What are beams and columns in construction and why are they important?
Beams and columns have been a staple in architecture since Ancient Egypt (1580-1085 B.C.). The column shafts of Ancient Egypt were not only architectural elements that served structural purposes, but they were decorative – typically with color depictions and carved reliefs. The Egyptian architectural element made its way to the Graeco-Roman Period when Egyptian columns were exported to Greece and Rome. Aside from their rich history, columns and beams are necessary functions of the superstructures made in today’s modern world. This article will touch on the significance of beams and columns in construction and why they are important.
Columns act as a structural element that transfers loads from the slab, (i.e., roof, upper floor) to the foundation and finally to the soil beneath a structure. They are typically vertically oriented. In construction, columns are used in trusses, building frames, and structure support for bridges. Columns support loads from roofs, floors, or bridge decks. Loads can be considered dead and live loads. Dead loads are fixed loads from permanent attachments, while live loads change in movement because they are temporary loads that can be applied on and off to the structure. The size of a column is calculated primarily based on the value of the axial loads that will be on them. Some of the loads to be calculated include the following:
Vertical forces, which are received toward the longitudinal axis of the column resulting from loads placed on the horizontal beams and slab loads placed above the columns.
Lateral forces are from wind and earthquakes. The column is exposed to the effects of these forces.
There are quite a few different types of columns. Some of the main column types are listed below:
Concrete columns can have a rectangular section or circular section.
Rectangular sections have a minimum design width of eight inches (8”) in the horizontal section (i.e., column width). These columns that undergo torque moments to resist wind and earthquake forces or dynamic loads must have a horizontal section above ten to twelve inches (10”-12”) per the American Concrete Institute (ACI) standard.
Circular sections have a minimum design diameter of twelve inches (12”), and the column area subject to static loads cannot be less than 100 square inches. Static loads are any load, on a structure that does not change in magnitude or position with time. The area of the column that is subject to dynamic loads cannot be less than 120-140 square inches per the ACI. Columns that are used for aesthetic purposes only are not required to adhere to the code minimums.
Steel columns can have three types of horizontal sections.
C-section columns consist of three sides; thin steel, and they are typically weaker and cheaper than other forms of steel columns. Some of the challenges C-section columns have are load stress, issues with high winds, and construction.
I-section consists of two flanges connected by one vertical component called the web. They can be identified as an “I” shape or “H” shape. Some codes also reference these columns as a “W” section. For construction, their use is based on deflection, vibration, bend, buckling, and tension. I-sections can bend under high stress instead of bucking.
Hollow section, also known as rectangular hollow section (RHS) columns, are fully enclosed steel sections (i.e., four sides). They are thicker, stronger, and they cost the most. RHS columns can withstand heavier loads and stresses. These columns have equal lateral strength in all four directions due to their consistent shape.
Composite columns are galvanized steel sections that are coated or filled with concrete. Typically, these columns are used when there are large loads on them or when additional corrosion protection or fire protection is warranted. These columns are usually used in the construction of multi-story buildings and industrial facilities. Although they are not architecturally appealing, composite columns can reduce the column section area.
Beams act as structural elements that transfer loads from the slab and to columns. This means transfer beams are installed to carry the load from one load-bearing wall to another. They are typically horizontal members. The purpose of a beam is to carry walls and to avoid loading a concrete slab. Beams are used to tighten columns in construction; this provides optimal distribution of the bending moment in the beams and reduces the length of the bending in the columns. Additionally, the length and width of the beams used will be determined by calculating the load being transferred to the beam to support the width in between them. The dimension of a beam is determined by calculating the value of internal forces located on them. Internal forces include the following:
Normal forces act perpendicular to the surface or object, which in this case is the beam. Normal stress is exerted.
Shear forces act parallel to the surface of an object, and they exert shear stress.
Bending Moment is the shearing force or the slope of the moment diagram at a given point.
There are two types of beams used typically. The beam types include the following:
Concrete beams have several types.
Falling beams are in a falling appearance from the concrete slab.
Inverted beam that lies above the concrete slab.
Hidden beams are within the thickness of the concrete slab. This means the width of the section is greater than the depth.
Cantilever beams are members that are fixed on one end and freestanding on the other. Typically used in trusses, bridges, and other structural members. These beams carry loads over the span that undergoes shear stress and bending moment.
Vierendeel beams are used in spaces that have wide-open areas. The members of these structures are joined rigidly together, and each member is required to transmit bending, shear, and direct stress.
C-section beams have two flanges and three sides. The flange includes a lip at the tip giving it the unique c-shape.
I-section beams have a high resistance to bending. The load is applied to the top flange, and the tension area is in the bottom flange.
T-section beams are similar to I-section beams; however, they only have one flange.
L-section beams are in the shape of an “L,” and they have half of a flange on one side.
Why are they Important?
The beams and columns work as a system to transfer loads from the slabs to the beams and then to the columns. This acts as a system to resist horizontal loads from the forces that can act on the structure. Some other types of beams and columns are listed below:
Jack posts are a type of lally column, which is a temporary column used to hold heavy structural weight when major wall renovations are taking place or when openings, such as windows or doors, are being installed. In some cases, lally columns are permanent and correct structural issues.
Microllam beams are engineered lumber used for structural support. This lumber consists of micro-thin layers of wood that are bonded together. Microllam beams span across openings and carry loads above the walls.
A lintel is a type of beam used to support the above wall or partition material between openings to provide the framing for a building structure.