In structural engineering, the tube is the name given to the systems where in order to resist lateral loads (wind, seismic, etc.) a building is designed to act like a three-dimensional hollow tube, cantilevered perpendicular to the ground. The system was introduced by Fazlur Rahman Khan while at Skidmore, Owings and Merrill's (SOM) Chicago office. The first example of the tubes use is the 43-story Khan-designed DeWitt-Chestnut Apartment Building in Chicago, Illinois, completed in 1963.The system can be constructed using steel, concrete, or composite construction (the discrete use of both steel and concrete). It can be used for office, apartment and mixed-use buildings. Most buildings in excess of 40 stories constructed in the United States since the 1960s are of this structural type. A tube, or tubing, is a long hollow cylinder used to convey fluids (liquids or gases).The terms "pipe" and "tube" are almost interchangeable, although minor distinctions exist generally, a tube has tighter engineering requirements than a pipe. Both pipe and tube imply a level of rigidity and permanence, whereas a hose is usually portable and flexible. A tube and pipe may be specified by standard pipe size designations, e.g., nominal pipe size, or by nominal outside or inside diameter andor wall thickness. The actual dimensions of pipe are usually not the nominal dimensions: A 1-inch pipe will not actually measure 1 inch in either outside or inside diameter, whereas many types of tubing are specified by actual inside diameter, outside diameter, or wall thickness.