Column & Footing details

Column and Footing details for Architectural and Engineering students.
What is a column. Parts of Columns. Types of Columns. Footings and footing details. Samples of different types of footings. Descriptions and Images.

1. COLUMN & FOOTING DETAILS

2. COLUMN A column is a vertical structural member designed to transfer a compressive load. For example, a column might transfer loads from a ceiling, floor or roof slab or from a beam, to the foundations. Columns are typically constructed from materials such as stone, brick, block, concrete, timber, steel and so on.

3. Shape Columns can be classified according to their cross sectional shape. Common column shapes include: Rectangular Square Circular Hexagonal Octagonal

4. Elements of classical columns Base The base is the lowest part or division of a column. Shaft The shaft is the portion of a column between the base and the capital Capital The capital comprises the uppermost elements of a column. While capitals differ according to the classical order, they usually include the following elements:

5. FOOTING Footings are an important part of foundation construction. They are typically made of concrete with rebar reinforcement. The purpose of footings is to support the foundation and prevent settling. Footings are especially important in areas with troublesome soils.

6. DIMINISHING SOIL PRESSURE As the load under a footing spreads out, pressure on the soil diminishes. Soil directly under the footing takes the greatest load, and therefore should be thoroughly compacted. Because the load spreads out, the pressure on the soil is greatest right beneath the footing. By the time we get down below the footing a distance equal to the footings width, the unit soil pressure has dropped by about half. Go down the same distance again, and the pressure has dropped by two-thirds. So it's the soil right under the footing that is the most critical and also, typically, the most abused.

7. WHAT ARE DIFFERENT TYPES OF FOOTINGS? Footings can be of the following types. Spread or isolated or pad footing Strap footing Combined footing Strip or continuous footing Mat or raft footing

8. SPREAD FOOTING OR ISOLATED OR PAD FOOTING It is circular, square or rectangular slab of uniform thickness. Sometimes, it is stepped to spread the load over a larger area. When footing is provided to support an individual column, it is called “isolated footing”.

9. STRAP FOOTING It consists of two isolated footings connected with a structural strap or a lever, as shown in figure below. The strap connects the footing such that they behave as one unit. The strap simply acts as a connecting beam. A strap footing is more economical than a combined footing when the allowable soil pressure is relatively high and distance between the columns is large.

10. COMBINED FOOTING It supports two columns . It is used when the two column are so close to each other that their individual footings would overlap. A combined footing is also provided when the property line is so close to one column that a spread footing would be eccentrically loaded when kept entirely within the property line. By combining it with that of an interior column, the load is evenly distributed. A combine footing may be rectangular or trapezoidal in plan.

11. STRIP FOOTING OR CONTINUOUS FOOTING A strip footing is another type of spread footing which is provided for a load bearing wall. A strip footing can also be provided for a row of columns which are so closely spaced that their spread footings overlap or nearly touch each other.

12. MAT OR RAFT FOOTING It is a large slab supporting a number of columns and walls under entire structure or a large part of the structure. A mat is required when the allowable soil pressure is low or where the columns and walls are so close that individual footings would overlap or nearly touch each other.

13. SAMPLES