Effect of seismic loads on water-retaining structures in areas of moderate seismicity

Fourie, Johanna Aletta (2010-03)

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010.

ENGLISH ABSTRACT: Water-retaining structures are commonly used in South Africa for the storage of potable water and waste water. However, a South African code pertaining to the design of concrete water-retaining structures do not currently exist and therefore use is made of the British Standard BS 8007 (1987). For the design of concrete water-retaining structures in South Africa, only the hydrostatic loads are considered while forces due to seismic activity are often neglected even though seismic excitations of moderate magnitude occur within some regions of the country. Hence, the primary aim of this study was to determine whether seismic activity, as it occurs in South Africa, has a significant influence on water-retaining structures and whether it should be considered as a critical load case. In order to assess the influence of seismic activity on the design of water-retaining structures the internal forces in the wall and the required area of reinforcement were compared. Comparisons were made between the seismic analyses and static analyses for both the ultimate and serviceability limit states. In order to obtain the internal forces in the wall use was made of an appropriate Finite element model. Three Finite element models were investigated in this study and the accuracy of each model was assessed based on the fundamental frequency, base shear force and overturning moment. These values were compared to the values obtained with the numerical method presented by Veletsos (1997) which was verified with Eurocode 8: Part 4 (2006). The results obtained indicated that seismic excitations of moderate magnitude do have a significant influence on the reinforcement required in concrete water-retaining structures. For both the ultimate limit state and serviceability limit state the required reinforcement increased significantly when seismic loads were considered in the design. As in the case for static design of water-retaining structures, the serviceability limit state also dominated the design of these structures under seismic loading.

AFRIKAANSE OPSOMMING: Beton waterhoudende strukture in Suid-Afrika word op ‘n gereelde basis gebruik vir die stoor van drink- sowel as afvalwater. ‘n Suid-Afrikaanse kode vir die ontwerp van hierdie strukture bestaan egter nie en dus word die Britse kode BS 8007 (1987) hiervoor gebruik. Vir ontwerp doeleindes word soms slegs die hidrostatiese kragte beskou terwyl kragte as gevolg van seismiese aktiwiteite nie noodwendig in berekening gebring word nie. Seismiese aktiwiteite van gematigde grootte kom egter wel voor in sekere dele van Suid-Afrika. Die hoofdoel van hierdie studie was dus om die invloed van seismiese aktiwiteite, soos voorgeskryf vir Suid-Afrikaanse toestande, op beton waterhoudende strukture te evalueer asook om te bepaal of dit ‘n kritiese lasgevalle sal wees. Vir hierdie doel is die interne kragte asook die area staal bewapening vir elk van die statiese en dinamiese lasgevalle vergelyk. Vergelykings is getref tussen die dinamiese en statiese resultate vir beide die swigtoestand en die diensbaarheidstoestand. Vir die bepaling van die interne kragte is gebruik gemaak van eindige element modelle. Tydens hierdie studie was drie eindige element modelle ondersoek en die akkuraatheid van elk geëvalueer op grond van die fundamentele frekwensie, die fondasie skuifkrag en die omkeermoment. Hierdie waardes was ondermeer bereken met twee numeriese metodes soos uiteengesit in Veletsos (1997) en Eurocode 8: Part 4 (2006). Die resultate dui daarop dat die invloed van seismiese aktiwiteite op beton waterhoudende strukture in Suid-Afrika nie weglaatbaar klein is nie en wel in berekening gebring behoort te word tydens die ontwerp. Die interne kragte vir beide die swigtoestand en diensbaarheidstoestand is aansienlik hoër vir die seismiese lasgeval as vir die statiese geval. Die diensbaarheidstoestand het deurentyd die ontwerp van beton waterhoudende strukture vir seismiese toestande oorheers.

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http://hdl.handle.net/10019.1/2061
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