Lefkada: Why 150-year-old buildings withstood the earthquake

More than ten days after the deadly earthquake in the Ionian Sea, scientists are still busy in Lefkada.

But it’s not just seismologists. Architects and civil engineers are expected to focus their attention in the coming period on the traditional houses of the city of Lefkada—buildings constructed in the early 19th century with a unique anti-seismic system found in very few areas of the world.

Buildings that are more than 150 years old emerged unscathed from the recent earthquake, withstood the powerful tremor of 2003 and survived major seismic events in the past, while buildings that are only a decade or two old bear the visible marks of the 6.4 Richter scale earthquake that struck on November 17.

Their structural model consists of a clever mixed construction system with stone on the ground floor and wood on the upper floors, while inside the ground floor walls there is a secondary supporting structure made of sparse wooden pillars, which support the upper floors. This has an unparalleled advantage: even if parts of the stonework on the ground floor collapse, the upper part continues to be supported until the damage is repaired. The earthquake-resistant construction method adopted during the Ottoman occupation, based on the experience of traditional craftsmen, was put to the test in 1825 with the powerful 6. 7 Richter scale earthquake that struck Lefkada and was subsequently codified in building legislation.

Exemplary constructions

The pedestrian walkway of Lefkada is adorned with many examples of this structural system, with the upper floor wall often covered with corrugated sheet metal to make the construction lighter. The old Town Hall and the Gymnasium of Lefkada, which were built as the residence and office of the British Commissioner, are considered exemplary works of this type of construction.

As explained by Ms. Elli Vintzileou, professor at the Department of Civil Engineering of the National Technical University of Athens, who is part of the scientific team that submitted the relevant research proposal, “This structural system is not found anywhere else in the world, but variations of such systems appear in Portugal. It is the famous casa pombalina, a type of house that began to be built after a devastating earthquake struck Lisbon 250 years ago. Structural systems are also found in Turkey and Iran, in areas where they were necessitated by earthquakes.

What is striking is that while we believed that the Lefkada system was not found in Kefalonia for historical reasons—because the locals there were wealthier and the English occupation lasted longer, resulting in the adoption of British construction standards — the earthquake that struck the island in January 2014 brought news: when some houses suffered damage, it was revealed that they were built in this way. They had withstood so many years, they had withstood the great earthquake of 1953 in Kefalonia, and they remain standing. Thus, for the first time, certain buildings were declared preservable due to their structural system.

The research proposal was submitted a few months ago and was drafted by professors from the National Technical University of Athens and a university in neighboring Italy. This is not surprising, given that the traditional anti-seismic system of Lefkada has, at times, attracted keen interest from European and Greek scientists.

Descriptions of residents:
Whole tree trunks were placed in the foundations.

The residents of Lefkada provide interesting descriptions of traditional building methods. Books written about the old houses on the island, such as that by the Municipality of Malakasi, reveal that entire tree trunks were coated with clay and tar and placed in the foundations along the entire length and width of the building. Previously, the wood had been placed in the mud of the lagoon near Chora. The trunks were covered with a mixture of three different materials: fine sand, chopped stones, and porcelain powder, so that the foundation would move as a single unit in the event of an earthquake.

Next, the stone walls of the ground floor were constructed, on the outer side of which, and mainly at the points between the openings, iron bars were placed that were hooked onto the wooden floor of the first floor, in order to hold the wooden structure on top of the stonework of the ground floor.

The construction of the first floor relied more on the use of wood, while the wall was constructed in a way that made the house flexible and formed the “infrastructure” for the wooden latticework that gave the building a distinctive style and lightness. The gaps left by the timber framing were filled with pieces of brick joined together with sand, lime, and porcelain, which protected the wide surface of the wooden wall from seismic vibrations, “precipitation,” deformations, and destruction. Finally, the roof of the house, which was also wooden, was installed.

Supports

The building was supported from the ground floor to the first floor by a second wooden system of columns, which were placed at a short distance from the stone structure so as to prevent the wood from colliding with the stone wall in the event of seismic vibrations. This was the so-called “anti-seismic joint.” With this auxiliary support, in the event of an earthquake, the outer stone wall of the ground floor could collapse from the vibration, but always towards the street and never towards the interior of the basement. Residents often made sure that the upper part was light and covered it with sheet metal painted in soft colors, a technique that is still used today.