Over the weekend a powerful 7.8 magnitude earthquake struck the Pacific coast of Ecuador. Earthquakes are not uncommon here; they happen in Ecuador and surrounding countries frequently, but this was a big one.
As an earthquake engineer, I look at the photos of devastation ion the news and can often see more than just the devastation. The collapsed or damaged buildings tell me stories of how and why they failed, and most importantly, what can be done to prevent this kind of disaster in the future.
Here I will share a few thoughts on photos I have found on social media. Perhaps it will get you thinking about the reasons that these tragedies keep on happening. Obviously, these are just my thoughts, and until engineers get to the buildings and can properly assess the structures, these are just opinions.
My first impressions are that many of the collapses are reinforced concrete buildings, i.e. concrete with steel reinforcement bars hidden inside. Concrete on its own is a great material for withstanding compression forces (think columns with a weight on top), but it is very poor at resisting tensile (or pulling) forces. In fact, in practice we often assume that concrete on its own has zero capacity in tension. So, the steel is included to enable the material to be strong in tension too. The amount and the location of the steel reinforcement bars is very important, and is fairly complex for engineers to design, and for builders to construct. In earthquake regions it is vital that this, what we call 'reinforcement detailing', is done correctly to ensure that buildings are earthquake-safe.
Below we can see a reinforced concrete (or RC) building that has completely collapsed. The floor slabs, which still sit fairly horizontally, have 'pancaked' down towards the left of the photo. A former white drain pipe now sits mangled and mostly horizontal. A column, with its reinforcement bars on show, sits leaning towards the right of the photo, totally disconnected from the structure it used to hold up. This is what we as engineers would call a catastrophic failure. These kinds of failure, as you can imagine, are the ones that kill people, and they can be prevented by proper design of the reinforced concrete.
Many RC buildings contain masonry walls in between the concrete columns, as can be seen on the building on the left below. This brick masonry is very vulnerable to earthquake shaking, especially when it is unreinforced. In earthquakes it is very common for masonry walls to collapse and these falling objects can be the cause of some deaths. You can see below that the masonry walls have simply fallen out of the upper floors of the building on the left.
In addition to this, it is often not considered that this infilled masonry sitting between the reinforced concrete columns, beams, and slab, actually significantly alters the behaviour of the structure. The masonry stiffens the building, reducing its ability to sway with the ground shaking caused by the earthquake. This is an important design consideration that, when designed properly can be beneficial, but when it isn't, it can be catastrophic.
The poor performance of masonry in earthquakes is something I demonstrate to school children when I visit them. We use fruitella sweets to act as the masonry bricks, and a chocolate roof, and shake the building, imitating an earthquake. The children are always so shocked to see how quickly and easily the model building collapses (as can be seen below). We then work out some steps to make our 'buildings' stronger. With their engineering hats on, even the youngest of children realised that we need to stick the bricks together (or in real life reinforce them) and then stick the walls to the roof, to make a stronger building.
The structure below, another RC building, has fallen to the right, and it appears that it has only been stopped from fully collapsing by a structure further to the right. One of the stories of the building has completely crushed as we can see a set of green columns all now sitting nearly horizontally - this may have been a soft-storey, or it may have been impacted at that level by the building in the far left. The columns at ground floor level are mangled, broken apart, and one of them appears to have buckled at mid-height (dead centre in the photograph). Towards the left of the building at the ground floor, the columns appear to be hanging in mid-air, indicating that they have broken away from their foundations. Most connections towards the bottom of the building show damage at the connection between the beams and columns. Interestingly, the damage is generally located in the beam elements, not the columns, which is important. Buildings are usually designed to allow some failure in the beams, before any failure in the columns. This is due simply to the fact that if a beam fails, part of a floor might collapse, whereas if a column breaks, it can lead to much larger collapses. The green elements do appear to be part of a decorative feature on the outside of the original building, however, it is likely that they were also part of the primary structure of the building.
Overall, this is another unfortunate example of poor RC design and construction.
So where does Ecuador, and the devastated communities who have lost so much, go from here? Hopefully it is clear that better buildings need to be designed and constructed in the place of those that have collapsed or been damaged beyond repair. This can be done only be competent engineers, according to strict building codes, enforced during both design and construction. Retrofit or strengthening of buildings that survived this time but are still at risk should also be prioritised to protect occupants during future earthquakes.
Unfortunately, we very often see that in the rush to rebuild (which is of course completely justified for the short-term social and economic reasons), sometimes people just paint over the cracks, ignoring the larger problems. The photo below from Kathmandu shows this happening literally in the months after the Nepal earthquake last year. Hiding from the problem will most certainly not take it away. Earthquakes will strike again. Let's hope Ecuador is more ready next time.