This paper briefly describes the key features of Sears Tower, a technological marvel of the 20th century. The
110 storied Sears Tower is an engineering wonder of the world. Sears Tower is 204 feet taller than the  Empire State Building but weighs far less than 223,000 tons. 42-inch deep steel beams at each floor level  brace the columns of this huge structure. The major “plant floors” contain electrical sub-stations, water and
air-handling machinery and elevator hoist motors. There are 28 double–decker elevators travelling at 1600
fpm, for the users of floors above the 34th  floor. Since each bank of single-decker elevators only serves a
small group of floors, people can change between local elevators in transfer floors at levels 10, 17, 23, 42 and  49.