Cyclic tests of an innovative seismic bracing member - multiple U-shaped flexural plates dissipater

Abstract

Following Canterbury earthquake sequence, there has been an increasing interest in development of low-damage structural design using supplemental damping such as the use of metallic dissipaters. In this research, an innovative seismic bracing member called multiple U-shaped flexural plates (UFP) dissipater (MUD) is proposed. It consists of two rows of UFPs bolted to an internal member and inserted inside a casing. The internal and external members move relative to each other under axial compression and tension loading. Energy dissipation comes from plastic deformation (rolling deformation) of the UFPs. A series of quasi-static cyclic tests were conducted with different arrangements of UFPs and various loading sequences. The mechanical properties, hysteretic characteristics and strength degradation of MUD were investigated. All specimens completed the cycles of displacement corresponding to a 2.8% story drift ratio. The dissipater exhibited stable force-displacement hysteresis and high energy dissipation capacity. Specimen 1, 2 and 3 have been through 28 loading cycles without significant degradation of strength. Specimen 4 has been through three times the maximum credible earthquakes and 46 loading cycles at 2% inter-storey drift ratio (corresponding to a diagonally braced frame with a storey height of 3.0m and a bay length of 3.1m). There was no significant degradation of strength until the last 10 loading cycles where the strength and stiffness started to reduce moderately due to cracking of UFPs.