Masonry construction dates back thousands of years. The builders of the past, took advantage of compression strength of stone and were still able to build amazing structures, without even possessing the technology to take on tensile forces, which only became possible in modern times with steel. In our age though, masonry is also combined with reinforcing steel, to make it much more ductile and resistant to loads. Masonry can be stone or brick. Today’s masonry is mainly in the form of manufactured bricks, such as CMU – Concrete Masonry Units, which are also reinforced with steel bars. From now we will mean brick masonry in this post. Both stone and brick are brittle materials.

Below are some of the most important structural considerations for masonry construction:

Masonry walls are strong in their plane and can very well be used as structural walls. This may not only be in the form of load bearing but also as lateral load resistance, where masonry can be the primary or secondary system resisting the lateral loads. Hybrid systems where masonry is used together with framing, will mean more complex design and construction.

Masonry walls when built as shear walls, can be made to fail from flexure or shear. Flexural failure is ductile, while shear failure is brittle. Ductile behavior is preferred, which means the wall should be tall enough with respect to its length and / or the compressive load on the wall should not be too high. Of course this is not always possible to achieve, mainly due to architectural reasons. Reinforcing also affects this behavior, where higher horizontal to vertical reinforcing makes flexural failure more likely. A flexure dominated wall will be more flexible, which reflects on the structure having more deformations and higher R Factor for earthquake design.

Similar to concrete shear walls, a masonry wall must be within the allowable limit set by M-N diagram which means the combination of bending moment and axial load on the wall. This determines the amount of rebar we need to use.

Similar to concrete shear walls, we can make tall masonry shear walls as coupled walls, which can together have far higher lateral load capacity than the sum of the individual walls. See our post on Construct Magazine for coupled walls.

Masonry walls are weak for out of plane loads. Proper attachment details are needed and there is a limit set by codes for the wall’s slenderness (maximum height to thickness). For example in Eurocode 6, this ratio is 27, when wall is loaded mainly vertically.

Structural masonry walls are reinforced to increase tensile strength, ductility and service limit. To ensure rebar and blocks behave as a whole unit, the voids of the blocks are grouted.

Openings in wall, if too much in number and size, may make a wall nonstructural. Openings will necessitate complex analysis, where a FEM analysis may be needed.

Arching action, used since ancient times, may be preferred over steel lintels, which also greatly improves aesthetics.

CMU blocks shrink over time, whereas clay bricks expand. These and the temperature related deformations must be accounted for during design such as by providing expansion and contraction joints.

Stability of walls during construction can become an issue, because the structure will not yet be in its final designed state. Temporary braces are often needed. The progress of masonry work needs to be coordinated with that of structural frame.

For a beginner, grout and mortar should not be confused with each other. Grout is the mix fill the block voids, to wrap rebar, protect them from corrosion and most importantly to ensure that the wall behaves as a whole single unit. Mortar is what we apply between blocks to make them stick to each other. Grout can sometimes be applied partially, to only to the cells that contain rebar, but regardless, fully grouted walls are stronger.

Also see our post: Advantages of Masonry Construction

Reference:“How to Construct: Introduction to Civil Engineering, Structures and Construction” – A. Tuter, August 2024

Post By: Ahmet Tuter

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