Masonry Magazine April 1984 Page. 1
masonry
MARCH/APRIL 1984
CONCRETE MASONRY WALLS FOR EARTHQUAKE RESISTANCE
Concrete masonry walls can be designed and constructed to provide excellent performance under earthquake loading. The relatively high mass of concrete masonry construction provides substantial resistance to lateral forces. Properly designed and constructed concrete masonry walls have performed well in past earthquakes.
# Design Considerations
The design of concrete masonry walls for earthquake resistance should consider the following:
* **Seismic Zone:** The seismic zone in which the structure is located will determine the design lateral forces.
* **Soil Conditions:** The soil conditions at the site will affect the ground motion during an earthquake.
* **Building Occupancy:** The occupancy of the building will determine the required level of seismic resistance.
* **Wall Configuration:** The configuration of the walls will affect their ability to resist lateral forces.
* **Material Properties:** The material properties of the concrete masonry units and mortar will affect the strength and stiffness of the walls.
# Construction Practices
The following construction practices are essential for ensuring the earthquake resistance of concrete masonry walls:
* **Proper Mortar Mixing and Placement:** Mortar should be properly mixed and placed to ensure a strong bond between the concrete masonry units.
* **Adequate Reinforcement:** Walls should be adequately reinforced with steel reinforcement to resist tensile forces.
* **Proper Grouting:** Grout should be properly placed to fill all voids in the wall and provide a solid, monolithic structure.
* **Good Workmanship:** Good workmanship is essential for ensuring the quality of the construction.
# Resources
The following resources are available to assist in the design and construction of earthquake-resistant concrete masonry walls:
* **TMS 402/ACI 530/ASCE 5, Building Code Requirements and Specification for Masonry Structures**
* **NCMA TEK 14-1B, Concrete Masonry Wall Design**
* **NCMA TEK 14-19A, Seismic Design of Concrete Masonry Buildings**
MORTAR FOR CONCRETE MASONRY
Mortar is a mixture of cementitious materials, aggregate, and water. It is used to bond concrete masonry units together to form a wall or other structure. The type of mortar used will affect the strength, durability, and appearance of the masonry.
# Types of Mortar
The following types of mortar are commonly used for concrete masonry construction:
* **Type M:** Type M mortar is the strongest type of mortar and is used for applications where high compressive strength is required.
* **Type S:** Type S mortar is a medium-strength mortar that is suitable for most applications.
* **Type N:** Type N mortar is a general-purpose mortar that is suitable for non-loadbearing applications.
* **Type O:** Type O mortar is a low-strength mortar that is used for interior, non-loadbearing applications.
# Mortar Selection
The selection of the appropriate type of mortar will depend on the following factors:
* **Compressive Strength:** The required compressive strength of the masonry.
* **Exposure Conditions:** The exposure conditions to which the masonry will be subjected.
* **Appearance:** The desired appearance of the masonry.
* **Cost:** The cost of the mortar.
# Mortar Mixing and Placement
Mortar should be properly mixed and placed to ensure a strong bond between the concrete masonry units. The following guidelines should be followed:
* **Mix the mortar according to the manufacturer's instructions.**
* **Use clean water.**
* **Mix the mortar thoroughly.**
* **Apply the mortar to the concrete masonry units before it begins to set.**
* **Use a full bed of mortar.**
* **Tool the mortar joints.**
# Resources
The following resources are available to assist in the selection and use of mortar for concrete masonry construction:
* **ASTM C270, Standard Specification for Mortar for Unit Masonry**
* **NCMA TEK 9-1A, Mortars for Concrete Masonry**
CONCRETE MASONRY UNITS
Concrete masonry units (CMUs) are precast concrete blocks that are used to construct walls, partitions, and other structures. CMUs are available in a variety of sizes, shapes, and colors.
# Types of CMUs
The following types of CMUs are commonly used:
* **Hollow CMUs:** Hollow CMUs are the most common type of CMU. They have hollow cores that reduce their weight and allow for the installation of utilities.
* **Solid CMUs:** Solid CMUs are used for applications where high compressive strength is required.
* **Specialty CMUs:** Specialty CMUs are available for a variety of applications, such as bond beams, lintels, and pilasters.
# CMU Selection
The selection of the appropriate type of CMU will depend on the following factors:
* **Compressive Strength:** The required compressive strength of the masonry.
* **Size and Shape:** The required size and shape of the CMU.
* **Appearance:** The desired appearance of the masonry.
* **Cost:** The cost of the CMU.
# CMU Installation
CMUs should be installed according to the manufacturer's instructions. The following guidelines should be followed:
* **Use a level and plumb line to ensure that the walls are straight and plumb.**
* **Use a full bed of mortar.**
* **Tool the mortar joints.**
* **Protect the CMUs from moisture during construction.**
# Resources
The following resources are available to assist in the selection and installation of CMUs:
* **ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units**
* **ASTM C129, Standard Specification for Nonloadbearing Concrete Masonry Units**
* **NCMA TEK 1-1A, Concrete Masonry Units: An Introduction**