Masonry foundations are essential components of building construction, providing the necessary support and stability for structures. These foundations can be constructed using concrete blocks or brick masonry units, with concrete block masonry often favored for its cost-effectiveness and minimal visibility. A well-designed masonry foundation must adequately support the weight of the structure while also withstanding lateral loads imposed by the surrounding soil. Additionally, the foundation should be durable enough to resist adverse effects from soil and groundwater. Masonry foundations can be categorized into two main types: plain masonry foundations and reinforced masonry foundations. This article explores the various types of masonry foundations, their construction methods, and their respective applications.
Types of Masonry Foundations
1. Masonry Strip Foundation
A masonry strip foundation is constructed directly below bearing walls using materials such as brick, block, or stone masonry. This type of foundation is particularly suitable for locations with stable soil conditions. The design features a wide base that gradually narrows, allowing for uniform load distribution across a larger area. This design helps to prevent cracks or damage to the foundation at the edges of the wall.
When constructing a masonry strip foundation on clay or silt, it is essential to use mortar to bed the masonry units, ensuring all joints are filled. Without mortar, groundwater may seep through the joints, weakening the clay and leading to significant settlement of the foundation. In areas with poor soil bearing capacity, it is advisable to include a concrete layer beneath the strip footing, typically between 100 mm to 225 mm thick.
2. Masonry Spread (Isolated) Footing
Masonry spread footings are constructed using high-quality bricks or stone, featuring a wider bottom compared to the load-bearing masonry wall above. This broader base is designed to distribute the applied load over a larger area, enhancing the stability of the structure. Spread footings are commonly used in residential buildings with basements.
The design and layout of masonry isolated footings are primarily dictated by the imposed loads. Similar to strip footings, it is advisable to incorporate a concrete layer of 100 mm to 225 mm in thickness beneath the isolated footing if the soil strength is inadequate.
3. Stepped Masonry Footing
The stepped masonry footing is essentially a variation of the strip footing, designed to prevent sliding on sloped grounds. It incorporates vertical steps to counteract the horizontal forces acting on the foundation, thereby providing horizontal bearing support.
Proper construction of the stepped footing is critical to ensure a strong bond at the steps, particularly when using stone masonry. It is essential to make the sections of the stepped foundation as long as possible to achieve stability.
4. Inverted Arch Masonry Foundation
An inverted arch masonry foundation consists of an inverted arch constructed from brick or stone masonry, on which a masonry wall or pier is placed. This type of foundation was historically used in multistory buildings, particularly in areas with soft soil conditions.
While inverted arch foundations were once common, they have largely been replaced by reinforced concrete foundations due to the complexities involved in their construction and the skill required to achieve the necessary strength.
Conclusion
Masonry foundations play a crucial role in the stability and longevity of structures. Understanding the various types of masonry foundations—strip, spread, stepped, and inverted arch—along with their specific construction techniques and applications is vital for selecting the appropriate foundation for any building project. By considering factors such as soil conditions and load requirements, builders can ensure that their masonry foundations provide the necessary support and durability for years to come.