In recent earthquakes, numerous RC buildings were severely damaged or had even collapsed as a result of the structural modifications during construction
KATHMANDU, JANUARY 17
The entire region of Nepal lies in an active seismic zone related to the movement of tectonic plates along the Himalayas.
Cities located in Nepal that face high seismic hazards have large numbers of buildings, which are mostly constructed out of reinforced cement concrete (RCC) moment-resisting frames – that is, a rectilinear assemblage of beams and columns, in which the beams are rigidly attached to the columns – with infill masonry walls that share common characteristics and seismic vulnerabilities. The collapse of such structures during the recent earthquakes has killed many people. The main reason behind the collapse of such buildings is the construction of additional storeys illegally for business purpose.
Similarly, carrying out building construction without soil tests, ductile detailing of reinforcements, constructing slender buildings without a seismic gap (that is,a separation joint provided to accommodate relative lateral movement during an earthquake), creation of a cold joint (that is, a plane of weakness in the concrete memberscaused by an interruption or delay in the concreting operations), and erecting buildings on sloping land without proper embedding of footings may cause buildings to collapse.
Though the government has introduced urban planning and building by-laws after the 2015 Earthquake, yet the buildings and structures constructed without following the building bylaws have added to congestion in Nepal's cities. Provision of open space requirement, set back distances or floor area ratio has not been effectively implemented, and haphazard plotting of land without a land use map has increased the risks of disasters like earthquakes, floods and landslides.
All the municipalities in Nepal are supposed to categorise the type of buildings and legality of maximum number of floors that can be constructed within the range of cities, but due to lack of supervision by the government and monopoly of the contractor, low quality materials are used in the construction of buildings in the Kathmandu Valley and other major cities of Nepal.
Secondly, the strong column and weak beam principle is not followed in most of the constructed RC buildings, making it one of the reasons for the damage and collapse of buildings during earthquakes.
Normally, reinforced concrete buildings using monolithic framed construction are in use in Nepal, and there is no tie with the infill walls except the shear wall when the basement was constructed. Low quality building materials like bricks, mortar and cement used to construct such infill walls leads to several cracks (horizontal, vertical and diagonal) in masonry works.
In recent earthquakes, numerous RC buildings were severely damaged or had even collapsed as a result of the structural modifications during construction by non-skilled contractors and absence of supervision by structural engineers as well. Infill masonry can drastically modify the intended structural response, attracting forces to parts of the structure that have not been designed to resist them.
Similarly, during construction of buildings, to ease formwork (shuttering) in RC columns and workability, various contractors apply their own methodology to cast in situ, with such RC columns having several joints in a single column. Then the column will be vulnerable during an earthquake as the lateral resisting capacity of the RC column is weaker at such joints.
Lack of development length, anchorage, hooks in reinforcement steels are applied not as per design but as instructed of the contractors who are after only profits in the construction of such buildings.
Furthermore, as most of the country is made up of rural areas, where people lack awareness about earthquakes, buildings are erected by depending solely upon skilled labourers' suggestions. People only give priority to the financial aspect while constructing a building, it is not analysed for vulnerability to an earthquake.
In such a scenario, the government has to launch awareness campaigns in the rural areas through experts so that the people there understand not only the economic aspect of building houses but also the safety aspect should there be an earthquake. A one-day orientation on Earthquake Day cannot help develop awareness among the people in the rural areas about the hazards earthquakes pose.
Remote villages of Nepal suffer from severe poverty, and therefore the people there cannot afford to build safe houses made out of reinforced concrete cement. They can, however, use local materials like bamboo, wooden tie, strings made up of local materials to provide ductility to the building.
Finally, we must be prepared for three phases of an earthquake. There is a saying 'earthquakes don't kill people, buildings do'. Safe buildings that meet the codal requirements are necessary, and are to be built in the pre-earthquake phase. The public buildings designed by various consultancies should be reviewed by experts for vulnerability assessment to mitigate even minor errors in the previous design.
During an earthquake, knowledge about safety, fire prevention, pounding of adjacent buildings and their influence should be provided through various trainings for people, especially in the rural areas. To renovate buildings in the post-earthquake phase, redesign of buildings should be followed by collecting samples of buildings weakened by the earthquake and the retrofitting process applied.
Research on structural defects, failures and construction defects should be done by scholars and related institutions so that we can prevent the collapse of structures and loss of lives and properties.
Lamichhane is Professor at Pokhara University and Neupane is Assistant Professor at the Graduate School of Engineering, Mid-West University
A version of this article appears in the print on January 18, 2023, of The Himalayan Times.