Throng

Thursday 10th September 8.00pm

Continuing this week is the documentary series that explores how disasters throughout the world have influenced the evolution of modern structural engineering. This instalment examines how a series of catastrophic events involving skyscrapers highlighted a number of threats to the buildings’ integrity and forced architects to incorporate new safety features into their designs for the superstructures of the future.

The titans of city architecture for over a century, skyscrapers dominate urban landscapes throughout the world. No other building design so readily accommodates the voracious need for space in urban centres, but there can be a high price for this solution to overcrowded city life. Within such high and crowded structures, the consequences of engineering errors can be catastrophic.

Structural engineers have identified four main threats to skyscraper integrity: structural collapse, earthquake, fire and blast. Architects strive to combat these threats using strategic planning, radical design and pioneering technology. In Moscow, the engineers working on the 365-metre Federation Tower believe their new skyscraper will be one of the strongest and safest buildings in the world, setting new standards and avoiding the pitfalls of the past. “We tried to do something never done before,” says project director Ara Aramanian.

In May 1968, the 23-storey tower block Ronan Point in East London fell victim to sudden and profound structural collapse. Four people died in the incident, while a further 17 were injured. “It fell like a house of cards,” recalls eyewitness Ray Hollands. The subsequent investigation highlighted a flaw in the building design and some poor construction standards. The tower was built using a large panel system, whereby precast concrete panels were arranged like giant building blocks. When one of these panels was blown out by a localised gas explosion, a whole corner of the building caved in on itself. This kind of failure is known as ‘progressive collapse’.

The first big tower built in London after the Ronan Point incident, the 183-metre Tower 42 completed in 1980, features a solution to progressive collapse called ‘alternative load paths’, in which strong and continuous connections throughout the building are linked by a robust central core –meaning the integrity of the structure is not dependant on any single section. “The beams and the columns here have continuity,” explains Dr John Roberts of the Institution of Structural Engineers. The Federation Tower in Moscow features three alternative-load systems: a central concrete core, a perimeter frame of concrete columns and concrete outriggers – reinforced beams that reach out from the central core to the perimeter. “It’s a kind of belt-and-braces approach,” says Dr Roberts.

The earthquake that killed 9,000 people in Mexico City in 1985 taught architects more about building design than any other quake in history. Among the 50,000 buildings destroyed, many were steel structures that failed because of weak welding. In Turkey, the 270-metre Diamond currently under construction features ‘full-penetration’ welding. Each steel beam is fixed to the adjoining column with 1,278 bolts, making the beams stronger at the joins than anywhere else. The new Torre Mayor skyscraper in Mexico City, now the tallest building in Latin America at 225 metres, features huge dampers designed to absorb the vibrations of an earthquake measuring up to 8.5 on the Richter scale.

To cope with the potential destruction caused by blast and fire, as exposed so fatally in the attacks on the World Trade Centre in New York in 2001, architects at the Federation Tower use a special fireproof coating and specially designed superstrength concrete to support the steel throughout the structure. The thick glass units on the outside of the building are designed to absorb missile attacks, while a revolutionary twin elevator system housed within the reinforced concrete core allows for a swift evacuation, even when the tower is on fire. The Federation could now burn at 1,200C for four hours before it collapsed. “It’s an extremely fine-tuned job,” says Ara Aramanian.