2. The Warsaw radio mast
It is located in Poland, and its height of 646.38 m. Prior to the collapse in 1991, this building is the highest in the world, and then, formally remained so until 2008. After the collapse of the Polish steel jokingly called his mast the longest building in the world.
The Warsaw Radio Mast was the world’s tallest structure from 1974 until its collapse on 8 August 1991. It is the second tallest structure ever built, being surpassed as tallest by the Burj Khalifa, completed in 2010.
The mast, which was designed by Jan Polak, was 646.38 metres tall. Its construction, started in July 1970, was completed on 18 May 1974, and its transmitter entered regular service on 22 July of that year. It was located in Konstantynów, Gąbin, Poland, and was used by Warsaw Radio-Television for longwave radio broadcasting on a frequency of AM-LW 227 kHz before 1 February 1988 and AM-LW 225 kHz afterwards. Its base was 115.2 metres above sea level. Because a voltage potential of 120 kV existed between the mast and ground, it stood on a 2 metres -high insulator. It operated as a mast radiator, so its height was chosen in order to function as a half-wavelength antenna at its broadcasting frequency. The signals from its 2 megawatt transmitters could be received across essentially the entire globe. Its weight was debated: Polish sources claimed 420 tonnes.