Response of a hyperbolic cooling tower under seismic excitations and wind load

Abstract

At the beginning of the 20th century, the consumption of electricity increased around the world remarkably. Therefore, the construction of thermal and nuclear power stations speared worldwide. The power stations needed a large quantity of water in the power generation process. To cool water and reuse it again, the hyperbolic cooling towers were built in the power stations. The hyperbolic cooling towers are designed as tall and thin structures. During the services-life, towers may be exposed to different load types such as wind load, seismic load, construction load, and thermal load in addition to self-weight of the towers. The external loads on the hyperbolic cooling towers may cause a failure or collapse of the towers. The case of collapsing cooling towers may have consequences on both society and the economy. The work presented in this thesis aims to assess the behavior of an existing reinforced concrete hyperbolic cooling tower located at the RWE power station in the Neurath city in western Germany under seismic and wind loads. The reinforced concrete hyperbolic cooling tower is modeled and analyzed utilizing ABAQUS CAE 2020 finite element software. To investigate the seismic response of the tower, dynamic nonlinear time history analysis was applied in accordance with Eurocode 8. Due to the axis-symmetrical nature of the hyperbolic cooling towers, the seismic load is applied only in one horizontal direction. Three ground motion records are chosen in accordance with Eurocode 8 and matched to the elastic response spectrum of Eurocode for 5 percent viscous damping by spectra matching method, using SeismoMatch software. To apply time history analysis in ABAQUS, the Time-Integration implicit method is followed. The dynamic implicit step of ABAQUS is using Hilber-Hughes-Taylor's method (HHT), which is an extension of the Newmark β-method. Modified Newton–Raphson iterative procedure is followed throughout the dynamic analyses. The effect of wind load on the tower is calculated according to the VGB R610U standard as equivalent static pressure on both the external and internal shell walls of the tower. The external and internal pressure distribution coefficients (C_pe and C_pi) are taken into account. According to the abovementioned standard, the pressure caused by wind load is calculated based on terrain category and geographical location of the tower in terms of height, circumferential direction, and fundamental period. The nonlinearity of the materials is taken into the consideration. The concrete damage plasticity model (CDP) is utilized to simulate the inelastic behavior of the concrete. This model accurately defines concrete behavior under cyclic or dynamic loads, as well as simulates residual damage of concrete. The isotropic hardening model is used to simulate the plastic behavior of the steel reinforcement. In this thesis, the stress distributions, lateral displacement, and compressive and tension damage of the hyperbolic cooling tower caused by seismic and wind loads are investigated.