Abstract:

In ESDU 13015, the effects of bolt and member stiffnesses on loads in pre-loaded bolted joints are reviewed. The stiffness of the bolt can be calculated simply by separating the gripped length of the bolt into an unthreaded and threaded portion. Bolt stiffness is then found to be a function of the gripped length, the cross-sectional area of the bolt and the Young's modulus of the bolt material (see ESDU 13008 and ESDU 85021 for further details). Determining the stiffness of the members is more complex, however. Member stiffness during pre-loading and external loading can be estimated using one or other of the following; the cylinder method, or the pressure cone method. Alternatively a finite element analysis can be applied. These three methods to calculate member stiffness are compared using a worked example.