x Abu Dhabi, UAE Thursday 20 July 2017

New earthquake code for Dubai's tall buildings

Despite not being on a fault line, buildings in Dubai with 10 or more floors will now have to be built to withstand a quake magnitude of 5.9.

DUBAI // New buildings in the emirate of 10 floors or more will be built to withstand forces created by an earthquake of up to a magnitude of 5.9.

Dubai is spread across an area rated by geologists as Zone 0, meaning there is absolutely no risk of seismic activity in the area because there are no fault lines.

To err on the side of caution, the civic body has always required buildings higher than 10 floors to be built to withstand a moderate earthquake of between a magnitude of 5.0 and 5.5 (Zone 2A).

The municipality has announced that buildings taller than 10 floors - as well as schools and hospitals - should be built to withstand quakes between 5.5 and 5.9 (Zone 2B). Buildings with between four and 10 floors will still be designed for Zone 2A.

According to Engineer Moawya Zafarini, head of the structural engineering unit at Dubai Municipality, the new measures were brought in as "an added safety precaution".

When the country experienced its most recent wobble after a 7.8-magnitude earthquake near the Iran-Pakistan border on April 16, it was reported the tremors felt here were equal to between 4.0 and 5.0.

Abdul Qader, a seismic researcher at the National Centre for Meteorology and Seismology (NCMS), explained that estimation was inaccurate.

The magnitude is only a measure of force at the epicentre of a quake and cannot be applied to the tremors further away.

The NCMS prefers to use the Mercalli intensity scale. "This measures the intensity of the earthquake on each part of the earth," Mr Qader said.

The April 16 earthquake measured IV on the Mercalli intensity scale and, while comparisons with the Richter scale should not be made, he said this was similar to a moderate quake.

An IV rating is classed as tremors "felt indoors by many, and outdoors by few during the day", according to the US Geological Survey's website.

"There has been an awful lot of work done by people experienced in predicting earthquakes in this area," said Mark Lavery, associate director for tall buildings at engineering consultant Buro Happold.

"According to most credible studies the risks are low with the only activity likely to come from Iran with not many other fault lines in the area."

Structural engineers are employed to ensure towers are designed to sway in high winds and earthquakes - bending to the peak gravitational forces that may be applied.

Mr Zafarini said for new buildings to meet the Zone 2B demands, engineers will increase the size of beams and columns with detailed reinforcement, meaning the iron rods would run in complex weight-bearing patterns. "Normally the critical force to contend is wind and is more significant than seismic forces. All of our towers are also designed for wind," he said. Buildings are able to withstand wind speeds of up to 160 kph.

Despite being at no risk for full-force earthquake, Mr Zafarini said the municipality used the Richter scale to determine its building code requirements because the Mercalli scale was not accurate enough.

"The Mercalli scale is not an accurate scale in terms of mathematical calculations. The Richter scale is related directly to the strength and energy of the earthquake," Mr Zafarini said.

eharnan@thenational.ae