World's tallest RCC structures - REACHING FOR THE SKY
#1

REACHING FOR THE SKY
Taken from : Ambuja Technical  Literature Series -10

Concrete has been in use for centuries in various types of structures as its versatile properties and function have made it the most useful material in the construction industry the world over. It has always been preferred to other materials due to either economy, ease of construction and I or durability. Most major metropolitan centres I boast of towering slender beauties in concrete or steel which form permanent landmarks and are visible from several corners of the city.

The C N Tower is the world's tallest free-standing structure built since 1974, and singly provides facility adequate for all of Toronto's (Canada) radio and TV requirements. The tower has a height of 549m which includes about 102m high antenna mast.
From the top deck, at a height of 446.5m, on a clear day, one can view the landscape as far as a \00 miles. The record prior to 1974 was held by the 537m tall Ostankino Tower for radio and TV broadcasting built in Moscow in 1971. The famed Stuttgart Engineer, Dr. Fritz Leonhardt, designed the first reinforced concrete tower for TV and radio broadcasting transmission in 1955. This 217m concrete beauty, constructed using normal formwork, took 20 months to construct and was commissioned on  February, 1956. The upper part of this tower has a basket-like casing for touristic and gastronomical
purposes, which made the television tower financially lucrative. The construction expenses of 4.2 million German Marks were recovered in merely five years, as the bold building, located on the hill, Hoher Bopser attracted thousands of visitors. Dr Leonhardt preferred a concrete needle to a 200m high iron gratting pole to be secured with wire ropes, which was a normal practice in those days. The idea could have struck as RCC chimneys were already being built to towering heights all over the world for environmental purposes. RCC chimney construction can be traced back to 1873.
With the developments in concrete technology, concrete admixtures and concrete construction equipment like slipforms, the construction of RCC chimneys became easier, faster and economical. 

The sky is the limit when one has to decide  the height of a chimney in a metropolitan city. The heights of chimneys have gradually increased due to a concern for environmental protection. Hence, the tallest RCC structure in India, the chimney for the 500 MW Unit 6 Thermal Power Station of the Tata Electric Company at Bombay, had to be 275m high. Between 1979 and 1988 this unit was the eleventh 500 MW Thermal Unit cleared for construction, and has the tallest chimney in the country.
Environmentalists have, quietly transferred their problems to civil engineers leaving it to them to design towers. One such tower has now become a permanent landmark on the eastern skyline of Bombay.

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#2

The shell construction

The shell construction of the 275 chimney commenced on 5th November, 1987 ,  and was completed on 7th August, 1988 . Thus within 9 months the chimney shell shot up from -0.4m below low ground level to its desired 275m height into the sky. The average speed of construction of the shell, at the rate of 3m per day, using slipform equipment, can be easily achieved in India. However, the rate of slipforming adopted in the Toronto tower was on an average of 6m per day, as quick-setting admixtures and perhaps faster winches to carry concrete and steel to the desired locations, were used.
Three winches (Table) were used to transport men material and concrete during the construction of the shell. Except for these winches
there was no other mode of transport available to reach the slipform platform. During the total construction period of 276 days, the slipform actually operated for only 105 days. Thus, on an average, the rate of slipforming was about 2.60m per day. The fastest rate of 3.4m per day was achieved at an elevation of 250m above ground level.

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[Image: pdf.gif] REACHING FOR THE SKY FD.pdf
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