24-01-2013, 04:40 PM
Earthquake Resistant Building Construction
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Introduction
On January 10, 2010, an earthquake of 7.0 M magnitude struck Haiti, killing more than 230,000 people. At least 300,000 Haitians were injured and around 1.5 million people became homeless (BBC News: One Minute World News, Americas, 2010). However, in October of 1989, the same magnitude of earthquake in San Francisco killed only 62 people and injured 3757 people (San Francisco Earthquake History 1915-1989). Why did Haiti suffer so much devastation and lost so many of its innocent citizens? (Joyce, 2010) states, “….buildings were barely built to engineering standards and were hopelessly fragile in the grip of such a strong quake.’’
It is clear that there is higher probability for earthquake occurrences in Haiti because it lies on the earthquake zone just above the fault of North American Plate and the Caribbean Plate. The potential for a major earthquake at any given time was always in Haiti. One of the major reasons for such an overwhelming loss of life and property in Haiti is due to inappropriate construction, which lacked earthquake proof designs. Most of the buildings in Haiti were constructed with whatever materials were available, and as the ground shook the un-reinforced masonry and insufficiently constructed frame structures resulted in collapse of buildings leading to unimaginable fatalities.
One of the major reasons for such an overwhelming loss of life and property in Haiti is inappropriate construction, which lacked earthquake proof designs. Now, there are many reliable high-tech practices such as ground isolation, damping of the seismic forces, retro-fittings, and active controls for seismic resistant construction used in developed cities. Unfortunately, constructing earthquake-proof building by these techniques is a challenging task for poor countries like Haiti because they require highly technical and skilled workforce,
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and are expensive as well. A poor country such as Haiti has neither sufficient financial resources nor the skilled workforce, and hence cannot benefit with those practices in spite of the availability of reliable technologies. The selection of affordable and safer construction technology is therefore the only option to overcome these challenges to provide safety to people in poor countries such as Haiti.
The purpose of this research paper is to present some cost effective solutions for constructing seismic resistant houses in developing countries like Haiti. The paper, first, explores and discuses some of the cost-effective housing construction models that are in practice in different parts of the world. Next, the paper identifies techniques and methods for making these buildings earthquake resistant. And, finally, it recommends some affordable construction methods that are earthquake resistant which might be applicable for cheaper and safer construction.
Some Concepts on Earthquake Resistant Construction
Earthquake Casualties
Earthquake is a frequent phenomenon in areas called ‘earthquake zones.’ Earthquakes may create various kinds of casualties like loss of life and damage of property depending upon its magnitude; causalities could range from small property damage to landslides and long range of liquefaction. Secondary effects like fire; blockage on services such as water supply, electricity and transportation; and communication disruption are sometimes even more disastrous. Manmade infrastructures are however the major contributor of casualties during earthquake devastations. These structures therefore should be carefully designed and constructed.
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For examples, the improper placement of partition wall, chimney, staircase, and how water supply, electrical systems are arranged, are responsible for killing people and in facilitating structural damage to property.
Reason for Buildings’ Failure during Earthquake
Vertical and horizontal shaking from earthquakes and inertia of buildings that causes frequent changes in building’s weight, and the use of poor quality materials and massive structures are some of the reasons for building failures. Greater the mass of building, more lateral force is exerted on buildings, and this alone is the major component behind building damages. When there are no strong joint-components like walls, beam, column, roofs, slabs, in buildings, the buildings move independently on their own direction, and velocity of their movements are dictated by the buildings’ weight and orientation, and all these result in separation of a building. The separation of building components and failure to support designed force is actually a building failure.
Earthquake-Resistant Buildings
Buildings with rigid layout (box like structure) with strong joints between different components are generally earthquake proof because rigid buildings react as a single unit to earthquake forces. This is a general practice of constructing an earthquake proof building. According to Ambrose, J. & Vergun, D. (1995),
“A major seimic consideration is that of typing the building together so that it is quite literally not shaken apart.With regard to the structure, this means that the various elements must be positively secured to one another. The detailing of
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construction connections is a major part of the structural designing for earthquake resistane”
However, there are other highly developed approaches as well. In designing and mitigating earthquake, Scawthorn (2007) states, “During the 1980s and 1990s, new approaches to seismic design emerged which involved modifying the structural response to reduce earthquake loads to more tolerable levels. These included base isolation, supplemental damping and active control. Base isolation involves placing special components called isolators within the structure, which are relatively flexible in the lateral direction, yet can sustain the vertical load.” Unfortunately, these techniques require highly technical workforce and is hardly affordable in developing countries.
Low Cost Earthquake Resistant Building Technology and Practices
There are conventional, economical and simple construction practices that can be incorporated in constructing quality earthquake resistant buildings, which can reduce cost and make it safer to live. According to Sarkar (2006), material cost accounts for 70 to 80 percent of the housing construction cost, and this cost should be optimized by choosing appropriate materials.
Adobe Buildings with Earthquake Resistant Components
According to Blondet et al (2003) in the article Earthquake-Resistant Construction of Adobe Building: A Tutorial, in 50 percent of developing countries, more than 30% people use adobe ‘rammed earth’ to construct their house. 73 percent of people in India and 60 percent of people in Peru have adobe buildings because they are less expensive to build for poor rural people. The earthquake resistance quality of these buildings are very weak. However, If properly constructed, adobe building can resist earthquake forces. The state-of-the-art
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research studies and field applications’s research recommend that when a robust layout (box type layout) is incorporated in construction of adobe block and when earthquake resistant components which imporoves adobe building’s seismic performance are used, these adobe structures can resist considerabe amount of lateral forces. Detail guidelines can be taken from ‘Earthquake-Resistant Construction of adobe Buildings: A Tutorial’
3.2 Rice Straw/Wheat Straw Buildings
Rice and wheat straw bale buildings are cheaper and stronger, and are constructed with easily available materials to rural people. These buildings are light and can be used as earthquake proof houses. In Battesby’s (2009) House of Straw, Donovan tries to make an earthquake proof straw house in Pakistan. Using straw, they have tested on shaking table and have achieved good results so far.
Bamboo & Wooden Houses
Stating the reason of earthquake casualties in Haiti, American Wood Council (2010) Says,
“Much of the severe devastation we’ve seen is from collapsed, older un-reinforced concrete and masonry structures and could have been prevented if these structures had been built from wood. Unfortunately, un-reinforced or lightly reinforced concrete and masonry structures can’t dissipate seismic energy or provide ductility under earthquake loads the way wood construction can. A recent full-scale test in Japan demonstrated that a six-story wood apartment building can withstand a 7.5 magnitude earthquake considerably more severe than the one that struck Haiti,”
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Wood being cheaper, wooden structure buildings have been tested during earthquakes, and building wooden houses as a means to safer buildings against earthquake forces are in practice these days. Similarly, bamboo is a well known cheap construction material found everywhere. It has good seismic performance properties; it is lighter in weight and is ductile.
Masonry Buildings with Earthquake-Resistant Components
Stone and brick are most commonly used materials in the world for making load bearing members (walls and footing) of buildings. They are cheaper and readily available. However, they are brittle and vulnerable to earthquake. Hence, most catastrophic effects on every earthquake happen to take place on masonry buildings. But where there is will, there is idea. Engineers and scientists have done plenty of researches on such construction practices for making buildings which can resist great amount of vertical and horizontal forces that resembles earthquake force. Findings from various kinds of shake table shows that masonry can be made earthquake-proof with application of earthquake resisting components. As per Sarkar (2006), earthquake casualties are caused by inappropriately built masonry. Therefore, construction of earthquake resistant masonry requires careful consideration and application of three reinforced cement concrete bands at three different heights of a building; plinth height, lintel height and roof height. Nowadays, this is a general practice in various earthquake resistant housing constructions. This practice helps enhance with the firmness of structures which then can sufficiently withstand average earthquakes forces. Making reinforced cement concrete band might be more reliable and more expensive as well. If Reinforced concrete band is unaffordable, finely seasoned good quality wood or bamboo can be used as a cheaper material for making the bands which also serves well enough.