Absence of tie beams at ground level led to collapse: Investigators

Absence of tie beams at ground level led to collapse: Investigators Friday, March 9, 2001

AHMEDABAD: * Builders, structural engineers, architects, civic bodies turn the needle of suspicion towards each other and disown responsibility for crumbled multi-storeyed apartments. * A day-long symposium at the Usmanpura office of the Ahmedabad Municipal Corporation on Wednesday saw renowned structural and civil engineers from across the country discussing ideal building practices in a seismic zone III city, namely Ahmedabad.

While the accused launch on to a sinister pass the buck game and analysts get busy devising a capacity building programme for civil, structural and construction engineers of Ahmedabad, independent investigations carried out by a team of structural engineers from Indore give the answer to an often asked question: How did the low-rise and high-rise buildings turned into a mass of debris ?

And, prima facie evidence holds the builder-politician-civic body nexus responsible for gross flouting of norms which caused the buildings to cave in.

Structural engineers of Kutumbale Consultants and Engineers Private Ltd from Indore (who are advisors to the AMC on ideal building practices in Ahmedabad) have found "concrete evidence" on how most of the concrete jungles at Bhuj, Anjar, Gandhidham, Bhachau and Ahmedabad were reduced to rubbles.

The team of "concrete investigators" have deduced: Buildings in places like Ahmedabad and Bhuj were not designed as per seismic forces specific to seismal zones like five for Bhuj, Bhachau, Anjar and Gandhidham and three at Ahmedabad. They also set aside an often cited excuse that soft floor (open parking space) at ground level was primarily responsible for collapse of maximum number of three or four-storeyed RCC and load bearing structures.

After inspecting, a number of collapsed buildings found a unique failure pattern. Most of the RCC and load bearing structures which had crumbled during the earthquake had no ground beams or tie beams at ground level.

This fact was confirmed by digging trenches to uncover ground beams at two collapsed building sites. The team which spend 15 days in these quake-affected zones, often working 12 hours every day, clicked over 700 photographs to document the reasons behind collapse of high and low-rise structures. The team from Indore have also summarised that the columns were extending from foundation to the bottom of first floor without any tie beams thus turning into "long columns" which buckled under seismic forces resulting in "total collapse."

"Apart from non-compliance with building bylaws effective in seismal active zones, most of the structures did not have tie beams connecting, strengthening parking level columns. Without this support the columns behaved as long column and buckled," said N Y Choudhary, director of Kutumbale Consultants Private Ltd.

The concrete investigators also pointed out that some buildings (in the same location) collapsed, some exhibited different levels of problems while others remained completely unharmed.

"Strange contrasting behaviour of buildings may be attributed to insufficient sections for deadload or liveload conditions, use of poor quality of building material. Add to that negligence in supervision at various stages of construction, defective or insufficient detailing of reinforcement and you have got the perfect recipe for disaster," said Choudhary.

The investigators have recommended that the structures should be properly planned for uniformity of strength in all directions (which was lacking in most collapsed buildings), structures should be adequately designed to handle seismic forces and that proper attention should be given to detailing of reinforcement and supervision during different stages of construction. That apart, the study holds the failure mechanism of structural element, particularly columns (through physical evidences) as the main cause behind buildings turning into death traps.

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