Correct Option: B

1. Tube system
⇒ Concept is based on the idea that a building can be designed to resist lateral loads by desi gning it as a hollow cantilever perpendicular to the ground.
⇒ In the simplest incarnation of the tube, the exterior consists of closely spaced columns that are tied together with deep spandrel beams through moment connections.
⇒ This assembly of columns and beams forms a rigid frame that amounts to a dense and strong structural wall along the exterior of the building.
The different tubular systems are-
➤ Framed tube
➤ Braced tube
➤ Bundled tube
➤ Tube in tube
BRACED TUBE
∙ A braced tube overcomes this problem by stiffening the perimeter frames in their own planes.
∙ This concept stems from the fact instead of using closely spaced perimeter columns, it is possible to stiffen the widely spaced columns by diagonal braces to create wall -like characteristics.
∙ The braces also collect gravity loads from floors and act as inclined columns.
∙ The diagonals of a trussed tube connected to columns at each joint effectively eliminate the effects of shear lag throughout the tubular framwork.
∙ Therefore, the columns can be more widely spaced and the sizes of spandrels and columns can be smaller than those needed for framed tubes, allowing for larger window openings than in the framed tubes (Khan, 1967).
FRAMED TUBE
∙ In a framed tube system, which is the basic tubular form, the building has closely spaced columns and deep spandrel beams rigidly connected together throughout the exterior frames.
∙ Exterior column spacing should be from 5 to 15ft (1.5 to 4.5m) on centers. Practical spandrel beam depths should vary from 24 to 48 in (600 to 1200 mm)
∙ The axial forces in the corner columns are the greatest and the distribution is non-linear for both the web frame (i.e, frame parallel to wi nd), and the flange frame (i .e., fr ame perpendicular to wind).


BUNDLED TUBE
∙ A bundled tube is a cluster of individual tubes connected together to act as a single unit.
∙ For such a structure, the three-dimensional response of the structure could be improved for strength and stiffness by providing cross walls or cross frames in the building.
∙ Also allowed for wider column spacing in the tubular walls, which made it possible to place interior frame lines without seriously compromising interior space planning of the building.
∙ It is possible to add diagonals to them to increase the efficient height limit.