disaster & settlements dinker

1

Construction Practices in Sikkim:with a special reference to traditional housing

Disaster and Settlements

Dinker Gurung, H/449: III Sem, SPA: 2011

Introduction to housing practices in Sikkim:


• The housing practices in Sikkim as like any early settlement was determined by its topography and climatic conditions.

Photo: A primitive house at Rhenock, Sikkim

Source: Author 2006

• The traditional housing practices of stone masonry, wood, bamboo and thatched roofs were the typical construction.

• Galvanized Corrugated Roofing was later introduced for pitched roofs since the advent of the British in its territories. • ikra house (Assam type) - a wooden

struc-ture with tin roof, the walls of which are made of split bamboo plastered with mud or cement.

Photo: A wooden house with ikra house in the side

Source: Author 2006

Introduction to housing practices in Sikkim:


• Post 1975, after the merger of Sikkim with India as one of its state, the construction scenario drastically changed

• Reinforced Cement Concrete became the most widely used construction material along with the bricks.

• Presently, RCC frame buildings with masonry in fills are mostly used in private as well as government constructions.• There is no formal design practice in

Sikkim even for RCC frame buildings.

Photo: A modern house in Rural Sikkim

Source: Author 2006

Photo: RCC building at Gangtok

Source: Author 2006

Vulnerability of the housing stock


• due to its geographic location and topography is exposed to various natural hazards like avalanche, landslides and earthquakes.

• due to its location in Zone IV of the seismic zonation of India, the entire state is exposed to the vulnerability to earthquakes .

• housing stock in Sikkim can be categorized in to rural, semi-urban and urban for assessment of its vulnerability to natural disaster.

• In addition, the long monsoons period experienced by Sikkim makes its fragile slopes exposed to high vulnerability due to landslides.

Photo: ikra construction in Sikkim

Source: Author 2005

Photo: rural house at Tholung Village

Source: Author 2006

Vulnerability of the housing stock in Rural areas


• Due to low height and good horizontal spread, the vulnerability of these structures to ground shaking is minimum.

• The low self weight of the single storeyed structure renders it less vulnerable to damages during earthquakes.

• Vulnerability due to mud/land slides in all areas depends upon the location.

• The random rubble masonry structures in the higher altitude are more vulnerable to damages due to earthquake..

Photo: periphery of Rhenock town, Sikkim

Source: Author 2006

Photo: ikra house on unstable land

Source: Author 2005

Vulnerability of the housing stock in Semi urban areas


• The semi urban areas are actually villages as defined by the Census but have the characteristic of the urban areas.

• These settlements are closely packed houses generally along an important road and acts as the local commercial centre for the villages.


Photo: changing typology of construction

Source: Author 2006

Photo: housing sin semi urban areas, Sikkim

Source: Author 2006

• The new typology of construction with poor construction practices have rendered them very vulnerable to earthquakes.

Vulnerability of the housing stock in urban areas


• There are 8 notified urban settlements in Sikkim with a population ranging from 5000 to the largest settlement Gangtok which has a population of 99,000. • The housing stock in these areas is mostly RCC framed G+5 structures or more.


• The construction of multistoried RCC frame structures with poor construction practices have rendered them very vulnerable to earthquakes.

Photo: Gangtok, Sikkim

Source: Author 2005

Photo: housing sin semi urban areas, Sikkim

Source: Author 2005

Traditional knowledge of housing construction


• Traditional construction consists mostly of typical bamboo houses, known locally as Ikra, otherwise known as Assam type housing.

• It is a wooden structure with tin roof, the walls of which are made of split bamboo plastered with mud.

• Generally, stone masonry structures in the area are of undressed stones with mud mortar.

Photo: stone masonry house in Sikkim

Source: Subharthi Basu 2011

Photo: ikra house in Sikkim

Source: Author 2006

• Earthquake resistant features such as horizontal bands at various levels and through stones at corners are not provided in these constructions.

Influence of new materials & technology on enhancement of vulnerability of housing stock in Sikkim


• The introduction of concrete and steel for the framed structures, ceramic tiles, marble and kota stone for decorative purposes, tubular truss for roof support, aluminium for openings have given rise to a new typology of construction.

• Generally, stone masonry structures in the area are of undressed stones with mud mortar.

Photo: construction wit modern materials

Source: NICEE@IIT Kanpur

Photo: faulty reinforcement

• Earthquake resistant features such as horizontal bands at various levels and through stones at corners are not provided in these constructions.


Performance of the built environment during the recent earthquake


• Housing built using traditional knowledge

• Only minor damages were reported with no loss of life due to the failure of traditional structure reported.

Photo: toppled wooden structure

Source: www.sikkimexpress.com

Photo: failure of RR masonry at basement

• Instances like toppling of the wooden house due to lack of foundation was one aspect.


• Housing built using traditional knowledge and materials performed well in the recent earthquake due to its simple configuration and inherent earthquake resisting features.



• Housing built using modern materials

Photo: damage of building at Gangtok


• Performance of the RCC buildings in the recent earthquake was poor due to poor design and construction practices.

• Pan caking of the intermediate floors due to the inability of the columns to take the load was seen in tall buildings built beyond the permissible limit of 6 storey’s.

• Failure at beam-column joint due to poor structural design and workmanship was seen in large buildings.

• Failure of concrete hollow blocks used as infill and cladding.



Photo: State Secretariat building building at Gangtok


• Failure of concrete block masonry cladding at the State Secretariat Building, Gangtok.

Source: NICEE@IIT Kanpur • Failure at beam column joint.



Photo: damaged building at Gangtok

Source: NICEE@IIT Kanpur Source: NICEE@IIT Kanpur

• Failure of unsupported wall on cantilever projection.

Photo: buildings at Gangtok

• Pounding between two buildings

Lessons learnt and suggestions for reducing vulnerability of existing housing stock of the state


• Locally available materials (such as bamboo and other sustainable timber alternatives) and traditional technologies should be reinstated and integrated with modern construction practices to have an appropriate design for safe housing.

• All stakeholders must be educated about importance of earthquake-resistant construction and its role in mitigating future risk.

• Good concrete and masonry construction practice and suitable material should be used for light or strong partition walls.

• New building typologies of proven earthquake performance, such as confined masonry need to be introduced for low rise buildings.

• Adhoc retrofitting practices of questionable performances do not necessarily make buildings resistant to future seismic events.

• Relevant BIS codes and guidelines like IITK-GSDMA guidelines for seismic evaluation and strengthening of building is recommended.

CONCLUSION


•Hazards are here to stay.

•All we have to learn is how to live with it.

• Till the invention of techniques to predict earthquakes, the only armour we have is preparedness.

THANK YOU

disaster & settlements dinker

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