twisted steel column
Twisted steel reinforcement (TS) in axially loaded columns revealed several important advantages over the more usual type of reinforcement, namely mild steel (MS). TS to C.P. 1144 is more efficient than MS and will develop a stress of 54,000 psi at ultimate load, whereas the useful strength of MS is limited to that at yielding and may only be about 36,000 psi. 'Toughness' is also a valuable feature in the behaviour of TS columns.
The effects of short column in an EARTHQUAKE
Many situations with short column effect arise in buildings,such as: a.When a building is rested on sloped ground, during earthquake shaking all columns move horizontally by the same amount along with the floor slab at a particular level (this is called rigid floor diaphragm action).If short and tall columns exist within the same storey level, then the short columns attract several times larger earthquake force and get damaged more compared to taller ones.
The short column effect also occurs in columns that support mezzanine floors or loft slabs that are added in between two regular floors. There is another special situation in buildings where the short-column effect occurs.Consider a wall (masonry or RC) of partial height built to fit a window over the remaining height.The adjacent columns behave as short columns due to presence of these walls.In many cases,other columns in the same storey are of regular height,as there are no walls adjoining them.When the floor slab moves horizontally during an earthquake, the upper ends of these columns undergo the same displacement.However, the stiff walls restrict the horizontal movement of the lower portion of a short column,and get deformed by the full amount over the short height adjacent to the window opening.On the other hand, regular columns get deformed over the full height. Since the effective height over which a short column can freely bend is small,it offers more resistance to horizontal motion and thereby attracts a larger force as compared to the regular column.As a result, the short column sustains more damage. The short-column situation,is created by large window openings. Difference in levels can lead to short column.
The short column effect also occurs in columns that support mezzanine floors or loft slabs that are added in between two regular floors. There is another special situation in buildings where the short-column effect occurs.Consider a wall (masonry or RC) of partial height built to fit a window over the remaining height.The adjacent columns behave as short columns due to presence of these walls.In many cases,other columns in the same storey are of regular height,as there are no walls adjoining them.When the floor slab moves horizontally during an earthquake, the upper ends of these columns undergo the same displacement.However, the stiff walls restrict the horizontal movement of the lower portion of a short column,and get deformed by the full amount over the short height adjacent to the window opening.On the other hand, regular columns get deformed over the full height. Since the effective height over which a short column can freely bend is small,it offers more resistance to horizontal motion and thereby attracts a larger force as compared to the regular column.As a result, the short column sustains more damage. The short-column situation,is created by large window openings. Difference in levels can lead to short column.
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