Nepalis may have been lulled into a false sense of security about the strength of reinforced concrete structures.
In a narrow alleyway deep in the heart of Patan adjacent to the ruins of a clay-mortar house, a four-storey concrete block stands tall, unscathed except for some minor cracks. In street after street of the ancient towns in the Valley, centuries-old temples and ancestral homes have been reduced to rubble right next to buildings made of concrete.
On another narrow lane near Mangal Bazar there is now a pile of bricks where there used to be a house with its first two floors made of bricks and clay. The owner had added three concrete floors on top of it. A family of seven lived there, and four of them were killed when the entire structure collapsed during the earthquake on 25 April. On either side of this house, two five-storey buildings made of reinforced concrete are still standing.
MUD VS CEMENT: Mira Maharjan points at her parent’s reinforced concrete structure in Patan that withstood the earthquake. Photos: Kunda Dixit
“We learnt during this earthquake that cement houses are stronger,” said 41-year-old mother of two, Mira Maharjan, who is afraid that her own brick-and-mud house may not withstand another quake. “But my parents live in a cement house, so I am not worried.” Maharjan works in Patan Museum and was lucky to survive the collapse of the east wing of Sundari Chok.
Because so many of Kathmandu’s concrete-built structures survived, it has confirmed public perception that these are structurally safer than traditional clay-mortar brick buildings. However, engineers specialising in seismic-resistant housing say Nepalis may have been lulled into a false sense of security with this renewed trust in concrete.
They say the way moulds for reinforced concrete beams and slabs are prepared and the use of substandard raw materials may make these houses less safe in future quakes. Reinforced concrete in itself isn’t bad, but it needs knowhow and training for the buildings to be durable.
“The only reason reinforced concrete structures survived this time was that the intensity and duration of the earthquake was not as big as predicted,” said Padma Sundar Joshi of the United Nations Human Settlements Program (HABITAT). “If the intensity was a notch higher and if the shaking had gone on for 10 seconds longer, reinforced concrete structures would have also come down.”
The 7.3 magnitude aftershock on Tuesday brought down concrete buildings already weakened by the main quake three weeks ago, and forced people back to shelters in open spaces. Maharjan had already gone back to her house, but returned to her shelter at the royal garden of Patan Darbar.
A brick and clay-mortar house that is in danger of collapsing.
“I was taking pictures of the damage of my brick house when another one hit us,” said Maharjan. “I don’t know when I’ll go back to my own house.”
The problem lies with traditional masons who lack the training and knowledge to ready concrete moulds, and often do not know how to prepare joints for iron rods, they do not follow time limits on mixing cement, and design houses with unsafe cantilevers and unnecessary decorations. Joshi warned: “If we don’t change the way we work with cement in Nepal, building more reinforced concrete houses will lead to disaster.”
Bijay Karmacharya is a Nepali engineer currently working for post-disaster housing in Burma, and likens building homes to visiting a doctor. “If you need an operation, you go to a qualified surgeon. But if you want to make a house, why don’t you go to a qualified engineer? After all, both professions are essentially about saving lives.”
Kathmandu already has a strict urban building code prepared in 1993 containing specific guidelines for the design, construction and mandatory rule of thumb (MRT) for buildings up to three floors. This code now needs to be revised and enforced.
Bijay Krishna Upadhaya of the National Society for Earthquake Technology – Nepal (NSET) advised the Pakistan government after the 2005 earthquake, and said disasters offer an opportunity to reform housing criteria and enforce safety guidelines.
“In Pakistan, reinforced concrete buildings collapsed even though it was an earthquake of much lower intensity because required procedures for concrete were not followed. The same could happen here next time,” he said.
Seismologists have been surprised by the scale of the destruction in the mountain districts north of Kathmandu because they had expected much more devastation in the Valley. Now, they worry that many families will build reinforced concrete houses in district headquarters or in villages where engineering norms are even less strictly followed than in the city.
Upadhyay said: “If new reinforced concrete houses are not properly made, you don’t even need a 7 magnitude earthquake to bring them down.”
The big challenge for rehabilitation in rural Nepal now will be to make sure that people have emergency shelters for the coming rainy season, and then build safe permanent houses for the future (see box). “We shouldn’t just be promoting emergency shelters for the monsoon, they should also be warm enough for the coming winter,” Joshi said.
At HABITAT and NSET, experts believe that the next phase after emergency tent and tarpaulin is for the mass distribution of corrugated sheets which can be used for roofing of improvised houses made from salvaged bricks which can be recycled for building permanent homes later. Nepal currently produces 80,000 tin sheets every day, and this production capacity is enough to meet demand.
The Nepal Engineering Association (NEA) has deployed 3,000 engineers to go house-to-house for a rapid assessment of buildings to categorise them as liveable, repairable and ones that need to be demolished. After the earthquake and aftershocks, many families haven’t gone back to their homes even though they are safe or can be retrofitted.
Upadhyay reckons that one-third of the 600,000 houses that were either destroyed or damaged in the earthquake can be repaired, and this would be cheaper than rebuilding them.
Cheap, light, quick
Two weeks after the 7.8 magnitude earthquake rattled central Nepal, attention is now turning to reconstruction of the estimated 600,000 houses that have been either damaged or destroyed. The government and relief agencies are struggling to provide emergency shelters suitable for both the approaching monsoon and winter, while trying to decide how best to ensure cheap, easy-to-make and safe permanent homes for the 8 million people in Central Nepal who are affected.
The scale of the need is overwhelming, and many survivors who have tents are now demanding tin roofing. Others have already started to rebuild destroyed homes with salvaged material, while some are using local bamboo and thatch to make temporary housing. City-based groups also offer a range of options for cheap, easy-to-build homes that can be mass produced.
Bamboo is perceived as a poor man’s building material, and is looked down upon. However, it is plentiful, strong and can be turned into light, cheap and attractive homes. There are many options available depending on the size of the family and can be constructed in three months, and can last at least 25 years. While a concrete building can cost Rs 3.5 million and nine months to build, a bamboo home with basic amenities will cost only Rs 500,000 and can be put up in three months after builders are trained.
Mud has got a bad reputation after this earthquake because so many clay-mortar brick buildings could not withstand the shaking. Even though it will be difficult to convince people to go for mud, adobe housing can be buttressed, made earthquake resistant and can be quite attractive. Mud construction is also light, and has better insulation properties. It just needs to be protected from rain and moisture.
‘Resilient Homes’ is promoted by Himalayan Climate Initiative (HCI) with steel frames as an option for rebuilding homes and schools. These low cost, quick-to construct modular prototypes can convert into permanent structures later. They are replicable and expandable meaning the owners can improve it when they can afford the time and money. The budget is comparable to current market prices for houses with the same floor area.
This method evolved from military bunker construction techniques is inexpensive and quick to put up. Earthbag schools in eastern Nepal withstood the 25 April earthquake, and temporary shelters made of earthbags have been used extensively in Pakistan after the Kashmir Earthquake of 2005. Plastic bags are filled with sand, stone dust, gravel and moulded into modular shape for stacking into walls. The roof can be made of bamboo, thatch or corrugated tin at the site itself.
Everything Organic Nursery located in Kavre has come up with a design for transitional homes for families of five to six that could be used for a year or more until a permanent house can be built. They are expandable and the design is based on the traditional thatch hut (chapro) and uses bamboo or wooden pole frame and corrugated metal roof. The walls are made of bamboo strips and are plastered with a clay/fresh cow dung plaster.
Possibly the easiest and fastest to build, there were several Nepali companies offering this method of construction even before the earthquake struck citing the seismic resistant properties of their homes in their websites. Pre-built wall panels can be transported and quickly assembled at the site with corrugated sheets for roofing. It doesn’t require water, bricks, cement, iron rods, sand or stone to construct. A typical two-room, one-bathroom home costs Rs 600,000.
Massive earthquake rattles Nepal, Om Astha Rai
Microcosm of a calamity, Cynthia Choo and Sonia Awale
Monumental loss, Stéphane Huët
Preparing to be prepared, Kunda Dixit
Mud, glorious mud, Nripal Adhikary