Questioning the adherence to local construction standards
FAnews recently received a submission from Dr Adam Goliger, a Structural and Wind Engineer, which followed the recent Cape storm and the issues around building design, construction standards and the insurance industry which we thought would make for an interesting read for our readers.
This article makes us question the adherence to local design, construction and building standards and sparks the thought of whether approvals and investigations should become compulsory, if not mandatory in relation to large scale wind related failures.
The inevitable damage
According to Goliger, every year strong wind events and their related damage are reported across the country. In winter months, these are typically caused by large synoptic fronts developing over the oceans, while in summer - by convective activity due to hot inland weather, generating thunderstorms, squall-lines and infrequently – tornadoes. Interestingly, about a year ago, Gauteng experienced a few unusual winter tornadoes.
“Severe wind events invariably attract the attention of the media because of the damage that they inflict. Areas of widespread devastation are occasionally proclaimed disaster areas and can thus receive national financial assistance,” he says.
Rightly so Goliger says, as the inevitable damage to informal infrastructure causes suffering to the less privileged sections of society. Formal structures (which, by definition, receive engineering and professional inputs) are usually covered by insurance.
“The insurance industry often classifies extreme wind events as Acts of God, enabling the settlement of claims. There is an additional dimension as soon as there is loss of life, such as the collapse of a banner at the Linkin Park concert in Cape Town or the collapse of a temporary bridge scaffold across the N1 in Sandton. By law legal inquests need to be instituted, involving a myriad of lawyers and experts,” he continues.
Design, approval and construction
Within the formal component of built environment, in principle, the wind resistance of structures Goliger says is influenced by a number of activities carried out by respective professionals, in the design, approval and construction phases.
“Regarding wind resistant design, there has been a significant amount of international and local research regarding the magnitude and probability of occurrence of the critical wind events in South Africa, as well as the aerodynamic functions which translate the critical wind speed into loading of structures and their elements. These outcomes form the basis for SANS 10160-3:2011, setting input parameters for wind-loading design,” he says.
The approval stage, Goliger mentions, relies on local authorities who critically and objectively examine submitted plans in terms of their suitability, social responsibility and safety.
He mentions that construction activities involve site preparation, supply of suitable materials, processes of their erection and integration into components, site management and various levels of supervision, involving Contractors, Manufacturers, Designers, Owners and Local Authorities.
“The recent strong wind events in the Cape took place over few days, with the worst day being 7 June. The related time trace of the average and peak wind speeds and directions on this day, measured by the South African Weather Service (SAWS), is included below. It can be seen that typical gusts oscillated around 20 m/s, with the highest peak gust of 23 m/s coming from a north-westerly direction, recorded in the early hours of the day. However, according to SANS 10160-3:2011, the minimum design value of the freestream wind speed for Cape Town is about 40 m/s,” he says.
Wind speed and direction record obtained from SA Weather Service (7 June 2017)
AWS at Cape Town International Airport
The situation will perpetuate
Due to the quadratic relationship between wind speed and pressures (i.e. loads), Goliger says the structural failures related to the Cape Storm occurred at loads, more or less, one third of that required by local design standards. “This implies that in those structures which failed the design, approval and construction processes were not diligently enforced, to the detriment of property owners and the insurance industry,” he emphasises.
“For as long as the insurance industry and owners of facilities are prepared to carry the costs of repairs, these processes will not be rectified and the situation will perpetuate,” he continues.
He concluded by saying each case of a substantial wind related failure should be investigated, the responsible parties be identified and carry the costs of repairs. “This is the only way to improve the situation and prevent future losses (most importantly human) and reduce the societal cost of substandard development processes.”
Editor’s Thoughts:
Having read what Goliger said, do you believe that investigations into the reasons of large scale wind damage should become compulsory, if not mandatory before insurers approve the claims? Please comment below, interact with us on Twitter at @fanews_online or email me your thoughts myra@fanews.co.za
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