Engineering a safer future in Nepal
Thursday, Aug 20, 2015, 03:57 AM | Source: Pursuit
Tilak Pokharel had just visited Christchurch, devastated by a series of earthquakes in 2011, and was checking the bus schedule for the next leg of his New Zealand trip when his phone buzzed with an urgent message from his brother in Nepal.
Mr Pokharel, an earthquake engineer, knew it was serious. He had sent his family the same message four years ago in 2011 while working in Japan during the 9.1 magnitude quake that led to the devastating tsunami and Fukushima disaster.
“My brother would not have sent something like that unless it was big. We checked the internet and TV to find a major earthquake had hit Nepal,” says Mr Pokharel, who is an engineering PhD student at the University of Melbourne.
“The first pictures we saw were of the famous nine-storey Dharahara Tower, which had fallen down. There were huge cracks in the road. I was really scared.” (The Dharahara Tower is a UNESCO-recognised monument in the Nepalese capital, Kathmandu.)
The April 25 earthquake was Nepal’s most destructive in 80 years. The epicentre of the 7.8 magnitude earthquake was in the Gorkha district, about 80km from Kathmandu. Villages were flattened, magnificent centuries-old temples were reduced to rubble. Yet other buildings survived with barely a scratch.
Some of the hardest-hit structures were the many poorly regulated residential buildings, built with inadequate reinforcement. These structural collapses contributed to the death toll of over 9000.
Mr Pokharel’s family is from Nepal’s low-lying Terai region of grasslands and plains, about 150km from the earthquake’s epicentre.
“There was not much damage and my family are doing fine,” says the 29-year-old. “But my brothers and in-laws live in the capital city. They slept in tents for several weeks as the aftershocks came and they were too scared to stay inside.”
Mr Pokharel, who has wanted to be an engineer since childhood, came to the University of Melbourne in 2013 to pursue his PhD in structural and earthquake engineering with one of Australia’s leading experts, Associate Professor Helen Goldsworthy.
He didn’t expect to put his work into practice so suddenly. “We knew an earthquake like this was going to happen some day, we just didn’t expect it would happen so soon,” says Mr Pokharel.
Determined to put his training to good use, he contacted Associate Professor Goldsworthy. With the help of the Dean of Engineering Professor Iven Mareels, she arranged funds to send him with a group of Australian and New Zealand engineers travelling to Nepal to help the recovery effort.
He flew to some of the hardest-hit areas, including the district of Sindhupalchowk. The death toll there was 3,531, and more than 65,000 buildings were damaged.
Working with with local engineers, students and lecturers from Tribhuvan University and Nepal Engineering College of Pokhara University, he presented seminars on the fundamentals of earthquake-resistant engineering; basic knowledge which before now has not been a standard part of training Nepal’s engineers and builders.
Mr Pokharel says earthquake-resistant design has often an elective subject within the Nepalese engineering curriculum.
Any student could become a civil engineer in Nepal and design buildings or other structures without having any knowledge of earthquake engineering.
Nepalese engineers oversee the design and construction of buildings in a country that straddles the volatile Main Himalayan Thrust faultline between the Indian and Eurasian tectonic plates.
Mr Pokharel says this lack of understanding of the dangers can pose to buildings has come about because many Nepalese have never experienced a major earthquake. “The last big earthquake we had was in 1934, and unfortunately, most people had forgotten about that,” he says.
He says there is also widespread misinformation about how people should respond during an earthquake. “Unfortunately, children had been told that during an earthquake they should go under the bed or under tables to protect themselves. There are stories of children who were outside playing when the earthquake started, and ran inside the buildings to hide under the bed as they were told. Many of these buildings that they ran into failed.”
There are fears another large quake could cause greater destruction. The United Nations Office for the Coordination of Humanitarian Affairs has reported a significant seismic event in the Kathmandu Valley has the potential to kill more than 100,000 people and displace millions.
Why did the buildings fail?
Many of the deaths and injuries happened because of poorly constructed buildings that were seismically vulnerable.
Some of the most deadly structures were the many brick/stone masonry buildings with little or no steel reinforcement, making the walls and facades dangerously fragile during movement.
“The brick masonry structures without reinforcement are very brittle. When an earthquake happens, they immediately collapse,” says Mr Pokharel.
“One of the villages I saw did not have a single building still standing. Most of those buildings were made from brick and stone without proper binding materials.
“We can still build using masonry, but we need to seriously consider the reinforcement, ensuring the structure is reinforced at regular intervals, which would create a ‘diaphragm effect’ to strengthen the capacity of the building to cope with earthquakes.
“Diaphragms are the horizontal elements – the floor or roof - which transmit the force of the earthquake to the vertical elements - the walls and frames. It helps the building to act as a whole, which is very important for good building performance during the earthquake.
“The diaphragm should distribute the earthquake force to all the load-bearing walls or frames properly, otherwise some of the vertical elements will receive greater forces than others. If the force is greater than the wall’s capacity, it will fail.”
Concrete frame buildings were also not immune from disaster. Mr Pokharel says there were dangerous faults in many of these concrete buildings that were constructed as “soft storey” structures; buildings that have inadequate stiffness at one of their stories relative to the other stories, often at the ground floor.
“One of the major problems that I saw, which resulted in many collapsed buildings, was when builders would leave the lower floor of the building empty, for use as car parking, or for shops, without adequate supporting walls.
“When an earthquake happens, the more heavily reinforced upper storeys move together in a block and the pillars below cannot support the structure. The upper part is stiff and damage concentrates at the lower level, then the building collapses.”
There are also structural problems during earthquakes in buildings that have used short columns in their construction. Short columns are more rigid than tall columns. They do not have the ability to absorb movement and are therefore more susceptible to horizontal forces during earthquakes. This is particularly problematic when the columns are supporting buildings on a sloping ground.
Mr Pokharel says Nepalese authorities also have the ongoing issue of illegal extensions and poor checks and balances from regulatory bodies.
“In Nepal we have this problem in which the grandfather will build a one-storey house. His son will then add another floor, and the grandson then adds the top storey.”
He says the Nepalese government has enacted laws to stop illegal extensions, but overseeing and enforcing these laws is problematic, compounded by instances of corruption among some officials.
“The good thing about this is, after the earthquake, many people have started removing their illegal top storeys by themselves. They have learned from the experience and they realise the importance of building according to the advice of engineers.”
More than 700 heritage sites were affected by the earthquake, with 95 structures completely destroyed and nearly 300 partially damaged. However Mr Pokharel says that many temples survived relatively unscathed. Despite being centuries old, many were designed in a way that made them resilient to seismic activity.
“They used some very good techniques in building temples. They used wooden frames at certain levels, effectively tying the temple together. When good ties and solid support were used around the temples, those temples survived.
“Another important factor is the shape of the temples. Most of the temples are square in plan and their floor area decreases as it goes up. This is the ideal earthquake-resistant configuration for any structure.”
He says that the worst structural damage to temples often occurred with the heavy metal pinnacles on the roof, the Gajur. If the Gajur are not properly anchored down, they will break free from the roof.
Mr Pokharel says it’s possible for developing countries such as Nepal to build earthquake-resistant housing and structures without it causing unreasonable expense.
“We can increase the capacity to withstand earthquakes, without increasing the cost significantly. All we need to do is change the way they use their building materials.
“In the damaged buildings there was lots of reinforcement that we could see, but they were not using it properly. If you place the reinforcement in the right position, then the building’s behaviour during an earthquake will be different. Doing this does not increase the cost.”
Mr Pokharel says that buildings also need to be built with the ability to move under stress, rather than remaining rigid.
“We call that property ductility. That means that before failing the material should deform. People in a structure will see that it is going to fail, giving them time to evacuate.”
Can this sort of disaster happen here?
Associate Professor Goldsworthy says there are faults close to Melbourne that could potentially generate an earthquake of a magnitude of up to Mw 7.
“The characteristics of the earthquake could be quite different to that experienced in Nepal, due to different faulting mechanisms and site conditions,” she says.
“It should also be added that the annual probability of an earthquake of this magnitude occurring is much smaller in Melbourne than in Nepal.
If an earthquake of this magnitude did occur close to Melbourne, certain types of buildings are likely to be damaged and even to collapse catastrophically.
Associate Professor Goldsworthy says Melbourne has a significant number of buildings constructed using unreinforced masonry, as well as reinforced concrete buildings with non-ductile reinforcement detailing. She says these have been shown to be vulnerable to earthquake ground motions.
“Before the advent of the 1993 earthquake loading standard, many buildings in Melbourne were not designed for earthquakes at all,” she says.
She says Melbourne’s buildings have been constructed to take into account the probability of strong winds, which provides the structure with some degree of lateral resistance.
“But for buildings less than 10 storeys or so that are naturally more susceptible to the high frequency earthquake ground motions, this lateral resistance is likely to be inadequate.
“The Canterbury earthquake sequence in New Zealand, which occurred from 2010 to 2012, demonstrates that the damage caused by very rare events striking close to the CBD of a major city is likely to be extensive and costly.”
Building a new future for Engineers in Nepal
Tackling the engineering skills gap in developing countries such as Nepal is an ongoing challenge. However, the University of Melbourne is establishing a new research unit on Earthquake Mitigation. One branch of this new unit will be dedicated to enhancing the capacity of developing countries to deal with these events, so that when earthquakes do occur, the overall impact is less devastating.
The Earthquake Mitigation Research Unit will be led by Associate Professor Goldsworthy, together with Associate Professor Nelson Lam.
One initial focus of the unit will be to improve the earthquake resistance of housing and other structures in Nepal and Bhutan, countries that are very susceptible to seismic activity. This branch will also offer advice and assist with rebuilding efforts in the current disaster areas within Nepal.
The group aims to offer research and training opportunities to engineering students and academics from these countries, allowing them to collaborate with leading researchers at the University of Melbourne, and bring this invaluable knowledge and experience back to their home countries. The group’s ability to provide these opportunities will rely upon obtaining sufficient philanthropic funding to provide the scholarships and living allowances that these students will need.
The Unit will operate out of the University of Melbourne’s Centre for Disaster Management and Public Safety, a multi-disciplinary centre conducting world-leading research into all facets of disaster management and public safety.
Mr Pokharel says he initially planned to stay on in Melbourne and gain further practical experience after his PhD, which he hopes to complete within a year.
But this earthquake has changed everything. Now, if I get any opportunity to contribute to the redevelopment and reconstruction of my country, I would go back.
Mr Pokharel says that in the meantime he is doing whatever he can from his Melbourne office to help with the reconstruction back home, by offering guidance to engineers who are working in Nepal.
“I am also facilitating investors from Australia who want to contribute to the rebuilding process.
“We are now working in one village in the Nuwakot District, which was devastated in the earthquake. We are developing a project to build earthquake resistant schools and to offer training for local masons, so there is better understanding of how buildings can be made earthquake resistant in future.”
Banner image: A house destroyed in the earthquake that hit Nepal on April 25 this year.Picture: Nirmal Dulal.
Other images: Courtesy of Tilak Pokharel.
To make a donation to ongoing relief efforts in Nepal, please visit the Australian Red Cross.