Bam! Adobe Takes Another Unfair Hit
In February of 1976 I happened to arrive in Guatemala on the heels of a massive (7.5) earthquake that claimed more than 20,000 lives. I stayed with an elderly friend in Guatemala City for a few days, through most of the aftershocks, then rented a small truck and began a two-week adventure in death and destruction that took me to just about every ravaged community in the Highlands.
Guatemalans, like many people who live in seriously seismic zones, seem to take the threat of earthquakes in a rather cavalier manner both personally and officially. On the personal level, my friend John Armstrong in Guatemala City refused to take a valuable collection of china off their hangers in the dining room because he liked them where they were. Any of the powerful aftershocks could bring them to the floor, I noted. Of course, he replied, and if I am awake I will rush over to touch them one last time as they fall.
On the official level, Guatemala had a planning code that included disaster response, but no building code that specifically addressed seismic issues in a zone that sits on the boundary of two tectonic plates. The result, of course, was tragic. The damage assessments, both by the Guatemalans and the Earthquake Engineering Research Institute in Oakland, California, instantly blamed the high fatality count on poor construction methods and adobe buildings. They were only half right.
In my two-week sojourn through the Highlands, I visited village after village of leveled homes. I did see hundreds of crumbled adobe houses most of fairly recent construction and on the edges of population centers. I also saw many concrete-block houses that came down in just as deadly a fashion. In both cases, it was not the fault of the material that it collapsed, but of the manner in which it was assembled. The concrete block had little or no rebar and a weak mortar; the newer adobe homes had broken with tradition and been built without the wooden bond beams and roof diaphragms that existed in earlier structures. Little was said of the concrete block failures. Adobe took the rap.
In thirty years, nearly nothing has changed. The day after the Bam earthquake in Iran in late December, I saw an engineer (credentials not specified) on the ABC Evening News blame adobe for the tens of thousands of deaths. Having just returned from Iran, and from the vicinity of Bam, I immediately contacted my colleagues at UNESCO and the Iranian Cultural Heritage Organization. I also began watching the broadcast news and internet articles very carefully to learn what I could of what had been destroyed.
Not many buildings, of any construction, stood a chance in Bam because the epicenter was directly beneath the city. Many adobe buildings perished and, looking at the disaster from a cultural heritage viewpoint, a large section of the amazing Arg-e-Bam earthen citadel also collapsed. What the news casts have failed to tell, and probably to note, is that the vast majority of collapses were of buildings of low-fired brick (by definition not adobe) and the damaged part of the citadel appears to have been a 1950 s reconstruction. Assessments are still ongoing and we don t have all the answers yet, but as usual with the media and the majority of the engineering community, the appropriate questions are not being asked.
It is a human frailty, in my mind, to assume with blanket confidence that modern is better. As nearly as I can tell, it was precisely this type of thinking that led to what might be called, in evolutionary terms, an unfortunate episode of punctuated equilibrium in Iranian architecture. Twenty or thirty years ago the Iranians made a move away from sun-dried bricks to low-fired ones. The modern version is precisely the same size as the older model, and made of the same materials. So why add the extra time and expense to fire it?
There is lots of oil and therefore plenty of oil by-products in Iran and one way to get rid of them is to burn it in brick kilns. I saw many of these filthy operations in central Iran and no one could give me a better answer as to their existence than to note that a fired brick is harder than an unfired one. No argument; but harder is not necessarily better, particularly when it provokes a false sense of confidence. The newer, harder bricks began to be stacked into multi-story buildings with single-wythe walls, without tie-beams and using only a soft mud mortar that does not bond well to the fired surface of the brick. In many instances I saw flimsy steel post-and-beam cages with field-welded joints being in-filled with the low-fired bricks. It doesn t take much of a rattling to bring down construction like that.
As I began my remote assessment of the collapses in Bam it became clear from the photographs that adobe was probably not the major culprit. A yellowish tint to the bricks in the rubble is the giveaway; low-fired material.
Regular readers of this column may recall my reports on the earthquakes in Turkey in 1999 and 2000. Again, there were thousands of deaths and an international outcry against soft building materials and poor building practices. When all the cement dust finally settled, it was clear to even the most conservative engineer that what failed and killed was not earth, but concrete with (a minimum of) steel. Twenty-odd thousand died in poorly constructed modern tenements and the fatalities from collapsing earthen structures? Eight known. Nevertheless, there was an immediate move to bulldoze any earthen building, historic or not, with a crack in it.
It is one thing to be cavalier, as my friend John Armstrong was, about the threat to his china collection from a seismic event. We all make choices. It is quite another thing when public policy specific to building codes fails as dismally as much modern construction does in earthquake zones. Codes, believe it not, are largely a product of public opinion, not empirical knowledge or even common sense. In our work it is a constant battle to demonstrate to the inspector that a well-constructed double-wythe cavity wall is stronger and many, many times more energy efficient than a 2 by 6 frame wall with R-19 spun fiberglass insulation. But there is a perception, exacerbated by most engineers and definitely highlighted by the media, that earth is both the building material of the poor and a poor building material.
When the final analysis of the collapses in Bam is revealed, the knowledge gained in Turkey will, I am sure, be cemented. Adobe will be seen as both safe and viable in seismic zones.