SAISC feature times
By Amanuel Gebremeskel, Technical Director SAISC
We are lucky in South Africa that we have few natural hazards of such magnitude and frequency. However South African seismologists have identified two types of earthquakes that are likely primarily in the Western Cape and Gauteng areas.
Scientists have warned that central Italy faces a serious risk of suffering further devastating earthquakes soon. On August 24th there was a 6.2-magnitude earthquake near Amatrice that killed more than 250 people. This was followed by a 6.1 earthquake which struck Visso on 26 October. The latest series of quakes have forced over ten thousand people to seek refuge in hotels and shelters, with many more sleeping in tents, cars or campers.
We are lucky in South Africa that we have few natural hazards of such magnitude and frequency. However South African seismologists have identified two types of earthquakes that are likely, primarily in the Western Cape and Gauteng areas. While Cape Town sits on crust that is vulnerable to natural earthquakes of the Italian variety, the area around Johannesburg is vulnerable to earthquakes caused by mining activities.
Cities and other large settlements are most at risk to earthquake damage because of large populations and buildings. The likelihood of death, injury and economic loss is much higher in built-up areas also because of fire risks from damage to electrical and gas lines. For these reasons, the Steel Institute has taken a leadership role in pushing for standards that aim to reduce seismic risks to South Africans.
Basic provisions for the design of buildings and other structures to withstand earthquake loads have been available in the SANS codes since 1989. However, compliance with the requirements has not been vigorously enforced by the authorities and owners over the past two decades. This is largely due to lack of awareness by design engineers and academics. In some cases, it has also been caused by scepticism about the level of seismic risk that exists in South Africa.
A forthcoming revision of SANS 10160-4 – Seismic actions and general requirements for buildings – addresses the omission of structural steel design provisions from the standard, as well as contradictions between SANS 10160 and SANS 10162, the steel design standard. The proposed revision is based on the American Society of Civil Engineers standard. Relevant parts of ASCE 7 have been adapted for the new SANS standard.
A paper that is authored by Amanuel Gebremeskel of the Steel Institute – chair of the South African Bureau of Standards seismic committee – and Chris Roth of the University of Pretoria, who chairs the overall loading code committee, discusses the background to the proposed provisions. The paper has now been refereed and accepted by the SAICE journal for publication.
We urge our readers to get a hold of it and familiarize themselves with the new standard. It should help to manage risks in these seismic times.
Photo courtesy en. wikipedia. org
RIGHT: On August 24th there was a 6.2-magnitude earthquake near Amatrice, Italy, that killed more than 250 people.
6 Steel Construction Vol. 40 No. 6 2016