There are different types of beams used in the construction of structures. We base different kinds of construction beams on support conditions, the choice of materials, cross-section types, geometry, and such factors. It is impossible to make concrete framed buildings without the use of beams.
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What is a construction beam used for?
Construction beams are structural elements used in buildings, and they resist loads applied laterally to their axis. They are characterized by the manner of their supports, shape of the cross-section, length, material, and equilibrium conditions. Beams transfer loads applied on their length to the endpoint and transmit the load to a column, wall, or foundation. The mode of deflection of beams is primarily by bending. Beams withstand shear forces, bending moments, and vertical loads.
What are construction beams made of?
There are different types of construction beams based on the choice of the construction material. Common materials are reinforced concrete, timber, steel, and fiber-reinforced polymeric materials.
Reinforced concrete beams are made when steel bars are embedded along the length of a structural member to increase the structure's tensile strength. These are the most common beam types.
On the other hand, steel beams are made from steel and molded into different shapes. Standard steel beams are I-beams, H-beams, W and S sections, rectangular hollow sections, plate girders, and circular hollow sections. Steel is a suitable material when constructing beams over long spans, and we also use it in making composite beams of concrete and steel.
Timber is the oldest material used in beam construction. Timber beams are constructed by jointing structural wooden members together.
We use fiber-reinforced polymeric materials to construct composite beams where we join two or more materials together to form a beam.
The different types of beams
There are different beams applicable in engineering and below are some of the most common examples applied.
1. Universal beam
We also commonly refer to a universal beam as an I-beam, and it is one of the most frequently used beams in steel structures. The horizontal elements of this beam are known as flanges, whereas the vertical element is the web. The web resists shear forces, and the flanges resist bending moments. Universal beams have a high moment of inertia, thus making them suitable for resisting shear and bending moments. We mainly make I-beams from steel, but there are some instances where we make them from aluminum. When it comes to their design for structural use, tables from design codes are available that make selecting suitable beam sizes easy. During design, we assess the strength of an I-beam by its deflection, vibration, bending failure, shear failure, and yielding.
We use universal beams when making critical support trusses or main building frameworks. Due to their strength, they ensure a structure has adequate structural integrity.
2. Hip beam
We use a hip beam in the design of most roofing designs. We use hip beams to make hip roofs where hip beams converge to the middle portion of a roof to create good roofing designs for residential construction. The hip beams support other load-bearing beams that are separated at proportioned angles.
3. Trussed beam
This is a stiffened beam by a system of braces to form a truss and a bottom chord. A trussed beam is made of either steel or timber sections. These beams are used when there is a lot of weight to be supported across vast spaces. A good example is in industrial buildings where there is a need for more space for working areas. Trussed beams span from 10 to 100 meters, depending on the building type. Trussed beams provide reasonable economical solutions for buildings with spans over 25 meters. Sections in trussed beams should be symmetrical to cater to bending on the vertical plane of the truss. We connect the members of these beams through bolting or welding. One of the significant advantages of these beams is their ease of fabrication which makes them an economical choice for design along large spans.
4. Lattice beam
A lattice beam is a girder whereby the web has diagonal pieces arranged in a lattice-like manner. We generally make these beams from iron or steel. The top chord acts in compression in lattice beams and should resist column loads without deformation. The bottom chord works in tension and lies on the line of support of the beam. These beams are desirable due to their lightweight. When the internals of lattice beams are made of stainless steel, it reduces their corrosion susceptibility and construction costs.
5. Composite beam
These beams are made from combining two or more construction materials. Composite beams are more robust than beams made from their constituent parts, and they provide a favorable combination of the materials used in their construction. Steel and concrete composite beams have both the inherent properties of steel and concrete, and they are the most common type of composite beams. There are other types of composite beams made from plastic composites and timber. Joining two materials combines their physical strength and enhances physical characteristics. For instance, concrete lends mass, stiffness, and compressive strength in steel-concrete beams, while steel reduces vibrations, deflections and increases compressive strength. One of the most critical parts of composite beams is shear connectors that fix the two materials. In steel-concrete composite beams, shear connectors are usually studded into steel beams and set into the concrete slabs. The number of shear connectors is carefully chosen as they affect the performance of these beams.
6. Chilled beam
Chilled beams are heating and cooling systems that are used for large buildings. These beams have heat exchangers attached to ceilings, and they have a series of pipes. These pipes can either heat or cool the room. Chilled beams are either active or passive depending on the mechanical system used to heat or cool a unit. Chilled beams are different from chilled ceilings, whereby the chilled beams rely on the beam as the delivery system for the heat or cold, and the chilled ceilings use metal plates in the roof to transmit the heat or cold. Chilled beams are cost-effective and easy to maintain. They do not create noise and do not require a lot of space for maintenance. Chilled beams, however, have some disadvantages as we cannot use these heating systems for rooms with a floor-to-ceiling height beyond 2.4m. This is because air will not adequately circulate, thus rendering the system ineffective.
7. Reinforced concrete beam
Reinforced concrete is a composite material made from concrete and steel bars. Steel bars are added to increase the relatively low ductility and tensile strength of concrete, and the reinforcement usually is passively embedded before the concrete sets. These are the most widely used beams in construction. Reinforced concrete is advantageous as it can take high compressive stresses. These beams take loads from walls and slabs and transmit them to columns. Reinforced concrete beams carry vertical and horizontal loads. They are used in constructing bridges, houses, foundations, and many other structures, and it would be impossible to construct modern facilities without the use of reinforcement.
8. Steel beam
As the name suggests, steel beams are made from steel, and they support heavy loads. Their specifications depend on their shapes and sizes. Steel beams are classified depending on their cross-sections into I-beams, T-beams, channels, and broad flange sections, and these beams can be straight or curved. Compared to other beams, steel beams have several advantages. Some advantages are that rodents or termites cannot attack these beams, unlike timber beams, and they can withstand high tensile stresses, therefore providing increased structural integrity. They are also resistant to fire and corrosion.
We mainly use steel beams in making warehouses, house frames, and roofing structures. They also secure houses from horrible weather conditions.
9. Timber beam
Timber beams are horizontal structural supports made from wood. These beams are standard in wooden frame structures like residential houses. The choice of wood depends on the type of construction. Wooden beams can be made either from sawn lumber or engineered wood products. Engineered wood products have a higher resistance to twisting and warping. Historically, timber beams are the oldest beams used in construction. The type and size of wood affect how much load the timber beam can bear. The most robust timber beams are dense-close grained beams.
Compared to other beams, timber beams are faster to erect. Timber beams also have a better thermal performance compared to other construction materials. However, if not properly maintained, these beams are prone to rotting and infestation. They are also more prone to fire than other construction materials. Timber beams are typical in house construction, temporary bridge construction, and roofing.
10. Straight beam
Straight beams are beams with a linear profile on their horizontal length. Most of the beams used in construction are straight beams. They are typical beams supported on their ends and can resist bending moments and shear forces. These beams are relatively easy to construct.
11. Curved beam
These are beams that have a curved profile on their horizontal axes. They are also supported on their ends and can resist bending moments, shear forces, and torsional forces. They are most common in the construction of circular buildings and arches. We also use them in cranes, construct balconies, and provide pre-camber for structures such as bridges. These beams are complex to design as they do not have a linear strain profile along their axes. If they are set up in an area prone to high wind forces, we have to make special considerations in design.
12. Beam bridge
These are the simplest types of bridges to construct. They consist of bridge spans supported by piers or abutments on each end. There are no moments transferred to the supports for these beams, and we thus term them as simply supported. The simplest beam bridge type would be a wooden log or plank placed across a stream. Modern beam bridges can be in the form of plate girders or box girders. They can be made by having main beams side by side with a bridge deck on top. These beams are meant for relatively short distances as they do not take moments.
13. Tie beam
These are horizontal beams that connect columns, rafters, or trusses. We primarily use tie beams in roofs, and when used on roofs, they cannot carry heavy vertical loads such as walls. They also act as strap beams to remove the eccentricity of columns in foundation footings. Tie beams also prevent highly stressed columns from buckling outwards. We also use tie beams to hold longitudinal bars in place during concrete placement.
14. Cantilever beam
A cantilever beam is a rigid horizontal beam supported only on one end. A cantilever beam can be in the form of a typical beam, slab, or truss. We use these beams in towers, bridges, and buildings over spans that need to allow for an overhang. Temporary cantilever beams are very common in construction to act as temporary supports, especially during bridge construction. Cantilever beams heavily rely on torque and rotational equilibrium for stability.
Below are answers to frequently asked questions on construction beams.
What is the strongest beam shape?
The I-beam is the most robust beam shape. It is strong in the vertical direction and has a uniform and equal response in other directions. We, therefore, use I-beams as the main beams in cranes and long trailers.
How long can a beam span?
Standard reinforced concrete beams in residential projects span up to 8 meters. However, one can use trussed beams that span up to 100 meters for more extensive spans.
What is the minimum size of a beam?
Different design standards have different beam sizes. The American Design standards for reinforced concrete beams state that beams should not be less than 230mm by 230mm.
What is a continuous beam?
This is a beam with more than one support along its length.
Beams have been a vital part of construction ever since the ancient world. Hopefully, this article gives you a good idea of the type of construction beams in a structure and why they are essential elements one cannot overlook. The type of structure determines the type of beam one uses and the next time you are around a building, try to identify the beams you come across.