Yesterday I attended the Living with Earthquakes conference which focused on the cities of Amandola, L’Aquila, and the March region in Italy. On 24th August 2016, Central Italy was hit by a first earthquake from a series that would last several months and include 9 makor shakes, two of which were Mw 6.0 and 6.5. There was extensive damage to infrastructure, buildings, and cultural heritage. Although there were over 300 casualties to these events, the numbers were still low for a series of earthquakes of this size, largely because of the affected areas being generally underpopulated villages or comunes.
The conference provided me with valuable information regarding the more technical part of building in a seismic area, consolidating buildings affected by earthquakes, recording affected heritage for the purpose of rebuilding, and general logistics for rehousing, assessment of casualties and damages, and proceedings for rebuilding. I also found it fascinating to hear how others approached the issue of lost cultural heritage – do we rebuild or do we forget? Trauma of such magnitude leaves a profound mark on communities and, as such, the decisions in the aftermath of the disaster have wide social and economic implications that go beyond the purely material considerations of the built fabric.
Dina D’Ayala, from UCL, focused on the protection of cultural heritage and urban settlements from natural hazard. She emphesised the need of a deep understanding of the construction techniques used in the building trying to be preserved. In Italy, the preservation techniques have evolved from an event to another, and past reconstruction often creates more risk than it solves. In Central Italy, after 1986, the standard reinforcements used were concrete ring beams and concrete columns, steel rods and mortar injections. Obviously the concrete frame construction often failed under the shear forces exerted during earthquakes to the point that they are now being replaced, where possible. New measures impose reinforced polymers instead of concrete beams.
Stefano Lenci, from University of Marche, presented an immensely useful lecture for non-insiders on elements of vulnerability in the built environment during earthquakes. There is a plethora of reasons why buildings fail, but here are a few to consider:
- irregular stonework and double leaf walls underperform during earthquakes
- horizontal and vertical regularities – oppenings (windows, doors) should preferably be aligned
- weak connections between orthogonal walls often make facades come away
- basements/caves/tunnels under buildings can introduce local amplification of the waves
- lack of stirrups in columns, coupling a weak column with a strong beam, or beam -column joints without reinforcement bars often causes failure in the structure
- soft storeys – pilotis – underperform (uproar when a picture of Villa Savoye flashed on the screen)
- external walls that are not sufficiently connected to the structure
- internal risks are represented by large furniture that is not fixed to the walls, shelving, movable walls, etc.
One other interesting piece of information that Professor Lenci offered was that, in general, structural engineers treat strategic buildings (hospitals, schools) as “no damage ever” while normal buildings “can damage but stand”. HOWEVER, damaged buildings will collapse in the event of a subsequent earthquake if steps were not taken to reinforce them. This is exactly the situation in Bucharest at the moment, where the majority of buildings with grade 1 seismic risk are expected to collapse in the event of an earthquake above 6 MR.