Issued by: Minister of Housing
28 May 1996
PRESS RELEASE STATEMENT
On the night of 6 February 1996 the residence of Mr V Pasquallie on Erf number 2839 in the suburb of Roosendaal in the Cape Province collapsed partially.
The surface bed under the bedroom in the south-west corner of the house as well as approximately half of the surface bed under the bedroom on the south-east corner of the house have failed due to overstressing. An instantaneous vertical displacement of between 100mm and 200mm took place at the time of failure.
The failure of the surface bed has resulted in the collapse of most of the southern wall of the house, the western wall of the bedroom on the south-west corner and a small section of the eastern wall of the bedroom on the south-east corner of the house.
No injuries were sustained during the collapse. The part of the residence that collapsed was evicted timeously as the owner became aware of cracks appearing upwards from the ends of lintels above the windows.
On 22 April 1996, following site visits by senior government officials, two professional engineers from the Division of Building Technology at the CSIR in Pretoria conducted a site investigation to determine the possible cause of collapse.
The proposed mechanism of failure is as follows:
The founding material for the residence is a non-cohesive dune sand. Wind gradually eroded the sand protecting the foundation of the house along the southern section, exposing the thickened edges of the surface bed over its full depth. Ongoing wind erosion over a significant period also removed sand from underneath the surface bed, until the surface bed structure could not carry the weight of the floor and walls.
The extent of the undermining of the surface bed became such that the combination of the resulting shear stress and tensile bending stresses in the concrete of the surface bed exceeded the tensile stress capacity of the concrete. This caused the surface bed to break instantaneously.
Conclusion:
Properly designed raft foundations would have to be sufficiently reinforced to be able to accommodate a certain amount of movement from the founding slab should its supporting foundation material fail in some way.
Based on the observations from an inspection of the condition of surrounding houses in the suburb and assuming that the same details had been used for all the Type C2.24 houses, it must be concluded that with proper protection around foundations to prevent soil from being eroded from beneath the foundation, the collapse of this houses could have been prevented.
A properly designed raft foundation would probably not have collapsed instantaneously, but severe cracking of walls and large deflections would still have occurred over time with erosion of the foundations.
Shoddy workmanship has resulted in different areas in the country to the reinforcement of hardened attitudes towards payment. But this government, within the MIS and Servcon institutions has been engaged in resolving these problems.
The old regime in a bid to win votes built houses that today show severe problems of sustainability. Poor quality housing, lack of interests in potential occupants will now cause the Mandela Government huge amounts of money.
The CSIR and the Ministry of Housing are looking at ways of how to address these issues. A report on the matter is due soon.
Tafelsig (Lost City) in the Western Cape has similar problems.
Enquiries: Ms Anita Viljoen Telnr: (012) 841-2501
Prepare for: Ms S. Mtembi-Nkondo Minister of Housing