Load-bearing seismic walls must satisfy in-plane, out-of-plane, gravity-load, and diaphragm-connection requirements, with the wall system rather than the individual masonry unit determining acceptance [S3].
Burned clay brick, concrete brick, hollow clay or concrete block, plain concrete, and hollow clay tile can form unreinforced masonry, while reinforced or confined systems require additional strength and detailing under the governing seismic code [S5].
Separate masonry units from the seismic system
The Seismic Design Guide for Masonry Buildings, Second Edition (2018), states that loadbearing walls resist superimposed gravity loads and lateral loads, while its reinforced-masonry design chapter addresses both in-plane and out-of-plane seismic loading [S3]. A brick or block that performs adequately in compression does not establish that the wall has adequate shear, flexural, sliding, or connection resistance.
The same guide identifies separate resistance checks for shear and diagonal tension, sliding shear, and flexure caused by combined axial load and bending. It also covers wall-height-to-thickness restrictions, plastic hinge regions, ductility checks, boundary elements, seismic reinforcement, wall-to-diaphragm anchorage, and construction issues [S3]. These checks determine whether a proposed unit belongs in an acceptable seismic system.
For material screening, the District of Columbia existing-building provisions define unreinforced masonry to include burned clay, concrete or sand-lime brick, hollow clay or concrete block, plain concrete, and hollow clay tile [S5]. The distinction matters because an unreinforced wall relying on the tensile strength of units, mortar, and grout is not equivalent to a properly detailed reinforced masonry wall [S5].
Use brick, concrete block, and AAC by structural role
Clay brick is suitable when the design uses its verified unit strength, mortar bed and joint behavior, wall dimensions, and reinforcement or confinement system. A fired-clay unit has no automatic seismic approval, even when it is described as a good earthquake-resistant brick [S2].
Concrete masonry block is appropriate where hollow or grouted construction forms part of a code-compliant reinforced system. The seismic design guide addresses reinforced masonry shear walls under in-plane seismic loading, including shear and diagonal-tension resistance, sliding shear resistance, in-plane flexural resistance due to combined axial load and bending, and general seismic design provisions [S3]. Hollow units may require grouting and reinforcement where the design demands them, rather than being selected solely for dimensional accuracy or low absorption [S2].
Autoclaved aerated concrete, or AAC block, should be selected only after checking the project-specific modulus, strength, density, mortar compatibility, wall slenderness, reinforcement, and anchorage. The supplied research does not provide an AAC seismic strength value, wall ratio, or qualifying test report, so no numerical AAC advantage can be claimed here. AAC’s lower weight may reduce inertial demand, but mass reduction alone does not demonstrate adequate lateral resistance [S2].
The relevant product guides for fired brick, concrete masonry block, and AAC block are useful for material and dimensional data, but the seismic design must still be established from the complete wall assembly and governing code.
Compare seismic candidates on measurable criteria
Clay brick, concrete masonry block, and AAC block should be compared using the same six project inputs: specified unit compressive strength, unit weight, permitted wall slenderness, in-plane strength, out-of-plane stability, and reinforcement or grouting requirement. No numerical candidate values can be ranked from the supplied research because it contains no comparable product test data; selecting a category before those checks would be premature. [S2]
Clay brick provides a long-established fired-clay option, but the wall still depends on mortar bond, joint quality, geometry, and anchorage. Poor bonding, improper masonry work, and poor curing are identified as contributors to earthquake damage, while proper brick selection is associated with improved bonding strength, crack resistance, and durability [S2].
Concrete block is directly covered by the CSA S304-14 reinforced-masonry framework used in the 2018 Seismic Design Guide [S3]. Its selection should therefore be tied to the applicable reinforced or unreinforced wall category, grout condition, reinforcement schedule, and wall-to-diaphragm anchorage.
AAC should remain off the generic seismic shortlist until the engineer has verified project-specific properties and an accepted design method. The brick-selection guide discusses lightweight versus heavy bricks, moisture resistance, and structural stability as considerations for masonry construction in seismic zones [S2].
Specify mortar, reinforcement, and anchorage as one package
Masonry performance depends on the bed and head joint treatment, not only on the strength of the brick or block. Weak mortar bonding and improper masonry work are identified as major causes of wall failure, and good brick selection supports bonding strength and crack resistance [S2].
The seismic design guide addresses shear and diagonal-tension resistance, sliding shear resistance, in-plane flexural resistance due to combined axial load and bending, ductile seismic response, and related design provisions for reinforced masonry shear walls [S3].
Diaphragm anchorage is a separate seismic demand. The 2018 guide treats wall-to-diaphragm anchorage and masonry veneers with their connections as distinct design topics, while the existing-building provisions identify the diaphragm edge as the intersection of the horizontal diaphragm and shear wall [S3][S5].
For unreinforced masonry, the 2015 District of Columbia provisions frame retrofit work around improving minimum seismic resistance, but state plainly that compliance “does not necessarily prevent loss of life or injury, or prevent earthquake damage to rehabilitated buildings” [S5]. This limitation applies to unreinforced bearing-wall buildings and should not be represented as a guarantee for upgraded construction.
Use field acceptance and tests before accepting the wall
Specified masonry strength is not established by visual appearance or by the label “seismic brick.” The 2024 research on in-plane seismic strengthening identifies brick walls as primary load-bearing elements resisting lateral forces, reinforcing the need to assess the wall system rather than isolated units [S1].
Acceptance should include verification of the specified masonry type, compressive strength, dimensions, moisture condition where relevant, mortar placement, joint fullness, grout, reinforcement location, wall geometry, and anchorage. The research identifies poor curing and weak foundation planning among contributors to earthquake damage, so inspection must extend beyond the visible wall face [S2].
Testing and inspection must follow the project specifications and adopted standards for the jurisdiction. The supplied material does not establish universal sampling rates, acceptance percentages, or one test method for every block and brick wall, so those values must not be inferred from this guide.
For engineering design, load combinations, drift, wall slenderness, reinforcement limits, diaphragm forces, and anchorage remain code-dependent. The Canadian guide addresses masonry design to CSA S304-14, while the District of Columbia chapter is an existing-building strengthening rule for unreinforced masonry bearing walls [S3][S5]. Neither establishes the governing requirements for every seismic jurisdiction.
Define the shortlist by wall system, then verify the product
Choose clay brick when the design team has established a compliant brick masonry system with acceptable unit properties, joint behavior, wall proportions, and anchorage. Choose concrete masonry block when it is supported by the applicable reinforced masonry design provisions, including grout and reinforcement details. Consider AAC only when project-specific seismic properties and an accepted design basis are available [S2][S3].
Do not pick unreinforced masonry as the mainstream option for a new seismic load-bearing wall without a code-based analysis and a documented strategy for out-of-plane stability, in-plane resistance, anchorage, and construction quality. Existing unreinforced buildings require a separate strengthening assessment under the adopted existing-building provisions [S5].
The final procurement check should contain 4 documents: the unit product data, the mortar and grout specification, the reinforcement and anchorage schedule, and the sealed seismic wall design. If any one is missing, the selection is incomplete rather than proven seismic-resistant.
Track two decision signals: approval of the project-specific seismic wall calculation and successful inspection of unit strength, joints, reinforcement, grout, curing, and diaphragm anchorage before concealment.