This article will explore why support is important in structural design and examine different types of support commonly used in structural design, as well as their advantages and disadvantages.
April 17, 2023
Supports and connections are key components of the structural design process.
Understanding the various types of supports and connections in structural design is critical for structural engineers, architects, and building designers. This is especially important to build safe buildings, particularly when it comes to determining the load and tributary width in residential buildings.
This article will examine different types of support utilized in structural design, as well as their advantages and disadvantages. We will go through fixed support, pinned support, and roller support, as well as their basic attributes, frequent usage and application in homes or light commercial structures, and actual instances.
In structural engineering, a support is a structural part or system that transfers loads to the foundation while limiting a structure's motion in certain directions and allowing it to move in others. Supports are sometimes defined as "constraints given at the ends of structural components to prohibit translation, rotation, or both".
Beams, columns, walls, and foundations are examples of supports in real-world constructions.
Supports are critical to the stability and safety of structures in structural engineering. Support systems distribute loads and pressures from the structure to the base, preventing collapse brought on by too much stress.
Therefore, structural engineers, architects, and building designers must have a solid understanding of the functions of support in order to create buildings that are both effective and safe.
In structural design, distributing loads and forces is one of the main functions of supports.
Gravitational, wind, and seismic loads are only a few types of loads that buildings are susceptible to. Therefore, determining the size and direction of these loads when constructing a structure is crucial to make sure the support system can manage them by transferring the loads from the foundation to the ground.
Controlling deflection is another crucial function of supports in structural design.
When a structure deflects, it moves or deforms to some extent in response to a load. A structure's integrity and safety might be compromised by excessive deflection. Deflection is restricted to allowable limits by supports like beams, columns, and walls.
Deflection can be significantly reduced by adjusting a support's tributary width. The part of the floor or roof that the support system directly supports is referred to as the tributary width. A wider tributary allows a support system to carry a heavier load, which reduces deflection.
Moreover, supports provide building stability. A stable structure is one that can withstand loads and external influences without collapsing.
By resisting lateral loads like wind or earthquake loads, supports like walls, braces, and shear walls give stability. The stability of the structure depends heavily on the placement and design of these supports.
Furthermore, supports aid in reducing vibrations inside a building. Many factors, like wind, traffic, or seismic activity, can cause vibrations.
In addition to making inhabitants uncomfortable, excessive vibrations may threaten the building's structural integrity.
To lessen vibrations in a structure, supports such as foundation isolators, tuned mass dampers, and dampers are used. Although tuned mass dampers dampen vibrations by oscillating in the opposite direction from dampers, dampers absorb energy from the vibrations.
In order to reduce vibration transfer to the structure, base isolators are utilized to isolate the building from the ground.
Figure 1: Different types of supports, the movement they restrict, and reaction forces (Reference)
Fixed supports can withstand a turning moment as well as horizontal and vertical forces.
They are also known as stiff supports since they prevent both rotation and translation (in the context of support structures, translation refers to the movement of a structure or component in a straight line without rotation or angular displacement). This means that for a structure to be stable, there only has to be one fixed support.
In residential or light commercial construction, fixed supports are frequently employed, especially for single-support applications.
These are often required for cantilevered constructions like balconies and overhangs, where the fixed support provides all the essential limitations to ensure the structure is secure.
Fixed support can also transfer moments between structural components, which is an important aspect of structural design.
There are many advantages to using fixed supports for a building, but perhaps the most important is that they guarantee the most rigidity and stability for the building.
As a result, they are highly recommended for use in areas prone to earthquakes and other situations calling for a rock-solid foundation. If a building has only one support column, they come in handy there, too.
Nonetheless, the fixed supports' rigidity can sometimes be a drawback. They are rigid and cannot bend or sway, which can cause difficulties. Sometimes, the safety of adjacent materials necessitates that a structure has some wiggle room, or deflection.
The durability of the support may also be compromised due to the expansion of materials like concrete if the support is improperly designed.
Figure 2: An example of a fixed support (Reference)
A pinned support can withstand both vertical and horizontal stresses, but not momentary ones.
They will permit rotation but not translation of the structural member in either direction. Even if they might only resist a small amount of moment, many connections are presumed to be pinned connections.
It is also true that a pinned connection might only permit rotation in one direction while obstructing rotation in all other directions. Usually, a structure cannot be made stable with just one pinned connection. To keep the structure from rotating, another support must be added at some point. Both horizontal and vertical forces are depicted in the illustration of a pinned support.
Pinned supports are commonly used in residential or light commercial applications for joining multiple members together, such as in trusses, three-hinged arched bridges, and simply supported beams.
They are also used in other structures where rotation is needed, such as in cranes, towers, and other similar structures.
One major benefit of pinned supports is that they may be rotated, making it much simpler to join together many members. Not only are they simple to design for, but they also eliminate the need for moment-resisting components.
Yet the main drawback of pinned supports is that they can't hold the whole structure down by themselves. For anchorage, at least two pins are required, and the pins themselves are helpless against any moments that might be applied to the structure.
Since extra supports or moment-resisting components may be required to ensure the stability and safety of structures with pinned supports, this restriction might complicate their design.
Figure 3: An example of a pinned support (Reference)
Roller supports are free to move laterally but can only withstand perpendicular stresses. They enable motion along surfaces devoid of opposition from horizontal forces. The surface may be vertical, horizontal, or inclined in any direction.
These supports allow for horizontal movement while enduring significant vertical stresses. Horizontal movement is crucial, especially when the structural member is expanding and contracting. They guard against a pinned support being damaged.
Rubber bearings or gears are two examples of roller supports. Think about a load on roller skates, for instance. If there is no horizontal force, the weight is held in place. Yet, the body begins to move as soon as a horizontal force is applied.
Long-span constructions, such as bridges, often use roller supports because of the large shifts that thermal expansion can induce.
Roller supports are commonly employed in residential and light commercial construction for applications where thermal expansion is a factor, such as with metal roofing systems or long-span wood trusses, pipes and other constructions like them that need a lot of wiggle room in their support systems.
The fundamental benefit of using roller supports is that they allow for unrestricted rotation and movement in a single direction. This safeguards a structure from potential damage due to temperature changes or other external influences.
However, due to their inability to sustain lateral loads, roller supports are not suitable for structures that must endure them. As they may move wherever they like, they are not as stable as a fixed one would be.
Figure 4: An example of a roller support (Reference)
The weakest kind of support is simple support (roller support), as it provides no restraint for a structure.
The load capacity and stresses that the structure would be subjected to are normally calculated by a structural engineer or architect while designing supports. The required supports' size and placement will be determined in part by this.
Supports give the structure strength and stability, especially in places where there are significant loads or where more support is required.
Concrete, steel, and wood are frequently utilized as supports. The material selection will be determined by the building's design, the required load capacity, and additional elements like price and availability.
The role of supports and connections in structural design is critical to ensuring the safety and stability of buildings. These components distribute loads and pressures, limit deflection, offer stability, and decrease vibrations.
There are various types of supports, such as fixed, pinned, and roller supports, each with advantages and disadvantages. Knowing the many types of supports and connections is critical for structural engineers, architects, and building designers to produce effective and safe buildings.
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