Some simple notes from an earthquake engineer on photos from Nepal

Following today's large earthquake in Nepal, I discuss some of the engineering failures that have caused this devastation to help you understand how these buildings have failed.

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  1. First up, a masonry building. Here a masonry façade has crumbled under the forces of the earthquake. This is common in small and large earthquakes and is caused by the masonry not being strong enough to withstand the horizontal shaking that an earthquake brings. It can be strengthened by reinforcing the masonry and tying it well to the other walls of the building, preventing damage or injury to those on the street.
  2. This building has, most likely, suffered a partially soft storey failure. Often, the ground floor of buildings have less columns or walls (read earthquake resisting structure) than floors above, as opens spaces are preferred for shops, restaurants, or garages. The right hand side of the ground floor of this building appears to have given way and it is likely that the building next door prevented it collapsing completely.
  3. These historical temples are built of unreinforced masonry which does not resist earthquakes well. Solutions to help strengthen the masonry include reinforcing it with steel, or confined it (i.e. holding it together by wrapping it in steel, concrete, or plastic). Obviously, solutions for retrofitting need to be culturally appropriate, but are possible, and have been achieved with success in places like Peru and Bhutan.
  4. Here you can see a concrete roof slab, which has 'pancaked' down because the columns and walls (the vertical structure) has given way. Heavy concrete roofs are sometimes preferred for their thermal properties or hurricane resistance, but are lethal in earthquakes. It is hard to tell exactly what has gone wrong here, but it is likely that the concrete columns supporting the roof and floors were not adequate to support the buildings mass as it accelerated from side to side. To stop this happening, we need to make sure that columns or walls are strong enough to withstand an earthquakes lateral forces.
  5. And finally, the bottom-right photo here is interesting. It looks like the building was under construction, and it has 'rocked' over on to its side. If you look closely, you can see the steel reinforcement hanging outof the column that is left, now horizontal, hanging in the air. This column hasessentially snapped (or failed in tension in engineering speak) off afoundation or a floor below. This is quite a rare form of building failure,and, as you can imagine, needs a very large earthquake to happen.
  6. Engineers know how to design against all of these types of building failure, but it isn't possible for us to strengthen every building the whole world. But it is important to remember that simply enforcing building codes, which is often given as the 'solution', only aims to help with new buildings. There are millions of existing buildings out there that need to be assessed for their vulnerability to earthquakes, and retrofitted to be stronger, so that disasters like this do not happen.
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