Seismic shock absorbers for woodframe houses

Jun 20, 2006
Seismic shock absorbers for woodframe houses
Michael Symans of Rensselaer (left) and Andre Filiatrault of the University at Buffalo with the seismic damper installed inside a bedroom wall of the NEESWood townhouse. Credit: Credit: University at Buffalo/Parisi

As part of a major international project to design more earthquake-resistant woodframe buildings, an engineer from Rensselaer Polytechnic Institute will be testing a damping system designed to act as a seismic shock absorber. The dampers, which have never been tested before in wood construction, will be installed inside the walls of a full-scale, 1,800-square-foot townhouse -- the world's largest wooden structure to undergo seismic testing on a shake table.

The unprecedented testing is part of a $1.24 million international project called NEESWood, funded by the National Science Foundation through its George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) program. The goal of NEESWood is to safely increase the height of woodframe buildings in active seismic zones through the development of a design approach that considers a wide range of performance levels -- from completely undamaged to almost collapsing.

The height of woodframe buildings traditionally has been limited to about four stories, mainly due to a lack of understanding of how taller structures might respond to earthquakes and other natural disasters. "We don't have accurate physical data to fully define how wood structures behave in earthquakes," said Michael Symans, associate professor of civil and environmental engineering at Rensselaer. "We have some models, but their accuracy has not been verified with full-scale test data. This experiment will help us to further evaluate and refine those models."

Symans will be supervising the damping tests at the University at Buffalo's Structural Engineering and Earthquake Simulation Laboratory (SEESL), which is home to two adjacent three-dimensional shake tables where the test structure is anchored.

On July 6, a demonstration of the damper test will be open to the media, as well as broadcast live on the Web at http://nees.buffalo.edu/projects/NEESWood/video.asp.

One approach to limiting the damage in woodframe structures is to look at the problem from an energy point of view, according to Symans. In an earthquake, the shaking ground imparts a certain amount of energy into the structure -- energy that must eventually be dissipated. During the earthquake, some of the energy is transformed to kinetic energy -- moving a building from side to side -- or to strain energy, in which the structural framing system becomes so deformed that it can be permanently damaged or even collapse. The goal of the dampers is to absorb a large portion of the earthquake energy, much like shock absorbers in a car absorb bumps in the road.

The damping system is essentially made up of fluid-filled shock absorbers installed horizontally throughout the walls of the house. "If we can channel some of the energy into the dampers, we can reduce the strain energy demand and thus reduce damage to the structure," Symans said. The damping technology has been applied to steel and concrete buildings, but never before to wood structures. For the NEESWood experiment, the fluid dampers are being donated by Taylor Devices Inc., of North Tonawanda, N.Y.

"For the longest time, building codes have been prescriptive -- the designer is told what to do to meet certain specifications, without explicit consideration given to the expected performance," Symans said. But lately there has been a shift in thinking as more large earthquakes have hit high-population areas. About half of the approximately $40 billion in loss caused by the 1994 Northridge earthquake in the Los Angeles region was associated with wood structures, Symans notes, and this was much more damage than the general public expected. "The perception among building owners and the general public is that if a structure is built according to code, it will perform well during an earthquake," he said. "This is true of snow, rain, and other typical severe weather conditions, but not necessarily for hurricanes and earthquakes."

Previous large-scale shake table tests have been performed on simple, box-like structures, but the NEESWood Project involves testing of a much more realistic building, Symans said. The townhouse in this experiment has balconies, an atrium, and other defining features that are more likely to be in the floor plan of a real woodframe residential building. As the testing progresses, the team will be adding finish materials to the building, culminating in November with the violent shaking of the furnished, three-bedroom, two-bathroom townhouse -- mimicking what an earthquake that occurs only once every 2,500 years would generate, according to Symans.

Phase 1 will be a benchmark test of the "bare bones" structure. Phase 2 will test the dampers on this benchmark building, and then finish materials will be added for each additional phase to test how these affect the response of the structure. Each phase will be run at increasingly higher levels of shaking, designed to simulate the increasing intensities that were recorded during the Northridge earthquake.

Source: Rensselaer Polytechnic Institute

Explore further: Reading speed harnessed to automatically control text display rates

add to favorites email to friend print save as pdf

Related Stories

How animals survive Norwegian winter nights

8 minutes ago

Norwegian mammals and birds have many different methods of surviving long, intense winter nights. A biologist from the Norwegian University of Science and Technology (NTNU) University Museum reveals their ...

Pollution documentary attracts huge interest in China

18 minutes ago

A slick new documentary on China's environmental woes has racked up more than 175 million online views in two days, underscoring growing concern in the country over the impact of air, water and soil pollution.

Giant methane storms on Uranus

18 minutes ago

Most of the times we have looked at Uranus, it has seemed to be a relatively calm place. Well, yes its atmosphere is the coldest place in the solar system. But, when we picture the seventh planet in our ...

Should Australia consider thorium nuclear power?

18 minutes ago

Australia has developed something of an allergic reaction to any mention of uranium or nuclear energy. Blessed as we are with abundant reserves of coal, oil and gas, we have never had to ask the hard questions ...

Recommended for you

Large-surface light-emitting plastic film

14 hours ago

Based on OLED technology and implemented by means of a printing machine, this method developed by VTT Technical Research Centre of Finland Ltd provides an opportunity to create patterned and flexible light-emitting ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.