Which of the following is used as relieving arches over wooden lintel?
🛡️ Core Concept: The Relieving Arch
A Relieving Arch (also known as a discharging arch) is a secondary arch built into a wall, typically above a primary structural element like a lintel. Its purpose is not to span the opening itself, but to intercept the load from the masonry above and divert it down to the walls on either side of the opening. This "relieves" the lintel below from carrying the heavy weight of the wall, which is especially important when the lintel is made of a weaker material like wood.
🧩 Analyzing the Suitability of Different Materials
The choice of material for a relieving arch depends on factors like weight, cost, and compatibility with the existing structure.
(B) Brick Arch: The Ideal Choice
A Brick Arch is the most suitable and common choice for a relieving arch over a wooden lintel. Here's why:
- Lightweight: Bricks are relatively light compared to stone, so the relieving arch itself doesn't add an excessive amount of new load to the wall.
- Ease of Construction: It's easy to construct a simple brick arch in place above the lintel. The joints between the bricks can be made wedge-shaped with mortar to create the arching action.
- Functionality over Form: Since relieving arches are often hidden within the wall's thickness, they are functional rather than decorative. Standard brickwork is perfect for this "inferior work" (meaning, not fine, exposed masonry). For higher quality work, soft bricks can be cut or rubbed to the precise wedge shape.
(A) Concrete Arch: Less Common
A Concrete Arch is generally not used as a relieving arch. If a concrete lintel is used in the first place, it is typically strong enough on its own and doesn't require relieving. Casting a concrete arch over a wooden lintel would be a complex and less practical solution compared to using brick.
(C) Ashlar Arch: Too Heavy and Expensive
An Ashlar Arch is constructed from precisely cut, dressed stones. This type of construction is very strong, but also very heavy and expensive. It is structurally illogical to use a heavy, high-quality ashlar arch to protect a much weaker wooden lintel. Ashlar arches are used as primary, decorative, and load-bearing structures themselves.
(D) Rubble Masonry Arch: Unsuitable and Heavy
A Rubble Masonry Arch is made from uncut, irregular stones. This makes it very heavy and less predictable in strength than a brick or ashlar arch. Placing such a heavy and rough arch over a wooden lintel would be counterproductive, as it would introduce a significant and uneven load onto the surrounding wall.