Picking up the pieces after an earthquake
THE aftershocks of earthquakes can cause as much damage to people’s lives as the initial earthquake itself. It was with great sadness and despair in April that I read an article in The Borneo Post entitled, ‘Billions to rebuild post-quake Nepal being misdirected’. We can all remember that magnitude 7.8 earthquake on the Richter scale in April 2015. Millions of dollars poured into Nepal, from donors worldwide, to assist the 708,000 families whose homes had been devastated.
An organisation, Build Change, looked at salvaging some houses by retrofitting their structures to not only secure fractured parts but to make them more resistant to future earthquake damage.
The day after that article another news item appeared entitled. ‘Scars begin to heal after the Sichuan quake’. This brought a ray of hope to my heart to see what had been achieved in China in the aftermath of the Beichuan centred 7.9 quake of May 2008. There many homes have been repaired to meet new health and safety standards. In both aforementioned earthquake zones, the grief of loss of life of loved ones still remains and it is easy to ask in hindsight how the collapse of buildings could have been prevented? Building designs A single-storey building responds quickly to earthquake forces with minimum damage. A high-rise building responds slowly as shock waves are increased as they move up the building’s structure. Should high-rise buildings be too close together, as occurs in the Central Business Districts of cities, where land rental values are high, vibrations may be amplified between buildings increasing the damage caused.
In any building, its weakest parts are where different elements/structures meet. Elevated motorways, flyovers and bridges are therefore more vulnerable in earthquakes because they have many interconnecting parts as exemplified in the San Francisco earthquake along the San Andreas Fault in 1989. A section of the San FranciscoOakland Bay’s concrete upper deck collapsed on to the lower deck and a short distance away a similar incident occurred in the collapse of a freeway both resulting in a total of 43 fatalities.
Some areas with mechanically weaker rocks, fault lines and softer soils are prone to earthquake events in the form of landslides and rock-falls, as witnessed in the Mount KinabaluRanau earthquake of 2015 with multiple aftershocks leading to building damage and loss of life on the mountain itself through rock-falls.
On steep slopes, cuttings are often made into a hillside to take new roads with the displaced material then tipped downslope for new housing developments. Alas, an earthquake can shake such unconsolidated material into a liquefied mass, which runs downslope taking houses with it. Earthquakes are not uncommon in Mexico City, where huge sprawling slums or barrios occupy steep surrounding hill slopes. These ramshackle houses containing four million people are built on unconsolidated material which, if triggered by an earthquake, could see them collapsing one on top of each other in a domino-like effect downslope. There is a disaster waiting to happen there.
Safer housing The more symmetrical a structure is about both axes, the safer the building. Asymmetrical buildings are subjected to torsional forces during earthquakes. Simple designs with rectangular shapes withstand earthquakes better than those buildings with protruding sides. Sixteen years ago, I visited Japan where my son was studying at a Tokyo university. I noticed that on the campus that the student accommodation was in wellspaced blocks no more than four stories high and not in tower blocks all for obvious reasons. Staying a few nights in a room on the 160th floor of a central Tokyo hotel, I was reassured by my son that the foundations of the hotel were on a concrete raft, which rested on rollers. These rollers ran along tracks so that in the event of an earthquake the whole building would move slightly, to then return to its original position later. In fact, Japan houses the largest earthquake simulator in the world where new building design models are tested.
In other high-rise building designs, Japanese civil engineers invented a system to allow a building to float on air during an earthquake, a bit like levitation. Sensors detect seismic activity and communicate with air compressors which instantly force out air between the base of a building and its foundation. This cushion of air lifts the building by three centimetres off the ground thus reducing the impact of the earthquake force. Once the shock waves have subsided the building gently return to its base. Other equally fascinating engineering schemes have involved the manufacture of quake resistant materials.
Low cost solutions Prevention is always better than cure and this adage can be directly applied to settlements in earthquake prone zones. In cities the added expense in making buildings quake resistant has become a fact of life. Concrete walls are reinforced with steel (ferro-concrete) and new houses rest on shock absorbers. The February 2010 Chilean earthquake (magnitude 8.8) caused few deaths owing to strict building regulations there. However, in the same year, the Haitian Port-au-Prince quake (magnitude7) resulted in 75,000 fatalities as houses crumbled. Their walls were mostly made of cheap, heavy, sun-dried bricks (adobe), which instantly cracked as the ground shook. Today, a cheap and effective way of strengthening such structures is by installing a strong plastic mesh under the plaster or around concrete walls.
In other earthquake prone areas in Northern India walls are reinforced with bamboo trellised structures and in Indonesia some houses use discarded car tyres, filled with sand or stones and fastened between the housefloors and foundations. These car tyres function as shock absorbers. In northern Pakistan, quake-resistant houses are built of bales of compressed straw held together with nylon netting sandwiched between layers of plaster. In such mountainous areas these straw bales are also excellent insulators against subzero winter temperatures.
It has been proven that light walls and gable structures are subjected to smaller forces and that light roofs of sheet metal on wooden trusses result in little loss of life compared with heavy concrete roofs. Large windows and doorways create structural weak spots in houses and thus smaller regularly spaced openings are better. In tectonically active areas such as Alaska and Iceland, oil and water supply pipelines are built on rollers so that they can move during a quake rather than fracture. Giant cardboard tubing coated with polyurethane and reinforced with wooden trusses has been found to be more light and flexible and moreover if the structure does collapse it is less likely to crush people inside buildings. This method has been used by a Japanese architect in the design of a new cathedral in New Zealand.
Currently civil engineers are testing biomaterials in stiffening building structures. By mimicking the sticky substance of a mussel’s flexible and elastic byssal threads, which allow the mollusc to withstand the shock of heavy battering by waves, such material could be incorporated into buildings.
Kilogram for kilogram, one of nature’s most resilient and resistant fibres is none other than spider’s silk – stronger than steel.
There is hope yet for reducing the loss of lives incurred by earthquake shock waves by rebuilding and repairing peoples’ damaged houses using new low cost and more ductile materials to resist further earthquake damage in the many, tectonically unstable areas of our world.