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The preferred bolt preload for structural applications should be at least 75% of the fastener's proof load [7] for the higher strength fasteners and as high as 90% of the proof load for permanent fasteners. To achieve the benefits of the preloading, the clamping force must be higher than the joint separation load.
ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1 ⁄ 2 to 1 + 1 ⁄ 2 inches (13 to 38 mm) in diameter.
6. (Now withdrawn) Nuts with specified proof load values – Fine pitch thread [7] 7. Torsional test and minimum torques for bolts and screws with nominal diameters 1 mm to 10 mm [8] With exception to part 7, which defines test standards, the parts of this standard define properties for fasteners made of carbon steel and alloy steel.
It is also used in testing a specimen, for a process where the crosshead moves to load the specimen to a specified value before a test starts. Data is not captured during the preload segment. When tensile specimens are initially placed into testing grips, they can be subjected to small compressive forces. These forces can cause specimens to ...
In engineering, a factor of safety (FoS) or safety factor (SF) expresses how much stronger a system is than it needs to be for an intended load.Safety factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the structure's ability to carry a load must be determined to a reasonable accuracy.
Strength depends upon material properties. The strength of a material depends on its capacity to withstand axial stress, shear stress, bending, and torsion.The strength of a material is measured in force per unit area (newtons per square millimetre or N/mm², or the equivalent megapascals or MPa in the SI system and often pounds per square inch psi in the United States Customary Units system).
Tension testing of a bolt up to the proof load should not cause permanent set of the bolt and should be conducted on actual fasteners rather than calculated. [56] If a bolt is tensioned beyond the proof load, it may behave in plastic manner due to yielding in the threads and the tension preload may be lost due to the permanent plastic deformations.
The number of instances the bolt shank can be reached by the feeler gage is then compared to either the results of a pre-installation verification procedure or the manufacturer's instructions. Applied Bolting Technology Products, LLC manufactures self-indicating DTIs, which are a subset of the standard DTIs described above.