PRESTRESSED NET REINFORCEMENT SECURES THE DOMES AGAINST EARTHQUAKES
In his diploma project at the Architectural Association, Christoph Klemmt developed an earthquake-resistant construction technique for the low-income population of Afghanistan.
Kabul, the capital of Afghanistan, currently faces a high demand for new houses due to both a high reconstruction need and a fast increase in its population. This lack of available housing results in the development of informal settlements. For example, unused government land on the hillsides in Kabul is illegally occupied by the poorer population.
The houses in the informal settlements are well built, but they are not earthquake proof. For economic reasons, they are constructed from mud bricks, with flat wood-beam ceilings.
This construction technique leads to an increased demand for timber, which is not available in sufficient amounts, and the dry country of Afghanistan will face increased desertification.
Another major problem is the limited accessibility for motorised vehicles. Most footpaths lead straight up the hill, and are too steep to be used by emergency vehicles or waste-disposal trucks. Rubbish fills the streets and causes infections among children, and no clean-water or waste-water systems have been installed. In addition, the fact that the occupation is not legal causes insecurity for the population.
The Kabul municipality cannot afford to construct proper neighbourhoods or provide the basic infrastructure, so the occupants have to develop the settlement themselves.
Therefore, I propose a solution that would grant occupational rights to the settlers if they adhere to basic rules during the construction of the houses. These rules include wood-less, earthquake-resistant construction and the installation of a drainage system which generates an accessible street network. NGOs would give instructions and supply basic construction elements for this.
Following investigations of soil properties and construction techniques, I focused my explorations on possible reinforcement against seismic activity. To counteract the limited tensile strength of the material - mud - a net reinforcement is fixed over the finished mud dome and tied strongly to a structural concrete base ring, resulting in a prestressed earth dome. The structure was tested against vertical loading and horizontal pulses, and especially against the dangerous collapse of the ceiling.
My proposal is that mud-brick domes would be an appropriate, inexpensive, wood-free construction technique for Afghanistan. Earth domes, vulnerable to tensile forces, must have bending-free shapes, which can be simulated by hanging-chain models. Only tensile forces act in this manner and, turned upside down, the shape will only act in compression. Chain-grid typologies were tested for their suitability in instrumented model tests. Ideal sectional shapes, different for vaults and domes and reacting to additional vertical loads, were subject to computational calculation, analysis and evaluation.
There are various techniques for the construction of earth vaults and domes that do not need temporary support.
Following experiments, a system was developed which allows for the construction of complex mud-brick domes without the use of wood. The domes are stable at every point during construction, and the prestressed net reinforcement secures them against earthquakes.
Construction starts with a preliminary distribution of arches that are extended into vaults, evolving into the continuous surface of the dome. This quasi-parametric structural design proliferates according to the quantity and configuration of the arches. The geometric characteristics have been explored with further chain models.
Agglomerations of domes establish room-cluster formations, connected through the initially placed arches.
Adjacent domes then fuse into continuous, compression-based surface morphologies spanning the length of the constraining arch components.
Computer software has been developed to digitally simulate the progressive development of the settlements. In each iteration, a new settler occupies land and extends the path network to his or her house, so that circulation patterns are generated which conform to similar existing street networks.
My proposed regulations will require the construction of a drainage system for each house that connects down to the next household. Alongside this drainage, public footpaths will also develop. Prefabricated drainage elements are provided, attachable only in such a way that a specified fall and curvature are not exceeded. Vehicle accessibility is therefore guaranteed to the accompanying paths.
The drainage system was included in the dynamic growth model. As well as creating roads leading uphill at regulated slopes, it resulted in the formation of house conglomerations around dead ends. These are similar to the street patterns in the old town of Kabul, with a gradation in privacy of the public spaces generated on both global and local levels, from the public main road to the private alley, which is used and maintained by the surrounding households only.
The development of the settlements correlates with an evolution of the individual houses, which is continuously adjusted to altering occupational needs. Density is increased through multi-storey construction. Organisation into room clusters re'ects family patterns, continuing the gradation of privacy inside the house itself. Any type of domestic spatial condition can be generated and adapted easily to the inclined terrain.
Christoph Klemmt is a recent graduate of the Architecture Association and works for Planungsbüro Gerhard Guckes & Partner in Germany