The tragic effects of the recent earthquakes in Nepal have highlighted just how fragile a home can be and the devastating effects of its collapse.
Sitting at home in a non earthquake zone may provide you with some comfort but if you own a property in Portugal which is in a seismic activity region of the world then you may have more to worry about than you think.
Take for example the typical building methods here.
Old stone houses with soil infill and cement/lime render on the outside.
Because the roofs on these houses are relatively light weight they do not add much stress to a properties structure and in some situation the earth shaking will just make the stones that the house is built with move and vibrate without falling down so you could say that they are slightly resistant. Obviously if there is a strong earth heave the whole property will fall down.
One area of weakness is the way that the ground floor doorways are often built below the first floor windows and doors. This is a week area and can lead to the front of the house bulging and in extreme cases collapsing.
Houses and apartments built in the last 60 to 20 years. These properties are the most at risk. They tend to be built badly and added too without regard to the overall structure or foundations. Often by unqualified DIYers using cheap and poor quality materials and skimping on the depth and size of foundations makes them susceptible to large scale collapse with even minor seismic movement.
Modern houses and apartments SHOULD have been built with the best available design ideas, have specific strengthening to withstand seismic effects and be altogether stronger because of the use of modern concrete mixes and high tensile steel reinforcing.
When I said “should” that was because there are three areas which give a modern building its strength.
1, The amount and quality of the concrete used,
2 The thickness, spacing and quality of the reinforcing steel,
The structural design
All of which are often “adapted” (lessened) on site in Portugal