A buttress wall is a specialized structural element designed to provide stability to a main wall by counteracting forces that push it sideways. This projection is built against or bonded into the wall it supports, acting as a brace to prevent movement. The primary function of a buttress is to distribute lateral forces safely down to the foundation and the ground. This reinforcement is a method for ensuring the longevity and structural integrity of various types of construction.
What is a Buttress Wall?
A buttress is a projection of masonry, concrete, or other material built against a wall to reinforce it against outward pressure. Unlike a simple column or pilaster, which primarily carries vertical weight, the buttress is specifically engineered to resist horizontal forces. These lateral loads can originate from several sources, including soil pressure, the thrust exerted by an arch or vault, or strong wind loads.
The structure works by increasing the wall’s effective thickness and mass at specific points, which significantly enhances its resistance to buckling or overturning. This added support is important for tall, slender walls or those constructed from materials like stone and brick, which are strong in compression but weaker when subjected to tension or bending forces.
Common Applications
Buttress walls are frequently encountered in modern residential and commercial construction, particularly in applications where a wall must resist earth pressure. The most common application is in a buttressed retaining wall, designed to hold back soil on sloped terrain. Buttresses extend perpendicularly from the main wall face, distributing the lateral earth pressure more evenly and allowing the main wall to be thinner than a plain retaining wall.
They are also used to stabilize foundation walls, especially in older basements showing signs of bowing or cracking due to hydrostatic pressure from saturated soil. A structural engineer may recommend adding interior buttresses to brace the wall and prevent further inward movement. Buttresses are also a defining feature of large-scale historic architecture, such as cathedrals and bridges, where they counteract the outward thrust from heavy stone roofs and arches.
How the Design Works
The effectiveness of a buttress wall is rooted in its geometry and the principle of transferring force. Most buttresses feature a tapered or stepped profile, meaning they are widest and thickest at the base and gradually narrow toward the top. This shape is engineered to efficiently channel the horizontal force acting on the wall down to the ground.
When a lateral force, such as soil pressure, pushes against the main wall, the buttress acts as a rigid brace that resists the bending moment. The increased mass and width at the base provide a larger footprint, which increases the structure’s resistance to overturning and sliding. The material, often concrete or masonry, utilizes its high compressive strength to absorb the force and redirect it vertically into the foundation and the stable subsoil beneath. This mechanical action effectively converts the sideways push into a manageable downward load, anchoring the entire structure firmly in place.