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from the I-feel-the-earth-move-under-my-feet dept.
Arthur T Knackerbracket has found the following story:
Given the choice between safer and cheaper construction, many housing design companies in earthquake-prone developing countries see themselves forced to save on expensive construction materials and opt for the latter. EPFL structural engineers have gathered new data on how these structures respond to earthquakes, and in which circumstances they may fail.
Earthquakes almost never kill people by themselves. Instead, the high toll they take can be explained by a lack of resilient buildings and infrastructure. In Chile in 2010, many thin-walled reinforced concrete buildings were damaged in one of the strongest earthquakes ever recorded. Yet today, more and more structures with even thinner walls are being built in some Latin American countries. Recently, engineers from EPFL evaluated the stability of thin reinforced concrete walls to understand how they fail. Their findings are published in the journal Bulletin of Earthquake Engineering.
To find out how very thin-walled structures behave in an earthquake, João Almeida and Angelica Rosso, two of the study's authors, tested two 80-millimeter-thick, 2-by-2.7-meter wall segments, similar to those used in low-income housing projects in some South American countries. By clamping the wall segments to the floor of the laboratory and loading them with five actuators strong enough to slowly bend the walls back and forth in different directions, they simulated the impact of an earthquake on the structure. By slowing down the process the researchers had time to watch the damage spread and to find out how cracks propagate across the wall, ultimately destabilizing it.
"The data we gathered in our experiment is unique," says Katrin Beyer, the principal investigator of the study. "It is the first to contain detailed measurements of a so-called out-of-plane wall failure, which means that the wall structure was irreversibly deformed perpendicularly to its surface." According to Beyer, it was also the first time that displacements greater than the wall thickness itself had been observed under these conditions. By the end of the test, the wall's reinforcement bars had bent, with the concrete crumbling in one corner of the structure. Thanks to an array of sensors, cameras, and strain gauges, the researchers were able to capture and analyze every motion leading up to the collapse of the wall.
(Score: 5, Informative) by Runaway1956 on Saturday November 07 2015, @04:39PM
Sorry, but 3 inches of concrete isn't "concrete" to me. Slabs start at 6 inches, and go up from there. Walls, roofs, floors, you name it - if it's not 6 inches thick, it's not worth messing with.
First or third world countries, it doesn't much matter - cheap bastards go cheap, and quality work is still quality work. Right here in the USA, I see homes built on 2 1/2 inches of concrete. Worse, I see no footers under the edges. Even worse, instead of digging into the ground when the terrain is uneven, they build up the low spots with sand.
Build cheap, you can expect crap to fall down, it's really that simple.
A proper slab is dug into the ground, with an ADDITIONAL 1 ft x 1 ft "footer" dug all the way around the perimeter. That gives you 18" of concrete to support your bearing walls, and 6" of concrete to support every thing else. If you have a center bearing wall, then you're going to dig a footer under that wall as well. All walls are going to be 6" thick, or more.
This has been a "standard" since Portland Cement was created.
Please note that I consider this to be "minimum" for quality work. For better, stronger structures, you'll specify rebar, and additionally either chicken wire or fiberglass. You can also specify 3500 pound mix (basic, standard strength) 5000 pound mix, or even 10,000 pound mix. An added premium is potash mixed into the concrete. For insulation value, air is blended in. And, finally, you can add liquid glass to help make it more waterproof.
At the end of the day, you get what you pay for. Go cheap, and it will fall down within a couple decades. Build quality, and you can expect that it will stand until someone willfully destroys it.
http://ceramics.org/wp-content/uploads/2015/01/0106ctt-coliseum-lo-res.jpg [ceramics.org]