Friction Rotational Link for Seismic Dissipation in Steel Frames

A novel seismic dissipater for steel beam to column joints, termed the Friction Rotational Link (FRL), is described. It comprises two fixed plates welded to an end plate, which is bolted to the column flange, and two plates each with circular arch slotted holes, termed external slotted plates and bolted to the beam web. Thin disks are placed between the fixed and external slotted plates to provide stable energy dissipation. All these plates are clamped by high strength bolts. In FRLs energy is dissipated when the slotted plates rotate relatively to the fixed plates. Quasi-static testing of 8 FRLs was undertaken using A325 bolts and disks with Brinell hardness of 91 - 533BH, such as aluminium, brass, steel, and tempered steel. It is shown the FLR hysteresis loop is rectangular. The FRL strength reduced between runs, and it is dependent on the hardness ratio, which is the ratio between the disk hardness and the slotted plate hardness. For high hardness ratios of 2.9, such as for tempered steel disks, the FRL strength was low and almost constant. For hardness ratios of unity, such as for steel disks, the strength was high with an increasing trend. It is also shown the reduction in FRL strength between runs is due to bolt tension loss caused by the degradation of the disks and the slotted plates surfaces (rotational interfaces). Two types of degradation of rotational interfaces were observed: abrasive for steel disks, and adhesive for aluminium, copper, and tempered steel disks. While in the abrasive degradation, the rotational interfaces are abraded producing high bolt tension loss, in the adhesive rotational mechanism, the rotational interfaces are only smoothly degraded producing low bolt tension loss.