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News Release from: Chartered Institute of Building [CIOB] | Subject: Quake damage report from Kashmir
Edited by the Buildingtalk Editorial
Team on 13 January 2006
Quake damage report from Kashmir
Quake damage reports expose scale of Kashmir rebuilding programme.
Reports filed under the Earthquake Engineering Research Institute's 'Learning from Earthquakes' program financed by the United States National Science Foundation demonstrate that only well-designed buildings of sound construction are able to withstand the shaking generated by shocks of the intensity suffered in the recent Kashmir earthquake Much, of course, depends on the terrain in which the buildings that survive are founded
This article was originally published on Buildingtalk on 12 Mar 2004 at 8.00am (UK)
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At Muzaffarabad, close to the earthquake's epicentre in rugged and mountainous country, the example is given of a reinforced concrete-framed hotel which collapsed.
Reporters from the North West Frontier Province University Department of Civil Engineering's Earthquake Engineering Center at Peshawar told the research institute that this five storey building was among the many of its type which failed due to deficient design for seismic forces.
They found that almost all other structures, mainly built with stone and rock masonry laid in cement mortar and with reinforced concrete slabs or galvanised iron sheet roofing, had collapsed in the areas closest to the epicentre.
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The proportion of buildings destroyed diminishes with distance from the epicentre, 25 per cent collapsing at 25 km and about 50 per cent severely damaged.
"For the past 15 years reinforced concrete frame buildings have been increasingly used for the construction of government offices, colleges, hospitals, hotels, markets and apartment houses", said the earthquake research centre's report.
"Many such buildings collapsed and more were seriously damaged".
"In severely damaged buildings, columns were observed to have cracked at the beam-column intersection." Observers from the Indian Institute of Technology Roorkee Department of Earthquake Engineering (the only one of its kind in India) who visited Kashmir said that tremors were felt in the adjoining States of Punjab and Himachal, and as far away as Madhya Pradesh and Gujarat.
They found as expected that structures designed and built in accordance with established engineering principles were in general found in satisfactory condition in urban areas such as Srinagar and Baramula where they are concentrated.
"There was no widespread damage reported to such structures, unlike the damage to non-engineered construction in the rural and remote areas." Such damage as there was in well designed structures was limited to non-structural cracking at locations where the builders had failed to comply with planning restrictions applying in highly seismic zones.
By contrast, the police station building at Salamabad constructed in 2003, a single storey construction in random rubble masonry, with 450 mm walls in cement mortar, suffered extensive damage in all the external walls with complete collapse on the south and west side.
On the other hand, Bailey bridges stood up well under this test.
The excellent performance of these bridges, common in the urban areas of Kashmir, is attributed to their flexible nature.
In the few cases where Bailey bridges had suffered extensive damage, the causes were not related to the structures themselves, for example the impact of boulders rolling down hillsides during the shaking.
Poor materials and weak mortars.
As to non-engineered structures, the findings of the Indian Institute Roorkee party in Kashmir agreed very well with those of their counterparts from the Department of Civil Engineering at Peshawar who reported: "A significant number of casualties and injuries in the rural areas were associated with the total collapse of single-storey unreinforced earthern wall stone masonry buildings".
"The stone masonry walls consisted of irregularly placed undressed stones, mostly rounded, that were laid in cement sand, mud mortar, or even dry in some cases".
""The quality of mortar and stones used and the level of workmanship are poor, due to the economic restraints on the people.
Stone masonry set in plain earth (i.e., mud) is not unusual.
Cement mortars when used consist of one part of cement to 10 parts sand".
""The crushing and shear strength of such mortar is approximately 300 psi and 5 psi respectively".
"The rounded and smooth stones also contribute to the poor bond.
"No horizontal bond beams are provided at the levels of plinth and roof.
Lintel beams are provided only above the openings and are not run continuously along the perimeter of the walls.
No vertical members of concrete or wood are provided in the walls and therefore the collapse of a particular portion of the wall progressed in an uninterrupted manner to other portions of the walls and buildings." The report goes on to say that the collapse of block masonry buildings (unreinforced) was responsible for a major portion of the deaths and injuries in the cities".
"As graphically illustrated in the document, most of these were flattened by the seismic shocks".
"Their failure was due to a number of factors: poor quality concrete and mortar, inadequate thickness of walls as the main shear-resisting elements, no integrity of the wall in the transverse direction, and weak connections at the corners".
"Unreinforced brick, the most common form of masonry in towns, fared better".
"One and two storey brick masonry buildings, with reinforced concrete slabs as roofing, comprised 25 per cent of the total building stock in the cities near the epicentre".
"About 30 per cent of these buildings collapsed while the rest suffered slight damage".
"Traditional structures pass the test".
"In Kashmir, says the research report based on material from the Indian Institute of Technology Kanpur, traditional timber-brick masonry (dhajji-dewari, meaning patchwork quilt) consists of burnt clay bricks filling in a framework of timber to create a patchwork of masonry confined in small panels by the surrounding timber elements".
"It has excellent earthquake-resistant features.
"The resulting masonry is quite different from typical brick masonry, and its performance in this earthquake has once again been shown to be superior, with no or very little damage.
No collapse was observed for such masonry, even in the areas of higher shaking." The report observes that timber-laced masonry can maintain its integrity even when the supporting masonry in lower storeys is severely damaged".
"But as the Roorkee report comments, buildings in burnt brick masonry are few in the rural areas they surveyed owing to scarcity of bricks and high cost of transportation.
"Further, scarcity of cement supply is evident from the adoption of mud mortar wherever such structures were encountered in rural areas.
Over the years the mud mortar has become so common that few buildings, probably of recent times, were observed to be with walls constructed in mud mortar and plastered on both faces in cement mortar".
""Single storied buildings with 230 mm thick walls is the common feature which also reveals that the skilled labour required to produce walls of higher thickness is not easily available." Damage in such structures usually starts with separation of walls at right-angled joints and corners, cracks along the bed joints followed by failures below the roof joists and collapse of the corner portions.
However, the extent of destruction in burnt brick masonry was less than that in rubble masonry where about 50 per cent showed partial collapse.
These commentaries surely illustrate the scale of the reconstruction problem in the Kashmir.
Traditional skills could be called upon in the effort to create sustainable communities in the face of the risk of further earth tremors.
But as these observations show, the combination of location and economics in the region make it difficult to apply them on the scale required.
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