Chapter 8: Masonry and Ordinary Construction

Types of Masonry Walls

• Masonry can be used for non-load-bearing curtain walls or partitions and load-bearing walls that provide basic structural support.
• Non-load-bearing masonry walls can be used in combination with a steel-frame multistory design to give the appearance of a masonry bearing wall.

Load-Bearing Masonry Walls

• Common materials used include brick, concrete block, and a combination of brick and block.
• Horizontal bonding can be accomplished with strategic placement of bricks or with corrosion-resistant metal ties between wythes.
• A non-reinforced bearing wall must have adequate thickness to keep compressive stresses within acceptable limits and provide lateral stability.

Limitations of Nonreinforced Masonry Construction

• Non-reinforced masonry walls are usually limited to a maximum height of six stories.
• Tall masonry structures are generally impractical or more costly than alternative designs unless the masonry is reinforced with steel.

Masonry Units

• Masonry units have no significant tensile strength and are used to support compressive loads.
• Density of masonry units varies depending on the specific type.

Stone Masonry

• Stone masonry consists of rock pieces that have been removed from a quarry and cut to the desired size and shape.
• Common types of stone used in construction include limestone, sandstone, and brownstone, granite, marble, and slate.

Bricks

• Bricks are produced from locally available clays and shales.
• Bricks are manufactured by placing moist clay in molds, removing them from the molds, and then drying the bricks, followed by firing in a kiln at temperatures as high as 2,400° F (1,300° C).

Concrete Blocks

• Hollow concrete blocks are the most common concrete masonry units (CMUs).
• Hollow blocks may be filled with cement or other material for added strength.

Other Masonry Units

• Clay tile blocks and gypsum blocks were once widely used for interior partitions, but their use has diminished in modern practice.
• Structural glazed tile is still frequently used where a smooth, easily cleaned surface is desired.
• Glass block is available in many textures and is architecturally popular for both interior partitions and exterior applications.

Mortar

• Mortar is an inherent part of most masonry construction and serves to bond individual masonry units into a solid mass.
• Mortar cushions the rough surfaces of the masonry units and serves to seal the joints.
• Spalling is the expansion of excess moisture within masonry materials, resulting in tensile forces within the material and causing it to break apart.

Portland Cement

• Portland cement is the most commonly used cement, consisting chiefly of calcium and aluminum silicate.
• It is mixed with water to form mortar, a paste that hardens, and is therefore known as a hydraulic cement.

Fire Resistance of Masonry Walls

• A well-constructed masonry wall is usually the last structural component to fail in a wood-joisted building.
• The fire resistance of a masonry wall depends on the type of masonry units used and the thickness of the wall.

Features and Functions of Masonry Structures

• Masonry structures may remain intact for many centuries.
• Masonry can be used for a variety of purposes in architecture, including primarily decorative functions.

Code Classification of Masonry Buildings

• The code classification of buildings with masonry components depends on the fire resistance of the joists, beams, and rafters that span the exterior load-bearing walls and interior columns.
• Buildings with masonry exterior walls can be classified as Type I (fire-resistive), Type II (protected noncombustible), or Type III (exterior protected) in the building codes.### Masonry Wall Construction
• A course is a horizontal layer of individual masonry units.
• A wythe is a single vertical column of masonry units in a wall.
• Header courses are used to provide a stronger horizontal bond between two wythes.
• Reinforced masonry walls can have a reduced thickness.
• Types of masonry wall construction include:
  • Concrete block brick faced (CBBF) masonry construction
  • Cavity wall construction

Reinforcement of Masonry Walls

• Reinforcement of masonry walls includes:
  • Architectural features such as buttresses, flying buttresses, and pilasters
  • Steel rods in the openings of individual blocks, filled with grout
• Buttresses are structures projecting from a wall, designed to receive lateral pressure action at a particular point.
• Flying buttresses include a gap between the lower part of the support and the structure.
• Pilasters are rectangular masonry pillars that extend from the face of a wall to provide additional support.

Interior Framing in Masonry Buildings

• Interior structural framing in masonry buildings includes:
  • Columns of materials that transfer loads to exterior bearing walls
  • Modern masonry buildings using materials including:
    • Masonry columns or interior bearing walls
    • Steel beams or trusses
    • Wood
• Interior framing can be finished with plaster, drywall, or other interior finish materials to provide required fire resistance.

Additional Notes on Masonry Wall Construction

• Grout is a mixture of cement, aggregate, and water that hardens over time, used to embed reinforcement materials in masonry walls.
• Fire spread through floor and ceiling spaces should be anticipated in masonry construction, especially where truss joists are used.
• Supporting openings in masonry walls:
  • Lintels are the most common method of supporting loads over openings.
  • Materials used in lintels include steel, reinforced concrete, or reinforced masonry.
• Designing lintels:
  • Engineers do not intend for the lintel beam to support the complete weight of the masonry wall above the lintel.
  • A lintel beam is required to support only the weight of a triangular section immediately above the lintel.

Fire Cuts and Corbels

• Fire cuts are angled cuts made at the end of a wood joist or beam that rests in a masonry wall to allow the beam to fall away freely from the wall in case of failure.
• Corbels are brackets or ledges made of stone, wood, brick, or other building materials, projecting from the face of a wall or column to support a beam, cornice, or arch.

Parapets

• A parapet is an extension of a masonry or steel wall that projects above the roof 1 foot (300 mm) or more.
• Parapets usually do not have lateral support.
• Parapets are found on exterior masonry walls and fire walls of buildings with combustible roofs.

Identification and Breaching of Masonry Walls

• Identification of reinforced masonry walls:
  • Reinforced and nonreinforced masonry walls may look identical from a building's exterior.
• Breaching masonry walls:
  • Caution must be exercised while breaching masonry walls due to the possible presence of utilities or the disruption of load-bearing walls.
  • Search for a weak point in the mortar or concrete, and work in a triangle shape from that point until the breach is large enough for the purpose.

Material Properties of Masonry Construction

• Masonry components include:

  • Stone
  • Bricks
  • Concrete blocks
  • Clay tile blocks
  • Gypsum blocks
  • Structural terra cotta
  • Structural glazed tile
  • Glass block

• Benefits of masonry components include:

  • Durability
  • Resistance to weather, fire, and insects

• Drawbacks of masonry construction include:

  • Long-term deterioration of mortar joints
  • Labor-intensiveness### Masonry Wall Construction

• A course is a horizontal layer of individual masonry units.

• A wythe is a single vertical column of masonry units in a wall.

• Header courses are used alternating with other types of courses to provide a stronger horizontal bond between two wythes.

• Reinforced masonry walls can have a reduced thickness.

• Masonry walls are reinforced to support the weight of a taller building or to provide stability against lateral forces.

Types of Masonry Wall Construction

• Concrete block brick faced (CBBF) masonry construction uses a brick wythe in combination with a concrete block wythe.
• A cavity wall is an exterior brick wall constructed with a vertical cavity between the exterior wythe and the interior wythe.
• Concrete block walls are reinforced with steel rods in the openings in the individual blocks and the openings are filled with grout.

Interior Framing in Masonry Buildings

• Interior structural framing in masonry buildings includes columns of materials that transfer the loads to the exterior bearing walls.
• Modern masonry buildings have interior framing systems using materials including masonry columns or interior bearing walls, steel beams or trusses, and wood.
• Both protected and unprotected steel interior framing can be used with masonry bearing walls.

Additional Notes on Masonry Wall Construction

• The existence of header courses in a wall is one way to identify the method of construction of a masonry wall.
• Grout is a mixture of cement, aggregate, and water that hardens over time; used to embed reinforcement materials in masonry walls.
• Buttresses are structures projecting from a wall, designed to receive lateral pressure action at a particular point.
• Flying buttresses include a gap between the lower part of the support and the structure.
• Pilasters are rectangular masonry pillars that extend from the face of a wall to provide additional support for the wall.

Supporting Openings in Masonry Walls

• Openings in masonry walls are provided for doors and windows.
• Masonry over an opening is supported by the use of a lintel, arch, or corbel.
• Lintels are the most common method of supporting loads over openings in masonry walls.
• Materials used in lintels include steel, reinforced concrete, or reinforced masonry.

Designing Lintels

• Engineers do not intend for the lintel beam to support the complete weight of the masonry wall above the lintel.
• A lintel beam is required to support only the weight of a triangular section immediately above the lintel.
• If the height of the wall above the opening is shorter than the height of the triangular section, the lintel is engineered to support the entire weight of the masonry above the opening.

Fire Cuts and Corbels

• A fire cut is an angled cut made at the end of a wood joist or wood beam that rests in a masonry wall to allow the beam to fall away freely from the wall in case of failure of the beam.
• Corbels are brackets or ledges made of stone, wood, brick, or other building material projecting from the face of a wall or column used to support a beam, cornice, or arch.

Parapets

• A parapet is an extension of a masonry or steel wall that projects above the roof 1 foot (300 mm) or more.
• Parapets usually do not have lateral support.
• Parapets are found on exterior masonry walls and fire walls of buildings with combustible roofs.

Additional Notes

• Wood joists or beams simply rest on the masonry wall in an indentation known as a beam pocket.
• A metal strap may be provided to function as a horizontal tie between the masonry and the end of the beam.
• When a beam transmits a large vertical load to a masonry wall, the wall may be increased in thickness at the point of support with a pilaster to reduce the compressive stresses in the masonry.

Factors that can Cause a Parapet Wall to Lose Structural Integrity

• Exposure to high wind, particularly if erosion of the mortar joints or other deterioration has occurred.
• Roof collapse during the course of a fire.
• Impact from aerial ladders, especially when forcefully extended or retracted.
• Force of master streams.

False Fronts and Voids

• A masonry building may have a decorative false front or facade through renovation or original design.
• A false front can create a combustible void that is not normally encountered with masonry walls.

Building Codes and Collapse of Masonry Construction

• Building codes require less clearance between buildings with masonry or other fire-resistive exterior walls.
• Exterior fire-resistive walls of masonry construction tend to reduce fire spread between structures.
• Collapse of masonry walls often occurs when interior wood framing fails.

Collapse Zones and Factors that Affect a Building's Structural Integrity

• Collapsing interior floor or roof members can exert horizontal forces against a wall and push the wall outward.
• The collapse of interior framing removes interior bracing for the wall and the wall may be simply pushed out from the building.
• Steel within a reinforced wall can withstand some tensile stress, making collapse less likely.
• Intersecting masonry walls support and reinforce each other, making the corners of the building the strongest points.

Identification of Reinforced Masonry Walls and Masonry Wall Breaching

• Reinforced and nonreinforced masonry walls may look identical from a building's exterior.
• Masonry walls are inherently difficult to breach, but newer reinforced walls may be easier to breach.
• Breaching masonry walls may be necessary to access trapped victims or accommodate hoselines or other extinguishing methods.

Breaching Masonry Walls

• Search for a weak point in the mortar or concrete, and work in a triangle shape from that point until the breach is large enough for the purpose.
• Maintain a corbelling shape to serve as a guide for choosing bricks that are likely to be safe to remove.

Tie Rods and Bearing Plates in Masonry Walls

• Tie rods and bearing plates are used to stabilize masonry structures under normal conditions.
• The tie rod usually has a turnbuckle to adjust the tension in the rod.
• Bearing plates can take several forms, and are usually easily visible on the outside of a building.

Non-Fire Related Deterioration of Masonry Walls

• Deterioration of masonry walls is normally a slow process that takes place over many years.
• Old buildings sometimes collapse without warning or apparent reason.
• Masonry walls may be repaired when deterioration has occurred.
• Masonry walls can deteriorate from several causes, including erosion of the mortar or reinforcing steel as a result of exposure to the elements, shifts in the foundation, and wooden interior members rotting and shifting from long-term exposure to moisture.

Indicators of Masonry Wall Structural Failure

• Cracks in masonry walls must be closely monitored as they may indicate structural failure.
• Some factors that determine fire behavior in a masonry structure are obvious and can be detected by visual observation, while others are subtle and not likely to be detected during the course of a fire.

Emergency Operations and Monitoring of Masonry Buildings

• During emergency operations, masonry buildings are monitored for change and growth.
• Indicators of imminent collapse include changes in the alignment of cracks.
• Indicators of imminent collapse in the case of a fire include the increased presence of light shining through the wall.
• Total collapse of a masonry building is possible if the structure becomes heavily involved in fire.