Changing codes for masonry structures

by Darren
Changing codes for masonry

Masonry consultant, Fred Crofts, shares his thoughts on the changing codes for masonry structures in South Africa.
In South Africa, the majority of masonry buildings are simple, basic structures and, according to Fred Crofts, masonry consultant from FSC Consulting Engineers, these are often built by people with rudimentary skills and very little understanding of the behaviour of masonry materials.

Still, no matter the skills set or building complexity, part of responsible construction is applying and adhering to the relevant national standards. Although the SANS 10400 series, which is the application of the National Building Regulations (NBR) and Building Standards Act, 1977 (Act 103 of 1977), have been updated over the last couple of years, the masonry design and material standards are now between 25 and 30 years old and currently under review.

Eurocode 6 to be adopted
According to Crofts, South Africa is expected to adopt Eurocode 6 (11) and supporting standards, with the addition of a SA Annex to address matters specific to local conditions, in the near future, for the design of all masonry structures. “Masonry” is used in the NBR as the collective word for hollow and solid masonry of brick and block format; the NBR does not differentiate between concrete and clay masonry units.

Crofts explains that the Eurocodes on the manufacturing of masonry are less descriptive than the local standard and are performance based; and they rely on the material knowledge of the consumer to specify masonry materials for a specific application. “Even with descriptive specifications (SANS 1215 and 227 addressing the manufacture of concrete and clay masonry units) the lack of understanding of durable masonry wall design and construction has resulted in problem walls, therefore the adoption of the Eurocodes will put the onus on architects, engineers and building industry professionals to stay informed regarding best practice,” he comments.

“However, this is the only way to move forward,” he says. “These standards are based on research done across the whole of Europe, whereas in South Africa there is little evidence of any research in this area to base any building standard updates on.”

Moisture movement in masonry walls
A significant point is that the Eurocode 6 declares critical design values for moisture movement and compressive strengths, an extremely important consideration in concrete masonry to prevent defects and failures.

In Crofts’ paper, “Sustainable concrete masonry in South Africa”, he notes that many problems experienced with concrete masonry today relate to moisture movement. This could be a result of poor architectural detailing where water is directed onto walls, poorly rendered or cracked rendered surfaces, and walls in contact with soil facilitating the ingress of moisture.

Moisture movement in walls is also caused by laying concrete masonry units as wet or wetting (docking) units, as is accustomed with fired clay masonry units. However, concrete masonry has a high water absorption rate and when subjec to damp and dry cycles, is prone to drying shrinkage and expansion or rewetting, which cause walls to crack. Also, if moisture reaches the steel reinforcement in reinforced masonry structures and they corrode, the structure can suffer irreparable damage and may collapse. Other problems are as a result of manufacturing defects such as insufficient curing and the use of waste products that are chemically unstable.

“Moisture movement, if not well understood or when ignored, can result in defects, which will add to the lifecycle and operating costs of a building and compromise durable construction,” states Crofts.

“Appropriate design, workmanship and the understanding of the behaviour of concrete masonry materials are the cornerstone for sustainability and resource conservation,” he concludes.

Full thanks and acknowledgement are given to Fred Crofts for the information given to write this article.

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