The unbonded post-tensioned rocking and dissipative technology was first developed as the main outcome of the PRESSS (PREcast Seismic Structural Systems) Program in US. After the first developments and significant refinement, the technology was extended to steel and, more recently, timber structures. The timber version, referred to as Pres-Lam (Prestressed laminated) system can be either implemented for timber walls (single or coupled) or frames or combination of the above, with unbonded post-tensioning and supplemental dissipation devices.
In unbonded post-tensioned dissipative wall systems a combination of re-centering capacity and energy dissipation leads to a “controlled rocking” mechanism which develops a gap opening at the wall base. This generates an uplift displacement which is transferred to the floor diaphragm. This vertical displacement incompatibility can represent a potential issue if the connection detailing between floor and lateral resisting system is not designed properly. The same issue can be mitigated by adopting an alternative configuration of the rocking/dissipative wall system, based on the use of a column-wall-column post-tensioned connection. This concept, originally proposed for precast concrete walls and referred to as PreWEC (Prestressed Wall with End Column), has been extended and adapted to posttensioned timber structures and validated through experimental testing.
The paper presents the design, detailing and experimental testing of a two-thirds scale wall specimen of this alternative configuration. Different wall configurations are considered in terms of post-tensioning initial force as well as dissipation devices layout. The experimental results confirm the excellent seismic performance of the system with the possibility to adopt multiple alternative configurations.
New Zealand Society for Earthquake Engineering Conference
March 21-23, 2014, Auckland, New Zealand
The paper presents the design and construction detailing of the quasi-static testing of two post-tensioned timber wall systems: a single (more traditional) wall system and a new configuration comprising of a column-wall-column coupled system (CWC). The latter allows avoiding displacement incompatibilities issues between the wall and the diaphragm by using the boundary columns as supports.
Different reinforcement configurations were taken into account for both the wall systems; the walls were subjected to different initial post-tensioning stress levels, and different dissipater options were considered: both internal and external replaceable mild steel tension-compression yield fuses, and U-shape Flexural Plates (UFPs) were used for the single wall and the CWC solutions respectively.
The experimental results showed the high-performance of both post-tensioned timber wall systems with negligible level of structural damage in the wall element and residual displacements and high level of dissipation.