Failing safely - why planning for the worst saves lives in an earthquake

The recent earthquakes in Haiti and Chile have highlighted the influence of economic wealth, robust governance, and social learning on societal resilience and human security. In Haiti, some 250,000 people may have lost their lives, with infrastructure and buildings devastated across the country. Its fragile economy is crippled and will no doubt take a decade or more to recover. In contrast, Chile, despite suffering one of the most powerful earthquakes ever recorded, has suffered relatively little loss of life, although infrastructure in particular is likely to have been badly affected in the epicentral region. The President of Chile has anticipated that it will take four years for her country to recover from the earthquake’s effect.

Haiti is one of the poorest nations on earth. It has an impoverished government, which has little scope for promoting economic development. The result is that many, if not most, of its citizens live in an informal subsistence economy, which lacks the robust governance frameworks that are necessary to ensure that local engineers are educated in good earthquake-resistant design practice and are able to implement it.

Chile, on the other hand, is a far more prosperous and wealthy nation. Its governmental structures are far more mature and robust. Its people are well educated and relatively wealthy, and they have more scope to look after their own safety and well-being.

But there is one additional important difference between Haiti and Chile. Haiti had not experienced such a potentially damaging earthquake for around 200 years. The societal awareness of such a potentiality simply did not exist. Consequently, it was unprepared and experienced a catastrophe. Chile, however, had experienced very powerful earthquakes in 1960 and 1985, and is shaken by smaller events many times each year. Chile’s societal awareness of earthquake risk is high, which translates itself into a demand for governmental action to minimise risk. Chilean engineers are well-educated with respect to earthquake-resistant design. Their universities have established a world class reputation for earthquake engineering research and dissemination. In turn, Chile’s engineers have adapted the internationally accepted principles of good earthquake-resistant design and produced an effective code of practice. This design code is enforced through good governmental regulation. The recent earthquake has demonstrated the positive impacts of this societal wisdom and learning.

I visited Chile in 1985 after the damaging Valpariso earthquake. In the coastal city of Vina del Mar, there was a row of high rise apartment blocks along the picturesque Pacific sea front. These blocks had been built over a 20 year period. The older ones had suffered significant damage, reflecting the still immature understanding of earthquake design in the 1960s and 1970s. But the damage diminished, the newer the high rise blocks were. Lessons had clearly been learned from earthquakes in Chile and around the world. In particular, the newer blocks used ‘capacity design’ principles in which the building is designed to fail in a controlled manner. The key is to ensure that the building’s columns, which support the weight of the building, remain intact and therefore prevent the building from a pancake collapse. The beams of the building, which support the floors, are deliberately designed to be weak at their ends so that they form ‘plastic hinges’.

Such plastic hinges damp out the vibrations that the earthquake induces in the building, thereby reducing the latter’s overall, mainly side-to-side, sway motions. If carefully designed, these hinges and beams will still ensure that the building will not collapse, thereby minimising risk to life. This is known as ‘strong column – weak beam’ design. Many buildings in Haiti were of ‘weak column – strong beam’ design, and collapsed. Why plastic? Try bending a wire coat hanger backwards and forwards many times. Eventually, the wire will form a plastic hinge and break. The break will be hot due to the energy that had been dissipated.

No doubt, Chile will learn the lessons from its recent earthquake and will increase its societal resilience. The greatest challenge in Haiti will be to put in place appropriate societal learning and governance systems before its earthquake lessons can be learned and acted upon too. Engineers must play a central role in this, illustrating the ever growing importance of the social dimension of engineering thinking and practice.