Graduate Thesis Or Dissertation
 

Slotted-bolted friction damper as a seismic energy dissipator in a braced timber frame

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  • Friction dampers have been used successfully to dissipate seismic energy in steel and concrete structures. The application is new to timber structures. The objectives of this research were to design a slotted bolted connection (SBC) and evaluate its potential as a passive energy damper in timber brace. The research was conducted in three phases: (1) preliminary tests, (2) single and dual SBC tests, and (3) tests of the dual SBC mounted to a timber brace. The preliminary tests showed that brass shims and compression spring washers contributed to repeatable performance, validated the SBC design using results from the literature, and demonstrated that an SBC with predictable hysteresis characteristics could be designed and fabricated. The expected slip force of 33.4 kN per bolt was reached. In Phase II, tests with six single SBC specimens were conducted following the International Organization for Standardization (ISO) cyclic test protocol. The six SBCs were later assembled in pairs to make three dual SBCs. These pairs were mounted to a metal anchor and tested to evaluate capacity and operational characteristics. The shapes of the hysteresis loops approached ideal and evaluation of the hysteresis diagrams showed that the six single SBCs were similar. The average slip force and energy dissipated for the dual SBCs were twice those of the single versions. For single and dual SBCs, fabrication tolerance reduced the equivalent viscous damping ratio to 0.3 and less for small displacements. However, the effect of fabrication tolerance diminished at greater displacements so that the equivalent viscous damping ratio reached 0.5 or more at larger displacement. Phase Ill evaluated the final design of the friction damper with its connection to the timber brace. The connection to the timber brace was designed so that the yield mode would be Mode llI. The coefficient of friction between the wood and steel surfaces was assumed to be 0.6. Spring washers were included and the bolts were tightened so that a compressive force perpendicular to the grain would be adequate to prevent steel-wood slip even if the block dimensions changed due to change in environmental moisture. Testing showed that bolt tension was sufficient to hold the connection in place so that energy could be effectively dissipated in the SBC5 rather than working the attachment connection. In conclusion, SBC friction dampers can be implemented in a timber brace although the effect on building performance remains to be studied.
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file details TjahyadiAlfred2002.pdf 2017-08-14 Pubblico Scaricare