Guidelines to Mitigate Cracking in Compressed Stabilized Earth Brick Shells

Abstract

Unreinforced compressed stabilized earth brick (CSEB) shell structures offer economic and environmental benefits that promote their adoption as an affordable housing alternative. Because these shells are unreinforced, designers normally apply methodologies such as thrust line analysis to ensure that internal force resultants remain within the middle third of the cross section (i.e., no tensile stress). Actions such as self-weight, wind, and asymmetric distributed loads are typically considered in design. Although a pure-compression design technique offers considerable safety against collapse initiated by the aforementioned actions, most structural damage (e.g., cracking) can be attributed to loads that appear to be regularly overlooked. In particular, extensive cracking caused by self-straining stresses (restraint of thermal and shrinkage movements) is observed in several dozen unreinforced masonry shells built in South Africa. The mitigation of cracks is important because they are the most common cause of a masonry structure’s failure to perform as envisaged. This is especially significant in adobe and CSEB shells because of the modest durability characteristics of these building materials. In this study, the causes of cracking in unreinforced shells are examined and, subsequently, the importance of self-straining stresses and concentrated loads is highlighted. The study demonstrates that unreinforced CSEB shells should be designed for a range of cracking factors. Several guidelines are proposed in this regard, which are particularly applicable in a low-cost setting, such as the use of white paint to attenuate large surface temperatures.