CHAPTER 9: COLUMNS
(ESSAY NO.5)
Chapter nine was introduced as the sector that revolved around columns, which are in the
presence of reinforcement also referred to as reinforced concrete columns. This chapter only
discussed mainly on short, sturdy columns that are exposed to minor bending moments aside from
long slender columns which will be further discussed on the succeeding chapters.
It was stated that concrete columns are divided into several categories namely, short
compression blocks or pedestals, short reinforced concrete columns, and long or slender
reinforced concrete columns. The short compression blocks or pedestals are characterized by
having the height of an upright compression member to be less than three times its least lateral
dimensions. In simple terms, pedestal may be designed with unreinforced or plain concrete. Next
category is known as short reinforced concrete columns which is characterized to fail due to its
(reinforced concrete column) initial material failure. Also notice that the load supported varies in
the dimensions of the cross sections and its material strength. Take note that same with the first
mentioned category, these columns are stocky yet it does pose flexibility as its difference. Lastly,
the long or slender reinforced concrete columns. These are characterized by direct proportion
between its size and bending deformation. Thus, stating that the more the columns become
slender, the higher its deformation will be causing secondary moment to occur.
Apart from the columns’ categories, further discussed was its types. These types of
columns are either in a form of tied or spiral which vary on the methods used for holding the bars
in position. First on the list is referred to as tied column. This type of column has a series of closed
ties which is known to be effective in strength increase of the column. Thus, prevent the
longitudinal bars from being displaced causing the outer concrete cover to spall off due to the
buckling of bars outward. This type of columns is generally in a form of square or rectangular
shape, but can also be in a form of octagon, round, L-shaped, and so on. Second and lastly is called
spiral column. This type of column is a continuous helical spiral made from either bars or heavy
wires wrapped around the longitudinal bars. Thus, prevent the columns to fail if and only if the
spiral yields at failure. This type of columns is generally round, yet this may also be in a rectangle,
octagon, or other customs of shape.
In a short comparison between tied columns and spiral columns, it is inevitable to conclude that
both add resilience to the columns’ strength. As stated on the context, the only difference is that
spiral cost higher compared to ties. Generally, spiral is the choice for large heavily loaded columns
aside from the fact that these columns that are subjected to seismic areas. Though it amounts at
high price, considering its resistance to earthquakes loadings would be a fair compensation for
choosing spiral columns.
It was also included in this chapter the axial load capacity of columns. Knowing that the
actual in comparison to theoretical differs vastly, it is also important to impart foundation of
knowledge when designing. The key notes to these concepts are Columns classified as short,
pedestal, or long. Pedestal only if the height is less than three times its least lateral dimension.
Short column if it fails due to its initial material failure. And Long column if the length increases
thus resulting to an increase also of lateral bulking causing the column to fail.
Knowing the concept of failure by each category, now focus on the failure of tied and spiral
columns. A tied column may place loads until it fails, thus resulting to the concrete covering to
spall off, except for the ties to be closely spaced causing the longitudinal bars to buckle
immediately. This failure may be sudden and can frequently occur to buildings lay open to quake
loadings. A spiral is designed to be of slight stronger than tied as its concrete covering is assumed
to spall off before the tied column. This failure creates a warning thus giving more masses before
it finally collapses.