Viscoelastic Material as a Seismic Protection System for Wood-Framed Buildings.
The Northridge earthquake demonstrated the susceptibility of wood-frame structures to seismic events. Approximately one half of the 40 billion dollars of damage was attributed to wood-frame construction, with a majority of the financial losses associated with non-structural damage (CUREe, 1999). One consequence of the Northridge event has been a focus on the development and implementation of innovative techniques to reduce the damage of wood-frame structures subjected to earthquakes. The objective of this study is to present recent innovative applications of viscoelastic (VE) material to wood. Twelve viscoelastic dampers were tested under static loading to failure. Half of the dampers were comprised of VE material and A36 steel, typical of most VE dampers, while the other half used wood in lieu of steel. Two wood and steel specimens were tested for each of the three different thicknesses of VE material used. Comparison of the replicate dampers showed that there was no difference between the performance of the steel and wood dampers. Failure was characterized by a shear failure in the VE material at strains in excess of 500%. There was no delamination between the wood and VE material. Based on the results of the static damper tests, one full-scale (2.4 m by 2.4 m) shear wall that incorporated a thin layer of VE material between the stud frame and sheathing was tested cyclically under the Sequential Phased Displacement, SPD, test protocol. The SPD test was conducted at a frequency of 1 Hz. to a maximum displacement of 76 mm. Comparison of the hysteresis of the damped wall to conventional (undamped) walls showed that the addition of the VE sheet material increased the energy dissipation capacity of the wall 20 percent over a range of displacements. The increase in energy dissipation capacity will aid in reducing the structural response; thereby reducing the costly secondary damage typically seen in wood-frame structures in seismic events. However, it must be emphasized that only one full-scale test was conducted and that further testing is necessary to verify these initial results. The damper tests indicated that VE material could be applied directly to wood. The initial fullscale results showed that the application of viscoelastic sheet material between the sheathing and wall frame could be an effective method for improving the energy dissipation characteristics of wood-frame shear walls. Furthermore, the installation of the sheet material was such that there was no impact to the dimensions of the wall. This innovative application of VE material could be used in new design or the retrofitting of wood-frame structures.
|Main Author:||Dinehart, David W.|
|Other Authors:||Lewicki, David E.|