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News Release from: Chartered Institute of Building [CIOB] | Subject: Pakistan earthquake
Edited by the Buildingtalk Editorial
Team on 12 October 2005
Collapsed buildings toll in Pakistan
earthquake
Collapsed buildings take heavy toll as Pakistan earthquake buries thousands.
The heavy toll of casualties caused by the earthquake that struck Northern Pakistan this week is undoubtedly due to the collapse of so many of the buildings under which people were buried, like the hundreds of children reported to have been killed while at school on Saturday morning, trapped in structures that were nowhere near strong enough to withstand heavy seismic shocks This area of Pakistan is in an earthquake zone and the least that should emerge from this tragedy is thorough reform of the building codes and determination on the part of the authorities to enforce them
This article was originally published on Buildingtalk on 12 Mar 2004 at 8.00am (UK)
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An example of how faulty construction can be exposed when subjected to the intense stresses exerted by seismic shocks comes from Islamabad, close to the epicentre of the earthquake that devastated Pakistan over last weekend.
This is a relatively new city, built to create a government centre in the 1960s.
On Saturday morning 8th October, under the impact of 7.6 Richter scale shocks, while most other buildings remained standing, the Margalla Tower block in one of the city's residential sectors collapsed, burying most of its occupants.
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Hammad Husain, former chairman of Pakistan's Institute of Architects (Islamabad Chapter) contributed the following commentary to the Islamabad News Internet edition: "If the earthquake ground motion is strong enough to shake up and damage buildings, then its effect in most cases is uniform on all buildings in the area".
"Then why do some buildings collapse and others don't? The answer to this question lies in the structural design and construction of the building".
"The world is broadly divided into four zones according to seismic activity risk.
Islamabad, which for years was in the 'moderate risk' category, was upgraded to 'moderate-high' a few years back.
However, most engineers in Islamabad failed to adapt to the change".
"I see three reasons for this:.
1 making a building earthquake resistant entails extra cost".
2 the Capital Development Authority [set up in 1960 to co-ordinate development of the city] has no strict building codes for seismic design, neither do they check or verify whether the design of a building is safe against an earthquake".
3 The engineers do not usually bother to go into complex calculations as it requires extra effort and time - and with nobody to check, why care?".
Shear walls only for structural stiffness "In mid-rise buildings, most Pakistani engineers only employ shear walls which are supposed to resist lateral forces and keep the building stiff".
"However, shear walls in regions with high seismic activity like Japan or Turkey (or Islamabad) are not enough to make a building earthquake-resistant".
"Since the devastating earthquakes of the recent past including Kobe (Japan) in 1995 and Turkey in 1999, engineers have devised various techniques for minimising risk of building collapse.
These include base isolation, diagonal bracing and passive damping".
"Base isolation works by separating the building from the moving ground".
"Teflon pads, large rollers, springs or other devices allow the ground to move under the foundation without transmitting all of that motion to the building (like pulling the tablecloth out from under the plate and having the plate stay still)".
"Diagonal bracing helps resist shearing forces that come from the swaying motion of a shaken building.
"The fact that only Margalla Tower collapsed while its neighbouring Al-Mustafa and Park Towers stood their ground indicates that the problem lies either in the structural design or the construction of the building, and not in the seismic wave caused by the earthquake".
"In the larger context, the problem lies with the regulatory authorities like CDA that have been negligent in enforcing proper checks on design and construction of large-scale buildings.
"The Pakistan Engineering Council and the CDA need to review their building code regulations and law enforcement and verification systems, especially for the high rise towers and apartment blocks mushrooming all over the capital with alarming speed, and make sure they are structurally sound and earthquake resistant".
"The command and control system should be made public so that greedy developers and callous engineers and contractors are not allowed to put precious human lives at risk".
Mr Husain apparently wrote his commentary prior to learning that the Islamabad police had filed a 'first information report' against the builders of the collapsed Margella Towers.
Knowing the area well he had probably deduced that the structural failure of this tower alone was not necessarily due to faulty design, maybe rather to weak supervision.
Later Ijazul Haque, Federal Minister for Religious Affairs, revealed that the Margella Towers had been declared dangerous ten months before, but explained as the reason for the failure to evacuate the building that the residents were not ready to vacate the apartments that they had bought at high prices.
However that may be, they certainly paid a high price for staying put.
As the Minister spoke, many people were still trapped under the collapsed blocks.
Why the Ballitt Fort is a survivor.
The North West frontier region of Pakistan is no stranger to earthquakes and indeed the Baltit Fort located in one of the high valleys between China and the Indian sub-continent is reputed to have been built some 700 years back.
There has been no mention of this splendid old building in the news reports from Pakistan, so one would hope that as a great tourist attraction, the fort is still standing.
Its longevity has of course been greatly assisted by its recent renovation at the hands of Aga Khan Cultural Services of Pakistan, whose project profile report when it received an award for excellence last year described the Baltit Fort as an impressive stone structure with intricately detailed timber features.
According to local accounts, confirmed by carbon dating, the fort, once part of a royal dowry, had remained in the possession of the ruling family of the Hunza region until relatively recently.
In brief, the conservation project restored the shell of the building to a satisfactory state of structural stability, including the strengthening of bearing walls, floors and roofs.
The work took six years to complete and employed numbers of dedicated artisans well versed in traditional construction technology and materials of Northern Pakistan.
Describing this work as a great international achievement, Richard Hughes, consultant to Aga Khan Cultural Services, said that the organisation had been encouraging the inhabitants of the highly seismic zones of Northern Pakistan to resist the trend to abandon high quality traditional construction techniques.
New buildings, he said, could be modified by better detailing, better site selection, introduction of timber lacing, use of reinforced concrete/steel mesh ring beams and by adding non-loadbearing vertical reinforcement.
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