The paper presents the design and detailing, and the experimental quasi-static 2/3 scale tests of two posttensioned wall systems: a single (more traditional) wall system (Figure 2) and a new configuration comprising of a column-wall-column coupled system (Figure 3). The latter allows avoiding displacement incompatibilities issues between the wall and the diaphragm by using the boundary columns as supports.
This article presents recent research on the seismic resistance of coupled post-tensioned timber walls for use in multi-story buildings. The walls are constructed from laminated veneer lumber (LVL), post-tensioned with unbonded vertical tendons, and coupled together with mild steel U-shaped flexural plates (UFPs) as energy dissipating elements. The timber wall design follows the same principles as used for post-tensioned precast concrete wall systems, using U-shaped plates to obtain a “hybrid” system, where energy is dissipated through yielding of the plates, while the vertical post-tensioning provides the restoring force. In this project, the same principles are applied to timber coupled walls. A series of quasi-static cyclic and pseudo-dynamic tests have been carried out to verify the applicability of the concept and the feasibility of the construction technology in timber buildings. The U-shaped plates showed stable energy dissipation characteristics and, in combination with the post-tensioning, desirable re-centering hysteretic behavior typically referred to as “flag-shape”. Because of the simplicity of these elements and the low cost of implementation, they have good prospects for practical application.
Timber-Concrete Composite (TCC) systems are comprised of a timber element connected to a concrete slab through a mechanical shear connection. A large number of T-beam configurations currently exist; however, the growing availability of panel-type engineered wood products (EWPs) in North America in combination with a concrete topping has offered designers and engineers greater versatility in terms of architectural expression and structural and building physics performance. The focus of this investigation was to experimentally determine the properties for a range of TCC systems in several EWPs. Strength and stiffness properties were determined for different TCC configurations based on small-scale shear tests. Eighteen floor panels were tested for elastic stiffness under a quasi-static loading protocol and measurements of the dynamic properties were obtained prior to loading to failure. The tests confirmed that calculations according to the -method can predict the basic stiffness and dynamic properties of TCC floors within a reasonable degree of accuracy. Floor capacities were more difficult to predict, however, failure occurred at loads that were between four and ten times serviceability requirements. The research demonstrated that all selected connector configurations produced efficient timber-concrete-composite systems.
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.
Laminated veneer lumber (LVL) structural members have recently been proposed for multi-storey timber buildings based on ongoing research at University of Canterbury, New Zealand. The members are designed with unbonded post-tensioning for recentering and energy dissipation through the ductile connections. This paper describes the experimental and numerical investigation of post-tensioned LVL walls coupled with plywood sheets, under quasistatic cyclic testing protocols. It is observed that energy is dissipated mostly through yielding of the nails, and the LVL walls return close to their initial position while remaining virtually undamaged. The same specimen has been tested under repeated cyclic loading to investigate the performance of the arrangement under more than one seismic event (a major earthquake followed by a significant aftershock). Different nail spacing and arrangements have been tested to compare their energy dissipation characteristics.
The results indicate good seismic performance, characterized by negligible damage of the structural members and very small residual deformations. The only component significantly damaged is the nailed connection between the plywood sheet and the LVL walls. Although the nails yield and there is a reduction in stiffness the system exhibits a stable performance without any major degradation throughout the loading regime. The plywood can be easily removed and replaced with new sheets after an earthquake, which are reasonably cheap and easy to install, allowing for major reduction in downtime. With these additional benefits the concept has potential for consideration as an alternative solution for multi-storey timber buildings.
New Zealand Society for Earthquake Engineering Conference
April 13-15, 2012, Christchurch, New Zealand
The following paper presents the seismic performance of a two storey
post-tensioned Laminated Veneer Lumber (LVL) building during the aftershock sequence
following the MW 6.3 Canterbury earthquake that occurred on 22nd February 2011.
Composed of post-tensioned walls in one direction and post-tensioned frames in the
other, the structure under analysis was originally tested quasi-statically in the structural
laboratories of the University of Canterbury (UoC), Christchurch, New Zealand.
Following testing the building was demounted and reassembled as the offices of the STIC
(Structural Timber Innovation Company) research consortium on the UoC campus with
several significant changes being made to convert the building from its initial use as a test
specimen into a functioning office structure.