Cyclone resistant housing for developing countries
Over the past 30 years, BRE staff have been engaged in assessing the effects of wind on buildings. This work has included studies of the effects of tropical windstorms throughout the world and many countries have benefited directly from the research expertise and technical advice made available because of these studies.
MAURITIUS. Following cyclone ‘Alix’ and ‘Carol’ which struck the island in 1960 causing severe and extensive damage to buildings an investigation was undertaken by BRE.
The distribution of wind forces on buildings and the resulting damage patterns were related lo ground topography, roof pitch, building shape and architectural features. This field experience confirmed the validity of much of the previous experimental work undertaken with models.
Suction forces were recognised as a major cause of damage and roof anchorage was shown to be the most critical factor requiring attention in efforts to reduce damage caused by wind. The beneficial effects of ridge ventilators were also noted. These lower the internal pressure within a building, thereby reducing the total force on those areas of roofs and walls subject to external suction forces.
PHILIPPINES. As pan of a research project initiated by the US National Bureau of Standards involving the Philippines, Jamaica and Bangladesh, collaborative work by BRE helped to establish a methodology for the estimation of maximum wind speeds and the development of wind tunnel modelling techniques.
Also. data were collected for analysis leading to the derivation of basic wind speeds and appropriate pressure coefficients which assisted with the development of construction details able to withstand high wind forces. Workshop presentations were held to disseminate the information gained from this work and the US National Bureau of Standards published a five-volume report on building in areas subject to severe wind conditions.
HUNG KONG. Much useful information was obtained on the effects of wind on high rise buildings because of cooperation between BRE and the University of Hong Kong over a period of seven years, data were collected on maximum wind speed gusts and the associated wind pressures on a ten-storey experimental building which was a half-scale replica of Royex House in London.
Both buildings were fully instrumented with anemometers and pressure transducers and useful comparisons were made between the two sets of data obtained. After analysis, this data provided a valuable input to both the UK and Hong Kong Wind-loading codes.
SRI LANKA. Following an aid project by the Australian Government, a wind-loading design manual was published and housing designed and constructed in accordance with it was assessed by BRE. This showed that the design manual was readily understood and applied by local technical staff, and it was clear that the standard of control and workmanship was good.
CARIBBEAN. A major project on cyclone-resistant housing has been undertaken by BRE. on the island of St Vincent, and much of the information obtained and advice given is applicable lo islands throughout the Caribbean. Following an appraisal of local information on wind speeds, basic design parameters were established and used to design three low-cost house types.
BRE also assessed the damage caused by cyclone ‘Oscar’ which stuck Fiji in March 1983 with wind speeds of 51 m/s. ln the vicinity of Nadi town on Viti Levu. several school classrooms were wrecked and other buildings in exposed areas like the airport suffered cladding damage. One hotel suffered both structural and cladding damage and many houses lost their roofs, some being destroyed. It was significant that the damage suffered by the traditional timber/thatch buildings was no more — and in some cases less — than that sustained by modern timber/corrugated sheet houses. Clearly, the condition of the structure and location of the buildings were more critical than the method of construction. As with most cyclones, damage was generally initiated by a failure of fixings in the roof, either fixing of the cladding or fixings of the roof structure.
Furthermore. it was notable that in one village of timber houses none of the roofs with hipped ends failed, unlike some adjacent roofs with gable ends which suffered serious structural damage. Following the devastation caused on islands of the Kingdom of Tonga by cyclone ‘Isaac’ in March 1982, a major house-building programme was undertaken using timber frame construction methods with the panels prefabricated under factory conditions.
The design was developed jointly by the Tongan Ministry of Works and BRE. with specialised advice provided by the Cyclone Testing Station in Townsville, Queensland. The walls were formed with modular panels 2.4 m long, fabricated with 50 x I00 mm studs at 600 mm centres and sheathed with plywood or fibre cement boards. The roofs were constructed with timber trusses jointed with plywood gussets or hammer-in type metal tooth plates, and clad with corrugated galvanised steel sheets. Proprietary steel snaps (framing anchors) were used to fix the roof purlins to the trusses.