Adobe Code -- Lessons from the Field
Back in November the International Congress on Monuments and Sites (ICOMOS) sponsored a conference in Istanbul around the theme "Earthquake Safe." The purpose of the gathering was to review the consequences of and draw some conclusions about the disastrous seismic events that occurred in Turkey in 1999 and 2000. Most of us remember seeing the images and hearing the news items that resulted from those events. They focused primarily on the multi-story reinforced concrete apartment buildings that collapsed like houses of cards, killing tens of thousands of people. There was a hidden story as well -- about people who survived because they were in other kinds of houses -- earthen ones: There were only eight known fatalities resulting from the collapse of traditional buildings.
It is, of course, no surprise to practitioners and advocates of traditional building technologies that "soft" buildings often out-perform "hard" ones during earthquakes. For several decades now the disciplines of architecture and engineering, in their authority as code and standard writers, have (with a few exceptions) turned a blind eye to the seismic survival of tens of thousands of earthen buildings while pointing critically to those that failed. The seismic events of the past several years, including those in Turkey, have provided us with a better understanding of the survival rates for earthen buildings, and provided the general public with a clear demonstration that reinforced concrete fails even more spectacularly than traditional construction. We are also beginning to comprehend the double whammy of poor code enforcement at the same time that we are learning that the useful life of reinforced concrete structures may be as short as 70 years.
I was asked to present a paper on some of the work we here in New Mexico are doing, not because we live in a particularly active seismic zone (though we do), but because we have a huge inventory of earthen buildings and we have learned a great deal about how earthen buildings perform under duress. I centered my comments on the utterly misguided thrust of building codes not just in the United States, but worldwide as they pertain to both new and historic earthen buildings.
Listening to the other speakers in Istanbul -- mostly professionals from seriously seismic zones all around the world -- it became clear that vernacular builders have understood for centuries how to build seismic-resistant multi-story earthen buildings. But in our modern arrogance and love of the new, the high tech, we have avoided to our detriment learning the lessons that have been passed down.
The weakness in most existing codes and in recommendations for new codes regarding adobe (I have been asked by the compilers to review several) is that they do not acknowledge success in earthen technologies and thus automatically disregard the reasons for it.
There is a very clear dichotomy in thinking between code-writers and, for lack of a better word, the traditionalists. Code writers tend to ask the question, "how much is enough?" Whether unfamiliar with the historic success of many earthen technologies in seismic zones, or having an inherent distrust of soft materials, they respond by seeking higher- and higher-tech solutions, typically incorporating dissimilar materials.
The traditionalists on the other hand change the question to read "how much is too much?" and are always mindful that whether the material is hard or soft, failure and success are linked to precisely the same phenomenon -- the use of high quality materials in a regime employing good building practice.
What we learned in Istanbul is that there is no such thing as "earthquake safe" -- buildings are dangerous things in heavy tremors -- but given a fair analysis and a fair shake by code writers, earth will outperform and certainly outlast reinforced concrete most of the time.