An investigation of South African low-income housing roof anchor systems

Abstract

The current roof anchoring methods for houses in South Africa are described in the standard SANS 10400. The adequacy of these prescribed roof anchoring methods for low-income houses (LIHs) is questionable, due to several recently reported failures caused by strong winds. This study quantitively investigates the performance of the prescribed roof anchoring methods through numerical methods, and focuses on LIHs with light-weight roofs supported on single-leaf masonry walls. The masonry walls comprise either solid bricks or hollow cement blocks. The peak wind reaction forces that are expected to occur at the roof anchor systems were determined through a series of static analyses. Finite element analysis techniques were performed to predict the capacity of the roof anchor systems. The predicted resistance of the roof anchor systems was compared to the calculated peak wind reaction forces at the roof anchors to determine the adequacy of the roof anchor systems. The results of the research suggest that, for LIHs constructed from solid bricks, the prescribed roof anchor systems perform poorly under the expected South African strong wind climate. The results indicated that the roof anchors will pull out at peak basic wind speeds of between 27 m/s and 32 m/s, and cracks will develop in the masonry prior to anchor pull-out. This study suggests that further research is required to develop adequate roof anchoring methods for LIHs with light-weight roofs, supported on solid brick walls, and that the relevant codes should be amended accordingly. Furthermore, the results showed that the prescribed roof anchor systems for LIHs constructed from hollow blocks performed well and were able to withstand the expected wind loads under the South African strong wind climate.