What Do Columns and Beams in Structural Engineering Do?

What Do Columns and Beams in Structural Engineering Do?

The safe load path that is created to transport the weight and pressures on a structure to the foundations and into the earth is largely dependent on the use of beams and columns, two significant types of structural elements. Although beams and columns could be constructed from the same materials and shapes, they serve different purposes and have different designs.

Typically horizontal in shape, beams carry loads that are perpendicular to their longitudinal direction. Consider a gymnastics balance beam. It is a 15-foot-long rectangle that is supported at both ends. A person's weight exerts a vertical downward force operating perpendicular to the longitudinal direction of the beam when they are walking on it close to the middle of the span.

In order to transfer the load to a vertical load bearing element of the building, beams are utilized to carry the weight of the building's floors, ceilings, and roofs. To support the combined weight of stacked walls or other beams and transfer the load to the supports, larger, heavier beams known as transfer beams are occasionally utilized.

The design or sizing of beams requires understanding of basic physics principles and engineering statics. A structural engineer is trained and fully equipped to check the loads acting on a beam, calculate the forces and stresses on it and choose the material, size and shape accordingly.  

In the case of a new building, there is more flexibility in choosing the size and type of materials for beams that work best for the structure. The most common types of materials that are recommended for my clients are beams made out of steel sections, reinforced concrete, grouted masonry, and beams made from wood. All materials have their pros and cons, but are usually selected based on their cost, size and fire rating.

When working on the structural design of a new beam or restoration of an existing one, there are a few factors that are taken into account. These factors include how much load is acting on the beam, the length or span of the beam, clear height available below the beam or any limitations on geometry, deflection limits of the beam, strength of the material, as well as fire rating and resistance. Similar factors are used when designing columns.

Columns are vertical structural elements where the load is transferred parallel to the longitudinal axis as compression, and sometimes as tension. For example, think of a rectangular table with four legs at the corners. The weight of the table and all the objects on the table is transferred to the floor through the legs acting in compression. In this case the legs can be considered as columns.

Columns are used to support floor/roof beams and the columns of the floor above. The columns at the bottom floor of a tall building must carry the accumulative weight of all the floors above. This is why the location of columns ideally should be consistent throughout all floors. This is not always possible especially with a challenging architectural design where each floor has a different layout. In such cases, it is often encouraged to clients to engage the structural design team early in the project to collaborate with the architects to brainstorm the most ideal column layout.

When designing a column in a new building a few factors into consideration must be taken into consideration. Start with calculating the weight of floors/roof supported by the column then choose the material and size as required. The height of the column plays a major part in the overall size of the column. A column that supports 1000 pounds and is 10 feet tall may need to be twice as large as a column supporting 1000 pounds and is 20 feet tall. It all depends on the columns geometry and material properties.

Hopefully this gives you a good idea as to what beams and columns are in a structure and building, and why they are very important structural elements that cannot be overlooked. Next time you walk into a building or drive over a bridge, try taking a look around and figure out which elements you see are used as beams and which are columns.  

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