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Malta: Building for catastrophes

Tall buildings, bridges and residential development may be potential victims of catastrophe. When architects and engineers make the right decisions, quality of life and longevity improve.

Planning ahead for unusual events such as exceptional wind storms, gas explosions, fires and earthquakes is made easier by a better understanding of how buildings respond to catastrophe.

European scientists and engineers are sharing knowledge on the behaviour of constructions when exposed to extreme actions. These include exceptional unforeseen fire, heavy snow loading, accidental impact and bomb blast during terrorist attacks.

Safety in structures can drop below acceptable levels when built-in resistance cannot withstand an extreme event. Extra load applied to a structure during a natural or man-made catastrophe can lead to collapse. Good planning predicts the response of a structure while aiming to prevent its premature collapse.

Buildings in urban areas are designed according to rules which seek to ensure adequate safety under normal loading conditions. Yet all structures can be exposed to extreme conditions at any time.

At an international symposium organised by architect and university lecturer Ruben Paul Borg last month, a book entitled Urban habitat constructions under catastrophic events was launched, supported by the European Science Foundation. The book contains numerous important contributions, including data sheets on the latest research in the field.

A number of keynote lectures were presented during the three-day symposium, including contributions on the seismic rehabilitation of buildings, the design of high rise buildings to survive terrorist attack, catastrophic events in bridge and wind engineering, catastrophic scenarios of volcanic eruptions, and risk management. Also discussed was the seismic risk to buildings in Malta.

Earthquake activity in Malta is generally characterised by small magnitude events. However, the occurrence of large magnitude earthquakes in the surrounding areas and reports of historic earthquakes indicate that it is necessary to give due attention to the seismic risk posed to buildings in Malta.

The authors of the paper addressed risk in terms of seismic hazard and building vulnerability with reference to the construction industry in Malta and common defects in construction.

It was noted that uncertainty about the seismic hazard and the lack of a national annex has led to uncertainties in the design process. The authors commented on the need for a seismic hazard assessment of the Maltese islands with required assessment of the vulnerability of buildings. This would provide the basis for a much needed national annex to which architects and engineers could refer.

Other contributors addressed the effect of various catastrophic events on structures. Rapid climatic changes are having a dramatic effect on the role of structural designers. Around the world, losses from the catastrophic effect of high winds is on the increase. After battering Haiti and Cuba, Hurricane Ike laid a two inch carpet of broken glass around the tallest building in Texas.

At first, it was thought that flying debris had broken glass windows in the Morgan Chase building of downtown Houston. But eye witnesses reported seeing whole panes being blown out and falling to the street below where they shattered.

A severe drop in pressure aggravated by the narrow space of the street canyon at lower levels caused the windows to be sucked out. Windows higher up were not displaced, as the pressure drop was not as strong as in the bottom half of the building. Past experience of disasters must be tied to monitoring and research for safer construction codes.

Rarely is any weather event linked to a structure as wind is linked to bridges. In early times, bridges were built to be dismantled quickly in case of invasion. Suspension bridges, inspired by the primitive swinging bridges of Africa and South America, were improved with every disaster. Stays were added and interaction between cable and deck introduced for greater stability.

The Brotonne bridge of Normandy, built in 1977, marked a decisive stage in the construction of cable-stayed bridges. On a rainy and windy day, some cables suffered violent and unexpected oscillations. Tests in the wind tunnel did not lead to a clear understanding of the phenomenon.

In the 20 years of wind engineering that followed, mechanised strategies for eliminating vibrations were developed with added aerodynamic control. Designers aiming for ever more slender bridge towers on increasingly longer bridges faced new challenges. A discussion on the use of dampers for wind-induced vibration arose from problems with the world's third largest bridge in Denmark.

About 100 international delegates, academics, experts and researchers from 22 different countries participated in the symposium hosted by the Department of Building and Civil Engineering of the University of Malta.

This event marked the second phase of an International Technical Action involving co-operation in the field of scientific and technical research, supported by the European Commission research arm under FP7 funding.

Additional information

http://www.timesofmalta.com/articles/view/20081109/environme...

Keywords

  • Themes:Structural Safety, Urban Risk & Planning
  • Hazards:Earthquake

  • Short URL:http://preventionweb.net/go/5620

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