ST : Can our buildings withstand quakes?

Dec 04,2010

Can our buildings withstand quakes?
More time needed for studies on impact of regional tremors

By Christopher Tan
JUST how vulnerable buildings in Singapore will be to tremors from major earthquakes in the region is still being investigated.

Two studies commissioned two years ago, following the massive quakes that devastated nearby Sumatra in 2004, 2005 and 2007, have yet to be completed.

They were initially expected to be ready this year.

Among other things, the projects set out to determine whether Singapore's construction codes need to include provisions for tremors. This is a consideration that had never cropped up before because the island was long deemed quake-free.

One study is by the Building and Construction Authority (BCA), which commissioned Nanyang Technological University (NTU) to conduct an 'earthquake vulnerability' study.

The BCA told The Straits Times last month that the study will take 'at least another year' to complete.

The other study, also not completed, is by the Housing Board (HDB), which engaged the National University of Singapore (NUS) to develop 'cost-effective monitoring sensors' to be mounted on HDB blocks, said an HDB spokesman.

He said these sensors will enable the HDB to prioritise building inspections in the event of tremors, not to assess the vulnerability of buildings to tremors.

NUS researchers involved in the HDB study declined to talk about it, describing it as 'a very sensitive topic'.

One of them, Professor Koh Chan Ghee of NUS' Centre for Hazards Research, told The Straits Times two years ago that it is not uncommon for building codes to be revised, if necessary, given that a big earthquake is 'a low-probability but high-consequence event'.

Over at NTU, however, geologist Kerry Sieh, the director of the university's Earth Observatory of Singapore, predicts that a quake of 8.8 magnitude will hit north of Padang in Sumatra within the next few decades.

Such a quake, considered a 'great' quake, can affect buildings several hundred kilometres away. Singapore lies about 450km from the predicted zone.

Professor Sieh's colleague, Assistant Professor Kusnowidjaja Megawati, said a real worry for Singapore is for buildings which stand on marine clay and some reclaimed land. These soil types tend to amplify low-frequency vibrations from quakes hundreds of kilometres away.

These soft soils make up about a quarter of Singapore's land mass, mostly in the south-east, like in Kallang.

Prof Megawati explained that geologists use a measure called centimetre per second squared (cm/ss) to indicate the degree of 'shaking' felt on the ground.

Recent simulations have shown that an 8.8-magnitude quake in Sumatra will create 'ground acceleration' of plus-minus 10cm/ss in Bukit Timah - an area with underlying hard rock - and plus-minus 30 to 40cm/ss in Kallang, he said.

In the 8.4-magnitude Sumatran quake in 2007 - the most severe quake felt here in recent times - the ground acceleration was less than 1 cm/ss in Bukit Timah and 3cm/ss in Kallang, he noted.

Even at that level, buildings as far inland as Toa Payoh and Little India shook, so if Prof Megawati is right and 'the next big one' happens, the effects felt here could be 10 times that.

But the experts do not all agree on the extent of Singapore's risk exposure to quakes and how it should respond to them.

Professor Pan Tso-Chien, the dean of NTU's School of Engineering, for instance, believes Singapore should not rush to change its building codes to guard against earthquake damage.

He said: 'It's a major issue in addressing a code change. It's not only a question of science or technology any more, but economics and costs as well.'

Arguing against jumping into a code change, he said: 'Are our current codes enough protection? Will we be over-providing? Are you going to make it so safe that it's safer than crossing a street? You have other competing needs for your resources - like terrorism, road accidents and defence.'

Prof Pan, who is also director of the Institute of Catastrophe Risk Management, a research body co-funded by the Monetary Authority of Singapore, said the issue may well resolve itself over time, as buildings 'are always getting stronger because of better materials, better engineering, better accuracy in design'.

At best, he said, resources should go into strengthening buildings gradually over time, systemically, so 'there's no need to rush or worry'.

Asked about the 'next big one', Prof Pan said: 'Personally, I'm not in favour of earthquake predictions because it's very difficult - you have to involve not only a place, but also time. It's too much consequence for one to be correct or incorrect.'

He also pointed out that the majority of deaths from earthquakes have been in rural areas, not urban high-rise ones.

Meanwhile, the insurance industry has not decided to start charging for earthquake coverage, even after having mulled over it in the past few years.

General Insurance Association president Derek Teo said 'exposures are still within a tolerable range'.

He added: 'Nevertheless, tremors here will be monitored on frequency and severity before a rate charge is considered.'

christan@sph.com.sg