Nonlinear behavior of single bolted flange joints: A novel analytical model

Flange joints are widely used in mechanical and civil structures. In this study joint deformations are investigated and a detailed model, which can demonstrate the actual joint behavior, is developed. This is done by modeling joint laps and bolts respectively as cantilever beams and springs. Then, an accurate relation between their load and deflection is obtained. It is shown that unlike the lap joints, the flange joints should be modeled using bilinear stiffness. Furthermore, the Euler-Bernoulli theory is used to model dynamic behavior of the beams, which are connected to the flange joint. An analytical procedure is introduced to calculate natural frequencies and mode shapes of two beams, which are connected by a single bolt flange joint. Two experimental setups consisting of a single bolt flange joint specimen and beam-flange system have been designed to investigate static and dynamic behavior of the system. One of the specimens is put into different loading configurations to obtain moment-slope curve. Another setup, consisting of freely suspended beams connected by a single bolt flange joint, is used to investigate natural frequencies of the system. Comparing the theoretical flange stiffness with the experimental and FEM results shows accuracy of the proposed model. Furthermore, dynamic behavior of the proposed beam-spring model is validated using empirical natural frequencies.