Architecture: Pilasters and Buttresses

Structural Components of a Building

• A building is comprised of many structural components that combine to form an enclosure for a given purpose.
• The primary structural elements of a building are foundations, columns, beams, and connections.
• These elements work together to transfer all loads to the earth.

Columns

• Columns can be vertical, diagonal, or horizontal in attitude.
• A column is compressively loaded, and its strength is proportional to the square of its depth.
• If the depth of a column is doubled, it can carry four times the load, and if tripled, it can carry nine times the load.

Pilasters and Buttresses

• A pilaster is an interior or exterior vertical stack that thickens a wall column, providing lateral support for roof beams and trusses.
• A buttress is a separate, diagonally-stacked brick, stone, or concrete wall that protrudes perpendicularly from the wall column, supporting the roof.

Masonry

• Masonry mixes have little to no tensile or shear strength, relying on compressive forces to give them strength.
• Masonry walls get stronger as axial loads are applied and compressive forces increase.
• There is an absolute maximum weight that can be applied before the brittle material fails.

Concrete

• Concrete is a heat sink that slowly absorbs and retains heat, rather than conducting it.
• Concrete contains moisture and continues to absorb and wick moisture as it ages, causing it to crack or spall when heated.
• Spalling can reduce the critical mass of the concrete, weakening its strength.

Precast Concrete

• Precast concrete is a type of concrete that is poured at a factory and then shipped to a job site.
• It can be used for walls, floors, or roofs.
• Common applications of precast concrete include tilt-up slabs for walls and twin-T slabs for floors and roofs.

Metals

• Cast iron is a brittle material that can fracture when heated in a fire and then exposed to water.
• Aluminum and titanium are abundant minerals with excellent strength-to-weight ratios, but are not commonly used for the structural bones of a building due to manufacturing costs.
• Aluminum fails quickly during fires, whereas titanium shows significant resistance to heat.

Engineered Wood Products (EWP)

• EWP uses modern methods to transform wood chips, slivers, veneers, shavings, and recycled wood products into components that replace sawn lumber, sheathing, and other composite structural materials.
• The wood used for EWP is typically derived from new-growth forests and rapid-growth tree farms, although it is possible to manufacture similar engineered cellulosic products from other lignin-containing materials.

Laminated Veneer Lumber (LVL)

• LVL is made from layering sheet veneers of wood with alternating grain directions (90° with each layer).
• Layers are glued together to achieve multidirectional and uniform strength.
• LVL is often used in place of cut lumber.

Laminated Strand Lumber (LSL)

• LSL is a structural composite lumber manufactured from flaked and chipped strands of native wood blended with an adhesive.
• Strands are oriented in a parallel fashion (also known as parallel strand lumber-PSL).
• PSL is similar to LVL in its use.

Oriented Strand Board (OSB)

• OSB is used extensively in new construction as a structural sheathing to form roof and floor assemblies (when glued to trusses) and as the web portion of a wooden I-beam.
• OSB is subject to degradation by direct sunlight, moisture, and heat.
• The heat of fire or smoke can cause rapid destruction of OSB, and direct flame contact will cause OSB to ignite and burn rapidly, emitting toxic gases from adhesives.

Other Wood Products

• Plywood is made from layering sheet veneers of wood with alternating grain directions (similar to LVL).
• Decorative wood paneling is not intended to resist loads and is merely decorative, with a high surface-to-mass ratio.
• Most decorative wood paneling is not allowed by code for interior wall finishing due to rapid flame spread characteristics.

Load Imposition

• Loads are imposed on a building through gravity, atmospheric conditions, and human-created forces
• There are three types of loads: axial, eccentric, and torsion
• Axial loads are imposed through the center of the material
• Eccentric loads are imposed off-center, causing a material to bend
• Torsion loads cause a material to twist

Loads and Materials

• Loads can be classified as live, impact, and distributed loads
• The imposition of loads refers to the contact or orientation of the load to the material(s)
• Loads can be imposed in three ways: axial, eccentric, and torsion
• The building industry classifies loads to understand how they affect buildings

Building Materials

• The four basic building materials are wood, steel, concrete, and masonry
• Wood is the most predominant building material of the past, present, and likely the future
• Steel is made from iron ore, carbon, and an alloy agent
• Cast iron is a material usually formed from pig iron, which is a high carbon content iron
• Concrete is a composite material that relies on the ratio of materials, especially the ratio of water to Portland cement

Concrete and Reinforcement

• Concrete has excellent compressive strength but poor tensile and shear strength
• Steel is often added to concrete as reinforcement when the concrete is being used in a way that will subject it to those forces
• Reinforced concrete is considered a composite material with brittle and ductile properties
• Pre- and post-tensioned concrete has steel cables placed through the plane of the concrete mass

Structural Elements

• The primary structural elements of a building are foundations, columns, beams, and connections
• These elements work together to transfer all loads to the earth
• Columns can be vertical, diagonal, or horizontal
• Pilasters and buttresses can be structural and can be differentiated by shape