Text by Ignasi Agustí Fusté, Lead Architecture
At Bhimphedi I was able to see firsthand the magnificent work of the Awasuka program team in the construction of new homes and the repair and reinforcement of homes damaged by the earthquake. The Awasuka program is developed by the NGOs of Amics del Nepal, Base-A and the Center for Development Cooperation of the UPC.
With the objective of transmitting knowledge of anti-seismic construction, there have been planned the construction of several prototypes. At the moment there is a wooden prototype already constructed, a confined concrete block prototype under construction, and a traditional technique prototype (made of stone walls and mud) under construction as well.
“Patra” prototype (wooden emergency refuge):
In Nepal, emergency refuges are usually constructed with metal sheet roof, and many people end up living for many years. These refugees have a poor behavior at the thermal and seismic level, so then Awasuka decided to give an alternative also using cheap material: the “patra” wood, a second quality wood that is normally used to make formwork, etc…
This prototype is already finished, and it was built for the cook of the orphanage and her husband. The set rests on a layer of cycloping concrete (mixtures of cement, sand and heavy stones) to improve contact on existing soil, and also rise about 50cm from this level with a plinth beam, or anti-seismic foundation base, to protect the house from torrential rains.
To build the entire prototype, we used ‘patra’ strips, which is the leftover wood pieces from the tree trunk, much more economical, and 2.5x10cm in section. The vertical walls are resolved with self-supporting wooden panels made up of studs and cross-sections and coated with diagonal slats that tighten the panel. The cover is lined with wooden beams, also formed by patch strips, plates of plywood and metal sheet. In the case of the porch, instead of a plywood, the cover is resolved with straps of bamboo as a belt, to improve the thermal behavior of the roof plate.
One of the important points is the horizontal triangulation in the corners, which, together with the diagonals of the vertical panels, they unite the set into the three dimensions of the space, thus constituting a compact box that is perfectly cohesive and resistant to earthquakes.
Concrete block prototype (confined rubblework):
The low-cost housing construction system called “confined rubblework” is an anti-seismic technique that is used in many countries in the world with the earthquakes problems. This system is not being promoted by the government of Nepal, so Awasuka decided to make its dissemination.
The concrete block is a relatively recent construction element that is increasingly being used in Nepal, instead of the traditional brick, which still predominates clearly. The quality of the blocks is still in process to be improved, but in spite of that it is an economical material, so we wanted to make this construction proposal with confined blocks in an armed concrete cage.
As in the rest of the prototypes, the project is elevated on the base of the anti-seismic foundation of reinforced concrete. Once this socket is made, the inside soil is compacted and then the first row of blocks is placed on the foundation. As the blocks are positioned, horizontal and vertical reinforcements must also be placed, they are a very important element of the confined block prototype. On the corners, there are the other reinforcements that will be the square section columns. Alternating rows we also put horizontal L bars on the corners, and inside the blocks, we put vertical bars that will sew the walls.
Once all the reinforcements are formed, the blocks will be confined inside, so the whole group will work solidarily. This concrete cage will be permanently closed once a perimeter beam, that will go to the above the door and the windows, will be concretized.
“Dhunga mato” prototype (stone and mud houses in rural areas):
The traditional stone and mud technique is the most commonly used in rural areas of the country. The government has made a catalog of different models of houses made with this technique, which historically already had anti-seismic criteria, and which are now recovering again. But all government models are based on houses with compartmentalized rooms with stone walls; The traditional typology of the perimeter wall and the internal wooden structure have been lost, which creates undifferentiated spaces and a free distribution in its interior. This model is what Awasuka is spreading, reinforced by rigidizing modules with diagonals in the three directions of space.
In this model under construction, the foundation is more important than in the rest of prototypes, due to the weight of the stone and the dimensions of the building, greater than the others and with two floors. Below the plinth beam, a large foundation with a stepped section has been constructed, because the transmission of forces from the wall to the ground does not occur perpendicularly, but with a 60º angle. The foundation, as well as all the rest of the set, is made of thick stones and mud, put with a specific technique that the ‘mistri’ (master bricklayer in Nepali) explains to the rest of the workers and bricklayers. To improve the mechanical properties of the clay as a binder material, 5% of cement is added to the mud mortar, in a proportion of 1 bucket of cement for every 19 buckets of soil. Once the foundation of stone is finished, the surrounding soil is compacted and the formwork is prepared for the concrete base.
The stone and mud walls rise on this concrete basin with the same technique used in the foundation, and the wooden frames are placed already to make the space reservation for the door. One meter above the base of the wall we put the first “ladder”, one of the basic elements of the project. These ladders are wooden slats that cover the entire longitudinal dimension of the inner and outer walls, sewn together with transverse slats.
This first ladder establishes the lower level for the windows, that lean on it, and the second ladder will define the upper level for these windows, coinciding with the upper level of the door frame. This is the way to fix the wall at its weakest point, the openings. In this second ladder, a diagonal plate is added to the corner to fix the whole enveloping, as well as in the wooden prototype in order to triangulate the other weak point of the buildings in front of the earthquakes, the corners.
In order to keep building up, a bamboo scaffolding has been built, which also serves to stack the stones. Half a meter above the level of the photographs a third ladder will be mounted, upon which the intermediate floor will be supported. In this case, the diagonal of the corners will go below the stairs to facilitate the continuous support of the floor.
This tied up between the stone walls with the ladders is a very ancient seismic technique in Nepal, but the progressive relaxation of the population due to the great lapse of time between large earthquakes (80 years) got it to waste. Other anti-seismic elements in this prototype the diagonals in the floor and roof slabs, and the vertical stiffening modules.
I take this opportunity to promote the work of the whole team through the different websites of the program’s collaborators:
FRIENDS IN NEPAL