The beam structure is a horizontal structural element used in construction to sustain and resist the laterally applied loads coming on it. It forms the traditional description of any building or civil engineering structural elements.
The beam structure can be made either by means of concrete, steel or wood, or composite materials. A beam is characterized based on its support, profile, length, and material. There are different types of beams in terms of supports provided, the material used, based on load conditions, etc.
5 Types of the beam structure
There are a few primary types of beams used in construction and engineering. These beams are typically classified based on their length, equilibrium, and cross-section and include:
A continuous beam is a structural component that provides resistance to bending when a load or force is applied. These beams are commonly used in bridges. A continuous beam is one that has two or more supports that reinforce the beam. These supports are used under and between the beams and are typically vertical in nature. A beam of this type has more than two points of support along its length. These are usually in the same horizontal plane, and the spans between the supports are in one straight line. Continuous beams are thought to be more economical when compared to other beam types.
In contrast to a simply supported beam, which has supports at each end and a load that is distributed in some way along its length, a continuous beam is much stiffer and stronger. A bridge that is made up of beams that span between only two supports is called a simply supported beam bridge. If two or more beams are joined together rigidly over multiple supports, the bridge becomes continuous.
Simply supported beams
The simply supported beam is quite possibly the most simple construction. It includes just two supports, one at each end. One is a pinned support and the other is roller support. These are most frequently utilized in general construction and are very versatile in terms of the types of structures that they can be used with. A simple support beam has no moment resistance at the support area and is placed in a way that allows for free rotation at the ends of columns or walls.
A fixed beam is one that is fixed on both ends of the beam with supports. This type of beam does not allow for bending moment production and will not have any vertical movement or rotation. Fixed beams are most frequently used in trusses and similar structures.
It has more load capacity than the simply supported beam for the same loading condition. It has a lesser value of maximum deflection than that for a simply supported beam. It is subjected to a lesser maximum bending moment than that for a simply supported beam.
An overhanging beam is defined as a beam, which is freely supported at two points and has one or both ends extending beyond these supports, typically at one end and in the middle of the beam, but does not have support at the other end of the beam, leaving it hanging. This type of beam extends beyond the walls or columns and the overhanging section of the beam is unsupported. An overhanging beam is a combination of a simply supported beam and a cantilever beam.
Mostly in the overhanging beam one support is hinge support while roller support has one end as free like a cantilever.
Cantilever beams are members that are supported from a single point only; typically with fixed support, it is one that is free-hanging at one end of the beam and fixed at the other. In order to ensure the structure is static, the support must be fixed; meaning it is able to support forces and moments in all directions. This type of beam is capable of carrying loads with both bending moment and sheer stress and is typically used when building bridge trusses or similar structures. The end that is fixed is typically attached to a column or wall. The tension zone of a cantilever beam is found at the top of the beam with the compression at the bottom of the beam.
A good example of a cantilever beam is a balcony. A balcony is supported on one end only, the rest of the beam extends over open space; there is nothing supporting it on the other side.
Cantilevers deflect more than most types of beams since they are only supported from one end. This means there is less support for the load to be transferred.
3 support conditions in beams
Roller, pinned, and fixed connections are the three most common types of supports in beams and structures to connect them to their foundation. Any of these supports can be seen at any point in the length of a structural element. They can be found at the ends, in the middle, or at some other point in between. The load that the support can withstand is determined by the type of support connection. The type of support has a significant impact on the load-bearing capacity of each element and, as a result, the system.
Fixed supports are important types of supports in beams and structures that can resist horizontal, and vertical forces and moments. They are also known as rigid supports because they prevent both rotation and translation. This indicates that for a structure to be stable, it only requires one fixed support. It is possible to satisfy all three equilibrium equations. This kind of support can be seen in a flagpole set into a concrete base or a beam connected to a wall. Fixed supports are often represented by two forces (vertical and horizontal) and a moment.
The greatest benefit provided by this support can also be its little sagging since the system can require a small amount of deflection or play to protect the surrounding materials. Concrete, for example, expands as it increases in strength. As a result, it’s critical that the support is properly designed; otherwise, the expansion may result in a decrease in durability.
Both vertical and horizontal forces can be resisted by pinned supports, but they cannot resist a moment. It means that the pinned support is kept in place to prevent translation. The components of horizontal and vertical forces can be determined using equations of equilibrium. The best example of pinned support is a door leaf, which rotates just along its vertical axis and does not move horizontally or vertically. The rotation of a pinned support is only permitted in one direction and is blocked in the other.
In trusses, pinned supports are often used. When several members are connected together with pinned connections, the members push against each other, causing an axial force within the member. The benefit of this support is that the members can have no internal moment effects and will only be designed based on their axial force.
Roller supports can rotate and translate along the roller’s resting surface. The surface may be vertical, horizontal, or sloped in either direction. In the type of bearing pads, roller supports are usually used at one end of long bridges. This support provides the bridge system to expand and contract in response to temperature changes, and without it, the stresses at the banks could fracture the supports. This support can not withstand lateral forces.
If no roller support is provided for a bridge structure, the bridge’s banks would be severely damaged. However, at least one other support should resist this horizontal force to prevent translation, so roller support should only be supported at one end, not both.
13 Differences and Uses of H-beam and I-beam
- Regardless of whether the I-beam is ordinary or light, due to the relatively high and narrow section size, the moment of inertia of the two main axes of the section is quite different. Bent members or form lattice-type stress members. It is not suitable for axial compression members or members that are perpendicular to the plane of the web and bending, which makes it very limited in the scope of application.
- H-beams are high-efficiency and economical section profiles (others include cold-formed thin-walled steel, profiled steel plates, etc.). Due to the reasonable cross-sectional shape, they can make the steel perform better and improve the cutting capacity. Different from the ordinary I-shaped, the flange of the H-beam is widened, and the inner and outer surfaces are usually parallel, which makes it easy to connect with other components with high-strength bolts. Its size constitutes a reasonable series, and the model is complete, which is convenient for design and selection (except I-beam for the crane beam).
- The flanges of H-beams are all of the equal thickness, with rolled sections and combined sections composed of three welded plates. I-beams are all rolled sections. Due to poor production technology, the inner edge of the flange has a 1:10 slope. The rolling of the H-beam is different from that of the ordinary I-beam, which only uses one set of horizontal rolls. Because its flange is wide and has no slope (or small slope), it is necessary to add a set of vertical rolls for rolling at the same time. , its rolling process and equipment are more complicated than ordinary rolling mills. The maximum height of rolled H-beam that can be produced in China is 800mm, which exceeds the only welded composite section.
- The side length of the I-beam is small and the height is large, so it can only bear the force in one direction.
- H-shaped steel grooves are deep and thick and can withstand forces in both directions.
- Thick I-beams are used for load-bearing columns that are prone to instability.
- I-beams can only be used for beams, while H-beams can be used for structural load-bearing columns.
- H-beam is an economical section steel with better section mechanical properties than I-beam. It is named because the shape of the section is the same as the English letter “H”. The flange of a hot-rolled H-beam is wider than that of the I-beam, with large lateral stiffness and strong bending resistance. Under the same specifications, the weight of the H-beam is lighter than that of the I-beam.
- The flange of the I-beam is the thickness of the web part of the variable section, and the outer part is thin; the flange of the H-beam is of equal section.
- H-beams are divided into two types: hot-rolled and welded. HW refers to wide-flange H-beams, such as HW300x300, which means the section height and width are both 300 mm; HN is narrow-flange H-beams, such as HN300x150, which means section height 300 and width 150; HMs have flange widths in between, such as HM300x200. HW, HN, and HM are all section types of hot-rolled H-beams. Soldered can generally write BH.
- HW is that the height and flange width of the H-beam is basically equal; it is mainly used for steel core columns in reinforced concrete frame structure columns, also known as rigid steel columns; it is mainly used for columns in steel structures.
- HM is the ratio of H-beam height to flange width is roughly 1.33~1.75; mainly in steel structures: used as steel frame columns, and used as frame beams in frame structures bearing dynamic loads. For example Device Platform.
- HN is the ratio of H-beam height and flange width greater than or equal to 2, which is mainly used for beams; the use of I-beams is equivalent to HN-beams.