Can coconuts help make earthquake-resistant buildings?
Coconuts are certainly having their moment in the sun these days, with nutritionists and health food addicts espousing their virtues for treating everything from high blood pressure, obesity and Alzheimer’s to acne and tooth decay.
Once maligned for their high saturated fat content (natural coconut oil is 90 per cent saturated fat), coconuts are now valued for their ability to improve HDL (so-called “good”) cholesterol levels while coconut water -dubbed Mother Nature’s sport drink- turns out to have five times the potassium of typical rehydrating and replenishing drinks like Gatorade.
The coconut plant itself is a survivalist’s dream. In one tough package, you get a high-calorie food, a source for potable water, strong fibres for making rope and a hard shell that makes a great charcoal. To top it off, the coconut works as a flotation device!
Researchers are now hoping that the unique energy-absorbing properties of the coconut shell will add one more bullet point to the coconut’s resume: earthquake prevention technology.
“By analysing the fracture behaviour [of the coconut shell] samples and combining this with knowledge about the shell’s anatomy gained from microscopy and computed tomography, we aimed to identify mechanically relevant structures for energy absorption,” says Stefanie Schmier of the Plant Biomechanics Group of the University of Freiburg in Germany, whose work focuses on the cell bundles within the coconut’s tough endocarp layer surrounding the fruit pulp.
The cells in the coconut’s endocarp layer have been found to possess an intriguing ladder-like construction which gives the endocarp its strength as well as its ability to withstand bending forces, while the research team believes that the secret lies in how the cells in the endocarp divert impact energy, a property highly sought after by engineers and material scientists.
“This combination of lightweight structuring with high energy dissipation capacity is of increasing interest to protect buildings against earthquakes, rock fall and other natural or manmade hazards,” says Schmier.
Because coconut palms can grow as high as 30 metres, the ripened fruit and the seeds inside have to be able to survive the fall without splitting open, hence the need for well-developed internal shock absorption.
And the prospect of a cheap, readily-available building material to construct earthquake-resistant buildings is especially alluring considering that much of the damage caused by natural disasters like earthquakes tends to hit impoverished areas the hardest, where the pressure to cut corners by using shoddy building materials is strong.
The damage caused by an earthquake is a result of several factors including the strength and length of the shaking, population densities and soil quality, but also of central importance are the types of materials used in building construction. The quake that hit Haiti in January 2010, for example, resulted in a death toll in the hundreds of thousands and destroyed over 250,000 residences, according to government reports, with an absence of building codes and the use of poor building materials like cheap concrete, earth and even sticks and twigs taking much of the blame. By comparison, the earthquake that hit Chile a week after Haiti’s was much more powerful (with a magnitude of 8.8 versus Haiti’s 7.0) but resulted in a reported 525 deaths.