Figure 1. Shows two basic construction systems in Kashmir Valley: (A) Taq system and (B) Dhajji-Dewari system
Earthquakes symbolise severe test for the stability of constructions than any other natural calamity. The construction of earthquake resistant buildings is one of the best steps one can take to ensure the safety of structures. Although steel and reinforced concrete have made it possible to design buildings which are likely to resist major tremors without threat to life of inhabitants, but the traditional constructions systems in most areas usually lack seismic resistant features. Kashmir valley is situated in NW Himalaya, prone to severe seismicity, poor and largely detached from mainstream of industrialised society, with construction methods remaining almost unchanged for generations. The area is regularly rocked by earthquakes. The traditional houses in Kashmir are built with a wooden framework, so as to resist them from earthquake shocks. Conventional Kashmiri construction pattern, to some extent, was well suitable for resisting earthquake damage, but as the rapid increase in population of the valley up to 10 million, elegant traditional buildings paved a way to unstable, poorly built structures, possessing little resistance to earthquake ground motions. Although there is a deficiency of industrial-level precision in old buildings, still they are resistant to earthquakes to some extent. The purpose of the study will be useful in knowing how people have dealt with earthquake hazards in the past, especially in Srinagar city. The outcomes of the study indicate that most of the buildings studied are vulnerable to earthquakes and immediate measures should be taken to make them safe for useful purposes.
Earthquake safety concerns are the prime goals of developing societies. Building material, technologies, and building practices have evolved through ages. The earliest building materials used for construction were stones, mud, thatch/leaves, and timber. With advanced technologies, the traditional construction material also changed as living standard changed. The past societies had limited resources dealing with seismic hazard. In rural areas of India, maximum houses are not constructed to persist seismic forces, subsequently has led to a lot of causalities even in moderate earthquake. Areas where earthquakes are common, people have adopted the precautionary measures of seismic resistant methods in their construction method. The use of steel or concrete for new buildings or the old ones does not, and indeed, cannot guarantee that they will always survive the earthquakes. Buildings that survive earthquakes may do so for several reasons: their structure and assembly may be unusually resilient to any form of shaking, they may be isolated by their local seismic setting (a vibratory node or some form of base isolation), or they may have been reconstructed following the damage (Bilham, et al., 2010).
Earthquakes leave hardly anything untouched on the ground. All types of constructions have been put to this type of severe test in one or the other earthquake. They cause a lot of damage to natural landscapes as well as manmade structures. The strong ground vibrations which propagate in all directions from the focus at speed greater than 5 km/s (upper crustal velocity) shake the structures. As a result, poor constructions collapse, weak ones suffer the damage to large extent, strong ones get away with minor damage, and the exceptionally sound constructions remain intact. Since all parts of a structure are shaken, the weak links fail first and lead to over stressing of stronger parts as well. The vulnerability of the building stock exposed to earthquakes varies enormously in space and time in the seismically active region (Ambraseys N. and Jackson D. 2003).
Distinct monuments, as well as whole historic places of most Kashmir valley are now recognized as vital elements of architectural heritage. They also often characterize the most susceptible class of buildings as far as seismic risk is concerned. Most of the conventional buildings in Srinagar are constructed on two basic construction systems, Taq and Dhajji-Dewari (Figure 1). The first system, built of load bearing masonry piers and infill walls with wood runners at each floor level, used to bind the walls together with the floors and the second system built of a braced timber frame with masonry infill (Hough, et al., 2009). In Kashmir, rigidity carries the potential for destruction. The more rigid a building is, the stronger it must be in order to avoid fracture. Because of the primitive materials and means of construction in Kashmir, strength was not possible, so flexibility was necessary.
Figure 1. Shows two basic construction systems in Kashmir Valley: (A) Taq system and (B) Dhajji-Dewari system
The Kashmir Valley, its structural disposition are the result of Himalayan Orogeny. The Kashmir Valley, an oval shaped basin, surrounded by Pir Panjal Range on the south and the Great Himalayan Range on north. Described by Wadia (1931) as 'Kashmir Nappe Zone' typical thrust-bounded basin, with Precambrian basement and the rocks of Palaeozoic–Mesozoic marine sediments being thrusted along a regional tectonic plane, viz., Panjal Thrust over the younger rocks of the autochthones belt. Two major axes of orogenic upheaval are present in the form of Pir-Panjal and the Great Himalayan Ranges. There is a complex pattern of faulting with the superposition of several thrusts to the southwest of the Pir Panjal Range like MBT/Murree, Riasi, and Kotli thrusts (Thakur, et al., 2010). Kashmir valley has experienced destructive earthquakes throughout its history (Iyengar and Sharma, 1998; Iyengar, et al., 1999). Most notable were the events of 1505, 1555, 1885 and 2005 (Ahmad, et al., 2005). Over the centuries earthquakes in Kashmir have occurred with a degree of regularity and the people of Kashmir have learnt to live with them. Within the memory of any living person in Kashmir, there had been no great earthquake recorded having epicentre within the Kashmir valley, except one about fifty years ago (1967) which was bit severe, with aftershocks lasted for a week (Bilham, et al., 2010). Srinagar (Figure 2), the summer capital city of Kashmir, had been shaken numerous times by earthquakes in the past millennia (Tables 1 and 2), recently by devastating earthquakes in 1885 (M 6.2, 30 km to the west) and 2005 (Mw 7.6, 2005 150 km to the west) with projected intensity VI–VII. National Earthquake Information Centre (NEIC) data suggests that most of the earthquakes within and around the Kashmir Valley were shallow (0–40 km) (Shah, 2013). Past geological and historical records show that the Himalaya arc can experience much bigger earthquakes than the 2005 event—much destructive than the previous earthquakes that have struck the Kashmir Valley in recent past. An earthquake of magnitude 8.9 is probable based on the past activities and the current motion of Indian plate accumulating lot of strain in this region (Schiefman, et al., 2013).
Figure 2. Shows the Location of the Srinagar City
Table 1. Historical Earthquakes reported in Kashmir (principally Srinagar) Since the Tenth Century {after Bilham et. Al., 2010, Iyengar and Sharma (1998)Iyengar et al. (1999), Bashir et al. (2009)}
Table 2. Shows details of Earthquakes that occurred in Kashmir (mainly Srinagar) from 1800 to 1900. (After Bashir et al. 2015).
Vulnerability is well-defined as an inherent property of buildings, that confines the certain level of damage to be sustained when imperilled to a determined seismic event of known intensity. The seismic vulnerability of buildings can be evaluated in ways more or less complex in function of the scale and specificity of the study case. The buildings taken for evaluation were categorized on the basis of Performance Modification Factor into five categories according (Table 3a) to the Basic Structural Hazard (BSH) (Agrawal, et al., 2004; Vulnerability Atlas of India, 1999).
Table 3 (a) Table for building categories for Basic Structural Hazard (BSH), (b) Earthquake Resisting Features
The overall vulnerability was calculated as the weighed sum of 11 parameters used in the formulation of the seismic vulnerability index of six buildings in Srinagar city (Table 4). These parameters are related to 5 classes of growing vulnerability classes: A, B, C, D, and E (Table 3b) based on the Value of “ah”
ah=a0Iβ
Table 4. Seismic Vulnerability Index of Buildings in Srinagar City {Inayat Manzil Dukan-I_Sangeen, Fateh Kadal (IM), Mather-I-Maharban, Daulat Abad (MM), Sri Pratap College, M. A. Road (SPC), Khanday Manzil, Safa Kadal (KM), Anand Niwas, Barbar Shah (AN) and Lal Ded Memorial School, Ganpatyar, Budyar (LDMS)}
where ah = design seismic coefficient for the building
a0 = basic seismic coefficient for the Seismic zone in which the building is located (IS 1893:2002 Part I),
I = Importance factor applicable to building (IS 1893:2002 Part I),
β = soil foundation factor (IS 1893:2002 Part I).
Table 4. Seismic Vulnerability Index of Buildings in Srinagar City {Inayat Manzil Dukan-I_Sangeen, Fateh Kadal (IM), Mather-I-Maharban, Daulat Abad (MM), Sri Pratap College, M. A. Road (SPC), Khanday Manzil, Safa Kadal (KM), Anand Niwas, Barbar Shah (AN) and Lal Ded Memorial School, Ganpatyar, Budyar (LDMS)}
Six century old buildings were taken as case studies and were evaluated for seismic vulnerability assessment.
The building lies in Fateh Kadal, Srinagar on the left bank of River Jhelum. Constructed in 1905, is a three storey building used for residential purpose, with bricks and wood. The shallow foundation of the building is on recent alluvium deposited by river Jhelum. Categorised as “B” type building according to BSH. The dimensions of the building are 13.5 x 9.2 m (l x b) with wall thickness 35 cm. The building is typical Taq System type with vertical walls and wall opening percentage of nearly 49%. Minor cracks has been reported past 2005 Kashmir Earthquake. The overall condition of the building is good. There are moderate chances of liquefaction/slope failure as the building lies close to river and high chances of dampness/waterlogging condition in the area. No Earthquake Resistant measures have been adopted for this building. The building is categorised as moderately Vulnerable to seismicity.
The building is situated in Daulat Abad, Srinagar. Constructed in 1895, is a two storey building under Government custody, with bricks and wood and is founded on unconsolidated river deposits, mainly clay and silt. Categorised as “A” type according to BSH with dimensions 30 x 23 m (l x b) with wall thickness 30 cm. With vertical walls and wall opening percentage of nearly 57%. The overall condition of the building is good. There are least chances of liquefaction/slope failure and least chances of dampness/waterlogging condition in the area. No Earthquake Resistant measures have been adopted for this building. The building is categorised as least vulnerable to seismicity, as no visible cracks have been found past 2005 earthquake.
Constructed in late 19th century, it is a two storey building used for college with bricks and wood. The foundation of the building chiefly lies on loose material (clay and silt). Categorised as “B” type according to BSH with dimensions 43 x 36 m (l x b) with wall thickness 37 cm. With vertical walls and wall opening percentage of nearly 54%. The overall condition of the building is good. Minor cracks opened in the walls of the building past 2005 Kashmir Earthquake. There are least chances of liquefaction/slope failure and least chances of dampness/waterlogging condition in the area. No Earthquake Resistant measures have been adopted for this building. The building is moderately vulnerable to earthquakes.
The building is situated on the right bank of River Jhelum at Safa Kadal. The base of the building is constructed using stones to prevent water logging. Constructed in 1855, it is a two storey building used for residential purpose. Categorised as “B” type according to BSH with dimensions 34 x 15 m (l x b) and wall thickness 25 cm. With vertical walls and wall opening percentage of nearly 35%. The overall condition of the building is good. There are high chances of liquefaction/slope failure and high chances of dampness/waterlogging condition in the area as the building lies close enough on the banks of River Jhelum. No Earthquake Resistant measures have been adopted for this building. The building is moderately to highly vulnerable.
The building is typical Taq system type and lies at Barbar Shah. The building lies on the left bank of the distributary of river Jhelum. Constructed in around 1860, is a three storey building used for residential purpose. Categorised as “A” type according to BSH with dimensions 35 x 15 m (l x b) with wall thickness 30 cm. With vertical walls and wall opening percentage of nearly 52.8%. The overall condition of the building is damaged. Lot of cracks developed in the walls of the building past 2005 Kashmir Earthquake. There are low chances of liquefaction/slope failure and low chances of dampness/waterlogging condition in the area. No Earthquake Resistant measures have been adopted for this building. The building is classified as highly vulnerable and must be reconstructed.
Situated at Ganpatyar, Srinagar, the foundation of the building is on loose alluvial material, constructed by using brick, wood and stones. The foundation of the building is shallow made up of stones. Constructed in 1875, it is a three storey building used for School purpose. Categorised as “A” according to BSH type with dimensions 30 x 25 m (l x b) with wall thickness 35 cm. With vertical walls and wall opening percentage of nearly 51%. The overall condition of the building is damaged. There are some chances of liquefaction/slope failure and high chances of dampness/waterlogging condition in the area. No Earthquake Resistant measures have been adopted for this building. The building has minor cracks in the walls and is highly vulnerable to earthquakes.
The method of building construction plays a vital role in reducing loss of life and property. The loss however cannot be reduced to zero, but can be mitigated when proper steps are taken at right time. The construction of earthquake resistant building is one of the best steps one can take to ensure safety. Buildings such as those found in Kashmir, if encountered in developed places, would probably be condemned immediately as unsafe. Although there is a lack of modern industrial-level precision in old buildings of Srinagar city, they have acted as earthquake resistant since past century, while the area being rocked by earthquakes regularly. The probability of a mega earthquake in Kashmir Himalaya in future will prove a real test to all types of construction in the Valley. The traditional pattern of construction is safer than the present form of unplanned construction. The progress of modernisation and industrialisation threatens to result in the eventual demolition of these buildings. The most recent developments in the field of seismic hazard assessment should be incorporated in the construction of new structures in the Kashmir Valley.