Investigation of the structural response of the groot Olifants River bridge to seismic excitation.
Phakwago, Jan Mabeke.
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South African freight railway owner (Transnet fright rail) has over 5000 bridges servicing its railway network. Majority of those bridges are deemed to have exceeded their proposed design lives and cannot support the increasing traffic loads which are significantly greater than the loads they were designed to carry. Moreover, most of those bridges were not designed for seismic excitation as the South African codes of practice at the time did not take seismic action into consideration. This study investigates the structural behaviour of the 32m span Groot Olifants river bridge to seismic excitation. The investigation focuses on the bridge superstructure. Numerical modelling of the Groot Olifants river bridge was carried out in order to simulate the experimental test performed in the field. Digital image correlation (DIC) techniques were used to take field measurements of the deformations on the bridge. The computational programme, ANSYS, was used to perform a finite element analysis in order to assess the structural response of the bridge. The deflection measurements obtained from the DIC were used to validate the accuracy of the FEA model. The ultimate load capacity of the main truss elements in the bridge was determined and compared to the response from the numerical analysis in order to evaluate the potential failure of the bridge when subjected to seismic excitation. The study incorporates field load tests, finite element analysis as well as a case study of a similar bridge tested to ultimate load failure in Sweden. The results indicate that the bridge can resist low intensity seismic events when evaluated using the response spectrum analysis. However, from the transient structural analysis it is concluded that the Groot Olifants river bridge is susceptible to the high intensity seismic event predicated by Visser and Kijko (2010). From the field tests, it is further concluded that the Groot Olifants river bridge can resist the heavier loads to be applied by the new 44D locomotives.