Abstract <p>In large gas turbines, rubbing between the rotor and casing is a common failure that can occur simultaneously at multiple locations. Bolted joints are widely used to fasten adjacent disks together for ease of maintenance and assembly. The stiffness softening effect caused by the piecewise linear stiffness characteristics of bolted joint has a significant impact on rotor dynamic properties, especially in the presence of a rotor-casing rubbing fault occurrence at multi position. In this work, a dynamic model of a bolted joint rotor-casing system is developed using the lumped mass method, incorporating the nonlinear stiffness of bolted joints, bearing forces, and fixed-point rubbing at multiple positions. The dynamic properties of the system under different rotor-casing clearances and the transition points of bending stiffness are examined in detail using bifurcation diagrams,spectrum cascade, etc. The results show that rubbing faults trigger earlier entry into the stiffness-softening area of the bolted joint and accelerate the softening process. This phenomenon is considered as one of the main causes of system response instability. These results are validated experimentally on a rotor test rig equipped with rubbing devices. The investigation results can provide a reference for diagnosing rubbing faults in large turbines with bolted joint structures.</p>