Earthquakes don't kill, buildings do! Not all buildings, but the structures built or renovated without respect to structural integrity, nature of terrain and building codes are most vulnerable to disasters like earthquakes. The April 25th and May 12th earthquakes destroyed more than 750,000 heritage sites, residences, schools, health facilities, infrastructure including roads, water supply system and public facilities.
In this post we list and discuss few of the steps that are important for the rebuilding of the devastated built environment. Forming the very heart of the country, physically and economically, it is vital that these steps be taken to ensure present stability as well as future safety. Cost-effective solutions are recommended, that can be quickly implemented without requirements of special skills or tools.
Transition Shelters to Permanent Houses For sustainable and low-cost transition shelters, the immediate availability of construction materials and skills play a very important factor in deciding the construction technology. This is addressed by using locally abundant resources such as wood and bamboo. Sal and Gwaisasi are traditionally used trees for timber based construction. Bamboo is one of the cheapest means to build a safe, earthquake resistant house. With a high tensile strength (up to 125 MPa) and elasticity, it is ideally suited for building low rise, single-story structures, quickly without requiring specialists. Various engineering organizations as well as not for profits such as Abari provide the technical expertise, handbooks and training for this purpose. A bamboo house can be completed in less than 2 weeks and the cost may depend on availability of bamboo in the area and various factors but is far lower than concrete or masonry building. Moreover these houses are safer and eco-friendly, with projected life-time of about 30 years. In terms of design and construction of such houses, we need to provide lintel breaks at the walls, proper connections to be made between wall and roof, the columns or central pole or the load bearing components should be well treated for rot and other defects before it is placed in the ground, the earth around the structure should be kept dry and well drained at all times and dead load of structure should be kept minimum.
Retrofitting In Urban areas where we have multi-storied structures, the first priority is to establish the integrity of the structure. Buildings may collapse days or even weeks after an earthquake as has been witnessed in the past. Using visual inspection, two areas of the structure have to be checked before any further action is taken. Firstly, all beams, columns and slabs must be carefully checked for cracks and damages. In case of development of heavy stress and strain, the concrete is designed to crack as an early warning before it fails. Special attention should be paid to the beam-column connections. The other area is the ground on which the structure rests. Checks to be carried out if there are any settlements or openings in the ground around the existing structure. The groundwater table should also be checked and kept well below bottom level of foundation. The earth should be dry and well compacted for safety and reliability of the building. If there are any structural defects that are detected, engineers should be consulted before any action is taken. Retrofitting of structure depends on various factors such as strengthening of existing joints as well as adding new columns and foundations as required. Seismic retrofitting is complicated and should be done by consultation with the professionals.
New Construction When construction of new buildings is concerned, extensive geotechnical studies to be carried out before foundation is laid. Proper compaction as well as lowering of groundwater table to below the bottom of foundation level is a must. In the beams and columns, reinforcement must be set up accurately as per drawings. Spacing and location of overlaps is very important here. Quality control and assurance of concrete material and casting process is also a priority. When cast correctly, a reinforced concrete framed structure is very stable during earthquakes. From architecture point of view, the rigid framing should go all around in each direction in symmetrical fashion, building should not be designed top-heavy, water tank should have suitable support, proper lintel, sills and breaks to be provided, all floors should be well-connected with the structural framing, wings should be connected with expansion/separation joint in middle and all slabs, roofs, partition walls etc should be made using light-weight material. Dead load on structure should always be kept to a minimum. Building codes for fire escape, emergency staircase and quick access to the nearest open and safe area should be followed extensively. For high rise buildings, Dampers must be placed at each level of a building, with one end attached to a column and the other end attached to a beam.
Modular Housing Concrete and Steel structure are soon going to be ancient. With the advanced technologies, design and prefabrication of modular housing is more feasible for both single storied as well as multi-storied structures. Using wooden panels, SIP (Structural Insulated Panels) or even paper tubes , permanent structures can be built. Integrating modular structures with solar panels for roofing, rain-water harvesting. low flow fixtures and recycling, sustainable and energy efficiency can be achieved.
Structural Health Monitoring Sensors Widely available electronic sensors alarms and sends notification when the structure is showing cracks and failure in structural elements. Both dynamic and passive sensors can be installed in infrastructures like bridges, roads, tunnels and monuments. These sensors give early warning signals which enable the responsible party to take preventive actions immediately. Only two weeks before the earthquake, I was discussing with the World bank and the Department of Roads to pilot the sensors technology in Structural Assessment of Bridges in Nepal.