Seismic design of multistorey post-tensioned timber buildings

Student: Michael Newcombe
Supervisors: Dr Stefano Pampanin, Prof. Andrew Buchanan, Dr Alessandro Palermo

ABSTRACT

A new seismic resisting system for multi-storey timber buildings has been developed based on the refinement and adaptation of jointed ductile connections, using post-tensioning technology, originally developed for precast concrete in combination with highly engineered timber, Laminated Veneer Lumber (LVL). The new structural form has been successfully implemented with extensive experimental testing carried out at the University of Canterbury. Herein an analytical and numerical design framework is considered for both the local connection behaviour and the global frame response under seismic loading. Hence, an analytical connection design procedure, originally proposed for precast concrete seismic structural systems, is adapted for the moment-rotation response. The analytically predicted response is then compared with experimental subassembly tests to verify its accuracy. This has been done for post-tensioned connections and a combination of post-tensioning and mild steel reinforcement. For the mild steel reinforcement, aspects of the connection detailing are examined and empirical estimations are made for the strain penetration of epoxied internally reinforcement. The connection response is then extended to the seismic design of frame systems using a Direct Displacement Based Design (DDBD) philosophy. The procedure is slightly modified to account for the special characteristics of the timber connections. The displacement response, interstorey shears and moments for several frames are compared for the design procedure and results from numerical time history analyses. The appropriateness of higher mode amplification factors used within the design procedure specified for reinforced concrete design are verified. In conclusion, guidelines are given that enable a complete design of post-tensioned timber frame systems.

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