Earthquake-proofing for buildings is an essential issue in geologically unstable areas. In order to assess on whether a region lies in an area where substantial earthquakes occur, we first take a look at the earthquake hazard map. Another thing to realize is that, despite the name, the building can (almost) never be made completely earthquake-proof, in most cases, the house will still suffer damage or may still be destroyed, but the "earthquake-proofing" will prevent or reduce the loss of human lives in the process.
Design principles[edit | edit source]
Design and choice of building materials have a major impact on a building's earthquake safety. 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. The most crucial parts of the house that need to be light/shock-proof are the roof, the walls themselves can also be made shock-proof with new structures however.
In general, the building thus needs to be well designed and built in order to ensure withstanding earthquakes. In most locations however, the buildings are already present, and rather than rebuilding the entire house, modifications are best done instead. Besides being faster and easier, this method also reduces cost.
Performance of construction materials[edit | edit source]
- Bamboo: Bamboo is lighter in comparison to timber, attracting less seismic forces. It has a high strength/weight ratio and higher bending strength than timber. However, it requires maintenance to protect it from biological decay.
- Timber: Seismic resistance is relatively high due to light weight (comparative to masonry) and flexibility of nailed joints. As long has materials and workmanship are of good quality, timber structures can perform very well in an earthquake. Infill walls that are not load-bearing provide a means of dissipating seismic energy as they crack. A wood frame house is usually considered to have medium-to-low vulnerability to earthquakes.
- Confined masonry: Performance under seismic load can be satisfactory, but failure will occur where tie columns and beams are not used, where there are poor roof-wall connections or if poor quality materials or workmanship is used.
- Reinforced concrete: There have been many instances where reinforced concrete frames have been inadequate to withstand earthquakes, not because they cannot be well designed, but because in many countries it is difficult to maintain good construction practice. This results in unpredictable modes of failure, like shear failure and concrete crushing.
- Unenforced masonry (brick, adobe, stone): Unenforced masonry has shown to perform poorly in an earthquake, performance depends on strength of mortar and units, interlock between walls, roof-wall and wall-wall connections and the quality of construction.
High technology solutions are used in modern cities that are prone to earthquakes, such as Taipei, Tokyo or Los Angeles. These include seismic isolation and passive energy dissipation devices. Multi-level concrete and brick housing can be designed to be highly earthquake resistant through reinforcing and flexibility of connections.
Implementation[edit | edit source]
Building modifications[edit | edit source]
Building modifications are, as mentioned above, the best option in most cases. They perform very well (depending of course on the execution), and are more affordable, or more suitable to rural contexts, or where modern exacting building techniques are not practical:
- Quake Safe: building with wires and sticks or poles inside and outside a house's brick or adobe walls, to prevent or slow their collapse. The wires are best made C2C-compliant;
- Super adobe, adobe reinforced with barbed wire or [plastic]] or nylon chicken wire/mesh. Plastic and nylon however are not cradle-to-cradle materials, and are thus best swapped for galvanized steel, ... Also, the adding of another layer (ie plaster; see PAKSBAB-project) to the walls is best either avoided or done in such a way that they can be easily separated, again a requirement for C2C building.
- Tyre filled with sand bags can be used as ground-motion dampers, particularly for brick buildings such as in Indonesia. John van de Lindt of Colorado State University. Since tyres contain several non-cradle-2-cradle materials, this method is not ideal from an ecological point of view.
- The Indonesia Aid Foundation, Inc has a design and a project to produce affordable houses (US$1000) on an assembly line.Quake Housing.
- Plates floating on ball bearings (on a curved metal surface) are another method. Similar to sand-filled tyres though, implementation to existing houses would require the temporarily lifting of the house to insert them. This method is by far the best, and appearantly, when done properly (ie with correct curvature of the underground) can withstand any earthquake, regardless of its force.
New building designs[edit | edit source]
- Bamboo is lightweight and bends, and does little damage if it falls. However a simple bamboo building provides little protection from weather.
- Timber is widely used in the USA (California)
- Reinforced concrete may be very resistant in the case of buildings designed for the purpose of earthquake resistance.
- Confined masonry, if built correctly, performs very well in earthquakes. It uses the same materials found in reinforced concrete frame masonry construction, in a different construction sequence and design.
- Straw can be used as building walls. See PAKSBAB project
How Did Eighty Nine Year Old House Survive Nisqually Earthquake?[edit | edit source]
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."
References[edit | edit source]
- EEarthquake-proof earth ships tested in Andaman islands, Haiti
- http://ngm.nationalgeographic.com/big-idea/10/earthquakes NGM The big idea: Safe houses]
- Plastic chicken wire
- Safe Houses, p2, 2010.
- Earthquake-proofing using ball bearings on curved underground
- Ball bearings description
- Ball bearings
- Characteristics of bearings platform