bolt with a J thread.