How Safe Are Historic Earthen Sites? Earthquakes and Engineers Can Tell You.

Historic masonry and earthen buildings, with their near-universal material availability and low-cost construction, represent a significant portion of the world’s built cultural heritage. The irreplaceable value of this heritage has long been recognized, as has our responsibility to preserve this heritage for future generations.

However, earthen sites are among the most seismically vulnerable building typologies. Damage to these sites from earthquakes has caused significant cultural and economic losses in addition to the loss of human life. During the twentieth century, 75% of fatalities attributed to earthquakes were caused by the failure of buildings, of which 60% were due to collapse of masonry and earthen buildings.

These buildings present some common seismic vulnerabilities: low mechanical properties, unfavorable geometrical layout, heavy weight, inappropriate floors and roofs, poor connections between structural parts, and an absence of concern for seismic issues at the time of their construction and subsequent alterations. In addition, deterioration and lack of maintenance can further contribute to reduced performance in an earthquake.

As a result, when subjected to seismic activity, these buildings respond by brittle collapses with out-of-plane mechanisms of isolated parts. These local mechanisms can cause irreparable damage and can compromise the overall stability of the building. Nevertheless, simple and appropriate remedial measures can dramatically change the situation. If the premature activation of out-of-plane failures is prevented, these structures can activate a global mechanism, reducing their vulnerability.

For a better idea, watch what can happen to an existing unstrengthened vs. strengthened masonry building during seismic activity.


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