Puzzle Factory - tower block - play for free

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A high-rise building is a tall building, as opposed to a low-rise building and is defined by its height differently in various jurisdictions. It is used as a residential, office building or other functions including hotel, retail or with multiple purposes combined. A residential high-rise building is also called tower block and may be referred to as an "MDU", standing for "Multi Dwelling Unit". A very tall high-rise building is referred to as a skyscraper. High-rise buildings became possible with the invention of the elevator (lift) and cheaper, more abundant building materials. The materials used for the structural system of high-rise buildings are reinforced concrete and steel. Most North American style skyscrapers have a steel frame, while residential blocks are usually constructed of concrete. There is no clear difference between a tower block and a skyscraper, although a building with fifty or more stories is generally considered a skyscraper. High-rise structures pose particular design challenges for structural and geotechnical engineers, particularly if situated in a seismically active region or if the underlying soils have geotechnical risk factors such as high compressibility or bay mud. They also pose serious challenges to firefighters during emergencies in high-rise structures.