Effect of faying surface condition on the dynamic response of bolted structures

Abstract

Bolted connections significantly influence the dynamic properties of built-up structures due to the nonlinear frictional behavior of the faying surfaces. These effects are influenced by bolt preload, faying surface roughness, interface condition, and excitation magnitude. This experimental study investigates these parameters' effects on the modal frequencies and damping characteristics of a jointed beam specimen. Three specimens with double-lap joints and different interface conditions (clean-mill, sandblasted, epoxied, and a monolithic specimen) were impact-hammer tested at three impact magnitudes and two bolt preloads. The first eight flexural modes and two longitudinal modes were analyzed in the frequency domain (up to 4000 Hz). The findings indicate that bolted joints reduce system stiffness, but adding epoxy to the joint mitigates this effect. A lower bolt preload was found to decrease the natural frequencies of steel-steel interface specimens, while minimal change was observed in the epoxied specimen. Increased modal excitation generally reduced the measured natural frequencies. Changes in damping were found to be mode-dependent, with increased modal excitation reducing damping in lower flexural modes but increasing damping in higher-order flexural modes.