Experimental Behaviour of Friction Joints with Different Bolting Assemblies and Disk Springs Layout

Recent research studies have demonstrated that Friction Joints (FJs) offer an optimal solution for Moment Resisting Frames in seismic regions. Unlike traditional beam-to-column joints, FJs can absorb significant amounts of energy while causing minimal structural damage. The slip resistance of FJs, whether utilizing Symmetrical or Asymmetrical Friction Connections is heavily influenced by factors such as initial friction coefficient, bolt preloading, and their behaviour under cyclic loading. Recent findings have highlighted how techniques such as bolt preloading, creep, vibration, and friction shimwear during post-sliding phases can diminish initial preload, thereby reducing joint flexural resistance. Installing Belleville Disk Springs (BDSs) in bolting assemblies presents a potential solution to mitigate preload loss. These conical washers adjust the bolting assembly's stiffness, compensating for short- and long-term effects and potential damage at the friction interface post-sliding. To assess BDSs' effectiveness in reducing preload loss, an experimental study was conducted at the STRENGTH Laboratory of the University of Salerno. This study monitored parameters including preload force evolution and slip resistance across four beam-to-column joints with varying BDS layouts. Ultimately, joint performance was compared based on the stability of their hysteretic response.