Behaviour of post-tensioned timber columns under Bi-directional seismic loading

Moment-resisting frames made of laminated veneer lumber (LVL) in combination with unbonded post-tensioning have recently been proposed for multi-storey timber buildings. Prefabricated and post-tensioned timber frames can be designed to have enhanced re-centering and energy dissipation after seismic loading. The unbonded post-tensioning provides re-centering capacity while energy is dissipated through the addition of special dissipating devices which also act as external reinforcing. As part of a research program on multi-storey timber structures, this paper describes experimental and analytical studies to investigate the behaviour of post-tensioned LVL columns under uni-and bidirectional seismic loading. The results show excellent seismic performance, characterized by negligible damage of the structural members and small residual deformations, even under the combined effect of loading in two directions. Energy is dissipated mostly through yielding of external mild steel dissipaters connecting the column and the foundation, which can be easily removed and replaced after an earthquake. Since post-tensioning can be economically performed on site, the system can be easily implemented for either column-to-foundation connections in multi-storey timber buildings as well as for pier-to-foundation and/or pier-to-deck connections in timber bridges.