Seismic Performance Assessment of Lightly Reinforced Concrete Intake Towers

Abstract eng:
In the UK, most of the existing stock of concrete intake towers in reservoirs has been constructed for gravity loading only, with limited amounts of steel reinforcement provided essentially for crack control. Typically reinforced concrete towers have circular or rectangular hollow cross-sections. The complex geometry of the towers, also complicated by the presence of various openings and appendages, makes the vibrational characteristics of such structures to vary considerably. This paper describes a series of tests aimed at investigating the seismic performance of typically reinforced, non-seismically designed towers. Monotonic and cyclic push-over tests were performed on 1/6th scaled models. The results from the physical tests were used to validate a 3D nonlinear finite element model of the towers, using embedded steel reinforcement and a smeared crack model to simulate crack properties of the concrete material. The dynamic performance of the structures was investigated by developing a simplified single degree of freedom model and performing a number of simulations to obtain fragility curves of the system. The degrading, hysteretic properties of the towers were simulated using a Bouc-Wen model. A probabilistic approach was selected as the basis of the performance evaluation process using fragility analyses as a tool for modelling the uncertainty associated with the parameter selection. Based on the experimental and analytical results, a staged assessment procedure for the seismic performance assessment of the towers was proposed.

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