On the re-evaluation of the clamped members stiffness of bolted joints

To address structural integrity of bolted joints and verify their capacity to withstand external loads and relaxation resulting from thermal expansion difference and creep, proper evaluation of the axial stiffnesses of bolt and clamped members are of vital importance. A number of finite element (FE) based methods are available for the calculation of the stiffnesses of joint elements, most of which rely on the displacement of arbitrarily selected nodes that has led to the improper evaluation of joint stiffness values. In this paper, the stiffness of clamped members is evaluated by a simple finite element methodology using a known bolt stiffness evaluated separately. Two load cases, one based on the application of external force (mechanical loading) and the other on temperature (thermal loading) are conducted using the FE method to validate the obtained results. The proposed methodology is also compared with other FE models and analytical methods obtained from literature. The new technique is based on an axisymmetric FE modeling and is applied to bolted joints with bolts ranging from M6 to M36 having various grip lengths. Finally, the stiffnesses of the bolt and clamped members can be determined accurately and a general formula is proposed to evaluate the stiffness of clamped members.