Bolted Joint Calculation Example and Conditions


Properly designed boltedjoint calculation example is extremely important for striking the balance between the cost and life of the joint.

As a design engineer, for a good bolted joint design, for a given loading conditions and materials of the abutments, you have to basically select the following design parameters: diameter or size of the bolt or screw, strength of the bolt or screw, preload or tightening torques, selection of the washers.

Bolted machine design
Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts and are secured with the mating of screw threads. There are two main types of bolted joint designs: tension joints and shear joints. In the tension joint, the bolted joint calculation example and clamped components of the joint are designed to transfer an applied tension load through the joint by way of the clamped components by the design of a proper balance of joint and bolt stiffness. The joint should be designed such that the clamp load is never overcome by the external tension forces acting to separate the joint. If the external tension forces overcome the clamp load the clamped joint components will separate, allowing relative motion of the components.

The second type of bolted joint transfers the applied load in shear of the bolt shank and relies on the shear strength of the bolt. Tension loads on such a joint are only incidental. A preload is still applied but consideration of joint flexibility is not as critical as in the case where loads are transmitted through the joint in tension. Other such shear joints do not employ a preload on the bolt as they are designed to allow rotation of the joint about the bolt but use other methods of maintaining bolt integrity. Joints that allow rotation include clevis linkages, and rely on a locking mechanism

How to increase the preload?
How does the preload of the bolt increase as you tighten the nut? Consider the bolt as a helical tension spring, as you tighten the nut you are actually elongating the spring which then, will try to contact itself to go to its natural position and thus will increase the preload. Now, the joint, which is in tension with applied tensile load, will experience the tensile load in the direction opposite to the preload. The resultant force of the preload and applied tensile load is the clamping force for the joint in tension. Clamping force is responsible for keeping any joint intact.

Simple, more the tightening torque you will provide to the bolted joint more preload it will have. The relation between the preload and tightening torque is. Maximum preload or tightening torque you can apply for a bolt is limited by its diameter and the yield strength of the bolted joint calculation example. Apart from the bolt diameter calculation for tensile application, you also need to calculate thread engagement length for the bolt.

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