Rebuilding Nepal Sustainably: Culture, Climate

Rebuilding Nepal Sustainably:
Culture, Climate and Quakes
Patti Stouter, May 22, 2015
www.BuildSimple.org, Build Simple Inc.
INTRODUCTION
Lessons from Nepal’s 2015 Earthquakes
The first earthquake on the 25th and the
smaller aftershocks on the 26th and 12th of
May caused massive damage to Nepal’s
traditional buildings, leaving upwards of a
hundred thousand people homeless.
Buildings of masonry or small stones without
reinforcement were destroyed, and poorly
reinforced buildings damaged.
Above: Collapsed brick wall in Nepal, Photo by Nabin K. Sapkota
These quakes caused a wide variety of levels of destructive ground motion to an area more than 150
miles wide. Because Nepal is subject to some of the highest seismic risk levels of the world, more
destructive earthquakes are likely in parts of Nepal in the future.
Aid builders with superior building techniques have seen success as their buildings weathered the
earthquakes without significant damage. Smart Shelter Foundation reports 16 buildings standing, of
reinforced stone and confined masonry. Engineering/ Construction advice NGO Build Change plans to
work in Nepal teaching better skills. But as their founder explained recently Scientific American, "If
people don't have the money to build a safe building, then they won't." i
One encouraging sign is a new facebook
page called Earthbag Rebuild Nepal. This
was recently formed because more than
50 independently built schools and
homes of the inexpensive technique have
survived undamaged. Earthbag contains
subsoil and barbed wire, and can cost 1/3
as much as concrete block in the
developing world.
Left: First Steps Himalayas earthbag
school with gabion retaining walls
Sometimes sustainable buildings can be very possible because high energy use to produce materials
means high cost. Nepal needs low-cost buildings.
But all builders planning to build in Nepal must know their level of risk, and choose both plans and
special construction techniques suited to it. The next quake could be 2 or 3x more severe.
Right: USGS map shows
the areas experiencing
different intensities of
ground motion from the
4/25/15 earthquake. Red
indicates >0.75 g peak
ground acceleration
(pga).
In the rush to bring
disaster relief and/ or reconstruction, many foreigners will be making decisions for Nepalis. Aid workers
first need to learn to understand Nepal’s climate and culture. Next comes understanding the seismic risk
of future earthquakes. Finally aid workers need to gain a Nepali attitude toward costs and what is
affordable. Only then can buildings appropriate to Nepal be planned.
WORKING WITH NEPAL’S CLIMATE
Nepal is a humid country. The lower elevations experience hot, humid summers. The mountains have
severe winters, with conditions near Mount Everest extreme year-round.
Nepal is not large enough north to south to have different climate zones determined by latitude. But the
extreme changes of elevation create a wide diversity of temperatures. It is important to know the
building site’s elevation and local climate.
Nepal is a land of high mountains and steep valleys. Only 240 km (150 miles) wide from south to north,
the middle mountain region ranges from 300 m (900’) elevation to 3000 m (9000’) at the edge of the
higher mountains. Above this area tree growth turns into stunted but fragile alpine ecosystems. Wood is
at a premium in Nepal.
Left: Topographic
map of Nepal by
Electionworld
showing the middle
mountain region in
browns
Kathmandu is located at 1300 m (4200’) elevation. From April to October average daily highs and lows
fluctuate at or above human comfort levels. Thick earth and stone walls provide thermal mass, helpful
to reduce high and low temperatures since the daily fluctuation is more than 10 degrees Celsius. Houses
facing 10° east of south will catch the sun in winter but avoid overheating on summer afternoons.
Roofing may need to radiate heat and cool the house at night.
High humidity from June- September make ventilation vital for comfort during the daytime. If possible
turn buildings to capture prevailing summer breezes, and or use porches or vertical elements like
ventilation stacks. During the winter, temperatures drop below comfort levels. Because these are drier
months with high elevation sunshine, passive solar heating can work well.
Left: Newari houses with unique decorations used wooden beams
to brace stone or brick. Similar styles work in drier regions, but many
in Nepal were destroyed because of unseen weakened beams. Photo
by Francisco Anzola
Traditional buildings in the city of Kathmandu are several stories in
height, using the ground floor for animals and farm tools. Yet many
are being torn down to build modern buildings. Current land
pressures are even more intense.
Research the traditional building styles before planning. There are
excellent
discussions
of how
traditional
buildings are
adapted to Kathmandu’s climate with
recommendations for new construction ii.
Before planning to build, learn. Try to
understand the culture and to appreciate their
old ways of building. Little innovation after a
disaster is welcomed or needed.
But also find out how your area is changing. Do
people still spend long hours outside, reducing
somewhat their need for light and ventilation inside? Do they still live in
extended family groups? How has their work schedule and location
changed? Do they use a porch or balcony?
Above right: Traditional Nepali village home,
photo by Nepalisam
Right: Light shelves keep heat out
and let sun bounce in on a shade
Schools or offices with little or no electricity need big windows for lighting, possibly with light shelves to
reduce overheating in the summeriii.
At higher elevations, the r-value is as important as thermal mass. If users can afford a heating system,
consider radiant heat with a rooftop solar collector or a mass heater like the Chinese kang. Forced air
heat does not work unless the windows
and doors are kept shut. And the vents
are perfect for rodents in the country.
Modern Nepalis are turning to concrete
and brick buildings because wood is
scarce and protected in their small
country. Bricks are costly to burn, and
often weak because they are not wellfired. It is a challenge to create affordable
houses out of these heavy materials that
can be safe during earthquakes.
Right: Traditional palace, photo by
Francisco Anzola
If carefully planned and built with a light
roof, earth buildings in moderate seismic
risk areas can have a second story or loft
of light weight materials. But for the high
seismic risk in most of Nepal, low strength
materials like earth are safest used for a
single story.
At higher elevations, insulation value is desirable. Cooler regions using winter heat will find earthen
walls cold.
Sustainable materials with some insulation value like light straw clay or straw-bale may be helpful in
cooler areas. These both have potential for flexing in earthquakes.
But if straw is not common enough to
create thick walls, added layers of
insulation material like rice hulls can
greatly improve a family’s way of life.
Left: Straw-bale house, photo by
Diamond Mountain
UNDERSTANDING EARTHQUAKE RISKS
Instead of the well-known Richter scale magnitude levels, like 7.9 and 6.7, builders need to discuss
exactly how much and how fast walls will move in a horizontal direction at a specific location.
At each site, the type of soil, depth of quake, and distance from epicenter determine how much stress a
building receives. Often local stresses are listed by the Modified Mercalli Intensity scale of I- XII. This
describes how the earthquake felt in the area and the general types of damage it caused.
Each Mercalli intensity has an approximate peak ground acceleration range or pgaiv. Earthquake
researchers map pga values at different locations. The pga tells us how far and how fast walls move, as a
% of the force of gravity.
Engineers and architects plan buildings to resist a certain
level of pga, a number considered the ‘design value’. In the
developed world the minimum design value is listed by the
building code, based on the level of quake motion with a
slight chance of happening every 50 years. This is because
less frequent, bigger quakes cause disasters.
In the developing world where there are no required codes,
it can be hard to choose a good design value. Limited funds
pressure builders to avoid the costs of preparing for
earthquakes that may not occur for decades. First,
understand what the design value would be under standard
codes like the International Building Code (IBC).
The soil conditions under a building also greatly influence the
stresses during an earthquake. The IBC requires buildings on
soft soils (like those in Kathmandu valley) to be stronger than
those on ordinary sites because soft soils amplify earthquake
motions (the codes have complicated charts for this). But the
IBC also allows buildings on bedrock to be built to 20% lower
pga levels because massive rock reduces vibrations.
A special word of warning about soils that can be flooded.
Sandy and silty soils that are sometimes flooded (near
beaches or rivers) should not have heavy buildings. Wet soils
without much clay tend to become liquid when shaken by an
earthquake, and heavy buildings can simple overturn or sink.
It’s not worth the risk.
Think about whether the building is an essential emergency
structure like a hospital or government disaster center. In the
recent Nepal quakes where surrounding villages were mostly
destroyed, surviving small schools became emergency
shelters/ aid centers.
Building stress :
quake increase in motion (pga)
x wall & roof weight
Peak Ground Acceleration = pga
Local Site Design Value= Ss pga
Pga that has a 2% chance of
happening in 50 years for fast
vibrations
Find your Ss pga from
’10 UFC or ’10 Eurocode at:
http://geohazards.usgs.gov/designm
aps/ww/ for your location
Buildings on rock- pga
x 0.8
Buildings on soft soil- ask an
engineer for advice!
Left: Pegasus Children’s Project’s
neighbors are using tents because
their home is destroyed
Peak ground acceleration levels
include different values at different
vibration speeds. Buildings of 6
stories or more are damaged by
slow vibrations. This paper
addresses one and two story
buildings, which are damaged by
faster vibration, called Ss values.
All discussion of recommended
pga limits for buildings in this
document will be Ss values.
The map below does not show exact locations of Ss values. It was drawn roughly because large scale
maps can’t be accurate enough. Much of central Nepal is likely to experience 1.5 g ground acceleration
or higher. These are numbers that are worth checking carefully.
GET STARTED
Find the Risk for your Site
Find out what forces your building might need
to stand up under.
Researchers continually find out more. Old
earthquake hazard maps may not be updated
with new information. Also, local slopes,
subsurface conditions and fault zones
influence exact local pga levels. Building
planners should use the best information they can get.
The online tool shown at left is found at: http://geohazards.usgs.gov/designmaps/ww/. This is the USGS
Worldwide Seismic Design Tool (Beta version).
Input latitude and longitude and receive a chart with several sets of Ss values (ignore the S1 numbers).
Or reset the layers (upper right) to greyscale view, and drag the marker and zoom in to find your area.
Which Values to Use?
The earthen building guidelines for New Zealand are a good starting point to understand earthbag
building strength. The 2010 UFC data are the most similarv. In Nepal the Eurocode information (from
2010) may be the best available. GSHAP maps published in the past, and those from other organizations
may use different probability levels and would require conversion of their pga levels to correspond to
those recommended.
Discussion of Nepal’s seismic hazard in this document uses the 2010 Eurocode Ss values from the USGS
worldwide tool, which are based on 2% in 50 years probability.
What risk do those who want to rebuild Nepal sustainably face?
Three aid groups who have recently built earthbag buildings in the quake-affected region of Nepal face
between 2g and 2.1 g risk. Kathmandu in general is about 2g. The Pegasus Children’s Project and First
Steps Himalayas both seem to face a little more than 2.1 g risk. Edge of Seven further east may face just
under 2 g pga risk.
Right: Map based on the USGS
pga data showing the location of
several earthbag building sites
HOW TO BUILD QUAKE RESISTANT?
The Smart Shelter Foundation has a wonderful slide show introducing principals for quake-resistant
design.
http://www.smartshelterfoundation.org/smart-shelter-techniques/22-earthquake-design-principles/
These concepts are important, but more apply to traditional masonry than to alternative materials.
Can we build sustainably and for earthquakes?
Light-weight and flexible walls like wood, bamboo, and straw-bale survive earthquake stresses more
easily than heavy masonry walls. But wood and bamboo are quickly destroyed by termites in humid
warm or temperate climates. Plastered straw-bale may be equally vulnerable. Nepal’s original forests
are under great pressures for cooking, brick making, and also for agricultural expansion as wellvi.
Subsoils containing some clay are available for earthen buildings. This is why Nepal’s traditional
buildings often are made from mud and small rocks.
Earthen construction moderates temperature and humidity fluctuations. A water-resistant foundation,
and lime plaster or cement stucco protect them from the climate. But raw earth is a low-strength
material that needs reinforcement for seismic risk areas.
Earthen walls of adobe or rammed earth can withstand some vibration if heavily reinforced with
bamboo or steel rods and steel or plastic mesh. But this is costly.
Flexible Earth Building
Earthbag is simpler to build than adobe, CEB, or rammed earth, and intrinsically more reinforced.
Barbed wire is laid between courses of poly bags filled with moist cohesive soil. Only a small proportion
of manufactured materials is required. This immediate technique can be used with a wide variety of
soils. Walls are built moist to full-height and plastered or cement stuccoed after air-drying.
Earthbag is a low-tech, labor-intensive way of building. It does not require power tools or much water.
But unreinforced earth is not recommended for stresses above 0.3 or 0.4 g (or force of gravity). Even
guidelines for strong fired bricks used in Confined Masonry, recommend engineering help for any design
values above 0.4 gvii.
Flexibility must be the reason that carefully built one-story earthbag homes and schools had no damage
or only slight plaster cracking after shaking as strong as 0.6 or 0.7 g motion.
Conventional earthbag test walls appear to be stable even when damaged, less likely to collapse than
other types of earthen walls. New types of earthbag that have stronger reinforcement may provide new
seismic wall materials.
Straight or Curved?
Domes are a special monolithic bearing wall with less material and less weight higher up. Well-built ones
can withstand earthquakes well. But domes provide less ventilation than vertical wall buildings, and
need either a lot of stabilizers to make the dome top waterproof, or a very carefully maintained
waterproof surface.
Round buildings with vertical walls offer more ventilation than domes, but still resist quake damage
better than straight, vertical walls.
Left: Dome bases for the Pegasus Children’s Project. Could
these strong shapes have been vertical walls for more
ventilation?
Building shapes are a cultural value absorbed very early in life.
Many cultures are group oriented and change slowly.
Traditional building shapes draw neighbors together, and are
especially desired after disasters.
Traditionally, domes and round homes with conical roofs are
beloved in certain cultures. There are many different types of
round buildings scattered across sub-Saharan Africa, and more
isolated clusters in South America, India, and Southeast Asiaviii.
Nepal does have some traditional domes and round-houses, but check what your local recipients’ think
about curves.
When discussing plans, ask whether there are different ethnic groups nearby, and whether they like
different building shapesix. Individuals helping may be from a different background than most locals.
Domes and circular buildings offered as aid structures to people who prefer other shapes have been
refused or abandoned in the past. Adding local style and small roofs may be vital.
CAN EARTHBAGS BE STRONG
ENOUGH FOR NEPAL?
Since many regions of Nepal are likely to receive 2- 3x as
severe earth movement in the future, builders need
stronger earthbag.
In New Zealand, unreinforced earthen buildings following
strict guidelines are allowed in areas with pga values up
to 0.56 g (or higher with specific engineering design).
Build Simple’s test results have shown that well-built
earthbag with plaster mesh can be as strong as NZ’s
tested wall strengths.
Earthbag domes built with barbed wire but little or no
rebar reinforcement, exceeded stringent seismic tests by
CalEarth for their California location by 200%. (Currently
Hesperia has a Ss design value of 1.5 pga.) Does that
mean that well-built domes should be safe up to the
highest seismic risk areas in Nepal?
EARTHBAG QUAKE
STRENGTH LEVELS
Conventional earthbag without extra
reinforcement
STRAIGHT WALL: 0.7 g
CURVED WALL: more?
DOMES:
1.5+ g
Reinforced earthbag (per NZS guidelines)
STRAIGHT WALL: 2.2 g?
CURVED WALL: more?
Earthbag technologies are rapidly developing. We have great hopes for new types of quake resistant
earthbag.
Please help Nepal build back betterBetter for their climate,
better for their culture,
and better for their seismic risk.
If you feel that earthbag may be a part of that rebuilding, more information is in Build Simple’s booklet
Earthbag Options for Nepal online at http://buildsimple.org/resource-lists.php.
Build Simple welcomes comments, project reports, and evaluations by engineering students and
professionals. We hope to have more solid data about building strengths this year.
[email protected]
i
David Biello, How to Prevent More Deaths When the Earth Quakes, Scientific American, May 12, 2015, Acessed
5/22/2105 at http://www.scientificamerican.com/article/how-to-prevent-more-deaths-when-the-earth-quakes/
ii
Anir Kumar Upadhyay, Harunori Yoshida, and Hom Bahadur Rijal, Climate Responsive Building Design in the
Kathmandu Valley, accessed 5/7/15 at http://personales.unican.es/rasillad/Mahoney_example.pdf ; another
example is: Prakash Subedi, A Sustainable Housing Approach to Kathmandu, Nepal, 2010 University of Florida,
accessed 5/7/15 at http://ufdc.ufl.edu/UFE0041662/00001.
iii
SKAT’s Climate Responsive Design has a chapter on Buildings in Kathmandu, Nepal 1993, accessed 5/7/15 online
at http://collections.infocollections.org/ukedu/en/d/Jsk02ce/4.7.html. Light shelves are well covered in G. Z.
Brown and Mark Dekay, Sun, Wind & Light 3rd edition, 2014, Wiley
iv
Correlation with Mercalli Scale chart by USGS in Wikipedia article ‘Peak Ground Acceleration’, edited 12 March
2015.
v
Engineer Gabriel Miller recently evaluated the pga levels where unreinforced earthen walls and reinforced
earthen walls are allowed according to the NZ standards, and developed full spectral response graphs to compare
the old NZ quake risk zones with newer risk descriptions. His information confirmed the evaluation of a previous
researcher, and will be posted online soon. Contact him at [email protected].
vi
Environmental Services and Software’s Case Study on Macro-scale, Multi-temporal Land Cover Assessment and
Monitoring of Nepal at ww.ess.co.at/GAIA/CASES/TAI/cst-np.html includes some maps of vegetation in Nepal
that may give aid workers a preliminary glimpse of the type of natural materials available for their target area.
vii
Roberto Meli et al, Seismic Design Guide for Low-Rise Confined Masonry. Confined Masonry Network, August
2011 accessed online at
http://www.sheltercentre.org/sites/default/files/16.02.2012_confined_masonry_design_guide_8_2011.pdf
viii
Marcel Vellinga, Paul Oliver, Alexander Bridge, Atlas of Vernacular Architecture of the World, 2007, Routledge,
Oxford UK, pp. 66-69
ix
Map of Nepal’s ethnic groups, from the University of Texas library, on a small Nepali website by Arodya Khadka
accessed online 5/7/15 at http://www.homeinc.org/somerville/?q=node/848