Design principles
Less rigidity in buildings and a combination of flexing and tensile strength allows for more resistance to earthquakes.[expansion needed] Lightness of the building material reduces likelihood of injuries or of people becoming trapped if the building does collapse,
In approximate order from most safe to least safe building materials:
- Bamboo (very safe)
- Timber
- Quake Safe building (with wires and sticks or poles frame
- Reinforced concrete (May be very resistant in the case of buildings designed for the purpose of earthquake resistance.)
- Brick or adobe (single storey)
- Unreinforced concrete (single storey) (Very unsafe)
- Brick, adobe, or unreinforced concrete, multi-storey. (Extremely unsafe)
More high tech solutions are used in modern cities that are prone to earthquakes, such as Taipei, Tokyo or Los Angeles. Even multi-level concrete and brick housing is made highly earthquake resistant through reinforcing and flexibility.
How Did Eighty Nine Year Old House Survive Nisqually Earthquake?
An old house and its occupant were kept safe by earthquake mitigation measures, including anchoring the house properly to the posts it sat on.
The neat little white house on a hill does not look its 89 years. It looks the same as it did before the February 28, 2001 earthquake that shook the Puget Sound area in Washington state, USA, with violence measured at 6.8.
But there is a hidden difference. Before the quake, the house was just there, sitting. Now it hunkers down, ready to stubbornly resist the next shaking by tectonic plates.
The difference cost barely $3,300 and is pretty much low tech: some hunks of plywood, a collection of two-by-six inch planks and two-foot metal straps, nails, anchor pins and about 40-hours of work by a contractor.
That is Mrs. Doris Chapot's dream home and it details in layman's terms the vaguely understood words "mitigation" and "retrofitting." Without that work, the home could well have been tipped from its underpinnings or maybe been sent on a downhill slide toward Liberty Bay, with the 80-year-old occupant along for a frightening ride.
Instead, "Not one thing in the house fell or broke. The house rode beautifully," she told a mitigation worker for the Federal Emergency Management Agency (FEMA).
When Mrs. Chabot, widow of a building contractor, moved from California in 1998, her home was perched on 40 six-by-six inch posts. Those posts, each about 24-inches tall, stood atop 10 or 12-inch high pier blocks and were spaced out every six feet around the circumference of the home. One row of them ran down the middle of home-only gravity kept things in place.
From her life in California, Mrs. Chabot knew about earthquakes and the importance of mitigation. After recovering from a health problem, she contacted Northwest Renovations and met contractor Rich Reidesel.
Reidesel learned that the comfortable home was built in 1902 as a church parsonage and was moved to its present location in 1940, when it was placed on the posts and pier blocks.
Working in the two feet of crawl space under the house, Reidesel linked the posts with stout planks and nailed metal straps to the posts. The bottom of each strap was anchored to a pier block with a stout sheer pin.
Slabs of thick plywood were nailed in place as gussets linking the beams under the home's floor to the posts and the planks. Reidesel's work is an example of only one of a variety of mitigation methods.
"I do know the importance of this work and I remember having my homes in California retrofitted because of earthquakes," Mrs. Chabot said. Those homes survived several good shakings.
"When this quake hit, I was in a little sitting room on the second floor, looking through some books. It felt like almost a circular rolling motion instead of a jolting," she said.
"The only things that moved in the house were a couple of pictures that tipped a little and some books on a table downstairs. There were too many books for the little book ends to hold," Mrs. Chabot said.
Prior to the Nisqually quake, Mrs. Chabot quickly learned that Reidesel's work had made her home safer.
"Before I could feel the house vibrate when heavy trucks drove by. I have my washer and dryer in a little service alcove at the back of the house. When they were running, my lamps would rattle.
"Now," Mrs. Chabot said proudly, "I don't feel anything. I don't feel the trucks, nothing moves when my washer and dryer are working." The house survived the quake with absolutely no damage, and Mrs. Chabot only had to straighten a couple of pictures and pick up a few spilled books.
Reidesel was equally happy with his work. "It withstood the quake the way we believed it would."
