Seismic performance of steel framed water tower structures

Vianney, Ntibaziyaremye (2016-12)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: From the year 1620 until June, 2008, more than 27000 earthquakes of magnitude ranging from 0.2 to 6.3 have been recorded by the South African National Seismological Database (SANSD). The most affected regions are Cape Town, Ceres, Koffiefontein, Lesotho and the Witwatersrand Basin. The historical record showed that the earthquake with the longest time duration was felt in South Africa on 4 December 1809. It caused small damages to buildings in Cape Town and caused liquefaction and cracks in the soil in the region of Blauwberg. However, the 29 September 1969 earthquake was the strongest and the most damaging in South African earthquake history. It was felt across Western Cape as far as Ceres, Tulbagh and Wolseley. It was of magnitude 6.3 on the Richter scale. Many building structures were seriously damaged, a few people were killed and others were injured. Old and poorly constructed buildings were completely destroyed. The total cost of the damaged infrastructure was estimated at U.S. $24million. Given this history, South African is classified as being at risk of moderate intensity earthquakes. The first version of seismic design code was released in 1980. It was updated in 1989 and 2010, but the updated code does not include all factors influencing the seismic response of the structures (e.g. soil foundation interaction). In addition, structures like dams, water towers, bridges, silos, pipelines, masts and chimneys were not covered. The new code limited its consideration to building structures. The concern is to know whether old structures or newer structures which are not covered by the new seismic designed code will be susceptible to damage by the seismic intensity assigned to the region of their location. Therefore, a methodology for seismic performance assessment of steel framed structures was presented from various publications and was applied to a typical water tower located in a high risk seismic zone of South Africa. The Winelands Engen 1-Stop water tower met the above criteria and was checked for its susceptibility to a seismic event. The results showed that the Engen 1-Stop water tower is vulnerable to the seismic risk attributed to its location. The seismic demand on the tower far exceeds its seismic capacity, which causes concern over whether the Engen 1-Stop water tower was designed to meet any seismic hazard.

AFRIKAANSE OPSOMMING: Vanaf die jaar 1620 tot en met Junie 2008, het die Suid-Arikaanse Nasionale Seismologiese Databasis (SANSD) meer as 27000 aardbewings, wat tussen 0.2 en 6.3 op die Richter skaal meet, opgeneem. Kaapstad, Ceres, Koiffiefontein, Lesotho en die Witwatersrand Kom is onder meer die areas wat die meeste geteister word deur aardbewings. Historiese opnames toon dat die langste aardbewing in Suid-Afrika plaasgevind het op 04 Desember 1809. Daar was minimale skade aangerig aan geboue in die Kaapstad-omgewing, alhoewel vervloeiing en klein krake waargeneem was op die grond in die Blauwberg-area. Inteendeel het die sterkste aardbewing, wat die meeste verwoesting gesaai het, plaasgevind op 29 September 1969. Dié aardbewing het 6.3 gemeet op die Richter skaal en was gevoel regoor die Wes-Kaap provinsie. Die aardbewing was veral gevoel in areas soos Ceres, Tulbagh en Wolseley. Die aardbewing het gelei tot die ernstige skade aan geboue, lewensverlies en die besering van tale mense. As gevolg van die sterkte van die aardbewing het tale ou geboue, sowel as die wat nie ontwerp is vir aardbewings nie, ineengestort. Die beraamde skade as gevolg van die aardbewing was ongeveer U.S. $24 miljoen. Suid-Afrika word geklassifiseer as ‘n area met ‘n risiko van middelmatige intensiteit aardbewings. skoorstene word ook nie gedek deur die nuutste kodes nie. Die ontwerpstappe en riglyne van die nuutste weergawe is beperk tot die ontwerp van geboue. Die vraag ontstaan dan of die ouer sowel as toekomstige nuwe strukture wat nie ingesluit is onder die nuwe ontwerp kode nie, nie dalk vatbaar is vir skade wat nie onder die nuwe seismiese intensiteit waaronder dit ge geklassifiseer word nie. Verskeie publikasies is geraadpleeg om ‘n metode vir die bepaal van die seismiese gedrag van staalraam strukture daar te stel. Hierna was die informasie gebruik en toegepas op ‘n watertoring in ‘n area met n hoë seismiese risiko in Suid-Afrika. Die Engen 1-Stop watertoring, geleë in die Wynland, is gekies vir die studie aangesien dit aan die vereiste kriteria voldoen het en is gebruik om die vatbaarheid daarvan te bepaal in die geval van seismiese gebeure. Die resultate het getoon dat die Engen 1-Stop water toring kwesbaar vir die seismiese risiko wat daaraan toegewys is aan die area waar dit is. Die studie het gevind dat die seismiese aanvraag op die toring veel meer is as die seismiese kapasiteit waarvoor dit ontwerp is. Die vraag kan dus gestel word of die Engen 1-Stop onder bespreking ontwerp is vir enige seismiese gebeure en die gepaardgaande strukturele impak daarop.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100262
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