Arches are curved features that are a blend of aesthetics and great strength and stability. There are numerous types of arches in the construction industry, among which segmental arch is something that has been used across decades, providing numerous benefits and applications. Here is a detailed view of segmental arches and everything you need to know about them.
What is a Segmental Arch?
A segmental arch is a type of rounded arch whose curve is formed by a small portion of a circle smaller than a semicircle. Unlike a round arch, it is flatter and has a less pronounced curve. This arch effectively resists thrust, making it one of the most durable arches available in the industry. It provides a blend of both practical and aesthetic benefits to the structure.
Features of Segmental Arches
- The segmental arch’s curve spans less than 180°, making it more flat and shallow with a less pronounced height.
- The centre of the arch lies below the springing line, forming a flatter semi-circular arch.
- It transfers less lateral thrust to the supporting structures, as it directly distributes the load downwards.
- This arch offers design flexibility and can be combined with a wide variety of shapes and styles.
- It is compatible with structures that offer very limited headroom.
- It is one of the most efficient and durable arches in the industry.
Advantages and Disadvantages of Segmental Arches
Advantages
- The segmental arch design requires less material compared to a rounded arch, making it more material and cost effective.
- It reduces the need for heavy or reinforced supports, as the structure itself has the ability to withstand lateral thrust.
- It provides wider openings without excess structural height, making it suitable for bridges, doorways and other places that need larger openings.
- It provides an elegant look to the structure and is ideal for doors, windows and other decorative parts of the building.
- Construction of a segmental arch requires less mortar and fewer building materials (bricks or stones), thus reducing the material and labour cost.
- It is a strong and stable structure and has the ability to transfer loads downwards.
Disadvantages
- Due to their flat surface, segmental arches may experience slightly higher vertical loads.
- Designing a segmental arch is complex, as it requires detailed calculations and careful construction.
- This design may not be suitable for all architectural styles, limiting the aesthetic ability to certain projects.
- It can experience more stress due to point loads, potentially leading to cracking at the springline.
- It is not suitable for tall and large spans, where additional reinforcement is required for stability.
Applications of Segmental Arches
- It is most commonly used for doorways and window openings in residential and commercial constructions.
- It is also popular in construction of small to medium spanned bridges, where obtaining a lower and flatter arch shape is crucial.
- It is historically used in aqueducts to handle weight and distribute overlying forces over a long distance.
- It is highly useful in the construction of tunnel entrances and underpasses.
- Segmental arches can be used for constructing subway and railway tunnels for underground spaces.
- It is widely used for constructing historical buildings in Georgian and Colonial-style.
- It is ideal for constructing large openings in parking garages, warehouses and industrial buildings.
- It can be used in vaulted ceilings and arcades in classical and modern buildings.
Step-by-Step Construction of Segmental Arch
Designing
The first step in building a segmental arch is determining its shape and size. This includes deciding the span and rise of the structure and choosing the right construction material (brick, stone, or concrete).
Preparing the Site
Ensure that the foundation is capable of holding the arch. Prepare the abutments on either end of the arch suitable to bear the lateral thrust for a stable and strong to hold the arch above it. Mark the spring line where the arch begins to curve and mark the level to position it across the width of the arch accurately,
Build Framework & Centering
Build a temporary framework to provide the correct shape of the arch and support it while constructing. The framework should be shaped like a scaffold to support the voussoirs. Position the centering in place to align the spring line with the framework that is suitable for carrying the loads of arch stones.
Lay the Voussoirs
Place the voussoirs on both sides of the spring line, ensuring that they are aligned and level. This will form the lower part of the arch. Closely place each voussoir with mortar so that the adjacent stones distribute loads evenly.
The voussoirs should be placed towards the apex of the arch and lean slightly against the underlying stones to form a smooth and even finish. The size of the voussoir varies based on the span and rise of the arch.
Place the Keystone
After completing both sides of the arch, a keystone is placed at the apex, locking the other voussoirs in place to complete the arch structure. After placing the keystone, the arch develops the ability to withstand on its own and becomes self-supporting.
Allow for setting
After laying the arch, leave the structure to set so that the stones can firmly hold together, making the arch stand stable.
Remove the Centering & Finishing
After setting, remove the centering carefully without affecting the arch’s stability. Depending on the construction needs, fill the spandrels with masonry or leave them open. Ensure that the arch does not have any misalignments or gaps and forms a properly integrated structure.
Conclusion
A segmented arch is one of the most practical and versatile architectural elements of a building and is known for its stability, aesthetics and efficiency. It is widely used in the construction of doorways, bridges and openings for underpasses and tunnels. It provides a wider opening and reduces the cost of materials and labour. However, it is not suitable for all types of architectural structures.
FAQs
The lifespan of the segmental arch depends on the construction materials used, quality of construction, environmental conditions, and types of use. Generally a well-constructed segmental arch can last from 50 to 120 years.
The segmental arch transfers the overlying compression loads to the abutments on either side of the supporting walls along the curve of the voussoirs.
Segmental arches can be used in seismic zones, however it requires precise design and careful construction to ensure the required safety and performance to resist earthquakes.