Aseismic Building Design in reference to Seismic Microzonation

Herojit Nongmaithem *

'Earthquake never kills; but the buildings do kill'.

Hope all can perceive the irony of the quote and is much in relevance with the present day. The process of globalization is at the peak throughout the world, and the best known impact is the present day urbanization which particularly for our state is seen agglomerated in and around the Imphal city.

Nevertheless, other parts of the state are on the boom of constructional phase. With the implementation of Atal Mission for Rejuvenation and Urban Transformation (AMRUT) and onset to launch Online Building Plan Approval System (OBPS), logical and scientific approach to the urban development needs to be sought or else will regret in the future.

Much insight needs to be considered for the interdisciplinary fields like social engineering and design sciences while focusing on urban planning. The primary concern is the public welfare, which includes considerations of efficiency, sanitation, protection and use of the environment, as well as effects on social and economic activities.

Although it predominantly concerns with the planning of settlements and communities, urban planning is also responsible for the planning and development of water use and resources, rural and agricultural land, parks and conserving areas of natural environmental significance. Practitioners of urban planning are concerned with research and analysis, strategic thinking, architecture, urban design, public consultation, policy recommendations, implementation and management.

Bureau of Indian Standards (BIS) [IS 1893 (Part I): 2002], has grouped the country into four seismic zones, viz. Zone II, III, IV and V and the entire state of Manipur falls under the zone V which defines the maximum seismic hazardous scale. In this perplex seismicity and earthquake hazard have a vital role to play owing to the location of Imphal city.

Seismic knowledge can be explained in terms of three basics; Source, Path & Site Response. Source here implies the origin of the earthquake wave or the epicentre. It depends on the depth of the earthquake. Path indicates the route which will propagate the seismic waves; so to say the material of propagation of the wave.

Practically it's the medium of seismic wave transmission. Lastly Site Response collectively represents the spot where the intensity of the earthquake responds to the earthquake wave. For our state, findings suggest higher risk as the Path- the medium of the transmission of the seismic waves prone to disaster as the underlying rocks are soft sedimentary rocks. The entire Imphal valley has a thick alluvial cover which is highly susceptible to seismic waves and tends to magnify the earthquake intensity.

Thus the Site Response factor also predict to a more disastrous outcome. It's the Source factor which may be the protective reason withstanding from a gloomy earthquake disaster in our area where the depths of most of the earthquakes are either medium to deep seated earthquakes. So whenever shallow earthquakes do happen, the extent of damage can be manifold as the other factors are catalysed to hazard.

Questionable thoughts nowadays; Are the buildings and constructional projects obey building bylaws? Are the projects have written approval from the concerned authorities? How much of the public have awareness of the building bylaws? Are the concerned departments do faithful researches about the seismic hazard zonation?

The author beliefs all the answers are negative. Then most part of the state, or to specify the urban Manipur itself is exposed to the most dynamic disaster EARTHQUAKE. Manipur itself by nature is prone to seismic which should be minimised by technical combat against earthquake. Few simplified basics could prevent possible wraths of earthquake.

An earthquake-resistant building has four virtues in it, namely:
(a) Good Structural Configuration: Its size, shape and structural system carrying loads are such that they ensure a direct and smooth flow of inertia forces to the ground.

(b) Lateral Strength: The maximum lateral (horizontal) force that it can resist is such that the damage induced in it does not result in collapse.

(c) Adequate Stiffness: Its lateral load resisting system is such that the earthquake-induced deformations in it do not damage its contents under low-to moderate shaking.

(d) Good Ductility: Its capacity to undergo large deformations under severe earthquake shaking even after yielding is improved by favourable design and detailing strategies. BIS has prepared guidelines for retrofitting in existing structures.

A list of code books on construction practices of buildings and structures, to minimize the earthquake losses, is available. In addition to this, Housing and Urban Development Corporation (HUDCO) & Building Materials & Technology Promotion Council (BMTPC) have also published guidelines and brochures for construction and retrofitting of buildings.

Loss of life and damage of property due to earthquakes could be considerably reduced through proper planning and implementation of pre- and post-disaster preparedness and management strategies by respective State and Central Government agencies in a coordinated manner following the above mentioned guidelines.

These studies involving preparation of geological, geomorphologic and land use maps followed by drilling, geological logging, standard penetration test and geophysical studies to demarcate the zones of least to most damage prone areas within the urban areas so as to helps the respective town and country planning agencies to formulate perspective planning within the overall earthquake impact minimization efforts.

Based on the above steps it is mandatory for all infrastructure/building/ development agencies (Public and Private) to design appropriate earthquake resistant building plans based on the relevant BIS Codes and other guidelines of BMTPC, HUDCO and NDMA for across the country.

Imphal Municipal Corporation Building Bye-laws (First Amendment) 2019 has incorporated all the 14 provisions of the Model Building Bye-Laws, 2016. However, only considering the provisions will not solve the issue. The reason is quite evident as symptomatic treatment will not cure this natural disaster. We need to diagnose the root cause of this disaster and pre channelize our efforts to minimize its impacts.

In the context, the scientific inputs about the seismically microzonated parts of Imphal city should be the base for any constructional projects. Recently concluded studies by GSI in 300 sq. km areas in and around Imphal City indicated 15.54 sq. km and 67 sq. km areas respectively as very high hazardous and high hazardous areas. Hencefort much technical rather strong administrative monitoring is vital to combat the menace of earthquake disaster.