Multistage Friction Connections

Abstract

Multistage friction connections (MFCs) are bolted connections for dissipating seismic energy while reducing peak displacements and encouraging recentring. MFCs comprise two symmetric friction connections co-linearly assembled. Each friction connection dissipates energy by sliding a slotted plate on high hardness shims placed either side of the slotted plate. One of these friction connections is assembled with fewer bolts than the other; thus, the MFCs ends are termed the weak and strong ends. MFCs have been recently proposed. However, to date, no experimental validation is available. This paper describes the assembly, sliding mechanism, and applications of MFCs in steel frames. Monotonic testing was undertaken on 3 MFCs assembled with tempered steel shims (hardness = 500BH), A36 steel slotted plates (Fy = 250MPa, Fu = 325MPa), and A325 bolts (Fy = 635MPa, Fu = 835MPa). Results show the MFCs force-displacement curve has two force steps representing the sliding of the slotted plate at the weak and strong ends. The ratio between these two forces, is the ratio between the number of bolts at the MFCs ends. The initial stiffness is steep and corresponds to the MFC axial stiffness without sliding. The second stiffness is less than the initial due to the combined action of the initial stiffness, and the bolt bending stiffness at the MFC weak end and resulting from bearing between the bolt and the slotted plate. These experimental results were used for proposing a simple model for the MFCs monotonic force-displacement curve.