Short columns are structural members that are unlikely to fail in compression if loaded uniformly along their axis. They can be made of various materials and have different lengths. Short columns are stiffer and more susceptible to damage during an earthquake. They can fail by buckling and are designed with a margin of safety. Short column design is especially important in earthquake-prone areas. The short column effect can cause visible X-shaped cracks on the outside of the column, and designers avoid using them whenever possible.
A short column is a structural member whose relatively short length virtually ensures that it will not fail in compression if it is loaded uniformly along its axis. Columns can be classified as short, intermediate or long, depending on their length, material properties and the lengths of other columns in the same structure. A short column differs from a medium or long column, either of which can fail by bending when loaded uniformly along the axis.
No specific length or range of lengths defines a short column. Rather, whether a column is considered short depends on a variety of factors. A short column can be made from various materials including structural steel, aluminum alloys, reinforced concrete, or even wood. Depending on which of these materials they are made of, short columns can have different lengths due to the different strengths of these materials. Structural columns that are short in length compared to other columns on a particular floor of a building are also considered short columns.
Columns typically fail in one of two ways. They can be pinched, meaning they have failed to compress, or they can bend, which is a phenomenon known as buckling. How they fail depends on a variety of factors, including the geometry of the column and the material properties of the column. The distribution of compressive forces across the cross-sectional area of the column is also important. If compression is applied unevenly across the column, with more force on one edge than another, the chances of buckling increase.
Relatively short columns are more likely to fail compression. The stress on a column due to the load must be less than the strength of the column for the column to support the load. The buildings are specifically designed to ensure this is the case; otherwise the building would collapse.
For safety reasons, the columns are designed to be stronger than necessary under the expected conditions. This is known as the margin of safety. A margin of safety helps ensure that the amount of stress each column can withstand exceeds the stress it experiences in actual use. In rare circumstances, such as a natural disaster, however, the stress on a column can unexpectedly exceed its strength, causing the column to fail. This poses an important concern for short column design.
Compared to other columns, short columns are relatively stiffer, resulting in a higher susceptibility to damage during an earthquake or other extreme event. Particular attention must therefore be given to their design to ensure sound construction. For this reason, short column design is especially important in less developed nations in earthquake-prone areas, such as Honduras and India.
Due to their relative stiffness compared to other structural elements, short columns experience greater seismic demand, subjecting them to more force in the event of an earthquake. This phenomenon is known as the short column effect. Short columns that fail in this way are characterized by visible X-shaped cracks on the outside of the column. Designers generally avoid the use of such columns in buildings whenever possible to avoid the short column effect. Where their use cannot be avoided, designers typically increase the strength of the structural design to compensate for the increased risk.
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