Bolts and other types of connectors in structures undergo forces as the structures are loaded and unloaded. One of the forces that affect bolts is shear stress. When a bolt connects two or more parts, each of the parts can impart separate forces on the bolt, often in different directions. The result of these opposing forces on the bolt is shear stress at the plane through the bolt between the two connected components. If the shear stresses in the bolt are too high, the bolt can break. An extreme example of shear is the use of bolt cutters on a bolt. The two blades of the cutters impart opposite forces on a single plane of the bolt, resulting in a cut bolt. Determining the shear stress in a bolt is a straightforward calculation using only a few inputs.
Use the ruler or digital calipers to measure the thickness of each part of the bolted assembly. Label each thickness t1, t2, t3, and so on.
Calculate the shear stress using the formula F/(d*(t1+t2)) if the bolt connects two plates where each plate is subjected to a force (F) in opposite directions. This load case is called single shear. For example, if two plates with 1-inch thicknesses are connected by a bolt with a diameter (d) of 1 inch, and each plate is subjected to a force of 100 lb, shear stress is 100 lb/ (1 inch * (1 inch + 1 inch)), or 50 psi.
Calculate the shear stress using the formula F/(2d_(t1+t2+t3)) if the bolt connects three plates, where the center plate experiences a force in one direction and the other two plates experience a force in the other direction. This load case is considered double shear because shear occurs in two different planes in the bolt. For example, if three plates with 1-inch thicknesses are connected by a bolt with a diameter (d) of 1 inch, and the plates are subjected to a force of 100 lb, shear stress is 100 lb/(2_1inch*(1 inch + 1 inch + 1 inch)), or 16.7 psi.