Reconsidering Urban Planning in Spain after the
Lorca Earthquakes (11th May 2011)
A. Aretxabala Díez & C. Sanz Larrea
School of Architecture, University of Navarra, Spain
In September 2011, a set of new Urban Planning Complementary Regulations were approved by Lorca’s Town Hall, with recommendations on earthquake-resistant design of staircases and basement floors structures (avoiding to include short pillars), sills and parapets (reproducing verbatim the text of PGS1, a building code from 1968 and PDS1 from 1974, about them), façade walls (requiring a minimum support base of 2/3 the thickness of the outer masonry sheet), partitions or masonry facades of soft storey floor plans and cantilever vertical elements (to be braced to the main structure).To avoid captive pillar effects, joints between façade ground walls and are finally required.
The two key factors in Lorca, ignoring the fact that the seismic acceleration exceeded the one estimated in NCSE02, were the number of victims in the streets caused by insufficient seismic-resistance of “non-structural elements” and the severe structural damages up to 1.650 million Euros due to seismic-resistant design criteria blunders in RC structures and bearing masonry walls Heritage. Spain has never had so many building standards in force. European standardization activity has a lot to do with it. ECs and Framework Directives have been the most important influences in the drafting of LOE (Organic Law for Buildings) and CTE (Spanish Buildings Technical Code), cornerstones of building standards. But standards’ key gap regarding building rehabilitation, Heritage restoration and assessment of existing building’s compliance to CTE requirements remains unsolved.
|THE "OTHER" HISTORY OF SEISMIC CODES IN SPAIN
On the other hand, there is a tendency to dispersion, duplication or standards content overlap (NCSE 02, EHE 08, EAE and Euro-Codes 7 y 8... in relationship to seismic-resistant structural design) as well as inconsistencies among CTE DBs (Basic Documents into the Spanish Buildings Technical Code). Structural Codes language is becoming cryptic since it is translated from Euro-Codes English versions. Their content focuses on new concepts and design methods, not exposing the fundamental design criteria. The number of Codes Annexes tends to infinity. Therefore, dealing with a new structural code it is not an easy task for an architect. The behaviour of existing buildings, the architects’ effectiveness in managing damages after the earthquake have shown the importance of the generalist character of the Spanish architect, ultimately responsible for design and construction and thus capable of adopting the urgent decisions required after a seismic event.
The question now is whether the urgent reinforcements may affect in a negative way the structural assembly behaviour, having modified so significantly the stiffness and resistance of certain elements. Another challenge is to create the right procedures to revise the compliance with newest Earthquake-resistant Construction Standards requirements of Public Use buildings (Lorca’s Hospital had to be evacuated and there were no victims in schools because they were empty) as well as residential existing buildings in seismic-risk zones, for which ITEs (Technical Inspection of Buildings) could become a first approximation tool.
|NCSE02 SEISMIC-RISK MAP
TRLS/2007 (Spanish Land Law, 2007) emphasizes the need to ensure urban planning’s future sustainability, from any point of view: economic, energetic, social or environmental. Lorca’s earthquake is a reminder for Spanish urban planners of the fact that an earthquake’s scenery is the city as a whole. In 1829, Torrevieja, a town close to Lorca, severely damaged in an earthquake, was rebuilt in a new location, not too far away from the original, but on a safer ground. In the XXIst Century, proposals of abandoning existing cities in seismic-risk areas are nonsense, but planning their urban development ignoring the importance of ground characteristics in an earthquake is unwise and irresponsible. A new approach on the matter is proposed, based on a transdisciplinary transference of experiences between building and Urban Planning.
Since Ground Reports are required for designing a building, advantages of all types have been obtained: Cost of over-dimensioned foundations has been reduced; long-term buildings’ structural safety has increased, reducing frequent pathologies due to foundations deffects, extremely expensive to repair. But it is still frequent to design single-family houses with deep foundations systems whose economic impact is unbearable for promoters and digging into rock to build underground multi-storey garages. In seismic risk areas, economy goes into the background, security of persons and their property becoming the priority. Not having a minimun information on the ground characteristics for urban planning may have consequences as serious as the demolition of entire squares, like La Viña and San Fernando in Lorca.
In the latter, ground floors plans were designed consciously, for it is a flooding area. Building in flood-risk zones is unfortunately quite common in Spain. In 1996, an intense summer storm caused 87 victims in a campsite in the bed of a ravine in Biescas in a valley in the Pyrenees. Local Flood Risk Maps are being drafted as a consequence of the requirements of Directive 2007/60/EC (2007/60 Euro-Code). Lorca’s experience should serve to adopt preventive measures in Spain before the UE requires it.
Urban Planning in seismic risk zones should be based both on local basic geotechnical information on the ground as well as on local Seismic and Flood Risk Maps and earthquake-resistant city design criteria implemented, in order to guarantee not only that FAM (Alhama de Murcia Fault, the tectonic accident responsible of these earthquakes is considered a scientific-geologic point of interest) will not be affected by urban development, but also, that urban development of those towns close it will be safe enough for the people and their property.